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ADVANCES IN AGRONOMY VOLUME VIII

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ADVANCES IN

AGRONOMY Prepared under the Auspices of the

AMERICAN SOCIETY OF AGRONOMY

V O L U M E VIII Edited by A. G . NORMAN University of Michigan, Ann Arbor, Michigan

ADVISORY BOARD G. H. AHLGREN G. W. BURTON J. E. GIESEKING W. P. MARTIN

R. W. PEARSON R. W. SIMONSON G. F. SPRAGUE H. B. SPRAGUE

1956 ACADEMIC PRESS INC., PUBLISHERS NEW YORK

Copyright @ 1956, by ACADEMIC PRESS INC. 125 EAST 23x1 STREET NEW YORK

10,

N. Y.

All Rights Reserved

N o part of this book m a y be reproduced in any form, by photostat, microfilm, or any other means, without written permission from the publishers.

Library of Congress Catalog Card Number: (50-5598)

PRINTED I N THE UNITED STATES O F AMERICA

CONTRIBUTORS TO VOLUME VIII

Senior Principal Research Officer, Commonwealth A. J. ANDERSON, Scientific and Industrial Research Organization, Canberra, A.C.T., Australia.

W. B. ANnREws, Agronomist, Department of Agronomy, Mississippi Agricultural Experiment Station, State College, Mississippi.

H. B. CHENEY,Head, Department of Soils, Oregon State College, Corvallis, Oregon.

J . RITCHIE COWAN,Agronomist, Department of Farm Crops, Oregon State College, Corvallis, Oregon. J . E. DAWSON, Associate Professor of Soil Science, Department of Agronomy, New York State College of Agriculture, Cornell University, Ithaca, New York. S. T. DEXTER, Professor of Farm Crops, Michigan State University, East Lansing, Michigan.

J . W . FITTS,I n Charge, Soil Research, Department of Agronomy, North Carolina State College, Raleigh, North Carolina.

W . H. FOOTE,Associate Agronomist, Department Oregon State College, Corvallis, Oregon.

of

Farm Crops,

E. G. KNOX,Assistant Soil Scientist, Department of Soils, Oregon State College, Corvallis, Oregon.

L. B. NELSON, Head, Eastern Soil and Water Management Section, Agricultural Research Service, U . S. Department of Agriculture, Beltsville, Maryland.

W .L. NELSON, Midwest Manager, American Potash Institute, Lafayette, Indiana. H . H . RAMPTON, Agronomist, Agricultural Research Service, U . S. Department of Agriculture, Corvallis, Oregon. D. C. SMITH,Chairman, Department of Agronomy, University of Wisconsin, Madison, Wisconsin. Y

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Preface

As one looks at the topics reviewed in this and the preceding seven volumes of this series, one cannot but be impressed by their diversity and breadth, yet all deal essentially with agricultural soils and the crops which they can support. Progress in soil and crop science in the past two decades has been greatly accelerated by the application of many disciplines to the solution of theoretical and applied problems in agronomic practice. The empiricism which characterized so much of the agronomic research of the past has given way to more rationaland more rewarding-approaches. Consider, for example, the chapter on grass breeding by D. C. Smith in this volume as evidence of the changes that have taken place. Studies on soil management and cultural practices, which have not seemed to lend themselves to the same sort of refinement, are nevertheless changing in character. The development of recommendations for economic applications of fertilizer and lime, based on chemical soil tests, as described herein by Fitts and Nelson, are becoming more solidly based as information is secured on the forms and availability of essential plant nutrients in soils. Other examples will readily occur to the reader. Once again there is included a regional survey, in which the soil resources and crop patterns of an area are reviewed in some detail. This time it is the “new agricultural empire” of the Pacific Northwest states, which, as shown by Cheney and his colleagues, presents a wide array of agronomic problems and an unusual challenge and opportunity to bring to bear on them the best agronomic skills. The overall objective of this series remains unchanged. It is to survey and review progress in agronomic research and practice. The central theme is soil-plant relationships, but in choosing topics the editor is not concerned about the precise boundaries of agronomy; only that the material presented should be useful to agronomists. Ann Arbor, Michigan August, 1956

A. G. NORMAN

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CONTENTS Page

. . . . . . . . . . . . . v . . . . . . . . . . . . . vii

Contributors to Volume VIII Preface . . . . . . .

Field Crop Production and Soil Management in the Pacific Northwest BY H B. CHENEY.W. H. FOOTE. E. G KNOX.Oregon State College. Corvallis. Oregon. A N D H H RAMPTON. Field Crops Research Branch. Agricultural Research Service. United States Department of Agriculture. Corvallis. Oregon

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1. Introduction . . . . . . . . . . . . . . . . . . I1. Regional Characteristics . . . . . . . . . . . . . . . I11. SoilResources . . . . . . . . . . . . . . . . . .

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IV Soil Management . . V Crop Zones of the Region VI Field Crops of the Region References . . . . .

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2 3 7 17 33 37 59

Anhydrous Ammonia as a Nitrogenous Fertilizer BY W B ANDREWS. Mississippi Agricultural Experiment Station. State College Mississippi

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I. Introduction . . . . . . . . . . . . . . . . . . I1. Behavior of Anhydrous Ammonia in the Soil . . . . . . . . I11. Response of Crops to Anhydrous Ammonia . . . . . . . . .

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IV Anhydrous Ammonia Equipment V.Summary . . . . . . . VI. Conclusions . . . . . . References . . . . . . .

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62 70 79 . 110 . 119 . 123 . 123

Progress in Grass Breeding BY D C. SMITH.University of Wisconsin. Madison. Wisconsin

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I. Introduction . . . . . . . . I1. Diversity of Grasses . . . . . . I11. General References . . . . . . IV. Nature of Varieties . . . . . . V. Environmental Effects . . . . . VI. Cytology . . . . . . . . . VII. Interspecific and Intergeneric Relations VIII. Fertility and Sterility . . . . . IX . Inbreeding . . . . . . . . ix

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128 129 130 131 134 . 135 . 139 . 141 . 142

X

CONTENTS

. Combining Ability . . Crossing Techniques .

. . . Hybrid Varieties . . . . Agronomic Aspects . . . Disease Resistance . . XV. Nutritive Value . . . XVI. Variety Maintenance . XVII . Discussion . . . . . References . . . . . X XI XI1 XI11 XIV

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Page 143 149 150 151 152 154 156 158 159

Molybdenum as a Fertilizer

BY A . J . ANDERSON. Commonwealth Scientific and Industrial Research Organization. Canberra. A.C.T., Australia I. Introduction . . . . . . . . . . . . . I1. The Field Occurrence of Molybdenum Deficiency . . I11. The Nature and Detection of Molybdenum Deficiencies IV. The Correction of Molybdenum Deficiency . . . . V. Factors Affecting the Response to Molybdenum . . . References . . . . . . . . . . . . . .

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164 166 173 182 184 199

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204 208 210 235 236

The Evaluation of Crop Plants for Winter Hardiness

BY S. T. DEXTER.Michigan State University. East Lansing. Michigan I. Introduction . . . . . . . . . I1. Theories of the Winter Hardiness of Plants I11. Methods of Testing for Hardiness . . 1V.Summary. . . . . . . . . . References . . . . . . . . . .

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The Determination of lime and Fertilizer Requirements of Soils Through Chemical Tests BY J . W . FITTS.North Carolina State College. Raleigh. North Carolina. AND WERNER L . NELSON.American Potash Institute, Lafayette. Indiana

I. Introduction . . . . . . . I1. Calibration of Soil Tests . . . I11. Representative Soil Samples . . IV. Chemical Testing Procedures . . V. Interpretation and Recommendations VI . Soil Test Summaries . . . . . VII Future Trends in Soil Testing . . References . . . . . . . .

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. 242 . 244 . 252 . 257 . 269 . 274 . 278

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280

Tall Fescue BY J . RITCHIE COWAN. Oregon State College. Coruallis. Oregon I. Introduction . . . . . . . . . . . . . . . . . . 283 I1. Production and Utilization . . . . . . . . . . . . . . 286 I11. Cultural Practices . . . . . . . . . . . . . . . . 292

xi

CONTENTS

IV. Genetics and Cytology . V Varieties . . . . . VI. Breeding Behavior . . VII . Seed Production . . . VIII Fescue Poisoning . . . IX Diseases . . . . . X . Future of Tall Fescue . References . . . . .

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Page . 295 . 298 . 303 . 310 . 313 . 315 . 316 . 318

The Mineral Nutrition of Corn as Related to Its Growth and Culture BY LEWISB. NELSON.United States Department of Agriculture. Beltsuille. Maryland I. Introduction . . . . . . . . . . . . . . . . . . 321 I1. Nutrient and Water Absorption by Corn Roots . . . . . . . . 323 111. Foliar Absorption of Nutrients . . . . . . . . . . . . . 334

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IV Growth and Accumulation of Dry Matter . . . . . . . . . . 336 V Accumulation and Movement of Elements within the Plant . . . . 338 VI Symptoms of Nutritional Disorders . . . . . . . . . . . 351 MI Effect of Fertilizers on Nutrition and Growth . . . . . . . . 355 VIII Influence of Plant Population . . . . . . . . . . . . . 362 IX Effect of Soil Moisture on Nutrition and Growth . . . . . . 363 Acknowledgment . . . . . . . . . . . . . . . . . 368 References . . . . . . . . . . . . . . . . . . . 368 Organic Soils BY J . E. DAWSON. New York State College of Agriculture. Cornell University. Ithaca. New York

I. Introduction . . . . . . . . . . . . . . . . . . I1. Organic Soil Materials . . . . . . . . . . . . . . . I11. Stratigraphy of Organic Soils . . . . . . . . . . . . . IV. Rate of Formation of Peat Soils . . . . . . . . . . . . V . Subsidence of Organic Soils . . . . . . . . . . . . . . VI. Some Chemical Properties of Organic Soils of Significance in Crop Production . . . . . . . . . . . . . . . . . . . . VII Recent Chemical Work on Peat Soils and Related Materials . . . . VIII . Some Problems in Stratigraphy, Formation. Subsidence and Chemistry of Organic Soils . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . .

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Author Index Subject Index

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378 378 381 384 385 387 390 398 399 403 417

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Field Crop Production and Soil Management in the Pacific Northwest'

.

H. B. CHENEY. W . H. FOOTE. E. G. KNOX. AND H H. RAMPTON Oregon State College. Corvallis. Oregon. and Field Crops Research Branch. Agricultural Research Service. United States Department of Agriculture. Corvallis. Oregon

I. Introduction . . . . I1 Regional Characteristics

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1.LandForms. . . . . . . . . . . . . . . . . 2.Clim~te . . . . . . . . . . . . . . . . . . 3. Water Resources . . . . . . . . . . . . . . . . 4.LandUse. . . . . . . . . . . . . . . . . . I11 Soil Resources . . . . . . . . . . . . . . . . . . 1. Sierozem Zone . . . . . . . . . . . . . . . . 2.BrownZone . . . . . . . . . . . . . . . . . 3. Chestnut Zone . . . . . . . . . . . . . . . . 4. Chernozem Zone . . . . . . . . . . . . . . . 5. Brown Forest-Gray Wooded Zones . . . . . . . . . . 6. Podzol-Brown Podzolic Zones (Mountainous Areas) . . . . . 7. Brown Podzolic Zone . . . . . . . . . . . . . . 8 . Brown Latosol Zone . . . . . . . . . . . . . . . 9. Reddish Brown Latosol Zone-Upland Areas . . . . . . . 10. Reddish Brown Latosol Zone-Lowland Areas . . . . . . . I 1. Reddish Brown Latosol-Noncalcic Brown Zones . . . . . . . IV. Soil Management . . . . . . . . . . . . . . . . . 1. Use of Soil Management Practices . . . . . . . . . . a. General . . . . . . . . . . . . . . . . . b. Irrigation . . . . . . . . . . . . . . . . c. Fertilizers . . . . . . . . . . . . . . . . d. Liming Materials . . . . . . . . . . . . . . 2. Sierozem Zone . . . . . . . . . . . . . . . . 3.BrownZone . . . . . . . . . . . . . . . . . 4. Chestnut Zone . . . . . . . . . . . . . . . . 5. Chernozem Zone . . . . . . . . . . . . . . . . 6. Brown Podzolic Zone . . . . . . . . . . . . . . 7. Brown Latosol Zone . . . . . . . . . . . . . . . 8. Reddish Brown Latosol Z o n e u p l a n d Areas . . . . . . .

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Approved for publication as Miscellaneous Paper No. 22 of the Oregon Agricultural Experiment Station I

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9. Reddish Brown Latosol Zon-T-wland Areas 10. Reddish Brown Latosol-Noncalcic Brown Zones. V. Crop Zones of the Region . . . . . . . . . M.Field Crops of the Region . . . . . . . . . 1. Cereals. . . . . . . . . . . . . a.Wheat . . . . . . . . . . . b. Barley . . . . . . . . . . . c. Oats . . . . . . . . . . . . d. Rye . . . . . . . . . . . . e. Corn. . . . . . . . . . . . 2. Forages . . . . . . . . . . . . a. Hay Crops . . . . . . . . . . b. Silage . . . . . . . . . . . c. Improved Pastures. . . . . . . . 3. Field Seed Crops. . . . . . . . . . a. Importance of the Region . . . . . b. Legume Seed Crops . . . . . . . c. Grass Seed Crops 4. Potatoes . . . . . . . . . . . . 5. Sugar Beets . . . . . . . . . . . 6. Annual Legumes. . . . . . . . . . References. . . . . . . . . . . . . .

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I. INTRODUCTION The Pacific Northwest is a region of contrasts in relief features, geology, climate, soils, natural vegetation, and water resources. Timber and agriculture have shaped its economy in the past but processing is increasing in importance. The Pacific Northwest is used here in its narrowest sense to include the states of Idaho, Oregon, and Washington, although many would also include western Montana. Some farming on a small scale was started in the western part of the region shortly after 1800. Major development of land for crop production has occurred during the past 75 years. Only 12 per cent of the region is used for crops. Owing to the wide diversity of physical characteristics a large variety of crops can be produced. Even within the Willamette Valley of western Oregon over 25 different crops are produced commercially. Major emphasis in this review is placed on the production of field crops and associated soil management in the Pacific Northwest. As a background for this discussion, land forms, climate, water resources, and soils of the region are considered. Since the soil is such an important factor in crop production and soil management, it is treated more thoroughly than the other regional characteristics. Owing to the broad scope of the subject, many of the generalities presented contain exceptions that cannot be discussed here.

FIELD CROP PRODUCTION A N D SOIL MANAGEMENT

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11. REGIONAL CHARACTERISTICS Land forms, climate, and water resources, along with soils, which are discussed under Section 111, markedly influence the entire economy of the region. Land use, field crop production, and soil management are all controlled to a large degree by these factors.

I. Land Forms Varied and strong relief is characteristic of the region. Six physiographic provinces are recognized in the region, namely: (I) Pacific Border Province, (2) Cascade Mountains, (3 ) Columbia Intermontane Province, ( 4 ) Northern Rocky Mountains, ( 5 ) Middle Rocky Mountains, and (6) Basin and Range Province. Only a small portion of the latter two provinces occur in the region in south central to southeastern Oregon and the southeast corner of Idaho (Allison, 1953). Mountains occur along the entire Washington and Oregon coast in the Pacific Border Province. Except for the Olympic Mountains in north Washington, which are higher, they are less than 4000 feet in elevation. The Brown Latosol Zone and adjacent Reddish Brown Latosol Zone-Upland Areas cover most of this area (see Fig. 3). The Willamette-Cowlitz-Puget lowlands are inland from the coastal mountains. They extend 350 miles from central Oregon to Canada and vary in width from 20 to 70 miles. These are primarily stream valleys containing alluvial terraces and, in the Puget lowland, glaciofluvial gravel. The Brown Podzolic Zone and Reddish Brown Latosol Zone-Lowland Areas occur in this province (see Fig. 3). The dominant feature of the western part of the region is the Cascade Mountains, which range in width from over 100 miles near the Canadian border to less than 50 miles at the California line. The crest of the Cascade Range is approximately 5000 to 8000 feet with many higher peaks, most of which are volcanic. The surface consists largely of extrusive igneous materials. This mountain range in many ways separates the eastern and western portion of the region into two separate spheres or realms. It is cut only by the Columbia River. The soils of the Cascade Mountains are mostly in the Podzol-Brown Podzolic Zones of western Washington and Oregon and in the adjacent Reddish Brown Latosol Zone-Upland Areas (see Fig. 3). The Columbia Intermontane Province covers nearly all of Oregon east of the Cascades, western and southern Idaho, and the southern part of eastern Washington. It is dominantly underlain by basalt lava flows. One of the largest areas of volcanic rock on the earth's surface occurs in the Pacific Northwest. Most of the province has elevations of 1000 to 5000 or more feet above sea level. The region has a highly

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H. B. CHENEY, W. H. FOOTE, E. G. KNOX, A N D H. H. RAMPTON

varied surface including mountains with peaks of 10,000 feet elevation. Within the area are found the Sierozem, Brown, Chestnut, Chernozem, and Brown Forest-Gray Wooded soil zones (see Fig. 3). The Northern Rocky Mountains contain deep valleys and high mountain ridges, often 2000 to 8000 feet above the surrounding land. Some of the valleys are large enough for agricultural development and settlement. The soils are largely in the Podzol-Brown Podzolic and Brown Forest-Gray Wooded Zones of Idaho and northeastern Washington (see Fig. 3). 2. Climate Climate in the Pacific Northwest is most variable. The Cascade Range divides the area into two realms-a more humid west side and a drier east side on the interior as shown in Fig. 1. The climate west of the Cascades can be characterized as follows: ( I ) abundant precipitation, most of which comes during the winter, (2) small range in temperature for the latitude, with relatively warm winters and cool summers, (3) long frost-free period, and ( 4 ) winds predominantly from the Pacific Ocean. Total precipitation is high in the Coast Ranges and the Cascade Mountains but in the “dry shadow” east of each of these barriers it drops rapidly. The Willamette-Cowlitz-Pget Sound lowland receives 30 to 40 inches. In the interior east of the Cascades precipitation falls below 20 inches and often below 10 inches, except where increased precipitation occurs over mountains. In the interior the climate is more continental than it is along the coast, although it is modified by winds from the Pacific Ocean. The interior has greater extremes of temperature in both summer and winter than the coast. Low humidities and abundant sunshine prevail. The growing season as shown in Fig. 2 is generally shorter and limits the type of crops that can be grown in some irrigated regions. The low amount of summer precipitation has a marked effect on crdp production. Even in the more humid region west of the Cascades the normal total precipitation during July and August is 1.5 inches or less in most agricultural areas. Consequently, irrigation is increasing not only in the drier area east of the Cascades but also in the more humid region. Selected climatic information is given with the description of each of the soil zones under Section I11 and with the discussion of crop zones under Section V. 3 . Water Resources The water resources of the Pacific Northwest are one of its most important assets. The stream runoff in the region is greater than the

FIELD CROP PRODUCTION A N D SOIL M A N A G E M E N T

5

Y

." l3

Bl

FIG.1. Anmial precipitation in the Pacific Northwest. (Source: Highsmith, 1956.)

6 H. B. CHENEY,

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d

FIG. 2. Growing season in the Pacific Northwest. (Source: Highsmith, 1956.)

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F I E L D CROP PRODUCTION A N D SOIL M A N A G E M E N T

total from all other areas of the United States west of the Mississippi River. This water resource is still being developed for irrigation, electric power, fishing, industrial and domestic use, and other purposes. Water for irrigation on 4.4 million acres is the most direct contribution to crop production. The availability of relatively low-cost electric energy also has contributed to the development of sprinkler irrigation. Moreover, since the agricultural production in a region is affected by its total development, the water resources have exerted many indirect effects on crop production and soil management. 4. Land Use

As given in Table I, over 88 per cent of the land is used for forests and range. Less than I2 per cent is used for the production of field TABLE I Land Use in the Pacific Northwest' (In thousands of acres) Land use Cropland Forest land Range land

Total

Idaho

Oregon

Washington

5,230 18,813 28,729

5,537 29,755 26,349

7,721 24,100 10,929

18,488 743,668 66,000

543,97Q

61,641

4'2,743

157,356

- -

Total

* Sourcea of data: Cropland acreage and total acreage from 1960 U. S. Census of Agriculture. Forest land acreage baaed on U. S. Department of Agriculture Forest Service Reappraisal Data, 1946. Range land acreage by difference.

and horticultural crops. Approximately one-fourth of the forest land is noncommercial owing to high altitude, rugged topography, and inadequate moisture, or because it has been set aside for recreation or watershed protection. Wild animals and domestic cattle graze much of the noncommercial forest area. T h e land used for crop production is widely distributed throughout the region (Fig. 4). One-fourth of the total cropland acreage is irrigated. In 1949 about 60 per cent of the total cropland was in harvested crops, 22 per cent was in cultivated summer fallow, 13 per cent was used only for pasture, and 5 per cent was idle or in crops not harvested. Owing to the diversity of climate and soil, the types of crops grown vary widely. Similarly, crop production and soil management problems change sharply from one area to another.

111. SOILRESOURCES The Pacific Northwest has been divided into 11 major kinds of soil area (Fig. 3), primarily on the basis of soil differences related to dif-

8 H. B. CHENEY,

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FIQ.3. Soils of the Pacific Northwest. (Source: Highsmith,1956.)

FIELD CROP PRODUCTION AND SOIL MANAGEMENT

9

ferences in climate. These 11 kinds of area or map units consist of single soil zones, combinations of soil zones, or subdivisions of a soil zone. (A soil zone is a geographic unit within which there is uniformity in those soil characteristics which are determined by climate.) Each map unit is described in terms of climate, natural vegetation, the common soils, map inclusions, and land use. The soils are characterized by reference to 28 great soil groups, in terms of horizon sequence and selected properties of the dominant horizons. In the descriptions, horizons designated with an asterisk are essential for the group. Those designated by parentheses are permissible but not common. Horizon nomenclature and descriptive terms are defined in the Soil Survey Manual (Soil Survey Staff, 1951). The concepts and nomenclature of the great soil groups are based on an unpublished family grouping of soils of the Far Western States made by Ray C. Roberts in May, 1952. For many groups the concepts and names are those given in the 1938 Yearbook of Agriculture (Baldwin et al., 1938) or by Thorp and Smith (1949).The names of other groups are designated by quotation marks. It is thought that there is general but not complete agreement about the groups among those concerned with classification in the three states. The map itself is compiled from many sources. The primary sources are unpublished soil association maps of the Far Western States prepared by members of the correlation staff (mainly by R. C. Roberts and W. J. Leighty) of the Soil Conservation Service, United States Department of Agriculture. Important revisions were suggested by R. C. Roberts, M. A. Fosberg (Idaho Agricultural Experiment Station), W. A. Starr (Washington Agricultural Experiment Station), and R. W. Chapin, W. W. Hill, and C. F. Parrott (Soil Conservation Service).

1. Sierozem Zone Precipitation: Mean Jan. temp.: Mean July temp.: Typical natural vegetation:

Dominant welldrained soils: Dominant wet soils:

5 to 10 inches 30 to 33” F. 65 to 75” F. Big sagebrush (Ariemisia trideniata Nutt.),bluebunch wheatgrass (Agropyron spicuturn (Pursh) Scribn. & Sm.), and hopsage (Gruya spinosa (Hook.) Moq.) on Sierozems. Shadscale (Atriplez confertifolia (Torr.) Wats.) and bud sage (Ariernisiu spinescens D. C. Eaton) on Desert soils. Greasewood (Sarcobntus verrniculutus (Hook.) Torr.) and salt grass (Distichlis stricta (Torr.) Rydb.) in saline and alkali areas. Sierozem, with Desert soils in the dryst areas. “Calcic Gley,” Solonetz and solodized-Solonetz soils. In irrigated areas there is an increasing proportion of artificially saline soils.

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Other soils: Inclusions of other soil zones: Land use:

Lithosols (especially on lava flows in southern Idaho), Regosols (especially in wind-deposited materials in Washington), and Alluvial soils. Brown, Chestnut, and Brown Forest-Gray Wooded Zones with increasing elevation and precipitation and decreasing temperatures. Range for cattle and sheep on Sierozems. Winter range for sheep on Desert soils, Horticultural and field crops with irrigation chiefly on soils from alluvium in the valleys.

Typical characteristics of common soils: Desert soils-A1*, BI, Bs*, Bs.., (Bm), Cca, (Cm), (D), C, Dr. The A is 1 to 4 inches thick, light gray when dry, low in organic matter, vesicular, and calcareous. There is a thin surface crust, polygonal cracking, and desert pavement. The B is commonly a horizon of clay accumulation, darker in color and higher in organic matter than the A, calcareous, and with small blocky or subangular blocky peds. Sierozem soils-Al*, B , Br*, BI, (Bats), Cca, (Cm), (D), C, Dr. The A is 3 to 6 inches thick, light brownish gray when dry, low in organic matter, vesicular, not calcareous, and has a thin surface crust, polygonal cracking, and pH values from 7.0 to 8.0. The B is commonly a horizon of clay accumulation, darker than the A in color and calcareous, with blocky or subangular blocky structure. Solonetz soils-A*, Bz*, Bs, (Bm), (Cm), (D), C. The A is 2 to 10 inches thick with properties which vary from zone to zone. The B is a horizon of clay accumulation, with dark-coated, prismatic, or columnar peds and pH values from 8.5 to 10.0. “Calcic Gley” soils-(A1), C,*, Cm, (D), G. The Cl is calcareous with pH values from 8.5 to 10.0. I t is a horizon of evaporation from a relatively high water table. Solodized-Solonetz soils-Refer to the Brown Zone. Lithosols-Refer to the Podzol-Brown Podzolic Zones. Regosols-(Aoo), (Ao), A,, C*, (Cca), (Cm). Regosols are from unconsolidated material other than alluvium. They have weakly expressed or no developed horizons. Alluvial soils-Refer to Reddish Brown Latosol Zone-Lowland Areas.

2. Brown Zone Precipitation: Mean Jm. temp.: Mean July temp.: Typical natural vegetation: Dominant welldrained soils: Dominant wet SO&:

Other soils: Inclusions of 0th- soil zones:

8 to 12 inches. 20 to 32” F. 65 to 75” F. Perennial bunch grasses and big sage. Greasewood and salt grass in saline and alkali areas. Brown soils.

“Calcic Gley,” Solonetz, solodized-Solonetz and “Humic Gley” soils. Alluvial soils and Lithosols (in southern Idaho). Sierozem Zone in the dryest parts of the delineation, especially on south-facing slopes and in shallow areas. Chestnut Zone in the parts of the delineation with highest rainfall espe-

FIELD CROP PRODUCTION A N D SOIL MANAGEMENT

Land use:

11

cially on north-facing slopes. Brown Forest-Gray Wooded Zones at high elevations. Range land, wheat-fallow cultivation in best areas, and horticultural and field crops with irrigation, chiefly on soils from alluvium in the valleys.

Typical characteristics of common soils: Brown Soils-A1*, b,Bl, &*,B,, Cca, (Cm), (D), C, Dr. The A is 5 to 10 inches thick, grayish brown when dry, with platy breaking to granular structure, and pH values from 6.5 to 7.5. The B is commonly a horizon of clay accumulation, slightly brighter in color (with higher chroma) than the A, with prismatic breaking to blocky or subangular blocky structure, and pH values from 7.0 to 8.5. “Calcic Gley” soils-Refer to the Sierozem Zone. Solonetz soils-Refer to the Sierozem Zone. Solodized-Solonetz-Al, A*, &*, B8, (Bm), (Cm), (D), C. The A is 5 to 15 inches thick with pH values from 6.0 to 7.0. The B is a horizon of clay accumulation, with prismatic or columnar structure, dark coatings on the peds, and pH values from 6.5 to 7.5. “Humic Gley” soils-Refer to the Chernozem Zone. Alluvial Soils-Refer to the Reddish Brown Latosol Zone-Lowland Areas. Lithosols-Refer to the Podzol-Brown Podzolic Zones.

3. Chestnut Zone Precipitation: Mean Jan. temp.: Mean July temp.: Typical natural vegetation: Dominant welldrained soils: Dominant wet soils: Other soils: Inclusions of other soil zones: Land use:

10 to 15 inches. 90 to 32” F. 65 to 75” F. Perennial bunch grasses. Greasewood and salt grass in saline and alkali areas. Chestnut soils.

“Humic Gley” soils, solodized-Solonetz soils (or Planosols), “Calcic Gley” soils, and Solonetz soils. “Grumusols” on parent materials very high in clay. Alluvial soils. Brown Zone in dryest parts of the delineation, especially on south-facing slopes and in shallow areas. Chernozem Zone in parts of the delineation with highest rainfall. Brown ForestGray Wooded Zones at high elevations. Dry land wheat-fallow or continuous wheat cultivation. Range. Horticultural and field crops with irrigation, chiefly on soils from alluvium in the valleys.

Typical characteristics of common soils: Chestnut soils-A1*, A, BI, &*, B,, Cca, (Cm), (D), C, Dr. The A is 7 to 15 inches thick, dark grayish brown when dry, with platy breaking to granular structure and pH values from 6.5 to 7.5. The B is commonly a horizon of clay accumulation, brighter in color (with higher chroma) than the A, with prismatic breaking to blocky or subangular blocky structure and pH values from 7.0 to 8.5.

12

H. B. CHENEY, W. H. FOOTE, E. G. KNOX, AND H. H. RAMPTON

“Humic Gley” soils-Refer to Chernozem Zone. Solodized-Solonetz soils-Refer to Brown Zone. Solonetz soils-Refer to Sierozem Zone. “Calcic Gley” soils-Refer- to Sierozem Zone. “Grumuso1s”-Refer to Reddish Brown Latosol-Noncalcic Brown Zones. Alluvial soils-Refer to Reddish Brown Latosol Zone-Lowland Areas.

4 . Chernozem Zone Precipitation: Mean Jan. temp.: Mean July temp.: Typical natural vegetation: Dominant welldrained soils: Dominant wet soils: Other soils: Inclusions of other soil zones: Land use:

15 to 22 inches. 20 to 32” F. 60 to 70” F. Perennial bunch grasses with shrubs such as snowberry (Symphoricarpos albw (L.) Blake.) and rose, and forbes especially in Prairie areas. There is a strong tendency for sod formation in Prairie areas. Chernozem and Prairie (Brunizem) soils.

“Humic Gley” soils, Planosols (or solodized-Solonetz), and “Calcic Gley” soils. Alluvial soils. Chestnut Zone in dry areas. Brown Forest-Gray Wooded Zones at high elevations. Dryland cultivation (continuous wheat or wheat-peas) Range. Horicultural and field crops with irrigation.

.

Typical characteristics of common soils: Chernozem and Prairie soils-Al*, As, B,, BZ*, Bs, Cca’, (D), C, Dr. (1. Cca is essential for Chernozem and not permissible for Prairie.) The A is more than 12 inches thick, very dark grayish brown or darker when dry, with granular structure and pH values from 6.0 to 7.0. The B is commonly a horizon of clay accumulation, lighter than the A in color, with blocky or subangular blocky structure and pH values from 6.5 to 8.0. “Humic Gley” soils-A,*, A, B,, Bt, Bs, (Cm) , (D) ,C. The A is 6 to 30 inches thick, dark gray to black, with pH values from 6.5 to 8.0. T h e B is a horizon of either clay accumulation or maximum color intensity. It may be gleyed. Planosols-Refer to Reddish Brown Latosol Zone-Lowland Areas. “Calcic Gley” soils-Refer to Sierozem Zone. Alluvial soils-Refer to Reddish Brown Latosol Zone-Lowland Areas.

5 . Brown Forest-Gray Wooded Zones Precipitation: Mean Jan. temp.: Mean July temp.:

15 to 30 inches, 15 to 25” F. 60 to 70“ F.

The growing season is short. Typical natural vegetation:

Ponderosa pine (Pinw ponderosa Laws.) or lodgepole pine (P.contorts Loud.), white fir (Abies concolor Lindl.), bitterbrush (Purshiu tridentata (Pursh) D.C.), manzanita (Arctostaphylos spp.) , and mountain mahogany (Cercocarpus ledifolius T. & G.).

FIELD CROP PRODUCTION A N D SOIL MANAGEMENT Dominant welldrained soils: Dominant wet soils: Other soils: Inclusions of other soil zones: Land use:

13

Brown Forest soils, with Gray Wooded and Prairie soils in northern Washington and Idaho. “Humic Gley” soils. Alluvial soils. Brown, Chestnut, and Chernozem zones at low elevations and in low rainfall areas. Podzol-Brown Podzolic Zones at the highest elevations. Forestry. Summer range, Gray Wooded and Prairie areas are cultivated.

Typical characteristics of common soils: “Brown Forest” soils--Am, A, Al*, (AS), B,, &*, Bt,(Cm), (D), C, Dr. The & is an F layer 0 to 2 inches thick. The A1 is 4 to 8 inches thick, dark grayish brown when dry, with granular structure and p H values from 6.0 to 7.0. The B is commonly a horizon of clay accumulation, warm brown (with high chroma) in color, with blocky or subangular blocky structure and pH values from 5.5 to 6.5. Gray Wooded Soils-&, A*, (A1), A*, B2*,Bs, Cca, (D), C, (Dr). The A includes F and H layers and is 1 to 6 inches thick with pH values from 5.0 to 7.0. The A is Ito 8 inches thick, light gray, platy or massive, with pH values from 5.5 to 7.0. The B is a horizon of clay accumulation, with blocky or subangular blocky structure and pH values from 6.0 to 8.0. Prairie soils-Refer to the Chernozem Zone. “Humic Gley” soils-Refer to the Chernozem Zone. Alluvial soils-Refer to the Reddish Brown Latosol Zone-Lowland Areas.

6. Podzol-Brown Podzolic Zones (Mountainous Areas) Precipitation: Mean Jan. temp. : Mean July temp.:

30 to 100 inches. 15 to 30’ F. 55 to 65” F.

The growing season is short. Typical natural vegetation: Dominant welldrained soils: Dominant wet soils: Other soils: Inclusions of other soil zones: Land use:

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) , hemlock (Tsugu heterophylla (Raf.) Sarg.), western redcedar (Thuju plicaiu Donn.), larch (Larii occidentalis Nutt.), spruce (Picea spp.), white fir, pine. Brown Podzolic soils and Podzols with “Mountain Meadow” soils at high elevations. “Humic Gley” and Alpine Meadow soils. Lithosols and Regosols on steep mountain slopes. Brown Forest-Gray Wooded Zones at lower elevations in Idaho and eastern Oregon and Washington. Brown Latozol Zone at lower elevations in the Oregon and southern Washington Cascades and on the Olympic peninsula. Forestry. Recreation. Summer range (in open areas especially).

Typical characteristics of common soils: Brown Podzolic soils-Refer to Brown Podzolic Zone. Podzol Soils-&, A*, (Al), AS*, &*, (Bm), BI, (D), C. The A includes F and H layers and is 2 to 10 inches thick, with p H values from 4.0 to 5.0. The b is 1 to 10 inches thick, light gray, platy or massive, with pH

14

H. B. CHENEY,

w. H.

FOOTE, E. G. KNOX, AND H. EI. RAMPTON

values from 4.5 to 5.5. The B is a horizon of humus and iron oxide accumulation, yellowish brown, with fine or very fine crumb structure, and pH values from 5.0 to 6.0. “Mountain Meadow” soils-AI*, AS, B,, Ba,Bi, (D), C. The A is 6 to 20 inches thick, very dark grayish brown or darker, with fme granular structure and pH values from 4.5 to 5.5. The B is a horizon of maximum color intensity, yellowish brown, with pH values from 4.5 to 5.5. “Humic Gley” soils-Refer to the Brown Latosol Zone. Alpine Meadow mils-A1*, A, BG*, (D), C. The A is 6 to 10 inches thick, nearly black, with pH values from 5.0 to 6.0. The BG is a gleyed horizon with gray and/or mottled colors and pH values from 5.0 to 6.0. Lithomls-((Am), (Ao), Al, C, Dr*. Lithosols are shallow to bedrock, with weakly expressed or no developed horizons. Regosols-Refer to the Sierozem Zone.

7. Brown Podzolic Zone This zone is in an area of continental glaciation. Precipitation: Mean Jan. temp.: Mean July temp.: Typical natural vegetation: Dominant welldrained soils: Dominant wet soils: Other soils: Land use:

20 to 60 inches. 35 to 40” F. 55 to 65” F. Douglas-fir, hemlock, alder (Alnus rubra Bong.), and western redcedar. Brown Podzolic soils, with “Gray Podzolic” soils in the dryer areas. Ground-Water Podzols and “Humic Gley” soils. Alluvial soils. Horticultural and field crops. Forages. Forestry. There is intensive cultivation on Alluvial soils.

Typical characteristics of common soils:

A’, AI, (At), Bz*, (Bm), Bs, (D), C. Brown Podzolic soils-&, The includes F and H layers and is 1 to 6 inches thick with pH values from 4.0 to 5.0. The Al is 0 to 3 inches thick. The B is a horizon of humus and iron oxide accumulation, yellowish brown, with fine or very fine crumb structure and pH values from 5.0 to 6.0. “Gray Podzolic” soils-&, A*, A*, B*, (D), C, (Dr). The A is 1 to 4 inches thick with pH values from 5.0 to 6.0. The At is 2 to 10 inches thick, light brownish gray or lighter, commonly with spherical concretions, and with pH values from 5.0 to 6.0. The B is darker than the AZ and has poorly defined subangular blocky structure and pH values from 5.0 to 6.0. Ground-Water Podzols--Am, &*,A,, A,*, Bh, B2*, Bs, (D), C. The A, is 2 to 8 inches thick with pH values from 4.0 to 5.0. The A1 is 1 to 10 inches thick and black with pH values from 4.5 to 5.5. The G is 3 to 15 inches thick, light gray or lighter, and mottled, with pH values from 4f.5 to 5.5. The B is a horizon of humus and iron oxide accumulation, and commonly cemented into a pan (orstein), with pH values from 4.5 to 5.5. “Humic Gley” soils-Refer to the Brown Latosol Zone. Alluvial soilsRefer to the Reddish Brown Latosol Zone-Lowland Area.

FIELD CROP PRODUCTION A N D SOIL MANAGEMENT

15

8 . Brown Latosol Zone Precipitation: Mean Jan. temp.: Mean July temp.: Typical natural vegetation: Dominant welldrained soils: Dominant wet soils: Other soils: Land use:

60 to 140 inches. 35 to 45” F. 55 to 65” F. Douglas-fir, hemlock, western redcedar, Sitka spruce (Picea sitchemis (Bong.) Carr.), and alder. “Brown Latosols.”

“Humic Gley” soils and Planosols. “Fern prairie” or “Ando” soils on nonforested areas near the coast. Podzols and Ground-Water Podzols on sands of the coastal area. Alluvial soils. Forestry. Cultivated crops (chiefly forages on dairy farms) on soils from alluvium in the valleys or on marine terraces along the coast.

Typical characteristics of common soils: “Brown Latosols”-&, A,*, A, BI, &*, BI, (D), C, Dr. The A is 10 to 20 inches thick, dark brown or darker, with strong granular structure and pH values from 5.0 to 6.0. The B is a horizon of residual iron and aluminum oxides, brown or dark yellowish brown, friable, with clay texture and pH values from 4.0 to 5.0. “Humic Gley” soils-A,*, G,BG*, CG, (D), C, Dr. The A is 6 to 30 inches thick, black or very dark gray, with pH values from 5.0 to 6.0. The BG is a gleyed horizon, mottled or gray, with pH values from 5.5 to 6.5. “Ando” soils-&*, A, &, &, B+ (D), C, Dr. The A is 10 to 30 inches thick, very dark grayish brown or darker, light in weight, with fine or very fine granular structure, and pH values from 5.5 to 6.5. The B is a horizon of maximum color intensity, of clay accumulation, or of residual iron and aluminum oxides, with p H values from 5.0 to 6.0. Podzols-Refer to the Podzol-Brown Podzolic Zones. Ground-Water Podzols-Refer to the Brown Podzolic Zone. Alluvial soils-Refer to the Reddish Brown Latosol Zone-Lowland Areas. Planosols-Refer to the Reddish Brown Latosol Zone-Lowland Areas.

9. Reddish Brown Latosol Zone-Upland Precipitation : Mean Jan. temp.: Mean July temp. : Typical natural vegetation: Dominant welldrained soils: Dominant wet soils: Inclusions of other soil zones: Land use:

Areas

40 to 60 inches. 32 to 40” F. 60 to 65” F. Douglas-fu; western redcedar. “Reddish Brown Latosols.” “Humic Gley” soils and Planosols. Reddish Brown Latosols Zone-Lowland Areas in narrow river valleys. Forestry. Field and Horticultural crops in areas of favorable topography.

16

H. B. CHENEY,

w. H. FOOTE,

E. G. KNOX, AND H. H. RAMPTON

Typical characteristics of common soils: “Reddish Brown Latosols”-&, AX*, A, B,, BI*, Ba, (D), C, Dr. The A is 6 to 12 inches thick, dark reddish brown or darker, with strong granular structure and spherical concretions, and with pH values from 5.5 to 6.5. The B is a horizon of residual iron and aluminum oxide accumulation (it may also show evidence of silicate clay accumulation), dark red or dark reddish brown, friable, with clay texture, and pH values from 4.5 to 5.5. “Humic Gley” soils-Refer to the Brown Latosol Zone. Planosols-Refer to the Reddish Brown Latosol Zon-Lowland Areas.

10. Reddish Brown Latosol Zone--Lowland Precipitation: Mean Jan. temp.: Mean July temp.: Typical natural vegetation: Dominant welldrained soils: Dominant wet soils: Inclusions of other soil zones: Land use:

Areas

35 to 50 inches. 35 to 40” F. 60 to 65’ F. Douglas-fr, Oregon white oak (Quercus garryam Hook.), and grasses. An unclassified group, “Reddish Brown Latosols,” and Alluvial soils. Planosols, “Humic Gley” soils. Reddish Brown Latosol-Noncalcic Brown Zones.

Horticultural and field crops with and without irrigation. Forages. Grass and legume seeds. There is intensive cultivation of horticultural crops on Alluvial soils with irrigation.

Typical characteristics of common soils: Unclassified group-Al*, A, BI, BI*, B , (D), C. The A is 6 to 15 inches thick, very dark grayish brown when moist, grayish brown when dry, with granular structure and pH values from 5.5 to 6.5; the B is a horizon of clay accumulation, with blocky, subangular blocky, or prismatic structure, and pH values from 6.0 to 7.0. “Reddish Brown Latosols”-Refer to Reddish Brown Latosol Zone-Upland Areas. Alluvial soils-(Aou), (AO), At, C*, (Cca), (Cm). Alluvial soils are from recent alluvium. They have weakly expressed or no developed horizons. Planosols-Al*, A*, BI*, BI, (D), C, (Dr). The A, is 2 to 10 inches thick, with pH values from 5.0 to 6.0. The A is 4 to 12 inches thick, grayish brown or lighter, with p H values from 4.5 to 5.5. The B, is a horizon of intense clay accumulation, with prismatic or columnar structure, and pH values from 4.5 to 7.0. “Humic Gley” soils-Refer to Brown Latosol Zone.

11. Reddish Brown Latosol-Noncalcic Brown Zones Precipitation: Mean Jan. temp.: Mean July temp.: Typical natural vegetation :

20 to 60 inches. 32 to 40” F. 62 to 70’ F. Douglas-fw, ponderosa pine, sugar pine (Pinus larnberiiam Dougl.), California black oak (Quercus kelloggii Newb.), madrone (Arbutus rnenziesii Pursh), grasses, manzanita, poison oak (Rhus diversiloba T. & G . ) , rose.

F I E L D CROP P R O D U C T I O N A N D SOIL M A N A G E M E N T

Dominant welldrained soils: Dominant wet soils: Other soils: Land use:

17

“Reddish Brown Latosols,” Noncalcic Brown soils, Prairielike soils, and “Grumusols.” “Humic Gley” soils and “Grumusols.” Alluvial soils. Forestry. Unimproved pasture (range). Cultivation of horticultural and field crops with irrigation.

Typical characteristics of common soils: “Reddish Brown Latosols”-Refer to the Reddish Brown Latosol Zone-Upland Areas. Noncalcic Brown soils-A,*, BI, &*, (Bm), Bs, (D), C, Dr. The A is 3 to 10 inches thick, low in organic matter, with weak structure, and pH values from 5.0 to 6.0. The B is a horizon of clay accumulation, reddish or yellowish in color, with prismatic, blocky, or subangular blocky structure, and pH values from 5.0 to 6.0. Prairie-like soils-Refer to Chernozem Zone. “Grumusols”-AI*, G,(D), C, Dr. The A (divided into A and B by some) is 8 to 41) inches thick, black, or less commonly gray, olive or red, extremely hard, very plastic, and very sticky, with clay texture. With drying, the horizon cracks deeply and the surfaces mulches into small granules. “Humic Gley” soils-Refer to the Brown Latozol Zone. Alluvial soilcRefer to Reddish Brown Latosol Zone-Lowland Areas.

IV. SOILMANAGEMENT Owing to the diversity of soil management problems and practices, they will be discussed largely by soil zones as shown in Fig. 3. The Podzol-Brown Podzolic Zones and Brown Forest-Gray Wooded Zones are not discussed. Crop production in these zones is largely confined to narrow alluvial valleys, many with unique local soil problems. The general use of soil management practices will be summarized for the entire region insofar as information is available. 1. Use of Soil Management Practices a. General. Information on the extent to which most soil management practices are used is not available for the region. Only general comments can be made about their use. For a few practical statistical information is available. Practices to reduce runoff and aid erosion control, such as contour farming, contour strip cropping, contour planting of orchards, vineyards, and cane fruits, terraces, field diversions, and wind strip cropping, are used to a limited extent. In 1953, 17 per cent of the total Agricultural Conservation Program payments in the region was used for mechanical practices primarily for erosion control. Crop residues are generally used and not burned, except in a few local areas. Stubble mulch is practiced in the drier wheat-growing areas. The use of crop rotations, green manures, and cover crops varies widely.

18

w. H. FOOTE, E. G. KNOX, AND H.H. RAMPTON Individual farmers, especially in western Oregon, have been making progress in improving drainage, Some community projects also are underway. Approximately 10 per cent of the total Agricultural Conservation Program payments in 1953 in the region were used for drainage. b. Irrigation. Approximately 25 per cent of the total cropland in the region is irrigated. As shown in Table 11, the number of acres irrigated is increasing. This increase in acreage is occurring largely in Oregon and Washington, but Idaho still has about one-half of the irrigated land in the region. Much of the increased acreage in Washington during the past five years is in the Columbia Basin Project of the Bureau of H. B. CHENEY,

TABLE I1 Irrigated Land in the Pacific Northwest' (In thousands of acres) Stat+!ear Idaho Oregon

Washington Total

1920

1939

1949

1954

$181 899 499

1896 1030 494

2137 1307 689

2144 1490 778

-

-

-

-

3579

3419

4033

4414

~

1 Source:

U. S. Ceniua of Agriculture for 1930. 1940,1960,

1964 (Preliminary).

Reclamation located in the central part of the state. In Oregon, 40 per cent of the increase from 1949 to 1954 occurred in the western part of the state. Much of the increased acreage is sprinkler irrigated. In 1949, sprinklers were used on 4 per cent of the irrigated acreage. Over onehalf of the sprinkler irrigation was in Oregon. Improvement in irrigation practices and improvement and development of irrigation systems is progressing. In 1953 over one-fourth of the total, or nearly 1.5 million dollars, spent under the Agricultural Conservation Program was used for irrigation practices. Irrigation will continue to expand, both in small tracts and in large projects such as the Columbia Basin Irrigation project in central Washington. Estimates of potentially irrigable land indicate that the acreage under irrigation in the region may eventually be twice the present acreage. c. Fertilizers. Fertilizer consumption in the region in 1953-54 was 438,665 tons, according to Scholl et QZ. (1955). This is approximately double the annual use from 1947 to 1950. Washington leads in fertilizer consumption, with Oregon second and Idaho third. Consumption in Washington increased 60 per cent from 195!2-53 to 1953-54. Consumption of nitrogen (N) , available phosphoric acid (P,O,), and potash (K,O) in the region during recent years is given in Table

19 111. Nitrogen use has been increasing rapidly whereas phosphate and potash consumption has held nearly constant since 1947. Phosphate use did increase markedly in 1953-54. A large portion of the increase in nitrogen use occurred in the dryland wheat area of the Chernozem and Chestnut Zones. The use of anhydrous and aqua ammonia have both increased rapidly in this area since they were introduced two to five years ago. The average content of available nutrients in the fertilizers used is relatively high, averaging 28 per cent in 1953-54. It increased from 24 per cent in 1947-48. For the region the average ratio of N-P,O,-K,O FIELD CROP PRODUCTION A N D SOIL M A N A G E M E N T

TABLE I11 Consumption of Primary Plant Nutrients in the Pacific Northwest' (Thousands of tons)

Year 1955-51 1953-5s 1951-5Q 1950-51 1949-50 1948-49 1

Nitrogen 74 59 40

Available pzos 41

3s

3% 3s 352

2s 16

31 528

K2O

Total

8 7

12s

7 7

80 73

8 6

63 60

98

Source: Scholl and Wallace (1050, 1951, 1050, 1055) and Sclioll el ul. (1954. 1955).

was 1.0-0.55-0.11 in 1953-54. However, this ratio varies widely in different areas. In 1953-54 only 13 per cent of the total tonnage of fertilizers used consisted of mixed fertilizers. Separate materials have always been popular in the region. Mixed fertilizers have been used most extensively in the western parts of Washington and Oregon. They are used to a greater extent on horticultural crops and potatoes than on other field crops. d. Liming Materials. The use of liming materials is confined largely to western Oregon and western Washington. The use of liming materials during the past 10 years has fluctuated between 40,000 to 60,000 tons annually in Oregon and between 20,000 and 40,000 tons in Washington. Ground limestone is used most extensively but other liming materials, such as waste sugar beet lime, are also important. Owing to lack of high-quality limestone deposits in the acid soil areas most of the high-purity limestone must be transported several hundred miles. Consequently, the price, which averages about $12.00 per ton, is high compared with the price in Midwest areas. Limestone quality is variable, but it has been improved in recent years.

20

H. B. CHENEY,

W.

H . FOOTE, E. G. KNOX, A N D H. H. RAMPTON

2. Sierozem Zone Irrigation is essential for crop production in the Sierozem Zone; hence soil and water management problems on irrigated land are the only ones considered. Similar problems also exist where land is irrigated in the Brown, Chestnut, and Chernozem Zones. Much of the earlier irrigation was started on the alluvial or lowlying soils, but an increasing acreage of zonal soils has been brought under irrigation as new projects have been developed. Most of the irrigated land in the drier regions east of the Cascades was developed on a project basis by the Bureau of Reclamation, or in some cases by private enterprise. Much of it depends on flood water stored in large reservoirs. However, an appreciable acreage is irrigated by individual ranchers or farmers from streams or from wells. A considerable acreage of wild meadows in the range area is flooded in the spring with little control of the water. Irrigating the “desert” provides abundant opportunities but at the same time creates many problems. Except for soil acidity, most of the problems of the humid or semihumid regions are encountered, plus a host of new ones. They may be listed briefly as follows: ( I ) quality of irrigation water, (2) irrigation practices, (3) fertility, ( 4 ) soil physical condition, (5) drainage, (6) salinity and alkalinity, (7) low organic matter content, and ( 8 ) erosion. The major irrigation waters are of high quality for irrigation usage (Jensen et al., 1951; Singleton et al., 1950). However, certain areas do have poor-quality water. Some water provides nutrient ions in sufficient quantities to meet crop needs. This is true of potassium, boron, and sulfur in some areas. Most of the irrigation water is applied by surface methods such as strip borders, basins, corrugations, and contour flooding. However, sprinkler systems are increasing. The agronomist is concerned primarily with water, soil, and plant relationships. Parks (1951) has reviewed the development, present status, and future trends of irrigation agriculture. Physical characteristics of the soil affect the design of irrigation systems and the water management programs to be followed. Moisture movement and its availability to plants is receiving increased attention in research programs. Nitrogen must be supplied in large amounts for all nonlegume crops and for some legumes such as peas and beans. Since the organic matter content of most of these soils is low-often less than 1 per cent -the reserve of total nitrogen in the soil also is low. Both legumes and fertilizers are used extensively to supply the ni-

F I E L D CROP PRODUCTION A N D SOIL M A N A G E M E N T

21

trogen needs. Alfalfa is grown on one-quarter to one-third of the land in some projects. The use of Ladino clover in pastures is a common practice. Sweet clover generally has not been satisfactory. Other legumes also are used in the rotation for hay, seed, pasture, green manure, or cover crops. These crops not only supply nitrogen but also aid in the control of erosion and maintenance of organic matter (Morrison et al., 1954; Nelson and Larson, 1946). Nitrogen fertilizers are used quite generally for crops such as sugar beets, corn, potatoes, and horticultural crops. Recommended rates are relatively high, especially in the Columbia Basin. For example, on sugar beets they range from 80 to 120 pounds of nitrogen per acre following alfalfa to 240 to 300 pounds per acre on new land previously in dryland wheat (Nelson, 1954). For corn following alfalfa the suggested rate is 80 to 120 pounds of nitrogen and on new land from 120 to 160 pounds per acre (Nelson, 1953). Hunter and Yungen (1952, 1955) and Yungen, Hunter, and Bond (unpublished data), after conducting a large number of fertilizer experiments in the Ontario area of eastern Oregon, concluded that somewhat lower rates of nitrogen generally would produce maximum yields in this area. For sugar beets, potatoes, and corn 100 to 120 pounds of nitrogen per acre was usually sufficient for optimum yields. Deficiencies of nutrients other than nitrogen vary. Most soils are well supplied with available potassium. Sulfur deficiencies occur in some areas but not in others. Phosphate fertilizers are used by many farmers f o r crops such as sugar beets, potatoes, and alfalfa. The response to phosphate fertilizers is quite variable. Significant increases in yield are obtained on many sites. Many farmers use phosphate fertilizers consistently even though field experiments show no response to phosphorus. All three states encourage the use of soil tests as a guide to the need for phosphorus. Trace element deficiencies exist under some crop and soil conditions. The zinc problem has been studied extensively in Washington by Wets et al. (1953a, b, 1954). Zinc deficiencies also are apparent under some conditions in Oregon and Idaho. Lime-induced chlorosis, for which ferrous iron has been used (Blodgett, 1946), and boron deficiency also occur. Drainage problems arise largely as the result of overirrigation, although some river bottom areas had a high water table before irrigation. Usually the low-lying land was irrigated first. Later successively higher areas may have been irrigated; often this has resulted in higher and higher water tables in the older irrigated section. If underlying geological formations are complex and variable, surface topography may give little information as to the real nature of the drainage prob-

B. I . C H E N E Y , W. H. FOOTE, E. G. K N O X , A N D H.’H. RAMPTON 22 € lem. This type of problem needs to be approached on a physiographic area basis. The State College of Washington (unpublished data) has developed and applied this approach in the Moxee Valley. Since much of the drainage problem results from overirrigation, greater use of presently known irrigation techniques for efficient water use will help, as will installation of drainage systems. High water tables in an arid area are usually accompanied by the formation of saline or alkali soils. Saline and alkali soil conditions reduce the value and productivity of a considerable acreage. Fireman d al. (1950) give the characteristics of saline and alkali soils in the Emmet Valley area of Idaho. These problem soils were characterized by high water table conditions, low salinity, high pH, high soluble and exchangeable sodium percentages, and low rates of infiltration and permeability. They suggest the following points for consideration in the proper management and reclamation of these soils:

“I. Control of excessive and wasteful use of irrigation water. 2. Improvement of the drainage system based upon studies of the subsoil and ground water conditions in the valley. 3. Use of gypsum and other chemical amendments for the reclamation of high sodium soils. Consideration should be given to the use of barnyard and green manures. 4. Investigation of leaching for reclamation, including the use of drainage water during the initial stages.”

The diagnosis and improvement of saline and alkali soils is reviewed and discussed thoroughly by Richards ( 1954). Mech (1949) points out that it is possible to have serious erosion on the upper end of irrigated fields even when neither soil or water is wasted at the tail end of irrigation runs. The control of wind erosion on the sandy soils in the Columbia Basin involves several practices, according to Mech (1955). These include cultivation when the soil is wet to produce clods, use of crop residues and plant cover, and leveling in late summer.

3. Brown Zone The amount of available moisture, more than any other factor, limits the production of wheat, which is the dominant cultivated crop grown without irrigation, in the Brown Zone. Although wind erosion predominates, some of the land also is affected by water erosion. Balancing the available nitrogen supply with the moisture supply is often difficult. Farmers of Brown soils must be satisfied with relatively low yields (10 to 30 bushels of wheat per acre). Even with summer fallow, which

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is nearly universally practiced in the area, the moisture supply is insufficient for higher yields. In addition to evaporation losses, some moisture is lost by runoff on certain slopes. Moreover, some soils are shallow in depth and lack sufficient storage capacity to conserve all the precipitation that falls. Since most of the wheat is seeded in the fall and most of the rainfall comes in the winter, there is always a considerable element of risk in this near-marginal rainfall area. Stubble mulch or trashy fallow is used extensively by farmers in this area. It is a very effective practice for reducing both wind and water erosion. Reduction in yield with trashy fallow in this area is much less (averaging 1 to 3 bushels per acre) than in the higher rainfall area (Chestnut and Chernozem Zones). Owing to low yields of straw, trashy fallow in the Brown Zone is far easier to prepare and till than is true in the higher rainfall area, where large yields of straw are common. Cushman (1955) and McKay and Moss (19M) give additional information on this practice. The supply of available nitrogen from soil organic matter is often adequate or even excessive for maximum yields where a low supply of available water is the limiting factor. In fact, additions of nitrogen fertilizer may cause “burning,” shriveled kernels, and reduced yields in some cases as a result of stimulation of excessive vegetative growth in the early spring and early exhaustion of available soil moisture. Nevertheless, in many instances improved yields can be obtained with the addition of nitrogen fertilizer, but the risk is greater &an in higher rainfall areas. From none to 20 pounds of nitrogen per acre is a customary recommendation. Large areas of the Brown soils and their associates are irrigated. The management problems are similar to those encountered in the irrigated areas of the Sierozem Zone. 4. Chestnut Zone

Soil management problems and practices in the Chestnut Zone of the Columbia Basin dryland wheat area are intermediate between those of the Brown and Chernozem Zones. Available moisture and nitrogen to a considerable extent control the yields of wheat, which is the dominant crop. Both erosion and the wheat-fallow system of farming have contributed to the decline of soil organic matter. Since many of the slopes average 5 to 10 per cent, sheet erosion by water is a problem. Especially in certain of the drier parts of the area wind erosion also occurs. The summer fallow practice aids in (I) increasing the supply of moisture, (2) the release of nitrogen from organic matter, and (3) control of weeds. On most soils in the area it is still considered an essential

24

H. B. CHENEY,

w.

H. FOOTE, E. G. KNOX, AND H. H. RAMPTON

practice for maximum wheat production. However, in recent years some growers are re-evaluating this practice. Nitrogen can be supplied from commercial fertilizers. Where the soils are shallow, 18 to 30 inches in depth, the entire soil profile may become wet to field capacity within one season. Chemicals are aiding in the weed control program. Consequently, before acreage allotments made decreases in wheat acreage mandatory, some farmers were trying either continuous wheat or only occasional fallow on their shallower soils. A careful check of rainfall and of soil moisture is used as a guide in determining when to recrop and when to fallow. In recent years, nitrogen fertilizers have been used extensively throughout most of the area. On deep soils, in years of average or above average rainfall, insufficient available nitrogen rather than moisture has limited yields. The need for balancing the rate of application of nitrogen fertilizer with the supply of available moisture is well recognized. From 20 to 30 pounds of nitrogen per acre for wheat following fallow is typical. On shallow soils or when moisture supplies are inadequate no nitrogen may be needed. But in the higher rainfall areas when wheat is grown without summer fallowing the rates may be doubled. Extensive research is now in progress to further clarify the relationship between moisture supply and available nitrogen. Also of considerable interest is the calibration of a soil test for estimating the available nitrogen. Current research by the Oregon and Washington agricultural experiment stations is designed both to evaluate existing methods critically and to explore new methods. A number of commercial soil-testing laboratories are collecting and testing soil for moisture and for nitrate and ammonia nitrogen. Samples are usually taken to 6 feet in depth or to a restricting layer. Rain gauges are used to get a better estimate of local rainfall. From existing research and experience on the relationship between moisture, nitrogen, and yield, nitrogen fertilizer recommendations are made. A considerable acreage is being tested and some fields have been sampled regularly for several years. The role of legumes or legume-grass mixtures in the cropping sequence has been given consideration to aid in maintaining organic matter, reducing erosion, improving soil tilth, and adding available nitrogen. Interest in this possibility has increased with wheat acreage allotments. Only a few farmers attempt to use legumes or grasses in their cropping sequence in this zone. Agronomists are not agreed as to the future of this practice. It takes large amounts of water to grow legumes to add nitrogen which now can be added relatively cheaply in commercial

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fertilizers. Existing research does not support the practice from the economic standpoint on most farms. Yet, some agronomists are concerned with the possible consequences of continuing the wheat-fallow system indefinitely. Continuous wheat, where it is practical, is an improvement over the wheat-fallow program. Returning the wheat straw and using nitrogen fertilizers also aids in maintaining soil organic matter. Trashy fallow is the most effective single practice for reducing erosion in the area. Yet, most farmers still use fallow prepared with a moldboard plow. Trashy fallow is practiced to a greater extent in that portion of the zone where yields are relatively low than in the higher yielding parts of the zone. Trashy fallow and other management practices for dryland wheat also are discussed for the Brown Zone and the Chernozem Zone, under Section IV, 3 and 5. Management problems and practices on the soils in this zone under irrigation are many and varied. They are discussed under Section IV, 2. Some of the fertility problems are complex in certain localized soil areas. For example, on the calcareous mucks in Klamath County, Oregon, deficiencies of phosphorus, zinc, copper, and manganese occur.

5. Chernozem Zone Water erosion and fertility are the dominant soil problems in the Chernozem Zone. Soil organic matter has declined from 20 to 40 per cent during about 50 to 65 years of cultivation. Inadequate moisture may limit crop yields in the drier portion of the Chernozem Zone, but generally it is adequate for high yields of wheat and peas, which are grown extensively in this zone. Soil erosion by water is considered to be more of a problem on cropland in this zone than in any other part of the Pacific Northwest. This led to the establishment of the Palouse Conservation Experiment Station (cooperative USDA and State) at Pullman, Washington, in 1930. The Pendleton, Oregon, Branch Experiment Station (cooperative State and USDA) also has given special attention to machinery and tillage practices in relation to erosion control. Soil losses occur largely during November through March. They result from rains of long duration and from snow melting on frozen soils (Kaiser et al., 1954; Horner et al., 1944). Numerous practices can be used to reduce erosion losses. Since the heaviest soil losses occur on land seeded to winter wheat, any practice that improves the growth of the wheat during the winter is beneficial. Crop sequence has a marked effect on soil losses. Greatest losses occur under the wheat-fallow system. Any system of continuous cropping such as is followed in most of the area helps reduce erosion. Continuous

26 H. B. CHENEY, w. H. FOOTE, E. G . KNOX, AND H. H. RAMPTON wheat, especially with stubble mulch, is superior to the wheat-peas rotation. The lowest soil losses occur when a legume-grass sod is included in the rotation, but the turning under of sweet corn with a moldboard plow and cultivating as is usually done may cause severe erosion losses. Crop residues can be used effectively in reducing soil erosion. In the earlier years straw burning was a common practice, but this is no longer true. Stubble mulch or trashy fallow does an excellent job of controlling erosion on summer fallow land. Kaiser et al. (1954) report a IO-year average annual soil loss per acre on winter wheat after fallow of only 3/4 ton when the fallow was prepared with a duckfoot cultivator (straw left as a mulch) and of 12 tons when the fallow was prepared with a moldboard plow (straw turned under). Trashy fallow as yet has not been adopted widely by farmers in either the Chernozem or higher rainfall part of the Chestnut Zone. New types of machinery such as the rotary hoe, skew treader, deep furrow drill, and “stubble buster” are necessary to handle the heavy stubble mulch. Control of weeds has been more of a problem under the trashy fallow than the clean fallow system. Yield of wheat averaged 38 bushels per acre for moldboard plowing and 32 bushels per acre where subsurface tillage was used during a 12-year period at the Pendleton Branch Experiment Station (unpublished data). This reduction of wheat yields on trashy fallow can be corrected by the use of nitrogen fertilizer. Since under the wheat-fallow system trashy fallow is such an effective erosion control measure, much research has been directed towards making it more practical and profitable. The results of the research at the Pendleton Branch Experiment Station have been summarized by Cushman (1955). In the wheat-pea area both soil and fall tillage may be saved by leaving the ground rough after plowing following pea harvest. Moreover, the yields of wheat have been just as high as when a fine tilled seedbed was prepared (Horning, 1955). Alfalfa and sweet clover alone or in a mixture with a grass aid in maintaining soil organic matter, decreasing erosion, and supplying available nitrogen. Continuous wheat with straw returned, plus nitrogen, has been equally effective in maintaining soil organic matter, In areas normally receiving 16 to 18 inches or more of precipitation legumes in the rotation usually increase yields of wheat. In lower rainfall areas this is not always the case. Legumes and grasses have been used to an appreciable extent in the cropping system only in the higher rainfall areas, principally the wheat-pea area along the WashingtonIdaho line. During the period 1935 to 1950 only about 14 per cent of the cultivated land in this area was in sod.

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Fertilizer usage has increased tremendously during the past 10 years. Wheat responds well to nitrogen fertilizer except following sweet clover or alfalfa. It is common to get a yield increase of 1 bushel of wheat from 3 to 4 pounds of nitrogen applied. Maximum yields are obtained only by balancing the generally favorable moisture supply with adequate available nitrogen from some source. Some excess of nitrogen results in inefficient use and under some conditions a large excess occasionally may reduce yield and quality somewhat. The wheats currently grown are of the soft wheat type, in which baking quality is reduced by excessive protein content. The generally recommended rates of nitrogen fertilizers vary as follows: none following a legume, 30 to 40 pounds of nitrogen following summer fallow, 30 to 50 pounds following peas, and 50 to 70 pounds following wheat. Commercial soil testing is being used by some growers as a guide to better balancing their nitrogen rate with moisture and available nitrogen in the soil. Sulfur deficiencies for legumes have long been recognized in this zone, especially in eastern Washington and western Idaho. I n recent years, where sulfur has not been applied for legumes, wheat has shown a response to sulfate sulfur. Sulfur responses have occurred generally in the higher rainfall area on recropped wheat, especially springseeded wheat. Deficiencies of phosphorus have been detected only rarely. Management problems and practices on the wet soils in the zone are varied, including drainage, fertility, and irrigation.

6. Brown Podzolic Zone Drainage, fertility, and irrigation are the management practices of primary importance in this zone. Major attention in the research program has been given to the proper use of fertilizers, particularly on horticultural crops. Drainage is essential on many soils. Although much land has been drained there is still need for additional surface and subsoil drains. Irrigated acreage has more than doubled in the past five years and approximately 25,000 acres are now irrigated. Sprinkler irrigation is used almost exclusively. Vegetables, small fruits, and forage crops are the main crops irrigated. Even though total rainfall is 30 to 50 inches, summer droughts often occur. Fertilizers are used extensively especially on the high acre-value vegetables and small fruits. These crops also have received the most attention by research workers in the area. Recommendations for nitrogen for field crops ranges from none to 60 pounds of nitrogen per acre.

28

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FOOTE, E. G. KNOX, AND H. H. RAMPTON

Most of the soils are deficient in available phosphorus and some in POtassium. From 40 to 60 pounds of P,O, and K,O per acre are commonly recommended for field crops. Larger applications of nitrogen, phosphorus, and potassium are used on horticultural crops (Tremblay and Harston, 1952).Research at the Western Washington Experiment Station, Puyallup, indicates no residual effects from applications of phosphate fertilizers (60 to over 100 pounds of P,O, per acre) banded for vegetables. The extent to which this occurs on other soils is not established. Since dairying and poultry are important, considerable manure is available to supply part of the fertility requirements. Little limestone is used in the area, but the soils often have a pH of 4.9 to 5.5 with some either lower or higher. Research on the value of limestone is limited but new work is being started. In recent years there have been some indications that magnesium is deficient on certain soils in the area. 7. Brown Latosol Zone

The soil management problems in this zone include inadequate drainage, insufficient summer rainfall, high acidity, and low fertility. Sand dune movement along parts of the coast is a unique special problem. Research information for this area is quite limited. Considerable progress has been made in improving the drainage on the tideland, river bottom, and terraces on which forage crops are grown. However, drainage has not been improved on much of this land. Moreover, even with drainage improvement the soil may be quite wet or flooded from November to April. During the winter, average rainfall of 6 to 12 inches per month is typical of most of the coastal area. However, the average rainfall of l to 2 inches during July and August is not sufficient for optimum forage production. Consequently, irrigation has been increasing for several years. Sprinkler systems predominate. The nature of the acidity and fertility problem is known only in a general way. The cation-exchange capacity ranges from 30 to 45 me./100 g.; base saturation from 10 to 40 per cent; exchangeable potassium and available phosphorus are often low; and nitrification is slow. The cost of agricultural limestone is quite high, approximately $13.00 per ton. Experimental results in the area that definitely establish the economic value of lime and fertilizer treatments are lacking. Currently, research is in progress in the laboratory, greenhouse, and field to aid in the solution of this problem. Farmers are making some use of lime and fertilizers in the area. However, they rely largely on forage species that grow reasonably well with a minimum modification of existing fertility conditions. The John Jacob Astor Branch Experiment Station located in Oregon at the mouth

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of the Columbia River has some excellent New Zealand white clovergrass pastures on reclaimed tideland where lime and phosphate fertilizer were used. Drifting sand dunes were a menace along parts of the coast in the 1930’s and 1940’s. Through the work of the Soil Conservation Service aiding Soil Conservation Districts large acreages have been stabilized with grasses and other permanent vegetation. 8 . Reddish Brown Latosol Zone-Upland

Areas

Soil acidity, low fertility, summer drought, and erosion are the dominant problems of this zone, in which a wide variety of crops are grown. The management problems on the alluvial soils are similar to those in the Reddish Brown Latosol Zone-Lowland Areas and are discussed under Section IV, 9. Although limestone has been applied for many years, its use is far below estimated needs. The high cost of limestone is a considerable deterrent to its use. High-quality limestone costs here about $12 a ton delivered and spread. This is two to four times the cost in Midwest areas, where limestone is used extensively. With lime requirements of 2.5 to 4 or more tons per acre the cost per acre appears prohibitive to many farmers, even though cost-sharing under the Agricultural Conservation Program will cover approximately one-half the cost. All the high-quality limestone must be shipped in from a distance, since only low-purity deposits are available in the area. Research information showing the effects of limestone on the yields of the wide variety of crops grown in the area is limited. Owing to the high cost of limestone more precise information is needed than in most acid soil areas of the United States. A comprehensive research program is being initiated by the Oregon Agricultural Experiment Station to study both fundamental and applied aspects of the soil acidity problems in the area. Field experiments also are being initiated by the Washington Agricultural Experiment Station. The fertility management programs followed on these soils varies widely. Small grain was grown extensively in earlier years and red clover reportedly grew well. Then more and more farmers experienced difficulty in growing red clover. Vetch has been grown for many years. In most cases no lime or fertilizer was used except land plaster or gypsum to supply sulfur for the legumes. In recent years the use of lime and fertilizers has increased. In 1939 the Oregon Agricultural Experiment Station established the Red Soils Experimental Area near Oregon City. The farm had been heavily cropped to small grain without lime, fertilizer, or manure.

30

w. H. FOOTE, E. G. KNOX, AND H. H. RAMPTON It has served as an excellent demonstration of how production can be increased on these soils with improved management. Nitrogen, phosphorus, potassium, boron, and sulfur deficiencies OCCUT. All are widespread except potassium deficiencies, which are more variable. The growing of legumes such as red clover and vetch to supply available nitrogen as well as for other purposes has been encouraged for over 50 years. Since 1940 the use of nitrogen fertilizers has increased rapidly. Nitrogen for grass seed production was adopted quickly by most growers when its value was determined about 1940. Its value for all crops except legumes is now well recognized. The need for regular additions of sulfur, especially for legumes, is widespread. Response of legumes to sulfur was established by Powers (1923) in 1912. For many years gypsum or land plaster was the only fertilizer or soil amendment used extensively. In recent years barley yields have been increased by additions of gypsum on land that had not had sulfur applied recently. Although the total phosphorus content of these soils is comparatively high, the available phosphorus supply is generally low. Phosphorus fixation is quite high. Farmer use of phosphate fertilizers, except on horticultural crops, is still far from universal. Potash fertilizers have not been used widely on these soils except for horticultural crops. Response to potash fertilizers on field crops has occurred only occasionally. Pope ( 1955) with greenhouse and laboratory methods found a wide variation in the potassium-supplying power of the soils in this zone. Additional research is needed to determine the need for potassium under field conditions. Many of these soils are deficient in available boron. Agricultural borax is used on alfalfa, broccoli, walnuts, and other crops. Powers and Wood (1947) have summarized the research work on boron. The fertility problems in this zone are complex. Multiple deficiencies of nitrogen, phosphorus, potassium, sulfur, and boron as well as strong soil acidity may occur. Interactions between several of the elements have been established in a number of unpublished field experiments. The application of one or even several of the deficient elements may give a poor response if all are not supplied in adequate amounts in proper balance. The lack of a full understanding of this fact along with inadequate information on the interactions involved may well have contributed to farmers’ reluctance to use lime and fertilizer extensively on much of their cropland. Summer drought limits both the kinds and yields of the crops that are grown. Some sprinkler irrigation is used for horticultural crops and pasture in the upland area, but most irrigation is confined to the lowland areas. H. B. CHENEY,

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Erosion is not a serious problem in most of the zone even though the slopes are often steep and long. A high per cent of the land is in forest trees or grass which provides a protective cover. Rainfall intensity is usually low. The soils are generally permeable and fairly resistant to erosion. Considerable erosion has occurred on some cultivated land, and a few areas are severely eroded. The most critical situations where erosion occurs are: (I) in clear cultivated orchards and small fruit plantings, (2) in strawberry plantings where the rows invariably run up and down the hill, and ( 3 ) on land where small grain crops fail to provide adequate cover in the fall and winter.

9. Reddish Brown Latosol Zone-Lowland

Areas The management problems on the alluvial soils in the Reddish Brown Latosol Zone include inadequate drainage, midsummer drought, stream flooding and erosion, low fertility, and some soil acidity. A large number of both field and horticultural crops are grown. The management problems of the upland areas in this zone are discussed under Section IV,8. The installation of open ditches and tile for drainage has increased during the past decade.' Approximately one million acres require improvement in the natural drainage for maximum crop production. About one-half of this wet land has been adequately drained and the other one-half would benefit from additional improvement in drainage. Because of the near drought-like conditions that prevail during the summer months irrigation is essential for intensive land use. The first recorded irrigation in the area was conducted at the Oregon Experiment Station, Corvallis, in 1896. Irrigation was proven practical and economical early in the present century, .but did not begin to receive popular support until sprinkler irrigation was developed. Irrigated land in the zone increased from 81,000 acres in 1949 to 153,000 acres in 1954. Sprinklers are used on nearly all this acreage. Irrigation undoubtedly will continue to increase in this area. The ground water supply is not adequate to permit much expansion. Additional water will be needed for flood control dams in the Willamette Basin Project Program, since practically all the usable summer flow of streams in Oregon is now appropriated or overappropriated. Blanch et al. (1955), reporting for the School of Agriculture Water Resources Committee at Oregon State College, estimate that by the year 2000 the irrigated acreage in this zone may feasibly increase fivefold over the present acreage. Vegetables, small fruit, mint, and pasture are the principal crops irrigated. Grass seed crops and fall- and spring-planted small grain and vetch are grown successfully without irrigation.

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H. B. CHENEY,

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H. FOOTE, E. G . KNOX, AND H. H . RAMPTON

Approximately 500,000 acres in the Willamette Valley of Oregon has been subject to damage from floods. The Willamette Basin Project Program includes the construction of numerous multiple-purpose dams. The Corps of Engineers estimates that these dams will largely eliminate the flood hazard on the valley floor. Some of the most productive soils are generally flooded during the winter. Protective plant cover during the fall and winter is an essential feature of the management program on such soils. Winter cover crops must be seeded early enough to provide a good growth by the time the floods start or serious erosion may occur. Nitrogen is the principal nutrient needed. Application of 80 to 100 pounds of nitrogen per acre on grass seed crops and vegetables is a common practice. Smaller amounts are used on small grains such as barley and oats. Since the soil rarely freezes and rainfall during the fall and winter season usually exceeds 20 to 25 inches, fall-applied nitrogen leaches readily. Sulfur is recommended especially for legumes but also for other crops. Sulfate from either gypsum or other fertilizers is preferred over elemental sulfur. Most of these soils are well supplied with available phosphorus and potassium. The Planosols, used largely for ryegrass seed production, commonly are deficient in available phosphorus. They also are relatively low in exchangeable potassium but have adequate amounts for grass seed crops. Growers generally apply nitrogen-phosphate-potash fertilizers in a band by the row at planting time for vegetables. Rates of 60 to 100 pounds of P,O, and K,O are not uncommon. Phosphate fertilizer, even on soils well supplied (by usual standards) with available phosphorus by soil test, has been quite effective in increasing the yield of pole beans and sweet corn. Potash responses have been less certain. Phosphate in combination with nitrogen is used somewhat on small grains and pastures but field crops do not respond to either phosphate or potash fertilizers on most of these soils. The need for boron on alfalfa and a number of horticultural crops is recognized. Other trace elements are also required on the small areas of organic soils. Soil acidity is not a major problem on most of the soils as yet. The soils formed on recent alluvium are mostly only slightly acid, usually above pH 5.7. The soils on the terraces are more acid. Some lime is used on these soils when less acid-tolerant legumes are to be grown. The Planosols are quite acid but owing to poor drainage are not adapted to crops requiring a high pH or high per cent base saturation. Few farmers follow a regular rotation. The cropping pattern con-

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tinually shifts as new crops are introduced and economic conditions or technology change. Many unanswered questions on crop sequence or rotations exist.

10. Reddish Brown Latosol-Noncalcic Brown Zones The soil management problems of this zone include insufficient summer rainfall, inadequate drainage, low fertility, and water erosion. Most of the cultivated land is confined to the alluvial soils and lower slopes. Gravity irrigation is used on most of the 85,300 irrigated acres, but sprinkler type irrigation has been increasing. Additional storage dams are needed to supply supplemental water on about one-half of this acreage (Beck et al., 1952). Improved irrigation practices will help to extend the existing supply of water for irrigation. Moreover, they will aid in alleviating the drainage problems resulting in part from overirrigation. As in most irrigated districts, especially where flood irrigation is practiced, the drainage problem is severe in parts of the area. The “Grumusols” or “sticky” soils are often nearly impermeable to water. The underlying strata are quite variable. Excess water in one area may move underground a considerable distance before causing a high water table. Crop response to additions of sulfur was established by Reimer and Tartar ( 1919) in the area over 40 years ago. The need for both nitrogen and sulfur is widespread. Many soils also are deficient in phosphorus, potassium, and boron. Greenhouse experiments indicate a few soils may be lacking in available molybdenum. Certain soils are quite high in exchangeable magnesium. It is possible that this condition may be associated with reduced yields of alfalfa. Most of the soils have a pH above 5.7 and practically no research has been conducted on the use of limestone. However, the yield of alfalfa was increased significantly by the application of limestone in one experiment in 1955 (unpublished data). The greatest erosion problem occurs on nonirrigated sloping land devoted to grain crops. It is also a problem where cultivated crops are irrigated by gravity irrigation on sloping land.

V. CROPZONES OF

THE

REGION

The crop zones of the Pacific Northwest region as shown in Fig. 4 and as referred to in the following crop discussions, have been arbitrarily drawn up to serve as a simplified guide under Section VI, “Field Crops of the Region.”

34 H. B. CHENEY, W. H. FOOTE, E. G. KNOX, A N D H. H. RAMPTON

B

a

e

a

4

U

ea

0

~-

FIG.4. Crop zones of the Pacific Northwest. (Sources: Cropland map from Highsmith, 1956; crop zones added by authors.)

F I E L D CROP PRODUCTION A N D SOIL M A N A G E M E N T

35

The following is an outline of the principal crops in each zone, and the range of climatic conditions found in the different cultivated land areas within each crop zone in the Pacific Northwest. Zone 1. Coastal-Lower Columbia River Belt. Practically all the cultivated land is in forage crops, used mainly for pasture and grass silage. Average precipitation: 55 to 100 inches. Mean temperature: Jan. 39 to 46" F. July 58 to 61" F. Extreme temperatures: Lowest, 0 to 16" F. Highest, 97 to 105" F. Average length of growing season: 185 to 285 days. Elevation of cultivated lands: 5 to 200 feet. Zone 2. Puget Sound Lowlands. The principal crops are forages, small fruits, fresh vegetables, vegetable seeds, potatoes, bulbs, and nursery stock. Average precipitation: 16 to 32 inches. Mean temperatures: Jan. 37 to 39" F. July 61 to 63" F. Extreme temperatures: Lowest, 2 to 5" F. Highest, 92 to 98" F. Average length of growing season: 184 to 255 days. Elevation of cultivated lands: 5 to 500 feet. Zone 3. Western Oregon-Western Washington Valleys. The crops are widely diversified. The most important crops are small grains, forages, grass and legume seeds, small fruit, tree fruits, nuts, vegetables, bulbs, and nursery stock. Average precipitation: 40 to 52 inches. Mean temperatures: Jan. 38 to 39" F. July 63 to 66" F. Extreme temperatures: Lowest, -20 to -2" F. Highest, 104 to 107" F. Average length of growing season: 164 to 191 days. Elevation of cultivated lands: 30 to 1000 feet. Zone 4. Rogue and Umpqua River Valleys. Diversity of crops characterizes this zone. The main crops are tree fruits, small grains, forage crops, legume seeds, vegetables, small fruits, and nuts. Average precipitation: 16 to 30 inches. Mean temperatures: Jan. 37 to 41 F. July 67 to 71' F. Extreme temperatures: Lowest, -6 to 2" F. Highest, 107" F. Average length of growing season: 170 to 234 days. Elevation of cultivated lands: 450 to 1500 feet. Zone 5. South Central Oregon-Southwestem Idaho Arid Highlands. The principal crops in this zone are forages, small grains, grass and legume seeds, and potatoes. Average precipitation: 8 to 13 inches. Mean temperatures: Jan. 21 to 32" F. July 65 to 77" F. Extreme temperatures: Lowest, -45 to -15" F. Highest, 102 to 119" F. Average length of growing season: 103 to 130 days. Elevation of cultivated lands: 2250 to 4500 feet. Zone 6. Blue Mountains. Crops produced in this zone are mainly small grains, especially wheat, forages, and grass and legume seeds. Average precipitation: 10 to 22 inches. Mean temperatures: Jan. 25 to 29" F. July 65 to 72" F. Extreme temperatures: Lowest, -38 to -24" F. Highest, 108 to 112" F. Average length of growing season: 108 to 168 days. Elevation of cultivated lands: 2700 to 3800 feet.

36

H. B. CHENEY,

w. H.

FOOTE, E. G. KNOX, AND H. H. RAMPTON

Zone 7. Columbia Basin Irrigated Lands. This zone is widely diversified as to crops. The most important crops are forages, tree fruits, small fruits, small grains, legume seeds, sugar beets, potatoes, vegetables, and dry beans. Average precipitation: 7 to 9 inches. Mean temperatures: Jan. 26 to 28" F. July 71 to 76" F. Extreme temperatures: Lowest, -33 to -23" F. Highest, 111 to 116" F. Average length of growing season: 149 to 190 days. Elevation of cultivated lands: 500 to 1500 feet. Zone 8. Columbia Basin Wheat-Fallow Lands. The principal crops in this zone are small grains, mostly wheat, and forages. Average precipitation: 10.5 to 16 inches. Mean temperatures: Jan. 29 to 33" F. July 68 to 72" F. Extreme temperatures: Lowest, -29 to -21" F. Highest, 109 to 119" F. Average length of growing season: 120 to 168 days. Elevation of cultivated lands: 1000 to 3000 feet. Zone 9. Northern Washington Mountain Valleys. The main crops in this zone are forages, small grains, and tree fruits. Average precipitation: 10 to 14 inches. Mean temperatures: Jan. 22 to 25" F. July 65 to 74" F. Extreme temperatures: Lowest, -35 to -23" F. Highest, 108 to 114" F. Average length of growing season: 96 to 173 days. Elevation of cultivated lands: 800 to 3000 feet. Zone 10. Northern Forest Cut-Over Lands. The crops produced in this zone are principally forages and small grains. Average precipitation: 16 to 23 inches. Mean temperatures: Jan. 22 to 24" F. July 64 to 67" F. Extreme temperatures: Lowest, -42 to -26" F. Highest, 102 to 107" F. Average length of growing season: 93 to 151 days. Elevation of cultivated lands: 1600 to 2500 feet. Zone 11. Palouse-High Prairie. The crops of this zone are mainly small grains, chiefly wheat, forages, dry edible peas, green peas for canning and freezing, and grass seeds. Average precipitation: 14.5 to 26 inches. Mean temperatures: Jan. 28 to 33" F. July 67 to 74" F. Extreme temperatures: Lowest, -39 to -22" F. Highest, 105 to 118" F. Average length of growing season: 118 to 210 days. Elevation of cultivated lands: 1000 to 3350 feet. Zone 12. Central Idaho Mountain Valleys. The main crops in this zone are forages and small grains. Average precipitation: 7 to 15 inches. Mean temperaures: Jan. 15 to 19" F. July 64 to 70" F. Extreme temperatures: Lowest, -46 to -28" F. Highest, 101 to 110" F. Average length of growing season: 75 to 148 days. Elevation of cultivated lands: 5000 to 6000 feet. Zone 13. Snake River Valley. The crops of this zone are diversified. The most important are forages, small grains, potatoes, sugar beets, legume seeds, dry beans, dry peas, tree fruits, small fruits, vegetables, and vegetable seeds. Average precipitation: 8 to 15.5 inches. Mean temperatures: Jan. 18 to 30" F. July 65 to 74" F. Extreme temperatures: Lowest, -44 to -21" F. Highest, 100 to 121" F.

F I E L D CROP PRODUCTION A N D SOIL M A N A G E M E N T

37

Average length of growing season: 97 to 177 days. Elevation of cultivated lands: 2100 to 5000 feet. Zone 14. Southeastern Idaho. The principal crops of this zone are small grains, forages, and sugar beets. Average precipitation: 10 to 17 inches. Mean temperatures: Jan. 16 to 28" F. July 62 to 71" F. Extreme temperatures: Lowest, -50 to -25" F. Highest, 97 t o 108" F. Average length of growing season: 74 to 128 days. Elevation of cultivated lands: 4500 to 5500 feet.

VI. FIELDCROPSOF

THE

REGION

1. Cereals a. Wheat. Wheat is the major cereal crop grown in the Pacific Northwest. It is grown extensively in crop Zones 3, 6, 8, 1 1 , and 14, with the bulk of the acreage found in the Columbia Basin area of Oregon and southeastern Washington, and the Palouse area of Washington and northern Idaho. Some wheat is grown in almost every agricultural zone of the region, Wheat production in the Pacific Northwest began about 75 years ago. Much of the wheat land was plowed directly from the native grasses, and wheat is the only crop that has ever been grown. The rolling topography characteristic of the wheat lands, particularly in Zones 8 and 11, and the establishment of large farm holdings have led to the development of many new farming practices unique to the area. Most of the wheat is produced under dryland conditions, using the summerfallow or alternate cropping system. By the nature of the rainfall pattern and the environment wheat is the crop best adapted to these areas and as such, it has become the dominant agricultural crop of the economy. In areas of higher rainfall, wheat may be grown each year or in a rotation with peas or other annual legumes. On the irrigated farms, wheat is commonly grown as a rotational crop when the price and other factors are favorable. The acreages and production of wheat for the three states for 1954 and the averages for the years of 1942-51 are given in Table IV. The production of fall- and spring-sown wheat in 1954 was about 128,656,000 bushels on some 4,173,000 acres. The total acreage seeded to wheat for 1954 harvest was about 10 per cent less than the average acreage for the years of 1942-51, whereas the production increased almost 5 per cent. Most of the wheat acreage is seeded to winter varieties but spring-sown varieties produce about one-quarter of the total crop. The spring varieties are grown mainly on the irrigated farms and to a certain extent replace the fall-sown wheats when the crop has been damaged by winter injury or when the weather or lack of moisture has prevented successful fall seeding and establishment.

38

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w. H.

FOOTE, E. G . KNOX, AND H. H. RAMPTON

Most types of wheat are adapted to the area and can be grown successfully. A varietal survey in 1954 listed some 57 varieties grown in the Oregon, Washington, and northern Idaho region of the Pacific Northwest. In the higher rainfall areas of Zones 6, 8, and 11 and in Zones 3 and 13, the white wheats are well adapted and high yielding and recently have been grown almost to the exclusion of other types. Hard red winter wheat is grown mainly in the drier areas of Zones 8 and 14.Hard red spring and soft red winter types are grown to a lesser TABLE IV Production and Acreages of Wheat for the Three States in the Pacific Northwest in 1942-51 and 1954 Acreages

Production

(1000 acres)

(1000 bu.)

1942-51

Oregon Winter Spring

Total Washinglon Winter Spring

Total Idaho Winter Spring

Total GRAND TOTAL 1

1954*

1942-51

1954

719 217 956

70 1 149 850

18,794 5,156 85,930

20,429 4,415 24,844

1,854 654 8,488

1,865 so5 2,168

61,069 14,854 65,905

61,059 8,247 69,306

768 470 1,328 4,653

646 509 1,155 4,175

18,606 14,505 55,111 128,944

17,202 17,504 54,506 128,656

Agricultural atatiatics 1954. U. S. Department of Agriculture.

* U. S. Bureau of Census, [email protected] Agricultural Census Preliminary.

extent. The production of the important wheat varieties in 1954 is given in Table V. Wheat grown in the Pacific Northwest is used primarily for food purposes, and, because the population in the region is not large, about 50 to 70 per cent of the crop must find a market outside of the region. Until rather recently, the bulk of the wheat was exported to other parts of the world, mainly the Orient. The wheat varieties grown produce a soft to semihard wheat with a medium low protein content. These wheats are used extensively for pastry and other specialty flours. They are often characterized as good milling wheats, but some varieties are notoriously poor. The hard red winter varieties can often be milled directly into bread flour, but are more often blended with other

F I E L D CROP P R O D U C T I O N A N D SOIL M A N A G E M E N T

39

wheats to extend their usefulness. The use of wheat as a livestock feed has expanded some in recent years with the increased interest in livestock feeding in the area, and wheat may become a much more important source of feed grain in the future. Industrial utilization of wheat has not proven to be of economic importance as yet. Diseases are one of the most important production problems in the region. Covered smut (Tilletia caries (D. C.) Tul.) and in some limited areas dwarf smut (Tilletia breuaficieus G. W. Fish.) are serious TABLE V Estimated Production of the 1954 Wheat Crop in the Pacific Northwest (Oregon, Washington, and North Idaho) by Varieties' Production Varieties White Wheat ELMAR BREVOR EMIN-ALICEL QOLDEN FEDERATION

REX IDAED BAART

Hard Red Winter Wheat TURKEY-RIO RIDIT WASATCB

Soft Red Winter Wheat R E D RUSSIAN TRIPLET

Hard Red Spring Wheat

(1000 bu.) 95,743 51,206 8,960 8.234 3,980 3,743 3,688 3,470 3,110 12,640 11,737 412 a13 347 229 73 786

HUSTON

258

MARQUIS

241 116

REDMAN

% of total

87.3 46.7 8.2 7.5 3.6 3.4 3.4 3.2 2.8 11.6 10.7 0.4 0.2

0.3 0.a

0.1 0.7 0.2 0.2 0.1

1 Pacific Northwest Wheat by Varietiea, Acreage Harveated and Production, I040 and 1964. U. S. Department of Agriculture. AMS.

diseases. Loose smut (Ustilago tritici (Pers.) Rost.) may be important in the irrigated humid areas. The smut diseases take their large annual toll by reducing yields and the quality of the wheat. Most of the seed is treated prior to seeding but soil infection often prevents complete control. The development and widespread use of resistant varieties has been a successful means of control. I n some areas, particularly the irrigated and higher rainfall areas, both stem rust (Puccinia graminis tritici, Erik. and Henn.) and leaf rust (Puccinia rubigo-Vera tritici, Erik.) may reach epidemic proportions. Foot rots, snow mold, and

40 H. B. CHENEY, w. H. FOOTE, E. G. KNOX, AND H. H. RAMPTON other soil-borne diseases are frequently found and cause serious damage in some areas. Insects on wheat have not been found to be an economic factor as yet. b. Barley. The principal barley-producing areas are the Willamette Valley of Zone 3, Klamath Basin of Zone 5 in Oregon, Zones 13 and 14 in Idaho, and the Nez Perce and Camas Prairie of Washington and northern Idaho. Barley, while not the major cereal, is grown extensively in almost every agricultural area and recently has become the replacement crop for wheat on the “diverted” wheat acres in the Columbia Basin. The acreages and production of barley for 1954 and the averages for the years 1942-5 1 are given in Table VI. TABLE VI Production and Acreages of Barley for the Three States in the Pacific Northwest in 1942-51 and 1954 Acreages

Production (1000 h . )

(1000 acres)

Oregon Washington Idaho Total

1944-5 1’

19542

1942-51

1954

299 174 345 818

484 597 541 1,622

9,907 6,332 11,961 28,200

17,851 29,136 17,749 57,736

* hgricultural Statistirs 1054. U. S. Department of Agriculture. 2

U. S. Bureau of Census, 1055. 1064 Agricultural Census Preliminary.

The total production of barley in 1954 of some 57,736,000 bushels represents an increase of 51 per cent over the average production for the 1942-51 period. This increase has largely taken place in the wheatproducing areas. Barley is grown primarily as a feed grain, but sizable quantities are grown for a specialized use as malting barley. The malting barley production is concentrated largely in the Klamath Basin and Willamette Valley of Oregon, the Camas Prairie and Palouse area of Washington and northern Idaho, and to a limited extent in Zone 14 of southeastern Idaho. Outside of these areas barley is grown largely as a feed grain, particularly in the irrigated areas where it is used as a rotational crop, often with legumes such as alfalfa or red clover. Both fall and spring varieties are grown with the production of the winter types in the areas west of the Cascades and in other areas where the winters are mild. Spring-grown varieties, both the common sixrowed and two-rowed types, predominate in the region. Most of the

FIELD CROP PRODUCTION AND SOIL MANAGEMENT

41

malting barley is the two-rowed type, with HANNCHEN and HANNA the leading varieties. WHITE WINTER, a six-rowed variety, is also grown and sold as a malting barley. Other leading barley varieties grown are TREBI, BONNEVILLE, GEM, WINTER CLUB, and FLYNN, which are grown primarily as feed grain. The future of barley production in the Pacific Northwest depends upon many factors, some of which are the governmental farm programs, the expansion of livestock feeding operations, the shifting and expansion of markets for malting barley. Barley is grown in the area without too many production hazards. Often winter killing occurs when attempts are made to grow spring or semiwinter types. Barley mildew (Erysiphe graminis D. C.) and TABLE VII Production and Acreages of Oats Grown in the Pacific Northwest in 1942-51 and 1954 Acreage

Production (1000 bu.)

(1000 acres) 1942-51'

Oregon

Washington Idaho Total 1

335 159 185 679

1954'

1942-51

1964

225 178 174 577

9,682 7,361 7,756 24,749

8,991 8,013 8,183 25,187

Agricultural Statistics, 1054. U. S. Department of Agriculture.

:U. S. Bureau of Censur, 1955. 1054 Agricultural Census Preliminary.

loose smut ( Ustilago nuda (Jens.) Rost.) are sometimes important. Excessive lodging of barley when grown under conditions of high soil fertility is an important production problem. On much of the irrigated land, barley is underseeded with legumes and excessive straw growth often results in reduced stands of the legume. The development of high-yielding, disease-resistant stiff-strawed barley varieties has been an important contribution to the success of barley in the region. c. Oats. I n the Pacific Northwest oats are used as a grain for livestock feed or as a forage. The production of oats is widely distributed throughout the area with the Willamette Valley of Crop Zone 3, the Palouse area of Zone 11, and the irrigated areas of the Snake River Valley in Zone 13 the most important. Oats are also grown to a limited extent as a hay crop in Zones 1,2, and 8. The acreages and production of oats for the three states are given in Table VII. The production of oats has changed very little during the past sev-

42

H. B. CHENEY,

w. H.

FOOTE, E. G. KNOX, AND H. H. RAMPTON

era1 years. Oats are used frequently as a nurse crop for legumes, such as red clover and alfalfa in the irrigated areas, and oats and vetch are grown together in western Oregon as a seed crop and to a limited extent as a hay crop. On the wheat farms oats are commonly grown around the edges of the fields and harvested for hay. Winter oats are grown in western Oregon and Washington, where the winters are mild, and the gray seeded types of WINTER TURF such as GREY WINTER and SUPPORT are the predominate varieties. The spring oats are mainly white but there are some yellow and red varieties grown on a limited scale. VICTORY, MARKTON, OVERLAND, BANNOCK, and CODY are some of the well-known present-day varieties. TABLE VIII Production and Acreages of Rye for the Three States in the Pacific Northwest in 1942-51 and 1953 Acreage (1000 acres)

Oregon Washington Idaho Total 1

Production (1000 bu.)

1949-61'

1963'

1942-51

1963

130 64 11 196

199 34 7 163

380 206 64 650

304 138 46

487

Agricultural Statistics. 1064. U. S. Department of Agriculture.

Little change in oat production in the region is anticipated. Oats will always occupy a favorable place in the crop rotations on the irrigated farms and as a support crop for some of the seed crops. Use as hay will fluctuate with the need for a supplemental hay crop in areas where wheat production is the main enterprise. Oats are not damaged seriously by diseases, although stem rust (Puccinia graminis avenae, Erik. and Henn.) may be important. d . Rye. Rye is grown mainly as a hay and cover crop in the Pacific Northwest and to a lesser extent as a grain crop. The acreages and production of rye for the three states for 1953 and the averages for 1942-51 are given in Table VIII. The production of rye is confined largely to Crop Zones 2 and 3, where it is grown as a cover crop in orchards and on vegetable lands and used as a pasture. I n areas east of the Cascades rye is grown for hay and grain usually on land unsuited for wheat production. Rye has become a serious weed on the wheat lands and the production of rye has not been encouraged.

F I E L D CROP PRODUCTION A N D SOIL M A N A G E M E N T

43

Both winter and spring types of rye can be grown but the predominant types west of the Cascades are winter types such as ABRUZZI and BALBO. On much of the acreage seeded to rye for hay and grain improved varieties are not used but the seed consists of a mixture of types. Seed is often bought and sold or exchanged among growers with little concern for varietal designation. Diseases are not important in the area. By f a r the most important problem if rye is to continue even as a minor crop is the acute seed problem of known adapted types. e. Corn. Corn is a minor crop in the Pacific Northwest when compared with some other crops and with other agricultural areas in the United States. The Pacific Northwest does not have strong factors favoring corn production in most of the region. Some of the warmer, TABLE IX Production and Acreages of Corn for the Three States in the Pacific Northwest in 1942-51 and 1954 Acreage (all corn) 1949-51'

Oregon Washington Idaho

Total

33 90 33 86

Production

1954' 1943-51 97 37 44 108

1918 1007 1504 3739

1954 744 1433 853

3098

* Agricultural 9

Statistics. 1954. U. S. Department of Agriculture. U. S. Bureau of Cenaua. 1955. 1954 hgricultural Censua Preliminary.

long-growing-season irrigated areas east of the Cascades and to some extent areas west of the Cascades are suitable for corn. Corn is grown on a sizable acreage, both irrigated and nonirrigated, in Crop Zone 3, while the bulk of the successful production is found in the Yakima Valley and the Grand Coulee irrigated area of Zone 7 and the Snake River and Boise valleys in Zone 13. The acreages and production of corn in the three states for 1942-51 and for 1954 are given in Table IX. Corn, where it can be grown successfully, is used either as a grain or as a silage crop. Production of corn for grain is highly competitive with other cereal grains, and corn silage with grass and legume silage. Hybrid varieties are grown almost exclusively in the area, with some emphasis placed on the development of hybrids for the areas. 2. Forages

a. Hay Crops. (Statistics are shown in Table X.) ( I ) Alfalfa. Alfalfa (Medicago saliva L.) is adapted in all crop zones of the region with the

4'4

H. B. C H E N E Y , W. H . FOOTE, E. G. KNOX, A N D H. H . R A M P T O N

exception of Zone I.Adaptation is limited by poor drainage and acid soils in Zone 2 and 3. East of the Cascade Mountains, most of the alfalfa is irrigated. There, the principal limiting factors on cultivated lands are insufficient moisture, short growing season, impeded drainage, and the often accompanying high salinity and alkalinity. Insects and diseases sometimes limit production, but development of resistant varieties has solved the most serious problems with the exception of outbreaks of such pests as cutworms, grasshoppers, and alfalfa weevil. The most popular alfalfa varieties and their special values are as follows: RANGER, ORESTAN, and VERNAL, having resistance to bacterial wilt of alfalfa; LADAK, which possesses a moderate amount of alfalfa wilt resistance and is suited to areas that are marginal for alfalfa production because of deficiency of moisture; TALENT, having resistance to the leaf and stem nematode; and LAHONTAN, having resistance to the spotted alfalfa aphid (not yet known to occur in the Pacific Northwest), bacterial wilt, and the leaf and stem nematode. The greatest concentration of alfalfa acreage and hay production is in the Snake River Valley of Idaho, which makes up almost all of Zone 13. Twin Falls County alone produced a quarter of a million tons of alfalfa hay in 1954.The second largest hay-producing area is in Zone 7, all of which lies in the state of Washington, the center of production being in Yakima County. Most of the alfalfa hay is baled for convenience in handling, especially in marketing the product. Considerable amounts are still stacked as loose hay, some is chopped and blown into stacks or barns, and a portion is made into alfalfa meal. Little alfalfa is grown primarily for pasture, although much of it is pastured at some time during the year. Some of the alfalfa crop finds its way into silage, particularly in areas where early summer rains cause difficulty in the curing of hay. Some alfalfa forage is utilized for winter livestock feed in the form of threshed alfalfa, a by-product of seed production. Practically all the alfalfa hay produced in the states of Oregon and Washington is fed within the state of origin, although sizable amounts are shipped from Zones 5, 6, 7, and 8, chiefly to dairy operators in Zones I, 2, and 3. The acreage of alfalfa for hay is increasing in the region. The increase in 1954 over the 1942-51 average was nearly 10 per cent in Idaho, 20 per cent in Oregon, and 23 per cent in Washington. ( 2 ) Red clover. Red clover (Trifolium pratense L.) is adapted in all crop zones of the region. The greatest production is in Zone 3, where growing the crop for forage is often combined with the seed production enterprise. Red clover is highly esteemed for its soil-improving qualities in Zones 1, 2, and 3, where it is an important feature in many crop rotations. On the cultivated lands west of the Cascade mountains the principal limiting factors in successful red clover production are soil

FIELD CROP PRODUCTION A N D SOIL MANAGEMENT

45

acidity, poor drainage, and shallow soils. On the cultivated lands east of the Cascade Mountains the principal factors limiting successful production of red clover are insufficient moisture, insufficient depth of soil, poor drainage, and soil salinity and alkalinity. The most serious pests of red clover in the region are the clover root borer and the clover root curculio, which have, for all practical purposes, made the crop a biennial. Other insect pests are the common garden slug and the western spotted cucumber beetle, both of which are particularly destructive in the seedling stage. Grasshoppers and cutworms also limit forage production at times. Diseases are present but generally are not of great effect on forage production. The principal variety grown is KENLAND, especially where seed and forage production are combined. Red clover production for hay has decreased markedly in the state of Idaho during recent years. There has occurred a slight decrease in Washington and a moderate increase in Oregon, mostly in Zone 3. (3) Vetches and peas for hay. These crops are generally fall-sown in combination with winter oats for hay, and under such culture, are best adapted in Zones 1, 2, 3, and 4.The vetches most used for hay are common vetch (Vicia sativa L.) and WILLAMETTE, a variety of common vetch on the better lands; hairy vetch (Vicia uillosa Roth), which has special value on the less productive hill lands; and Hungarian vetch (Vicia pannonica Crantz) on poorly drained soils. The Austrian winter pea (Pisum satiuum L. var. arvense) is the most popular of the forage peas. Over 80 per cent of the vetch and pea hay production occurs in Zone 3, and most of the remainder is in Zone 4.The common hazards of production are unusually low winter temperatures, plant damage caused by soil heaving in periods of nighttime freezing and daytime thawing, seedling loss due to depredations of the garden slug, plant loss during winter and spring due to one or more of a number of diseases, and aphid attacks. ( 4 ) Cereal grains for hay. The cereal grains are widely used for hay in the Pacific Northwest. They have broad adaptation and are represented by the four principal species, wheat, oats, barley, and rye. The greatest tonnage is produced in Crop Zone 8, where most of the cultivated land is cropped to wheat and portions of wheat fields may be regularly cut for hay. Zones 3 and 5 are practically identical in tonnage of cereal grains grown for hay, but the use of winter oats is much more intensive in Zone 3. In Zone 5 winter rye is frequently used. Little of this type of hay enters into commerce except in Zone 3, most of it being fed on the farms and ranches where it is produced. The use of cereal grains for hay, especially in the wheat-growing areas, has markedly declined because of the replacement of horses and mules by tractors and the gradual expansion of the use of alfalfa.

46

H.B. CHENEY, w. H.

FOOTE, E. G. KNOX, AND H. H. RAMPTON

( 5 ) Wild hay. Wild hay production occurs chiefly in high mountain valleys where winter and spring moisture may be excessive, drainage poor, and saline and alkali soils are often present. The plants are mainly native species, mostly perennials, having considerable winter hardiness and tolerance to excessive moisture and soil salinity and alkalinity. The principal grasses are Nevada bluegrass (Poa nevadensis Vasey ex Scribn.) , meadow barley (Hordeum brachyantherum Nevski), tufted hairgrass (Descharnpsia caespiiosa (L.) Beauv.) , and beardless wild rye (Elymus triticoides Buckl.) . Various rushes (Juncus spp.) and sedges (Carez spp.) are generally important components of the forage. Numerous legumes are found but it is seldom that they make up important amounts of the forage. The most common ones are cow clover (Trifolium wormskoldii) , a perennial, and white-tipped clover (Trifolium variegaturn Nutt.) , an annual. By far the greatest production of forage from wild meadows is in Crop Zone 5, of which Harney County, Oregon, is the highest producing county. Ranchers in Zones 14 and 6 also produce appreciable amounts of this type of hay. Such forage is used primarily for winter feeding of beef cattle, and a lesser amount for sheep roughage. This hay is generally of rather low feed value owing to the advanced stage of growth at which much of it is cut, and to the long period of exposure generally permitted before stacking. These objectives are difficult to overcome because ( I ) yields are generally quite low, averaging a little over 1 ton per acre, and (2) areas of harvest are large. Quality can be improved by use of fertilizers, by earlier cutting, and by handling more quickly, but the values of the first two have not yet been fully demonstrated to ranchers, and considerable time is always necessary to handle the large acreages involved. Acreages of wild meadow hay are decreasing in all three states of the region. ( 6 ) Other hay. This forage is chiefly made up of miscellaneous cultivated forage grasses that occur commonly in the region. Legumes vary considerably in prominence in this forage. They are chiefly the common cultivated species. The main producing areas, in order of importance, are Crop Zones 3,1,and 2. b. Silage. (Statistics are shown in Table X.) The four principal silages of the Pacific Northwest are sugar beet pulp, pea vines, grasslegume mixtures, and corn. Most of the corn silage is produced in Crop Zones 13 and 7. It is principally field corn, but some is the by-product of sweet corn processing. About 682,000tons were grown in 1954. Most of the mixed grass-legume silage is produced in the western part of the region, with Crop Zone 2 the highest producer, followed by Zones 3 and Iin descending order. The use of this type of silage is

F I E L D CROP PRODUCTION A N D SOIL M A N A G E M E N T

47

expanding rapidly. Its use fits well into conditions in Zones 1,2, and 3, because of rains which usually occur in late May and early June, making hay curing in the field extremely difficult and wasteful. Over 600,000 tons were produced in 1954. Pea vine silage is a by-product of the green pea freezing and canning industry. The greatest production in the region is located in the narrow neck of Zone I1 extending to the southwest. Almost 700,000 tons were produced in 1955. Most of it is fed in the area of production, but some is hauled considerable distances. Sugar beet pulp silage is a by-product of the sugar beet industry. The greatest amount is produced in Zones 13 and 7. The 1954 production is estimated to be over 2,000,000 tons. c. Improved Pastures. (Statistics are shown in Table X.) Most of the improved pastures in the Pacific Northwest region are irrigated, but some, under the relatively favorable rainfall of Crop Zones 1, 2, 3, 6, and 11, may not be irrigated. Most of the improved irrigated pastures contain either Ladino clover (Trifolium repens L. var. Ladino) or white clover ( T . repens L.) and one or more of the better grasses such as orchard grass (Dactylis glomerata L.) , Alta fescue (Festuca arundinacea Schreb.) ,perennial ryegrass (Lolium perenne L.) ,smooth bromegrass (Bromus inermis Leyss. ) , and timothy (Phleum pratense L.) . The plants commonly used in nonirrigated pastures include Ladak alfalfa, sweet clovers (Melilotus alba Med. and M. oficincinalis), desert wheatgrass (Agropyron desertorum Fisch.) , intermediate wheatgrass ( A . intermedium (Host) Beauv.) , pubescent wheatgrass ( A . trichophorum (Link) Richt.), slender wheatgrass ( A . trachycaulum (Link) Malte), and smooth bromegrass in the crop zones east of the Cascade Mountains. I n the zones west of the Cascades, nonirrigated pastures commonly include subclover (Trifolium subterraneum L.) , red clover, white clover, orchard grass, Alta fescue, and perennial ryegrass. The greatest concentration of improved pastures occurs in Zones 13, 7, and 5. Acreage is being expanded rapidly in Zone 7. Production of nutrients per acre varies widely, depending upon the pasture plants used, cultural and management practices, and length of growing season. Irrigated Ladino grass pastures may yield less than 1 ton of alfalfa hay equivalent per acre, or up to 10 tons per acre.

3 . Field Seed Crops a. Importance of the Region. The generally favorable climate of the Pacific Northwest provides good conditions for seed production. Adequate natural rainfall in the more favored areas, well-developed irrigation water supplies in some of the drier portions, and growing seasons

P

03

x

TABLE X

and Production, by States, in the Pacific Northwest'.'

Forage Crops-Acreage Idaho

B

Oregon

0

Washington

4

1942-51

Alfalfa hay Red clover hay3 Vetch or pea hay Cereal grain hay Wid hay Other hay Corn silage Grass-legume silage Pea vine silage4 Sugar beet pulp silage6 Improved pastures

1945-51

1954

1954

1942-5 1

000 Acres

000

000

000 Acres

000

000

Acres

000 Tons

000

Tons

Tons

Acres

Tons

756.0 199.0

1919.0 172.0

830.9 95.9

2387.0 137.0

239.0 126.0

654.0 227.0

-

-

-

151 . O

292.0

330.0

-

-

53.3 154.1 19.8 393.7

-

139.0

58.2 129.9 14.8 28.4

-

-

587.0 148.3 48.1 143.1 276.3 59.0 12.3 36.6

900.7

-

77.5 1176.7

799.4 577.6 85.9 183.3 300.3 94.7 131.9 248.3 295.0 291.7

-

248.6

-

559.5

-

-

-

398.3

000 Acres

1954

000 Tons 684.0 410.0

63.0

000

000

Acres

Tons

375.4 188.2 6.5 92.9 45.9 43.9 12.7 54.0

839.7 374.8 .!! 10.5 M 128.6 9 64.4 w 6 9 . 0 2! 156.7 $ " 356.7 395.0 570.7

291.2

-

-

137.2

-

"2 3 ?

3

3

-

.z

Y

I4

Data from 1954 Agricultural Censua. Preliminary, unless otherwise noted. 2 Figures in units of thousands. a Reported as clover or timothy for hay. Presumed t o be chiefly red clover. 4 Estimates based on produrtion of green peas in 1955, reported by U. S. Department of Agriculture, .4grirultural Marketing Service, Crop Reporting Board. Estimates based on production of sugar beets in 1954. reported by U. S. Department of Agriculture, Agricultural Marketing Service. Crop Reporting Board 1

'

s >

5

H

0

z

F I E L D CROP PRODUCTION A N D SOIL M A N A G E M E N T

49

of adequate duration make it possible to produce a variety of field seeds over much of the region. Not the least of the conditions favorable for seed production is the generally warm, dry summer which provides excellent conditions for retention of high quality as to germination and appearance of the seed. These natural advantages, plus the long distances to large markets for produce of the land, have made the region well suited to the development of field seed production. The industry is not confined to just growing seeds. The segments of it have become highly specialized with many skilled growers, research and promotion by public agencies, exacting seed certification systems, and a welldeveloped seed processing and handling business. The result has been that the Pacific Northwest has become important in the production of seeds of cool-season grasses and legumes for forage, soil conservation, and turf, and for seed of winter legumes, most of which are marketed outside of the region. The seed production enterprise on a farm generally fits in well with livestock production. Most of the seed crops provide pasture in substantial amounts at sometime during the year, and the threshed straw can generally be utilized as roughage. b. Legume Seed Crops. (Statistics are shown in Table XI.) ( I ) Alfalfa seed. The successful production of alfalfa seed requires, in general, the same conditions as those that result in high production of alfalfa hay. Alfalfa seed is produced in most of the crop zones of the Pacific Northwest, with the bulk of production centered in Zones 7 and 13. Seed production is heaviest in the Yakima Valley of Zone 7, where about 50 per cent of all the alfalfa seed of the whole region was grown in 1954. Most of the production is of varieties and types that are adapted to use in the northern half of the United States. I n addition to common alfalfa seed, considerable acreage is devoted to the production of certified seed of a number of varieties. These include the bacterial wilt-resistant varieties RANGER, VERNAL, BUFFALO, ORESTAN, and LADAK. The principal non-wilt-resistant varieties are G R I M M , NARRAGANSETT, and TALENT. Some of the problems faced by seed producers include weed control, pollination, and disease and insect depredations. The use of chemicals in weed control is assuming an increasingly important place in the handling of this problem, with most of the chemical treatments being applied during the dormant stage of the alfalfa. I n the larger producing areas adequate pollination is obtained by the now standard practice of placing bee stands at desired intervals through the fields. Bees are usually obtained through commercial beemen. Fees for this service are generally quite standardized. The most troublesome disease problem is that of stand loss due to bacterial wilt. This problem has been

Field Seed Crops-Acreage

TABLE XI and Production by States, in the Pacific Northwest'.'

Idaho

Oregon

1944-53

Alfalfa seed Red clover seed Ladino clover seed White clover seed Alsike clover seed Crimson clover seed Austrian winter field pea seed Hairy vetch seed Other vetch seed. Common ryegrass seed Perennial ryegrass seed Tall (Alta) fescue seed Chewings fescue seed Red fescue seed Ben tgrass seed Merion Kentucky bluegrass seed

1954

1944-55

Acres Pounds

000 000 Acres Pounds

27.9 50.5 1.7 6.9 15.6

27.0 14.5 0.1 4.1 10.0

000

-

000

5,470 7,946 175 1,458 2.593

-

45.6 34,752

-

5.1

-

0.5

-

x

-

4.050 6.655 12 1,046

2,300

-

12.0 15,000

000

000

1954 000

0

Washington

000

1944-55 000

;

1954

000

000

*

000

Acres Pounds

Acres Pounds

Acres Pounds

Acres Pounds

6.0 18.4 11.5 1.5 11.6 3.1 24.9 56.7 65.0 89.7 16.1 14.7 12.4 5.9 10.9

6.0 1.500 16.5 2,592 1.5 247 0.9 155 7.0 2,855 4.5 1,161 24.8 21.600 26.0 7,150 14.0 8,260 112.0 105,000 24.0 21,000 12.0 4,020 95.0 6,785 7.0 5,560 15.5 2,902 2.0 400

12.1 3.6 1.7

25.0

1,149 2,666 1,562 160 5,469 914 24,880 15,988 28,560 52,210 7.155 5,758 2,806 1.171 1,598

-

8.5 1.9 1.4

-

1.0

-

0.7 2.4

-

6.063 565 126

3.3 0.1

10,580 726

-

1o.oso

18.0 0.2 0.2

2,160 60 100

0.5

150

696 853

389 30s 185

-

-

-

1.5 1.7 1.6

n r

0

8

1s F. - p J 0

-

-

5

-

--

804 170 554

w

3 * 3 4 !-.

x .

x 5

6

-z cj

U

1 Data

1

F

obtained from Seed Crops, U. S. Department of Agriculture, Agricultural Marketing Service. Crop Reporting Board. w in units of thouspndb

51 largely eliminated or at least minimized for growers of wilt-resistant varieties, but stands of non-wilt-resistant alfalfas are generally shortlived owing to this trouble in the irrigated sections east of the Cascade Mountains. Other diseases such as black stem, leafspot, and mildew may be responsible for losses, but generally these ailments more seriously affect the early and late hay crops. The insect pest giving most concern to alfalfa seed growers is the Lygus bug. The population of this insect must be watched and controlled during the period of early flower bud stage to the end of bloom. Control measures which involve the use of insecticides must be judiciously applied to avoid excessive mortality among the bees that are frequenting the crop during this same period. Other insects frequently needing control are the alfalfa weevil, cutworms, and grasshoppers. The first growth of the season is usually removed for forage. The second growth is then the seed-producing crop. The principal exception to this rule is in the case of short growing seasons or where LADAK alfalfa seed is produced. In these situations, the first crop is usually the seed-producing crop. (2) Red clover seed. Some red clover seed production occurs in almost every crop zone of the Pacific Northwest. The most important are Zone 13, practically all of which lies in the Snake River Valley of Idaho, and Zone 3, with most of the production occurring in the Willamette Valley of Oregon. Both common red clover and certified varieties are grown. The most important of the certified varieties is KENLAND. The PENNSCOTT variety is increasing in production. In Zone 3, forage and seed production generally go hand in hand, the first growth being removed for forage in late May or in June. The seed is produced by the second growth. The whole season’s production is usually utilized in developing the seed crop in the other producing areas, namely, those east of the Cascade Mountains. Pollination of red clover, as with alfalfa, is usually accomplished through hiring the services of commercial beemen, especially in Zone 13. This is not so often the case in Zone 3, where bumblebees and other wild pollinators are largely relied upon. The weed control problem is met with a combination of cultural methods and sprays, especially sprays applied during the dormant period. Insect pests, in addition to the clover root borer and the clover root curculio, are chiefly limited to the clover leaf weevil, the small clover leaf weevil, the clover seed Chalcid, and the Nitidulid beetle. The latter two have been difficult to control by chemical means. Acreage for seed has undergone a marked decline recently in the state of Idaho. Oregon and Washington are holding nearly steady with slight declines in acreage. FIELD CROP PRODUCTION A N D SOIL MANAGEMENT

52

H. B. CHENEY,

w. H.

FOOTE, E. G . KNOX, AND H. H. RAMPTON

( 3 ) Ladino and other white clover seed. Ladino clover (Trifolium repens L. var. Ladino) seed production has been carried on in Crop Zones 3, 4, 5, 7, and 13. Most of the acreage has been concentrated in Zone 5, centered in Jefferson, Crook and Deschutes counties of Oregon. The highest production of seed was in 1953. Since then, acreage and production have declined rapidly owing to an oversupply of seed. The greatest production continues to be in Zone 5 . White clover (Trifolium repens L.) seed production is centered in Zone 13, with a considerably smaller amount in Zone 3. Production of seed has declined recently, with Zone 3 suffering the sharpest reduction. Production problems of both Ladino and commercial white clover producers are somewhat similar, especially with respect to disease, insect, and pollination problems. All the seed is produced under irrigation with the exception of the white clover acreage in Zone 3. Adequate pollination is obtained through hiring the services of commercial beemen. Principal insect pests of these crops are the clover leaf weevil, the small clover leaf weevil, the clover root curculio, clover seed weevils, red spider, the Ladino clover seed midge, Lygus bugs, slugs, and cutworms. Considerable emphasis is placed upon excluding such crops as white clover, birdsfoot trefoil, alsike clover, and timothy from areas producing Ladino clover seed, because these seeds are inseparable from Ladino seeds. ( 4 ) Alsike clover seed. The Pacific Northwest region is the center of production of Alsike clover (Trifolium hybridum L.) seed in the United States. In 1954, over half of the domestic production of this commodity occurred in Oregon and Idaho. Practically the whole acreage occurs in Crop Zones 5 and 13, with the most concentrated area of production in the Klamath Basin of Zone 5. Alsike clover is esteemed as a soil-improving legume in the areas of seed production. Production problems are somewhat similar to those of Ladino and white clover, especially in regard to obtaining adequate pollination and to the insect pests involved. The most troublesome insect pests are clover aphids, clover leaf weevils, the clover root curculio, clover seed weevils, the Ladino clover seed midge, and Lygus bugs. Mixtures of other crop seeds are troublesome to Alsike seed growers. The most common other crop seed mixture is white clover. (5) Crimson clover seed. Crimson clover (Trifolium incarnatum L.) is adapted in Crop Zones 2 and 3 of the Pacific Northwest. It lacks winter hardiness in areas east of the Cascade Mountains. The crop prefers deep, well-drained soil, but will grow satisfactorily on rather shallow hill lands having good drainage. Crimson clover is a good soil im-

FIELD CROP PRODUCTION AND SOIL MANAGEMENT

53

prover and fits well into rotations on seed-producing farms. Practically all the seed production in the Pacific Northwest is concentrated in the Willamette Valley area of Zone 3. The climate of this area with its mild moist winters and generally warm, dry summers is favorable for the development and harvesting of crimson clover seed crops. Most of the seed produced is exported to the southeastern states for forage and cover crop plantings. The principal variety grown in DIXIE, which is preferred over much of the southeastern United States. Opportunities for increased production are good. The 1954 seed crop from Zone 3 was 1,161,000 pounds. The annual use of crimson clover seed in the United States during the past two years was over 24,000,000 pounds. ( 6 ) Austrian winter field pea seed. The Austrian winter field pea (Pisum satiuum L. var. arvense.) is grown for seed on the better soils in Crop Zones 3,4, 5, 6, and 11. Most of the production occurs in Zones 3 and 11. From about 1930 to 1950, most of the seed was used in the southeastern states for green manure and winter cover crop plantings. More recently, this legume has been largely replaced by other winter cover crops, and production of seed in the Pacific Northwest has declined. Most of the seed now grown is used as a source of protein in concentrated livestock feeds. The most common pest in seed-growing areas is the pea weevil. This insect is controlled by properly timed applications of DDT to the growing crop, and by proper fumigation of the seed after harvest. The pea aphid, also, may be destructive during some years. (7) Hairy vetch seed. Hairy vetch (Vicia villosa Roth.) seed production in the Pacific Northwest is almost entirely confined to the Willamette Valley of Crop Zone 3. In the past, this area produced about 90 per cent of the domestic seed crop. More recently other areas in the central south have become important in seed production. This has resulted in a decrease of acreage in the Pacific Northwest. About 23 per cent of the crop originated in the region in 1954. Hairy vetch seed is chiefly used for green manure and winter cover crop plantings in the southeastern states. The most important pest of the hairy vetch seed crop is the vetch bruchid, an insect similar to the pea weevil. Control is effected by application of DDT to the growing crop and by prompt fumigation of the harvested seed. ( 8 ) Other uetches for seed. These vetches are grown for seed on the better soils in Crop Zones 3 and 4, with most of the production in Zone 3. Common vetch and WILLAMETTE, a strain of common, occupy most of the acreage. The seed is used for green manure and winter cover crop plantings in the southeastern states, and for hay and silage growing in Zones 1,2, 3, and 4, Most of the domestic-grown seed comes

54 H. B. CHENEY, W. H. FOOTE, E. G. KNOX, A N D H. H. RAMPTON from the Pacific Northwest, Reduction in use of the seed in the southeastern states has caused a marked decline in acreage devoted to seed production in the Pacific Northwest. ( 9 ) Miscellaneous legume seeds. Other legume seeds produced in commercial quantities for use principally within or near the region are NOMAD and ORESTAN alfalfa; GRANGER, CASCADE, and DOUGLAS birdsfoot trefoil (Lotus corniculatus L.) ;COLUMBIA and BEAVER big trefoil (Lotus uliginosus Schhhr.) ; the MT. BARKER, TALLAROOK, and NANGEELA varieties of subclover (Trifolium subterraneum L.) ; sweetclover (Melilotus alba Med.) , and strawberry clover (Trifolium fragiferum L.) . c. Grass Seed Crops. (Statistics are shown in Table XI.) (1) Ryegrass seed. Seed production of common ryegrass (Lolium spp.,) and perennial ryegrass (Lolium perenne L.) is mostly concentrated on the poorly drained valley floor soils of the Willamette Valley of Crop Zone 3. The climate in this area, being moist and mild in the winter and warm and dry in the summer, favors the growth and seed production of these grasses. Common ryegrass lacks sufficient winter hardiness for survival east of the Cascade Mountains. Perennial ryegrass is more hardy but is seldom grown for seed outside of Zone 3. Most of the ryegrass seed is grown for export to other states. Perennial ryegrass seed is widely used in pasture mixtures in the more temperate portion of the country and in low-priced lawn mixtures. Common ryegrass seed is much used in the southern and southeastern states for sowing in winter lawns, for winter pastures, and for winter cover-cropping. Some of it also goes into cheap lawn mixtures. Production of common ryegrass seed varies considerably, being about 61,000,000 pounds in 1953 and 105,000,000 pounds in 1954. The production of perennial rye-grass seed is considerably less than that of common ryegrass, but it has been steadily increasing for several years. The 1954 production was about 21,000,000 pounds of seed. Both of these crops often contribute considerable forage as sheep pasture during the winter and early spring, especially during years when winter temperatures are mild and early growth is profuse. Few other crops grow well on the wet soils on which ryegrass is grown. This is especially true on the more imperfectly drained soils where most of the common ryegrass seed is produced. This situation has led to much continuous cropping and increase of weeds, many of which have seeds not readily separable from ryegrass seed. To overcome this difficulty, growers are increasing the practice of summer fallowing and late spring planting. The seed crop is harvested the following year. (2) Tall fescue seed. Tall fescue (Festuca arundinacea Schreb.) prefers deep soils having good water-holding capacity but is adapted on

FIELD CROP PRODUCTION A N D SOIL MANAGEMENT

55

most of the soils and in all crop zones of the region where moisture is adequate. It will endure poorly drained conditions, especially in winter, and has more salt and alkali tolerance than most other cultivated grasses grown in the region. It is winter hardy throughout the region but does not endure long snow cover. The variety ALTA is grown almost exclusively. Ten years ago most of the domestic seed was produced in the Pacific Northwest. Since that time seed production has become important in other states so that now the region produces about 16 to 20 per cent of the domestic seed crop. The 1954 production in the region was about 4,740,000 pounds of seed, of which 3,745,000 pounds was grown in the Willamette Valley of Zone 3. Most seed producers grow this crop in cultivated rows for better weed control, greater yields of seed, and increased productive life of stands. ( 3 ) Chewings and red fescue seed. Red fescue (Festuca rubra L.) and chewings fescue ( F . rubra var. commutata Gaud.) are similar in appearance, adaptations, and uses. They prefer well-drained soils and are tolerant of moderate soil acidity. They possess good winter hardiness but prefer mild winters and temperate summers. These grasses are grown in both cultivated rows and in solid stands. Most of the red fescue is grown in cultivated rows. The solid stand method is used by the majority of chewings fescue seed growers. The most important improved varieties of red fescue in the region are ILLAHEE, RAINIER, and PENNLAWN. Most of the seed of chewings and red fescue is used in mixtures with other grasses for lawn and turf plantings. Practically all the domestic chewings fescue seed crop is produced in the state of Oregon, with most of the acreage located in the Willamette Valley of Crop Zone 3 and a lesser amount in the Grande Ronde Valley of Zone 6. The 1954 production was 6,785,000 pounds of chewings fescue seed. The domestic production of red fescue seed is also almost entirely in the Pacific Northwest. The most concentrated area is in the Grande Ronde Valley of Zone 6. Other producing areas are in Zones 3, 5, and 11. The 1954 domestic production of red fescue seed was 4,452,000 pounds. Recently, large imports of red fescue seed from new producing areas in western Canada have resulted in greatly increased supplies, sharply reduced prices to growers, and a reduction in acreage in the region. ( 4 ) Bentgrass seed. Bentgrasses have wide soil adaptations. They perform well on a wide variety of soils where moisture is plentiful and temperature is favorable. These grasses are tolerant of poor drainage and soil acidity. They endure soil salinity and alkalinity, SEASIDE creeping bentgrass (Agrostis palusiris Huds.) being especially tolerant. They prefer a moist, mild climate, but seed-producing stands possess considerable winter hardiness. The principal bentgrasses grown for

56

H. B. CHENEY,

w. H. FOOTE,

E. G. KNOX, AND H. H. RAMPTON

seed in the region are COLONIAL bentgrass (Agrostis tenuis Sibth.), grown chiefly in the Cowlitz Prairie area of Crop Zone 3; HIGHLAND, a variety of colonial bentgrass produced in the Willamette Valley of Zone 3; ASTORIA, also a variety of colonial bentgrass, produced in the lower Columbia River area of Zone 1, in the Grande Ronde Valley area of Zone 6, and in the Klamath Basin area of Zone 5; and SEASIDE creeping bentgrass, produced in the Klamath Basin area of Zone 5 and the Grande Ronde Valley area of Zone 6. The bentgrass seeds are used almost solely for the planting of lawns and turfs. Practically the entire domestic crop of seed is produced in the Pacific Northwest. ( 5 ) Kentucky (Merion) bluegrass seed. The Pacific Northwest is of little importance in the production of common commercial Kentucky bluegrass (Poa pratensis L.) seed. It is of major importance, however, in the seed production of MERION, an improved turf variety. In 1954, practically the whole supply of MERION seed was grown in the region. The principal centers of production are in the Grande Ronde Valley of Crop Zone 6 and the Spokane area of Zone 11. (6) Miscellaneous grass seeds, Seeds of other grasses produced in commercial quantities for use principally within or near the region are tall oatgrass (Arrhenatherurn elatius L. var. Tualatin), Welsh S. 143 and Akaroa varieties of orchard grass (Dactylis glomerata L.) , meadow foxtail (Alopecurus pratensis L.) , Sudan grass (Sorghum sudanense (Piper) Stapf.) , tall wheatgrass (Agropyron elongatum (Host) Beauv.) , intermediate wheatgrass ( A . intermedium (Host) Beauv. var. Greener), pubescent wheatgrass ( A . trichophorum (Link) Richt. var. Topar), slender wheatgrass ( A . trachycaulum (Link) Malte var. Primar), beardless wheatgrass ( A . inerme (Scribn. and Smith) Rydb. var. Whitmar), Siberian wheatgrass ( A . sibiricum (Willd.) Beauv.), desert wheatgrass ( A . desertorurn (Fisch. ) Schult.) , crested wheatgrass ( A . cristatum (L.) Gaertn.), Manchar and Lincoln varieties of smooth bromegrass (Bromus inermis Leyss.) , big bluegrass (Poa ampla Merr. var. Sherman), hard fescue (Festuca ovina var. duriuscula (L.) Koch), and sheep fescue ( P . ovina L.) .

4 . Potatoes The Pacific Northwest has several important potato-producing areas and the production is a very important segment of the economy of the region. Both early to intermediate and late crops of potatoes are produced on the irrigated soils of the region. The production of potatoes is heavily concentrated in the Klamath Basin and Deschutes area of Zone 5, in the Yakima Valley in Zone 7, and throughout the irrigated Snake

FIELD CROP PRODUCTION AND SOIL MANAGEMENT

57

River Valley, in Zone 13. Some potatoes are grown in most other agricultural areas but often only to supply a local demand. The production and acreages of potatoes in the Pacific Northwest for 1942-51 and 1954 are given in Table XII. The acreage of potatoes has decreased slightly but the total production has increased. This is a direct result of better farming practices such as more fertilizer, better irrigation, improved insect and disease control, and better adapted varieties. I n Idaho, one of the leading states in potato production, the crop is grown chiefly on the irrigated soils of the Snake River Valley, and to a lesser extent in northern Idaho, where they are grown without irrigation. Over 90 per cent of the crop is of the RUSSET BURBANK variety, with some WHITE ROSE and TRIUMPH grown. TABLE XI1 Production and Acreages of Potatoes for the Three States in the Pacific Northwest in 1942-51 and 1954

Oregon Washington Idaho Total

* Agricultural Statistics, 1964. U . S.

Acreage

Production

(1000 acres)

(100-lh. bags)

1942-51'

19542

1942-51

1954

42 34 160 236

37 26 146 209

6,758,400 6,126,000 24,141,600 36,996,000

8,041,354 6,316,249 45,504,638 39,861,241

Department of Agriculture.

* U. S. Bureau of Census, 1955. 1954 Agricultural Census Preliminary.

Oregon has four distinct potato-producing districts. The Klamath Basin, central Oregon, northern Willamette Valley, and the Snake River Valley area of Malheur County are the important areas. The RUSSET BURBANK, WHITE ROSE, and TRIUMPH are the leading varieties. I n recent years, certified potato seed stock has been grown for shipment to California. Washington has three principal potato-producing areas, located in Yakima, Kittitas, Spokane, Benton, and Grant counties. Important commercial varieties are the RUSSET BURBANK and WHITE ROSE. Potatoes grown under irrigation are usually grown in a rotation with alfalfa and grain. The use of phosphate and nitrogen fertilizer has been increasing rapidly. Diseases and insect pests are often very serious on potatoes, seriously reducing yields and quality of the crop. The virus diseases, including

H. B. CHENEY, w. H. FOOTE, E. G. KNOX, AND H. H.RAMPTON

58

mild mosaic, rugose mosaic, leaf roll, and others, are often very serious. Scab (Streptomyces scabies), late blight (Phytophthora infectans) ,ring rot (Corynebmterium sependoricum),rhizoctonia (Rhizoctonia solani), and nematodes (Heterodera marioni) take their annual toll. The Colorado potato beetle, flea beetles, wireworms, aphids, and leaf hoppers are often serious insect pests.

5 . Sugar Beets The important sugar beet producing areas are in the irrigated section of the Snake River Valley Zone 13 and to some extent in Zone 7. The acreages and production of sugar beets for 1942-51 and for 1954 are given in Table XIII. TABLE XI11 Production and Acreages of Sugar Beets for the Three States in the Pacific Northwest in 1942-51 and 1954 Acreage (Acres)

Oregon Washington Idaho Total 2

Production (1000 tons)

1942-51'

1954'

1942-51

1954

16,700 14,800 68,700 100,200

18,378 92,622 85,844 196,844

314 308 1,142 1,743

396 728 1,558 2,689

Agricultural Statistics, 1964. U. S. Department of Agriculture. U. S. Bureau of Census, 1956. 1964 Agricultural Census Preliminary.

The acreage of sugar beets has increased slightly over the 1942-51 average, while the production is up some 54 per cent over the same period. One of the contributing factors to this increased production has been the widespread use of curly top resistant varieties, more careful farm planning or rotations, and a higher level of soil fertility through better rotations and extensive use of commercial fertilizer. Curly top, a virus disease carried by the beet leaf hopper (Eutettix tenellus), has been the most serious disease. Damping-off, nematodes, and some insects, namely, beetles, armyworms, wireworms, and aphids, are often serious in localized areas. Sugar beets are grown for seed as a specialized crop in the Willamette Valley and in southern Oregon.

6 . Annual Legumes The annual legumes such as field peas and beans are produced in several areas of the Pacific Northwest. The primary areas are in southeastern Washington and adjoining portions of Idaho, in Zones 11 and

FIELD CROP PRODUCTION A N D SOIL MANAGEMENT

59

13, and to a lesser extent in the Blue Mountains area, Zone 6, and in western Oregon and Washington Zone 3. The production and acreages of the annual legumes for 1942-51 and for 1954 are given in Table XIV. During recent years, the acreage and production of field beans and peas has declined. TABLE XIV Production and Acreages of Annual Legumes for the Three States in the Pacific Northwest in 1942-51 and 1954 Acreage

Production

(1000 acres)

(1000 pounds)

1944-51l

Oregon Washington Idaho Total 1

27 242 277 546

19542 1944-51 8 119 250

377

33,048 318,655 411,071 763,774

1954 8,568 163,870 409,372 574,810

Agricultural Statistics, 1954. U. S. Department of Agriculture.

* U. S. Bureau of Censua, 1955. 1964 Agricultural Census Preliminary.

Field peas often replace summer fallow in the wheat rotation in the Palouse area of Washington and northern Idaho. The principal varieties are the Canadian, Austrian, and the dry edible pea variety, ALASKA. The common field beans are grown successfully on both irrigated and nonirrigated soil. The Great Northern type is grown mainly in the area with some Red Mexicans, and other small white types.

REFERENCES Allison, I. S. 1953. In “Atlas of the Pacific Northwest Resources and Development” (R. M. Highsmith, Jr., ed.), pp. 3-5. Oregon State College, Corvallis. Baldwin, M., Kellogg, C. E., and Thorp, J. 1938. Soil. U.S. Dept. Agr. Yearbook, pp. 979-1001. Beck, J. R. et al. 1952. Oregon State Coll. Oregon Agr. 9. Blanch, G. E. et al. 1955. Oregon State Coll. Oregon Agr. 22. Blodgett, E. C. 1946. Idaho Agr. Ezpt. Sta. Circ. 1 1 0. C u b a n , H. 1955. Oregon Ext. Ser. Circ. 588. Fireman, M., Mogen, C. A., and Baker, G. 0. 1950. Idaho Agr. Expt. Sta. Research Bull. 17. Highsmith, R. M., Jr., ed. 1956. “Atlas of the Pacific Northwest Resources and Development,” rev. ed. Oregon State College, Corvallis. Homer, G. M., McCall, A. G., and Bell, F. G. 19M. U.S. Dept. Agr. Tech. Bull. 860. Horning, T. 1955. Oregon Agr. Progr. 3 , No. I,15. Hunter, A. S., and Yungen, J. A. 1952. Proc. A m . SOC.Sugar Beet Technol. 180-188. Hunter, A. S., and Yungen, J. A. 1955. Soil Sci. SOC.Amer. Proc. 19, 214-218. Jensen, M. C., Lewis, G. C., and Baker, G. 0. 1951. Idaho Agr. Expt. Sta. Research Bull. 19.

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w.

H. FOOTE, E. G . KNOX, AND H. H. RAMPTON

Kaiser, V. G., Pawson, W. W., Groeneveld, M. H. H., and Brough, 0. L., Jr. 1954. Washington Agr. Expt. Sta. Circ. 255. McKay, M. C., and Moss, W. A. 19M. Idaho Agr. Expt. Sta. Bull. 256. Mech, S . J. 1949. Agr. Eng. 30, 379-383. Mech, S. J. 1955.Agr. Eng. 36, 318. Morrison, K. J., Viets, F. G., Jr., and Nelson, C. E. 1954. Washington Ext. Ser. Bull. 489.

Nelson, C. E., and Larson, C. A. 1946. Washington Agr. Expt. Sta. Bull. 481. Nelson, C. E. 1953.Washington Ext. Ser. Bull. 481. Nelson, C. E. 1954. Washington Ext. Ser. Bull. 365 (Revised). Parks, R. Q. 1951. Advances in Agron. 3,323-344. Pope, A. 1955. Ph.D. Thesis, Oregon State College. Powers, W. L., 1923.Oregon Agr. Expt. Sta. Bull. 199. Powers, W. L., and Wood, L. K. 1947. Oregon Agr. Expt. Sfa. Circ. 418. Reimer, F. C., and Tartar, H. V. 1919.Oregon Agr. Expt. Sta. Bull. 163. Richards, L. A., ed. 1954. U.S. Dept. Agri. Handbook No. 60. Scholl, W., and Wallace, H. M. 1953. Agr. Chemicals 5, No. 6, 32-38. Scholl, W., and Wallace, H. M. 1951.Com. Fertilizer 82, 21-32. Scholl, W., and Wallace, H. M. 1952. Corn. Fertilizer 85, 19-35. Scholl, W., and Wallace, H. M. 1953.Corn. Fertilizer 87, 21-34. Scholl, W., Wallace, H. M., and Fox, E. I. 1954. Agr. Chemicals 9, No.6, 62-82. Scholl, W., Wallace, H. M., and Fox, E. I. 1955. Corn. Fertilizer 91, 3 5 4 . Singleton, H.P. et al. 1950. Washington Agr. Expt. Bull. 520. Soil Survey Staff 1951. US.Dept. Agr. Handbook, No. 18. Thorp, J., and Smith, G. D. 1949.Soil Sci. 67, 1 1 7-126. Tremblay, F. T., and Harston, C. B. 1952. Washington Agr. Ext. Ser. Bull. 386 (Revised). U.S. Bureau of Census 1931-32. Fifteenth Census of the United States: 1930, Agriculture. U.S. Government Printing Office, Washington. US. Bureau of Census 194M3. Sixteenth Census of the United States: 1940, Agriculture. U.S. Government Printing Office, Washington. US. Bureau of Census 1952.United States Census of Agriculture, 1950. U.S. Government Printing Office, Washington. U.S. Bureau of Census 1955. 1954 Agricultural Census, Preliminary. U.S. Department of Agriculture, Conservation Program Service 1954. Agricultural Conservation Program Summary, 1953. U.S. DeRartment of Interior, Bureau of Reclamation 1954. Columbia Basin Joint Investigation, Problem Two. Types of Farming. Viets, F. G., Jr., Boawn, L. C., Nelson, C. E., and Crawford, C. L. 1953a. Washington Agr. Expt. Sta. Circ. 215. Viets, F. G., Jr:, Boawn, L. C., Crawford, C. L., and Nelson, C. E. 195313. Agron. J . 45, 559-565. Viets, F. G., Jr., Boawn, L. C., and Crawford, C. L. 1954. Soil Sci. 78, 305-516.

Anhydrous Ammonia as a Nitrogenous Fertilizer

. .

W B ANDREWS Mississippi Agricultural Experiment Station. State College. Mississippi

I. Introduction .

1 . Use of Anhydrous Ammonia . . . . . . . . . . 2. Manufacture of Anhydrous Ammonia . . . . . . . . 3 . Historical Experimental Use of Aqua and Anhydrous Ammonia . 4. Early Work on the Use of Anhydrous Ammonia in Mississippi . 5 Physical and Chemical Properties . . . . . . . . . . I1. Behavior of Anhydrous Ammonia in the Soil . . . . . . . . 1 . Fixation by the Soil . . . . . . . . . . . . . . 2. Effect on Structural Stability . . . . . . . . . . . 3. Effect on Availability of Plant Nutrients . . . . . . . . 4. Effect on Lime Content of Soil . . . . . . . . . . 5 . Effect on the Soil Fauna . . . . . . . . . . . . 6. Effect on the Microbial Flora in Soil . . . . . . . . . 7. Nitrification of Ammonia . . . . . . . . . . . . I11 Response of Crops to Anhydrous Ammonia . . . . . . . . . 1 Form of Nitrogen Used by Crop Plants . . . . . . . . 2. Response of Cotton . . . . . . . . . . . . . . 3. Response of Corn . . . . . . . . . . . . . . . 4. Response of Small Grains . . . . . . . . . . . . a . In Mississippi . . . . . . . . . . . . . . b . In Other Humid Areas . . . . . . . . . . . c. In Dryland Farming . . . . . . . . . . . . 5 . Response of Pasture and Hay Crops . . . . . . . . . 6. Response of Sorghum and Sugar Cane . . . . . . . . 7. Response of Truck Crops and Potatoes . . . . . . . . 8 . Response of Rice . . . . . . . . . . . . . . . 9. Work in Other Countries . . . . . . . . . . . . 10. Placement of Anhydrous Ammonia . . . . . . . . . IV Anhydrous Ammonia Equipment . . . . . . . . . . . . 1 Storage and Application . . . . . . . . . . . . . 2. Bleeding Losses in Filling Tanks . . . . . . . . . . 3 Distribution Pattern . . . . . . . . . . . . . . V Summary . . . . . . . . . . . . . . . . . . . . VI. Conclusions . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . .

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I. INTRODUCTION Anhydrous ammonia is used as a nitrogenous fertilizer in most of the states in the United States, in Canada, and in several foreign countries. Though some anhydrous ammonia was used in irrigation water prior to 1947, its use in large quantities, mostly applied directly to the soil, has taken place since that time. During the 1947-1954 period, the total quantity of fertilizer nitrogen used almost tripled, and ammonium nitrate became the leading source of nitrogen, though in 1954 the quantity of nitrogen supplied by ammonium nitrate was only slightly more than that supplied by anhydrous ammonia.

1. Use of Anhydrous Ammonia In 1943, a number of farmers in the Tennessee Valley states used aqua ammonia as a source of nitrogen. A few of them continued to use TABLE I

T h e Use of Fertilizer Nitrogen in the United States, Alaska, Hawaii, and Puerto Rico Tons of nitrogen

As anhydrous Year 1900 1910 1930 1930 1940 1945 1948 1949 1950 1951 1952 1953 1954

Total

ammonia

63,000 146,000 328,000 377,000 4 19,000 641,000 841,000 913,000 1,136,000 1,265,000 1,485,000 1,648,000 1,847,000

36,566 53,789 70,122 97,107 137,984 178,089 287,389

it for several years. In Mississippi, the number of farmers using aqua ammonia increased in 1947 and 1948. However, most of those in Mississippi who formerly used aqua ammonia are now using anhydrous ammonia. In recent years, a little aqua ammonia has been used in other states, though the extent of such use is not known. The total tonnage of nitrogen and tonnage as anhydrous ammonia used in selected years in the United States, Alaska, and h e r t o Rico are reported in Table I (Scholl, personal communication; Scholl et al., 1955). The use of nitrogen increased slowly until 1945, and since has increased rapidly to 1,847,000 tons in 1953-1 954.

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Prior to 1947, little anhydrous ammonia was used for crop production and that which was used was applied in irrigation water, primarily in California. In the 1947-1948 fertilizer year, 35,566 tons of nitrogen as anhydrous ammonia was used in the United States. Mississippi used 10,556 tons for direct application. If other states used a similar quantity for direct application, the quantity applied in irrigation water was only about 15,000 tons in 1947-1948. In the 1953-1954 fertilizer year, anhydrous ammonia supplied 287,389 tons of nitrogen and ammonium nitrate, 309,780 out of 1,044,876 tons used as materials. It is probable that anhydrous ammonia supplied more nitrogen than ammonium nitrate for direct application in the 1954-55 fertilizer year. From 1942 to 1954, the supply of nitrogen was less than the demand, and in many cases farmers had little choice between materials and mixed fertilizers, or between sources of nitrogen. Between 1947 and 1954 the supply of anhydrous ammonia was far less than the demand and there was often a shortage of steel for making tanks. Since the present and expected immediate future capacity to produce all sources of nitrogen is larger than the demand and steel is plentiful, anhydrous ammonia will have a chance to adjust to its competitive position as a fertilizer in this country. The very rapid increase in the use of anhydrous ammonia soon after its introduction for direct application to the soil in 1947 may be attributed partly to the shortage of other sources of nitrogen at that time, but its continued increase must be attributed to its competitive position from the standpoint of cost and ease of application as well as to the good results which have been obtained from its use. In addition to its use for direct application to the soil, anhydrous ammonia is also used for the ammoniation of superphosphate and in the manufacture of ammonium nitrate, urea, nitrate of soda, sulfate of ammonia, and many other chemicals, and in many industrial processes.

2. Manufacture of Anhydrous Ammonia The capacity to produce nitrogen synthetically in the United States was estimated by Mehring (1955) to be as follows: January 1, 1954 1955 1956 1957

2,191,000 2,785,000 3,440,000 4,050,000

tons tons tons tons

The location and capacity of the plants are reported in Table I1 (Mehring, 1955, and others). In general, the location of plants is determined by the cost and availability of natural gas and coke and proximity to the anticipated area of consumption.

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TABLE I1 Syhthetic Nitrogen Plants, Capacity and Location in the United States, August I,1955 Plants in operation WEST COAST Brea Chemicals, Brea, California Dow Chemical, Pittsburg, California Hercules Powder Co., Pinole, California Hooker Electrochemical Co., Tacoma, Washington Pennsylvania Salt Manufacturing Co., Portland, Oregon Shell Chemical Co., Shell Point, California Ventura, California MIDCONTINENT AND SOUTH Allied Chemical & Dye, South Point, Ohio Allied Chemical & Dye Corp., La Platte, Nebraska American Cyanamid Co., Fortier, Louisiana Commercial Solvents Corp., Sterlington, Louisiana Coop. Farm Chemicals, Lawrence, Kansas Deere & Co., Pryor, Oklahoma Dow Chemical Co., Freeport, Texas Midland, Michigan Grace Chemical, Memphis, Tennessee Hercules Power Co., Louisiana, Missouri Lion Oil Co., El Dorado, Arkansas Luling, Louisiana Mississippi Chemical Co., Yazoo City, Mississippi Olin Mathieson Chemical, Lake Charles, Louisiana Pennsylvania Salt Manufacturing Co., Wyandotte, Michigan Phillips Chemical Co., Etter, Texas Fort Adams, Texas San Jacinto Chemical Corp., Houston, Texas Spencer Chemical Company, Pittsburg, Kansas Henderson, Kentucky Vicksburg, Mississippi TVA, Muscle Shoals, Alabama U. S. Industrial Chemicals Company, Tuscola, Illinois EAST COAST Allied Chemical & Dye Corporation, Hopewell, Virginia Atlantic Refining Co., Point Breeze, Pennsylvania Columbia-Southern Chemical Corp., Natrium, West Virginia DuPont de Nemours & Co., Niagara Falls, New York Belle, West Virginia Olin Mathieson Chemical Corporation, Niagara Falls, New York Morgantown, West Virginia Plants under Construction Calumet Nitrogen Products Hammond, Indiana Escambia Bay Chemical Corporation Pensacola, Florida Food Machinery & Chemical Corporation Charleston, West Virginia Ketona Chemical Company Ketona, Alabama Mississippi River Fuel Corporation Crystal City, Missouri

Capacity, tons nitrogen per year 70,500 6,000 90,000 18,000 90,000 53,000

234,000 62,000 90,000 110,000 52,000 54,000 58,000 72,000 34,400 170,000 88,000 54,000 84,000 26,000 126,000 128,000 30,000 145,000 65,000 59,000 74,000 41,000 328,000 '27,000 27,000 8,000 190,000 5,000 154,000

A N H Y D R O U S A M M O N I A AS A N I T R O G E N O U S FERTILIZER

65

TABLE I1 ( Continued) Plants in operation

Plants under Construction Sohio Chemical Company Southern Nitrogen Company Standard Oil Company Sun Oil Company U. S. Steel Geneva Works Utah Chemical Company Plants Projected but Not under Construction Ammonia Chemical Company Arizona Gas & Chemical Company Atlas Powder Company Canadian Hydro-Carbons Canadian Industries, Ltd. Celanese Corporation of America Cities Service Columbia River Chemical Co. Dow Chemical Company Gulf Improvement Corporation Gulf States Utility Northern Chemical Industries, Inc. Northwest Nitro-Chemicals, Ltd. Phillips Pacific Chemical Co. Quebec Ammonia St. Paul Ammonia Products Co. Salt Lake Chemical Co. Southwest Agrochemical Corporation Thunderbird Chemical Company

Capacity, tons nitrogen per year

Toledo-Lima, Ohio Savannah, Georgia Richmond, California Marcus Hook, Pennsylvania Geneva, Utah Mt. Pleasant, Utah Merced, California Northern Arizona Atlas, Missouri Winnipeg, Canada Milhaven, Ontario Baton Rouge, Louisiana Lake Charles, Louisiana Pasco, Washington Buras, Louisiana Pascagoula, Mississippi Beaumont, Texas Searsport, Maine Medicine Hat, Alberta, Canada Southeastern Washington Montreal, P. Q. St. Paul, Minnesota Salt Lake City, Utah Chandler, Arizona Kyrene, Arizona

The direct synthesis of anhydrous ammonia was accomplished first in 1908, and the first commercial plant came into production in 1913 in Germany. Construction of two major plants was begun in the United States during World War I and finished after World War I. On October 1, 1955, there were 37 plants in operation, 10 in the process of construction, 16 projected plants not under construction in the United States, and 3 projected plants to be located just inside Canada. Anhydrous ammonia is made by compressing three volumes of hydrogen and one of nitrogen in contact with a catalyst. The pressure is 4000 to 5000 p.s.i. in most plants, but as much as 15,000 p.s.i. in some plants. The temperature in the reaction chamber is about 1000"F., depending upon the activity of the catalyst. The catalyst is carefully purified magnetic iron oxide, promoted with small percentages of aluminum and potassium oxides (Thompson and Shearon, 1952). The nitrogen for making ammonia is obtained from the air, which contains about 12 pounds over each square inch of the earth's surface,

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or about 1700 pounds over each square foot. Where petroleum products are used, the oxygen is separated from the nitrogen simultaneously with the production of hydrogen. The oxygen in the air and steam combine with the carbon of the petroleum product, methane (CH,), for example, forming hydrogen gas and carbon dioxide and monoxide; the nitrogen remains in the mixture. Primarily, hydrogen is obtained by reacting petroleum products with steam which releases hydrogen and forms carbon dioxide and monoxide. Formerly, and to some extent today, hydrogen was obtained from water by applying steam to glowing coke. The carbon of the coke

FIG. 1 . Bulk storage of anhydrous ammonia (courtesy of Mississippi Agricultural Experiment Station).

combines with the oxygen in the steam, forming hydrogen gas and carbon dioxide and monoxide. In this process the coke is alternately treated with air and steam and part of the nitrogen is obtained and oxygen removed as where a petroleum product is used. Nitrogen is also obtained by liquefaction and distillation of the air. Nitrogen boils at -196O C.,while oxygen boils at -183O C. Most of the carbon monoxide is reacted with steam to give more hydrogen and carbon dioxide. The carbon dioxide is removed by absorption in water under pressure. In the process there remains a small quantity of carbon monoxide which would poison the catalyst if it should remain as such. It is removed chemically, or reacted with hydrogen, producing methane and water. The water is removed and the

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small quantity of methane goes through the process as an inert gas. In an economical size plant, the present cost of equipment to produce 1 ton of nitrogen as anhydrous ammonia annually is $100 to $125, as compared to $200 to $240 for ammonium nitrate. The cost of tanks for storing anhydrous ammonia is $150 to $200 per ton of ammonia capacity. The cost of good storage for ammonium nitrate is considerable, though it may be stored in buildings which are also used for other purposes. The cost of producing 1 ton of anhydrous ammonia is essentially the same as the cost of producing 1 ton of ammonia nitrate; on a pound of nitrogen basis, the cost of producing anhydrous ammonia is only about 40 per cent of the cost of ammonia nitrate. The relative costs of the two materials suggest that where suited the use of anhydrous ammonia will continue to increase relative to the solid sources.

3 . Historical Experimental Use of Aqua and Anhydrous Ammonia The first reference to the use of free ammonia in fertilization was by Johnston (1853) in England, who discussed the use of “ammoniacal liquor” for grasslands and grain crops. In 1930, Smith (cited by Andrews et al., 1951), applied anhydrous ammonia directly to the soil by means of a small cylinder attached to a one-mule plow.- In 1931, Tiedjens and Robins reported data on the use of aqua ammonia in greenhouse cultures. Waynick (1934) recommended the use of anhydrous ammonia in flood irrigation water and a small quantity has been used in this manner, primarily in California. Chapman (1936) reported greenhouse data in which aqua ammonia was used as a source of nitrogen. In 1939, Leavitt applied for a patent on the application of anhydrous ammonia to arable soils, which was granted as U. S. Patent No. 2,285,932 (1942). In 1943, Andrews et al. (1947a, b), of the Mississippi Agricultural Experiment Station, experimented with aqua ammonia for direct application to the soil in the field. Later in the year, some of the experiment stations in the Tennessee Valley area applied aqua ammonia on an experimental basis, and a limited number of farmers in this area also applied aqua ammonia on a demonstration basis. MacIntire et al. (1944) reported data on the use of aqua ammonia in greenhouse tests. The Mississippi Agricultural Experiment Station began experimental work on the use of anhydrous ammonia for direct application to the soil in 1944 (Andrews et aZ.,1947a, b). Though the work of Smith in 1930 and Leavitt in 1939 suggested that anhydrous ammonia might be applied directly to the soil, the development in the use of anhydrous ammonia came after and was based on the principles outlined by Andrews et aZ. (1947a, b) and first published in 1947.

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4 . Early Work on the Use of Anhydrous Ammonia in Mississippi The Mississippi Agricultural Experiment Station began work on the use of anhydrous ammonia in the spring of 1944. The Tennessee Valley Authority helped to finance the work. The equipment used in applying anhydrous ammonia consisted of ( I ) a “Flowrator” and fittings, ( 2 ) a cylinder of refrigeration grade anhydrous ammonia, and ( 3 ) a knifelike applicator which released the ammonia in the soil and covered it simultaneously, all of which was mounted on a tractor (Edwards and Andrews, 1947). The author still prefers the Flowrator for application of anhydrous ammonia in experimental work. In the spring and summer of 1944 side dressing tests in which anhydrous ammonia was compared with ammonium nitrate were conducted with corn and cotton. In the fall of 1944, tests were started in which fall and spring applications of these sources of nitrogen were made to fall-planted oats. In the spring of 1945 tests were started in which time and rate of application of nitrogen from anhydrous ammonia and ammonium nitrate were compared for the production of corn and cotton. Because of a shortage of solid sources of nitrogen in the winter of 1946-1947, some farmers became interested in the experimental work with anhydrous ammonia which had been conducted. An investigation revealed that sufficient anhydrous ammonia and steel for making equipment would be available to permit some use of anhydrous ammonia by farmers in the spring of 1947. Because the Flowrator used in the experimental work was both almost unavailable and considered unsuited for farm use, another metering device was developed. This metering device consisted of ( I ) a pressure gauge on the tractor tank, (2) suitable valves and connections for conducting the ammonia to ( 3 ) a manifold and orifices, before which there was a pressure gauge, for dividing the ammonia into two or more streams which were conducted into the soil. In the original equipment 3/32-inchorifices were used. The rate of flow per hour through the metering equipment was found to be a function of the pressures of the anhydrous ammonia in the tank and on the orifices, both of which vary with temperature. The rate of flow was varied by a needle valve located between the tank and the orifices. The rate of nitrogen applied per acre is a function of rate per hour and acreage covered. Specifications for the equipment were drawn up and tables were prepared which enabled farmers to apply anhydrous ammonia accurately. Though the instructions enabled accurate application of anhydrous ammonia, in practice, as has been the case with other fertilizers, farm-

ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

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ers often controlled the rate of application by adjustments made on the basis of the area covered by a prior tank of ammonia rather than by following the instructions. However, the instructions enabled the manufacturer of equipment to supply farmers with starting information. The first equipment for applying anhydrous ammonia was assembled and made in local shops. Steam fittings were often used on tanks because the supply of refrigeration fittings was inadequate, and even the latter were not entirely satisfactory. Since 1947, industry has made suitable fittings for anhydrous ammonia, and several different metering devices have been developed which will be discussed in Section IV, 1 ; however, metering devices based on the principles outlined here are widely used at present. 5 . Physical and Chemical Properties

Anhydrous ammonia is a liquefiable gas which is handled in commerce as a liquid. The liquid phase boils at -28O F. at atmospheric pressure. It has a gauge pressure of 74 p.s.i. at 50" and 197 pounds at looo F. The critical temperature is 271.4O F.; the critical pressure is 1652 p s i . Though its density varies with temperature, it weighs 5 pounds per gallon at 80°F. It contains 82.26 per cent nitrogen. The fertilizer grade contains at least 82 per cent nitrogen. When air contains 16 to 25 per cent ammonia, it can be ignited, though ignition is unlikely. Because of the possibility of an explosion, tanks should not be welded where there is a mixture of air and ammonia. Ammonia is less than two-thirds as heavy as air, and when released into the air, rises quickly unless brought down by air currents. Ammonia readily corrodes copper, brass, and some of the lighter metals. It does not attack steel. Tanks for containing ammonia have a working pressure of 250 p.s.i., and are equipped with relief valves, and excess-flow valves. Tanks should never be completely filled because of the possibility of relief valve failure and an explosion from liquid pressure. In very low concentrations, ammonia is irritating to the eyes, nose, throat, and skin; high concentrations are dangerous. The characteristic odor and irritation produced by ammonia serve as signals when danger approaches. Those who work with ammonia should wear rubber gloves, and protective glasses and clothing when they are possibly needed. Water and a special first-aid kit should always be available for an emergency. In practice, there is little danger in the use of agricultural ammonia because it is handled outside of buildings, though one should always keep in mind that it is inherently dangerous. Hydrocyanic acid, a deadly poison, is formed when a mixture of anhydrous ammonia and fuel gases burns. For this reason, fuel gases

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W. B. ANDREWS

for open heating should never be put in tanks which have previously contained anhydrous ammonia, unless the complete removal of the anhydrous ammonia has been determined by one who is competent to pass judgment. 11. BEHAVIOR OF ANHYDROUS AMMONIAIN

THE

SOIL

1. Fixation by the Soil On application to the soil, anhydrous ammonia reacts with water to form ammonium hydroxide and diffuses through the soil solution and air until it comes in contact with sufficient clay and organic matter to take it up. Ammonium ions replace hydrogen ions readily; some data (Stanley and Smith, 1955; Anderson, 1955) and observations that alkaline soils retain applied anhydrous ammonia or ammonia released on decomposition of organic matter, suggest that the ammonium ion may replace some calcium from the base exchange complex. The loss of nitrogen into the air from surface applications of ammonium salts to alkaline soils is, no doubt, a phenomenon which is not related to fixation of the ammonium ion within an alkaline soil. Unpublished data by the author show that the application of excess ammonia, as ammonium hydroxide, to strongly acid soils followed by air drying to remove the excess ammonia, results in the fixation of a quantity of ammonia, as determined by distillation, which is essentially equivalent to the lime requirement. However, soils which are only slightly acid fix a quantity of ammonia which is in excess of the lime requirement, the mechanism of which is not fully understood. Though experiments have not yet been made, it is suggested that the ammonia fixed by soils on application of an excess in a dilute solution followed by boiling off the excess is probably closely related to the lime requirement. Under wetting and drying in laboratory experiments, it has been shown that the ammonium ion may be fixed in a form which is not readily exchangeable with neutral salt solutions. However, the fact that for crop production anhydrous ammonia has usually been equal or superior to other sources of nitrogen under field conditions suggests that either anhydrous ammonia is not fixed in a position unavailable to plants or that this fixation is at least offset by additional losses from the other sources of nitrogen which have been compared to it. In field use a good job of application of anhydrous ammonia is being done if a puff of ammonia is rarely seen and if ammonia cannot be smelled by putting the nose close to the soil soon after application. A broad-pointed applicator, 3 to 4 inches wide, increases the soil exposed to ammonia and reduces the loss in application; a disk hiller, or other sealing device, facilitates the retention of ammonia by the soil.

ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

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The cross-section pattern made by anhydrous ammonia depends upon the physical condition of the soil. If the soil is friable, the cross section tends to be circular. If the soil is compact and wet, the ammonia would be more concentrated along fractures made by the knife applicator and the possibility of loss in application is increased. If the soil is heavy, cloddy, and dry, much of the ammonia escapes into the air. As an illustration, in Ohio on a heavy soil which was in large dry aggregates, Mederski (personal communication) found that anhydrous ammonia was largely lost in application. Under field conditions on a sandy loam soil, Andrews et al. (1951) found that 100 pounds of nitrogen as anhydrous ammonia in 42-inch rows was absorbed in a zone with a cross section having an area of about 16 square inches. The determinations were made by applying a moist filter paper, impregnated with indicator, to a cross section of the area involved. Even though the soil was in excellent physical condition, the indicator suggested variations in the concentration of the ammonia corresponding to fractures in the soil produced by the applicator. Calculations made on Stanley and Smith's (1955) laboratory data on a silt loam soil indicate that 100 pounds of nitrogen as anhydrous ammonia per acre in 40-inch rows was absorbed in zones having cross sections of less than 13, 12, and 9 square inches where the moisture content was 2, 15, and 23 per cent, respectively. These calculations and the findings of Andrews et al. (1951) suggest that little ammonia diffuses beyond 2 inches from the point of application where 100 pounds of nitrogen per acre is applied in 40-inch rows, except in very sandy soils. As Stanley and Smith conducted their laboratory experiments, 100 pounds of nitrogen per acre as anhydrous ammonia was applied at points 40 x 12 inches apart. Their chemical data from soil taken in a plane through the point of application show the equivalent of about 262, 323, and 240 pounds of nitrogen per acre (2,000,000 pounds of soil) in 40-inch rows where the moisture content was 2, 15, and 23 per cent. Though Stanley and Smith found that the depth of application and moisture content of the soil affected the loss of ammonia at the high rates of ammonia applied, such high concentrations of ammonia are unlikely in field applications. The following differences in laboratory experiments and field applications are more favorable to retention of ammonia in field application: (1)with a starting temperature of 80° F., in field application, anhydrous ammonia leaves the applicator as about 84 per cent liquid and 16 per cent vapor and at -28O F.; in laboratory experiments, the metering equipment, no doubt, largely vaporizes the small amount of ammonia involved; because of differences in heat of ab-

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sorption, liquid ammonia is more easily absorbed by the soil water than vapor; (2) shattering of the soil by field applicators increases the exposure of the clay and organic matter and facilitates absorption and retention of ammonia by the soil; and (3) field application of ammonia is in a continuous volume of soil which is small in comparison to the total volume of the soil, whereas laboratory applications are made discontinuously and give, for the same rate of application per surface acre, much higher concentrations of ammonia at the points of application. Comparative crop yields may be the only practical means of measuring losses of anhydrous ammonia in application, though very valuable information may be obtained by applying indicator-impregnated moist filter paper to a cross section of the soil at the point of application in the field. 2 . Effect on Structural Stability In laboratory experiments, Anderson (1955) found that ammonia treatment of a sandy loam soil reduced structural stability, as shown by decreased percolation and by the appearance of “copious quantities” of clay and organic matter in the leachate. An apparent contradiction was found in that ammonia treatment and subsequent drying increased the aggregates retained in a wet-screening procedure. Though Anderson suggested the possibility of attributing the increase in the retention of aggregates to solution and reorientation of the organic matter, it appears to the author that the organic matter may have gone into solution in the wet-screening procedure as well as in the leaching procedure, and that the increase in the retention of the aggregates may have been produced by swelling of ammonium colloids. From a practical viewpoint, there is little, if any, possibility that anhydrous ammonia as applied in the field affects structural stability unfavorably because too small a percentage of the soil is affected for too short a time. From a theoretical viewpoint, it appears that in the zone of application anhydrous ammonia does affect structural stability unfavorably for a short time. As is the case with all other factors which increase yield, the application of anhydrous ammonia increases crop yields and the crop residues returned. Though the improvement is small, increases in crop residues affect structural stability favorably.

3 . Effect on Availability of Plant Nutrients When anhydrous ammonia is applied to the soil, the reaction in the area of concentration approaches pH 9.0. However, within a few weeks, as nitrification progresses, the reaction drops down to or below the original pH of the affected soil. It therefore appears that any increase

ANHYDROUS AMMONIA AS A NITROGENOUS

FERTILIZER

73

in the availability of plant nutrients produced by the alkalinity of freshly applied anhydrous ammonia would disappear on return of the soil to the original reaction, or, in the case of phosphorus, be decreased with a depression of the p H below that of the original soil. In the final analysis, the effect of anhydrous ammonia on the available nutrients probably should be no different from that of ammonium nitrate or urea. Craddock, Wisconsin (personal communication), found that increasing the quantity of ammonium hydroxide progressively increased the phosphorus soluble in water or 0.002 N sulfuric acid. Where the reaction was increased from p H 5.4 to 8.4 by ammonium hydroxide, water-soluble P& was increased 12.1 and acid-soluble P,O, 22.0 pounds per 2,000,000 pounds of soil. It is readily seen that these increases drop to insignificance when applied to a surface acre, only 5 to 10 per cent of which is affected by the anhydrous ammonia applied under field conditions. In this case, 1000 pounds of nitrogen per acre was applied as anhydrous ammonia to Spencer silt loam subsoil; at 100 pounds per acre of nitrogen, the increase is calculated to be 1.2 pounds of water-soluble and 2.2 pounds of acid-soluble P,O, per acre. The application of a quantity of anhydrous ammonia which resulted in 189 pounds of ammonium nitrogen being present, after being subject to nitrification for eight weeks in a soil of pH 6.0 under laboratory conditions, increased the soluble phosphorus 3.3 pounds of P,O, per surface acre (Stanley and Smith, 1955). With a lower rate of application of anhydrous ammonia, the increase would be smaller. Anderson (1955) found that treatment of a soil with ammonium hydroxide increased the water-soluble phosphorus. Though his data were not reported in pounds per acre, the effect on the treated zone is likely to be in line with the data of Craddock (personal communication) and Stanley and Smith (1955) when applied to a surface acre in quantities normally used in the field. According to the experience of Lancaster (personal communication), soil phosphorus brought into solution on contact with ammonia has an availability to plants of about one-third that of superphosphate; this appears to reduce further the significance of the small increases in the solubility of phosphorus reported. Where the alkali-soluble phosphorus content of the soil is very high, the application of ammonia would bring into solution larger amounts of P,O,; however, this probably would have no practical value because it is likely that additional available phosphorus is not needed on such soils. Where alkali-soluble phosphorus in soils is very low, no doubt the effect of the application of anhydrous ammonia on the solution of P,O, would be much less than that noted above. I n any case, the response of crops to the increased solubility of the phosphorus probably would not

74 W. B. ANDREWS be measurable and the quantity of phosphate ordinarily applied would not be reduced.

4 . Effect on Lime Content of Soil Anhydrous ammonia, as well as most sources of nitrogen, is acidforming when applied to the soil. For all practical purposes, the acidity of anhydrous ammonia is the same as that of ammonium nitrate and urea, and one-third that of sulfate of ammonia. The use of high rates of nitrogen in humid climates, where the soils are normally acid, speeds up the time when the application of lime is needed. Many mixed fertilizers contain sufficient lime for them to be labeled “neutral” according to the Official Method, though it is doubtful if they contain sufficient lime completely to offset their acid-forming properties (Andrews, 1954a). Because of the high cost of buying lime in mixed or nitrogenous fertilizers, applying lime, as such, directly to the soil is the most practical means of offsetting the acidity of fertilizers. According to the Official Method, 1.78 pounds of CaCO, is needed to offset the acidity of 1 pound of nitrogen applied as anhydrous ammonia. However, it is suggested (Andrews, 1954a), that a more reliable approach to the problem is to assume that all nitrogen which is applied and not recovered by the plant leaches out as Ca(NO,),. On this basis, where 3 pounds of nitrogen increases the yield 1 bushel of harvested ear corn, about 2 pounds remain in the stalks, etc., and in the soil, and which may take about 2.38 pounds of CaCO, out of the soil per pound of nitrogen applied.

5 . Eflect on the Soil Fauna Though no data have been reported on the effect of anhydrous ammonia on the insects, worms, etc., in the soil, its toxicity to other living things suggests that it may kill these in the volume of soil affected. Since the numbers of these organisms are controlled by the food supply and they multiply rapidly, they would reinvade the affected volume of soil in a short time after nitrification of the ammonia. The total effect of anhydrous ammonia should be no different from that of other sources of nitrogen, all of which should slightly increase insects, worms, etc., because of increased crop residues.

6. Effect on the Microbial Flora in Soil “Anhydrous ammonia was applied to Arredondo loamy fine sand and Lakeland fine sand at rates of 100 and 250 pounds of nitrogen per acre [Eho and Blue, 19541. In all soils, the numbers of fungi were decreased. The numbers of bacteria and actinomycetes were increased except for a period not longer than 3 days after application on the

A N H Y D R O U S A M M O N I A AS A N I T R O G E N O U S FERTILIZER

75

neutral soil, during which time they were decreased. A more detailed study of the zone of retention showed that both the numbers of fungi and bacteria were decreased on the first day. This decrease occurred in both acid and neutral soil. On the tenth day the numbers of bacteria had increased to 6 to 25 times those in the check soil. The changes in the microbiological population were noticeable while high concentrations of ammonia were present and were restricted to a 3-inch zone centered on the injector row; this corresponded to the zone in which most of the ammonia was retained. From a total population standpoint, none of the changes noted are likely to permanently disturb the ecological balance in the soil. “The drastic reduction in numbers of fungi in the anhydrous ammonia treated soil indicates that there may be a possibility of it being used as a fungicidal agent in soil.” I n another series of experiments, Eno et al. (1955) found that “The numbers of fungi and nematodes were reduced by all levels of ammoniacal nitrogen from 136 to 741 ppm. Compared to untreated soil, only 0.6% of the nematodes and 4.9% of the fungi survived when 608 ppm. of nitrogen were present in the soil. This level of ammoniacal nitrogen occurs regularly in the retention zone when anhydrous ammonia is applied in the field. The largest reduction in both nematodes and fungi occurred above 365 ppm. Field studies showed a drastic reduction in all nematodes in the retention zone. Plant parasitic nematodes were greatly decreased and in many cases certain species could not be detected during counting. Re-establishment of the nematodes was greatest among the saprophytic species and was of the same character as that following fumigation with conventional nematocides. The economic value of the reduction of plant parasitic nematodes by anhydrous ammonia, applied primarily for its nitrogen content, will require further work on a field basis. Gross elimination of nematodes is not necessary for successful crop production. Thus, it can be seen that in addition to the primary use of anhydrous ammonia as a fertilizer, the destruction of plant parasitic nematodes in the retention zone also may be of value.” 7. Nitrification of Ammonia Because ammonium nitrogen is not leachable and nitrate nitrogen is subject to leaching, the use of anhydrous ammonia for direct application has stimulated interest in rate of nitrification as related to soil properties. The interest in fall application of anhydrous ammonia for spring consumption by fall-sown and spring-planted crops has stimulated interest in rate of nitrification as related to temperature and soil properties.

76

W. B. ANDREWS

Andrews et al. (1951) found that soils with pH of 5.0 or less nitrified ammonium nitrogen much more slowly than those with pH of 5.5 or higher, and that, in general, soils with a higher pH nitrified ammonia more rapidly than those with a lower pH. When applied in October to soils of pH of 5.0 or less, anhydrous ammonia was a very satisfactory source of nitrogen for spring consumption by f all-planted oats, but it was not on soils with pH of 5.5 or higher. The relation of rate of nitrification to soil reaction and to carry-through the winter of anhydrous ammonia applied in the fall is evident. Jenny et al. (1945) found that the rate of nitrification of sulfate of ammonia was the same as that for ammonium hydroxide. Anderson (1955) found that ammonium hydroxide nitrified more rapidly than sulfate of ammonia at pH 4.9, but there was no difference at pH 6.8. Eno et al. (1955) found that concentrations of ammonia which raise the pH above 8.5 markedly reduce the rate of nitrification. In experiments conducted by the author and associates (unpublished), it was found that aqua ammonia applied in the center of a beaker of soil nitrified more slowly than the nitrogen in readily decomposable organic matter which was uniformly distributed in the soil. As pointed out in Section 11, 1 on application of anhydrous ammonia to the soil, there appears to be considerable variation in the concentration of ammonia within the affected soil because of soil fracturing by the applicators. These variations in concentration of ammonia could result in retarded nitrification where the concentration of ammonia produces a pH of 8.5, as well as rapid nitrification in much of the zone where the pH may be less than 8.5. Though for the present it is necessary to depend upon laboratory data for information on nitrification of ammonium nitrogen, there are misgivings about applying such data to anhydrous ammonia applications in the field. Most of the data have been collected using sources of nitrogen which have been mixed with the soil, whereas anhydrous ammonia is applied in a limited volume of soil; if ammonium salts are applied, the reaction of the soil is changed little whereas anhydrous ammonia raises the pH of the soil markedly; if aqua ammonia is applied in a localized area in laboratory experiments, the concentration of ammonia would probably be uniformly high in the affected volume of soil as compared to marked variations in concentration which appear to exist in the zone of application of anhydrous ammonia under field conditions. In general, the rate of nitrification is higher in soils which are high in lime than in strongly acid soils, but the correlation between lime content and rate of nitrification is not perfect. The data of Frederick (personal communication), reported in Table 111, show a good correla-

77

ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

tion between soil reaction and rate of nitrification. However, the rate of nitrification in a soil of pH 6.1 (Anderson, 1955) was higher at all temperatures than that of soils with pH of 6.3 and 6.8 (Table IV). There was considerable nitrification in five soils at 52O F. and in one soil at 37O F. TABLE I11 The Effect of Soil Reaction and Temperature on Rate of Nitrification'

Temp. OF.

34 45 60

70 80 95

Genesee silt loam p H 7.7

Mellott silt loam subsoil pH 7.8

Chalmers Clermont silty silt loam subsoil clay loam 1st run 2nd run p H 6.2 p H 5.0 p H 6.2 p H 7.4 Pounds nitrate nitrogen per acre in two weeks

8 40

0

180 240 3362 3602

20 100 125

180

0 0 4 80 90 60

4 15 40

0 40 300 480 500 560

0

70 90 100

1

Frederick, unpublished.

2

All NHI-N added was converted to nitrate between the first and second weeks.

0 0 25

0 0

70

110

450

230

480 380

110

TABLE IV T h e Effect of Temperature on Nitrification of NH,OH in Four New Jersey Soils -200 Pounds of Nitrogen Per Acre'

Soil type Freehold loamy sand Washington loam Annadale loam Nixon sandy loam Nixon sandy loam 1

pH 6.8 5.9 6.1 4.9 6.8

21-days-temperature "F. 42-days-temperature "F. 37 42 47 52 37 42 47 52 Pounds of nitrogen nitrified per acre 6 2 26 0 6

20 6 54 4 0

68 14 70 12 20

92 30

8 4 42 10

84

8

86 26

114 58

122

16 90 36 48

110 72 108

102 96 118

60

84

Anderson, 1955.

The effect of temperature on rate of nitrification (Anderson, 1955) is shown by data reported in Table IV. In 21 days, three soils nitrified 84, 86, and 92 pounds of nitrogen per acre at 52O F., whereas the rate of nitrification was much lower for two soils. Even at 37O F., one soil nitrified 26 pounds of nitrogen per acre in 21 days. There is no evident explanation for the differences in nitrification rate of the soils at low temperatures unless the soils with low nitrification rates at low temperatures contained few nitrifying organisms, as suggested by Frederick (personal communication) in explaining the

78

W. B. ANDREWS

lack of nitrification in two soils with high and low pH values. Evidence of the build-up of nitrifiers is shown in Table I11 by the increased nitrification following an initial application of ammonium nitrogen. The Indiana data of Frederick (personal communication) show much higher nitrification rates at high temperatures, and by soils well supplied with lime than by soils low in lime (Table IV) . Two soils failed to nitrify any nitrogen at or below 4 5 O F., which Frederick attributed to lack of a nitrifying population. One soil nitrified 8 pounds of TABLE V The Nitrification of Ammonium Phosphate in Genesee Silt Loam, at pH 7.7, for 16 Weeks ~

~

~~

~~

Temperature, O F . Average

High

Low

Nitrate nitrogen, pounds per acre per week

PO

20

20

0

35

35 60 45

35

1.5 3.3 1.6

45 45

45 70 60

46 35

45

60

PO

6 10 10 16

60

60

33

95 80

45

29 28

35

35 45

60 60 60 60 60

70 70

80

20

36

45 45 35

33 37

nitrogen per acre in two weeks at 34O F. The New Jersey data of Anderson (1955) show nitrification proceeding down to 3 7 O F. on four of the five soils and one soil nitrified 26 pounds of nitrogen in 21 days at this temperature. The effect of fluctuating daily temperature on the rate of nitrification is shown by the data of Frederick (personal communication) reported in Table v. The rate of nitrification at low temperatures was much faster where temperatures fluctuated daily above and below a mean than for a constant temperature, suggesting that nitrification begins immediately when the temperature becomes favorable, and for some soils a favorable temperature appears to be only slightly above freezing, though higher temperatures are more favorable.

ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

79

The rate of nitrification does not appear to be reproducible, or there are uncontrollable factors which affect it as shown by: 1. The data in Table IV show that two soils which had a low rate of nitrification for the first 21-day period had a much higher rate during the second 21-day period, and that the rate was much slower in the second period for three soils which nitrified more rapidly in the first period. 2. Nitrification by a subsoil was many times faster the second time than the first time the nitrification test was made, suggesting that the nitrifiers were built up during the first period (Table 111). 3 . Samples taken at different times from the same area of a field had markedly different rates of nitrification (Frederick, personal communication). The data reviewed on the effect of temperature on rate of nitrification show that there are some soils that nitrify considerable nitrogen at temperatures which approach freezing and that nitrification by these soils appears to be resumed immediately when the temperature rises above freezing.

111. RESPONSEOF CROPSTO ANHYDROUS AMMONIA

I. Form of Nitrogen Used by Crop Plants Many young plants utilize the ammonia form of nitrogen more efficiently than the nitrate form, whereas the reverse is true for older plants. When the ammonium form of nitrogen is present, young corn grows more rapidly than with nitrate nitrogen; however, the author has not observed any differences in the response of corn to anhydrous ammonia and ammonium nitrate applied as early and late side dressings. Seedling cotton utilizes ammonium nitrogen more effectively; later the presence of both forms is more effective, while, in the fruiting stage, nitrate nitrogen is more effective, but fruiting and growth are better if both forms of nitrogen are present (Naftel, 1931). As applied, the author has not observed any difference in the response of young oats to ammonium nitrate and anhydrous ammonia; however, in the spring, fall-planted oats respond more quickly to nitrate than to ammonium nitrogen, suggesting that they make little use of ammonium nitrogen at this stage of growth. Though the author does not have data, it is presumed that other small grains respond similarly to oats. In the case of rice the response to nitrate nitrogen as compared to ammonium nitrogen is sometimes good and sometimes poor. However, the response is complicated by the fact that most of the ammonium form is attached to the clay, where it has less chance of being utilized

80

W. B. ANDREWS

by algae, etc., in the water, as contrasted with the nitrate form, which is in the water where it is accessible to the algae and, in addition, it may be subject to loss by denitrification. As observed by the author, nitrate nitrogen has shown up more favorably as compared to ammonium sources where the response of rice to nitrogen was low. The preference of plants for one of the two primary forms of nitrogen at different. stages of growth, the nonleaching properties of the ammonium form of nitrogen as compared to the leachability of nitrate nitrogen, and the possibility that nitrate nitrogen may be denitrified make it difficult to conduct tests comparing forms of nitrogen. Where nitrate is more effective than ammonium nitrogen, it is evident that the last optimum date for application of the ammonium form is earlier than that for the nitrate form. Under leaching conditions, the earliest optimum date for application of nitrate nitrogen is later than that for ammonium nitrogen; this relationship is further complicated by the fact that the rate of nitrification is slow in some soils and fast in others. From the standpoint of crop response, it is the objective of this paper to review the experiments in which anhydrous ammonia and other sources of nitrogen have been compared. Because of the newness of the use of anhydrous ammonia by farmers, there are very few data available on comparative responses of crops. Because of the scarcity of data on time of application of anhydrous ammonia and because of the tremendous interest in off-season application of anhydrous ammonia, some data are reviewed from tests which did not include anhydrous ammonia as a source of nitrogen. Though, inherently, there is a possibility that off -season applied anhydrous ammonia may not behave exactly as other sources of nitrogen, the shortage of actual data on anhydrous ammonia and the rapidity of nitrification, particularly by some soils at low temperature, appears to justify the use of other data until such time as there are sufficient data to describe adequately the behavior of anhydrous ammonia. When applied at a considerable time in advance of utilization, the difference between the leaching of nitrogen applied as ammonia and nitrate is probably negligible on soils which nitrify ammonia rapidly, but appreciable where the rate of nitrification is slow. However, it is likely that the behavior of anhydrous ammonia is not markedly different from that of sulfate of ammonia. For these reasons, data on time of application of sources of nitrogen other than anhydrous ammonia are also reviewed in this paper. The most intensive research work on the use of anhydrous ammonia has been done by the Mississippi Agricultural Experiment Station. This work up to 1951 was published in bulletins (Andrews et al., 1947a, by 1948, 1951) . Summaries of the published work of the Missis-

A N H Y D R O U S A M M O N I A AS A N I T R O G E N O U S FERTILIZER

81

sippi Agricultural Experiment Station and other applicable data were presented in the author’s book (1954~) ,The Response of Crops and Soils to Fertilizers and Manures, published by the author, and they are used in quotation in this paper by permission of the publisher. Republication rights to the quoted material, of course, remain with the original copyright, though the original data are available for any use which may be made of them. 2. Response of Cotton Cotton, Gossypium hirsutum L., is normally planted from three to five weeks after the last killing frost in the spring. Flowering begins about eight weeks later. Small cotton grows very slowly and makes only a small part of its total growth before flowering begins. Normally, the fruit-setting period is six to eight weeks, but may continue until frost. The fruit is normally mature in six to eight weeks after blooming. As has been pointed out, seedling cotton makes better use of ammonium than nitrate nitrogen; from the seedling stage to the beginning of fruiting, the presence of both forms is more favorable for growth than only one form; during the fruiting stage, the nitrate form of nitrogen is more efficient than the ammonium form, but growth and fruiting are better where both forms are present. “Anhydrous ammonia is slightly superior to ammonium nitrate for cotton production when applied before planting. As an average of 31 tests conducted in Mississippi, anhydrous ammonia made 38 pounds of seed cotton per acre more than ammonium nitrate [Table VI]. The depth of application was four inches; the slight superiority of anhydrous ammonia is attributed to less leaching during the first few weeks after application. “A six-inch depth of placement of anhydrous ammonia produced an average of 39 pounds more seed cotton than a four-inch depth in 18 tests when applied before planting. It should be pointed out that anhydrous ammonia is more easily sealed in the soil when applied six inches deep than at shallower depths. “Anhydrous ammonia was slightly superior to ammonium nitrate, cyanamid, nitrate of soda and sulphate of ammonia for cotton production in six tests in the Mississippi Delta. The increases in yield of seed cotton were: anhydrous ammonia 542, ammonium nitrate 530, nitrate of soda 518, sulphate of ammonia 500, and cyanamid 489 pounds of seed cotton per acre. The data are averages for 30, 45, and 60 pounds of nitrogen per acre. The slight superiority of anhydrous ammonia to sources which contain nitrate nitrogen is attributed to less leaching during the first few weeks after application. “Ammonium nitrate was superior to anhydrous ammonia for side-

a3

W. B. ANDREWS

dressing cotton when both were placed four or five inches deep. As an average of 31 tests applied as an early side dressing, ammonium nitrate increased the yield 325 pounds of seed cotton per acre and anhydrous ammonia 281 pounds. The superiority of ammonium nitrate as a side dressing is attributed to the preference of cotton at this stage of growth for nitrate nitrogen. “When moisture was adequate ammonium nitrate applied on the surface and anhydrous ammonia applied four to five inches deep as side dressings produced identical increases in yield of seed cotton. In 1944, TABLE VI The Response of Cotton to Anhydrous Ammonia and Ammonium Nitrate in Mississippi Source of nitrogen Ammonium nitrate

Pounds nitrogen per acre

Time of application

32

Early side-dress

64 33

Preplant Preplant

33

Early side-dress

Anhydrous ammonia Surface 4-5 inches deep 4-5 inches deep Increase in yield, pounds seed cotton per acre

154

Average 280

Average of 10 tests-dry year 217 Average of 31 testr 443 397 370

472 344 408

325

esi

Average of 13 tests 33 32

May side-dress June side-dress

260 277

343 356

26 1 276

when rainfall was very low, anhydrous ammonia applied five inches deep was much superior to ammonium nitrate applied on the surface, which emphasizes the need for applying fertilizers in the root zone when dry weather is likely to follow. An examination of the weather records for Mississippi suggests that surface applications of nitrogen to crops in May or later are likely to be much less effective than deeper applications in one-third of the years, because of dry weather. No doubt, deep application of nitrogen is much more effective than surface application in dry climates. “Early and late side dressing of cotton with both anhydrous ammonia and ammonium nitrate were equally effective. The early side dressing was applied soon after the cotton was chopped out and the late application about a month later. Applications of nitrogen in July

83 are usually much less effective than when applied by the middle of June, but good increases in yield may be obtained from July applications. It is doubtful if July applications of nitrogen are effective where insects are destructive; however, where insects are controlled very late applications of nitrogen may give good increases in yield, even though they might have been more effective applied at an earlier date. “Anhydrous ammonia should be applied so that it does not come in contact with banded applications of superphosphate (unpublished data from Mississippi). In three tests, where the treatment was 60 pounds of nitrogen, phosphate and potash per acre, placing the anhydrous ammonia in contact with the superphosphate and muriate of potash reduced the average yield of seed cotton 86 pounds per acre as compared to separating them. “In three other tests with 60 pounds of nitrogen, 20 pounds of phosphate and 50 pounds of potash per acre, the average reduction in yield was 211 pounds of seed cotton for putting them together as compared to separating them. In the latter tests 20 pounds of phosphate was apparently sufficient; and where 40 or 60 pounds was used, applying the ammonia with the phosphate and potash did not reduce the yield. In one test on an alkaline clay soil there was no reduction in yield at any of three rates of phosphate. “When anhydrous ammonia is applied in contact with superphosphate, no doubt, the water-soluble phosphorus is converted into less soluble forms, as takes place when superphosphate is treated with anhydrous ammonia. The data . . . show that ammoniation of 20 per cent superphosphate with an average of 4.78 per cent ammonia reduced its value to less than one-half that of untreated superphosphate” (Andrews, 1954b). “The reduction in yield obtained for placing anhydrous ammonia in contact with superphosphate would also take place with aqua ammonia or solutions of aqua ammonia and ammonium nitrate or urea. “The time of application of nitrogen to cotton may be influenced by the grass and weed problem. Since nitrogen makes weeds and grass, as well as crops, grow it may be desirable to delay application of the nitrogen until the crop is cleaned out even though earlier application might have been more effective in the absence of a weed and grass problem. “Fall and winter application of anhydrous ammonia and ammonium nitrate for summer crops is often much less effective than spring application [Table VII]. In two tests on sandy loam soils December application of anhydrous ammonia was as effective as May application. In one test on sandy loam and in one on clay soil May application of ammonium nitrate was superior to December application. On the clay ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

84

W. B. ANDREWS

soil both ammonium nitrate and anhydrous ammonia applied in December were much less effective than May application of ammonium nitrate, which is attributed to both leaching and consumption of nitrogen by weeds and grass. The low increase in yield from anhydrous ammonia applied in May on the heavy soil was attributed to observable loss of ammonia in application.” In addition to -the work in Mississippi on anhydrous ammonia for cotton production, one test has been conducted in South Carolina (Wolf and Hoyert, 1952); one in Oklahoma (Pack, 1954); and two in Texas TABLE VII The Influence of Time of Application of Anhydrous Ammonia and Ammonium Nitrate, Applied at the Rate of 60 Pounds of Nitrogen Per Acre on the Yield of Cotton in Mississippi

Time of application December (preplant) May (preplant) June (side-dress) July (side-dress)

Clay soil, 1950 Sandy loam soil, 1949-1950 Test 1 Test 2 Test 3 Anhydrous Anhydrous Ammonium Anhydrous Ammonium ammonia ammonia nitrate ammonia nitrate Increase in yield, pounds seed cotton per acre 758 716

568 585

462 624

626

-

-

485

-

315 319

378 787

_.

-

-

-

(Flake, personal communication). Their data are essentially in agreement with those reported above, except that in the dry climate of Oklahoma, January application of anhydrous ammonia was equal to spring applications in the one test.

3 . Response of Corn Corn, Zea mays L., is normally planted from about the average date of the last killing frost until the middle of June. The data for Mississippi, reported in Table VIII (Andrews, 1954c) are for a total of 36 tests, which are averages of 7, 5, 11, and 13 tests. The nitrogen sources were paired for time of application, and there were six replications, which tends to give significance to rather small differences. When anhydrous ammonia was applied 4 to 5 inches deep and ammonium nitrate was applied on the surface of the soil as early sidedressings, the seven-test average shows that the increase in yield was 7 bushels for ammonium nitrate and 10 bushels for anhydrous ammonia. The inferiority of surface-applied ammonium nitrate is attributed to the lack of sufficient rain to leach it into the root zone. As an average of five tests, anhydrous ammonia was slightly superior to

85 ammonium nitrate for both preplanting and side-dressing. The thirteen side-dressing tests also show a slight superiority f o r anhydrous ammonia. The rate of application was 32 pounds of nitrogen per acre in these tests. In eleven tests at the rate of 100 pounds of nitrogen per acre, when applied before planting, anhydrous ammonia made 41 bushels increase in yield as compared to 36 for ammonium nitrate. The difference in the response to these two sources of nitrogen, applied before planting, is attributed to greater leaching of the nitrate of ammonium nitrate, as ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

TABLE VIII The Response of Corn to Anhydrous Ammonia and Ammonium Nitrate in Mississippi Source of nitrogen Ammonium Anhydrous nitrate ammonia Surface 4-5 inches deep 4-5 inches deep Increase in yield, bushels corn per acre

Pounds nitrogen per acre

Time of application

32

Early side-dress

32 32

Early side-dress Preplant

38

Side-dress

14

Preplant Early side-dress Late side-dress Preplant

-

100 100 100 200

7 12 -

40 41

Average of 7 tests-dry year 10 Average of 5 tests 12 15 12 13 Average of 13 tests 15 17 Average of 11 tesds 36 41 40 40 44 43 50 52

compared to all ammonium nitrogen, during the nitrification period, which should have been less than six weeks at most locations. The data suggest that application at a sufficient time before planting so that all nitrogen would have been converted to nitrates at planting would have made about 10 bushels less corn per acre than all ammonium nitrogen. There was no difference between anhydrous ammonia applied as an early or late side-dressing, and ammonium nitrate applied 4 to 5 inches deep, and surface application of ammonium nitrate as an early side-dressing was as effective as deeper application. Ammonium nitrate applied 4 to 5 inches deep produced 3 bushels more corn than when applied on the surface as a late side-dressing. These tests were run in years with normal rainfall; the tests, above, in which depth of application in side-dressing was important, were conducted in a dry growing season.

86

W. B. ANDREWS

With ammonium nitrate, early side-dressing produced 4 bushels more corn than preplanting application; there was no difference for these two times of application of anhydrous ammonia. When applied as a late side-dressing, ammonium nitrate made 4 bushels more corn than when applied as an early side-dressing and 8 bushels more than when applied before planting. When applied as a late side-dressing, anhydrous ammonia made 2 bushels more than when applied before planting and 3 bushels more than when applied as an early side-dressing. Similar differences are reported below, which, no doubt, are not significant in themselves, but the similarity of data

FIG.2. Local bulk storage, transport truck, and application equipment for anhydrous ammonia (courtesy of Mississippi Chemical Corporation).

from many different tests throughout the country adds significance to the small differences in favor of side-dressing as compared to preplanting application of nitrogenous fertilizers. When applied before planting, anhydrous ammonia made an average of 5 bushels more corn than ammonium nitrate and only 2 bushels more at 200 pounds of nitrogen per acre. When applied before planting, 100 pounds of nitrogen was used efficiently, producing a yield increase of 1 bushel for 2% pounds of nitrogen; whereas 200 pounds per acre was used inefficiently, producing a 1-bushel increase in yield for about 4 pounds of nitrogen. These eleven-test average data suggest that differences in efficiency of sources of nitrogen or times of application can be determined only where the nitrogen is utilized efficiently, and that large numbers of tests and replications are needed to measure small real differences. “The yield of corn was reduced eight bushels per acre by December application of both anhydrous ammonia and ammonium nitrate as compared to April application in one test. The rate of application was 120 pounds of nitrogen per acre and the top increase was 40 bushels.

87 The difference may have been greater if conditions had been favorable for high yields.” In Delaware, Cotner (personal communication) conducted separate tests (Table IX) on time of application of anhydrous ammonia and sulfate of ammonia for corn. The efficiency of both sources of nitrogen increased progressively as time of application was delayed from atplanting until the corn was 3% feet high. The difference between at-planting and side-dressing at 3% feet high was 15.7 bushels with anhydrous ammonia and 26.8 bushels with sulfate of ammonia in favor of the late side-dressing. The differences for time of application are highly significant, and they were obtained in a dry year. A N H Y D R O U S A M M O N I A AS A N I T R O G E N O U S FERTILIZER

TABLE IX Time of Application of Anhydrous Ammonia and Sulfate of Ammonia to Corn in Delaware Source of nitrogen

Time of application None At planting 8 inches tall 2% feet tall 8% feet tall L.S.D. (0.05)

NHa (NH4)zSOs Yield, bushels corn per acre 34.6 92.5 96.0

42.2 48.2 8.5

34.7 31.7 40.0 52.4 58.5 5.2

In Florida, Robertson (personal communication) showed that anhydrous ammonia, ammonium nitrate, and nitrate of soda produced about the same increase in yield when applied as a side-dressing. Anhydrous ammonia applied as a side-dressing produced 2.0 and 5.1 bushels more corn than when applied before planting at 40 and 80 pounds of nitrogen per acre; at 160 pounds of nitrogen per acre there was no difference for time of application. In Michigan, anhydrous ammonia produced slightly higher yields (7.0 bushels more) than sulfate of ammonia in two tests and about the same yields in one test (Robertson, personal communication). In the two test average, July side-dressing with anhydrous ammonia produced 5 bushels more corn than the June side-dressing; time of application was not a factor in the one test. The Minnesota Agricultural Experiment Station found that the response of corn to nitrogen is a factor in time of application (MacGregor, 1955a). Typical of the results are: on fields which gave high

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W. B. ANDREWS

response to nitrogen the yield increases for 60 pounds of nitrogen as anhydrous ammonia were 25, 31, and 35 bushels per acre for beforeplanting in April, as a side-dressing one month later in May, or as a side-dressing two months later in June or July. The respective representative increases on more fertile soils were 10, 9, and 8 bushels per acre. In Nebraska, when the nitrogen was applied as a side-dressing at the rate of 80 pounds of nitrogen per acre in eight tests, six of which were irrigated, the average yield of corn was increased from 77 to 108 and 107 bushels per acre by ammonium nitrate and anhydrous ammonia, respectively. The average yield of corn (six irrigated tests) was 7 and 6 bushels more for the respective sources when applied as a sidedressing than when applied before planting (Lowrey and Dreier, 1951; Lowrey and Ehlers, 1954; and Lowrey et al., 1954). In Wisconsin, ammonium nitrate produced slightly higher yields of corn than anhydrous ammonia in November and April application; however, June applications of anhydrous ammonia made 5.3 and 3.2 bushels more than April applications at 67 and 100 pounds of nitrogen per acre. The increases in yield for 67 pounds of nitrogen were 27 to 33 bushels, which is efficient utilization of nitrogen (Marriot, personal communication). In three different comparisons for before-planting applications in North Dakota, Puhr (personal communication) found that anhydrous ammonia made 4.2 bushels more corn than ammonium nitrate. In one test in Louisiana, ammonium nitrate was slightly superior to anhydrous ammonia for corn production (Oakes and McCormack, 1954). In two tests in Texas, Flake (personal communication) showed that anhydrous ammonia and other common sources of nitrogen produced about the same increase in yield of corn. In nine tests in Missouri, 80 pounds of nitrogen as anhydrous ammonia or ammonium nitrate increased the yield 17 bushels of corn per acre (Smith, 1952). With rainfall normal to below normal from the fall of 1951 to the summer of 1954, Dumenil (1955) found that fall application of ammonium nitrate for 1952, 1953, and 1954 and sulfate of ammonia for 1954 was as effective for corn production in Iowa as when broadcast and disked in late April in 1952 and 1953, and side-dressed in early June of 1954 (Table X). “These tests indicate that fall application is as good as spring application in some years. But remember that the rainfall from fall of 1951 to summer of 1954 was normal to below normal at these locations.” In most comparisons, the responses to nitrogen were rather low, and there could be some doubt about the applicability of the data to conditions where applied nitrogen is more fully utilized.

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In three tests in Minnesota, MacGregor (1955a) found no difference between fall and spring application of nitrogen for corn; however, the average increase in yield was less than 10 bushels per acre for 60 pounds of nitrogen-a requirement of 6 pounds of nitrogen per bushel increase in yield. Since 60 pounds of nitrogen should increase the yield as much as 24 bushels, the data may not be applicable where normal response to nitrogen is obtained. In two of the tests (MacGregor, 1955b), the residual nitrogen from 60 pounds applied to corn increased the yield of oats 5.6 bushels per acre with little difference for time of application to corn. It is estimated that the increase in yield of corn utilized about 15 pounds of nitrogen and the oats about 7 pounds, which TABLE X The Response of Corn to Fall and Spring Applications of Nitrogen in Iowa Increase in yield

No. of Year

tests

1952

4

1953

4

2 1954

Fall

Pounds nitrogen per acre

Bushels corn

per bu.

40 40 80 30 60 30

10.9 18.7 22.4 9.5 8.2 11.8

3.7 2.1 3.6 3.2 7.3 2.5

Lb. N

Spring Lb. N Bushels corn per bu.

11.4 14.4 20.0 10.8 10.8 12.2

3.5 2.8 4.0 2.8 5.6 2.5

leaves 38 pounds not accounted for. The low efficiency of the estimated 7) pounds of nitrogen, which was not utilized by corn, for 45 (38 the production of oats, suggests that fall application of nitrogen for spring consumption is not very satisfactory. Grissom (unpublished) applied rates of nitrogen as anhydrous ammonia and ammonium nitrate to corn and cotton in Mississippi in 1952. Yields were taken in 1952-1 955 without additional nitrogen. Though there was an excellent residual effect from the high rates of application, it should be borne in mind that the 1952-1954 period was unusually dry and that the data may not be applicable under conditions of more normal rainfall. In one long-time test on a heavy soil in Mississippi, fall-applied nitrate of soda and sulfate of ammonia produced increases in yield of corn, cotton, and oats which were only about 12 per cent less than spring applications (Pitner and Kuykendall, 1943). Other data (Section 111, 4a) from many tests show that fall application of nitrogen on similar soils has been unsatisfactory for oats, suggesting that the data are

+

90 W. B. ANDREWS not widely applicable for small grains and probably not for row mops either. The residual effect of two years of nitrogen fertilization of corn on the yield of the following wheat crop was determined in Missouri, where the response of corn to nitrogen was low (Smith, 1954). The rates of nitrogen were 33, 66, 132, and 200 pounds per acre; the estimated pounds of nitrogen per acre which was not recovered by the corn were 19, 42, 90, 155, annually, or 38, 84, 180, and 310 pounds for the two-year period; the increases in the yield of wheat from the nitrogen not recovered by the corn were 2, 3, 7, and 12 bushels per acre. To illustrate, the estimated 90 pounds of nitrogen annually, or 180 pounds for the two-year period, which was not recovered by the corn, increased the yield of wheat only 7 bushels per acre under conditions where more nitrogen was needed; the ‘/-bushel increase in the yield of wheat should have been made with about 20 pounds of nitrogen applied at an appropriate time. It is evident that most of the nitrogen which the corn did not recover was not effective in increasing the yield of wheat; these data suggest that nitrate nitrogen applied or derived from other forms in the fall would be very inefficient for wheat production in a similar climate. In most cases, where good response has been obtained, side-dressing corn has been superior to at-planting application of nitrogen, regardIess of the source, and late side-dressingshave usually been superior to early side-dressings. The superiority of side-dressings as compared to atplanting applications of nitrogen may be attributed to ( I ) leaching of nitrate nitrogen where the ground water is recharged before nitrates are consumed by the plant, (2) microbiological immobilization of nitrogen where considerable quantities of carbonaceous crop residues exist, and (3) increased efficiency in the use of water as well as nitrogen because of delayed or reduced vegetative growth. As an average of five tests in Missouri (Missouri Growers, Inc., 1954a) 40, 80, and 120 pounds of nitrogen per acre increased the yield of corn 8.4, 12.6, and 17.2 bushels when applied before plowing and 3.5, 15.4, and 18.7 bushels per acre when applied after seed bed preparation and before planting; the increases for side-dressing were 14.7, 18.4, and 17.2 bushels. As compared to preplanting, side-dressing increased the yield 11.2, 3.0, and -1.5 bushels of corn per acre at the respective rates. The amount of nitrogen required to increase the yield one bushel of corn varies markedly and should receive more attention. Though under conditions where corn is very responsive to nitrogen and growing conditions are favorable the yield may be increased one bushel of corn by as little as two pounds of nitrogen, much more is required in most

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tests. The most extensive work reported on this subject was carried out by the Missouri Growers, Inc. (1954b, 1955). During the 1950-1955 period they applied an average of 69 pounds of nitrogen as anhydrous ammonia in 320 tests which increased the average yearly yield 18.4 bushels per acre which is a requirement of 3.74 pounds of nitrogen per bushel increase in yield. Though there is considerable information on leaching and microbial immobilization of nitrogen, the author is not aware of information on the effect of time of application of nitrogen on the growth curve of corn, on the total amount of stover produced, or on the stover-grain ratio, variations of which may markedly influence efficiency in the utilization of moisture, particularly when limited, as well as in the utilization of nitrogen to produce grain. There could be a parallel between the relative efficiency of side-dressing as compared to at-planting application and the early practice in this country of plowing young corn closely to retard or reduce vegetative growth and favor fruiting. Though the early close-plowing practice has been discarded, it may not have been shown that the practice does not have merit. Though delayed application of nitrogen may not be favorable for maximum yield by a single corn plant with all production factors unlimited, under field conditions the yield of the plants involved is normally limited by the factors of production to less than one-half of the potential of the plant, and it appears that retarded growth of young corn may reduce or delay the production of vegetative growth, thereby increasing efficiency in the utilization of moisture and nitrogen.

4 . Response of Small Grains The small grains which are commonly grown are oats, Auena satiua L.; wheat, Triticum vulgare, Vill.; barley, Hordeum uulgare L. ; and rye, Secale cereale L. In the South, all small grains are planted in the fall; in the central part of the country, all are planted in the fall except oats, which are spring-planted; in the northern part of the country, all are planted in the spring. The small grains are normally planted with a 7-inch drill or broadcast. These crops are not cultivated. The climate covered in these studies varies from warm to cold winters, from hot to cool summers, and from humid to arid. In the South, small grains are planted to some extent for fall, winter, and spring grazing. In other areas, excessive fall growth is often grazed before cold weather. However, these crops are grown primarily for grain. When young, oats and presumably all the other small grains use ammonium nitrogen as well as nitrate nitrogen insofar as can be observed under field conditions. I n the spring, when rapid growth and the

92 W. B. ANDREWS beginning of fruiting are initiated, oats and presumably the other small grains require nitrate nitrogen for maximum growth. a. In Mississippi, “Fall application of ammonium nitrate was unsatisfactory for oat production in all 10 tests conducted [Table XI]. It was less effective on the less acid than on the strongly acid soils, which parallels the behavior of anhydrous ammonia. As was pointed out above, in North Mississippi late October-planted oats make little growth before spring, and in order for fall-applied nitrogen to be utilized by them it must be carried through the winter in the soil. “When applied during the third week in February anhydrous ammonia increased the yield of oats 20 bushels per acre as compared to TABLE XI The Effect of Soil Reaction on the Response of Oats to Fall-Applied Anhydrous Ammonia in Mississippi Lime content of soil, test number High, pH 5.5 or higher Low, pH 5.1 or less Source of nitrogen 32 pounds per acre

Time of application 1

2

9

4

5

6

7

25 90 15

12 19 8

9

10

15 14 2% 24 8 10

6 24

8

Increase in yield, bushels oats per acre Anhydrousammonia Ammonium nitrate Ammonium nitrate

Fall Spring Fall

30 21 16

32

SO

26

25

15

16

29 27 20

19 20 10

4

15 bushels for ammonium nitrate in six tests in which the rate of nitrogen was 32 pounds per acre. The data suggest that a considerable amount of the ammonium nitrate nitrogen leached out before the oats were able to utilize it. The data also suggest that nitrate nitrogen should not be applied to fall-planted small grains until the weather is warm enough for vigorous growth to begin. “The stand of small grains is not damaged materially by anhydrous ammonia applicator knives in top dressing. If the small grains are well rooted the applicator knives usually go between plants without uprooting them. “On soils which are low in lime anhydrous ammonia applied from the last of October until (possibly) February 15 is as effective for producing oats as ammonium nitrate applied the first of March. In five tests (32 pounds of nitrogen per acre) which were low in lime (pH 5.1 or less), anhydrous ammonia applied the last of October increased the yield 28 bushels of oats per acre as compared to 23 bushels for ammonium nitrate applied in March. On one soil (pH 4.95) aqua ammonia applied the last of January increased the yield 30 bushels as compared to 27 bushels for ammonium nitrate applied early in March.

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“On a soil which was low in lime (pH 5.1 ) , anhydrous ammonia was not a satisfactory source of nitrogen for oats when applied in early March. When applied to this low-lime soil in early March the ammonia was changed into nitrate nitrogen so slowly that the increase in yield of oats was only 10 bushels per acre as compared to 19 bushels for fallapplied anhydrous ammonia and 20 bushels for spring-applied ammonium nitrate. The rate of application was 32 pounds of nitrogen per acre. “When applied the first of March on soils which are medium to low in lime, anhydrous ammonia is much less effective than ammonium nitrate for the production of oats. In an average of eleven tests applied the first of March anhydrous ammonia increased the yield of oats only 19 bushels as compared to 26 bushels per acre for ammonium nitrate. “On soils of medium to high lime content (pH 5.5 or higher) anhydrous ammonia applied the last of October increased the yield an average of only 13 bushels of oats per acre as compared to 23 bushels for ammonium nitrate applied the first of March (five tests). In three tests with 32 pounds of nitrogen per acre the following increases in yield of oats were obtained:

Date of application

Last of October Last week in November Third week in February

Source of nitrogen Anhydrous ammonia Ammonium nitrate Increase in yield, bu. oats per acre 6.6 13.4 31.3

16.9

“The last week in November is too early to apply anhydrous ammonia to oats for grain. When applied during the third week in February anhydrous ammonia is superior to ammonium nitrate. Apparently the third week in February is too early to apply ammonium nitrate to oats because of the leaching of the nitrate nitrogen. “On a high-lime soil (pH 7.8) anhydrous ammonia applied in March increased the yield 25 bushels of oats per acre as compared to 4 bushels for October-applied and, 24 bushels for March-applied ammonium nitrate. The rate of change of ammonia into nitrate nitrogen was rapid in this soil and nitrate nitrogen was available to the oats in a short time after application as anhydrous ammonia in the spring; when applied in October anhydrous ammonia was converted into nitrate nitrogen and leached out of the soil during the winter. “Anhydrous ammonia applied the last of October in four tests increased the yield of oats only 7 bushels per acre as compared to 20

94 W. B. ANDREWS bushels per acre for application during the third week in February. The lime content of the soils was high enough for nitrification to take place during the winter months. Thirty-two pounds of nitrogen per acre was applied. “A reasonable spacing of anhydrous ammonia applicators for top dressing oats for grain is 24 inches. When anhydrous ammonia applicators are spaced farther apart than 16 inches a strip of oats down the middle usually fails to send roots to the place where the ammonia was applied and they do not get nitrogen. However, the oats which do get nitrogen grow more and largely make up the difference [Table XII] . TABLE

XI1

The Effect of Applicator Spacing on the Response of Oats to Anhydrous Ammonia in Mississippi Pounds of nitrogen per acre

Spacing of applicators, inches

32 48 64 Average Increase in yield, bushels oats per acre

as

a1

81 18 18

a8 84

6

2

4

16 a4

a3 a2

S6 No. of tests

a4

as 21 1%

“Applicators spaced 24 inches apart shed trash more readily than when spaced closer, and a 24-inch spacing is recommended. On very wet and heavy soils oats may not grow roots to ammonia placed more than six inches away; however, though no data are available, it is not improbable that a good 12-inch band of oats every 24 inches will make about as much oats as uniform growth over the entire area. “Anhydrous ammonia and ammonium nitrate have been equal in value on oats for forage. As an average of 14 tests, the following yields were obtained by the first of March: Source of nitrogen

None Ammonium nitrate Anhydrous ammonia

Yield-pounds air-dry forage per acre

648 1644 1711

“A spring application of nitrogen is necessary for the production of oats for grain even though a large quantity is applied to them for forage in the fall. When 96 pounds of nitrogen per acre, which is much more

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95

than needed, was applied to oats for fall- and winter-forage production the yield of grain in the spring was only one bushel more than was produced with no clipping and no nitrogen in the fall or spring. Where nitrogen was applied in the fall and spring, clipped oats made 17 bushels more than where they were not clipped and received no nitrogen (9 tests).” b. In Other Humid Areas. Most of the tests on anhydrous ammonia for small grains, outside of those in Mississippi, have been conducted since 1950 and there has been less rainfall than normal in many areas. For this reason, many of the data should be regarded as tentative. “Fall-applied anhydrous ammonia was unsatisfactory for wheat in Indiana [Peterson, 19521. The average increase in yield of wheat for three rates of nitrogen was as follows:

Source of nitrogen

4.8

4.8

pH of soil in tests 5.5

6.5

6.7

Increase in yield, bu. wheat per acre Ammonium nitrate-spring Anhydrous ammonia-fall

5.1 4.0

11.4 9.5

11.9 8.4

8.9 4.3

8.0 3.0

Even on strongly acid soils anhydrous ammonia applied in the fall was less satisfactory than ammonium nitrate applied in the spring. The increase in yield for anhydrous ammonia applied in the fall on soils of pH 4.8, 4.8, 5.5, 6.5, and 6.7 was 1.1, 1.9, 3.5, 4.0, and 5.0 bushels less than where ammonium nitrate was applied in the spring. “The efficiency of fall-applied anhydrous ammonia for wheat in Indiana was similar to that for oats in Mississippi on strongly acid soils, though in Mississippi fall-applied anhydrous ammonia was equal to or superior to spring-applied ammonium nitrate. In both states fall-applied anhydrous ammonia was unsatisfactory on soils having a pH of 5.5 or higher. “In Indiana and Mississippi the f all-applied anhydrous ammonia was applied at about the same time, which suggests that soil reaction is a more important factor in nitrification of ammonia than the differences in fall and winter temperature. “In the Indiana experiments anhydrous ammonia applied in the spring and ammonium nitrate applied in the fall were unsatisfactory for wheat in all of the tests.” In New York, Musgrave (personal communication) found that 40 pounds of nitrogen as ammonium nitrate or 40 per cent nitrogen solutions (largely ammonium nitrogen) increased the yield of wheat only

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W. B. ANDREWS

1.7 bushels when applied at planting time, while 20 pounds at planting time and 20 pounds in the spring increased the yield 7.5 bushels. The

temperature was 55OF. at planting time and dropped to 30° within 30 days. In another test, Musgrave (personal communication) obtained 3.2 bushels increase in yield of wheat for 40 pounds of nitrogen as anhydrous ammonia applied before planting and 12.6 bushels increase for 20 pounds at planting and 20 pounds in the spring as ammonium nitrate. He has “yet to observe a significant carry-over effect of summer or fall applications of NH, at any rate between 20 and 400 lb. N/A [nitrogen per acre]”; the 400 pound rate was applied to corn. The soils studied have impervious subsoils and they are giving consideration to horizontal movement of nitrate nitrogen in the plow zone and to denitrification. “Fall application of anhydrous ammonia and sulphate of ammonia on fall-planted crops should have the same efficiency. Spring application of sulphate of ammonia was much superior to fall (drilled) application for wheat in Pennsylvania [Merkle, 19521. When 20 pounds of nitrogen was applied at planting time, between September 15 and October 18, the average yield of 17 tests over a period of years was 4.6 bushels of wheat per acre less than where the nitrogen was applied in the spring. In six tests where 40 pounds of nitrogen was applied one month after sowing (freezing weather usually begins the last of November) the average yield was 4.8 bushels less than when applied in the spring. As an average of six tests, 20 pounds of nitrogen applied in the spring was superior to 40 pounds applied in the fall where good increases for nitrogen were obtained. On the basis of the above data, anhydrous ammonia applied in the fall would not be expected to go through the winter in a climate as cold as Pennsylvania.” In Missouri (Smith, 1954), before-seeding application of anhydrous ammonia was superior to December and March applications in one test with wheat. As an average of eight other tests 12-12-12 or 8-24-8 starter fertilizers containing 24 to 36 pounds of nitrogen increased the yield of wheat 8.1 bushels per acre. An additional 66 pounds of nitrogen from a solid source increased the yield 7.9 bushels when applied before seeding, 11.4 bushels when applied in December, and 8.5 bushels when applied in the spring. With the December application, which was the best treatment, 5.8 pounds of nitrogen was required to increase the yield of wheat 1 bushel, whereas in the first test 2 pounds of nitrogen increased the yield a bushel. It appears that the nitrogen treatment, 90 to 102 pounds per acre, was excessive and that the data may not provide a satisfactory basis for a critical evaluation of time of application of nitrogen to wheat.

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The relation of rainfall to the efficiency of fall, winter, and spring applications of solid sources of nitrogen is shown by data from Illinois (Tyner, personal communication), reported in Table XIII. On both years at Westfall, soil moisture was not recharged below the 24-inch depth by the last of March or the first of April when the spring applications were made; fall applications were made after seeding and TABLE XI11 T h e Effect of Time of Application of Nitrogen on the Increase in Yield of Wheat for Three Sources of Nitrogen in Illinois ~

Source of Nitrogen 30 pounds per acre

Time of application Fall Winter Spring Increase in yield, bushels wheat per acre

Westfall 1968-54; no movement of water into gh-inch depth. Cyanamid 2.5 Ammonium nitrate 11.4 Urea 5.9 Sulfate of ammonia 7.5 Solution 32 6.6

3.5 6.4 3.9 8.0 7.6

Average, except cyanamid and urea 8.5 6.5 Time of application not significant; urea and cyanamid significantly inferior. Westfall 1954-55; no leaching. Nitrate of soda 7.9 6.1 Ammonium nitrate 1.8 7.2 Sulfate of ammonia 2.6 7.1 Average Time of application not significant. Rogers 1964-55; recharge of water to 6-feet normal. Nitrate of soda Ammonium nitrate Sulfate of ammonia

3.7 9.8 4.8 6.1 6.3 6.8

8.1 6.5 10.6

4.1

6.5

8.3

2.4 -0.2 3.7

1.6 3.6 3.7

6.4 2.6 9.4

Average 2.0 3.0 6.1 Time of application significant; sulfate of ammonia significantly superior to other sources.

winter applications were made late in January. Under these conditions of no leaching, there was no significant difference for time of application of nitrogen. At Rogers, soil moisture was recharged to a depth of 6 feet by the January application date, suggesting that considerable leaching may have taken place. Under these conditions, spring application was significantly superior to fall and winter application, and sulfate of ammonia was superior to ammonium nitrate and nitrate of soda. These tests (1954-55) were both in the same county on well-drained dark-

98 W. B. ANDREWS colored soils. The differences in the leaching and in response to time of application of nitrogen are indicative of local variations which may be encountered. In Michigan, as an average of six tests, the yields of wheat with anhydrous ammonia were 41,38,38, and 34 bushels for before-planting, September-October, November-December, and March-April applications (Robertson, personal communication), The respective yields for sulfate of ammonia were 42, 41, 39, and 44 bushels. Since there were no yields without nitrogen, the data are not necessarily indicative of the results which would be obtained on responsive soils. The reason for inferior results for spring-applied anhydrous ammonia is not known. The application of 30 pounds of nitrogen per acre as anhydrous ammonia on December 1 was as effective as ammonium nitrate in the spring for spring-planted wheat and as mixed-fertilizer nitrogen in the spring for spring-planted oats in New Jersey (Anderson, 1955). The increase in yield for 30 pounds of nitrogen from both sources was 8 bushels per acre for wheat and 11 and 12 bushels for oats. For oats, at least, the response to nitrogen was too low for the data to be valid for time of application comparisons. Top-dressing with nitrogen was superior to broadcasting or spraying it on the crop residues before plowing for spring oats in Michigan (Robertson et al., 1955). The respective increases in yield for broadcasting, spraying, and top-dressing 20 pounds of nitrogen were 8.9, 12.7, and 13.6 on Fox sandy loam and 11.7, 12.3,and 21.3 bushels on Conover loam. The inferiority in the yields where the nitrogen came in contact with the carbonaceous crop residues may have been due to immobilization of nitrogen. In West Virginia, Pohlman (personal communication) found that 25 pounds of nitrogen as ammonium nitrate increased the yield of wheat 3.7 bushels when applied in the fall and 12.7 bushels when applied in March. The soil was Wheeling sandy loam, pH about 6.5. c. In Dryland Farming. Data are reported in Table X N on wheat from the Columbia Basin of Oregon (Hall, personal communication). The longtime average rainfall is 11.54inches. From 1930 to 1940,the average rainfall was 9.92inches and no response was obtained to nitrogen. Since 1950, the rainfall has averaged 13.45 inches; the data are for 1952-1 954. For 1952,which was dry, ammonium nitrate applied in the fall was superior to fall-applied anhydrous ammonia and spring-applied ammonium nitrate. Depth of nitrogen in the spring, no doubt, explains the difference between fall-applied anhydrous ammonia and ammonium nitrate in these tests. In 1953, when rainfall was good, fall-applied anhydrous ammonia

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and spring-applied ammonium nitrate at the 20- and 40-pound rates were equally effective and much superior to fall-applied ammonium nitrate. It is suggested that most of the nitrogen in the ammonium nitrate applied on the surface in the fall was immobilized in the decomposing crop residue even though the land had been fallowed. In 1954, with more rainfall, with both sources applied in the fall, anhydrous ammonia was slightly superior to ammonium nitrate. TABLE XIV The Response of Wheat to Fall- and Spring-Applied Anhydrous Ammonia and Ammonium Nitrate in Oregon Pounds nitrogen per acre

Source and time of application

NHa

NHdNOa

NHdNOp

LSD

Fall

Fall

Spring

(0.05)

Yield, bushels per acre 1952, dry year 0

20 40 60

42.7 46.1 49.0 51.0

3.9

49.9 56.5 52.7

43.6 45.6 49.2

Yield, bushels per acre 1955, more rain 0

20 40 60

42.8 48.0 50.3 49.9

3.6

41.8 43.3 45.4

48.7 52.6 44.4

Yield, bushels per acre 1954, more rain 0

20 40 60

28.6 34.4 38.7 38.9

3.0 33.3 30.0 38.9

For winter wheat production in eastern Washington (Table XV), with an average rainfall of less than 13 inches, anhydrous ammonia was as effective as sulfate of ammonia and calcium nitrate when all three sources were applied 6 inches deep and 12 inches apart at planting time. When the solids were broadcast, calcium nitrate produced 3.6 bushels more wheat than sulfate of ammonia at Lind, where straw was light, and 2.8 bushels more at Ritzville, where straw-was heavy (Jackson et al., 1952). On the average, deep-banded placement increased the yield with sulfate of ammonia 6.6 bushels of wheat as compared to 0.9 bushel for broadcast application. At another location in Washington, with surface stubble mulch, broadcasting sulfate of ammonia (40 pounds N) on the surface produced 6.3 bushels less winter wheat than banded plow sole application (Reisenauer et al., 1953). Surface banding of the sulfate of ammonia

100

W. B. ANDREWS

increased the yield 3.2 bushels over broadcasting. Where there was no surface stubble mulch, banded deep placement of the nitrogen was not superior to surface applications. The lower yields obtained for surface application of nitrogen as compared to placement 6 inches deep in bands 12 inches apart were attributed to nitrogen immobilization in the decomposition of the straw. With a rainfall of less than 13 inches, nitrogen applied as calcium nitrate on fallowed land two falls prior to seeding spring wheat was very inefficient, indicating that much of the nitrogen was made unavailable or lost during the interim. Sulfate of ammonia so applied was TABLE XV The Effect of Source of Nitrogen and Placement on the Yield of Wheat in Eastern Washington Location and placement Lind Source of nitrogen Broad20 pounds per acre cast

No nitrogen 20.5 Anhydrous ammonia Sulfate of ammonia 21.4 Calcium nitrate 25.0 Significant difference

Ritzville

Average

6 inches deep 6 inches deep 6 inches deep 12 inches Broad12 inches Broad12 inches

apart

cast

apart

cast

Yield of wheat, bushels per acre 28.5 24.5 28.2 34.1 -

2.9

apart

-

-

25.3 27.4

31.2 31.1 32.1

29.4 341.2

36.8 37.0 1.4

25.4 28.6

somewhat more efficient, but the difference may be attributed to a direct response to sulfur. Allison (1955) studied “the fate of carbon in carbonaceous crop residues decomposing under different levels of nitrogen . . . . Laboratory and greenhouse results show that although nitrogen additions offset the harmful effect of such residues on crop growth, and often accelerate decomposition, such added nitrogen does not appreciably increase the percentage of the crop residue carbon that remains in the soil as humus. Nitrogen added to cropped soils does tend to maintain soil organic matter at a higher level than in its absence, but this is due to the increased crop yields and resulting larger crop residues available for humus formation.” In Nebraska, where the climate varies from subhumid to dry, when applied in the fall, anhydrous ammonia increased the yield of wheat 10.0 bushels as compared to 8.9 for ammonium nitrate and 10.2 for spring-applied ammonium nitrate (Olson, 1955). When both were applied in April, the increase was 5.3 bushels for anhydrous ammonia

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101

and 9.3 for ammonium nitrate. The rate of application was 40 pounds of nitrogen per acre. The effect of rainfall on the response of wheat to fall and spring applications of ammonium nitrate is brought out by data from Oklahoma (Eck and Stewart, 1954). In 1951-1952, when the annual rainfall was more than 20 inches and most of the yields of wheat were 30 bushels or more, spring-applied ammonium nitrate (average of eight tests) made 1.8, 3.4, and 3.2 bushels more wheat than when applied in the fall at the rate of 20, 40, and 80 pounds of nitrogen per acre. In 1952-1953, when rainfall was 20 inches or less, time of application of ammonium nitrate did not affect the yield as an average of nine tests. In the year with more plentiful rainfall, 20,40, and 80 pounds of nitrogen applied in the spring increased the yield 5.6, 10.4, and 11.2 bushels; in the dry year 20 pounds increased the average yield 5.6 bushels, the higher rates giving no larger yields. In the moister year, the average protein content of wheat was increased only slightly by the 20- and 40-pound rates of nitrogen at both times of application and the 80-pound rate applied in the fall, and rather significantly by the 80-pound rate applied in the spring, indicating that the nitrogen available to the plants had been fully utilized, except from the 80-pound rate applied in the spring. In the dry year, all applications of nitrogen increased the protein content of wheat markedly.

5. Response of Pasture and H a y Crops “Anhydrous ammonia was superior to ammonium nitrate on an established stand of fescue, Festuca elatior L. var. arundinacea, and hop clover, Trifolium dubium [Table XVI]. The increase in yield for 67 and 100 pounds of nitrogen, respectively, was 1113 and 2006 pounds of air-dry forage per acre for ammonium nitrate and 2665 and 3252 for anhydrous ammonia. The superiority of anhydrous ammonia is attributed to the fact that the soil below one inch had a pH of 4.9, which retarded nitrification and subsequent leaching of the nitrogen. The top inch of the soil had a pH of 6.2, which was conducive to nitrification of the ammonia in the ammonium nitrate, making all of the nitrogen in the ammonium nitrate subject to leaching. With a pH of 6.2 in the top inch of soil there was a reasonable supply of calcium for the spring hop clover and the grasses. “Conservation of the ammonium form of nitrogen is promoted by strongly acid soils, as borne out by the above data on fescue and on oats. However, the pH should approach 7 to supply lime to many plants, to maintain phosphorus available, and to reduce the leaching of potash. These conditions may be obtained on strongly acid soils devoted to

I 02

W. B. ANDREWS

pastures and other sod crops by lightly liming the top soil after the crops are planted, and applying the ammonium form of nitrogen in the soil. With some other crops the conditions may also be obtained on strongly acid soils by applying a limited quantity of lime with or near the seed. “The nitrogen conserved by maintaining most of the soil strongly acid must be weighed against some sacrifice in the available phosphorus, and the possibility that maximum yields may not be produced under TABLE XVI The Response of Fescue and Hop Clover to Anhydrous Ammonia and Ammonium Nitrate in Mississippi

Source of nitrogen

No nitrogen Ammonium nitrate Ammonium nitrate Ammonium nitrate Anhydrous ammonia Ammonium nitrate Ammonium nitrate Anhydrous ammonia Anhydrous ammonia Anhydrous ammonia

Time, rate per acre Sept. Feb.

Applicator spacing, inches

33

33 67 67 67 100 100 100 100

18 18 a7 36

Air-dry yield, pounds per acre Feb. April May 14 8 21 Total 346 661 693 739

lO%O 769 1166 1319 1248 890

679 846 11a9 1138 a166 1694 1611 2370 2043 1987

1370 1327 1416 1425 1667 1375 1426 1850 1843 1839

2187 2724 3138 8500

4862 3836 4193 6439 5155 4716

these conditions. However, the most profitable yields may be somewhat less than maximum yields. “On a silt loam soil, spacing anhydrous ammonia applicators 18 inches apart for fescue and clover produced 5439 pounds of air-dry forage as compared to 5133 and 4716 pounds for 27- and 36-inch spacings. A 24-inch spacing is suggested for most conditions. “The use of anhydrous ammonia on very poor land to be planted to fescue produces a narrow band of excellent fescue directly over the ammonia, and that in between sometimes dies. If a solid stand of fescue is desired a solid source of nitrogen should be used and applied uniformly at seeding time. Anhydrous ammonia may then be used for later applications. “Anhydrous ammonia and ammonium nitrate produced equal increases in the yield of pasture forage in a season of normal rainfall [Table XVII]. The f i s t application of nitrogen was made during the fist part of July, which is too late for maximum response to nitrogen. The increase in yield of air-dry pasture forage was essentially the

103 same for ammonium nitrate and anhydrous ammonia. With sufficient rainfall to carry the nitrogen applied as ammonium nitrate into the root zone, surface application of ammonium nitrate was as effective as anhydrous ammonia applied in the root zone, which contrasts sharply with the results reported below for a dry year. The difference between the 16- and 32-inch spacings of the anhydrous ammonia applicators was small. “Higher yields of Dallis grass pasture forage, Paspalam dilatum poir., were produced by anhydrous ammonia applied in the root zone than A N H Y D R O U S A M M O N I A AS A N I T R O G E N O U S FERTILIZER

TABLE XVII The Response of Pasture Grasses to Anhydrous Ammonia and Ammonium Nitrate in a Season of Normal Rainfall, Average of Five Tests in Mississippi Pounds of nitrogen per acre Source of application Ammonium nitrate Anhydrous ammonia Anhydrous ammonia Yield without nitrogen

Spacing of applicators

45

99

Increase, pounds dry forage

Broadcast 16 inches 32 inches

768 753 714

1304 1328 1198 1392

TABLE XVIII

The Response of Pasture Grasses to Anhydrous Ammonia and Ammonium Nitrate in a Dry Year-Average of Five Tests-Mississippi Nitrogen Source

Ammonium nitrate Anhydrous ammonia Anhydrous ammonia Yield without nitrogen

Pounds nitrogen per acre Spacing

Broadcast 16 inches 24 inches

33

66

99

Increase i n yield, pounds air-dry forage 624 1094 1665 1053 1461 a014 1503 1692

by ammonium nitrate applied on the surface during a dry year [Table XVIII]. Ammonium nitrate failed to make yields equal to those produced by anhydrous ammonia because of differences in placement. The anhydrous ammonia was placed in the soil where the plants could recover it. The nitrate part of the ammonium nitrate, no doubt, was leached into the soil by a small amount of rain; however, it is necessary for the ammonium part of the ammonium nitrate to be changed into the nitrate form before it can be leached into the root zone. Even though plants have active roots in the surface soil during periods of wet

I04 W. B. ANDREWS weather, feed roots, no doubt, disappear from the surface soil or become inactive during dry weather. “In one test in a relatively dry year anhydrous ammonia was much superior to ammonium nitrate for forage production by Dallis grass pasture: ~

Treatment, June 17 66 lb. nitrogen per acre Anhydrous ammonia, 4“ deep Ammonium nitrate, surface

July 22 3085 1826

Date of clipping Aug. 23 Oct. 6 Total 981 908

1533 1114

5599 3848

Increase 3263 1514 ~

The total rainfall for the duration of the test was only 8.3 inches from June 17 to October 6. The placement of anhydrous ammonia in the root zone resulted in high yields of forage even though the rainfall was very low. The data suggest that very high yields of forage would be produced during a full season having normal rainfall and sufficient nitrogen. “Pasture sods are usually not damaged by anhydrous ammonia applicator knives, provided the grass is short. Where the grass is tall some of it may be pulled out of the ground. Where soils are so dry and hard that the knives shatter the soil instead of cutting through it, the grass on the shattered soil may die if rain does not follow in a short time. For application to sod crops a knife with a wide point, as described .below, is much superior to conventional knives.’’

6 . Response of Sorghum and Sugar Cane “The yield of sugarcane, Saccharum oficinarum L., syrup was 617 gallons with anhydrous ammonia and 598 gallons per acre with ammonium nitrate, as an average of three comparisons in six tests. The rate of application was 60 pounds of nitrogen per acre. Split applications of nitrogen were not superior to one application before planting or as an early side dressing. “The yield of sorghum, Sorghum vulgare, pers. var. sorgo, symp with anhydrous ammonia was 318 gallons per acre as compared to 308 for ammonium nitrate, 311 for nitrate of soda, 310 for sulphate of ammonia, and 322 gallons for sulfate of ammonia and lime. The data are from two four-year tests, and nitrogen was applied at a rate of 48 pounds per acre.’’ 7. Response of Truck Crops and Potatoes “Anhydrous ammonia compared favorably with ammonium nitrate for beans, Phaseolus vulgaris L., cabbage, Brassica oleracea capitata L.,

105

ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

tomatoes, Lycopersicon esculentum Mill., and sweet potatoes, Iponaea batatas, La. [Table XIX]. The six-inch depth of application was superior for tomatoes. In order to avoid injury to young plants, a six-inch depth of application and placement about five inches to the side of the place where the seed or young plants are to be placed is suggested. “The application of anhydrous ammonia as a side dressing to short season truck crops three weeks earlier than is usual for nitrate of soda and ammonium nitrate is recommended. Many of these crops require nitrate nitrogen at side-dressing time. The earlier application is suggested to provide time for the ammonia to be converted into nitrate TABLE XIX The Response of Truck Crops to Sources of Nitrogen in Mississippi

Sources of nitrogen

Ammonium nitrate Anhydrous ammonia Anhydrous ammonia Anhydrous ammonia Nitrate of soda Sulfate of ammonia

Depth of application

Cabbage’ 1

4 4 6 63 4

lb. 18,077 18,613 18,404 18,513 18,186

Crop, years of test, measure Tomatoes’ Beans’ S. potatoes* 2

2

Yield per acre lb. bu. 10,003 184 837% 180 9,976 171 8,727 176 9,763 153

a

bu. 186 183 184 150

’ 7 2 pounds of nitrogen before planting and 3%pounds as a side dressing. 48 pounds of nitrogen per acre. 8 All nitrogen before planting. 3

nitrogen. When anhydrous ammonia is applied close to planting time, no doubt only one application is necessary, which would save one trip over the land.” In Michigan ammonium nitrate was slightly superior to anhydrous ammonia for cabbage and pickle, Cucumis sativus, L. (Robertson et al., 1955). Though the differences were not large, the data suggest earlier application of anhydrous ammonia to vegetable crops in order to provide nitrate nitrogen earlier. The response of cabbage and cabbage greens to anhydrous ammonia and ammonium nitrate applied at the rate of 63 pounds of nitrogen per acre as a side dressing is shown by the data in Table XX from Virginia (Dunton, personal communication). With cabbage the same yields were made by the two sources in one test, and in two tests ammonium nitrate was superior, though the differences were not significant. In one test with cabbage greens, the difference in favor of ammonium nitrate was highly significant, which is attributed by the author to the need

106

W. B. ANDREWS

for nitrate nitrogen before a sufficient quantity of the ammonia had been nitrified, suggesting the desirability of earlier application of anhydrous ammonia. For potatoes, Solanum tuberosum, L., in California, Lorenze et al. (1954) showed that application of part of the nitrogen in the bed as sulfate of ammonia and part 6 inches to each side of the seed piece as anhydrous ammonia at emergence was just as effective as applying all the nitrogen as sulfate of ammonia in the bed at planting time. However, in two other tests, the increase in yield of potatoes for 100 pounds of nitrogen as sulfate of ammonia applied in the bed was 200 and 171 bushels; where 33 pounds of nitrogen as sulfate of ammonia was applied in the bed at planting and 67 as ammonium hydroxide in flood TABLE XX The Response of Cabbage and Cabbage Greens to Anhydrous Ammonia in Virginia

Source of nitrogen

Ammonium nitrate Anhydrous ammonia No side-dressing

Cabbage, 50-lb. boxes Test 1 Test 8 Test 5

458 579 378

565 $14

837

Cabbage greens, 80 lb. bu. Test 1 Test 8 Test 3

Yield per acre 551 889 353 766 815 677

1544 1405 776

931 604 587

irrigation water, the increases in yield were 104 and 126, respectively. Where all the nitrogen was applied at emergence in the irrigation water as sulfate of ammonia, nitrate of soda, or ammonium hydroxide, the results were much less favorable than with sulfate of ammonia applied in the soil at planting time. The loss of ammonia in sprinkler irrigation water was 36, 52, and 60 per cent when the concentration was 10,20, and 60 or more pounds per acre inch of water (Henderson et al., 1955). The pH of the water used was 8.3. The losses recorded do not include those which may have taken place after the solution came in contact with the soil. 8 . Response of Rice

In Louisiana, according to Miears (personal communication), three experiments have been conducted in which there were no significant differences between the increase in yield of rice, Oryza satiua L., produced by anhydrous ammonia, sulfate of ammonia, and ammonium nitrate. In other tests, the ammonium form of nitrogen has been superior to the nitrate form for rice production; in these tests, the failure of the ammonium form of nitrogen to be superior to ammonium nitrate

107 is attributed, by the author, to the small increases in yield of rice caused by nitrogen fertilization. For rice production in Texas, Fisher (personal communication) showed that anhydrous ammonia or sulfate of ammonia applied in the soil just prior to planting and five weeks later produced top increases in yield. When applied in the irrigation water in any manner, the response to these sources of nitrogen was much less satisfactory, producing as much as 21 bushels less than in the soil placement (Table XXI) . A N H Y D R O U S A M M O N I A AS A N I T R O G E N O U S FERTILIZER

TABLE XXI Comparison of Sources of Nitrogen and Methods of Application for Rice 1951-1954 in Texas

Method of application (80 pounds nitrogen per acre)

Without nitrogen In soil 6 weeks before planting In soil just prior t o planting I n flushing water I n 2 inches water 4-5 weeks after planting In 6 inches water 4-5 weeks after planting I n water on wet soil 4-6 weeks after planting' I n water on dry soil 4-5 weeks after planting' In water before muddying In mud during muddying In soil 5 weeks after planting

3

Drill planted Anhydrous Sulfate of ammonia amnionie

60.4 73.3 100.5

Water planted Anhydrous Sulfate of ammonia ammonia

Yield, bushels of rice per acre 63.6 80.5 99.0

93.4

86.4

70.5 90.8 96.8

94.6

77.0 79.1 79.3 76.8

80.g2

84.9

90.52

Before flooding. Broadcast.

In Arkansas (Beacher, 1955), placement of 60 pounds of nitrogen as anhydrous ammonia in the soil increased the yield 39 bushels of rice, but only 24 bushels when applied in irrigation water. When nitrogen is applied in irrigation water, the clay takes ammonium nitrogen out of the water as it flows across the field, which results in the rate of application being higher in the soil which receives the water first and lower in the soil which receives the water last. In addition, more nitrogen would be applied where the water is deeper and less where the water is shallow. Since the water goes fiist to the lower areas and is deeper in these areas, they receive considerably more nitrogen than the higher areas within the terraces. Irregularity in the

108

W. B. ANDREWS

distribution of nitrogen may result in uneven ripening of rice, which presents problems in harvesting. In Texas, the five-year average increase in yield of rice for 80 pounds of nitrogen as anhydrous ammonia was 12.9 bushels when applied five weeks before planting and 40.1 bushels when applied just before planting. In Arkansas, the average increase in yield of rice for 60 pounds of nitrogen as anhydrous ammonia in four one-year tests (Beacher, 1955) was 12,22, and 18 bushels for late-fall, late-winter, and before-planting applications (Table XXII) . Evidently, the response to TABLE XXII The Effect of Time of Application of Anhydrous Ammonia on the Yield of Rice in Arkansas Time of applying 60 pounds nitrogen

Late fall Late winter Before planting

Test 1

18 19 21

Test 2

Test 9

Test 4

Increase in yield, bushels per acre -6 16 18 2s 26 16 15 a0 16

Average

12

ee 18

anhydrous ammonia five or more weeks before planting rice as compared to at planting in Texas is not in agreement with that in Arkansas. One difference is that high response to nitrogen was obtained in Texas, while a low response was obtained in Arkansas. The comparative responses suggest that more nitrogen may have been applied in the Arkansas tests than needed, which, in turn, suggests that the Arkansas data may not be indicative of the effect of time of application on the efficiency of anhydrous ammonia. With conventional application equipment, there is sometimes streaking of crops like rice where anhydrous ammonia is applied. However, combination planting and anhydrous ammonia application equipment enables anhydrous ammonia to be applied at a fixed position relative to the seed, eliminating irregular response to the nitrogen. In a one-year test in Mississippi, Hogg (personal communication), with 60 pounds of nitrogen from ammonium nitrate applied at the second flooding, rice produced a total yield of 3992, 5027 and 5854 pounds per acre when seeded in lo-, 20-, and 30-inch drills. The yield with anhydrous ammonia applied two inches below the seed at planting was 5530 pounds per acre in 20-inch drills, an increase of 503 pounds of rice for anhydrous ammonia over ammonium nitrate with the same spacing. Where anhydrous ammonia was applied under the seed, the seedlings grew off more rapidly, they competed more favorably with the

ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

109

weeds and they were ready for flooding earlier which also favors weed control. There was much less lodging of rice in the wider spacings. Since these data are for only one year, additional experiments are needed before a generalization on their application in practice can be made.

9. Work in Other Countries Though the detailed data are not available, summaries of the work in northern Europe by Tonnesson (1953) show that: 1. In Denmark, anhydrous ammonia was equal to calcium nitrate for oats, was less effective than calcium nitrate for wheat, barley, and rye, was equal to calcium nitrate for kohlrabi, Brassica oleracea var. Cdo-Rapa, was inferior to calcium nitrate for rutabagas, Brassica Oleracea var. Napo-Brassica L., and was superior to sulfate of ammonia for potatoes. 2. In Norway, anhydrous ammonia and calcium ammonium nitrate had practically the same effect on the yield of potatoes, kohlrabi, wheat, barley, and oats. 3. In Sweden, the action of anhydrous ammonia compares favorably with that of the solid nitrogenous fertilizers with which it has been compared. In Formosa, Wang (1954) reported that the response of sugar cane to aqua ammonia is essentially the same as that to sulfate of ammonia.

10. Placement of Anhydrous Ammonia As has been pointed out, when anhydrous ammonia is applied it is fixed in a relatively small volume of soil. After nitrification, movement is largely up or down, probably with little lateral movement. In order for plants to get nitrogen applied as anhydrous ammonia, or any other source of nitrogen, essentially they must grow roots to the vertical plane of application. I n order for slow-growing plants to get nitrogen while they are still young, it is evident that it must be applied relatively close to them. For crops like corn, which grow rapidly, application midway between the rows is as effective as application closer to the plants (Robertson and Ohlrogge, 1952); though there are no data available for corn, it is likely that placement of anhydrous ammonia in every other middle would be as effective as in every middle. However, placement close to the plants is necessary for early response. When a large quantity of nitrogen as anhydrous ammonia, or any other source, is applied in contact with or just below the seed, there is danger of killing the seed or seedlings. If a moderate rate of anhydrous ammonia is applied and sealed in the soil 6 inches below where the seed are to be placed, there is little danger of damage. In practice, the

110

W. B. ANDREWS

opening made by the knife may be loosely filled with soil up through which anhydrous ammonia may rise a considerable distance, thereby increasing the possibility of seed and seedling injury. On nitrification of anhydrous ammonia, the nitrate nitrogen formed is subject to movement with the soil water. If nitrification of large quantities of nitrogen directly under the seed is followed by only sufficient rainfall to wet the soil to the depth of the nitrate nitrogen, movement of soil water may bring up sufficient nitrate nitrogen to kill seed and seedlings. The quantity of nitrate nitrogen necessary to kill seedlings is less on sandy and more on heavy soils, and less in dry weather and more in wet weather. Under most conditions the risk of damage to seed and seedlings is not large when applied 5 to 6 inches below the seed of row crops; however, unusual rainfall conditions justify the application of all nitrogen to the side of the seed. Where the rate is not more than 50 pounds for the heavier soils and not more than 25 pounds per acre for the lighter soils, placement directly under the seed is usually satisfactory; however, with these low rates care should be taken to place the nitrogen well below the seed. In side-dressing crops, escaping ammonia may burn the leaves of young plants. Though the damage to young plants is usually overcome in a short time, the ammonia which escapes is lost.

N.ANHYDROUS AMMONIA EQUIPMENT 1. Storage and Application “Anhydrous ammonia has no pressure at 28O F. below zero. At a pressure of 197 pounds per square inch. At first the high pressures exerted by anhydrous ammonia appear dangerous; they are dangerous, but they are no more dangerous than steam boilers, which have been in common use for a long time. “Many states have rules and regulations concerning equipment for handling anhydrous ammonia. In most cases the regulations should be satisfactory, though improvements no doubt will be made as the information warrants. Those who handle anhydrous ammonia should have a copy of the regulations. “Anhydrous ammonia tanks have a working pressure of 250 pounds per square inch. The test pressure is normally 400 pounds per square inch. The bursting pressure is normally over 1000 pounds per square inch. Tanks are equipped with sufficient pop-off valve area to relieve too much pressure by releasing the gas phase. The release of gas permits more gas to evaporate from the liquid phase; the evaporation of

looo F. it has

111 the liquid phase has a cooling effect on the tank and its contents, which reduces the pressure.” “High pressure tanks are most common. Horton spheres are large spherical tanks which are refrigerated. They may be of any size but 210,000-gallon capacity is a common size.” The operating pressure is normally less than 60 p s i . “All tanks and fittings are made from steel, which is not attacked by ammonia. Hose is ammonia resistant. Bronze and brass are attacked by ammonia and they should not be used for anhydrous ammonia. “Incomplete filling of tanks is a safety feature. The percentage fill of anhydrous ammonia tanks should not exceed the following: A N H Y D R O U S A M M O N I A AS A N I T R O G E N O U S FERTILIZER

Temperature of liquid ammonia in tank Degrees F. 30 40 50

Maximum volume filled with liquid Per cent 86 88 89

60 70 80

91

90

93

100

96

90

9%

Tanks are made to withstand much more than the gas pressure developed under ordinary circumstances. However, if a tank were completely filled with liquid only a little rise in temperature would be sufficient to cause an explosion if the pop-off valve failed to work. “A 30,000-gallon tank holds about 65 tons of anhydrous ammonia, which is sufficient to fertilize about 1,000 acres at a rate of 100 pounds of nitrogen per acre. Ammonia is shipped in 10,000-gallon tank cars, containing 25 to 26 tons. A 30,000-gallon tank is about the smallest size unit necessary for establishing a business. The effective size of the business may be increased by supplying farmers transport tanks and tractor equipment, or by applying the ammonia to the soil for a fee. Anhydrous ammonia is transported to the farm in 500- to 1000-gallon tanks where it is to be applied directly to the land. Where farm storage is available transport trucks are used. “Nitrogenous fertilizers are produced throughout the year. It is necessary for the manufacturing plants to run continuously. Since most of the nitrogen is applied in the spring it is necessary for it to be stored until used. During periods of scarcity farmers buy solid nitrog-

112 W. B. ANDREWS enous fertilizers when they become available; during periods of plenty they tend to buy their fertilizer only as needed. “The rate of delivery of anhydrous ammonia to the soil is controlled by the following devices: I.Needle valve and pressure gauge 2. Pressure regulating valves 3. Flowrator 4. Pump All of the regulating devices are accurate provided they have been calibrated and the orifices, delivery lines, and applicator knife openings are of a uniform size. The manufacturer should provide calibration data for each machine. The devices are listed in order of increasing cost. “The rate of application of anhydrous ammonia per acre by the needle valve and pressure gauge and the pressure regulating valves depends upon tank pressure, orifice size, orifice pressure, and acreage covered per hour. “Even though very accurate metering may be obtained with the needle valve and pressure gauge and pressure regulating valves, the rate of ammonia through them varies with the tank pressure and the valve gauge settings. For example, where it is desired to apply 300 pounds of anhydrous ammonia per hour through four 3/32-inchorifices, an orifice gauge pressure of 37 pounds per square inch is required with a tank pressure of 90 pounds per square inch, while an orifice gauge pressure of 52 pounds is required when the tank pressure goes up to 150 pounds per square inch. If a regulating valve is set so that the orifice gauge pressure is 37 pounds with a tank pressure of 90 pounds per square inch, only 220 pounds of ammonia would be delivered as compared to the desired 300 pounds per hour when the tank pressure goes up to 150 pounds per square inch, even though the orifice pressure is maintained at 37 pounds per square inch. “There is one automatic regulating valve which partially compensates for changes in tank pressure so that little change in rate of flow of anhydrous ammonia takes place even though the tank pressure varies markedly. “The flowrator is a tapered glass tube, graduated in pounds of nitrogen per hour, the rate of flow is indicated by a rotor which rises as the rate increases. Flow through this instrument is controlled by a needle valve. “The rate of delivery of ammonia by all of the metering devices, except the pump, is a function of time, and a constant speed of the tractor is necessary to maintain a constant rate per acre. The pump is

ANHYDROUS A M M O N I A AS A N I T R O G E N O U S FERTILIZER

113

geared to the tractor and should maintain a constant rate of application per acre even though the speed of the tractor varies. “A cooler is used with the pump and flowrator to prevent the formation of vapor in these instruments. The cooler is made from coiled %-inch pipe in a 3 x 12-inch pipe, with the proper fittings. The ammonia comes from the tank through the coil and leaves the pump or flowrator through the larger pipe around the coil. The pressure of the outgoing ammonia is lowered, and the evaporating anhydrous ammonia cools the incoming ammonia, thereby preventing it from bubbling. “Farm tractors are usually equipped with 70- to 110-gallon anhydrous a m m o n i a tanks which are mounted on the tractor. Trailing equipment carries much larger tanks. A 110-gallon tank holds about 420 pounds of nitrogen, equivalent to 1% tons of nitrate of soda. “Anhydrous ammonia is conducted into the soil through hose connected to the back of applicator knives. Almost any type of knife does a good job in soils which are loose and friable and free of trash. Difficulty in sealing ammonia increases as soils become less friable, more compact and more trashy, and as the rate of application per foot of row increases. “The applicator knife should slope backward and not be sharp above a vertical distance of four inches from the point. The backward slope enables the knife to take the ground and helps it to shed trash. The dull edge also helps in shedding trash. The bottom of the knife should carry a n addition to loosen and increase the amount of soil available for absorbing the ammonia. The knife . . . has a 3-inch point of a 10-inch sweep welded on the bottom, which loosens the soil so that a good job of sealing may be done in compact soils and pastures. “A covering device helps seal anhydrous ammonia in the soil. The disk hiller . . . crowds loose soil against the applicator from near the bottom up and prevents the escape of ammonia. Shovels or other covering devices may be used. Even though a covering device is not needed on soils which are loose and friable, it is usually desirable to use one. “In filling tanks the outlet valve on the storage tank should be opened last and closed first. I n filling tanks by bleeding, pumps, and compressors all connections are made and all valves are opened with the outlet valve on the storage tank being opened last. Then the pump or compressor (if used) is started and the bleeder valve is opened. The escape of a spray from the bleeder valve indicates that the liquid ammonia is up to the filling level, after which the pump or compressor (if used) is stopped, the outlet valve on the storage tank is closed, the bleeder valve is closed, the other valves are closed and the hose disconnected.”

114

W. B. ANDREWS

“The gaseous anhydrous ammonia should not be removed from anhydrous ammonia tanks. At 80° F., a 30,000-gallon tank contains 2040 pounds of anhydrous ammonia as a vapor, a 1,000-gallon tank contains 68 pounds, and a 100-gallon tank contains 6.8 pounds. At $150 per ton, the ammonia lost in bleeding these tanks after the liquid has been removed is worth $153.00, $5.10 and $0.51, respectively. “Allllllonia reacts with the inside of steel tanks in such a way that a protective coating is formed. This layer is lost on exposure to the air

FIG. 3. Transferring anhydrous ammonia to tractor equipment (courtesy of Mississippi Agricultural Experiment Station).

and rusting proceeds. Preventing rust is another reason for not releasing the ammonia vapor from tanks.” 2 . Bleeding Losses in Filling Tanks Anhydrous ammonia is usually transferred from transport to tractor tanks by bleeding gaseous ammonia from the tank being filled. Though pumps and compressors are available for this use, a discussion of them is beyond the scope of this paper. To date, bleeding losses have not been determined experimentally. The calculated bleeding losses reported by Andrews et al. (1951) are in error. Andrews and Caveness (unpublished) calculated bleeding losses based on the thermodynamic properties of anhydrous ammonia by Hodgman (1947). The calculated bleeding losses of ammonia, as obtained under the conditions prescribed, are the least that can be obtained; however, it appears that the

ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

115

calculated losses should be obtained in practice provided the equipment is correctly designed and operated (Andrews and Caveness, 1956). The calculations presented in Table XXIII show some of the changes which take place in both the 1000-gallon transport and the 100-gallon tractor tanks. The starting temperature is 80° F., which gives an absolute pressure of 153 p.s.i. The transport tank is filled to 90 per cent of capacity with liquid anhydrous ammonia. Ten liquid transfers of 90 gallons each were calculated. It was assumed that the fraction of the 1000-gallon tank in contact with the liquid at the start of filling and all of the 100-gallon tank supplied heat to the respective systems. On removing the 90-gallons of liquid from the 1000-gallon tank, its place is taken by both the evaporation of liquid and the expansion of the gases originally present. The evaporating ammonia is derived from the 90 gallons involved in each transfer. For the first removal from the I 000-gallon tank, there remains a large quantity of liquid ammonia to give up heat to the evaporating ammonia and only a small amount of gas to expand, which reverses as successive removals are made. Within the 1000-gallon tank, the absolute pressure drops from 153 to 151.42 p.s.i. for the first transfer and the drop increases progressively until the tenth and last transfer, where the pressure drops from 153 to 142.90 p s i . Where the pressure in the 100-gallon tank is maintained at 10 pounds less than in the 1000-gallon tank while transferring, the pressure in the 100-gallon tank decreases from 153 to 141.42 p.s.i. for the first transfer and decreases progressively with successive transfers to 132.9 pounds for the tenth and last transfer. The mean temperature of the ammonia leaving the large tank decreases only onehalf as much as that of the larger tank and its contents. The quantity of liquid ammonia which must be vaporized in the 100-gallon tank to obtain the ending pressure is 4.72, 4.76, 4.81, 4.89, 4.97, 5.09, 5.26, 5.56, 6.12, and 7.78 pounds for the ten successive transfers. In practice, when filling is started the 100-gallon tank contains a small residue of liquid ammonia and essentially 6.82 pounds of gaseous ammonia at 80° F. The total gas which must be accounted for is 4.72 . . . 7.78 plus 6.82 or 11.54 . . . 14.60 pounds. When filling of the 100-gallon tank with liquid is completed to the prescribed level, the 100-gallon tank contains 0.80, 0.80, 0.80, 0.80, 0.80, 0.79, 0.79, 0.78, 0.77, and 0.75 or an average of 0.79 pound of gaseous ammonia. Subtracting the weight of the remaining gas from the above quantities gives 10.74 . . . 13.85 pounds of gaseous ammonia which is bled off, or 2.42, 2.43, 2.44, 2.46, 2.47, 2.50, 2.54, 2.60, 2.73, and 3.09 per cent for the successive fillings, or an average loss of 2.57 per cent. Though calculations have not been made, the losses in bleeding are some less

c. Q,

TAB- XXIII Losses in Transferring Anhydrous Ammonia from 1000-GallonTransport to Tractor Tanks

1 I

1000-gal. tank 80' F., 153 lb. pressure pre square inch, absolute, a t start 100-gal. tank, 80' F., 153 lb. pressure a t start

Filling no.

Changes in 1000-gal. tank

Small tank, 80° F., atmospheric pressure a t start Tank size, gallons

Changes in 100-gal. tank 10-lb. difference in pressure 100

Ending, temp., OF.

Ending pressure. lb.

Ending, temp.,

OF.

Ending pressure, lb

.

NH* evap., lb.

NHa loss, %'

10

100 140 Pressure difference lb. 5

5

150

5

Per cent loss in bleeding

~

1 2 3 4 5 6 7 8 9 10

79.38 79.32 79.24 79.13 78.99 78.80 78.51 78.04 77.16 75.96

151.42 151.27 151.06 150.78 150.49 149.94 149. 20 148.00 145.84 142.90

75.36 75. 29 75.21 75.09 74.95 74.75 74.45 7%.96 73.04 71.79

141.42 141.27 141.06 140.78 140.43 139.94 139.20 188.00 135.84 132. 90

Average 1 f

See text for the details. The difference in preasure L slightly more than 6 pound. when fillins M complete.

4.72 4.76 4.81 4.89 4.97 5.09 5.26 5.56 6.12 7.78 5.40

2.42 2.43 2.44 2.46 2.47 2.50 2.54 2.60 2.73 3.09 2.57

1.00 1.01 1.02 1.04 1.06 1.09 1.12 1.19 1.32 1.69 1.15

0.50 0.51 0.52 0.53 0.55 0.57 0.61 0.66 0.76 1.02 0.62

0.002

0.00' 0.002

0.002 0.02 0.04 0.08 0.15 0.26 0.050 0.11

0.00' 0.00' 0 .OO' 0.00' 0.002 0.00'

0.00' 0.01 0.11 0.40 0.05

a pl G 3

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117

where larger storage tanks are used; likewise, filling tractor tanks larger than 100-gallonsfrom the storage tank increases the loss slightly. Accumulating, on the average, of the 449.76 pounds of ammonia involved in the transfer, 4.89 pounds evaporates in the 1000-gallon tank and is not lost; 5.40 pounds evaporates in the 100-gallon tank which contains 6.82 pounds of gas at the start and 0.79 pound of gas when filling is complete, which gives 433.44 pounds of liquid available for application plus 6.03 pounds to replace the gas in the tank as the liquid is removed; 11.43 pounds or 2.57 per cent is lost in bleeding. Since the 100-gallon tank contains 6.82 pounds of gaseous ammonia at 80° F. and 153 pounds of pressure and only 0.57 pound at 80° F. and atmospheric pressure, 6.25 pounds of ammonia may be saved by applying the gas to the soil until atmospheric pressure is reached. This change in practice would reduce the average bleeding loss from 2.57 to 1.15 per cent. By using a £ difference in final pressure and applying the gas to atmospheric pressure the loss is reduced to 0.62 per cent in a 100-gallon tank, and 0.11 and 0.05 per cent where 449.76 pounds of ammonia is involved in the transfer to 140- and 150-gallon tanks, respectively. When starting with the 100-gallon tank filled with gas in equilibrium with residual liquid and bleeding with a 10-pound difference in pressure, the average bleeding loss was calculated to be 1.79,2.10, 2.57, and 3.08 per cent at 40°, 60°, 80°, and looo F. The above calculations were based on ten transfers of ammonia from a 1000- to a 100-gallon tank. Calculations made for transferring the contents of a 1000-gallon tank at 80° F. to another 1000-gallon tank give a bleeding loss of 3.67 per cent as compared to the average loss of 2.57 per cent for the ten individual transfers. The calculations show that losses obtained on completely transferring ammonia between tanks of equal size are not applicable to bleeding losses obtained in practice. As pointed out above, the 100-gallon tank contains 6.82 pounds of gaseous ammonia at 80° F. and 153 pounds pressure, 6.25 pounds of which may be saved by applying the gas to the soil until atmospheric pressure is reached. In order to remove the gas to atmospheric pressure, it is necessary to remove the liquid phase completely, which is not feasible with a down pipe outlet; however, it would be feasible with the outlet through a sump in the bottom of one end of the tank toward which the tank is sloped downward. Larger fittings would reduce the time required in filing. Unconfirmed reports suggest that bleeding losses in transferring ammonia may be much larger than those shown in these calculations. In the opinion of the author, bleeding losses significantly larger than those calculated here can be obtained only with improperly designed equip-

118 W. B. ANDREWS ment, with differences in pressure much larger than 10 pounds, or where bleeding is continued after the liquid level has reached the end of the bleeder valve. If experiments, conducted as specified here, should show that bleeding losses with the present equipment are significantly larger than those calculated, the larger losses would be attributed to the loss of liquid entrained in the bleeder gas. With the presently used equipment, the bleeder valve is often located next to the filler valve, which may facilitate the entrainment of droplets of liquid ammonia in the bleeder gas; the separation of the filler and bleeder valves by the length of the tank would provide the least possible opportunity for the loss of liquid in bleeding. As the equipment is now used, filling is stopped when a mixture of liquid and gaseous ammonia starts discharging continuously from the bleeder valve as a spray. The entrance of the incoming liquid at the top of the tank produces turbulence which facilitates intermittent release of spray before the filling level is reached. In the opinion of the author, the bleeding losses should be essentially the same as those calculated provided the discharge of the spray is prevented which can be done by nonturbulent entrance of the ammonia, shortening the pipe to the bleeder valve, and using a gauge to indicate the filling level. To date there has been no work reported on the design and operation of the equipment in bleeding. On the basis of the theoretical studies presented here, for filling by bleeding, it is suggested that the ideal tractor tank for anhydrous ammonia would be either oblong with spherical heads, mounted vertically, or spherical. The outlet valve would be placed in the center of the bottom and the bleeder valves without a down pipe, would be placed in the center of the top; the pop-offvalve would be placed close to the top. The inlet valve would be placed near the bottom of the cylinder of oblong tanks and near the center of spherical tanks. The filling level would be indicated by a sight gauge. It may be desirable to provide a special manifold to speed up application of the gaseous ammonia to the soil after the liquid has been removed. The final difference in pressure in bleeding need not be more than 5 p s i . and the bleeding loss should be essentially 0.64 per cent when starting at 80° F. The ideal tank for transferring anhydrous ammonia by bleeding should also be ideal for liquefiable petroleum gases which are transferred by bleeding.

3. Distribution Pattern For individually owned equipment, anhydrous ammonia is, of course, best suited for large farm use. However, the anhydrous am-

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monia equipment needs of small farmers are being supplied on a rental basis and by custom applicators in many areas, and the cost per pound of a medium to high rate of nikogen applied in the ground as anhydrous ammonia is no more than the cost of that in solids at the market place. This relationship is conducive to continued increase in the use of anhydrous ammonia. There are, at present, many distribution patterns in existence some of which are as follows: 1. Producer to farmer in the farmer’s transport equipment. 2. Producer to farmer in farmer’s storage equipment. 3. Producer to local distributor to farmer. 4 . Producer to jobber to local distributor to farmer. 5 . Producer to fertilizer manufacturer to local distributor to farmer. With the present surplus capacity to produce, it may be anticipated that the trend in the distributing pattern will be influenced by costs which may be more favorable to farmer-owned storage, particularly in areas where delivery may be made by truck from the plant.

V. SUMMARY Aqua ammonia was mentioned as a source of nitrogen more than a century ago. Anhydrous ammonia was first used as a source of nitrogen in 1930 by J. 0. Smith of the Mississippi Delta Branch Experiment Station. Later aqua ammonia was used in greenhouse experiments. I n 1934, Waynick recommended the use of anhydrous ammonia in flood irrigation water. In 1939, Leavitt applied for a patent on the use of anhydrous ammonia on arable soils which was granted in 1942. The Mississippi Agricultural Experiment Station experimented with aqua ammonia in 1943 and started experimental work on anhydrous ammonia in 1944. The results of this work were first published in 1947. Since that time, anhydrous ammonia has become a leading source of nitrogen. The present capacity to produce anhydrous ammonia and other sources of nitrogen synthetically is larger than the present demands. In synthetic plants, anhydrous ammonia is produced first and is then used as such or converted into other sources. The cost of producing 1 ton of anhydrous ammonia is essentially the same as the cost of producing 1 ton of ammonia nitrate; on a pound of nitrogen basis, the cost of producing anhydrous ammonia is only about 40 per cent of the cost of ammonia nitrate. The relative costs of the two materials suggest that where suited the use of anhydrous ammonia will continue to increase relative to the solid sources. When applied to the soil, anhydrous ammonia is held by the clay and organic matter, affecting only about 5 per cent of the volume of

120 W. B. ANDREWS the surface 6 inches when applied at the rate of 100 pounds of nitrogen per acre to the average soil, and with a coverage of about 10 per cent of the surface area. These, of course, vary with soil texture and organic matter. In the zone of application of anhydrous ammonia the soluble phosphorus is increased and the soil structure could be impaired, though neither effect is of significant magnitude and both are temporary. When applied in contact with superphosphate, anhydrous ammonia markedly reduces the availability of the phosphorus. Anhydrous ammonia is acid-forming, as are ammonium nitrate and urea. In the zone of application, anhydrous ammonia markedly reduces the number of fungi and nematodes, suggesting the possibility that it may be useful as a nematocide. For 3 days after application, anhydrous ammonia reduces the number of bacteria and actinomycetes, after which the numbers increase markedly, to 6 to 25 times as many for the bacteria 10 days later. The worms, insects, etc., no doubt, are killed in the zone of application. Because of the small volume of soil affected by anhydrous ammonia and the capacity of these organisms to reproduce, any effect of anhydrous ammonia should be temporary. The rate of nitrification of ammonia is affected by both the temperature and pH of the soil. Nitrification is much slower in the strongly acid soils than in those with more lime. Nitrification is rapid at 70 to 80° F. and the rate decreases as the temperature drops. On strongly acid soils nitrification may stop below 50° F., but in soils containing a good supply of lime considerable nitrification may take place so long as the temperature is above freezing, and on these soils nitrification may be resumed immediately when the temperature increases from below to above freezing. The partial sterilization of the soil in the zone of application of anhydrous ammonia, combined with the fact that nitrogen in readily decomposable organic matter nitrifies more rapidly than ammonia which is concentrated in a small volume of soil, suggests that nitrification data collected where the nitrogen was mixed throughout the soil may not be wholly applicable for anhydrous ammonia under field conditions. Nitrogen applied in the ammonium form does not leach before it is converted into nitrate nitrogen, which may take less than three weeks under favorable conditions for nitrification. Differences in the leaching of nitrogen applied in the nitrate and ammonium forms may be of practical significance only on strongly acid soils, or when applied close to the time of utilization on soils with a fair supply of lime. The highest efficiency is obtained from the application of anhydrous ammonia, or any other source of nitrogen, as close as practicable

A N H Y D R O U S A M M O N I A AS A N I T R O G E N O U S FERTILIZER

121

to the time that it will supply the form of nitrogen needed by the particular growing plant. Corn, and probably sugar cane, sorghum, and some other plants, prefer the ammonium form of nitrogen when young and may utilize it equally as well as nitrate nitrogen as late as the application may be applied with conventional equipment. At normal side-dressing time, cotton has a small preference for nitrate nitrogen, and oats (probably other small grains also) and some of the truck crops have a strong preference for nitrate nitrogen at this stage of growth. When applied before or at planting time anhydrous ammonia has been equal or superior to ammonium nitrate. Where anhydrous ammonia has been superior to ammonium nitrate when applied before or at planting, the author attributes the difference to the leaching of nitrate nitrogen as a result of the ground water being recharged below the root zone. When applied as a side- or top-dressing, anhydrous ammonia has been equal or inferior to ammonium nitrate. Where ammonium nitrate has been superior to anhydrous ammonia in side-dressing, the author attributes the difference to higher efficiency of the nitrate form of nitrogen at this stage of growth; the difference may be overcome by earlier application of anhydrous ammonia. In most of the tests with corn where nitrogen has been utilized efficiently, side-dressing has been superior to preplanting application and late side-dressing has been superior to early side-dressing. Though the superiority of side-dressing has been higher in some tests, the most common increase is between 3 and 10 bushels. The superiority of sidedressing corn as compared to preplanting application is often larger with ammonium nitrate than with ammonium sources of nitrogen. Though less time for leaching and microbial immobilization of nitrogen may be partly responsible for the superiority of side-dressings for corn, it is probable that later applications increase the efficiency of the utilization of moisture as well as nitrogen in the production of grain because of delayed or reduced vegetative growth. When applied in the late fall on soils which are strongly acid, anhydrous ammonia is equal to spring-applied ammonium nitrate for the production of oats and, no doubt, other small grains. When anhydrous ammonia and other sources of nitrogen have been applied at efficient rates in the late fall on soils which nitrify ammonia readily and in which the ground water is recharged below the root zone prior to utilization of the nitrogen, the efficiency has been less than that of spring applications in most tests which have been conducted with fall-planted small grains and spring-planted crops. The percentage recovery of applied nitrogen by plants is low. With an increase in yield of 1 bushel for 3 pounds of nitrogen only about 50

122 W. B. ANDREWS per cent of the nitrogen applied is utilized by the corn. Following corn on dry years where most of the applied nitrogen was not utilized by the corn, its recovery by small grains has been disappointingly low. The low recovery of unused nitrogen by a following crop, in itself, raises a question concerning off-season application of nitrogen. Unfortunately, most of the tests which have been run in the Middle West on fall vs. spring application of anhydrous ammonia have been conducted during drier than normal years and the response to nitrogen has been low. The data may not be applicable for determining time of application with normal seasons and efficient utilization of the nitrogen by crops. In the South, the data on fall vs. spring application of anhydrous ammonia as well as other sources of nitrogen for row crops are inadequate; the behavior of fall applications on small grains suggests very strongly that fall application would be inefficient for spring-planted crops. The application of nitrogen in contact with carbonaceous crop residues does not increase the amount of organic matter derived from the crop residues, but it does markedly lower the potential efficiency of the applied nitrogen. Though other sources of nitrogen may be so applied, normally anhydrous ammonia is applied so that it comes in contact with a minimum of crop residues, resulting in a minimum loss in efficiency because of nitrogen immobilization. In dryland wheat growing there may be insufficient moisture for efficient utilization of nitrogen. In addition, microbial immobilization of nitrogen rather than leaching appears to be the problem in utilization. For the solid sources of nitrogen as ordinarily applied, with adequate moisture in the fall, fall-applied nitrogen may be immobilized so that spring application is superior; while with low moisture in the fall and winter fall applications appear to be superior. Drilled applications of nitrogen, as anhydrous ammonia is applied, lead to more efficient utilization of nitrogen where significant quantities of carbonaceous residues are present. The study of the data suggests, to the author, that late-winter applications of nitrogen which are drilled 4 to 6 inches deep may be superior to other times and methods of application of nitrogen to wheat in dry areas. The application of anhydrous ammonia or aqua ammonia in (1) sprinkler irrigation water, (2) flood irrigation water for drilled plantings such as rice, and (3) furrow irrigation has been very inefficient as compared to soil application where normal responses to nitrogen were obtained. When applied in sprinkler irrigation water, much nitrogen is lost into the air. When nitrogen is applied in flood or furrow irrigation water, the soil closest to the entrance and that where the water is

123 deeper receives much more nitrogen than that which is farther away or where the water is shallow. ANHYDROUS AMMONIA AS A NITROGENOUS FERTILIZER

VI. CONCLUSIONS Within a span of a few years, anhydrous ammonia has probably become the leading source of nitrogen for direct application. No doubt, its use will continue to increase more rapidly than that of other sources of nitrogen. The primary losses in efficiency of nitrogen are produced by leaching and by microbial immobilization in the decomposition of carbonaceous crop residues. As compared to other sources of nitrogen, anhydrous ammonia has accounted for itself favorably under most circumstances. In the case of some crops, corn, for example, it appears that time of application of nitrogen may have a significant influence on the efficiency in the utilization of moisture as well as of nitrogen. The application of anhydrous ammonia, or any other source of nitrogen, as close as practical to the time that it will supply the form of nitrogen needed by the particular plant has proven to be a good practice. Except for small grains on strongly acid soils, fall application of any source of nitrogen in humid climates has not often been equal to spring application for spring and summer consumption by crops where the efficiency of utilization of nitrogen and rainfall were both normal. There are insufficient data to describe adequately the conditions under which favorable results from off -season application may be obtained in humid climates. More data are also needed in subhumid climates.

ACKNOWLEDGMENT The author wishes to express his sincerest appreciation to agronomists throughout the country who made both published and unpublished data available for this paper, to J. D. Lancaster for consultation throughout the preparation of the manuscript, and to Lloyd R. Frederick and W. B. Dunwoody for reviewing parts of the manuscript.

REFERENCES Allison, F. E. 1955. Soil Sci. Soc. Amer. Proc. 19, 210-211. Anderson, 0. E. 1955. Ph.D. Thesis, Rutgers University. Andrews, W. B. 1954a. “The Response of Crops and Soils to Fertilizers and Manures,” pp. 105-151. W. B. Andrews, State College, Mississippi. Andrews, W. B. 1954b. “The Response of Crops and Soils to Fertilizers and Manures,” p. 2888. W. B. Andrews, State College, Mississippi. Andrews, W. B. 1954~.“The Response of Crops and Soils to Fertilizers and Manures,” pp. 40-75. W. B. Andrews, State College, Mississippi. Andrews, W. B., and Caveness, E. W. 1956. Mississippi Agr. Expt. Sta. Mem. Andrews, W. B., and Edwards, F. E. 1947. Agr. Eng. 28,394-396. Andrews, W. B., Edwards, F. E., and Hammons, J. G. 1947a. Mississippi Agr. Ezpt. Sta. Prelim. Bull.

1%

W. B. ANDREWS

Andrews, W. B., Edwards, F. E., and Hammons, J. G. 194713. Mississippi Agr. Ezpt. Sta. Bull. 440. Andrews, W. B., Edwards, F. E., and Hammons, J. G. 1948. Mississippi Agr. Expt. Sta. Bull. 451. Andrews, W. B., Neely, J. A., and Edwards, F. E. 1951. Mississippi Agr. Expt. Sta. Bull. 402. Beacher, R. L. 1955. Agr. Ammonia News. 5(2), 9-11. Chapman, H. D. 1936. J . Am. SOC.Agron. 20,135-145. Dumenil, L. 1955. Agr. Ammonia News 5 (3), 22,24-25. Eck, H. V., and Stewart, B. A. 1954. Oklahoma Agr. Expt. Sta. Bull. 0-432. Edwards, F. E., and Andrews, W. B. 1947. Agr. Eng. 20,396396. Eno, C. F., and Blue, W. G. 1954. Soil Sci. SOC.Amer. Proc. 10, 178-181. Eno, C. F., Blue, W. G., and Good, J. M., Jr. 1955. Soil Sci. Soc. Amer. Proc. 19, 55-58.

Henderson, D. W., Bianchi, W. C., and Doneen, L. D. 1955. California Agr. Expt. Sta. Mern. Hodgman, C. D. 1947. “Handbook of Chemistry and Physics,” pp. 1888-1891. Chem. Rub. Pub. Co., Cleveland, Ohio. Jackson, T. L., Reisenauer, H. M., and Homer, G. M. 1952. Washington Agr. Expt. &a. Circ. 179. Jenny, H., Ayers, A. D., and Hosking, J. S. 1945. Hilgardia 16, 249-457. Johnston, J. F. W. 1853. “Elements of Agricultural Chemistry.” Blackwood, London. (Cited by MacIntire et al., 1944.) Leavitt, F. H. 1942. U. S. Patent No. 2,285,932. Lorenze, A. O., Bishop, J. C., Hagle, B. J., Zobel, M. P., Doneen, L. D., Minges, P. A., and Ulrich, A. 1954. California Agr. Ezpt. Sta. Bull. 744. Lowrey, G. W., and Dreier, A. F. 1951. Nebraska Agr. Expt. Sta. Outstate Testing Circ. 20. Lowrey, G. W., and Ehlers, P. L. 1954. Nebraska Agr. Ezpt. Sta. Outstate Testing Circ. 35. Lowrey, G. W., Ehlers, P. L., and Pumphrey, F. W. 1954. Nebraska Agr. Expt. Sta. Outstate Testing Circ. 42. MacGregor, J. M. 1955a. Agr. Ammonia News. 5(2), 12-13,15-16. MacGregor, J. M. 1955b. Plant Food Rev. 1 (2), 4-5. MacIntire, W. H., Winterberg, S. H., Dunham, H. W., and Clements, L. B. 1944. Soil Sci. SOC.Amer. Proc. 8, 205-210. Mehring, A. L. 1955. Quoted in Agr. Ammonia News. 5(2), 22. Merkle, F. G. 1952. Pennsylvania Agr. Ezpt. Sta. Mem. (Cited by Andrews, 1954.) Missouri Growers, Inc. 1954a. “1954 Results, Anhydrous Ammonia,” p. 8. Carrollton, Missouri. Missouri Growers, Inc. 1954b. “1954 Results, Anhydrous Ammonia,” p. 3. Carrollton, MisSOuri. Missouri Growers, Inc. 1955. “Agricultural Ammonia Pays Off,” pp. 6 1 5 . Carrollton, Missouri. Naftel, J. A. 1931. J . Am. SOC.Agron. 23, 142-158. Oakes, J. Y., and McCormick, L. L. 1954. Louisiana Red River Valley Agr. Expt. Sta. Prelim. Rept. p. 9. Olson, R. A. 1955. Agr. Ammonia News. 5(3), 12, 14-15. Pack, M. R. 1954. Oklahoma Agr. Ezpt. Sta. Mem. Peterson, N. K. 1952. M.S. Thesis, Purdue University.

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Pitner, J. B., and Kuykendall, R. 1943. Mississippi Agr. Expt. Sta. Farm Research 6 , (6198. Reisenauer, H. M., Leggett, G. E., and Nelson, W. L. 1953. Washington Agr. Expt. Sta. Mem. Robertson, L. S., Guttay, J. R., and Hansen, C. M. 1955. Quart. Bull. Michigan Agr. Expt. Sta. 37, 420424. Robertson, W . K., and Ohlrogge, A. J. 1952. Agron. J . 44, 170-173. Scholl, W., Wallace, H. M., and Fox, E. I. 1955. U.S. Dept. Agr. Agr. Research Service Mern. 1820. Smith, G. E. 1952.Missouri Agr. Expt. Sta. Bull. 503. Smith, G.E.1954. Missouri Agr. Expt. Sta. Mern. Stanley, F. A., and Smith, G. E. 1955. Agr. Ammonia News. 5(2), lS21. Thompson, H. L., and Shearon, W. H. 1952. Ind. Eng. Chem. 44, 254-264. Tonnesson, R. D.1953.Norsh Hydro. No. 3, 3-5, 16. Tiedjens, V. A.,and Robins, W. R. 1931.N e w Jersey Agr. Expt. Sta. Bull. 526. Wang, Shih-Chung. 1954. Taiwan Sugar J. Quart. 1 (9), 15-22. Waynick, D.D. 1934. Calif. Citrograph 19,295. (Cited by MacIntire et al., 1944.) Wolf, J. J., and Hoyert, J. H. 1952. South Carolina Agr. Expt. Sta. 64th Ann, Rept. p. 133.

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Progress in Grass Breeding

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D. C SMITH University of Wisconsin. Madison. Wisconsin

I. Introduction . . . . . . . . 1. Nature of Review . . . . . 2. History and Scope . . . . . I1. Diversity of Grasses . . . . . . 1. Species and Varieties . . . . 2. Certification of Seed . . . . I11. General References . . . . . . IV Nature of Varieties . . . . . . V. Environmental Effects . . . . . VI. Cytology . . . . . . . . . I. Variability . . . . . . . 2. Smooth Bromegrass . . . . 3. Other Grasses . . . . . . VII. Interspecific and Intergeneric Relations I . Bromus Species . . . . . . 2. Stipa Species . . . . . . 3. Festuca and Lolium . . . . 4. Elymus Species . . . . . . 5 Poa Species . . . . . . . 6. Triticum-Agropyron . . . . VIII. Fertility and Sterility . . . . . IX. Inbreeding . . . . . . . . . X . Combining Ability . . . . . . 1. Parent-Progeny Relations . . . 2. Interpollination . . . . . . 3. Statistical Approach . . . . 4. General . . . . . . . . XI . Crossing Techniques . . . . . . XI1. Hybrid Varieties . . . . . . . XI11. Agronomic Aspects . . . . . . XIV . Disease Resistance . . . . . . XV. Nutritive Value . . . . . . . XVI. Variety Maintenance . . . . . XVII . Discussion . . . . . . . . . References . . . . . . . . .

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I. INTRODUCTION I . Nature of Review

This review of grass breeding is intended to indicate something of the background for present-day points of view and to describe progress which has been made in the last decade. Since space does not allow a comprehensive and complete summary the author has chosen to refer to certain illustrative work and to omit references and aspects which others may think are more vital. Only breeding of perennial forage grasses is considered. 2. History and Scope

It is difficult to ascertain when recognition was given to the possibility that grass species might be subject to variety differentiation and improvement. Perhaps the earliest grass-breeding project in the United States was that to improve timothy (Phleum pratense) begun in Minnesota in 1889 by W. M. Hays. A few years later Hopkins in West Virginia started similar work. Shortly after 1900 an extensive program was begun by Webber at the Cornell Experiment Station. Intensive work in northern Europe began at about the same time. Real emphasis on the improvement of forage crops in the United States was an outgrowth, in part, of the soil conservation program begun in the early nineteen-thirties, as well as of a growing need that available plants be obtained and improved. Dale and Brown (1955), writing broadly of the use of grass, continued the earlier established campaign for the use of grasses and legumes in conservation of soil and water. Recently the expressions “Grassland Agriculture” and “Grassland Farming” have been widely used, these being traceable to Great Britain, Australia, New Zealand, and South Africa and perhaps more directly to Sir R. G. Stapledon, formerly Director of the Welsh Plant Breeding Station. The first International Grassland Congress was held in Germany in 1927 and the sixth at State College, Pennsylvania, in 1952. This movement has been highly successful in stimulating research in all phases of grassland problems. In Northeast Regional Publication No. 19, New Jersey Agricultural Experiment Station Bulletin 777 published in 1954, it is of interest to find the opening sentence to be “Forage crops are the foundation for a stable agriculture in the Northeastern United States.” Improvement of forage crop varieties has received increasing emphasis. In the broad sense grassland improvement involves many aspects, among which are land clearing and brush removal, control of runoff

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and water supply, tillage, fertilization and other amendments, irrigation, drainage, improved species and varieties, management, machinery and utilization. Breeding of improved strains is therefore but a small part of the whole program, though in many instances it may be a critical one. Owing largely to improved machinery and changes in crop, soil, and livestock management, hay and pasture production on tillable soil is undergoing revolutionary changes at present.

11. DIVERSITY OF GRASSES

I. Species and Varieties In the 1948 Yearbook of Agriculture Hoover et al. listed 60 grass species as being the “main” ones in the United States. In a tabular summary elsewhere in the Yearbook 158 species were listed as of interest. The 10 most prominent genera included 79 species. These figures illustrate the great extent and diversity of the grasses as a group of forage plants. Forty-nine species were classified as “Grasses of the Southern Great Plains .” Thus far the recognition and designation of varieties in the perennial cultivated grass species have been of generally little significance in the United States. Most of them have been named on the basis of relatively minor differences or advantages and many have failed to become important in agricultural use. In Europe, while more varieties have been named, few have been widely grown.

2 . Certification of Seed Introduction of improved varieties of grasses, as well as of other crops, and accompanying difficulties of uncertain identification, have resulted in development and utilization of certification procedures to solve this problem. In Table I a summary is given of the variety certification of grass stocks in the United States for the 1954 crop year. Some of the species listed as the bentgrasses (Agrostis spp.) and red fescue (Pestuca rubra) are principally for turf. Sudan grass (Sorghum vulgare var. sudanense) is a large-seeded annual species with a high seed requirement in pounds per acre. On the basis of an average seeding rate of 10 pounds per acre only 2,500,000 acres could be sown with the certified perennial grass seed available in the United States. It should be recognized that the data referred to cannot be taken to include all the seed of superior varieties since uncertified seed may be in use also. It is well known, however, that unless marked practical advantage is to be derived from a particular variety, certification of it may not develop. The conclusion is reached therefore that variety in most species of

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D. C. SMITH

TABLE I Species and Varieties of Grasses Certified in the United States in the 1954 Crop Year'

Common name Bentgrasses Bermuda Bermuda Big blue Hard fescue Crested wheatgrass Intermediate wheatgrass Kentucky bluegrass Lovegrass Mountain bromegrass Tall oatgrass Orchardgrass Prairie bromegrass Red fescue Russian wild rye English ryegrass Slender wheatgrass Smooth bromegrass Sudan Switchgrass Tall fescue Tall wheatgrass Misc. grasses Totala pounds

Species

Agrostis spp. Cynodon dactylon Cynodon dactylon Poa ampla Festuca duriuscula Agropyron cristatum, etc. Agropyron intermedium. etc. Poa pratensis Eraprostis spp. Bromus can'nalus Arrhenatherum elatius Dactylis glomerata Bromus Festuca rubra Elymus junceus Lolium perenne Agropyon trachycaulum Bromus inernis Sorghum vulgare Panicum virgatum Festuca elatior var. arundinacea Agropyron elongatum (Five species)

No. of varieties

Pounds certified

4 4 1 1 1

2,012,150 91,919,000* 6,490 4,200 55,910 57,825 987,020 697,850 1,890 205,400 24,515 99,827 66,000 2,299,950 6,900 15,974,530 6,600 684,919 15,074,%80 18,899 10,649,170 18,865 5,875 46,826,940

4

6

a 9 1 1 4 1 4 1 1 1 8 9

a 8

a

-

1 Compiled from Report of Seed Certified in 1964 by State Certifying Agencies by J. M. Saundera. U. S. Department of Agriculture. a Certified atolona. 8 Stolona not included (Bermuda graaa).

forage grasses has little practical significance. In contrast approximately 68,000,000 pounds of certified alfalfa seed were produced in 1954.

111. GENERAL REFERENCES The cytogenetics and breeding of forage crops were reviewed by Atwood (1W7). Myers (1947) prepared an extensive s u m m a r y of the cytogenetics of forage grasses. Smith, Hafenrichter and Stoez, Musser et al., and Keller presented information especially pertinent to the subject of grass breeding in the 1948 Yearbook of Agriculture entitled Grass. More recent consideration was given to this subject by Burton (1951) and Hayes et al. (1955). It should be noted that almost no information on qualitative character inheritance is available for the polyploid forage grasses. This is

131 due largely to lack of emphasis but also to difficulties arising from cytology of the species concerned. General problems of studying quantitative inheritance in grasses were reviewed by Burton (1952). PROGRESS IN GRASS BREEDING

IV.

NATURE OF VARIETIES

Among cross-pollinated field crop plants studies with corn have tended to set the pattern for improvement and an attempt has been made to adapt corn-breeding techniques to the breeding of grasses. T o date this has not been especially helpful, though general broad principles are applicable. Grasses usually have relatively small, delicate, and

FIO. I.Timothy individual plant nursery with selected individuals bagged for selfing (Wisconsin Experiment Station).

hermaphroditic flowers and manipulation of selfing and crossing is difficult. An additional consideration is that whereas corn is cross-pollinated normally, it is rather highly self-fertile. Perennial grasses are usually cross-pollinated also but they are often quite self-sterile. While inbreeding, isolation of superior plants, and subsequent crossing have been attempted in strain improvement programs (Fig. 1 ) , there has been little practical progress made as a result of this system. It is of interest to note the type of origin of some of the grass varieties which have been developed. LINCOLN, ACHENBACH, FISCHER, and HOMESTEADER smooth bromegrasses (Brornus inerrnis) are from natural selection over a long period. MARTIN was more definitely a “bred” strain, having been produced from a recombination of 21 selected plants from stock obtained from an old bromegrass field in Minnesota. ITASCA

132 D. C. SMITH timothy, also from Minnesota, was derived from an interbreeding of six highly selected inbred lines, one of which was developed from commercial stock and five of which had their origin from inbreeding Cornell strains. LYON smooth bromegrass arose from mass selection from

FIG.2. Individual plants of smooth bromegrass (Brornus inermis Leyss), illustrating the variation in vegetable and seed characters often found in cross-pollinated grasses. The two left plants have good seed character (Wisconsin Experiment Station).

two generations of plants grown in breeding nurseries. The variety LANCASTER was a result of synthesis of a strain from five selected plants whose self- and open-pollination progenies had been tested. SOUTHLAND smooth bromegrass was described by Harlan (1954) as originating from five open-pollinated lines bulked and increased.

133

PROGRESS I N GRASS BREEDING

Some grass varieties have been started by selection and subsequent increase of seed of single plants. Examples are S48, S50, PRIMUS, and GLORIA timothies; SKANDIA 11 and BRAGE orchardgrasses (Dactylis glomerata) ; VICTORIA ryegrass (Lolium perenne) ; VIKING red fescue; and BLACKWELL switchgrass (Panicum virgatum) . The variations cited in mode of origin indicate the diversity in procedure which may be followed in developing new varieties. Considerable attention has been given to the lack of uniformity in commonly grown forage crop species and varieties (Fig. 2). This was referred to previously in the discussion of the nature of grass species. TABLE I1 The Yield Performance of Various Mechanical Mixtures of Parent and Hybrid Pearl Millet Seed Planted at a Rate of 10 Pounds per Acre in 30-Inch Rows' Proportions of mechanical seed Total forage production in pounds per l6-foot row mixture Hybrid 100 90 80 50 20 0

Parent 1941 1942 1943 1944 1945 1946 Average Actual Theoretical 0 10 20 50 80 100

5% L.S.D. 1 Burton,

Relative average production

51.6 49.0 51.0 51.g

62.1 62.9 61.0 58.0 - 53.8 1 1 . 3 59.6 6.5

7.9

35.5 35.5 36.5 36.3 35.5 25.1 5.2

39.0 39.5 40.4 41.7 39.1 36.5

-

49.8 49.1 50.7 45.9 43.5 41.7

_

37.8 43.4 41.1 40.5 37.6 34.4

46.0 46.6 46.8 45.6 41.9 38.6

3.1

2.4

119.1 120.7 121.2 118.1 108.5 100.0

119.1 117.9 115.5 109.6 105.8 100.0

1947.

Most workers have agreed that uniformity is desirable only for those characters such as disease resistance or similar traits where variation would lead necessarily to inferiority. There is, however, the matter of maintaining a plant population through a period of seed propagation if, by chance, selection factors favor certain characters associated with unfavorable ones. Data provided by Burton (1947) and included in Table I1 emphasize the ability of superior types seeded en masse to dominate a forage planting. The data resulted from conducting yield trials of seed mixtures composed of a graded proportion of superior hybrid and of parental type pearl millet (Pennisetum glaucum). It may be noted that significant reductions in yield did not occw until the proportion of the hybrid strain was less than 50 per cent of the total. Similar results have been obtained with other forage plants. Although

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D. C. SMITH

perhaps not applicable to other grasses and environmental situations, the data emphasize the importance of the vigorous component.

V. ENVIRONMENTAL EFFECTS The effects of natural selection on plant type have been described for many species. There is evidence also that introduced cultivated grasses such as smooth bromegrass have undergone considerable natural selection and thus types and local varieties have evolved. On the basis of observations in Turkey and other experience Harlan (1951) concluded that “No form of husbandry is too primitive or too specialized to have its effect upon the development (genetic) of crop plants.” Workers in Great Britain especially have placed emphasis on plant type and growth habit in relation to farm use. This has been partly the result of the finding in studies of pasture and hay plant populations that use and management have seemed to favor certain plant types. This may have tended to place more emphasis on persistence and longevity than on productivity and vigor. It was suggested by Julen (1947),as is well recognized in Sweden and elsewhere for several forage species, that farmers growing seed locally maintain adaptability better than when seed is grown on fewer, larger farms. It was suggested that local strains might be secured eventually by assembling and mixing all good strains and growing them as a bulk in various localities. It is of interest to note that concentration on development of a hay strain may result in a type which may also be highly superior in pasture. The production and behavior of S24 perennial ryegrass (Lolium perenne) as described by Hughes (1953)is a case in point. Timothy plants occurring in New Zealand pastures were classified as “hay,” “pasture-hay,” and “pasture” types by Gorman (1950).This was primarily on the basis of vigor and growth habit. The pasture-hay type was thought best, as both the hay type and pasture type were poor in pastures. Following a study of collections of perennial ryegrass in which 41 lots from southwestern England and 49 from Ayrshire, Scotland, were compared, Gregor and Watson (1954)concluded that it was very difficult to relate a particular ecotype to a total of habitat factors. Effects of individual factors might well be considered. It was indicated that ecotype differentiation had occurred and that the ecotype should be regarded as an aggregate of cultivars. Ecologic terminology was reviewed. Cornelius (1947) found wide variations in character of 16 lots of little bluestem (Andropogon scoparius) collected from a range of latitudes in the great plains and grown at Manhattan, Kansas. Northern types were earlier in maturity, more susceptible to heat, and lower in

135 forage yields. Southern collections were more susceptible to frost and winter injury. It was concluded that adaptations of collections from various areas should be checked carefully before moving them far from the point of collection for farm use. Southern-type smooth bromegrass from central United States was found to be inferior in seed production, equal in forage yield, and superior in disease resistance to Canadian stocks in trials in prairie Canada (Knowles and White, 1949). The southern type was superior in forage yield in the drier brown soil areas. Considerable variability was noted in studies of strains of smooth bromegrass by Lebsock and Kalton (1954). Evidence was found for regional strain differentiation. In comparisons of seed sources of the LINCOLN and ACHENBACH varieties differences in hay vigor, average fall vigor, and spread exceeded the 0.01 point. Harlan (1954) suggested that yields of varieties of smooth bromegrass were stratified based upon variety origin, those from more adjacent and similar areas being more alike in performance. A specific example of the rapidity and degree of natural selection in a grass was presented by Stebbins (1949) in describing the behavior of diploid and autotetraploid Ehrharta erecta. Following mixed planting of these types at ten sites near the campus at Berkeley, California, the diploid predominated markedly in eight sites after four and one-half years, owing to reseeding. The tetraploids produced seed in only four plots. In one plot, however, the tetraploid was very predominant. This site was a strikingly different habitat, and it was concluded that this favored the tetraploid over the diploid. The results cited and the general experience of taxonomists, ecologists, and plant breeders in sampling plant populations give ample support to the conception of extensive genetic variability existing within species and varieties of grasses. PROGRESS IN GRASS BREEDING

VI. CYTOLOGY Several examples of cytological studies as indicating the nature of many grass species will be cited. In reviewing the occurrence of species hybrids in grasses Stebbins (1952) stated that 70 to 80 per cent of the grass species are polyploid and that perhaps 60 per cent had arisen at least in part as a result of hybridization. It was suggested that in developing strains of practical value parents of widely different adaptation should be crossed. I . Variability Extensive polymorphism with general conformity to principal species characters was described among 59 isolates of switchgrass from 20 locations in central United States (Nielsen, 19M). Chromosome

136 D. C . SMITH numbers ( 2 n ) found were 18, 36, 54, 72, 90, and 108. Size and shape variations were noted. Chromosome number did not appear to be associated with a particular habitat or location. Results of studies by Nordenskiold (1949) suggested that timothy may have arisen from the much less important species P . nodosum following chromosome doubling. Snyder (1951 ) considered Elymus glaucus to consist of a complex of closely related and mostly self-pollinated races. It was found that hybrids between races were usually sterile and origin through alloploidy was postulated. Stebbins (1955) suggested that the existence of numerous intersterile races in Elymus glaucus may have resulted from crosses with Sitanion jubatum and backcrossing to Elymus glaucus. Evidence concerning species variability in Agrostis was obtained by Stuckey and Banfield (1946). Chromosome numbers were determined for 45 plants in progenies, presumably Agrostis tenuis. Numbers varied from 28 to 42 with all intermediate numbers except 38 and 40. Nine open-pollination progenies appeared to be uniform A . tenuis, 5 were classified as variable, and 29 as extremely variable. Only 10 per cent of 758 progenies grown were A . tenuis and reasonably uniform. In one instance A . alba, A. tenuis, and A . palustris forms were found among descendents of one plant. Davis (1953) reported results of crossing British species of Agrostis. Hybrids between A . gigantea and A. stolonifera and A . tenuis were obtained readily and the F, plants were quite fertile. Crosses of A. gigantea with two A . canina strains were unsuccessful. Bjorkman (1954) recently reported results of extensive cytologic studies of Agrostis species. A . canina was recognized as having two varieties arida and fasicularis for which 2n chromosome numbers were found to be 28 and 14, respectively, on the basis of examination of 600 plants from a wide area of Europe. Some pentaploids were found in four populations of the arida variety. In A . stolonifera about 900 plants, chiefly from Sweden but also from elsewhere, were examined. Three chromosome number groups were found, about 600 plants having 2n of 28, 160 plants 2n of 35, and 135 plants 2n of 42 chromosomes. The pentaploids usually had 14 bivalents and were fertile. The 2n = 42 plants showed autotriploid behavior. Only two plants were aneuploid. In A . gigantea ( A . alba) 217 plants from native habitats were studied. All but two plants had 2n = 42 chromosomes, the exceptions having also supernumeraries. A . tenuis was found to have 2n = 28 chromosomes in 90 plants; others had, in addition, supernumerary chromosomes. A few trisomics were found. It was suggested that the aneuploids found by Stuckey and Banfield in A . tenuis may have been from A . alba )( A . tenuis hybrids.

PROGRESS IN GRASS BREEDING

137

2. Smooth Bromegrass Knobloch (1943) found meiosis in smooth bromegrass to be fairly normal at metaphase, though “marked irregularity” occurred at anaphase. Univalents and micronuclei were reported though multivalents were not noted. Nielsen (1947) found smooth bromegrass to follow the normal pattern in macrosporogenesis, in fertilization, and in embryo and endosperm formation. The open-pollination fertility of a polyhaploid plant of smooth bromegrass with 28 chromosomes was found by Elliott and Wilsie (1948) to be about equal to that of a normal 56-chromosome sister plant. Meiosis was also relatively normal. Chromosomal relations were not simple since both pairs and multiple associations occurred. It was suggested that both auto and allopolyploidy might be involved in the genomic origin of smooth bromegrass. Meiotic behavior in smooth bromegrass was found to be very irregular by Elliott and Love (1948). Few to many chromosome pairs and many multiple associations were noted. It was proposed that cytologic analyses should accompany breeding studies better to evaluate progeny behavior. On the basis of root-tip counts of 193 plants of smooth bromegrass Hill and Myers (1948) found 192 to have a chromosome number of 56 and one to show accessory fragments in addition. It was concluded by Nielsen (1951) that the cytology of smooth bromegrass was complex and that behavior suggested allopolyploid origin. Barnett (1955) reported chromosome counts of pollen mother cells for 18 species in four sections of the genus Bromus. With one exception diploid, tetraploid, and hexaploid species showed complete pairing or nearly so. Octoploid and decaploid species studied showed varying numbers of univalents and multivalents, with quadrivalents predominating in the latter class. It was noted that chromosome size differences seemed evident both within and among the species. This conforms to the results of Nielsen (1944) in studies of switchgrass. 3. Other Grasses

On the basis of studies of white seedling inheritance Nordenskiold (1953) concluded that the six genomes of timothy have considerable homology. Meadow fescue (Festuca elatior) and tall fescue ( P . e. arundinacea) have been considered as questionably different and closely related species. Myers and Hill (1947) found the chromosome numbers to be

138

D. C. SMITH

2n = 14 and 2n = 42, respectively. Hybrids were obtained infrequently and they were both male- and female-sterile. Bosemark (1954) reported upon cytologic studies of Festuca pratensis in which accessory chromosomes occur. Among 69 plants examined 17 had no accessories, 18 had one, 5 had four, 4 had ten, and 1 had sixteen. No pairing was noted between accessories and normal chromosomes and the accessories formed bivalents at pachytene. The number of accessory chromosomes was highly constant in various plant parts and meiotic elimination was low. In Poa irrigata, considered to be a subspecies of Kentucky bluegrass ( P . pratensis), Love (1952) found higher chromosome number of plants to be positively correlated with morphological characters of economic value and greater chromosomal number stability. In extensive studies of chromosome number in relation to polymorphism in Poa alpina Muntzing ( 1954) found no correlation between chromosome number and morphological characters. All plants in progenies having the same appearance had the same chromosome number. Plants morphologically dissimilar within progenies differed in chromosome number. Grun (1955) reported great irregularity in the cytology of seven species and subspecies of Poa investigated. Juhl (1953), after studies of aneuploidy in creeping bent (Agrostis stolonifera) ( A . palustris) and red fescue from Schleswig-Holstein, concluded that there was no relation between chromosome number and growth form or habitat. Nygren (1954) reported the results of cytological and breeding studies with North American species of Calamagrostis. C. canadensis, C. purpurascens, and C . rubescens form apomictic strains through diplospory with mitotic division. Some species intercross, although this was not noted for C. canadensis. Recent studies of Jones (1954) with Holcus mollis have emphasized further the difficulties of chromosomal determination and the probable inadequacy of available information to classify most grass species as to either chromosome number or polyploid status. Grass genera of importance to the southwestern United States were described by Harlan et al. (1952) as being cytologically complex. These were Andropogon, Bouteloua, Buchloe, Panicum, and Sorghastrum. It was considered that these genera were “currently engaged in rather intense evolutionary activity.” It is possible for polyploid types of forage grasses to maintain a high degree of irregularity in sexual and cytologic behavior and still possess a practical level of seed setting. In studies of smooth bromegrass Sorensen (1955) found that pollen germination of 50 plants ranged from 37.9 to 92.0 per cent, with an average of 68.2 per cent. Apparent normality,

139 using the stainability test with IKI and lactophenol, varied from 53.2 to 99.0 per cent, with an average of 90.6.Open-pollination seed set ranged from 20.0 to 90.0per cent, the average being 64.0.Highly sigPROGRESS IN GRASS BREEDING

nificant interannual correlations were found for these characters. Pollen germination was highly and positively correlated with pollen normality, self-fertility, and cross-fertility, though the r values were not high. VII. INTERSPECIFIC AND INTERGENERIC RELATIONS Stebbins and co-workers at the University of California have made extensive studies of species and generic relations in the grasses from the viewpoint of cytologic behavior, species variation, and intercompatibility. These investigations have served to delineate more clearly origins and taxonomic relations in Stipa, Bromus, and the Hordeae especially. A more recent example of this is the study of genomic relations in crosses between strains of Elymus and Sitanion in which considerable compatibility was found (Stebbins and Vaarama, 1953).

I . Bromus Species Elliott ( 1949a) called attention to the interbreeding (introgression) of the native and introduced species, Bromus pumpellianus and B. inerrnfs,within the range of distribution of the former. Some seed was obtained by Elliott (1949b) in paired crosses of Bromus erectus, B. inermis, and B. pumpellianus. The F, hybrids were intermediate and partly sterile. B. inermis and B. pumpellianus have 2n = 56 chromosomes and B. erectus, 2n = 70. 2. Stipa Species Following earlier studies in which intercompatibility was shown to exist in Stipa the genomic relations of three species were designated by Love (1954)as follows:

Stipa lepida 14A Stipa pulchra 14A Stipa cernua 14A

+ 3B chromosomes + 3B + 15C chromosomes + 21D chromosomes

Multiple associations in the hybrids were rare, possibly owing to small chromosomes. It was considered that the hybrids might have economic value. The genetic relations of Stipa and Oryzopsis present an interesting example of grass evolution. Johnson (1945) found that Oryzopsis hymenoides crosses readily with seven species of Stipa. 0. bloomeri was Stipa occifound to be a result of combination of 0. hyrnenoides dentalis. It was named Stiporyzopsis. Subsequently Nielsen and Rogler (1952) described an amphidiploid arising from one seed as XStipory-

x

140

D. C. SMITH

zopsis. Its progeny proved to be highly fertile, cytologically regular, and true-breeding. 3 . Festuca and Lolium Seeds were obtained by Crowder (1953) in all hybrid combinations of meadow fescue, tall fescue, perennial ryegrass, and Italian ryegrass (L. multiflorum). Not all the seeds obtained germinated and all hybrid plants were sterile. It was concluded that the genomes of Festuca and Lolium were related, though the manner was undetermined. Jenkin (1955a, b) reported results of studies of interspecific and intergeneric hybrids in Festuca and Lolium. Festuca arundinacea and F. pratensis intercrossed readily, the hybrids being highly though not entirely sterile. F. e. arundinacea and F. gigantea also crossed to produce sterile hybrids. Crosses of F. rubra X F. arundinacea resulted in weak plants. Other crosses made and for which F, plants were established were sheep fescue ( F . ovina) X F . rubra, ( F. ovina X F . rubra) X F. ovina, ( F . ovina X F . rubra) x F. rubra, and Lolium perenne x F. rubra. Successful hybrids reported by Bjorkman (1954) were Agrostis stolonifera x A . tenuis, A . stolonifera x A. gigantea, A . stolonifera x A. canina, A . tenuis x A . stolonifera, A . gigantea X A . stolonifera, and A. gigantea X A . tenuis. 4 . Elymus Species

Church (1954) reported hybrids between Elymus wieganii, E. riparius, E. virginicus, and E. canadensis. E . interruptus and E. canadensis tended to intergrade. Sterile hybrids were obtained in crosses between Elymus spp. and Hystrix patula. Boyle and Holmgren (1955) in studies of Elymus macounii and hybrids derived from crosses of slender wheatgrass (Agropyron trachycaulum) x Hordeum jubatum concluded that the latter two species had given rise to the former, as previously suggested by Stebbins and co-workers. An extensive study of the nature of seed failure following mating of Elymus virginicus X Agropyron repens was.made by Beaudry (1951). It was found that though fertilization occurred and seed development was initiated, further growth failed because of disturbed nutrition. This may be a rather frequent barrier in interspecific and intergeneric crosses. Relatively few attempts have been made to culture embryos of grass hybrids. 5. Poa Species Recombination and rearrangement of Poa genomes from contrasting species were described by Clausen (1952). Seven hundred F, hybrids

141 were obtained from 80,000 seedlings grown. Successful crosses were Poa scabrella X P . pratensis, P. ampla x P. pratensis, P . scabrella X P. ampla, and P . ampla x P. pratensis L. var. alpigena, of which approximately 700 F, plants were obtained. It was concluded that more pracPROGRESS IN GRASS BREEDING

tical improvements might be made from crossing good distantly related types. It was suggested by Juhl-Noodt (1955) that apomictic types in Poa pratensis might have a selective advantage under natural conditions. Akerberg and Bingefors (1953) reported crosses of apomictic Poa pratensis X apomictic Poa alpina and sexual P. pratensis X apomictic P . alpina. Since the apomictic parents were not entirely so, there was marked segregation in the progenies. Sexual and apomictic types were derived. 6. Triticum-Agropyron A brief review of the status of the hybridization studies of TriticumAgropyron was presented by Armstrong and White (1952). This work has been of interest to both grass and wheat breeders since 1936, and though no directly practical results have been obtained, new, potentially useful characters such as disease and insect resistance have been found. On the basis of experiences primarily with wheat )( Agropyron and Stipa interspecific crosses, Love (1947) arrived at the following conclusions with respect to the use of wide crosses. “Interspecific and intergeneric hybrids are potentially valuable in the improvement of forage crops in three ways, as follows: 1. Sterile hybrids themselves may be useful as the Stipa studies indicate. Natural cross pollination between species and ease of establishment of the hybrids is helpful. 2. The amphidiploids may be used in three ways depending on the nature of the amphidiploids.

A. Nonsegregating amphidiploids-an end in themselves. B. Hybridization of related nonsegregating amphidiploids, followed by selection. C. Selection in progeny from amphidiploids that do not breed true. 3. Fertile derivatives produced by natural crossing of the nearly sterile hybrids may or may not have the amphidiploid chromosome number, but in any event, they would be used in the same way as the segregating amphidiploids previously mentioned.” VIII. FERTILITY AND STERILITY The determination of the nature of reproduction, whether apomictic or amphimictic, and the self- and cross-fertility of a particular species

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D. C. SMITH

is of primary importance to the establishment of a breeding procedure. Brief reference will be made to recent studies in relation to self- and cross-fertility. More inclusive studies of the nature of pollination and fertilization in grasses were made by Beddows (1931), Nilsson (1934), Smith (1944) and others. Subsequently more detailed information has been obtained for many species. A number of more prominent species were classified for self- and cross-pollination by Hayes et al. (1955). Nielsen (1952), in reviewing the cytology of forage grasses and possible relations to breeding behavior, indicated that considerable additional information was needed, especially in relation to sterility. Variation in sexual behavior of some of the important southern grasses was described by Burton (1951). Common Bahia grass (Pmpahm notatum) is apomictic while the Pensacola strain is highly or entirely sexual. According to Burton (1955) Pensacola Bahia grass set seed well in 694 of 705 mutual pollinations made between 47 clones. The existence of a diploid personate type of sterility was suggested. Dallis grass (Paspalum dilatatum) is thought to be apomictic. Coastal Bermuda grass (Cynodon dactylon) and Pangola grass (Digitaria decumbens) must be propagated vegetatively. It was found by Lowe and Murphy (1955) that smooth bromegrass plants previously selected for self-sterility varied significantly in openpollination seed set. In 30 plants examined percentage of florets setting seed varied from 2.6 to 75.8. Harlan (1945) reported facultative cleistogamy to exist in mountain brome (Bromus carinatus), an individual plant possibly producing both cleistogamous and chasmogamous panicles. Crossing and subsequent inbreeding would then result in race diversification, according to Harlan. Adams ( 1953) presented evidence to establish significant differences in cross-compatibility in smooth bromegrass, using 15 open-pollination plants as one group and 14 plants from selfing in the other. Diallel crosses, including reciprocals, were made within each group and selfand open-pollination seed set was determined. Differences in seed set were noted in reciprocal crosses. A positive and significant correlation existed between open-pollination seed set and that of the most compatible single-cross combination. It was concluded that oppositional factors might be operative in determining fertility.

IX. INBREEDING Inbreeding as an improvement and selection procedure, following the pattern of studies with corn, was undertaken early in the development of grass breeding. Wexelsen (1952) presented a review of the re-

PROGRESS IN GRASS BREEDING

143

sults of inbreeding grasses and the problems in the practical utilization of the inbreeding procedure. In view of the results available he concluded: “The justification of the use of inbreeding must be that selection can be made more effectively in inbred than non-inbred material.” Hayes and Schmid (1943) found that enough selfed seed was set in smooth bromegrass, meadow fescue, and orchardgrass to make selection in selfed lines feasible. Some inbred lines of meadow fescue and orchardgrass were as vigorous as the open-pollinated checks. Crosses of S, inbreds of smooth bromegrass grown as spaced plants yielded from 126.5 to 220.9 per cent of the check strain. In D. glomerata 49 I?, crosses yielded about the same as a check variety. Julen (Akerman et al., 1948) indicated that in the progenies of crosses of inbreds of perennial ryegrass inbreeding could be continued without marked depression in vigor. Julen (Akerman et al., 1948) wrote that 27 of 199 S, lines of timothy tested yielded more than the respective So plants. Among the 2272 S4 plants, 366 were superior to their respective So origins in green weight. Work with other grass species was cited. It was concluded that effects of inbreeding depended upon the species concerned but that generally lines could be obtained which would be practically useful in crossing to obtain superior strains. Wilsie et al. (1952) found that there was little reduction in selffertility of smooth bromegrass following two generations of selfing in studies of 25 plants. Lines varied considerably in their fertility response. Thus far in the breeding of perennial forage grasses the effects and probable value of inbreeding as a procedure to obtain improvement have not been fully determined. Myers and Hill (1943) found that inbreeding in orchardgrass resulted in more extensive meiotic irregularity, although heritable differences existed among inbred plants and progenies. However, fertility might be improved by selection during inbreeding. Zimmerman (1954) indicated that inbreeding and subsequent crossing appeared to be promising in grass improvement, on the basis of results obtained in Germany with tall oatgrass (Arrhenatherurn elatius) and orchardgrass. The results presented indicate that selfed seed may be obtained in some species and that inbred lines can be established.

X. COMBINING ABILITY 1 . Parent-Progeny Relations Johnson (1952) reviewed problems and methods for evaluating breeding material for combining ability. A very good review of per-

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D. C . SMITH

tinent literature was included. It was considered that “The most critical need in forage breeding is additional information on the relationships between general combining ability and yields of synthetic varieties.” Tsiang (1944) studied the relationships of clonal lines and their first-generation self progenies in smooth bromegrass. The correlation coefficients obtained for several characters are indicated in Table 111. TABLE I11 Relationship between Characters of Parental Clonal Lines and Their One-Year-Selfed Progenies of Parkland and Creeping Smooth Bromegrass as Indicated by Correlation Coefficients’ ~~~~

~

~~

Parkland Character studied

No. of lines

r

22

0.472 0.7a3

Plant height

10

Basal diameter

22 10 22

10 2%

Degree of leafiness Degree of culmage

10 22 10

2%

Leaf width Heat and drought resistance

8

2% 1

9

*

No. of lines

r

20 20

0.06 0.68a

20

0.29

20

0.452

20

0.30

20

0.0

-

Hay yield

Vigor of recovery

Creeping

0.40 0.03 0.693 0.04 0.452 0.32 0.38 -0.06 -0.28 0.94s

-

-

20

0.32

0.20

Taiang, 1944. Exceeds the 6 % level of significance. Exceeds the 1 % level of significance.

Except for leaf width and plant height the values obtained are not large and leave a considerable part of the variation shown to nonheritable causes. Weiss et al. (1951)in studies with orchardgrass obtained no correlation between clonal yield and that of the open-pollination progenies. A low r value was observed between yields of single crosses and the averages of the parent clones. Though the relation was variable, singlecross yields were correlated with those of the average of the openpollination progenies of the parent clones. Hawk and Wilsie (1952)found a positive correlation between the yields of open-pollination progenies of smooth bromegrass and those of

145

PROGRESS IN GRASS B R E E D I N G

their parental clones. Other progeny relations are indicated in Table IV. While the values are not consistently high, they may be as expected when environmental influences are active. Wilsie et al. (1952) found no significant relation between self-fertility and general combining ability in smooth bromegrass. Results of extensive observations of progenies from self- and mutual-pollination of smooth bromegrass at Madison, Wisconsin, have shown no relation of self- or mutual-pollination fertility to vigor of progeny. Average TABLE IV Regression Coefficients and Correlation Coefficients Showing Offspring-Parent Yield Relationships in Smooth Bromegrass' Regression coefficient2

Correlation coefficient2

0.30 0.33

0.28

So O.P. progeny on So clones S1 O.P. progeny on So clones SZ O.P. progeny on So clones

0.22 0.07 0.05

0.33 0 . 12

SI O.P. progeny on SI clones SOO.P. progeny on S1 clones SZO.P. progeny on Sz clones

0.25 0.19 0.34

0 .5 1 0.24 0.55

S1 O.P. progeny on SOO.P. progeny SZ O.P. progeny on SI O.P. progeny

0.48 0.79

0.49

Relationship Regression of: SI clones on SOclones S2 clones on S1 clones

1 2

0.26

0.06

0.56

Hawk and Wilsie, 1959. Significance not indicated.

vigor and coefficients of variability within progenies have been negatively correlated. Kneebone (1951) compared the performances of eight selected plants of smooth bromegrass with those of their polycross progenies for forage quality and other characters. It was concluded that progress might be made in breeding for higher protein content by selecting plants on the basis of their polycross performances. While not highly heritable in the studies made it was suggested that selection for leaf percentage should aid in raising protein percentage. Problems in determining breeding behavior using different types of progenies were reviewed by Murphy ( 1952). Results of tests of progenies of orchardgrass, smooth bromegrass, and red fescue were cited. Clonal replications of the parents, self seedlings, and polycross progenies were

146

D. C. SMITH

compared. Clonal differences were highly significant in all tests using space-planted rows and were higher than the clone x progeny interaction. When parental clonal plantings and polycross drilled rows were studied, differences of progenies from clones were significant in 17 of 19 trials. The performances of the parent clones were positively correlated with progeny behavior whether space-planted in rows, drilled in rows, or broadcast seeded. A summary of the correlations found in TABLE V Average Simple Correlation Coefficients Calculated from 19 Tests for Three Grass Species and the Range for Each' Correlation coefficient2 Characters correlated Same progeny and different method of planting Spaced vegetative vs. drilled vegetative Spaced polycross vs. drilled polycross Spaced polycross vs. broadcast polycross Drilled polycross vs. broadcast polycross Different progeny and same method of planting Spaced vegetative vs. spaced polycross Spaced vegetative vs. spaced self Drilled vegetative vs. drilled polycross Spaced polycross vs. spaced self Different progeny and different methods of planting Spaced vegetative vs. drilled polycross Spaced vegetative vs. broadcast polycross Spaced self vs. drilled vegetative Spaced self vs. drilled polycross Spaced self vs. broadcast polycross Spaced polycross vs. drilled vegetative Drilled vegetative vs. broadcast polycross 1 Murphy,

Average

Range

0.878 0.766 0.473

0.50 t o 0 . 9 8 -0.01 to0.08

-0.93toO.96

0.607

-0.63 to 0.89

0.739 0.781 0.784 0.698

-0.11 toO.96 -0.aato0.99 0.36toO.99 -0.81to0.93

0.603

-0.a2to0.96

0.496 .O .688

-0.40 to 0.93

0.6%9 0.556

0.693 0.548

-0.85t00.99 -0.03t00.84 -0.81to0.98 -0.61t00.99 -0.50 to 0.91

196%

All the average correlation coefficients are highly significant.

the experiments is given in Table V. It was concluded that selection of parents on the basis of progeny behavior should be effective. Heritability for yield was fair in intermediate wheatgrass according to Heinrichs (1953). It was suggested that possibilities of mass selection might be good if heritability reached reasonable levels for particular characters. Heritability for forage yield in smooth bromegrass as determined by Thomas and Kernkamp (1954), for 50 selected clones and their polycross progenies, varied from 0 to 31 per cent in tests at four locations. Heritability for protein content ranged from 1 to 25 per cent. Fertility evaluations as related to clonal performance and com-

PROGRESS IN GRASS BREEDING

147

bining ability in orchardgrass were studied by Leffel et al. (1954). Little association was found between self-fertility and panicle production, blooming date, or forage or seed production of parent clones. Selffertility was not related to combining ability of parent clones in singlecross, top-cross, or polycross tests for panicle production, green weight, or blooming date. Oldemeyer and Hanson (1955) studied combining ability in orchardgrass using seven early- and five late-maturing plants. A wide polycross of 112 clones, restricted polycrosses of 5 and 7 clone combinations, single crosses, and tiller plots of parent plants were utilized. Polycross and single-cross progeny yields were correlated. There was evidence for specific combining ability in single-cross differences. Parent-progeny reactions to leaf diseases were highly correlated. Following studies of specific and general combining ability of 11 noninbred plants of orchardgrass it was concluded by Kalton and Leffel (1955) that differences in general combining ability were more prominent than those for specific combining ability. Early spring vigor, leaf disease reaction, panicle production per unit area, and forage yield were the characters studied. In such material determination of general combining ability appeared to be most useful in development of superior synthetics, with the expectation that yield decline in successive generations would be less. Difficulties in extensive testing of selected plants in single crosses were also indicated. Combining ability in orchardgrass was found to be about equally well determined by average single-cross, polycross, or top-cross tests. The use of the top-cross was favored, advantages being fewer replications required, less effect of differences in blooming dates, smaller effects due to nonrandom mating, and ability to space plants more widely. A plan for top-cross testing was outlined (Kalton et al., 1955). Knowles (1955) in studies of smooth bromegrass found an r of 0.79 between forage yields of open-pollination selections and average yields of three test crosses of the same selections. Seed from open-pollination of replicate clones in different nursery positions resulted in progenies with rather similar forage yields. 2. Interpollination Using homozygous recessives for anthocyanin coloration Griffiths (1950) studied the relation of distance to pollen movement in perennial ryegrass. The rate of pollen dispersion decreased rapidly from 0 to 20 feet and more slowly beyond this distance. In a study of perennial ryegrass using a simple dominant character, roughness vs. smoothness of culm and upper leaf sheath, Wit (1952) determined amount of cross-pollination. Percentages of cross-

148

D. C . SMITH

pollination decreased rapidly at distances of 48 to 64 inches and subsequently decreased more slowly. It was concluded that adequately replicated polycross plantings of plants flowering about the same time were required for homogeneous pollination as desired in a polycross test. The author did not indicate what replication might be adequate, though in other studies ten replications had been used. Interreplicate progeny variation was studied by Hittle (1954) as a measure of the efficiency of the polycross test in smooth bromegrass. Twenty plants studied were replicated ten times and progenies were space-planted. Height, hay vigor, spread, hay weight, aftermath weight, and brown spot (Pyrenophora brorni) reaction were studied. Results indicated that significant differences in progeny behavior occurred among clonal replicates of individual plants, owing to heterogeneity in the pollen source.

3 . Statistical Approach Statistical aspects of determining parent-progeny relations and of minimizing environmental effects for selection purposes were reviewed and procedures suggested by Comstock and Robinson (1952). Information indicated by the authors as being most critical and generally obtainable in the breeding program included: I. Estimates of genotypic covariances, particularly those involving seed production. 2. Unbiased estimates of genotypic variances. 3. Estimates of variance from interactions of genotype with location. 4 . General It was concluded by Johnson (1952) that “The data available to date on forage crop breeding show that testing outcross progenies derived from seed produced either in polycross blocks, by open-pollination in breeding nurseries, or in top-cross blocks provides a useful means of screening non-inbred plants and inbred lines for subsequent study in more detailed tests.” Frandsen (1952) indicated that the polycross test had been effective in Denmark in breeding of grasses, though in some instances 20 replications have been used. Evaluation of spaced plants, determination of what characters to test, and lack of sufficient information for quantitative characters were indicated as special problems. Schaepman (1952) elaborated upon the use of the polycross test in grass breeding. Frandsen (1952) outlined systems of breeding cross-fertilized forage plants in such a manner as to indicate clearly the alternatives in selection and utilization of superior plants. His outline is as follows:

PROGRESS IN GRASS BREEDING

149

Selection of Individuals I. Breeding by deliberate selection of individuals. A . Selection of individuals without progeny test (mass se1.e~tion). B. Selection of individuals based on progeny test (family breeding often combined with mass selection). I . Testing of mother plants. a. After free-pollination (male parents unknown, comparison on u n e q u a 1 basis) b. After top-cross (male parents known, comparison on equal basis) c. After polycross (male parents known, comparison on equal basis) (male parents known, comd. After diallel cross parison on equal basis) 2. Testing of plant pairs. (after controlled crossing, male parents known, comparison on unequal basis) 11. Breeding by natural selection. A. Breeding for improved adaptation by testing local varieties in different places. B. Resistance breeding. 1. By natural infection (frost or other natural influence). 2. By artificial infection (freezing or other artificial influence). Strain Building I. Strain building on the basis of one or more families (lines) multiplied in mixture (synthetics). Market seed later generations than F,. 11. Strain building by crossing for the production of F, market seed. Multiplication of two or more families (lines) separately, by inbreeding and outbreeding. XI. CROSSING TECHNIQUES Crossing techniques with smooth bromegrass were described by Keller (1944). Emasculation and pollination techniques useful in the breeding of perennial cross-pollinated grasses were described by Keller (1952). Efforts have been made to obtain hybrid seed by interpollination of two plants in single-cross combinations. I n such instances mutual pollination or bagging of inflorescences together during the flowering

150 D. C. SMITH period has been practiced as well as paired isolations in the field. Bag switching (Keller, 1952) has been used also. Seed set using such techniques usually has been poor or fair only. Results with smooth bromegrass (unpublished) at Madison, Wisconsin, have indicated that small amounts of seed, sufficient for spaced plant progenies, may be expected from mutual pollination. In field and greenhouse crosses with intermediate wheatgrass (Agropyron intermedium) Heinrichs (1953) obtained 14.0 and 27.3 per cent seed set as compared with open-pollination.

XII. HYBRID VARIETIES Reference was made in Section X,1, to the need for information on synthetic varieties. It is generally accepted that selected plants will be used in initial hybrid combinations by free interpollination and that in succeeding generations of increase the variety would become synthesized and stabilized at an approximate level of behavior, depending upon conditions of culture. Graumann (1952) indicated the need for more information on late generations of synthetic varieties. Synthetic generation data including Syn 4 were cited for alfalfa. Comparisons of 5 two-clone synthetics and 14 multiple-clone synthetics grown for forage resulted in yields of 114, 102, 103, and 103 per cent of the check variety, respectively, for each of the four years based upon two second-year cuttings. Comparable yields for the multiple-clone combination were 110, 109, 105, and 104 per cent. On the basis of the available data it was concluded that 1. Two-clone combinations are more productive than multiple-clone in the first synthetic generation. 2. Forage yields decline with the advance in seed generation, the rate of change during early generations being inversely proportional to the number of parental clones comprising the synthetic. 3. Synthesis appears to be completed by the third or fourth seed generation. 4 . Upon completion of synthesis there is little or no difference in forage yield between the two-clone and multiple-clone combinations. Inclusion of the varying numbers of clones from four to ten in synthetic combinations of orchardgrass did not appear to influence significantly the performances of the recombinations in the Syn 1 or S y n 2 generations (Weiss et al., 1951) . Several first-generation synthetic strains developed by Knowles (1955) on the basis of selection for open-pollination progeny performance produced significantly higher forage and seed yields than commercial check varieties.

PROGRESS IN GRASS BREEDING

151

Results of testing synthetics of bromegrass and timothy at the New York (Cornell) Experiment Station have shown some to be superior in yield to better check varieties. Other workers are utilizing synthetic combinations.

XIII. AGRONOMIC ASPECTS One of the most difficult aspects of grass breeding is the determination of the comparative value of plants and strains in such a manner as to correlate with probable behavior under farm conditions. Burton (1951) and Kramer (1952) presented very good reviews and illustrations of the problems involved. A few selected examples will be cited to illustrate cultural and physiologic studies pertinent to determining plant behavior. Lebsock and Kalton (1954) reported a good agreement to exist in smooth bromegrass between plant performance in spaced-plant nurseries and that in solid stands simulating field conditions. There has been considerable speculation in this matter by breeders and others and few critical studies are available. One of the few reported tests of drought resistance determined artificially was made by Carroll (1943). Twelve pasture grasses were grown as sods in earthenware jars. Half of the samples were “hardened” by exposure to a temperature of 35O to 37O C. for 5 hours on 3 successive days. The relative humidity was 20 per cent during hardening. No watering was done during hardening. Samples were then subjected to 12-, 18-, and 24-hour periods with temperature and humidity as previously. After exposure plants were placed in the greenhouse and watered periodically. Wide differences in species response occurred. It was noted that hardening was helpful in enabling the plants to withstand the drought. In studies with orchardgrass Keller (1954) compared two genotypes previously selected for high and low water requirement, in greenhouse culture varying water, nitrogen, mulch, and depth of container. The yield results indicated that the genotypes varied significantly in yielding ability under the treatments given and interactions of genotypes with water levels and mulches were significant also. It was considered that the best technique on the basis of results obtained would be the use of deep cans (those used were 7 inches in diameter and 20 inches deep), high nitrogen level, and low water level. Differences of timothy seedlings within a variety in ability to resist drought under controlled moisture conditions were observed by Williams (1954). Atwood and MacDonald (1946) studied the heat resistance of individual plants of smooth bromegrass grown under greenhouse conditions. Thirty clones were grown seven weeks at 70°F.,

152

D. C. SMITH

then cut for hay. The temperature was then raised to 80° F. and two crops were taken, after which the temperature was raised to 85O F. and one harvest made. Highly significant differences were observed among plants at the several harvest periods. The use of photoperiod and low temperature as aids in rapid selection and progeny testing was proposed by Cooper (1954). Growth response and behavior and ecological classification would be observed. Genotype-environment interactions in perennial ryegrass were studied by Fejer (1955) using spaced plants in the field. Significant interactions were obtained between frequency of cutting, fertility level, and genotype. In more precise studies of temperature and light effects on selected clones it was found that high temperature increased tiller weight and decreased tiller number. Light effects were less obvious owing possibly to the fact as shown by others that “under certain conditions while light intensity increases tiller number and average tiller weight, high temperature decreases tiller number and increases tiller weight.” A reference was made to unpublished work of Corkill in New Zealand, where significant interactions were found in clonal material of perennial ryegrass at three New Zealand stations at different latitudes. Fejer emphasized also the importance of knowing the relation of nursery spaced plant behavior to that under pasture conditions. Owen (1951) has shown that selection for seed production can be highly effective as evidenced in results with Dallis grass. Variation among strains and plants of smooth bromegrass for seed quality and vigor was studied by Tossell ( 1952). Sixteen varieties, ten polycross progenies, and one hundred open-pollination plants were included. Significant differences were found in all groups for seed weight, rate of emergence, and seedling height and vigor. While vigor and seed weight were associated, significant differences were found among lots of equal seed weight. Among seven adult plant characters recorded only seed yield per plant was correlated with rate of emergence and seedling stand, height, and vigor. It is of interest to note that since Harvey (1939) reported differential responses of corn inbreds and hybrids to ammonia and nitrate nitrogen, little if any additional information is available in this respect for forage plants. XIV. DISEASERESISTANCE Although good general correlations may exist between observations for disease reactions in the field from one season to another, efficiency in screening for disease resistance requires that more certain measures be used. Dependence on natural occurrence of pathogenic organisms in

153

PROGRESS IN GRASS BREEDING

relation to favorable climatic conditions for development of epiphytotics is often impracticable. An example of a favorable interseasonal result of observation for reaction to Pyrenophora bromi on smooth bromegrass is shown in Table VI. Though a good correlation (uncalculated) may exist between the data for the two years, it should be noted that unless few plants are highly susceptible the frequencies of such plants suggest doubt as to whether disease intensity was sufficient for certain classification. Tests for reaction to leaf diseases of smooth bromegrass were made by Carter and Dickson (1952) using 10 plants previously classified as resistant and 10 as susceptible under field conditions. These plants were TABLE VI Reaction' of Smooth Bromegrass (Bromus inermis) Plants to Brown Leaf Spot (Pyrenophora bromi) in the Second and Third Years of Growth at Madison, Wisconsin Second-year reaction 2 3 4 5 Totals: 0

1

Third-year reaction

2

203

3

19 4

4 134

76

30

14

-

1737

' 0 = no disease, 1 = resistant, 6 = highly susceptible.

transferred to a clonal block in the field and artificially inoculated with Pyrenophora bromi in two successive years. The results are presented in Table VII. Although there is some irregularity in the data, the correlation coefficient for the October 1948 and October 1949 results was 0.95. Comparable results were obtained following inoculations in the field with Pseudomonas coronafaciens var. atropurpurea, the bacterial blight organism. However the correlation coefficient for results between years was 0.76, which was highly significant. Results of artificial inoculation trials verified the previous classifications made without artificial inoculation in the field, in most instances. Attempts have been made at Madison, Wisconsin, since 1941 to select plants of smooth bromegrass for resistance to bacterial blight and other diseases. Studies by Fang et al. (1950) concerning the nature of the organism and its hosts illustrate a type of investigation which is

154

D. C. SMITH

helpful to the breeder. Cultures were made from barley, wheat, rye, bromegrass, quackgrass, timothy, and Sudan grass. In artificial inoculations five special forms were differentiated, though cultures from different hosts were partially cross-pathogenic.The five forms arranged themselves into four serological types based upon cross agglutination and agglutinin absorption tests. XV. NUTRITIVE VALUE

Summaries of known available literature on breeding for quality in forage plants were given by Sullivan and Garber (1947) and Smith (1952). Recent pertinent studies will be referred to briefly. TABLE VII Disease Indices' for Lines of Smooth Bromegrass Inoculated with Pyrenophora bromi in the Field' Resistant clones

Susceptible clones

No.

19488

1

5.3 2.6 2.0 5.4 2.4 1.8 2.8 1.8

2

3 4 5 6 7 8 9 10 Mean

2.8

2.5 3.0

194Q4 6.8 5.7 5.0 4.9 4.3 5.8 5.4 4.0 4.0 4.3 4.8

6.8 5.3 3.9 4.2 2.9 3.3 4.2 3.5 4.0 3.5 4.2

Mean

No.

19486

6.8 5.3 3.9 4.2 2.9 3.3 4.2 3.5 4.0 3.5 4.2

11 12 13 14 15 16 17 18 19

1.0 1.0 1.3 1.1 1.1

20

Mean

1.2

1.0 1.2 1.0 1.1 1.1

1949' 1.0 1.9 3.3 2.3 1.8 2.0 1.7 3.0 1.9 2.3 2.2

1.8 1.3 2.6 1.8 1.3 1.6 1.2 2.0 1.4 1.7 1.6

Mean 1.4 1.4 2.4 1.7 1.4 1.6 1.5 2.1 1.4 1.7

f Average of 1% observations. *Carter and Dickson, 1960. 8 Data obtained Oct. 9. 4 Data obtained July 8 and October 14.

Levels of protein and carotene content were determined by Pickett (1950) among unrelated first-generation inbred families of smooth bromegrass. Highly significant differences between and within families for protein and carotene content were found for each of the two seasons in which studies were made. Exemplary data are shown in Tables VIII and IX. There was a high correlation between years for individual plants. Carotene and protein content were positively correlated and darker green color accompanied higher protein analysis. Protein content was found to be negatively associated with yield in intermediate wheatgrass in studies by Heinrichs (1953). Phillips et al. (1954) found that some early-maturing species were

155

PROGRESS I N GRASS BREEDING

higher in protein than late-maturing ones when harvested at the same growth stage. Sullivan and Routley (1955) determined that early and late plants of orchardgrass varied in percentage of protein, early types being favored. No significant differences were found in timothy or Reed canary grass (Phalaris arundinacea) when comparisons were made similarly. TABLE VIII Analyses of Carotene Contents of Inbred Families of Smooth Bromegrass Harvested at the Early-Pasture Stage of the Third Year of Growth* * Inbred family

Carotene content, family mean in p.p.m.

4 7 20 30

Between plants F value 6.51* 13.95** 3.39 17.126**

203 133

164 340

1 Pickett, 1860. *Exceeds the 0.06 level of significance. Exceeds the 0.01 level of significance.

**

TABLE IX Analyses of Crude Protein Contents of Selected Inbred Families of Smooth Bromegrass Harvested at the Early-Pasture Stage of the Second Year of Growth'

1

Jnbred family

Range of clonal means, %

Family means, %

F value between plants

4 11 15 20 25

49.04-38.1212 !25.80-30.73 46.4S129.44 31.74-36.00 98.82-35.37

31.53 28.SO 127.80 33.97 31.47

10.912** 9.04** 2.07 4.20* !22.89**

Pickett, 1950.

* Exceeds the 0.06 level of significance.

** Exceeds the 0.01 level of significance. An illustration of the striking differences present in palatability of grass strains was reported by Burton (1947), following studies of Bermuda grass strains. Nine strains were planted clonally in duplicate plots 30 X 60 feet in size and subsequently were grazed by Jersey cattle. The results are shown in Table X. The differences in palatability were not associated with several chemical characters studied or with observable morphological differences of the strains in question. Unpublished work was cited by Burton (1951) indicating almost a 100 per cent increase in cattle weight gains when pastured on Pensacola as compared with Paraguay Bahia grass, although yields and chemical

156

D. C. SMITH TABLE X The Comparative Palatability of Nine Strains of Bermuda Grass Grown in Duplicate Pasture Plots'

Strains Common Coastal 3 1s 36 60 85 99 107 1

Average percentage of the total cow hours spent on each strain in two years 9.1 14.9 13.8 14.1 7.8 6.8 8.1 14.3 11.0

Rating August 14 on the amount of grass left after a period of continuous grazing2 Rep. 1

Rep. 2

Avg.

5.0 1.o 4.5 1.0 3.5 5.0 3.0

5.0 1.5 5.0 1.0 4.0 5.0 3.0 e.0 4.0

5.0 1.3 4.8 1.0 3.8 5.0 3.0

2.0 3.5

2.0 3.8

Burton, 1947. Plots rated 1 were grazed closely; those rated 6 were grazed very little.

analyses were quite similar. The difference was ascribed to differential palatability. MAINTENANCE XVI. VARIETY The effects of region of seed production on performance of RANGER alfalfa are of interest in relation to forage variety adaptation. Variations in seed lots of the RANGER variety were first noted at Madison, Wisconsin, in 1945. When plants in the field were cut in early September Smith and Graber (1950) noted variations in proportions of tallgrowing plants in the later fall, this being related to latitudinal location of parental seed production. Subsequent studies by Smith (1955) showed that RANGER alfalfa grown for one generation of increase in southern latitudes showed more tall plants following early fall cutting than identical seed stocks grown comparably in a northern latitude. Tall plants were found to be less winter-hardy. It was suggested that environmental influences, perhaps associated with latitude, were having a selective effect upon seed production of various plant types within the RANGER variety. Beard and Hollowell (1952) discussed the effect on performance, of growing seed of forage varieties outside of the area of adaptation. This has been an especially serious problem with red clover and alfalfa, as previously illustrated. Although there is little information as to the effects on grass varieties so grown, it seems probable that changes may occur that are not always favorable. The reasons given for producing

157

PROGRESS IN GRASS BREEDING

seed in distant areas are more rapid and dependable seed production and more certain control of supply because of relatively sure production. In production of seed outside of the area of adaptation a program has been developed on a state and national basis to safeguard varietal characteristics and to increase efficiency in getting superior varieties into use. Preservation of varietal identity includes emphasis on the following points as listed by Beard and Hollowell. TABLE XI Frequency Distributions of Yields of Different Lots of Tennessee AnthracnoseResistant Red Clover Seed Grown in Oregon for Different Generations When Tested at Three Locations in the East Central States, 1928-1938' Lots in each yield class of Tennessee anthracnose-resistant seed grown in Oregon for indicated generations Yield class per cent2

1

110-100 100-90 90-80 80-70

1 3

6

6

3 4

9

1

1

1

1 1

1

1

1

3 3 1 3 9

9

4

3

3

3

8

4

Total lots Lots yielding significantly less than check at 5 % level 1

3

4

4 4

3 4

7 3

1 1

70-60

60-50

3

1

3

9

9

Beard and Hollowell, 1953.

' Forage yields of Tennessee Anthracnose-resistant seed grown in Tennessee equals 100 per cent. 1. Periodic return to foundation stock seed of a variety for establishing new seed production fields outside the area of its adaptation for forage to minimize genetic changes that may occur in successive seed generations. 2. Effect of cross-pollination from adjacent fields of other varieties. 3. Disappearance of plants with increasing age of stand. 4. Control of volunteer stands arising from shattered seed. 5. Availability of production fields free from old plants of other varieties. 6. Differential seed-producing capacity of plants within the variety. It should be noted also that research in determining effects of environment on varietal changes has been in progress. In this respect * notesome of the results with red clover are of interest (Table XI). It is worthy that seed lots grown in Oregon for successive generations de-

158 D. C. SMITH teriorated progressively when tested in Tennessee in comparison with locally grown seed. XVII. DISCUSSION Many fruitful areas in grass breeding remain to be more adequately explored. Although the tempo of investigations has been greatly accelerated in recent years, progress in solving technical problems has been necessarily slow. The large number and diversity of perennial forage grasses has resulted in extended scope and reduced intensity of research effort. Technically, appreciable progress has been made. Efforts have been increased to obtain and evaluate both exotic and endemic strains of grasses. Much remains to be learned of cytotaxonomy and the relations of species and genera in hybridization. The value and importance of induced polyploidy in forage plant breeding were reviewed by Love (1952). It was considered that the principal advance in polyploidy knowledge of the previous decade had been “clarification of types of polyploids.” Induction of somatic reduction and segregation was mentioned as a possible new approach to increasing variability. Hybrids otherwise unavailable may be obtained and propagated by embryo cultural methods. The possibilities of using radiation for induction of mutational and other changes in forage grasses are relatively unexplored. Results in Sweden of studies by Julen (1954) are of interest in this respect. In X-ray treatment of dry seeds of Kentucky bluegrass the percentages of aberrant plants were increased from 2.0 in the control to 14.1 when irradiated with 20,000 to 25,000 r units. Some of the aberrants were chimeral. Affected sectors could be cloned and propagated. Most of the new types were smaller than normal plants and only one appeared to be equal to the parent clone in vigor. Chimera frequencies were increased from 0.1 per cent in the control to 8.3 per cent in that given 20,000 to 25,000 r units. The X-ray treatments did not affect chromosome number and effect of treatment was not related to chromosome number. Though related in principle to those for corn, grass breeding methods are being subjected to exploration and modification. The practical value of inbreeding remains unestablished. Recent studies with corn by Robinson et al. (1955) are of interest. Genetic variances were determined for eight quantitative characters in three open-pollinated varieties of corn. Additive genetic variance was found to be surprisingly high in proportion to dominance variance. The writers suggested that selection in such populations should be effective, contrary to the general experience of corn breeders. This may have some application to selection in grasses.

PROGRESS I N GRASS BREEDING

159

Combining ability has received much attention during the past decade. The polycross and other types of parent-progeny tests have been used as a basis of selection, for yield particularly. In writing of methods of evaluating breeding behavior of forage plants Murphy (1952) stated “It seems that at an advanced stage in the breeding program, the differences among the parents in yield of forage become of less practical significance and that the final selection of the parents for inclusion in an experimental variety will be determined primarily by such characteristics as disease resistance, insect resistance, quality, maturity, growth habit and others.” Available experimental data indicate that differences among grass varieties in forage production and quality may be small, particularly when the grasses are grown with legumes. This has held for such important species as timothy, smooth bromegrass, and orchardgrass. It would appear, however, that yield of forage will continue to receive prominent consideration. Estimation of heritability for such characters may be helpful. Recombination of selected plants or lines to constitute synthetic varieties has been based upon insufficient information and experience. Additional data are needed concerning genetic stability and modification of synthetic variety behavior under different conditions of propagation in successive generations. Effects of area and manner of seed production in relation to forage character are of interest similarly. The relatively few investigations reported in the literature concerning chemical analysis have been relatively encouraging to the possibility of improvement of nutritive value. Little has been done on the latter aspect. Results of disease and insect resistance studies of forage grasses have suggested that major improvements may be made in varietal composition, particularly in the former case. Little is known concerning insect resistance. Agronomic problems are numerous and involve ecology, physiology, plant nutrition, and other aspects. Future improvements in strains of grasses may depend to a large degree on the development of more highly correlated results of early nursery or greenhouse trials and behavior under farm conditions. REFERENCES Adam, M. W.1953. Botan. Gaz. 1 15,95-105. Akerberg, E., and Bingefors, S. 1953. Hereditas 39, 125-136. Akerman, A., Tedin, O., Froier, K., and Whyte, R. 0.1948. “Svalof 1886-1946.” Bloms Boktryckeri A-B, Lund. Armstrong, J. M., and White, W. J. 1952. Proc. 6th Intern. Grasslands Congr. 1, 222-227. Atwood, S . S. 1947. Advances in Genet. 1 , 1-67.

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Atwood, S. S., and MacDonald, H. A. 1946. J. Am. SOC.Agron. 38, 824-832. Barnett, F. L. 1955. Agron. J. 47. 88-91. Beard, D. F., and Hollowell, E. A. 1952. Proc. 6th Intern. Grasslands Congr. 1, 860-866. Beaudry, J. R. 1951. Genetics 36, 109-133. Beddows, A. B. 1931. Welsh Plant Breeding Sta. Bull. Ser. H. No. 12, 5-99. Bjorkman, S. 0. 1954. Hereditas 40, 254-258. Bosemark, N. 0. 1954. Hereditas 40, 347-376. Boyle, W. S., and Holmgren, A. H. 1955. Genetics 40, 539-545. Burton, G. W. 1947. I . Am. SOC.Agron. 39,551-569. Burton, G. W. 1951. Aduances in Agron. 3, 197-241. Burton, G. W. 1952. Proc. 6th Intern. Grasslands Congr. 1,277-283. Burton, G. W. 1955. Agron. J . 47, 311-313. Carroll, J. C. 1943. I . Am. SOC.Agron. 35, 77-79. Carter, J. F., and Dickson, J. G. 1952. Agron. J . 44, 119-125. Church, G. L. 1954. Rhodora 56, 185-197. Clausen, J. 1952. Proc. 6th Intern. Grasslands Congr. 1, 216-221. Comstock, R. E., and Robinson, H. F. 1952. Proc. 6th Intern. Grasslands Congr. 1, 284-29 1. Cooper, J. P. 1954. Repts. and Communs. 8th Intern. Botan. Congr. pp. 356359. Cornelius, D. R. 1947. J. Agr. Research 74, 133-143. Crowder, L. V. 1953.1. Heredity 44, 195-203. Dale, T., and Brown, G. F. 1955. U . S. Dept. Agr. Farmers Bull. No. 2080. Davis, W. E. 1953. British Agr. Bull. 5, 313-315. Elliott, F. C. 1949a. Euolution 3, 142-149. Elliott, F. C. 1949b. Agron. J . 41, 298-303. Elliott, F. C., and Love, R. M. 1948. J . Am. SOC.Agron. 40, 335-341. Elliott, F. C., and Wilsie, C. P. 1948. J. Heredity 39, 376-380. Fang, C. T., Allen, 0. N., Riker, A. J., and Dickson, J. G. 1950. Phytopathology 40, 44-64. Fejer, S. 0. 1955. Nature 175, 944-945. Frandsen, K. J. 1952. Proc. 6th Intern. Grasslands Congr. 1, 306313. Gorman, L. W. 1950. N e w Zealand I . Sci. and Technol. 32, 1-15. Graumann, H. 0. 1952. Proc. 6th Intern. Grasslands Congr. 1, 314-319. Gregor, J. W., and Watson, P. J. 1954. N e w Phytologist 53, 291-300. Griffiths, D. J. 1950. I . Agr. Sci. 40, 19-38. Griin, P. 1955. Am. J. Botany 42, 11-18. Hafenrichter, A. L., and Stoez, A. D. 1948. U.S. Dept. Agr. Yearbook, pp. 354-356. Harlan, J. R. 1945. Am. J . Botany 32, 66-72. Harlan, J. R. 1951. Am. Naturalist 85, 97-103. Harlan, J. R. 1954. Oklahoma Agr. Expt. Sta. Bull. No. 0444. Harlan, J. R., Snyder, L. A., and Celarier, R. P. 1952. Proc. 6th Intern. Grasslands Congr. 1, 228-232. Harvey, P. H. 1939. Genetics 24,437461. Hawk, V . B., and Wilsie, C. P. 1952. Agron. J . 44, 112-118. Hayes, H. K., and Schmid, A. R. 1943. J. Am. SOC.Agron. 35, 934-943. Hayes, H. K., Immer, F. R., and Smith, D. C. 1955. “Methods of Plant Breeding,” pp. 347-391. McGraw-Hill, New York. Heinrichs, D. H. 1953. Can. J. Agr. Sci. 33, 470493. Hill, H. D., and Myers, W. M. 1948. J. Am. Soc. Agron. 40,466469. Hittle, C. N. 1954. Agron. J. 46, 521-523.

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Hoover, M. M., Hein, M. A., Dayton, W. A., and Erlanson, C. 0. 1948. U. S. Dept. Agr. Yearbook. pp. 639-700. Hughes, R. 1953. J . Agr. SOC.Uniu. Coll. Wales 34, 1-4. Jenkin, T. J. 1955a. 1. Genet. 53, 81-93. Jenkin, T. J. 1955b. J. Genet. 53, 125-130. Johnson, B. L. 1945. Am. J. Botany 32, 599-608. Johnson, I. J. 1952. Proc. 6th Intern. Grasslands Congr. 1, 327-334. Jones, K. 1954. Repts. and Communs. 8th Intern. Botan. Congr., pp. 75-77. Jiihl, H. 1953. Chem. Ber. 55, 331-338. Julen, G. 1947. J. Brit. Grasslands SOC.2, 57-62. Julen, G. 1954. Acta Agr. Scand. 4, 584-593. Juhl-Noodt, H. 1955. Zuchter 25,8046. Kalton, R. R., and Leffel, R. C. 1955. Agron. J. 47, 370-373. Kalton, R. R., Leffel, R. C. Wassorn, C. E., and Weiss, M. G. 1955. Iowa State Coll. 1. Sci. 29, 631-657. Keller, W. 1944. J. Heredity 35, 49-56. Keller, W. 1948. U . S. Dept. Agr. Yearbook, pp. 347-351. Keller, W. 1952. Proc. 6th Intern. Grasslands Congr. 2, 1613-1619. Keller, W. 1954. Agron. I. 46, 495499. Kneebone, W. R. 1951. University of Minnesota Ph.D. thesis. Unpublished. Knobloch, I. W. 1943. Bull. Torrey Botan. Club 70, 467472. Knowles, R. P. 1955. Agron. J. 47, 15-19. Knowles, R. P., and White, W. J. 1949. Sci. Agr. 29, 437-450. Kramer, H. H. 1952. Proc. 6th Intern. Grasslands Congr. 1, 341-346. Lebsock, K. L., and Kalton, R. R. 1954. Agron. J. 46, 463-467. Leffel, R. C. Kalton, R. R., and Wassom, C. E. 1954. Agron. I. 46, 370-374. Love, R. M. 1947. J. Am. SOC.Agron. 39. 41-46. Love, R. M. 1952. Proc. 6ih Intern. Grasslands Congr. 1, 292-298. Love, R. M. 1954. Am. J. Botany41, 107-110. Love, A. 1952. Hereditas 38, 11-32. Lowe, C. C., and Murphy, R. P. 1955. Agron. J. 47,221-223. Muntzing, A. 1954. Hereditas 40, 459-516. Murphy, R. P. 1952. Proc. 6th Intern. Grasslands Congr. 1, 320-326. Musser, H. B., Burton, G. W., and Schoth, H. A. 1948. U.S. Dept. Agr. Yearbook, pp. 354-356. Myers, W. M. 1947. Botan. Revs. 13, 319-421. Myers, W. M., and Hill, H. D. 1943. Genetics 28, 383-397. Myers, W. M., and H l l , H. D. 1947. Bull. Torrey Botan. Club 74, 99-111. Nielsen, E. L. 1944. J. Agr. Research 69, 327-353. Nielsen, E. L. 1947. Am. J. Botany 34, 431-433. Nielsen, E. L. 1951. Botan. Gaz. 113, 23-54. Nielsen, E. L. 1952. Proc. 6th Intern. Grasslands Congr. 1, 233-239. Nielsen, E. L., and Rogler, G. A. 1952. Am. J. Botany 39, 343-348. Nilsson, F. 1934. Hereditas 19, 1-162. Nordenskiold, H. 1949. Hereditas 35, 190-202. Nordenskiold, H. 1953. Hereditas 39,469-488. Nygren, A. 1954. Hereditas 40, 377-397. Olderneyer, D. L., and Hanson, A. A. 1955. Agron. J. 47, 158-162. Owen, C. R. 1951. Louisiana Agr. Expt. Sta. Bull. No. 449. Phillips, T. G., Sullivan, J. T., Loughlin, M. E., and Sprague, V. G. 1954. Agron. 1. 46, 361-369.

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Pickett, R. C. 1950. Agron. J. 42,550-554. Robinson, H. F., Comstock, R. E., and Harvey, P. H. 1955. Genetics 40,45-60. Schaepman, H. 1952. Euphytica 1, 105-111. Smith, D.1955. Agron. J. 47,201-205. Smith, D.,and Graber, L. F. 1950. Wisconsin Agr. Expt. Sta. Research Bull. No. 171. Smith, D.C. 19M.J. Agr. Research 68, 79-95. Smith, D.C. 1948. U.S. Dept. Agr. Yearbook, pp. 331-341. Smith, D. C. 1952. Proc. 6th Intern. Grasslands Congr. 2, 1597-1606. Snyder, L. A. 1951. Am. J . Botany 38, 195-202. Sorensen, E.L. 1955. University of Wisconsin Ph.D. thesis. Unpublished. Stebbins, G. L. 1949. Proc. 8th Intern. Congr. Genet. Stockholm, pp. 461485. Stebbins, G. L. 1952.Proc. 6th Intern. Grasslands Congr. 1, 247-253. Stebbins, G. L. 1955. Science 121, 625. Stebbins, G.L.,and Vaarama, A. 1953.Genetics 39,378395. Stuckey, I . H.,and Banfield, W. G. 1946.Am. J . Botany 33, 185-190,. Sullivan, J. T., and Garber, R. J. 1947. Pennsylvania Agr. Expt. Sta. Bull. NO. 489. Sullivan, J. T., and Routley, D. J. 1955. Agron. J . 47,206-207. Thomas, H. L.,and Kornkamp, M. F. 1954. Agron. J . 46,553-556. Tossell, W. L. 1952.University of Wisconsin Ph.D. thesis. Unpublished. Tsiang, Y. S. 19M.J . Am. Soc. Agron. 36,508-522. Weiss, M. G.,Taylor, L. H., and Johnson, I. J. 1951. Agron. J. 43,594-602. Wexelsen, H.1952. Proc. 6th Intern. Grasslands Congr. 1,299-305. Williams, S. S. 1954. J . Ecol. 42, 445-459. Wilsie, C. P.,Ching, C. B., and Hawk, V. B. 1952.Agron. J . 44, 605-609. Wit, F. 1952.Euphytica 1, 95-104. Zimmerman, K. 1954. Zuchter 24,33-39.

Molybdenum as a Fertilizer A. J. ANDERSON Commonwealth Scientific and Industrial Research Organization, Canberra. A C T . , Australia Page I . Introduction . . . . . . . . . . . . . . . . . . . 1% I1 The Field Occurrence of Molybdenum Deficiency . . . . . . . .166 I. For Nitrogen Fixation . . . . . . . . . . . . . . 166 a Herbage Legumes . . . . . . . . . . . . . . 166 b. Other Legumes . . . . . . . . . . . . . . . 169 c. Nonlegumes. . . . . . . . . . . . . . . . 169 2. For Metabolism in the Plant . . . . . . . . . . . . 170 a.Legumes. . . . . . . . . . . . . . . . . 170 b Nonlegumes . . . . . . . . . . . . . . . . 171 3 . F o r Animals . . . . . . . . . . . . . . . . . 172 111. The Nature and Detection of Molybdenum Deficiencies . . . . . . 173 I Compound Deficiencies . . . . . . . . . . . . . . 173 2 Visual Symptoms . . . . . . . . . . . . . . . . 174 3. Chemical Composition of the Plant . . . . . . . . . . . 177 a. Molybdenum Content . . . . . . . . . . . . . 177 b . Protein and Nonprotein Contents . . . . . . . . . 179 c. Ascorbic Acid, Dehydrogenase. and Phosphatase Contenta . . 180 4. Molybdenum Content of the Soils . . . . . . . . . . 181 IV The Correction of Molybdenum Deficiency . . . . . . . . . 182 I. Method of Application . . . . . . . . . . . . . . 182 2. Form of Molybdenum . . . . . . . . . . . . . . 182 3. Amount of Molybdenum . . . . . . . . . . . . . . 182 4. Frequency of Application . . . . . . . . . . . . . 184 V. Factors Affecting the Response to Molybdenum . . . . . . . . 184 I Deficiencies of Phosphorus. Sulfur. and Other Essential Elements . . 185 2. Nitrogenous Fertilizers . . . . . . . . . . . . . . 187 3.Lime . . . . . . . . . . . . . . . . . . . 189 a. Through Effects on Availability of Molybdenum . . . . . 189 b . Through Effects on Legume Nodulation . . . . . . . . 192 c. Through Effects on Other Elements . . . . . . . . . 193 4. Sulfur. Manganese. Iron. and Other Elements Which May Decrease the Uptake of Molybdenum . . . . . . . . . . . . . 194 5 . Vanadium and Other Elements That Have Been Reported to Replace Molybdenum . . . . . . . . . . . . . . . . . 195 6. Molybdenum Present in Commercial Fertilizers . . . . . . . 196 7. Cultural Practices . . . . . . . . . . . . . . . . 196 8. Differences between Species . . . . . . . . . . . . . 197 Referaces . . . . . . . . . . . . . . . . . . . 199 163

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I. INTRODUCTION Just a quarter of a century has passed since Bortels in 1930 reported the first growth responses of a living organism to molybdenum. Over those 25 years research workers have transformed molybdenum from an element of no known biological significance to a fertilizer of widespread importance. In some areas spectacular increases in pasture and crop growth have been obtained with molybdenum and every year new areas that can benefit from molybdenum are being found. Bortels (1930). found that the aerobic nitrogen-fixing bacterium Azotobacter responded to molybdenum. This discovery resulted from experiments done by him to determine the reason why soil extracts increased the amount of nitrogen fixed by Azotobacter cultures. Molybdenum was included in the test because it is used as a catalyst in the commercial production of ammonia. Over the first 10 to 15 years following Bortels’ discovery, the biological importance of molybdenum for many plant species became established. Responses of Azotobacter to molybdenum were soon confirmed by Birsch-Hirschfeld (1932), Bortels (1933, 1936), and Burk ( 1934). Steinberg ( 1936, 1937, 1939) showed that Aspergillus, which does not fix nitrogen, also responds to molybdenum. Bortels (1936) reported responses of Azotobacter to molybdenum when nitrate nitrogen was used as the source of nitrogen as well as when this organism was fixing nitrogen, and also obtained responses of Clostridium to molybdenum. Beneficial effects of molybdenum were also reported for soya bean and alfalfa (Bortels, 1937), for red clover (Bortels, 1937; Dmitriev, 1939), for peas (Obraztzova et al., 1937; Bobko and Savvina, 1940), and for lupins (Obraztzova et al., 1937). These higher plants were grown in soil for the experiments and the responses appear to have been of doubtful significance. Arnon and Stout (1939) reported clear-cut responses of tomato plants to molybdenum in water culture. The molybdenum-deficient tomato plants developed mottling of the leaves and involution of the lamineae, showing that some specific metabolic processes in the plant had been affected by the deficiency. In 1940 and 1941 deficiency of molybdenum was shown to induce specific symptoms in oats (Piper, 1940), in lettuce and white mustard (Arnon, 1940), and in plum seedlings (Hoagland, 1941), and was also shown to be an essential element for the blue-green algae Anabaena and Nostoc (Bortels, 1940). In Australia Anderson ( 1942) reported marked responses of subterranean clover (Trifolium subtenaneum) and alfalfa (Medicago sativa) to molybdenum. The commercial use of molybdenum on nearby deficient pastures followed almost immediately. The first use of

165 molybdenum as a fertilizer on a commercial scale was in the spring of 1942 on the property of Mr. Don V. Chapman, “Highercombe,” Houghton, South Australia, and in the autumn of the following year on the property of the late Mr. Norman Brookman, “Burbrook,” Meadows, South Australia. Mr. Brookman and Mr. Chapman had both cooperated wholeheartedly in the experiments on their properties and had provided many of the facilities necessary for the conduct of the field experiments. Over the last 10 to 15 years molybdenum has taken an important place in the list of elements essential for plant growth. In that period the expansion of the use of molybdenum as a fertilizer has occurred. MOLYBDENUM AS A FERTILIZER

FIG. 1. Showing a response of subterranean clover to 2 ounces of molybdenum trioxide per acre on land in southeastern Australia that had failed to respond to pasture improvement because of molybdenum deficiency. On all plots the clover was s o w n with superphosphate, but normal growth occurred only where molybdenum was also applied.

The importance of molybdenum for nitrogen fixation and for nitrate reduction has become established. For many soils, effects of lime and other alkaline materials can now be explained in terms of their effect on the availability of molybdenum. A number of plant diseases, such as “whiptail” of cauliflower and “yellow spot” of citrus, which had baffled pathologists, are now known to be due to molybdenum deficiency. Discoveries of molybdenum-deficient areas have explained some of the past failures of crops and pasture. In places, particularly in Australia and New Zealand, discoveries of molybdenum deficiency have made possible the agricultural development of extensive areas of land which had previously been neglected. These transformations can be achieved usually with as little as 1 or 2 ounces of molybdenum per acre (Fig. 1). The research with molybdenum on pastures in New Zealand and Australia has recently been reviewed by Davies (1952) and Anderson

166 A. J. ANDERSON (1956b). The role of molybdenum in legumes and nonlegumes has been reviewed by Hoagland ( 1945), Hewitt ( 1951) , Purvis (1955), and Anderson (1956a). The present paper deals with the general aspects of the use of molybdenum as a fertilizer.

11. THEFIELD OCCURRENCE OF MOLYBDENUM DEFICIENCY It is important to realize that in areas where there is a potential deficiency of an element, but where the deficiency has not been recognized, responses to the element may not be obtained when the effect of the element is tested only on crops and pasture normally grown in the area. These particular crops are grown because they have been tested and found successful. Marked benefit might well be obtained, for example, with molybdenum, in such areas on crops which are not being grown because they have not been successful. In Australia there are areas where clover had failed completely in the past, and where responses to molybdenum can be obtained only when clover is sown. It is clear that when this factor is taken fully into account by testing molybdenum on crops and pasture not normally grown in an area, many new areas of molybdenum deficiency will be found. I . For Nitrogen Fixation Molybdenum is needed generally by microorganisms that fix nitrogen. By increasing the amount of nitrogen fixed, particularly in symbiotic nitrogen fixation, molybdenum can wholly or partly correct nitrogen deficiency. On the other hand, molybdenum is also needed generally for metabolism in the plant. This section deals with responses to molybdenum which appear to be mainly due to the effect of molybdenum in correcting nitrogen deficiency. a. Herbage Legumes. Many of the field responses to molybdenum that have been obtained with herbage legumes have been due to the effect of molybdenum on symbiotic nitrogen fixation (Anderson and Thomas, 1946; Anderson, 1956a). Molybdenum is needed generally for metabolism in plants, but frequently the small amount of molybdenum that the herbage legumes do obtain from deficient soils is sufficient for metabolism in the host legume. This is because less molybdenum is needed for general metabolism in the legume than for symbiotic nitrogen fixation. Where molybdenum is deficient for nitrogen fixation but not for metabolism in the host plant, a deficiency of nitrogen is induced. The responses of herbage legumes to molybdenum where combined nitrogen fertilizer has not been used are considered in this section. The responses of clover to molybdenum reported by Anderson (1942) were obtained without lime on an ironstone soil where responses to lime were known to occur. This was consistent with evidence ob-

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tained by Ferguson, Lewis, and Watson (1940)that pastures containing toxic amounts of molybdenum for stock occw on neutral to alkaline soils, but not on acid soils with an equally high molybdenum content. It had been thought that the lime counteracted the fixation of phosphate in the soil, because responses to superphosphate were much greater in the presence than in the absence of lime. This explanation became suspect when it was found (Anderson, 1946) that oats responded to phosphate but not to lime, and that the phosphorus content of stunted clover plants receiving only superphosphate was considerably higher than the phosphorus content of well-developed plants treated with wood ash. It seemed more probable therefore that the positive interaction between the lime and phosphate-that is, the effect of lime in increasing the response to phosphate-was due to the fact that the lime and the phosphate corrected different deficiencies. There was also evidence that this unknown element occurred in wood ash but not in lime, as it had also been noted (Anderson, 1946) that on another property, at Houghton where an apparently identical problem occurred, the clover plants responded to wood ash but not to lime. A search for the element concerned in the effects of lime and wood ash resulted in responses to molybdenum (Anderson, 1942). Many of the early field responses to molybdenum were obtained on liie-responsive soils or in areas where effects of wood ash had been noted. Others were obtained by testing molybdenum in areas where clover had failed or where it showed evidence of nitrogen deficiency. Ferres and Trumble (1943)obtained responses of subterranean clover to molybdenum on a wide range of soils in South Australia. Also, in South Australia a wide range of herbage legumes responded to molybdenum (Anderson, 1946; Anderson and Thomas, 1946). Stephens and Oertel ( 1943) and Fricke ( 1943) reported responses of subterranean clover to molybdenum on a lime-responsive ironstone soil in Tasmania. Responses to molybdenum in Tasmania were obtained by Fricke ( 19M) with white clover and red clover. In Western Australia responses of clover to molybdenum were obtained by Teakle (1944) and Rossiter

(1952). On the acid soils of the Tablelands of eastern Australia, effects of molybdenum have been obtained on the Southern Tablelands of New South Wales and in the Australian Capital Territory, on alfalfa (Shaw, Barrie, and Kipps, 19&), on subterranean clover grown on basaltic soils (Parbery, 1946), and on granitic and sedimentary soils (Anderson, 1948; Anderson and Spencer, 1950a; McLachlan, 1955). Responses of herbage legumes to molybdenum have now been found on or near the Eastern Tablelands in Victoria (Newman, 1955) and through New South Wales north into Queensland (McLachlan, 1955; Weir, Hart-

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ridge and Fawcett, 1955;von Stieglitz and Chippendale, 1955); on the adjoining coastal soils (Anderson and k n o t , 1953;Strang, 1954); and on the western plains (Andrew and Milligan, 1954). McLachlan (1953)has reported the occurrence of molybdenum deficiency also in some acid soils from the Northern Territory. In South Australia (Anderson and Thomas, 1946),in New South Wales (Anderson and Spencer, 1949,1950a),and in Western Australia (Rossiter, 1952) the effect of molybdenum on the herbage legumes was examined and shown to result from an increase in symbiotic nitrogen fixation. Australian work so far indicates that deficiency of molybdenum occurs in a wide variety of soils scattered mainly throughout eastern and southeastern Australia. McLachlan ( 1955) compared the effects of molybdenum on a wide range of soils in eastern Australia and concluded that the response was influenced most by deficiencies of phosphorus and sulfur. This is discussed later under Section V, 1. The other significant correlation with molybdenum response obtained by McLachlan was the tendency for greater responses to occur in the more acid soils. As pointed out later in this article under Section V, 3 soil acidity may decrease or increase the effect of molybdenum, depending upon conditions. Responses of herbage legumes to molybdenum in New Zealand were found first on an ironstone soil in the North Island at North Auckland (Davies, 1952).Later, responses were obtained in Otago in the South Island (Davies, Holmes, and Lynch, 1951; Lobb, 1952, 1953; Cullen, 1954).Molybdenum deficiency is now known to occur over a wide area of both the North and South Islands in New Zealand (Davies, 1952). In places considerable areas of third-class land have been transformed to first-class land by the use of molybdenum. Lobb (1953) has described the remarkable responses that have been obtained with molybdenum in North Otago, New Zealand, on pasture and also on other plants. The experiments of Walker, Adams, and Orchiston (1955a)indicate that on New Zealand soils the effect of molybdenum on herbage legumes is to correct nitrogen deficiency. The importance of molybdenum on herbage legumes in Australia and New Zealand has recently been discussed by Kline (1954). Responses of herbage legumes to molybdenum have now been found on alfalfa in New Jersey (Evans and Purvis, 1951), on alfalfa in Hawaii (Younge and Takahashi, 1953), on white clover in Ireland (Walsh, Neenan, and @Moore, 1952), and on a number of herbage legumes in Holland (Mulder, 1954).The responses obtained by Younge and Takahashi (1953)were on a soil with a very high manganese content. Walsh, Neenan, and OMoore (1952) found responses on acid organic as well as mineral soils.

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b. Other Legumes. Responses of peas to molybdenum through effects on symbiotic nitrogen fixation have been reported in Australia by Wade (1952) and Crofts (1954) and in New Zealand by Blomfield ( 1954). The molybdenum-treated pea plants were larger and greener and had larger nodules. Blomfield (1954)noted that the large nodules on the healthy treated plants were pink in color compared with the gray color of nodules on the deficient plants, as occurs when molybdenum stimulates symbiotic nitrogen fixation. It is interesting that there have been so few recorded responses of legumes other than herbage legumes to molybdenum. There are several possible reasons for this. Often these other legumes, such as peas, beans, and other pulses, are grown in market garden soils with sufficient nitrogen applied for the requirements of the plants. This would not always apply, for example, where the legumes are grown as a green manure crop. Many of these plants have large seed, which may contain ample molybdenum for the full growth of the plant and for seed production (Meagher, Johnson, and Stout, 1952).This also cannot alone explain why molybdenum deficiency has seldom been found to induce nitrogen deficiency in legumes other than herbage legumes. Deficiency of molybdenum for the host legume, which has an even lower requirement than for symbiotic nitrogen fixation, has been reported for beans and for peas in Australia (Wilson, 1949a; Drake and Kehoe, 1954). A factor possibly of greater importance is that special attention often is not paid to the nodulation of legumes. Perhaps absence of response to molybdenum has in many cases resulted from ineffective nodulation of the legume. c. Nonlegumes. The early work of Bortels (1930,1936) and others clearly demonstrated the effects of molybdenum on Azotobacter. Other free-living nitrogen-fixing organisms such as Clostridium (Bortels, 1936; Jensen and Spencer, 1947) and the blue-green algae Anabaena and Nostoc (Bortels, 1940) also respond to molybdenum. In fact the evidence indicates that molybdenum is needed generally by all organisms, and that deficiency of molybdenum may well influence nitrification and other nitrogen transformations in soils. Lobb (1953) has observed that grasses in mixed pasture in New Zealand are often darker green in early growth where molybdenum has been added. The writer has observed a similar effect on grasses in mixed pasture in Australia. Stephens and Oertel (1943) reported a small increase in the final yield of ryegrass following the application of molybdenum. The greening of the grasses might be due to an effect of molybdenum on the nitrogen supply. In experiments with a number of grasses and legumes on a molybdenum-deficient soil, Anderson and Thomas (1 946) found that only the legumes responded to molybdenum.

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On that soil the grasses did not respond to molybdenum either when they were nitrogen-deficient or when combined nitrogen fertilizer had been added, The evidence outlined above indicates that any effect that molybdenum may have on nitrogen fixation or other nitrogen changes in soils is insignificant in comparison with the effect on symbiotic nitrogen fixation. This is probably due to the fact that the Rhizobium organism in the nodule is much more favorably situated with respect to the supply of sugar as a source of energy than are the free-living organisms. Furthermore, it is possible that the greening of grasses that does occur may be due not to any increase in nitrogen supply but to an effect of molybdenum on protein metabolism in the plant. This is a common effect of molybdenum on nonlegumes (Anderson, 1956a). 2. For Metabolism in the Plant

Deficiency of molybdenum in plants interferes with protein metabolism, and the deficient plants are often pale green with symptoms resembling nitrogen deficiency. Where nitrate is the source of nitrogen the molybdenum-deficient plants may contain high concentrations of nitrate nitrogen. Molybdenum-deficient plants which have taken up ammonium nitrogen from the soil may be dark green. The molybdenum deficiency, if sufficiently acute, often causes specific and well-defined symptoms. This section deals with responses to molybdenum which appear to be mainly due to the effect of molybdenum on metabolism in the plant. a. Legumes. It has been established by experiments in water culture that molybdenum is needed for metabolism in the host legume (Evans, Purvis, and Bear, 1950; Hewitt, 1951; Meagher, Johnson, and Stout, 1952). The evidence with herbage legumes so far has not revealed field deficiencies of molybdenum for metabolism in these plants, apart from effects in symbiotic nitrogen fixation. The available evidence indicates that molybdenum deficiency either is not sufficiently acute to induce molybdenum deficiency in the host legume, or, where the deficiency is acute, it is masked by nitrogen deficiency. On the other hand, deficiency of molybdenum for metabolism in the plant may become evident where a nitrogenous fertilizer has been applied. In Australia, Wilson (1949a) found that a scald disease of beans (Phaseolus vulgaris) was due to molybdenum deficiency. This disease occurred on certain acid coastal soils in New South Wales. It had been thought that the disease was due to excess manganese, as the plants often contain high concentrations of this element. Furthermore, application of lime to the soil reduced the uptake of manganese and alleviated the condition. However, it is known that the uptake of manganese by plants is greater in acid soils and that the affected plants on

171 the more acid soil would therefore have been expected to contain more manganese. Before the use of molybdenum the disease had been largely overcome by using seed that had been produced in unaffected areas, presumably because of the higher molybdenum content of the imported seed. Nitrogenous fertilizer had been applied to the soil on which scald disease of beans was found (Wilson, 1949a). A similar disease of peas (Pisum sativurn) has recently been identified in Australia, in the Bairnsdale district of Victoria (Drake and Kehoe, 1954). A marked scorching of the lower leaves occurred where superphosphate and sulfate of ammonia had been applied to a sandy-loam soil of pH 5.4. Tests with diphenylamine showed a high concentration of nitrate in the affected plants. A striking response was obtained by spraying the plants with a solution containing 1/3 ounce of ammonium molybdate in 2 gallons of water. b. Nonlegumes. In his work with Aspergillus, Steinberg (1936) showed that molybdenum is needed for growth apart from any effect on nitrogen fixation. Arnon and Stout (1939) showed that molybdenum is essential for higher plants. Although there is considerable evidence that more molybdenum is needed for growth with nitrate nitrogen than where ammonium nitrogen is used, at least for some organisms, there is no doubt that molybdenum is needed by plants for the utilization of both forms of nitrogen (Vanselow and Datta, 1949; Agarwala, MOLYBDENUM AS A FERTILIZER

1952). The first field response of a nonlegume to molybdenum was obtained by Davies (1945) in New Zealand. This response resulted from a study of the disease “whiptail” of cauliflowers, which could be controlled by liming. Working with an affected soil, Davies was able to demonstrate characteristic symptoms for the treatments lacking the element molybdenum. In these experiments the plants treated with molybdenum, though superior, did develop whiptail-like symptoms. The same year Mitchell (1945) was successful in controlling “whiptail” of cauliflowers in New Zealand with application of 1 pound of ammonium molybdate per acre. The reported effects of molybdenum on cauliflowers in New Zealand were shortly followed by similar effects in Australia. Waring, Shirlow, and Wilson (1947, 1949) in New South Wales were the first in Australia to show that “whiptail” of cauliflower could be corrected by the use of molybdenum. This was confirmed in Western Australia by D u n e and Jones (1948). Using sand cultures Hewitt and Jones (1947) studied the effect of molybdenum deficiency in cauliflower and showed that the deficiency in the plant induces “whiptail.” Responses of other plants to molybdenum were soon obtained in

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Australia. Fricke (1947) reported a response of oats to molybdenum in Tasmania in an area where responses of clover had been found. The deficiency severely restricted the production of grain, indicating that the molybdenum was deficient for metabolism in the plant. Wilson (1948) obtained responses of lettuce to molybdenum in New South Wales in an area where the responses of cauliflowers had occurred. Millikan (1948) found that molybdenum corrected a lower leaf necrosis in flax. At about this time also Walker (1948) in California, reported molybdenum deficiency in tomato plants grown in a serpentine soil. The symptoms were similar to those described by Arnon and Stout (1939) showing that the molybdenum was deficient for metabolism in the host plant. “Whiptail” of cauliflower has a wide distribution in many countries. The effectiveness of molybdenum for correcting this deficiency disease is now well recognized. In England effects of molybdenum on “whiptail” in the field have been reported by Jones and Dermott (1950) and by Plant (1951). Similar results with molybdenum on “whiptail” of cauliflower have been reported in Florida by Eddins et al. (1952) and Gammon et al. (1954) ; in Holland by Mulder (1954); and in new areas in Australia and New Zealand by von Stieglitz and Chippendale (1955) in Queensland and by Lobb (1953) in otago. Responses of many plants to molybdenum have now been found, generally on acid soils, and many of them in areas where responses of a legume or cauliflower had previously been obtained, or where the reason for responses to lime have been investigated. The importance of molybdenum for broccoli and for lettuce on certain soils in England has been reported by Plant (1950, 1952). In Florida it has been found that a disease known as “yellow spot” of citrus is due to molybdenum deficiency (Stewart and Leonard, 1952). Responses of a wide range of species to molybdenum have been reported by Johnson, Pearson, and Stout (1952) on a serpentine soil in California; by Lobb (1953) in Otago, New Zealand; by Mulder (1954) in Holland; and by von Stieglitz and Chippendale ( 1955) in Queensland, Australia.

3. For Animals Molybdenum is known to be an essential component of certain enzymes in animals, in xanthine oxidase (Richert and Westerfeld, 1953; Totter et al., 1953), and in aldehyde oxidase (Mahler et al., 1954). There is an important relationship between copper, sulfur, and molybdenum in animal nutrition (Dick, 1953), and it would appear that a high molybdenum intake by the animal in relation to the copper intake may induce copper deficiency, while a low molybdenum intake

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may induce effects that have been recognized as copper toxicity. It is important to appreciate the significance of these relationships, and to avoid, for example, inducing copper deficiency in stock by the application of excessive amounts of molybdenum in the field. On the other hand, heavier dressings of molybdenum may be needed in places, as in Australia in certain parts of New South Wales and Victoria, where heavy losses of stock may occur through the effects of toxic amounts of copper which accumulate in the liver and are later released suddenly into the blood (Dick, 1953, 1956).

111. THENATURE A N D DETECTION O F MOLYBDENUM DEFICIENCIES Methods used for detecting molybdenum deficiency vary with circumstances. Often in Australia compound deficiencies occur, so that there is no evidence of molybdenum deficiency in the existing pasture plants. Where there is a simple deficiency some species show welldefined symptoms while others do not. Molybdenum has certain welldefined effects in plant metabolism, and in some cases these effects have already been used as a means of detecting molybdenum deficiency. It is necessary to understand the effects of molybdenum deficiency in the plants in order to understand the methods of diagnosis of the deficiency. The matters just outlined are discussed below.

I . Compound Deficiencies Often the growth of plants in the field is restricted by the deficiency of more than one element. In general, where other elements are deficient the response to molybdenum is restricted. However, heavy dressings of lime may decrease the response to molybdenum by correcting or partially correcting the deficiency of molybdenum. Nitrogenous fertilizer may correct the nitrogen deficiency induced in the legume by molybdenum deficiency. On the other hand, a dressing of lime may be needed to induce nodulation on the clover roots before responses of clover to molybdenum can be obtained. Factors affecting the response to molybdenum are discussed later in this paper under Section V. It is apparent from the studies of factors affecting the response to molybdenum that compound deficiencies may prevent not only the response to molybdenum but also the detection of molybdenum deficiency by visual or chemical methods. This may be illustrated by observations of the writer that pasture which has been sown on molybdenum-deficient land, and hence has not responded well to superphosphate, may not be treated further by the landholder with superphosphate. Such pasture may show symptoms of phosphorus deficiency or sulfur deficiency rather than symptoms of molybdenum deficiency.

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The variation in the effects of other factors on molybdenum response shows that care must be taken to select the right conditions when testing for field responses to molybdenum. Methods of taking account of these factors in field tests for deficiencies in Australia have been described (Anderson, 1952c; Anderson and Moye, 1952). It is important to stress that the strongest molybdenum deficiencies may occur in places where the plants normally grown do not respond to molybdenum. In Australia, there are no visual symptoms due to molybdenum deficiency in the plants growing in the unimproved native pasture. In a good deal of this country there are no legumes and the native grasses do not respond to molybdenum even where superphosphate has been applied (Anderson, 1946; Anderson and Thomas, 1946). Without superphosphate deficiencies of phosphorus and sulfur are so severe that in native pasture even legumes do not respond to molybdenum. The evidence shows that any variation in soil molybdenum status would have no effect on individual plants or on the ecological association of plants on untreated land, since molybdenum becomes deficient only when other deficiencies are corrected. 2. Visual Symptoms

The symptoms of uncomplicated molybdenum deficiency are sometimes a clear-cut and reliable guide to the occurrence of the deficiency. For example, “whiptail” of cauliflower and “yellow spot” of citrus are most useful symptoms for detecting the need for using molybdenum on these crops. Symptoms of molybdenum deficiency have been described in most cases where responses to molybdenum have been recorded. Deficiencies of a number of species have been described by Hewitt and Jones (1947, 1948) and Lobb (1953). In many cases photographs of the symptoms have been reproduced in color, particularly by Wallace ( 1951) and von Stieglitz and Chippendale (1955). The effect of the deficiency on the symptoms may vary considerably. For example, where a legume is deficient in molybdenum for symbiotic nitrogen fixation the plant shows symptoms of nitrogen deficiency (Anderson and Thomas, 1946), but where the molybdenum is deficient for metabolism in the plant other symptoms usually become apparent (Evans, Purvis, and Bear, 1950; Meagher, Johnson, and Stout, 1952). Whether one or other of these symptoms on a legume is dominant depends upon the degree of the deficiency and upon the nitrogen supply (Anderson and Spencer, 1950a; Anderson, 1956a). With cauliflowers, Hewitt and Agarwala (1951) found that the appearance of “whiptail” symptoms is inhibited by severe molybdenum deficiency when the nitrogen level is also low.

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Molybdenum deficiency often induces interveinal chlorosis. Johnson, Pearson, and Stout (1952) have pointed out that whereas some species show interveinal chlorosis, in others the chlorosis is more diffuse, resembling nitrogen deficiency. Some species show cupping of the leaves, which may develop towards the upper or lower surface of the leaf. The cupping is caused by a diminished rate of expansion of the leaf edges relative to the expansion of the remainder of the leaf (Johnson, Pearson, and Stout, 1952). In New Zealand, Lobb (1953) found that a general paleness or yellowing and poorer growth were the main symptoms of molybdenum deficiency in plants of the families Chenopodiaceae (mangolds, silver beet, and chard) ,Umbelliferae (carrots and parsnips), and Graminae (wheat, oats, rye, corn, and pasture grasses). Various Cruciferae (rape, chou mollier, turnips, kale, swedes, and radish) gave stunting; paleness; often a yellowish mottling of the leaves; sometimes a marked yellowing around the margins; often cupping of the leaves of young plants; and sometimes irregular leaf margins which may run into the midrib, producing the effect recognized as “whiptail.” Where molybdenum deficiency is sufficiently acute to cause visual effects, the molybdenum-deficient pastures are a pale green color indicative of nitrogen deficiency. The grasses and clovers are in fact both deficient in nitrogen. This is because of the low nitrogen status of the soils, and because the molybdenum deficiency inhibits symbiotic nitrogen fixation in the clover. The leaves of the deficient clover plants are smaller than normal and pale green or yellow and the stems and petioles generally show a reddish-brown coloration. The stunted clover plants are nodulated, and develop to maturity, producing viable seeds which maintain some plants of the species in the pasture (Anderson, 1946). Where the deficiency is acute, the plants may measure only 1 or 2 cm. in diameter and height at maturity. Sulfur deficiency and defective nodulation of the clover roots also induce nitrogen deficiency symptoms in the clover plants, and these may be readily confused in the field with molybdenum deficiency. Both problems may occur in country where molybdenum is deficient (Anderson and Moye, 1952; Anderson and Spencer, 1950b). Sulfur deficiency can often be detected by examining the effects of current dressings of superphosphate, which correct sulfur deficiency but intensify molybdenum deficiency where they increase the growth of the clover. Furthermore, plants deficient in sulfur do not become green and grow normally when nitrogen is applied without sulfur. Defective nodulation can usually be detected by the occurrence of nodulated green plants

176 A. J. ANDERSON scattered among the much smaller, yellow, unnodulated plants, but this effect is masked if molybdenum or sulfur deficiency is severe. The nodules of molybdenum-deficient legumes are often a gray or brownish color compared with the pink color of nodules of the plants which are not deficient (Mulder, 1948, 1954). The molybdenum-deficient legumes have more nodules than a normal plant, but the nodules are smaller. This is not only because there are often many very small nodules scattered over the root system of the deficient plants, but because the deficiency restricts nitrogen fixation and restricts the size of the nodules (Anderson and Spencer, 1950a). In some cases field responses of legumes to molybdenum have been associated with marked effects of the molybdenum on the color and size of the nodules (Blomfield, 1954; Newman, 1955). In practice, the appearance of the nodules is seldom a useful guide to the occurrence of molybdenum deficiency. The effect of molybdenum on their size is often not apparent except where soil conditions are unfavorable for the survival of Rhizobium. Very large pink nodules occur where conditions are favorable for symbiotic nitrogen fixation and where, at the same time, the number of nodules is restricted by the low numbers of the Rhizobium organism in the soil, as on very acid soils (Anderson, Meyer, and Fawcett, unpublished data). By increasing the number of effective Rhizobium organisms in the soil, either by increasing the amount of inoculum or by counteracting the soil acidity, the number of nodules is increased and the amount of nitrogen fixed per nodule and the size of the nodules is decreased. Where sufficiently large numbers of nodules have formed, conversion of some of the red hemoglobin pigment to the ineffective green bilirubin pigment may occur (Anderson, Meyer, and Fawcett, unpublished data). In addition, the occurrence of small nodules deficient in the red hemoglobin pigment can be caused by infection of the roots with an ineffective strain of Rhizobium and also by deficiencies of sulfur or molybdenum, or by the application of combined nitrogen. A very common feature of land that has been sown with cl.over and is severely deficient in molybdenum is the occurrence of vigorous dark green clover plants in patches where trees have been burned. The ash of trees that have grown on molybdenum-deficient land may contain about 10 p.p.m. of molybdenum (Anderson and Oertel, 1946). Therefore, apart from increasing the pH of the soil, the ash adds significant amounts of molybdenum, and may correct molybdenum deficiency even on soils where lime is not effective. Ash patches are evident also in land where other deficiencies occur, especially in land with problems of defective nodulation, and therefore do not necessarily indicate the occurrence of molybdenum deficiency.

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The effect of molybdenum deficiency on the color of the clover plants naturally depends upon the degree of the deficiency. It is often impossible visually to detect the nitrogen deficiency symptoms. However, the paler green color often becomes apparent when a molybdenum treatment has been applied alongside a control plot for comparison. Where there is only a simple deficiency of molybdenum, this can be done by spraying a solution of molybdenum in water onto field plots, or by applying molybdenum in some other conyenient way with suitable replication and controls. Very wet sawdust is useful for confining molybdenum within plot boundaries when it is applied by hand (Anderson, 1948). Details of simple field tests for molybdenum deficiency in places where other elements are not also deficient have been described (Anonymous, 1954). It is important to note that painting or injecting a portion of a plant or leaf with molybdenum, as is used for testing for deficiency of some elements, may lead, in the case of molybdenum, to a rapid recovery of the whole plant (Meagher, Johnson, and Stout, 1952).

3 . Chemical Composition of the Plants Deficiency of molybdenum particularly affects the nitrogen content as well as the molybdenum content of the plants. The effect on the nitrogen content varies, depending upon the role of the molybdenum, and is different for legumes and nonlegumes. Other effects of molybdenum are on the ascorbic acid (vitamin C) , dehydrogenase, and phosphatase contents. a. Molybdenum Content. It is well known that there is generally only a poor correlation between the concentration of an element in plants and responses to the element. Molybdenum is no exception. However, where there is ample molybdenum in the soil, molybdenum may accumulate in the plant to quite high levels. Molybdenum deficiency is unlikely where the molybdenum content of the plants exceeds certain levels, the particular level depending upon many factors. A value of about 0.1 p.p.m. of molybdenum in the dry matter of the plant tops is regarded in a general way as a value below which molybdenum deficiency is likely, but the value may vary widely. For example, good responses of legumes to molybdenum have been found where the plants contain even 0.5 p.p.m. of molybdenum, whereas in other cases the clover may not respond to molybdenum when it contains just over 0.1 p.p.m. (Anderson and Oertel, 1946; Walker, Adams, and Orchiston, 1955a). In experiments with citrus, Vanselow and Datta (1949) found that the leaves were just beginning to show mottling, the symptom of deficiency, when they contained 0.024 p.p.m. of molybdenum. As a result of studies with a range of species, Johnson, Pearson,

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and Stout (1952) concluded that broad generalizations regarding the significance of molybdenum concentrations in plants as related to their growth are not warranted. One important factor which affects the critical level of molybdenum needed is whether the molybdenum is deficient for nitrogen fixation or for metabolism in the plant. Anderson and Oertel (1946) pointed out that in addition to a possible minimum molybdenum requirement in host plant metabolism, there would also be a minimum requirement for nitrogen fixation, and that the latter would not necessarily be reflected in the concentration of molybdenum in the tops. It is now known that there is a molybdenum requirement for metabolism in the clover plant, and that this requirement is lower than for symbiotic nitrogen fixation (Anderson and Spencer, 1950a; Anderson, 1956a). It is well known that the concentration of molybdenum is different in different plant tissues. The concentration of molybdenum in a sample taken for analysis can therefore vary according to the proportion of the different tissues in the sample. Using radioactive molybdenum, Stout and Meagher (1948) found that molybdenum may concentrate strongly in the interveinal areas of leaves. In general, leaves contain a higher concentration of molybdenum than do stems (Barshad, 1948; Evans, Purvis, and Bear, 1950), although a few exceptions have been reported (Anderson and Oertel, 1946; Barshad, 1948). Furthermore, the distribution of molybdenum between the roots and other plant parts may be influenced by phosphate and sulfate (Stout et al., 1951), and possibly also by the level of molybdenum and by the soil reaction (Anderson and Oertel, 1946). Molybdenum is more highly concentrated in the nodules of legumes than in the roots, stems, and leaves (Bertrand, 1940; Jensen and Betty, 1943; Mulder, 1948). It is probable that this higher concentration is needed in the nodule for symbiotic nitrogen fixation. Jensen (1948) found that nitrogen fixation in lucerne was restricted when the molybdenum content of the nodules fell below 3 to 10 p.p.m. This is a much higher concentration than is needed generally in plants. Seed of legumes also frequently contains high concentrations of molybdenum (Bertrand, 1939; Meagher, Johnson, and Stout, 1952). Well-grown plants treated with molybdenum do not necessarily contain a higher concentration of molybdenum than deficient untreated plants. Anderson and Oertel (1946) found in some cases that light dressings of molybdenum considerably decreased the concentration of molybdenum in the dry matter of alfalfa tops. Plant (1952) found that a dressing of even 4 pounds of sodium molybdate per acre had no significant effect on the molybdenum content of lettuce. The molybdenum increased the yield of lettuce from 3584 to 7168 pounds per acre. The

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molybdenum content of the untreated plants was 0.06 p.p.m. and that of the plants receiving 4 pounds of sodium molybdate per acre was 0.08 p.p.m. b. Protein and Nonprotein Contents. Molybdenum increases the percentage nitrogen in legumes which are nodulated but deficient in molybdenu& for symbiotic nitrogen fixation. An increase in percentage nitrogen occws even when the effect of molybdenum on color and yield is very small (Anderson and Thomas, 1946). As would be expected, by increasing symbiotic nitrogen fixation the molybdenum increases the concentration of both the protein and nonprotein nitrogen in the plant (Anderson and Spencer, 1950a). These deficient plants, which are grown on soils comparatively deficient in nitrogen and which depend on symbiotic nitrogen fixation for their nitrogen supply, do not contain high concentrations of nitrate nitrogen. Furthermore, they usually contain sufficient molybdenum for the utilization of any nitrate nitrogen which they may have obtained from the soil, as the molybdenum requirement for this is considerably less than the requirement for nitrogen fixation. When the molybdenum is needed for metabolism in the plant the effects of molybdenum on the nitrogen content are quite different from the effects described for legumes. Plants deficient in molybdenum for the utilization of nitrate nitrogen may accumulate high concentrations of nitrate (Hewitt and Jones, 1947; Wilson and Waring, 1948; Mulder, 1948; Stout and Meagher, 1948). This accumulation occurs mainly in the interveinal tissues (Johnson, Pearson, and Stout, 1952). As the molybdenum is needed in the plant for the utilization of the nitrate nitrogen, application of molybdenum decreases the concentration of nitrate and concomitantly increases the concentration of protein (Mulder, 1948j Anderson and Spencer, 1950a). The concentration of most amino acids is increased by the molybdenum (Hewitt, Jones, and Williams, 1949). There may be no effect on the percentage total nitrogen as there is when nitrogen fixation is increased (Anderson and Spencer, 1950a). The darker green color of the legumes and nonlegumes treated with molybdenum is in each case associated with the higher protein content. It is interesting to note that pale green legumes deficient in sulfur, like legumes deficient in molybdenum, have a low percentage nitrogen when grown on nitrogen-deficient soil. The sulfur deficiency decreases the percentage protein nitrogen but not the percentage nonprotein nitrogen (Anderson and Spencer, 1950b). It has recently been found that molybdenum is an essential component of the enzyme nitrate reductase, which has been obtained from Neurospora and Aspergillus (Nicholas, Nason, and McElroy, 1953). The niolybdenum undergoes oxidation reduction and serves as a carrier

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in electron transport between flavine and nitrate (Nicholas and Nason, 1954). It would seem to be beyond doubt that there is often a greater need for molybdenum for nitrate reduction than for the utilization of ammonium nitrogen (Anderson, 1956a) and that this is due, at least in some cases, to the need for molybdenum in nitrate reductase. Wilson (1949b) has used a test for nitrate in diagnosing possible Golybdenum deficiencies. However, it must be noted that nitrate accumulation in plants may result also from deficiencies of manganese (Leeper, 1941) and sulfur (Anderson and Spencer, 1950b), and may therefore occur when the deficiency is not directly involved in nitrate reduction. When nitrate has accumulated in a plant because of molybdenum deficiency, the response to molybdenum may be very rapid. Possingham (1954b) found that the application of molybdenum to deficient plants gave clear-cut increases in the concentration of amino acids and amides within 2 hours after treatment. By contrast, application of copper, zinc, manganese, and iron to correct deficiencies decreased the concentration of amino acids. Spencer and Wood (1954) found that the concentration of nitrite increased to a maximum 4 hours after molybdenum had been applied. Within 2 days the decrease in the concentration of nitrate was accompanied by an increase, first in the concentration of nitrite, then in the concentration of ammonia, amide, amino acid, and protein nitrogen. Deficiency of molybdenum can occur in plants which have been provided with ammonium nitrogen. In general, nitrification will occur in the soil and the ammonium fertilizer may result in nitrate accumulation in the plants (Drake and Kehoe, 1954). However, nitrate accumulation does not always occur in plants provided with ammonium nitrogen and deficient in molybdenum (Anderson and Spencer, 1950a; Aganvala, 1952). Mulder (1954) has reported that plants deficient in molybdenum in the field and receiving ammonium fertilizers had darker green young leaves than corresponding plants provided with nitrate nitrogen, indicating that protein synthesis had occurred. The plants also showed cupping and withering of the leaves. c. Ascorbic Acid, Dehydrogenase, and Phosphatase Contents. Deficiency of molybdenum has been reported to decrease markedly the ascorbic acid content and to lower the reducing activity of plants (Hewitt, Agarwala, and Jones, 1950; Hewitt and Agarwala, 1952). A low ascorbic acid content was found in cauliflower plants deficient in molybdenum, irrespective of the nitrogen source and accumulation of nitrate (Aganvala, 1952). Low reducing activity in molybdenum-deficient plants has been reported also by Evans, Purvis, and Bear (1950) and Mulder (1954). Spencer (1954) has shown that tomato plants deficient in molybde-

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num have a higher phosphatase activity associated with a higher rate of respiration than normal plants. The molybdenum deficiency results in a waste of energy. This effect of molybdenum is supported to some extent by the results of Possingham (1954a), who found that the application of molybdenum to deficient tomato plants decreased the inorganic phosphorus and increased the organic phosphorus content of the plants within 2 days of treatment.

4 . Molybdenum Content of the Soils Apart from a few exceptions, the total molybdenum content of soils varies from 0.5 to 3.5 p.p.m. (Robinson et al., 1951; Evans and Purvis, 1951). The most important factor affecting the molybdenum supply to the plant is variation in the soil reaction. Walsh, Neenan, and O’Moore (1952) found soils ranging from 0.4 to 3.5 p.p.m. of total molybdenum where deficiency of molybdenum occurred and also where the pasture contained excess molybdenum for stock. The soils where deficiencies were found were all acid. Excess molybdenum occurred only on alkaline soils. The yield of mycelium and sporulation of the fungus Aspergillus niger may be increased to a varying degree, depending upon the molybdenum level, by increasing the supply of molybdenum to the organism when it is cultivated in a solution supplied with nitrate nitrogen (Mulder, 1948). This fact may be used for the microbiological assay of molybdenum in soil (Mulder, 1948; Nicholas and Fielding, 1950). Grigg (1953a) has developed the use of a chemical extractant for determining “available” molybdenum, by comparing the amount of molybdate extracted by phosphate, hydroxyl, oxalate, and acetate solutions from soils showing graded field responses to molybdenum. The oxalate extraction was the only one which gave reasonable agreement with the order of the response of the soils. Ammonium oxalate is being used for measuring available molybdenum in a survey of New Zealand soils. Grigg (195313) has described the method used to counteract the influence of interfering substances encountered in determining molybdenum in the soil extracts. Some results obtained with the method in New Zealand are indicated by Davies and Grigg ( 1953). Using ammonium oxalate extraction, Walsh, Neenan, and O’Moore (1952) found 0.04 to 0.12 p.p.m. of molybdenum in the soils where molybdenum deficiency occurs. These soils were mostly within the range of pH 5 to 5.5. Soils of the same total molybdenum content (0.4 to 3.5 p.p.m.) but of pH 7 to 8 gave excess molybdenum for livestock, and by the ammonium oxalate extraction method were found to contain 0.2 to 0.7 p.p.m. of available molybdenum. Stout et al. (1951) have shown that the ability of a plant to take up

182 A. J. ANDERSON available molybdenum is greatly influenced by the level of phosphate, and to a lesser extent also by the level of sulfate present and have pointed out that these effects on molybdenum uptake may be so great as to question the value of soil tests for molybdenum.

IV. THECORRECTION OF MOLYBDENUM DEFICIENCY Molybdenum deficiency is one of the simplest and least expensive of all deficiencies to correct, mainly because of the very low levels of molybdenum required. The application of 2 ounces per acre presents no difficulty. 1. Method of Application Molybdenum can be successfully applied in a variety of ways. It is rarely applied alone in a separate operation, but is mixed with materials normally used on the crop or pasture. For pasture in Australia it is mixed with superphosphate as molybdenum trioxide or sodium molybdate at the level of 1% pounds of molybdenum trioxide per 2240 pounds of superphosphate. This molybdenum-superphosphate, as it is called, is now an important commercial fertilizer. The mixture provides for a dressing of about 2 ounces of molybdenum per acre, depending upon the amount of superphosphate applied. Molybdenum may be sprayed onto the plants in solution, as is being done to correct yellow spot of citrus, by including molybdenum with other materials used in the normal spray program (Stewart and Leonard, 1952). Molybdenum is readily absorbed by the leaves and translocated in plants (Meagher, Johnson, and Stout, 1952). It can also be applied mixed with the seed, but with some seeds it may tend to separate and even block the drill (Lobb, 1953). Molybdenum may possibly be harmful to Rhizobium when applied on inoculated seed. 2. Form of Molybdenum Molybdenum is quite effective when used as sodium molybdate, ammonium molybdate, or as the less soluble molybdenum trioxide, and appears to be needed at about the same level of application for each of these forms (Anderson, 1946). Molybdenite, the molybdenum sulfide ore, is not satisfactory. Anderson (1946) found that a dressing of 1 pound of molybdenite per acre containing 92 per cent MoSz increased the yield of clover, from 224 to 448 pounds dry matter per acre, while only 2 ounces per acre of the roasted ore (MOO,) increased the yield to 2688 pounds per acre. 3 . Amount of Molybdenum The amount of molybdenum required per acre to correct deficiencies may vary with the crop, the soil, the method of application, and other

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factors. In experiments with herbage legumes Anderson (1942) found that 1 pound of molybdenum per acre was a much heavier dressing than was needed. In subsequent experiments on very deficient soil, Anderson (1946) compared the effects of levels of molybdenum trioxide ranging from one thousandth of an ounce to 4 pounds per acre. The molybdenum was mixed with superphosphate for application to the plots. No increase in yield was obtained with less than l/la ounce of molybdenum trioxide per acre, although a slight improvement in the color of deficient plants was observed where the next lower level of l/a4 ounce per acre was applied. The response to l/ls ounce per acre was quite marked in all experiments, but significantly less effective than 1 ounce per acre or higher levels. The dressing of 1/4 ounce per acre was not shown to be significantly less effective than 1 ounce per acre but appeared to be somewhat inferior. No further benefit was obtained with levels higher than 1 ounce per acre. In general, 2 ounces per acre, which is about the average dressing applied commercially on pasture, appears to be fully effective in Australia. In New Zealand, Cullen (1954) tested levels of sodium molybdate ranging from !iG ounce to 4 ounces per acre, and obtained responses of pasture to the molybdenum at all levels. The magnitude of the response increased with the rate of application up to the 1 ounce dressing. The 1 ounce dressing was as effective as 2 or 4 ounces per acre. In New Zealand also Lobb (1953) has had marked responses of many different crops to 2 to 3 ounces of sodium molybdate per acre. Blomfield (1954) used 2 ounces of sodium molybdate per acre on peas with good result. The effectiveness of about 2 ounces per acre has been confirmed in experiments in many places. Higher levels of molybdenum sometimes appear to be needed. Waring, Shirlow, and Wilson (1947) found that a good deal of “whiptail” still remained in plots of cauliflowers where 1/4 pound of sodium molybdate per acre had been applied. The application of 1 pound per acre was adequate to prevent all but a trace of whiptail. In other experiments (Wilson and Waring, 1948) have found % pound of sodium molybdate per acre sufficient. As indicated under Section V, the amount of molybdenum needed should be increased by high levels of sulfate, iron, and manganese, by low soil pH, and by low phosphate. An indication of the variation in the level of molybdenum needed on different soils was obtained by Mulder (1948), who demonstrated that soils vary appreciably in their effect on the availability of molybdenum to the plant. Mulder (1954) reported that cauliflowers usually responded well to 1/2 kg. of sodium molybdate per hectare (about 1/2 pound per acre) but were often better with 4 kg. per hectare.

184 A. J. ANDERSON Younge and Takahashi (1953) in Hawaii obtained results indicating that alfalfa grew much better with 4 pounds of sodium molybdate per acre than with 2 pounds per acre on a soil high in manganese. However, there were no strict controls to test this comparison in the experiment, which was primarily designed to compare the effect of molybdenum on different varieties of alfalfa. In England, Plant (1952) found that 2 pounds of sodium molybdate per acre was less effective than 4 pounds per acre on lettuce. The significance of the effect on yield was not stated, but the difference was large, and it was shown that the concentration of molybdenum in the lettuce plants was still less than 0.1 p.p.m. where 4 pounds per acre had been applied, and was not significantly higher than in the control plants. The levels needed for spraying in water solution on a commercial scale do not appear to have been fully worked out. As molybdenum is directly absorbed by the leaves, less molybdenum per acre than is used for soil application should be required. Among the levels that have been used for spraying are 2 ounces per acre on peas, before and after emergence (Blomfield, 1954), and 1/4 ounce of ammonium molybdate in 3 gal. of water for spraying on molybdenum-deficient peas (Wade, 1952). 4 . Frequency of Application The bulk of the evidence on residual effects of molybdenum shows that a single dressing of 2 ounces per acre remains effective for many years (Anderson, 1946; Anderson, 1952b; Newman, 1955). In a recent experiment (unpublished data) it has been found that a dressing of 2 ounces of molybdenum trioxide per acre applied to a subterranean clover pasture in 1946 is fully effective in 1955, with marked responses to a current dressing of molybdenum where none had been applied previously, but no responses to a current dressing where molybdenum had already been applied in 1946. Hence, the one dressing of molybdenum had remained fully effective for 10 years. There is evidence that on some soils, and perhaps for some crops in particular, heavier dressings may be needed more frequently. Mulder (1954) has observed that whereas cauliflowers may sometimes require 4 pounds of sodium molybdate per acre, a dressing of 1 pound per acre may be sufficient for cabbage for three years.

V. FACTORS AFFECTING THE RESPONSETO MOLYBDENUM Many of the matters already discussed concern factors which influence the response to molybdenum. These include differences between legumes and nonlegumes; the nature of the effect of molybdenumwhether it is deficient for nitrogen fixation, for the utilization of nitrate

185 nitrogen, or for some other metabolic reaction; the molybdenum content of the plant and soil; and the method, form, amount, and frequency of application of the molybdenum. A very important factor which also influences the response to molybdenum is the nature of other fertilizers and soil amendments which have been applied, or the level of certain elements already present in the soil. The cultural practices that are employed are naturally important, and so are differences between species. MOLYBDENUM AS A FERTILIZER

1. Deficiencies of Phosphorus, Sulfur, and Other Essential Elements The importance of correcting other deficiencies, apart from nitrogen for nodulated legumes, has already been discussed under Section 111, 1. Very frequently responses to molybdenum do not occur in the field because of the deficiency of other elements. The difficulty is increased by the fact that where molybdenum is deficient, the benefit from other fertilizers applied without molybdenum is restricted, and on such land therefore these other elements have been used less and are often very deficient in the soil. In areas where insufficient superphosphate has been applied, sown pasture may remain dominantly composed of low-yielding, low-quality native grasses, or may remain dominantly low-yielding clover (Anderson and McLachlan, 1951) . When sufficient superphosphate has been applied, provided molybdenum and other deficiencies are also corrected, a vigorous stand of clover rapidly increases the fertility of the soil, leading to a vigorous growth of associated sown grasses such as Phalaris tuberosa and ryegrass, and to the production of superior hay and grain crops. Phosphorus and sulfur are both important factors concerned in this effect of superphosphate (Anderson, 1952a). In a study of a wide range of previously untreated virgin soils in eastern Australia, McLachlan (1'955) obtained responses to molybdenum on a third of the soils when phosphorus and sulfur deficiency were corrected, but no responses to molybdenum at all when no phosphorus or sulfur had been applied. Phosphorus deficiency was the most acute, and restricted responses to molybdenum more than did sulfur deficiency. It is apparent from these results that the effect of phosphorus deficiency in restricting responses to molybdenum was of much greater significance than the known' effects of phosphorus in increasing the uptake of molybdenum by the plant, or in increasing the availability of molybdenum in the soil by exchanging with adsorbed molybdate on the clay, as reported by Stout et al. (1951) and Barshad (1951b). In no case was there evidence in the results obtained by McLachlan (1955) that the applied phosphate had corrected molybdenum deficiency. Furthermore, it is interesting that the sulfate increased the

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responses to molybdenum by correcting sulfur deficiency and did not merely induce the deficiency by decreasing the uptake of molybdenum. The sulfate treatment increased the response to molybdenum only where it increased the yield. The interaction between molybdenum and superphosphate on the yield is invariably either positive or nil, depending upon the magnitude of the response to molybdenum and superphosphate (Anderson, 1946; Anderson and Oertel, 1946). Where there are strong responses to molybdenum and superphosphate, the interaction is strongly p o s i t i v e that is, the response to molybdenum is much greater in the presence than in the absence of superphosphate. Where the responses are small there may be no significant interaction, but not a negative interaction. The above is true for the interactions between molybdenum and phosphorus and between molybdenum and sulfur so far recorded (Anderson and Spencer, 1950b; McLachlan, 1955; Walker, Adams, and Orchiston, 1955b). However, Mulder (1954) has reported that he has observed plants not treated with phosphorus showing intense molybdenum deficiency symptoms, and plants on adjoining plots treated with phosphorus showing only slight deficiency symptoms. It is possible that in areas where the phosphorus and sulfur requirements of the plant are already more nearly satisfied, the direct effects of phosphorus and sulfur on molybdenum uptake by the plant may be of much greater significance than in areas where these elements are more deficient. Before molybdenum deficiency had been detected on some properties in Australia comparatively heavy dressings of superphosphate had been applied over a number of years in order to encourage the unthrifty clover. Very marked responses to molybdenum could be obtained on these pastures, at least in the year of application, without any further superphosphate with the molybdenum (Anderson, 1946). Superphosphate applied without molybdenum to molybdenum-deficient pasture further decreases the percentage nitrogen in the clover and intensifies the pale green or yellow color of the plants where it increases the yield (Anderson and Thomas, 1946). Where no superphosphate or insufficient superphosphate has been applied, the plants may be dark green because of phosphorus deficiency, or pale green because of sulfur deficiency, irrespective of molybdenum treatment (Anderson and Spencer, 1950b; Anderson, 1952a). Other deficiencies have been reported to occur along with molybdenum deficiency and to restrict the response to molybdenum. In Australia a most important factor affecting responses is the nodulation of the clover, which is often defective on acid soils where molybdenum deficiency occurs, unless proper precautions are taken to counteract the

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problem as discussed under Section V, 3b. It should be mentioned here that recent evidence (Loneragan et al. 1955b) indicates that ammoniation of superphosphate may be a useful way of counteracting the problem. Boron deficiency (Anderson, 195213) and potassium deficiency (Rossiter, 1952) also restrict the response to molybdenum in places. Conversely, molybdenum deficiency restricts the response to these elements where the deficiencies occur. 2 . Nitrogenous Fertilizers

A good deal of evidence on the effect of nitrogen on the response to molydenum has already been given, particularly under Section I1 and under Section 111, 2 and 3. In general, where the effect of molybdenum is directly to increase nitrogen fixation, as is usually the case with nodulated legumes, the application of nitrogenous fertilizer tends to correct the nitrogen deficiency in the plant and decreases the response to molybdenum. The application of nitrogen, either as ammonium or nitrate nitrogen, improves the color and increases the yield of the molybdenum-deficient nodulated legumes, even when the nitrogenous fertilizer decreases the amount of molybdenum taken up by the plants (Anderson and Thomas, 1946; Anderson and Spencer, 1950a). The nitrogen-molybdenum interaction for these legumes is negative or nil, depending upon the magnitude of the response to the molybdenum and nitrogen, and is not positive-that is, the response of the legumes to molybdenum is either decreased by the application of nitrogen or is not significantly affected, but is not increased. The molybdenum always increases the percentage nitrogen in the nodulated clover plants where it increases the yield, but the nitrogenous fertilizer may increase the percentage nitrogen for only a limited time after application, and after a growth response has occurred may even decrease the percentage nitrogen. This may be true even for sodium nitrate (Anderson and Thomas, 1946), which increases the pH of the soil and should therefore increase the availability of molybdenum in the soil (Anderson and Oertel, 1946). In spite of the results described, it is possible to increase the response of nodulated legumes to molybdenum by applying nitrogenous fertilizer. Anderson and Spencer (1950b) obtained responses of clover to molybdenum where ammonium sulfate was applied, and no response in the absence of ammonium sulfate. This was because the ammonium sulfate corrected sulfur deficiency and was not sufficient to correct nitrogen deficiency. It is important to note that on nitrogen-deficient soil, legumes are pale green with a low percentage nitrogen when they are unnodulated,

188 A . J. ANDERSON when they are nodulated with an ineffective strain of Rhizobium, or when the nodulated legume is deficient in sulfur or molybdenum. The application of combined nitrogen improves the color and increases the yield in all these cases except for sulfur deficiency (Anderson and Spencer, 1949, 1950b; Anderson, 1951). The nature of the interaction will also depend upon the particular molybdenum levels involved. Less molybdenum is needed in the host legume than is needed for symbiotic nitrogen fixation. It has therefore been postulated (Anderson, 1956a) that a positive interaction between molybdenum and nitrogen would be obtained for nodulated legumes under conditions where the molybdenum is very deficient, and where the level of molybdenum used is sufficient to correct the deficiency in the host plant but not sufficient to satisfy the requirements for symbiotic nitrogen fixation. Anderson and Spencer (1950a) have shown that the nitrogenmolybdenum interaction for nonlegumes is positive, by contrast with the negative nitrogen-molybdenum interaction for nodulated legumes. It would also be positive for unnodulated legumes, which depend upon combined nitrogen in the soil for their nitrogen supply. By contrast with the nitrogen-molybdenum interaction, the nitrogen-sulfur interaction is positive for nodulated legumes as well as for nonlegumes (Anderson and Spencer, 1950b). This is because sulfur, unlike molybdenum, increases symbiotic nitrogen fixation through its effect in the host plant, and therefore does not correct only nitrogen deficiency in the nodulated legume. There is evidence that, at least for some organisms, more molybdenum is needed for the utilization of nitrate nitrogen than for the utilization of ammonium nitrogen (Bortels, 1936; Steinberg, 1936; Mulder, 1948). Plants deficient in molybdenum, when provided with nitrate nitrogen, may therefore not require added molybdenum when ammonium nitrogen has been applied, provided the molybdenum is not completely deficient. However, molybdenum deficiency in nonlegumes which has so far been reported, appears to occur in soils irrespective of the nitrogen source (Anderson and Spencer, 1950a; Mulder, 1954), indicating either that the differential effect is small or that it does not occur in most species. In assessing the effect of nitrogenous fertilizer on the molybdenum response it is important to take account of the effect on the soil reaction and on the availability of molybdenum. It is well known that the continued use of ammonium sulfate without occasional dressings of lime can have very marked effects in decreasing the pH of the soil. Ammonium sulfate markedly decreases the uptake of molybdenum by plants (Lewis, 1943; Anderson and Oertel, 1946).

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3. Lime The effect of lime on molybdenum deficiency varies with conditions. It may correct or partially correct molybdenum deficiency, it may have practically no effect, or it may increase the response to molybdenum. Some of the general effects of lime in relation to responses to molybdenum have recently been discussed by Kline (1955). a. Through Eflects on Availability of Molybdenum. Acid materials decrease the uptake of molybdenum, and alkaline materials increase the uptake of molybdenum, by plants (Lewis, 1943; Anderson and Oertel, 1946). Various acid clays and clay minerals strongly adsorb molybdate ions (Barshad, 1951a; Stout et al., 1951). In experiments described by Stout et al. (1951), molybdenum was removed from a column of hydrated halloysite, a clay mineral characterized by its exposed hydroxyl ions, by leaching with 0.1 N sodium carbonate. The column was then leached with dilute hydrochloric acid, followed by distilled water until free from chlorides, and a solution of sodium molybdate was poured into the column. No molybdenum could be leached through the column with water. The column was divided into segments, and it was found that nearly the whole of the molybdenum had been held by the top 1.5 cm. of clay. The molybdenum was readily displaced from the clay with 0.5 N sodium carbonate. The results show that the molybdate was very firmly adsorbed on the acid clay and was not measurably leached by water, but was readily displaced from the clay by dilute sodium carbonate. Stout et al. (1951) reported that the uptake of molybdenum by plants from a culture solution is favored by acid reactions. This contrasts with the results obtained in soil. Thus the effect of lime in increasing the uptake of molybdenum by plants is due to the effect of the lime in increasing the supply of available molybdenum in the soil, rather than to any effect of the lime in increasing the ability of the plants to take up molybdenum. The increase in the supply of available molybdenum to the plant, in those experiments where the lime samples have been examined, has been due not to molybdenum present in the lime (Anderson and Oertel, 1946; Evans, Pwvis, and Bear, 1951) but rather to the effect of hydroxyl ions in replacing molybdate ions on the clay, o r to some other mechanism affecting the availability of molybdenum in the soil. An increase in the concentration of hydroxyl ions results in the displacement of phosphate ions (Stout, 1940) as well as molybdate ions. It might therefore seem that if the effect of lime on the availability of molybdenum in the soil is through an exchange reaction between hydroxyl and molybdate ions, then the application of lime should

190 A. J. ANDERSON increase also the availability of phosphate. However, as already mentioned under Section 11, la, it was the finding that effects of lime and woodash on plant growth were not due to an increase in the availability of phosphate that led to a search for the element concerned in the response, and led to the finding of molybdenum deficiency in that soil (Anderson, 1942, 1946). The lack of response to superphosphate where no lime had been applied was due not to fixation of phosphate in the soil but to deficiency of molybdenum. There was no evidence with this soil that the effect of lime was due even in the least degree to an effect on the availability of phosphate (Anderson, 1946; Anderson and Oertel, 1946). Similar results have been obtained with a number of soils, even including a basaltic red loam of pH 5 to 6 which contains a high percentage of free iron oxide and a high percentage of phosphorus of low availability (Anderson and h o t , 1953). The evidence just discussed does not rule out the possibility that lime increases the availability of molybdenum to plants by an anion exchange reaction between hydroxyl and molybdate ions. In fact it would seem likely from the other evidence already discussed that this is at least one of the mechanisms by which the availability of molybdenum is influenced. It is suggested that differences in the effects of lime on molybdenum and phosphorus deficiency may be due, at least in large measure, to the great difference in the number of molybdate and phosphate ions that would need to be displaced to produce measurable effects on plant growth. It is possible also that lime may influence the availability of molybdenum through its effect on ions which in turn influence the availability of molybdenum, as indicated under Section V, 4. Barshad (1951a) and Evans, Purvis, and Bear (1951) showed that Lime increased the amount of water-soluble molybdenum in the soil, and that in most cases this was associated with an increase in the molybdenum content of the plants. Barshad (1951a) found that the concentration of water-soluble molybdenum in the soil increased as the soil reaction was increased to above pH 8. The concentration of molybdenum in the plants was increased to a maximum at about pH 7.5. It seems possible therefore that under some conditions the effect of lime in increasing the availability of molybdenum in the soil may be counteracted, or perhaps reversed, by the depressing effect of higher pH on the ability of plants to take up molybdenum. By increasing the availability of molybdenum in the soil, lime stimulates symbiotic nitrogen fixation in nodulated clover plants (Anderson and Oertel, 1946). In this case the effect of lime on color, percentage nitrogen, growth, and nodulation of the clover plants is similar to the effect of molybdenum. Where the lime is not concerned also in other

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effects on the plant, the response to lime disappears where either molybdenum or nitrogen has been applied. In that case the lime-molybdenum and lime-nitrogen interactions are negative, like the molybdenum-nitrogen interaction. These negative interactions with lime are due to the effect of lime in increasing the uptake of molybdenum hom the soil where no molybdenum has been applied. It occws even when the combined nitrogen treatment decreases the amount of molybdenum taken up by the plants, showing that the lime actually corrects nitrogen deficiency in the plants by increasing the uptake of molybdenum, and hence increasing symbiotic nitrogen fixation. Lime also counteracts molybdenum deficiency in nonlegumes, and has long been known to counteract the molybdenum deficiency diseases “whiptail” of cauliflower (Davies, 1945) and “yellow spot” of citrus (Stewart and Leonard, 1952). The evidence discussed shows that lime can decrease the response to molybdenum by correcting or partially correcting molybdenum deficiency. It might be suspected that under some conditions lime would be needed to increase the availability of the molybdenum which has been added to the soil, and in this way might increase the response to molybdenum. Lime does markedly increase the uptake of added molybdenum, but so far there is no evidence that this is an important effect of lime for plant growth. Molybdenum applied to unlimed soil corrects the deficiency and as indicated under Section IVY4 may remain eff ective for many years, even on soils which already contain high levels of unavailable molybdenum. The extent to which lime corrects molybdenum deficiency varies considerably. Where the soil contains sufficient unavailable molybdenum, lime may fully correct the deficiency. Where the total molybdenum content is very high, as in a soil containing 31.5 p.p.m. of Mo examined by Robinson et al. (1951), lime may increase the molybdenum content of the plants to levels harmful to livestock. Often the effect is partially to correct the deficiency of molybdenum. Where the total molybdenum content of the soil is low, lime may have no significant effect. Anderson and Oertel (1946) obtained marked responses to either molybdenum or lime on a soil containing 10 p.p.m. of molybdenum, and responses to molybdenum buj not to lime on a soil which contained less than I p.p.m. of molybdenum. Newman (1955) has also reported marked responses of clover to molybdenum on soils where the effects of lime are negligible. Lobb (1953) found that responses to lime were often not as great or as rapid as responses to molybdenum. Cullen (1954) also has obtained substantial responses to molybdenum after lime has been applied. On some soils lime may be needed in addition to molybdenum, as

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discussed under Section V, 3b, and V, 3c. On other soils a dressing of molybdenum can replace the need for lime. Soils where lime has given no response after molybdenum has been applied, have been found in many parts of Australia (Fricke, 1944; Parbery, 1946; Anderson, 1946; Newman, 1955) and in New Zealand (Davies, Holmes, and Lynch, 1951; Cullen, 1953; and Lobb, 1953). b. Through EfJects on Legume Nodulation. Molybdenum deficiency occurs most commonly on acid soils. Where the soils are more acid than about pH 5.5, clover sown on new land is often unnodulated, or ineffectively nodulated, and because of this may not respond to molybdenum (Anderson and Moye, 1952; Newman, 1955). The plants may also show little or no response to molybdenum where lime has been used at normal levels, as the lime may not only correct the problem of defective nodulation but may also correct molybdenum deficiency by releasing molybdenum from the soil (Anderson and Moye, 1952). However, the amount of lime needed to correct defective nodulation is considerably less than the amount of lime needed to release sufficient molybdenum from the soil. In Australia, vigorous growth of clover, essential for increasing the fertility of these naturally infertile soils, can now be achieved by the use of a small dressing of lime to induce nodulation, together with molybdenum to stimulate symbiotic nitrogen fixation. The results of Anderson and Moye (1952) showed that good results can be obtained with subterranean clover, even on the poorest land on soils of less than pH 5, by mixing inoculated clover seed with lime (CaCO,) , drilling at 224 pounds of lime per acre, and .applying molybdenum-superphosphate separately. Satisfactory results can also be obtained by mixing the lime and molybdenum-superphosphate together, and mixing the inoculated seed with this for sowing. More recent evidence indicates that it will be possible to correct the problem of defective nodulation over a great deal of land by pelleting the seeds with lime after inoculation (Loneragan et al., 1955a) or by ammoniation of the superphosphate (Loneragan et al., 1955b). In practice, each of these methods would have its own special place, depending upon circumstances. Further work may reveal that legumes such as lucerne, which are particularly responsive to lime, may be grown on a much wider range of soils than at present by the use of molybdenum combined with low levels of lime. Evans, Purvis, and Bear (1951) obtained a response of alfalfa to molybdenum on soil limed to pH 5.5, and where molybdenum had been added there was very little benefit from liming the soil to a pH higher than 5.5. The problem of defective nodulation, as it occurs on acid soils in

193 eastern Australia, is due mainly to the harmful effect of excess soil acidity on the survival of Rhizobium in the soil. Spencer (1950) was able to obtain abundant nodulation of clover on an affected soil by greatly increasing the amount of inoculum and sowing immediately. Anderson, Meyer, and Fawcett (unpublished data) have shown that calcium sulfate which for a time increases the acidity of the soil, increases the proportion of unnodulated plants. This effect can be counteracted by increasing the amount of inoculum. By contrast, magnesium carbonate or calcium carbonate can be equally effective in improving nodulation where superphosphate has been applied, and may have the same effect as greatly increasing the amount of inoculum. Thus the effect of the lime is through its effect in counteracting soil acidity rather than through the effect of the added calcium. Furthermore, when used at low levels the alkaline materials often have little or no effect where the seed is not inoculated, the interaction between alkaline material and inoculum being strongly positive. The effect of the lime is to increase the survival of the Rhizobium in the soil, and for successful nodulation the seed must be inoculated and the excess soil acidity around the seed must be counteracted. Where the herbage legumes have become satisfactorily nodulated, the problem does not recur if the land remains in pasture. This is so even for annual legumes like subterranean clover. Anderson and Moye (1952) found that where no lime was used clover on small ash patches was nodulated in the year of sowing, and that plants over the whole area gradually became nodulated, resulting in substantial responses to molybdenum in later years of the experiments. These results show that the lime treatment f o r inducing nodulation is required only in the year of sowing. It is most important to ensure that a well-tested effective strain of Rhizobium is used. Anderson, Meyer, and Fawcett (unpublished data) have found that in some cases lack of nodules on clover on molybdenum-deficient soil has been due to the use of inoculum which, after subculturing a number of times, has become ineffective, presumably owing to mutation of the Rhizobium. c. Through Effects on Other Elements. Lime increases the calcium content of the soil and the pH of the soil, and these in turn influence the solubility and availability of other elements present in the soil. These other elements either through exerting some direct effect on molybdenum or by correcting deficiencies of the element in the plants, may be expected to influence the response of the plants to molybdenum. The possible significance of effects that come within this category has been suggested from time to time in the literature, but the evidence so far appears to be inconclusive. MOLYBDENUM AS A FERTILIZER

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4 . Sulfur, Manganese, Iron, and Other Elements Which M a y Decrease the Uptake of Molybdenum It has been suggested that one function of molybdenum is to act as a reduction catalyst to counteract the oxidizing effects of certain other metals. Burema and Wieringa (1942) claimed that molybdenum counteracts the oxidizing effect of copper in Azotobacter. Mulder (1954) subsequently tested this suggested relationship but could find no evidence of an interaction between copper and molybdenum. Millikan ( 1947, 1948, 1949) claimed that molybdenum counteracts effects of the elements manganese, nickel, cobalt, copper, and zinc on the physiological availability of iron, and hence counteracts some of the toxicity effects of these elements. Lohnis (1951) was unable to find any evidence that molybdenum can counteract the toxicity of manganese, while Hewitt (1948) and Warington (1951) found that molybdenum may actually accentuate the harmful effects of an excess of heavy metals. Wilson (1949a) examined the cause of scald disease of beans, which was previously thought to be a manganese toxicity because affected plants contained a high concentration of manganese, and found that the disease is due to molybdenum deficiency. Anderson and Spencer (1950a) found that the application of heavy dressings of manganese sulfate to soil considerably decreased the concentration and amount of molybdenum in the plants, and induced molybdenum deficiency. The induced deficiency inhibited nitrogen fixation in clover and inhibited the utilization of nitrate nitrogen in a nonlegume, and in each case was corrected by the application of molybdenum, The effect of manganese sulfate on molybdenum deficiency has been obtained on other soils (Anderson and Arnot, 1953; Mulder, 1954). Furthermore, it has been shown by Mulder (1954) that the manganese and sulfate ions are both involved in the effect. Increasing the amounts of either manganese or sulfate applied to the soil increased the amount of molybdenum that had to be applied to correct molybdenum deficiency in the plant. The effect of manganese sulfate was greater than the effect of either manganese or sulfate applied alone. It is very interesting to note that this effect of manganese was not obtained with all species. Stout et al. (1951) found that sulfate and phosphate affect the uptake of molybdenum by plants, but in opposite ways. The uptake is decreased by sulfate and increased by phosphate. In the experiments different sulfate salts decreased the concentration and amount of molybdenum in the plants in comparison with the molybdenum contents where corresponding phosphates, nitrates, and chlorides were used. The sulfates decreased the uptake of molybdenum from water

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culture as well as from soils, and there was no evidence that they decreased the availability of molybdenum in the soil. The effect was therefore due to an influence of the sulfate on the plants. Plant (1951) has noted that “whiptail” of cauliflower can be induced by gypsum. It should be noted that sulfate also increases the response to molybdenum where it corrects sulfur deficiency in the plants (Anderson and Spencer, 1950b). There is some evidence that the availability of molybdenum is influenced by iron. Anderson and Oertel (1946) found a high concentration of molybdenum unavailable to plants in a soil which contained large amounts of ironstone gravel. High concentrations of molybdenum may occur in ironstone concretions (Stanfield, 1935; Oertel and Prescott, 1944). Williams and Moore (1952) found a correlation between the concentration of soil iron and the availability of the molybdenum present in normal soils. It is of interest that the first responses of clover to molybdenum in Australia (Anderson, 1942) and New Zealand (Davies, 1952) were obtained on ironstone soils with unusually high total molybdenum contents. Mulder (1954) has indicated that in Holland molybdenum deficiency often appears to be influenced by the iron content of the soil. More work is needed to determine whether there is a causal relationship between iron concentration and molybdenum deficiency.

5 . Vanadium and Other Elements That Have Been Reported to Replace Molybdenum Vanadium has been reported to replace molybdenum in a number of experiments, and in some cases so also have tungsten, titanium, and cadmium. On the evidence it is not possible to be certain whether these effects have been real or whether they have been based on insufficient statistical evidence, or perhaps in some cases whether they have been due to an impurity of molybdenum in the salts used. Similar effects of vanadium and molybdenum have been reported for Azotobacter (Bortels, 1933, 1936; Horner et al., 1942), for Clostridium (Jensen and Spencer, 1947), for alfalfa, soya beans, and red clover (Bortels, 1937), and for other pasture plants (Lynch, 1954). On the other hand, in other experiments vanadium did not replace molybdenum in tomatoes (Arnon and Stout, 1939), in clover (Anderson and Oertel, 1946), or in the enzyme hydrogenase (Shug et al., 1954). It would appear that further work is needed to determine the extent to which these elements may be replaceable in their effects. Effects of tungsten and molybdenum have been reported for Azotobacter (Bortels, 1936) and for pasture plants (Lynch, 1954). Horner et al. (1942) found that responses to tungsten treatments in

196 A. J. ANDERSON their experiments were due to molybdenum impurity in the tungsten. Dmitriev (1939) has claimed to have obtained similar effects of titanium, cadmium, and molybdenum on red clover.

6. Molybdenum Present in Commercial Fertilizers As discussed under Section IV, 3, levels of molybdenum as low as

l/ls ounce per acre (about 2 g. per acre) may have quite significant effects on plant growth, depending on conditions. A dressing of 2240 pounds per acre of a treatment containing 1 p.p.m. of molybdenum would add about 1 g. of molybdenum per acre, which could well be of significance. Alternatively, a fertilizer containing 10 p.p.m. of molybdenum and used at 224 pounds per acre could add significant amounts of molybdenum. Where treatments are applied every year even a lower concentration of molybdenum in the fertilizer could be important. However, it is by no means certain that the molybdenum which occurs naturally in fertilizers is available to plants. Much of it may not be, as naturally occurring molybdenite is very &available (Anderson, 1946). Anderson and Oertel (1946) found less than 1 p.p.m. of molybdenum in the calcium and magnesium carbonates, calcium hydroxide, dolomite, superphosphate, ammonium sulfate, and sodium nitrate used in their experiments. Furthermore, there was no evidence that plants benefited from any molybdenum that may have been present in any of these fertilizers. Even heavy dressings of superphosphate, which had been used in an endeavor to grow better pasture on molybdenum-deficient land, resulted in severe molybdenum deficiency. Only wood ash, which contained 10 p.p.m. of molybdenum, had significant effects through its molybdenum content. Phosphatic rock varies considerably in its molybdenum content (Oertel and Stace, 1947; Robinson, 1948), some samples containing only 1 p.p.m. and some up to 100 p.p.m. or more. The availability of any molybdenum present may depend upon the treatment of the rock in the preparation of the fertilizers. Evans, Purvis, and Bear (1951) found that some limestone samples contained over 2 p,p.m. of molybdenum. Walsh, Neenan, and O’Moore (1952) found 4 to 5 p.p.m. of molybdenum in basic slag. However, most evidence indicates that molybdenum is rarely present in significant amounts in the fertilizers generally used. 7. Cultural Practices Studies have not been made to determine the specific effects of various cultural practices on the response to molybdenum. Cropping would be expected to induce molybdenum deficiency, especially for nodulated legumes, by lowering the level of available molybdenum and nitrogen. Lobb (1953) observed that the greatest responses to molybde-

197 num occurred where heavy cropping had been practiced, and also where the land had been eroded to the subsoil. Erosion would particularly lower the soil nitrogen status and in that way might increase the demand for molybdenum. Cultivation of the soil would increase the nitrogen status, and might well also influence the supply of available molybdenum through its effect on other elements and soil organic matter. These effects would increase or decrease the response to molybdenum, depending on the relative significance of the different effects. In fact it is quite possible that a cultural practice which increases the response to molybdenum on one soil, or on one occasion, may decrease the response on another. It would be necessary to understand fully the factors involved before it would be possible to forecast what the effect would be. MOLYBDENUM AS A FERTILIZER

8 . Diferences between Species

Species differ in their response to all elements; molybdenum is no exception. They also differ widely in the amount of molybdenum that they take up from the soil, as shown in the early surveys of ter Meulen (1930) and Bertrand ( 1939) and in the more recent studies of Barshad (1948), Johnson, Pearson, and Stout ( 1952), and Robinson and Edgington (1954). The results of ter Meulen ( 1930) indicated that legumes generally contain more molybednum than other vegetable matter. Bertrand (1939) found a high molybdenum content in legumes and crucifers and in some legume seeds. As discussed under Section V, 2, nodulated legumes may respond strongly to molybdenum where the soil nitrogen status is low, and may not respond on the same soil when it is high. Conversely, nonlegumes and unnodulated legumes may respond to molybdenum only after nitrogen deficiency is corrected. The results of Anderson and Thomas (1946) with legumes and grasses showed that nodulated legumes on nitrogen-deficient soil responded strongly to molybdenum, whereas on the same soil molybdenum was not deficient for the host legume and was not deficient for grasses. Where no nitrogen was applied to the grasses they remained pale green and nitrogen-deficient, with or without added molybdenum, showing that there was no measurable effect of the molybdenum on the soil nitrogen status, for example, through free-living nitrogen-fixing organisms such as Azotobacter or Clostridium. Where nitrogen had been applied the grasses were all dark green and well grown, and again did not respond to molybdenum, even when the nitrogen fertilizer used decreased the uptake of molybdenum. Thus the soil which was strongly deficient in molybdenum for symbiotic nitrogen fixation, was not deficient in molybdenum for grasses. Where sufficient nitrogen was applied to legumes they also did not require molybdenum.

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Johnson, Pearson, and Stout (1952) compared the response of many plants to molybdenum on a deficient soil to which nitrogen had been applied. None of the 5 grasses or 7 legumes responded to molybdenum, apart from a response of Phleum pratense in one experiment. On the other hand, all of the other 18 species responded to molybdenum. These belonged to the families Chenopodiaceae, Compositae, Cruciferae, Solonaceae, Polygonaceae, Cucurbitaceae, and Umbelliferae. It is evident from these results that the host legume and the grasses are less likely to respond to molybdenum than most other plants. Lobb (1953) has listed a number of species in order of the response to molybdenum obtained. Of the legumes, sweet clover, alfalfa, and trigonella gave the greatest responses; Montgomery red clover and cow grass gave very marked responses; and white clover, zigzag clover, and subterranean clover gave marked responses. Lobb (1953) also obtained responses of many grasses, as well as various species of Cruciferae, Chenopodiaceae, and Umbelliferae, to molybdenum. No response was obtained with barley or with beans, peas, lupins, or tares. The lack of response of the large-seeded plants was probably due mainly to molybdenum already present in the seed, as indicated by the results of Wilson (1949a) and Meagher, Johnson, and Stout (1952). It is clear that comparisons between species in their molybdenum response should take account of any differences in the molybdenum content of the seed. In a number of experiments alfalfa (Medicago sativa) has been found to respond more strongly to molybdenum than most other legumes (Anderson and Thomas, 1946; Lobb, 1953; Mulder, 1954). Andrew and Milligan (1954) have reported a response of Medicago hispida to molybdenum on a soil where subterranean clover did not respond. It seems possible that species of Medicago, which are usually found on the less acid soils, may require more molybdenum than the Trifolium species. However, Anderson and Thomas ( 1946) have pointed out that the response of different species of legume to molybdenum will depend upon the strain of Rhizobium and that comparisons between species are valid only for the existing conditions. In some experiments Anderson and Thomas (1946) obtained very poor responses of alfalfa and of Medicago hispida to molybdenum because of defective nodulation of these plants in the acid soil. On the Southern Tablelands of New South Wales, Anderson (1948) obtained responses of subterranean clover to molybdenum on a variety of soils. In an experiment on established pasture where the subterranean clover responded to molybdenum, alfalfa grew well in association with it and did not respond to molybdenum. None of the other legumes tested in these experiments on the Southern Tablelands responded to molybdenum as well as did subterranean clover. The summer was too dry for white clover to grow well. The soil was too acid for satisfactory nodulation of

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the alfalfa and other Medicago species. Grasses did not not respond to molybdenum in the year of treatment, partly because of the low molybdenum requirement of these plants, but mainly because of the very low nitrogen status of the soils. Ultimately the grasses did benefit from the additional nitrogen fixed by the clover following the application of molybdenum. Mulder (1954) found that the application of manganese sulfate to the soil increased molybdenum deficiency for some species but not others. This suggests the possibility that soils may vary in their molybdenum status in different ways for different species. If this occurs, the species most likely to require molybdenum treatment will depend upon the nature of the soil molybdenum, or upon the effect of some soil constituent, for example, sulfate or manganese, on the ability of different species to take up or utilize molybdenum. This would make still more difficult the task of assessing which species are most likely to respond to molybdenum on a particular soil. REFERENCES

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The Evaluation of Crop Plants for Winter Hardiness S. T. DEXTER Michigan State University. East Lansing. Michigan Page I. Introduction . . . . . . . . . . . . . . . . . . . 204 1. Agronomic Significance of Winter Hardiness . . . . . . . 204 2. A Cross Section of the Agronomic Problem of Hardiness or Cold Tolerance . . . . . . . . . . . . . . . . . . 204 a . Genetic and Other Relationships . . . . . . . . . . 204 b. Sources of Seed . . . . . . . . . . . . . . . 206 c. Stage of Growth . . . . . . . . . . . . . . . 206 d. Hardiness of Seed . . . . . . . . . . . . . . 207 3. The Problem . . . . . . . . . . . . . . . . . 208 I1. Theories of the Winter Hardiness of Plants . . . . . . . . . 208 1. Development of Tolerance to Freezing in a Single Specimen . . . 208 2. Differentiation between Varieties . . . . . . . . . . . 209 3. Recently Proposed Methods . . . . . . . . . . . . 210 111. Methods of Testing for Hardiness . . . . . . . . . . . . 210 1. Field Testing of Winter Hardiness . . . . . . . . . . 210 a. “Test” Winters . . . . . . . . . . . . . . . 210 b. Management of the Plots . . . . . . . . . . . . 211 c. Criteria of Injury or Recovery . . . . . . . . . . 213 d. Injury, a Composite of Factors . . . . . . . . . . 213 2. Refrigeration Machines as a Substitute for Field Hardening or Freezing 214 a. Early Work and Findings . . . . . . . . . . . . 214 b. Growing and Hardening Plants . . . . . . . . . . 216 c. Maximum vs. Field Hardening . . . . . . . . . . 217 d. Preparation for Freezing . . . . . . . . . . . . 218 e. Difficulties . . . . . . . . . . . . . . . . 219 f . Correlation with Field Tests . . . . . . . . . . . 221 g. Limitations of Artificial Hardening and Freezing . . . . . 224 3. Freezing of Hardened Plants Followed by Electrical Conductivity Measurements of Exosmosis . . . . . . . . . . . . 225 4. Other Methods of Estimating l‘njury after Freezing . . . . . . 229 5. Winter Hardiness Tests on Seeds or Small Seedlings . . . . . 230 6. Estimation of Winter Hardiness without Freezing . . . . . . 232 IV. Summary . . . . . . . . . . . . . . . . . . . . 235 References . . . . . . . . . . . . . . . . . . . 236 203

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I. INTRODUCTION During the past century, a vast literature has been built up dealing with the physiological nature and the practical evaluation of winter hardiness in plants. Publication of additional research reports each year gives evidence of continued active interest in these problems. Since extensive reviews and bibliographies (Maximov, 1929; Belehradek, 1935; Harvey, 1936; Luyet and Gehenio, 1940; Tumanov, 1940; and Levitt, 1941) have been made of the literature, no attempt will be made to include earlier papers unless they contribute directly to the subject of methods of evaluation of winter hardiness. Nor will papers dealing with the nature of horticultural problems be mentioned except when they contribute specifically to the problem of evaluation.

1 . Agronomic Significance of Winter Hardiness From an agronomic standpoint, the characteristic of winter hardiness in perennials, biennials, and winter annuals is of such importance that it frequently overshadows many other characteristics, particularly in colder climates. Thus, a variety of alfalfa (Medicago saliva) in the northern dairy regions may have the attributes of rapid recovery after cutting, large yields, desirable disease resistance, and abundant growth for fall pasture, and yet find no acceptance by farmers because of failure to survive winter conditions. A variety of winter wheat (Triticum sativum) or winter barley (Hordeum sativum) may have various desired characteristics but fail because of lack of winter hardiness. Similarly, the agronomist is interested in the effects of management on winter hardiness. Crops of great potential value may be ineffectively used when knowledge of helpful managerial practices is lacking or not applied. Thus, rotation management to control winter crown rots in alfalfa, etc., or satisfactory inoculation and subsequently increased vigor in birdsfoot trefoil (Lotus comiculatus) might completely alter the winter survival and agronomic value of these crops in many regions. 2. A Cross Section of the Agronomic Problem of Hardiness or Cold Tolerance

a. Genetic and Other Relationships. Certain vegetative characteristics are rather commonly associated with winter hardy varieties of crop plants, and various genetic complications often result from this. Johnson and Goforth (1953)have shown in genetic studies with sweet clover (Melilotus alba) that the plants selected for the best vigor in the first year of growth had such a poor average winter survival that their value

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as breeding material for colder climates was questionable. Coffman et al. (1949) and Atkins and Coffman (1951) found almost complete correlation between decumbency and winter survival in winter oats (Avena byzantina). They report a decided varietal and location interaction of hardiness. The fact that a variety was decumbent, with little fall growth, did not prevent comparatively early rapid spring growth, possibly because of lack of injury during the winter. Rosen et al. (1940) report attempts to hybridize oats to combine desirable fall pasturing characteristics with winter hardiness and disease resistance, but do not report favorable results, describing the attempt as a paradox. Coffman ( 1955), reporting the results of extensive winter oat trials, remarks that “obtaining oats having both hardiness and disease resistance is clearly difficult. Genes for disease resistance were originally located almost exclusively in spring-type oats (Avena sativa) .” Murphy (1939) reports the expected detrimental effects of diseases on winter hardiness in oats. Quisenberry and Bayles (1939), in a study of growth habits of winter wheat in relation to winter hardiness and earliness at eight stations, found all degrees of “winterness” or “winter habit” (as contrasted with spring habit) in 30 varieties planted in a wide range of climates. The rank of “winterness” was much the same for all stations, but it was not closely related to earliness of heading, nor with winter hardiness. Similarly recumbence in alfalfa varieties has been associated with winter hardiness for many years, and yet is not infallibly related. For example, it is doubtful if the alfalfa variety RHIZOMA is as hardy as GRIMM, although it is more decumbent. Great emphasis continues to be given to the relationships between ease or condition of vernalization and winter hardiness (Dexter, 1941b; Timofeeva-Tjulina, 1949). Kostjucenko and Zarubailo (1937) describe the subsequently adverse effect on winter hardiness when grains are vernalized on the mother plant in cold weather during ripening. Rudorf (1938) lists numerous papers on this general subject in relation to the objectives of plant breeding. Smith (1951) reports a confirmation of the idea that there is a “measureable difference in the root development (branching) of alfalfa varieties and strains” and that in general much branching is associated with winter hardiness. Arakeri and Schmid (1949) indicate that various legumes and grasses vary widely in the stage of development that is optimal or necessary for winter survival. Brink et al. (1939) and S m i t h (1949, 1952) tested several alfalfa and clover varieties and found varietal differences in survival under ice sheets. They suggest that, even when noninjurious temperatures are used, this characteristic is rather closely associated with winter hardiness. Myers and Chilton (1941) found a correlation between winter

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hardiness and rust resistance in timothy (Phleum pratense) clones but not in orchardgrass (Dactylis glornerata). Schultz (1941) found great variation in the winter hardiness of orchardgrass strains. “NOcorrelation was found between winter hardiness in the field and cold resistance in the freezing chamber. . . . Under Minnesota conditions yield was positively and significantly correlated with winter hardiness, plant height, and number of culms in the first crop, and negatively and significantly correlated with erect plant type, percentage rust infection, and number of culms in the second crop.” Bowden (1940) concluded, from a study of about 100 species and varieties, that the data do not support the theory that polyploids are more hardy than diploids. Seth (1955) studied root sections of several varieties of alfalfa representing a wide range of winter hardiness and bacterial wilt resistance, but was unable to find any anatomical characteristics that were correlated with either of these two characters. Corns (1953) describes an improvement or hastening of hardening of parsnips (Pastinaca sativa) in cool weather as a result of spraying the plants with growth regulators such as naphthaleneacetic acid. Since such treatments have been shown to change osmotic pressure, sugar content, respiratory rate, enzyme systems, and general growth behavior, some effect on winter hardiness might be expected. In a trial conducted by the author in Michigan, however, some years ago, no effects were observed when alfalfa seedlings were similarly sprayed in early winter. The matter needs more detailed investigation. Most of these relationships seem reasonable and pertinent, although sometimes reversed, but there are also genetic and structural or anatomical relationships which seem completely unrelated from a survival standpoint. Middleton and McMillen (1944) found that in barley their data “seem to show that a fairly close relationship exists between roughawnedness and the winter habit and smooth-awnedness and the spring habit.” b. Sources of Seed. Sprague and Fuelleman ( I W I ) , Smith and Graber (1950), Graber and Smith (1951), Smith (1955), and many others have studied the relationships between source of seed of a given variety and its winter hardiness characteristics. Rogler (1943) and Law and Anderson (1940) have compared the hardiness of strains of various species of “wild grasses, grown from seeds produced in various regions. Uniformly, seedlings of southern or mid-northern grasses were more hardy when produced from seed of northern than from seed of southern origins. Even with characteristically northern grasses, this same difference was seen, but to a lesser degree.” c. Stage of Growth. Varietal differences in winter hardiness have also been found to exist at different stages of growth. For example,

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hardiness rank may be quite different in the spring than in the winter. Bud hardiness and stem hardiness may differ erratically with the weather. Varietal respiratory differences may occur and influence hardiness under various conditions (Newton and Anderson, 1931; Sprague and Graber, 1940, 1943). Wilmer (1952) emphasizes the hazard of dry soil in winter survival. Livingston and Swinbank (1947) describe two types of spring frost injury in winter wheat. Head injury leads to sterile florets, whereas injury at the base of the stem leads to lodging. Great varietal differences in these two regards were observed, especially in stem injury. Suneson (1941), in speaking of frost injury to cereals in the heading stage, remarks that “Breeding for protection against frost damage seems impracticable, because the spread in cold tolerance appeared to be limited to temperature differences of only 2 or 3 degrees F.” He describes the widespread planting of a new and very early wheat variety which vastly increased the hazard from frost during heading. In this case the advantages of an otherwise desirable variety were canceled by undue earliness in heading and subsequent frost damage. Even in annual plants, considerable varietal differences of frost resistance in the seedling stage may exist. Dillman (1941) sowed flax (Linum usitatissimum) at several dates during the fall in order to obtain differing stages of growth when frost occurred at Arlington, Virginia. No consistent relationship was found between wilt and cold resistance, as has sometimes been claimed, but varieties with upright growth were generally less hardy than those with a more branching habit. Holbert et al. (1933) have described a machine to be used in the field for testing the frost resistance of such plants as maize (Zea mays). Ivanov (1941) reports that fertilizers generally helped the frost tolerance of several spring-sown plants, obtaining considerable tolerance in plants ordinarily very sensitive. Laude (1937a,b) examined the hardiness of several varieties of winter grains as in the greenhouse they changed from the field-hardy condition to that of active growth. He found that the normally very hardy varieties lost this characteristic so rapidly that they were sometimes actually less cold resistant in the spring than were varieties commonly considered tender. There appears to be some divergence of opinion on this point (Rudorf, 1938). d. Hardiness of Seed. Rossman (1949) found significant varietal differences in tolerance of maize seed to freezing prior to harvest. Tolerance was significantly related to varietal seedling vigor and to physiological maturity of the seed, rather than to moisture content as such. Maternal seed characteristics were more important than was embryo constitution. Haskell and Singleton ( 1949) used controlled low temperatures in testing inbred and hybrid maize from the standpoint

208 S. T. DEXTER of vitality following exposure to low soil temperatures, and suggest that this method is more convenient in some ways than that of planting in the field. Bennett and Loomis (1948) tested the freezing injury of seed corn with 2,3,5-triphenyltetrazolium chloride, and found that the method, while rapid, gave a somewhat high estimate of germinability. Kinebacker and Laude (1955) have devised a method for artificially testing the heaving resistance of seedlings. 3. The Problem This sampling of comparatively recent papers gives some idea of the range of interest relating to the evaluation of cold resistance in economic plants. In any one of these cases, the problem o€ objective numerical evaluation of injury or recovery exists. This is the problem.

11. THEORIES OF THE WINTER HARDINESS IN PLANTS 1. Development of Tolerance to Freezing in a Single Specimen The winter hardiness of plants has been attributed to many factors. In certain early work, the opinion was stated that some winter-hardy plants escaped injury because of the heat evolved in their life processes; repeatedly it has been suggested that hardy forms did not freeze. Supercooling, without ice formation, has been described in hardened and unhardened plants, under which circumstances little or no injury was seen. Protection from low temperatures and freezing has been shown to be the cause of winter survival in various plants. Roots, rhizomes, or crowns of plants may survive low air temperatures when buried deeply in the soil, whereas in similar plants less adequately covered, death may follow exposure during the same period. Conversely, the roots of many woody plants are reported to be far less cold tolerant than their stems. Snow cover is often an important factor in the overwintering of plants. Many of the older studies showed that the injury suffered by plants on exposure to cold was closely associated with ice formation within the tissues. Ice formed in the intercellular spaces has been shown to be less injurious than that formed within the cell itself. Other work has contrasted injury due to ice formed within the vacuole with that of ice formed within the protoplast. Since the correlation between ice formation and injury has been so marked, a great many papers have dealt with the mechanisms of prevention of ice formation. Higher osmotic concentration of the cell sap, with a consequent lower freezing point, has been described in an effort . to explain the phenomenon of winter hardiness. High sugar concentrations in hardy varieties of wheat and other species have been found. To this high sugar content has been attributed not only the osmotic protec-

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tion described above but also an effect inhibiting the precipitation of protoplasm when the cell sap is concentrated by ice formation. The possibility that the protoplasm is “salted out” when water is withdrawn has been suggested. Protection against this effect has been attributed not only to sugars but also to soluble organic nitrogen compounds which have been shown to increase upon exposure of the plant to low temperatures. An increase in the hydrophilic colloids in the tissues has been shown during the hardening process in plants. That these colloids “bound” the water, making it unavailable for ice formation, has been suggested. A change in the ioselectric point of the protoplasm has been described by Sarina (1937). He concludes that this makes precipitation of the protoplasm more difficult in hardened than in unhardened plants; an increased buffer action of the sap during hardening has been described. Low respiration of hardy varieties during winter and conservation of the soluble carbohydrate reserves has been described in an attempt to differentiate hardy and nonhardy varieties. As has been suggested, the cause of injury due to ice formation has not been clear. The removal of water on freezing is so considerable that desiccation has been considered by some to be the injurious factor. By others, the idea of protoplasmic precipitation by increased salt or acid concentration has been stressed. Others have emphasized the mechanical injury to various parts of the cell by ice crystals or pressure. In several recent papers, the idea of too rapid plasmolysis and deplasmolysis has received vigorous support as an explanation for the injury due to ice formation.

2. Differentiation between Varieties Of the many suggested theories, few have been shown to be useful in differentiating between varieties on a low temperature survival basis. Within one variety, or specimen, as it changes from a nonhardy summer condition to a hardy winter condition, many or most of these “protective” processes are readily detectable. Increasing surcrose concentration is particularly a regular concomitant of increasing winter hardiness o r cold tolerance, but this may have little to do with species or varietal differences. Percentage dry matter commonly increases; soluble minerals may decrease per gram of green weight or dry matter (Dexter, 1934). Cell sap concentration may increase (Greathouse and Stuart, 1936; Wang et al., 1953), concentration of soluble organic nitrogen compounds commonly increases, protoplasmic viscosity may decrease, and cell membrane permeability increases as a specimen becomes more tolerant of freezing, or merely as it is exposed to low temperature (Dexter, 1935). Only in rare cases, however, have these and other properties been shown to differentiate reliably between varieties on a winter

210 S. T. DEXTER hardiness basis (Ireland, 1939), whereas failures to differentiate have been common (Steinmetz, 1926; Weimer, 1929; Megee, 1935).

3. Recently Proposed Methods Although many of these methods have been repeatedly explored by agronomists, the methods proposed by Levitt and Scarth ( 1936), Scarth and Levitt (1937), and Simiiiovitch and Briggs (1953, 1954) do not seem to have been adequately investigated, so far as their utility in varietal evalution is concerned. See Section 111, 6c for further discussion and details. 111. METHODS OF TESTING FOR HARDINESS

I. Field Testing of Winter Hardiness The most common method of evaluating varieties of plants for winter hardiness or cold injwy is by ordinary field testing. This is usually carried on in connection with other determinations. In this method, either greenhouse, or, more commonly, field grown plants are exposed to ordinary growing, hardening, and freezing conditions in the field. The injury to the plants may be determined by bringing samples into the greenhouse at intervals during the winter (Worzella and Cutler, 1941), or by examining them in the spring. Although most agronomists and farmers would feel that this practical test is essential to confirm any other test, the complications and difficulties with ordinary field testing are exceedingly great and well recognized. There have been set up in the United States of America at various times special “uniform winter hardiness nurseries” for several crops in several regions of different climatic conditions. These include a series of varieties of well-established degrees of winter hardiness, together with others of unknown hardiness. It is evident that such nurseries can furnish essential information. Even with all due caution in the selection of the site for the nursery, statistically significant differences are often hard to obtain, particularly between varieties of somewhat the same degree of hardiness. Agreement between various tests is by no means perfect, either in different locations or in several years at the same location. Such difficulties are expected in agronomic work, and are perhaps little more pronounced in winter hardiness testing than elsewhere. One of the complicating features that delays the accumulation of significant data on hardiness differences is the scarcity of “test winters” in which conditions are precisely right to give differential injury (Ausemus and Bamberg, 1947). a. “Test” Winters. Winter weather of something like “average” severity is essential for such tests to be locally reliable. A suitable hard-

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ening period, with properly grown plants, is essential, lest all varieties be killed by untimely autumn freezes. Suitable snow cover, uniformly distributed, without drifts or bare spots is needed. Avoidance of ice sheets or standing water is a necessity. Particularly, these desired conditions must exist before perennial plants become so old or diseased or insect-ridden that effects of cold cannot be differentiated from other injuries. Tregubenko (1940) believes that alfalfa roots should be tested the first winter. Worzella and Cutler (1941) and Jones (1945) have analyzed the weather conditions and types of injury that are responsible for the death of winter wheat and alfalfa in the field. A recent example may be given from Michigan conditions in alfalfa-variety tests. Twenty-two varieties, planted in 1952, went through the three following winters (1952-53, 1953-54, 1954-55) without appreciable injury even to CALIFORNIA COMMON alfalfa. Obviously nothing was learned of the hardiness of SEVELRA, DUPUITS, NOMAD, etc. By this time, bacterial wilt had made the plots valueless for winter hardiness tests and they were plowed up. During the first and second winters, however, other tests (Section 111, 3) had classified the varieties as to cold resistance. b. Management of the Plots. ( I ) Cutting treatments. A great volume of literature has been published upon the effect of management of the crop upon the subsequent winter hardiness. Only a few of the papers will be cited as representative. Hardy varieties may be rendered more sensitive to low temperatures and tender varieties at least moderately resistant by appropriate management. Too frequent defoliation, or defoliation during certain critical periods, has been shown to have a great influence upon the winter hardiness, survival, or production of various plants (Graber and Sprague, 1938; Rather and Harrison, 1939; Grandfield, 1943; Smith and Graber, 1948; Tesar and Ahlgren, 1950). (2) Eflects of fertilizers. Certain types of fertilization have been long recognized as highly influential in winter hardiness. For example, in old bulletins it is reported that “common” alfalfas are as hardy with potash as GRIMM is without it (Kucinski et al., 1938; Wang et al., 1953). Carroll and Welton (1939) report the harmful effects of nitrogen fertilization in the fall on the winter survival of bluegrass (Poa pratensis). Tumanov (1931) and Dexter (1933b) report the effects of nitrogen and other fertilizers in combinations with exposure to low temperature with and without illumination of the plants. Plants high in nitrogen may completely fail to harden at a low temperature when not illuminated. Complications of species competing for nutrients (Blaser and Brady, 1950) may, for example, eliminate alfalfa in grassy plots. Rohde (1942) in reviewing the literature (117 references) con-

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cludes that potassium is beneficial to winter hardiness development in all plants. Ivanov (1941) found fertilizers beneficial to hardiness in spring-sown plants. ( 3 ) EfJects of diseases. In some regions, winter survival of some species is scarcely a problem of the ability of the plant to endure low temperatures, since most strains of a given species may be so susceptible to locally prevalent diseases that suitably disease-resistant varieties alone attain a condition such that they can survive low temperatures (Cormack, 1952; Slykius, 1952). Thus southern anthracnose of red clover (Trifolium pratense) or bacteria wilt of alfalfa may be determining factors in winter survival rather than low temperatures. Yarwood (1946) indicates that “giant hill” disease in potatoes (Solanum tuberosum) increases frost resistance. ( 4 ) EfJects of insects, ice sheets, etc. In other cases, damage from insects or ice sheets may differentiate the varieties rather than winter conditions as such. The differential effects of various factors have been studied by Graber (1941) , Dexter (1941a), and Jones ( 1945), who report rather contrasting findings even on one variety of alfalfa and one insect. In some climates and some soils freezing and thawing of the soil throughout the winter is so common that resistance to heaving and strength of roots rather than resistance to cold, as such, is the characteristic sought (Worzella, 1932; Lamb, 1936, 1939). (5) Seasonal variations. In the light of all these managerial complications, it is not remarkable that year to year and location to location variations in winter hardiness of varieties are sometimes inexplicable. Varieties have been shown not to respond equally to fertilizer, to cutting treatments, to early or late planting, to length of day, etc., and their winter hardiness rankings may be correspondingly varied. For example, although cutting on September 15 is ordinarily severely damaging to winter hardiness of alfalfa at East Lansing, Michigan, in the very dry fall of 1952 it was harmful only to the one variety (TALENT) that made appreciable growth after that date (Beatty, 1954). In 1953 the incidence of bacterial wilt was the controlling factor. As another example, the mature alfalfa plant that reacts to short days by producing recumbent growth does not appear to be injured in the development of hardiness by this condition (Tysdal, 1933; Dexter, 1933a). Yet there is reason to suppose that August seeding of these varieties, with subsequent inhibited growth and small seedlings, puts these varieties at a relative disadvantage in comparison with varieties that have more active fall growth. Thus, LADAK alfalfa, August-seeded, has appeared comparatively more hardy in the second than in the first year, whereas, if spring-seeded its roots may be developed sufficiently to show its proper varietal rank.

213 (6) Varietal winter hardiness. It is, then, of general interest to the agronomist to know whether the winter hardiness rating of a variety is largely due to tolerance of winter conditions and low temperatures. or whether it is a false reading, compounded of reactions to the numerous factors which may or may not be readily controlled o r which are only locally or temporarily applicable. c. Criteria of Injury or Recovery. Probably the most common agronomic measure of the comparative winter hardiness of a variety is accomplished by means of “percentage stand counts” or estimates thereof. For example, if on a suitable area there are 100 live plants in the fall and only 60 in the spring, GO per cent survival would be a measure of winter hardiness or survival. In other cases, “percentage ground cover” or “vigor” in the spring may give an equally good or better measure, particularly in cases when few or none of the plants actually die outright. In cases where only one variety is used, yield of dry matter per given area may be a reasonable method of judging injury (Sprague and Graber, 1943). In most species, and in woody species particularly, killing usually is not complete. Buds or small branches may be killed but nothing else. Here, the percentage of tissue browned or killed has been used as a measure of hardiness. Turgidity or firmness of tissue (Bunakov, 1949) after 3 days in damp sand was a fair measure of winter hardiness of alfalfa roots dug from frozen soil. “Vital” staining of live cells and examination under the microscope has been proposed (Iljin, 1934; Levitt and Scarth. 1936). d. Injury, a Composite of Factors. In any case, it is traditionally difficult to arrive at a n acceptable figure for injury. Frequently plants that are apparently dead recover almost completely after a period of several weeks. Foliage and terminal buds may be dead and brown but regeneration from new buds (Dexter, 1930; Smith, 1950) may give a contradictory value. Often “winter killing” is little more than the thinning out of weak plants in an overthick stand and has little effect on the subsequent yield. This is particularly true when plants are in a thick drill row rather than more or less evenly spaced. Furthermore, many of the forage crop varieties contain plants of many degrees and proportions of winter hardiness (Dexter, 1932; Hollowell and Heusinkvelt, 1941). One severe winter may kill many of the tender plants, but leave a residue of plants almost as hardy as an apparently more hardy variety. The investigator should examine his “winter hardiness” results with some care in observing extenuating circumstances. Field trials may be expected to give a composite of many factors, varying from year to year and from place to place. MINHARDI wheat, for example, may be EVALUATION O F CROP PLANTS FOR WINTER HARDINESS

214 S. T. DEXTER hardy in the bare frozen fields of Manitoba, but not in water-soaked Indiana or Ohio because of heaving (Worzella, 1935; Lamb, 1939). NARRAGANSETT alfalfa is reported to endure wet heavy soils where RANGER cannot survive. VERNAL alfalfa was released as a variety instead of a higher yielding experimental synthetic on the basis of the belated discovery of superior survival under ice-sheet conditions. In other cases, the problem may be “spring” rather than “winter” survival. In northern Michigan, Vander Meulen (1942) found that alfalfa stands were usually lost in the spring rather than in the winter. At the Lake City Experiment Station in north central Michigan, spring frosts appeared to be a considerable factor in the survival of slow-starting LADAK in comparison with rapid-starting BUFFALO and RANGER alfalfa. Invasion of grasses after defoliation by spring frosts became a second factor. Recent reports indicate that “snow molds,” giving rise to ‘‘Winter crown rot” in alfalfa, may be the most important cause of loss of alfalfa stands in various parts of Canada (Cormack, 1952) and Norway (Ekstrand, 1947, 1949). In these climates one might expect that low winter temperatures ordinarily would be the deciding factor. Many other species were similarly affected, but usually to a lesser degree. About three years of fallow was found necessary before alfalfa seedings could be made without severe losses from winter crown rot. 2. Refrigeration Machines as a Substitute for Field Hardening or Freezing a. Early Work and Findings. Following the improvement and common distribution of mechanical refrigerators, the study of winter hardiness passed into a somewhat different phase. Harvey, at the University of Minnesota, perhaps was the first investigator to make use of artificial refrigeration on a large scale in hardiness investigations. Akerman, in Sweden, carried on similar investigations at an early date. From experiment stations in the United States of America and several other countries have come reports and descriptions of equipment, techniques, and experiments. By the use of such machines, plants could be grown under more accurately prescribed conditions than when grown in the field, Day length and temperature and night temperature could be controlled. Plants could be frozen at selected, controlled temperatures, and examined for stand count, injury, etc., much as in the field. As a result of early work with these machines, the concept of winter hardiness as a definite developmental, physiological condition was clearly established. It was shown, for example, that alfalfa varieties of known variability in hardiness were equal in ability, as nearly as could be determined, to withstand low temperatures when taken from the

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field in early autumn. Varieties of recognized field hardiness, however, developed a capacity to endure freezing as winter approached (Steinmetz, 1926). Varieties of winter wheat likewise were found to be tender until subjected to hardening at low temperatures. Varietal differences were not clear in unhardened plants. Salmon (1933) reported, however, that varietal differences in hardiness in rye (Secale cereale) were much the same before as after hardening. Many studies were made, attempting to correlate physical and chemical characteristics with actual ability to endure low temperatures. No clear-cut undisputed relationships were found. It was shown, however, that when environmental conditions during hardening favored growth, elongation, and respiration, hardening was slower and less complete than when environmental conditions favored storage (Dexter, 1933a; Tysdal, 1933). During the past 25 years the use of such machines has become established as a great convenience, if not a virtual necessity, in winter hardiness studies. Not only have they shown their usefulness in winter hardiness studies, but also in investigations of the frost resistance of annual plants such as maize. For detailed descriptions of several rather different arrangements, see Steinmetz (1926), Peltier (1931), Dexter et al. (1932), Salmon (1933), and Worzella (1935). In some of the temperature chambers, all illumination is furnished by electric lights; in other cases, a portion of a greenhouse is refrigerated in such a manner that sunlight is adequate for the growth of plants. It is convenient, in any case, to have the low-temperature room located in such a manner that plants, pots, and soil can be conveyed to it from the greenhouse or beds with a minimum of handling. If the hardening room is tightly sealed or insulated and large quantities of plants are hardened at one time, some supply of carbon dioxide should be arranged, since otherwise hardening proceeds very slowly in the plants so handled (Tumanov, 1931; Dexter, 1933a). The atmosphere in the hardening room is generally very dry. Considerable attention must be paid to adequate watering of the plants, to avoid experimental inconsistencies. It is highly desirable to provide thermostatic control in the hardening room to avoid too high as well too low temperatures. When large electric lights provide illumination for the plants, unobserved failure of the refrigeration unit may lead to such excessively high temperatures in the room that the plants are lost, and, of course, the entire experiment ruined. A thermostat may easily be installed that will turn off the lights when the temperature reaches, let us say, 5 O C. above the desired hardening temperature. The many complications involved in prescribing the thermostatic control of a cold chamber require the services of a competent refrigera-

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tion engineer. For example, thermostatic control that merely turns off the compression motor when the desired low temperature is reached, may be entirely inadequate to give satisfactory temperature control. Even with considerable precautions, the temperature variations in a small cold chamber are likely to be excessive. It is sometimes convenient to provide inside the thermostated freezing chamber, a large container filled with a suitably concentrated solution of alcohol and water, which, when frozen to a thick slush, will maintain a remarkably uniform temperature in spite of variations in the air temperature of the chamber. In this slush, suitable containers of experimental material may be immersed for freezing at the desired temperature. The accurate control of freezing temperatures is perhaps unnecessarily stressed here; but when the process of hardening of a plant is being followed, one finds that variations in freezing temperatures lead to large differences in injury, so that determinations on successive dates on various lots are not comparable unless every precaution is taken. b. Growing and Hardening Plants. Although our knowledge of the optimum hardening requirements of plants (light, duration, age of plants, etc.) is very incomplete, it is certain that small differences in temperature produce large differences in hardening (Harvey, 1930; Peltier and Tysdal, 1932; Tysdal, 1933; Dexter, 1933a, 1935; Rachie and Schmid, 1955). It is difficult, at best, to preserve an approximately equal temperature in different parts of a refrigerated room. Stratification of the air is frequently very noticeable. Even when the air in a closed room is stirred with an oscillating electric fan, considerable temperature variation occurs throughout tlie room. This lack of uniformity in temperature is increased by the use of large electric lights. The plants in pots or flats near the lights are heated more than those at a greater distance. It is particularly difficult to maintain a temperature at, or very near, Oo C. The inevitable fluctuations in temperature within the room, particularly when the lights are turned off or on, when doors are opened, or when warm pots are brought in from the greenhouse, may lead to unpredictablc experimental errors when a hardening temperature of Oo C. is used. Frequently the soil in individual pots freezes, while surrounding samples do not. Most of the evidence from artificial hardening of herbaceous plants suggests that a hardening temperature below 2 O C. is not necessary. The Russian literature (Tumanov, 1940) strongly emphasizes two stages in hardening, the second of which occurs usually at freezing temperatures. Rodger (1955) found little or no secondary hardening in alfalfa seedlings as a result of exposure to freezing temperatures. There is considerable evidence of a benefit of lower temperatures in hardening woody plants. At the Minnesota Experiment Station, Brierley

217 (1942) found that temperatures much lower than freezing may be necessary and effective in the adequate hardening of apple twigs. Basal branches that were covered with snow, and at a temperature of about 23O F., were uncovered in subzero weather. These suffered more severe damage than did branches higher up on the same tree, to which the snow cover had not reached. Basal branches that were left covered with snow also escaped freezing injury. These results are somewhat similar to those concerning the mulching of strawberries which were reported by Brierley and Landon (1944). They found that a considerable decrease in winter hardening can be brought about by applying the mulch too early in the season. In Michigan there are regions where early snowfall often prevents the freezing of the soil until the snow melts in the spring. In these regions, survival of alfalfa is generally poor, and winter wheat is rarely successful. Several methods have been used to grow and harden the plants to be tested in the freezing chamber. Steinmetz (1926) dug alfalfa plants from field plots at intervals during the year and subjected the roots to controlled freezing, both in the soil and in the open air. Distinct varietal differences in recovery after freezing were found which corresponded to those recognized in field experiment. In experiments by Dexter et al. (1930, 1932) , alfalfa roots were dug from field plots, washed, rinsed in distilled water, surface-dried, weighed into several samples, and frozen in test tubes. Some of the samples were planted in greenhouse soil to observe recovery and others were covered with measured quantities of distilled water, into which exosmosis of electrolytes occurred. The electrical conductivity of the resulting solution was determined, and correlated with the degree of injury (see Section 111, 3). Peltier and Tysdal (1932) grew alfalfa seedlings in flats in the greenhouse, and subjected them to a hardening treatment of two weeks duration at several ages, usually about one month. The plantings in each flat included rows of one or more check varieties. They found that considerable replication is necessary and that edge rows may need to be discarded. Salmon (1933) grew winter wheat seedlings in small pots (4to 6-inch), both out of doors and in the greenhouse for use in freezing tests. Fuchs (1934) recommends growing wheat plants for 30 days at 5 O to l o o C., then hardening for 3 days at 2 O C. before freezing. c. Maximum us. Field Hardening. In connection with the hardening of plants in preparation for freezing it is not at all clear that agronomists should be concerned with the maximum attainable winter hardiness in their varieties. The actual hardiness attained under local conditions may be more significant than maximum hardiness. An investigator might, therefore, prefer to let his plants grow and harden in the field, bringing them in for artificial freezing. Ausemus and Bamberg EVALUATION

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218 S. T. DEXTER (1947), in testing winter wheat strains and varieties both in the field and in the cold chamber, found significant correlation of winter hardiness estimates in only one year out of five (1935-41), and negative correlations in two years. They remark that “Perhaps the field test does not always bring out true differences in cold resistance.” Fuchs and Rosenstiel (1 939) strongly emphasize the necessity of considering local early winter conditions of growing and hardening, as well as spring conditions, in making hardiness tests. Extensive Russian tests with day length and fall cutting of red clover varieties (Schulz, 1949; Gupalo, 1953; Ermilov, 1954) show marked effects on fall growth and subsequent winter hardiness, espe cially with seed from southern sources. Straib (1946) and Becker et al. (1947), after making extensive tests with over 1000 varieties and strains of winter wheat, concluded that winter hardiness is induced, increased, or decreased by environmental conditions, and that varieties are variously affected and suffer from several types of winter injury at different times of year. They conclude that the inheritance of the winter hardiness character is governed by at least several genes. Wheat from various regions, Russia, the United States, Australia, etc., reacted more or less in groups of hardiness patterns. Mere cold resistance was not a sufficient test of winter hardiness, but artificial freezing tests with the more hardy varieties agreed well with field tests. They found no relationship between winter hardiness and early growth in the spring. d. Preparation for Freezing. Uniformity of preparation OI the samples for the actual operation of freezing is of extreme importance. Almost every investigator in this field has reported necessary precautions. The size of pot or flat in which the experimental material is grown should be uniform; the moisture content of the soil at the time of freezing should be regulated; and pots should be prechilled to about Oo C. before freezing (Platt, 1937). Tysdal (1933) says that “12 to 16 hours before exposure in the freezing room the porous pots or flats were saturated with water. Natural drainage left the soil in different pots or flats at approximately the same moisture content.” The rapidity of freezing of the soil and the plant, and the final temperature reached, in short exposures to low temperature, is greatly influenced by the soil moisture. The degree of injury from the exposure to low temperatures is affected by either the rate of freezing or the rate of thawing (Levitt, 1939). Methods used with wheat are fully described by Salmon (1933) and Worzella (1935), and those used in experiments with alfalfa are described by Peltier and Tysdal (1931,1932). Other authors have described sampling direct from the field plots, freezing small clumps of soil and plants, or potted plants, as Timmons and Salmon (1932) did with alfalfa, with subsequent counts of per-

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centage survival, or estimated injury in the greenhouse. In decided contrast with the recommendations of Peltier and Tysdal, with alfalfa, Meader et al. (1945) emphasize the necessity of a slow lowering of the temperature when artifically freezing peach (Arnygdalus persica) twigs in a hardiness test. Eades and Wade (1944), working with garden peas (Pisurn sativurn), suggest that an unusually accurate procedure for freezing is to dip the tops of rooted plants for a few minutes directly in a solution of ethylene glycol and water. This solution was held almost precisely at the freezing point of the plant by the addition of frozen solution of the same concentration. They suggest this method as a means of avoiding what they state to be the two “most obvious defects of the conventional freezing box technique,” namely, the “freezing patterns that develop in the plants on a tray” and the “inability to duplicate actual temperatures from one series to another.” They report that such a solution is nontoxic, and that a freezing treatment of 10 minutes at 26O F. gave considerable killing. e. Dificulties. Two fundamental difficulties invariably arise in the use of the refrigerator to determine winter hardiness. Only by long experience can one select a freezing temperature that will differentiate hardy and medium hardy varieties. Sometimes all plants of all varieties are killed, or conversely, none are killed. Suneson and Peltier (1938), working with wheat, suggest that a medium hardy variety be included in the trials as a check, and that the freezing treatment be adjusted to attempt to kill about 40 to 60 per cent of the standard variety. Injury to varieties can then be expressed in per cent of the check. Fuchs (1934) found that recovery following freezing winter wheat for 36 to 48 hours at -8O to -12O C. agreed well with field results. Assuming that the investigator is able to select such a freezing method, the second problem faces him. How shall he determine the extent of the injury from cold? Some investigators have counted the living plants in each pot or row or flat before exposure to the testing temperature, and, after a specified number of days, have counted the surviving plants. The results are then expressed in percentages. All authors agree that the method leaves much to be desired. Invariably, all degrees of survival are found. One sample may survive 80 per cent, and yet none of the surviving plants actually live to maturity. One sample may survive at the end of a recovery period to the extent of 60 per cent and all surviving plants be relatively vigorous. Following experiments conducted with winter wheat over a period of five years in which more than 30,000 four-inch pots, containing between 125,000 and 150,000 plants, were frozen, Salmon (1933) reports that the percentage survival criterion of relative injury “was soon found

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to have some more or less serious limitations. One of the more serious was that in many cases the plants after freezing died as a result of a secondary effect, probably physiological after-effects of injury to the roots. The plants turned yellow a few days after freezing and soon thereafter were dead. Invariably the inside crown tissue was badly discolored. There seems to be no relation between varieties and the degree of this injury. Plants which appeared to have been only slightly injured by low temperatures were often killed completely by this secondary effect. Another objection to this criterion is the fact that in many experiments no plants whatever are killed, even though there may be obvious and marked differences in injury. Thus it is not uncommon for certain susceptible varieties to be frozen almost to the ground level and yet completely survive. The survival in such cases gives no indication whatever of the degree of injury. . . . 9 3 For these reasons, Salmon placed major dependence upon “the degree of injury.” Salmon continues “This is, of course, somewhat arbitrary, insofar as intermediate degrees of injury are concerned, since they must be estimated. The upper and lower limits are easily established in that plants are considered as 100 per cent injured if, in the judgment of the operator, none of them will survive, and they are recorded as not injured at all if there is no apparent effect of the low temperature. Ordinarily there are no difficulties in establishing these limits. It is more difficult to estimate the degree of injury to plants that are injured but not killed. The tips of the leaves are the first to be injured and the amount of killed tissues increases more or less uniformly from the tip of the leaf to the crown of the plant, and, consequently, it is not usually difficult to differentiate between plants or lots according to the percentage of total leaf tissue that is injured. In those cases where the injury is nearly 100 per cent, the turgidity of the base of the plant, as well as the percentage of the tissue that appears to be killed, is taken into considera tion.” In spite of the obvious difficulties in estimating the “degree of injury,” this method has often been found to give a high correlation with recovery, and a given investigator, after sufficient experience, can usually get reasonably consistent estimates as shown by correlations between repeated estimates, on the same material. Timmons and Salmon (1932), working with field-grown alfalfa plants, frozen in a cold room, give comparative results for “per cent dead,” “per cent dead and badly injured,” and “percentage injury.” Varietal characteristics in recovery varied somewhat and had to be taken into consideration. In a series of articles from the Nebraska Experiment Station, Peltier ( 1931) , Peltier and Tysdal ( 1931, 1932), and Tysdal (1 933) have presented the results of experiments leading toward the establishment of a

221 “method for the determination of comparative hardiness in seedling alfalfas by controlled hardening and artificial freezing.” Following work With two-year-old alfalfa plants, which were unsatisfactory in their tests, since the plants within a “variety” were too variable, they attempted a different procedure. “In order to decrease this variability materially, and shorten the time element, seedling alfalfa plants, grown entirely under controlled conditions in the greenhouse, were studied to determine whether or not they can be employed in comparative hardiness tests” (Peltier and Tysdal, 1932). After experimenting with several types of containers, they concluded that cypress flats containing 6 inches of soil were the most satisfactory. Alfalfa seedlings 25 to 60 days old showed well-marked comparative varietal differences in cold resistance. A hardening period of two weeks appeared to be more effective in producing maximum cold resistance in month-old seedlings than a period either shorter or longer. The flats, following hardening treatment, were taken directly to a freezing chamber, where the plants were exposed to a temperature designed to kill about 50 per cent of the plants of the control variety. The most suitable temperatures appeared to be between -loo and -20° C., but a short exposure to a relatively low temperature was found better in differentiating hardiness than a long exposure to a higher temperature, during which the soil more closely approximated air temperatures at the end of the freezing treatment. In order to insure differentiation in injury, flats were exposed to a temperature, usually about - 1 5 O C., for periods ranging from 1 hour to 4 hours in length. Not even in this controlled experiment, where “enough soil was prepared at the beginning of each year for the entire season,” can the authors definitely recommend a testing temperature or its duration. Following the freezing, in the Nebraska trials, the flats of plants were removed to the greenhouse and two weeks later recovery counts were made. Since the control variety of alfalfa was planted in alternate rows in the flat, percentage survival of the alfalfa varieties was calculated in terms of the control alfalfa, and comparisons between alfalfas were made by this standard. According to these investigators, “This method gives reliable and consistent results in the determination of relative hardiness in different alfalfas.” f. Correlation with Field Tests. Several experiment stations in the United States have conducted freezing-chamber tests of varieties of plants and have attempted to correlate them with concurrent tests in field plots (Peltier and Tysdal, 1932; Salmon, 1933; Weibel and Quisenberry, 1941; Worzella, 1935; and others). In spite of the many possibilities of divergency, very favorable results have been obtained when winter conditions in the field have been favorable for differentiaEVALUATION OF CROP PLANTS FOR WINTER HARDINESS

222 S. T. DEXTER tion. To a remarkable degree, winter survival of varieties of wheat, alfalfa, clover, etc., seems correlated with the ability of the plant to endure low freezing temperatures. See also Straib (1946). Salmon (1933), after extensive comparisons of survival in field plots and in freezing chambers states, “It appears that a single artificialfreezing test under the conditions specified may be expected to furnish a more reliable prediction of relative winter hardiness in the Great Plains than would the survival of a single winter hardiness nursery selected at random, but less reliable than the average of all winter hardiness nurseries for a single season. Without exception the injury by artificial freezing of regional varieties of winter wheat, other than those included in the winter hardiness nurseries, was in agreement with their relative hardiness under field conditions in the Great Plains, so f a r as information regarding the latter is available. It is also in agreement with the supposition that the distribution of varieties in other portions of the United States is often limited by their inability to survive low temperature. The resistance to low temperature of winter barley, winter oats, and varieties of winter rye is also in accordance with the supposition that resistance to cold is a predominating factor in determining adaptation and distribution. Artificial refrigeration was used apparently with success to eliminate non-hardy varieties in mixtures and non-hardy segregates in hybrid populations of a number of crosses.” For two years, Weibel and Quisenberry (1941) found high correlation (0.8656) between survival of 24 varieties of winter wheat in field and in controlled freezing, and very high (0.9298) between controlled freezing tests and plants taken from the field in December for freezing. The plants became more hardy as the winter advanced, and in general correlations were poorer. Emmert and Howlett (1953) had much the same results in testing the winter hardiness of apple (Malus s p ) varieties. Peltier and Tysdal (1932) state “The agreement between the (survival) rank of the alfalfas (artificially) tested in the flats and pots corresponds very nearly with the relative hardiness found with these same alfalfas in field experiments. During the past season (1930-31) individual hardiness tests have been made on 100 different sorts of alfalfa and, in general, as judged by those whose hardiness was known, the results have been uniform and consistent in giving an expression of their relative hardiness. With a sufficiently large number of replications, the results obtained indicate the possibility of a wide application of this method. In addition to its adaptability for testing new strains, selections and introductions, it would appear to be valuable for selecting hardy types within a mass population.” Since the publication of this paper (1932), further evidence has

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been presented to show the practicability of this testing method with alfalfa and other forage crops. Tysdal and Crandall (1948) obtained, at best, a correlation coefficient of 0.62 between field survival and controlled freezing tests in strains from a polycross nursery. Arakeri and Schmid (1949) and Rachie and Schmid (1953) report further trials in which they attempted to find the best stage of seedling growth for freezing trials. For two or three years the author attempted to work this method out, using seedlings, according to the directions of Peltier and Tysdal, with but mediocre success. It was not difficult to distinguish extremes in hardiness when three control varieties were used, one very hardy, one medium hardy, and one nonhardy, but small variations in percentage survival were not consistent or significant. In the case of frozen alfalfa plants, the “degree of injury” estimate has little if any significance when taken, as in wheat, shortly after the plants have thawed. If the temperature used is sufficiently low to cause injury to even the least hardy variety, the leaves and branches of all varieties will probably show a 100 per cent degree of injury. With alfalfa seedlings a few weeks of age it is usually possible to decide whether or not the plant is dead after a period of two weeks has been given for recovery. With older plants, however, there are complicating factors. Dexter (1930b) and Smith (1950) describe the development of adventitious buds below the crowns on alfalfa roots. Frequently the more mature buds at the crown of the plant are killed by freezing. The very immature buds and the root may be essentially uninjured, and may eventually grow, after a period of 2 or 3 months. Allowance may be made for characteristic varietal slowness of 5ecovery after defoliation, when that is known (Timmons and Salmon, 1932). Other complexities in determining winter hardiness of alfalfa varieties by controlled hardening and freezing are indicated by Tysdal (1933). Varietal differences in response to length of day, hardening temperature, and combinations of the two are described. He shows clearly, as does Dexter (1933b), that the response in hardening to length of day is closely associated with the temperature of the plant while receiving illumination. Furthermore, it is closely related to the typical growth response of the variety to length of day (Oakley and Westover, 1921). Tysdal (1933) found in varieties of alfalfa where a short day at ordinary growing temperatures inhibits growth and elongation of the branches, marked improvement in hardening at relatively high day temperatures when the day length is short. To the contrary, at a lower temperature, 4 O C., for example, hardening was less complete, and survival lower where a short day was substituted for a long day. At a continuous low temperature, continuous light produced better hardening response than any other light treatment. It is, there-

224 S. T. DEXTER fore, obvious that any one specified hardening treatment is likely to favor the survival of certain types of plants in subsequent freezing, whereas another somewhat different system of hardening may favor other types (Rudorf, 1938; Becker et al., 1947). g . Limitations of Artificial Hardening and Freezing. In spite of the apparent partial success of this method, it is essential to consider its limitations. For example, it has been recommended more than once (Suneson and Kiesselbach, 1934; Becker et al., 1947) that successive fall plantings of winter wheat be made, so that the onset of winter could occur at several stages in the development of the various varieties, much as would occur in agricultural practice. It appears that differential varietal responses are observed when this procedure is followed. Yet in the controlled hardening, controlled freezing procedure, this is meticulously avoided. All are grown and hardened at the same day length and temperature, and yet we know that striking varietal differences in responses in both growth and hardening occur as these environmental influences are changed. It is quite true that the cold room method offers extraordinary opportunity for controlled investigation of the influence of these factors. By no means sufficient work along those lines has been done. It seems highly likely that there is no one combination of day lengths, hardening temperatures, alternations of temperatures, etc., that is suitable for use to develop the maximum hardiness of all varieties equally (Tysdal, 1933; Becker, 1947). In some plants, the restricted root growth in small pots or flats may have a significant effect in winter hardiness. It has been shown clearly that artificial freezing that produces unduly low soil temperatures must be avoided (Peltier and Tysdal, 1932). Thus the more deeply buried parts of an alfalfa root are ordinarily more readily injured by low temperature than is the crown (Weimer, 1929; Dexter, 1932; Megee; 1935). The roots of alfalfa plants may be killed by a relatively mild freezing temperature, of long duration, but the plant may survive owing to regeneration of new roots from the crown. In spite of these objections, it should be re-emphasized that the method has been found to give hardiness results remarkably comparable to those found in field conditions. It may be possible that the environmental conditions, as provided in the hardening chamber, actually surpass most ordinary weather conditions in efficiency of hardening plants (Ausemus and Bamberg, 1947). When the experimental plants have been grown to a suitable stage of development, persistent low temperature with adequate light, etc., may develop a more hardy plant than would be developed in the uncertain fluctuating conditions ordinarily occurring in the fall of the year. Statistical studies of weather conditions during the fall in relation

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to winter survival of winter wheat have shown that the following conditions are the most favorable (Suneson and Peltier, 1938): ( I ) a period of relatively high temperature, during growth, with high illumination; (2) following this, a period of about three weeks of persistently low temperatures, near freezing. By comparing the degree of low-temperature endurance in the temperature chamber of field grown plants, it was shown in six successive seasons that maximum hardiness was by no means always developed in the field. Kabanov (1939) reports that essentially these same conditions are favorable to hardening under the conditions at Saratov, U.S.S.R., and that one can tell in the fall if winter wheat plants will survive the winter well. The conditions that these investigators describe as most effective in the field are precisely the ones used in the controlled growing, hardening, and freezing researches. However, in many localities such ideal conditions may occur only rarely. Presumably the investigator is more interested in the actual than in the theoretical maximum in hardiness, and thus may require field-grown plants. As previously mentioned, it has been suggested by more than one investigator that, when either greenhouse or refrigerator space is not available, combinations of the two methods can be used. Thus, plants can be grown in pots or flats in the greenhouse, hardened there during the early winter, and exposed out of doors to freezing weather. Salmon (1933) reports “the results were found to correlate very well with artificial freezing.” Conversely, plants grown out of doors, either in pots or flats or under ordinary field conditions, may be brought into the refrigerator for controlled freezing and subsequent observation. It is necessary in any case to make certain that the pots or clumps of plants are of equal size, since injury is regularly greater in smaller clumps. Jurjev (1939) describes the use of the refrigerator to obtain the desirable freezing temperatures, thereafter permitting recovery under field conditions. This method is intended to provide a “test winter” every year.

3 . Freezing of Hardened Plants Followed by Electrical Conductivity Measurements of Exosmosis In the studies discussed thus far, the common method of determination of injury has been by either (I) percentage survival or (2) estimated degree of injury based on the general appearance of the plant, the apparent amount of killing of foliage, or perhaps the vigor of renewed growth. In view of the difficulties described by Salmon, Steinmetz, and others and in order to provide an objective technique the electrical conductivity method of measuring injury was suggested by Dexter (1930a, b) and Dexter et al. (1930, 1932).

226 S. T. DEXTER In this method, samples of the plant tissue in question are washed, superficially dried, weighed, placed in suitable test tubes, and chilled. The tubes are then immersed in an alcohol-slush bath at the desired freezing temperature for the desired time (usually about 4 hours). They are then removed and placed in water at 2O C. for thawing, after which a measured volume of distilled water at 2O C. is added to each tube. They are then stored at 2O C. for a suitable interval to permit solutes to diffuse from the tissue that is injured. The concentration of the electrolytes in the resulting solution is determined by electrical conductivity measurements. This measurement takes only a few seconds per sample, and is much more than sufficiently accurate, even with ordinary apparatus. The tubes with the samples and supernatant liquid are then placed in boiling water to kill the tissue completely. The samples are again placed at 2O C. to allow extraction of all electrolytes. Again the concentration is determined electrically. Percentage extraction following freezing may then be calculated as an indication of the degree of injury from freezing. Comparatively slight extraction is found with unfrozen, uninjured samples. In some cases it may be more convenient to measure the conductivity of the plant tissue itself, as reported by Dexter et al. (1932) with alfalfa roots, and Filinger and Cardwell (1941) with raspberry (Rubus sp.) canes. The electrical conductivity method of determining injury has been particularly convenient in making detailed studies of winter hardiness relationships. Bell (1940) showed that the lack of injury from freezing in alfalfa roots was closely correlated with starch content in the fall, when starch was determined by lack of light transmission through iodine-treated microscopic slide sections. In the early winter, however, he found that hardy roots were characterized by the early hydrolysis of starch, as compared with less hardy roots, as was shown chemically by Janssen (1929). Bell, however, was able to use a larger assortment of degrees of winter hardiness and a large number of samples because of the ease of the method. Although the characteristic of starch hydrolysis may have, at this time, little use in evaluation of the winter hardiness of alfalfa varieties, it is of some interest in connection with the suggestion of Siminovitch and Briggs (1954) “that the observed increase in hardiness which accompanies the disappearance of starch can be ascribed in part to this circumstance, rather than to an increase in soluble sugars.” Similarly, Emmert and Howlett (1953) classified 55 standard apple varieties as to winter hardiness by comparing the percentages of extraction of electrolytes after freezing. Results with samples taken in the early winter agreed well with current ideas of the hardiness of the varieties, from field trials. Tests with samples taken at later dates in the

227 winter indicated that many of the less hardy varieties had become far more hardy, whereas comparatively little change was found with the varieties commonly recognized as hardy. These findings are stated to be in accord with the previously expressed idea that injury, in the case of apples, very often occurs in the fall, before full hardiness has developed, and that early and prompt hardening may be an important factor in field hardiness. Suneson and Kiesselbach (1934) have made much the same point in the case of winter wheat. Bula and Smith (1954) have attempted to compare the winter hardiness of species, i.e., alfalfa, red clover, and sweet clover, by this method, using total rather than percentage extraction of electrolytes as a criterion. This seems a somewhat questionable procedure. In the original work with the method (Dexter, 1930b), where the hardiness of varieties of apples, alfalfas, clover, small grains, raspberries, etc., was compared, no method seemed fully suitable in comparing species, even when total electrolytes were taken into consideration, since contents of dry matter, electrolytes, etc., varied so greatly, and since the speed of exosmosis was not comparable. For example, exosmosis from 1 g. of wheat leaf tissue seems difficult to compare with that from 1 g. of apple twigs, on any one of several bases. It cannot be emphasized too strongly that this method requires as thorough a standardization as has been described for other freezing methods. Carelessness in handling samples, in freezing or thawing, and in other details of standardization will lead to unreliable results. For example, a wilted sample may be frozen with very much decreased injury. Levitt and Scarth (1936) and Levitt (1939) have made considerable point of the speed of freezing and thawing. Harvey (1930) has described the effects of drops of surface water in increasing freezing injury. The results obtained by this method agree closely with those obtained by the field method of determination of varietal hardiness, or by visual determination after controlled freezing. Megee (1935), Silken et al. (1937), and Grandfield (1943) have used it successfully in alfalfa varietal trials, Greathouse (1938) with red clovers, Bula and Smith (1954) with various legumes, Van Doren (1937) with winter wheat, Swingle (1932), Stuart (1937), and Emmert and Howlett (1954) with apples, Carrier (1951) with roses (Rosa, sp.), Filinger and Cardwell (1941) with raspberries, and Dexter (1937) with various perennial weeds. It has been used repeatedly in studies of the effect of management on the winter hardiness of various plants. Several advantages are inherent in the method; small samples from one or many plants can be used to make up a sample for freezing; entire plants need not be destroyed; relatively small amounts of exEVALUATION OF CROP PLANTS FOR WINTER HARDINESS

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perimental material are needed in most cases; detailed and frequent tests of the degree of hardening are possible; virtually identical freezing treatments in a series of determinations are readily obtained. This is well illustrated by a study of the hardiness of apple varieties, reported, in abstract, by Rollins and Howlett (1955). “The hardiness of a plant cannot be considered as an absolute value, but rather as continually changing under the influence of numerous environmental and genetic factors. Therefore, in order to better understand the influence of a factor upon the hardiness of a plant, it must be studied over the entire dormant season. The electrolytic technique was found to be an accurate means of determining the extent of the injury, if properly used. Tests were conducted on the various phases of the technique in order that maximum sensitivity could be attained. Hardiness comparisons were made on the basis of the low temperature treatment necessary to result in injury corresponding to 15 per cent diffusion of electrolytes, which corresponded closely to the point at which the cambium was killed. Hardiness comparisons made in this manner were then developed into hardiness curves depicting the hardiness of specific individuals over the entire dormant season.” Differences in the hardiness curves of various varieties and the effects of various management practices were determined. Although reasonable judgment in the precise freezing temperature will add to the usefulness of the method, as indicated above, an especially convenient point in variety testing is the fact that the freezing temperature need not be such that part of the plants survive, since even when all the plants are killed, a hardiness rank is still obtained. Only a small freezing chamber is required. Results are obtained promptly after freezing, before complications develop. Since the method is free from personal bias, all observers obtain the same value which is mechanically obtained and mathematically expressed. The method has several inherent difficulties. The preparation of samples is time-consuming in some cases. Alfalfa roots, for example, must be dug, washed, trimmed, and surface-dried. Winter wheat crowns must be cleaned of dead leaves. Samples must be weighed. In the process, the samples must not wilt. Since tissues lose their hardiness comparatively rapidly, this should be done expeditiously. Furthermore, the total soluble electrolyte content per gram of fresh tissue changes somewhat as the plant passes from an actively growing stage into one of comparative dormancy, and vice versa (Dexter, 1934). Samples injured by freezes in the field may have lost a considerable amount of electrolytes by leaching, either before the sample was taken, or during its preparation (Dexter, 1930b; Dexter et al., 1932), and obviously, varieties may differ in their total electrolyte content (Dexter, 1934;

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Megee, 1935; Greathouse, 1938). Samples must be protected from mineral contamination, glass tubes must be clean, etc., since the solutions obtained by exosmosis are usually rather dilute. Since the samples are weighed, the water is added with a pipette, and the conductivity measurements are taken at an accurately specified temperature (error about 2% per cent per degree centigrade) with sensitive electrical instruments, much of the work must be performed by a reliable technician. If large numbers of winter wheat varieties, for example, were to be tested, where abundant facilities were available for growing, freezing, and handling potted plants, it is likely that less work and time would be required by the professional staff, by the method of freezing with subsequent visual estimation of injury than by the electrical conductivity method. An advantage for the visual method of determining injury has been described in that in segregating crosses the range of winter hardiness in a population can be estimated directly, whereas conductivity measurements on large numbers of individual plants would be required by the other method. Of course, in the second case the data would be objective rather than subjective. In either case, however, it has been found that, under actual conditions of hardening, highly noticeable variations in hardiness develop in plants of a pure line. This would normally be expected, since shading (Dexter, 1933b; Suneson and Peltier, 1938), day length (Kramer, 1937), mineral nutrition (Tumanov, 1931), watering (Graber and Sprague, 1938), etc., have all been shown t o affect winter hardiness. 4 . Other Methods of Estimating Injury after Freezing

Other methods have been proposed and used in determining the extent of injury from freezing. Microscopic examination of the browning of the tissues following freezing has given useful results. Vital stains (neutral red, etc.) on sections of frozen tissue appear to differentiate living from dead cells. Iljin (1933, 1934, 1935) has used this method in studies of the injury that occurs during the thawing of frozen tissue. The use of red cabbage (Siminovitch and Scarth, 1938) in hardiness experiments was convenient owing to a characteristic change in the appearance of the cells when frozen and injured. Carrier (1951) used 2,3,5-triphenyltetrazolium chloride to differentiate injured from uninjured tissue in frozen roses, but found the method unreliable. He states that the specific conductivity method when used in conjunction with observation after storage is more reliable than either method used by itself. Newton and Jones (1945) found that freezing injury in potato or apple tissue could be detected by fluorescence under ultraviolet lamps. The fluorescence in apples disappeared on thawing, while that

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in potato did not. Many other tissues were studied without finding this effect of freezing injury. From McGill University and the University of Minnesota in recent years have come a number of papers in which microscopic examination of the process of freezing and thawing has been a prominent method of determining injury (Levitt and Scarth, 1936; Scarth and Levitt, 1937; Siminovitch and Scarth, 1938; Siminovitch and Briggs, 1953). By their methods, ice formation can be observed in various parts of the cell as well as in the intercellular spaces. The degree of contraction in volume of hardened and unhardened cells during freezing was determined (Levitt and Scarth, 1936; Levitt, 1939) both by microscopic measurements and by calculation from calorimetric determinations of ice formation. Stuckey and Curtis (1938) and Maximov (1938) also have used a microscopic technique to study ice formation and injury.

5 . Winter Hardiness Tests on Seeds or Small Seedlings Upon the supposition that the embryo of the seed possesses all the inherent characteristics of the plant, various studies have been made of the seeds or the slightly sprouted embryos. Sergeev and Lebedev (1936) describe a method for testing the winter hardiness of winter wheat by testing the grain. Seeds are germinated in solutions of salt or sugar of several concentrations. Solutions from 0.2 N to 0.8 N are utilized to bring out varietal differences. It is claimed that seeds of hardy varieties swell and germinate in more concentrated solutions than do those of tender varieties. By using a series of concentrations, an osmotic pressure characteristic of 50 per cent germination for each variety can be established. Extensive tests of this method in the author’s laboratory have shown that the technique, as described, is difficult to duplicate. An easier, but essentially identical, technique has been developed, to check the findings described. With grain from the 30 varieties in the “uniform winter hardiness nursery” for winter wheats, from two locations and for three years it was shown beyond doubt that marked varietal differences in ability to swell and sprout in salt solutions do exist. From the recorded winter hardiness rankings, both in Michigan and in other states, however, winter hardiness could not clearly be associated with ability to sprout. Similarly, no relationship was found between sprouting ability and winter hardiness in alfalfa varieties of a considerable range of winter hardiness. The method has not been checked widely in this country, and although Sergeev and Lebedev cite theoretical studies to substantiate their claims, other writers feel that the findings are physiologically

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unsound (Skazkin, 1934). A seemingly identical method has recently been described by Rodger (1955) in which alfalfa seeds are germinated in Petri dishes on filter paper moistened with water or salt or sugar solutions of several osmotic concentrations up to about 9 atmospheres. He reports that when seed of several alfalfa varieties was tested, germination was depressed by the solutions and that “this effect was significantly greater for the hardy than for the non-hardy varieties.” This is precisely the opposite of the findings claimed for winter wheat varieties. He found, however, that the hardiness of known RANGER seed, so tested, varied greatly and erratically with the source of the seed. In the author’s laboratory, since the publication of the above report, similar large and erratic differences in the behavior of seed lots of certified and foundation RANGER alfalfa were found. In 38 lots of seed tested, differences were not consistent either between varieties or between lots of the same variety. Before this method can be used reliably, as suggested by Rodger, for ascertaining the admixture of seed of nonhardy and hardy varieties in commercial seed, further investigation and clarification will be necessary. Many investigators have attempted to find the best age of plants or seedlings for freezing tests, and have made recommendations for the particular species involved. Ivanoff ( 1951) has conducted trials with “activated” oats. Grain of four varieties was used to give a considerable range in winter hardiness. The grain was soaked for about 20 hours in running water at several temperatures (well above freezing) and then frozen for 7 days at -6O to -30° C. The survival after freezing at -6O and -8O C. left from 10 to 38 per cent of the two hardier strains alive, and 0 to 11 per cent of the two varieties of spring oats. It is stated “By using this method, from many viable seeds, a few viable seeds could be selected which would possess germ plasm for cold resistance, acquired possibly as a result of unusual hybridization, gene arrangement, or spontaneous mutations and other alterations of the hereditary structure of the seed.” Large-scale tests were run, from which surviving seeds were obtained which gave plants with the growth characteristics of winter-hardy strains. Surviving seeds also gave plants with rooting stems, and possibly a perennial habit. For a further discussion of the practice of testing very young seedlings, Tumanov’s (1940) book is helpful in presenting the Russian practice in this regard. They report a greatly decreased hardening of seedlings when vernalized seeds are used (Timofeeva-Tjulina, 1949; Kostjucenko and Zarubailo, 1937). Methods are reported (Kalmykov, 1937; Henkel and Kolotova, 1938) that, it is claimed, produce improved subsequent hardening by suitably soaking and drying the seed several times before sowing.

232 S. T. DEXTER In connection with the testing of seeds, the work of Worzella and Cutler (1938) seems particularly significant. An analysis was made of 11 characters of 30 varieties of soft and semihard winter wheat, over a period of the five years 1933 to 1937. After showing the relationships between these various properties, including winter hardiness, they state, “At first thought it might seem that these data support the supposition held by many plant breeders that a linkage exists between strong gluten and winter hardiness and weak gluten and non-winter hardiness. However, when we consider the locations under which these varieties were bred and the specific purposes for which they were selected, it seems to help to explain this relationship. First of all, most of these semi-hard wheats were selected under conditions where the winters are rather severe, and with the objective of producing a winter hardy wheat with strong gluten quality. On the other hand, the typical soft wheat varieties, as a rule, were selected for soft or weak gluten under conditions where rather mild winters prevail. Consequently the writers believe that the relationship between winter hardiness and quality shown in the above data is the result of selecting varieties which possessed this relationship because of the conditions under which they were grown and the objectives sought, rather than linkage. With the typical soft wheats, the data show no correlation between winter hardiness and quality.” Precisely the same could be said of the selection of varieties for drought resistance. Generally speaking, a region of high rainfall during the growing season breeds and produces soft wheat varieties, since hard wheat of good quality cannot be grown in the region. It is possible that a recent paper (Dexter, 1955) showing the variations in hard seed content in alfalfa seed in relation to the climate of the seed source, may be pertinent in explaining the contradictions in testing alfalfa seed for varietal winter hardiness.

6 . Estimation of Winter Hardiness without Freezing As has been stated in Section 11,1,2, on theories of winter hardiness, many physical and chemical characteristics of plants have been suggested as indicative of winter hardiness in varieties, and still more as characteristic of the hardening process as such. From the data it would appear that several processes are responsible for the characteristics of winter hardiness, and that they do not appear in equal prominence in the various species. It has been observed that sucrose content, or refractive index of the expressed sap, in wheat varieties correlates rather well with winter hardiness (Ilgin, 1935), but that in alfalfa the relationship is highly unreliable (Steinmetz, 1926; Weimer, 1929; Megee, 1935; Ireland, 1939). Similarly, tolerance of high mechanical pressure (Dex-

233 ter, 1932) with wheat gave a good indication of varietal hardiness, but similar tests by Steinmetz (1926), Megee (1935) , and Weimer (1929) failed with alfalfa varieties. Some methods have not been sufficiently tested to allow judgment as to their general merit, such as the method described by Nizenjkov (1935) in which the electromotive force between arbitrarily fixed points on winter wheat plants was shown to vary more or less in accordance with the varietal hardiness. Newton and Anderson (1931) found reduced respiration in hardy varieties in comparison with nonhardy, at least under some conditions, and similarly enzyme systems have been compared in hardy and nonhardy types (Tysdal, 1934; Megee, 1935; Greathouse and Stuart, 1937; Vetukhova, 1938a, b), but the methods are hardly ones to be recommended for easy or rapid evaluation of winter hardiness. Furthermore, none of these methods appears related to such hardiness features as branching roots (Burton, 1937; Smith, 1951), or roots with high tensile strength (Worzella, 1932; Lamb, 1936, 1939). As previously mentioned, there has been a considerable series of papers on winter hardiness, with which the names of Scarth, Levitt, Siminovitch, and Briggs have been associated, from about 1936 until the present time. Particular emphasis has been placed upon an increase of permeability of the plasma membrane as hardening advances. A series of selected quotations may give, briefly, their viewpoint (Levitt, 1939). “Hardiness is therefore not determined simply by resistance to dehydration, or to the amount of ice which forms, but by some increased ability to resist the e#ects of freezing [italics mine].” “One factor in frost injury is the protoplasmic strain described by Iljin; the greater resistance to plasmolysis and deplasmolysis injury found in hardened plants is due to a greater resistance to the injurious effects of the strain.” “Another hardiness factor is permeability. Since the rate of freezing is of no detectable importance insofar as unhardened plants are concerned, and since ice forms inside the cell only as a result of rapid freezing, intracellular ice apparently does not arise at the temperatures and the rates of freezing to which they were subjected. Permeability is therefore not the limiting factor in the first injury of unhardened plants. Hardened plants, on the other hand, are less injured by slow than by rapid freezing, an indication that intracellular ice is involved, and that (in rapid freezing) the permeability rate, even that of unhardened plants, is sufficient to keep up with ice formation under a small temperature gradient, and so to permit extra-cellular ice formation. In this case, however, protoplasmic strain kills the cells.” “On account of its greater resistance to protoplasmic strain, the cell, after hardening, is now able to withstand a lower temperature . . . until the EVALUATION OF CROP PLANTS FOR WINTER HARDINESS

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protoplasmic strain is increased sufficiently to injure the cell.” Under conditions of very rapid freezing, the hardened cell is injured because the permeability is insufficient to prevent ice formation within the cell. Ice formation within the cells has been shown to be more injurious than ice formation in the intercellular spaces. In a recent paper Siminovitch and Briggs (1953) describe the “Validity of plasmolysis and desiccation tests for determining winter hardiness . . . ” as follows: ( I ) “Dehydration (or plasmolysis) tests for frost hardiness have tremendous advantages over actual freezing tests with regard to the time required to make a test, the amount of test material required, and the cost of the equipment required.” (2) “While dehydration tests should serve equally as well as actual freezing tests for routine measurements of frost resistance in agricultural and horticultural practice [italics mine], some modifications of the procedures as they are described here may be required.” (3) “The results indicate, however, that such tests yield comparative values for hardiness. On Feb. 6, a 5M plasmolysing solution or a relative humidity of 65% was required for 50% killing (as tested with neutral red), while on July 28 only a 1M solution and a 96% relative humidity was required.” As nearly as has been ascertained, these methods have not been used extensively in varietal trials, although Levitt and Scarth ( 1936) have classified 10 apple varieties as to winter hardiness by measuring their permeability to potassium nitrate. In 1931-32, in the Botany laboratories at the University of Chicago, and on several occasions at Michigan State University, very similar tests of winter hardiness were attempted, both before and following the description of the method by Iljin and after the strong re-emphasis by Scarth, Levitt, and Siminovitch. Primarily the difficulty appears to arise in distinguishing staining with neutral red. Siminovitch remarks on the difficulties such as “precautions to avoid toxic effects of the dye itself.” “Staining alone, without subsequent immersion in water for a period of time, is not a sufficient criterion of survival, because accumulation of the dye is observed to occur in partially injured cells [italics mine]. After transfer to water, the dye leaches out of these injured cells more rapidly [italics mine] than from healthy cells.” It may well be that their samples, often consisting of such simple material as epidermal cells from cabbage leaves, are easier to examine than are samples of cross sections of alfalfa roots. Similarly, tests for differential varietal desiccation injury have not been promising in relation to winter hardiness evaluation of alfalfa (unpublished). Megee (1935) did not find varietal differences in injury to alfalfa roots that were slowly desiccated. Although he found substantial changes in all varieties, as winter approached, not only in this factor, but also in heat of wetting, moisture equivalent, freezing point de-

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pression, respiratory rate, etc., there was no correlation with varietal winter hardiness. In spite of these and other difficulties and contradictions, the method deserves further study with economic plants, from a varietal standpoint, although it may be necessary for Siminovitch and Briggs, themselves, to outline and standardize the “modification of procedures” before the test is as valuable for “routine measurement of frost resistance in agricultural and horticultural practice” as they suggest. Since the change in permeability to nonlipid and to polar substances is particularly affected by hardening, Levitt and Scarth (1936) state that “the change is inferred to be a widening of its (the membrane’s) aqueous pores.” Perhaps Wilhelm’s (1935) study of the distribution of phosphatides in plants, as winter hardiness develops, may eventually aid in the understanding of permeability and winter hardiness relationships and lead to a more fundamental evaluation.

IV. SUMMARY From the standpoint of the plant breeder, agronomist, or horticulturist, in the evaluation of crop plants for winter hardiness, the physical and chemical changes or properties that accompany winter hardiness should be found easily and reliably and to a greater degree in varieties that are winter-hardy than in those that are not. In spite of the extensive work with sugars, soluble nitrogen fractions, respiration rates, etc., insofar as the reliable and general evaluation of varieties is concerned, it seems certain that no method has yet been devised that does not involve the freezing of the plant. Maximov (1929) expressed this same opinion 25 years ago. Since that time, extensive studies with refrigeration machines have been made, in which plants in the hardened condition have been frozen at specified temperatures. Examination of the injury from freezing has given varietal ratings in close conformity with field experience. The electrical conductivity method of estimating injury has been more and more commonly used, especially in horticultural evaluation, because of its convenience and objectivity. In spite of many complications due to diseases before and after hardening and other similar difficulties, winter hardiness in plants has been shown to be remarkably well correlated with tolerance to low temperatures. The literature of comparatively recent years has presented several methods that have seemed to have promise, and numerous physiological studies, many not cited, have considerably advanced our knowledge of winter hardiness and the hardening process. Since parts of this fundamental research have not been applied or appraised adequately by agronomists, an excellent opportunity exists for the development of new

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Straib, W. 1946. Ziichter 17,1-12. Stuart, N.W. 1937. Proc. Am. SOC.Hort. Sci. 35,386-389. Stuckey, I . H., and Curtis, 0. F. 1938.Plant Physiol. 13, 815-833. Suneson, C. A. 1941.1. Am. Soc. Agr. 33,829-834. Suneson, C. A., and Kiesselbach, T. A. 1934. I. Am. SOC.Agr. 26,687-693. Suneson, C. A., and Peltier, G. L. 1938. I . Am. SOC.Agr. 30, 769-778. Swingle, C. F. 1932.Proc. Am. Hort. Sci. 29, 380-383. Tesar, M. B., and Ahlgren, H. L. 1950.Agron. I . 42, 230-235. Timmons, F.L.,and Salmon, S. C. 1932. J. Am. SOC.Agr. 24, M2-655. Timofeeva-Tjulina, M. T. 1949.Proc. Acad. Sci. U.R.S.S. 8, 153-156. Tregubenko, M. J. 1940. Doklady Vsesoyuz. Akad. Sel’skokhoz. Nauk im.V.I. Lenina (1952.Herbage Abstr. 22, 278). Tumanov, J. J. 1931.Phytopathol 2. 3,303-334. Tumanov, J. J. 1940. “Physiological Bases of Winter Hardiness in Cultivated Plants.” Seljhozgiz, Moskva-Leningrad (Review in 1940.Herbage Abstr. 8,214-223). Tysdal, H. M. 1933.J. Agr. Research 46,483-517. Tysdal, H . M. 1934.I . Agr. Research 48,219-240. Tysdal, H.M., and Crandall, B. M. 1948. J . Am. SOC.Agr. 40,293306. Vander Meulen, E.1942.M.S. Thesis, Michigan State University. Van Doren, C.A. 1937. J. Am. SOC.Agr. 29,392402. Vetukhova, A. 1938a. Zhur. Inst. Botan. Akad. Nauk U.R.S.S. 18, 26-27 (1939.Herbage Abstr. 9, 633). Vetukhova, A. 1938b. Zhur. Inst. Botan. Akad. Nauk U.R.S.S. 19, 57-59. Wang, L.C., Attoe, 0. J., and Truog, E. 1953.Agron. J . 45,381-384. Weibel, R. O.,and Quisenberry, K. S. 1941. J . A m . SOC.Agr. 33, 336-343. Weimer, J. L. 1929.1. Agr. Research 39, 263-283. Wilhelm, A. F. 1935.Phytopathol. 2. 8,225-236. Wilmer, J. A. 1952.Sci. Agr. 32, 651-658. Worzella, W. W. 1932.J . Am. Soc. Agr. 24, 626636. Worzella, W. W. 1935.J . Agr. Research 50, 625-635. Worzella, W. W., and Cutler, G. H. 1938. J . Am. SOC.Agr. 30, 430433. Worzella, W. W., and Cutler, G. H. 1941. J . Am. SOC.Agr. 33, 221-231. Yarwood, C. E. 1946. Am. Potato J. 23, 352-369.

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The Determination of lime and Fertilizer Requirements of Soils through Chemical Tests

.

J . W FITTS AND WERNER L. NELSON North Carolina State College. Raleigh. North Carolina. and American Potash Institute. Lafayette. Indiana

1. Introduction

Page

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1. Objectives of Soil Testing

2. General Trends in Extent of Testing . . . . . . a. United States . . . . . . . . . . . b. Other Countries . . . . . . . . . . 3. Phases of Soil Testing . . . . . . . . . . I1. Calibration of Soil Tests . . . . . . . . . . . I . Field and Greenhouse Studies . . . . . . . . 2. Correlation Studies . . . . . . . . . . . 3. Frequency Distribution . . . . . . . . . . 4 Probability . . . . . . . . . . . . . 6 Soil and Plant Characteristics Affect Calibrations . . I11 Representative Soil Samples . . . . . . . . . . I. Area to Sample . . . . . . . . . . . . 2. Depth of Sampling . . . . . . . . . . . 3. Sampling Tools . . . . . . . . . . . . 4. Time of Sampling . . . . . . . . . . . 5. Frequency of Sampling . . . . . . . . . . 6. Soil Containers . . . . . . . . . . . . IV. Chemical Testing Procedures . . . . . . . . . . 1.Drying. . . . . . . . . . . . . . . 2.Crushing . . . . . . . . . . . . . . 3. Volume vs. Weight in Measuring Samples . . . . 4.pH. . . . . . . . . . . . . . . . a. Methods . . . . . . . . . . . . b. Some Factors Affecting the pH Value . . . 5. Lime Requirement . . . . . . . . . . . 6. Phosphorus . . . . . . . . . . . . . a.Extractants. . . . . . . . . . . . b. Measurement . . . . . . . . . . . 7. Cation-Exchange Capacity and Percentage Base Saturat 8. Potassium . . . . . . . . . . . . . . a . Extractants . . . . . . . . . . . . b. Measurement . . . . . . . . . . .

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243 243 243 244 244 245 246 248 250 251 252 253 254 255 256 257 257 257 257 258 258 258 259 259 259 260 261 262 262 262 263 263

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J. W. FITTS AND WERNER L. NELSON

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9. Calcium and Magnesium . . 10. Organic Matter . . . . 11. Nitrogen . . . . . . . a. Methods . . . . . 12. Minor Elements . . . . . . 13. Soluble Salts . . . . . 14. Soil Solution Ratio . . . 15. Labor-Saving Devices . . V. Interpretation and Recommendations 1. Reporting Results . . 2. Recommendations . . . . 3. Familiarity with Local Conditions 4. Information Sheets . . 5. Liming and Fertilizing Soils . . 6. Soil Tests and Soil Surveys VI. Soil Test Summaries . . 1. Areas for Preparing Summaries . 2. Two-way Tables . . . 3. Nutrient Index . . . . 4. Accuracy of Summaries . . . VII. Future Trends in Soil Testing . . . References . . . . .

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Page 263 264 264 . 265 . 266 . 267 . 267 . 267 . 269 269 . 270 270 271 . 272 .273 . 274 . 275 . 275 . 277 . 278 . 278 , 280

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I. INTRODUCTION Information on the plant nutrient status of the soil is essential in predicting lime and fertilizer needs. Soil tests, along with cropping history, past fertilization practices, and observations on the growing plant, give information that helps greatly in formulating the fertilizer and liming programs. For over 100 years there has been interest in soil analyses. Many scientists have conducted research on methods but numerous problems have been encountered. First attempts were generally unsatisfactory but much progress has been made in the last three decades. A report of the National Soil Test Work Group (1951) states: “For years various individuals have assigned a wide range of values to soil testing-from a psychological extension tool to a single value soil management cure-all. The proper place for soil testing is doubtless near the center of these two extremes. There is good evidence that the competent use of soil tests can make a valuable contribution to the more intelligent management of the soil.” Soil tests assist in extending the usefulness of soil fertility research. The experimental work is of necessity confined to a relatively small number of locations in comparison to the number of farms in the area. A suitable evaluation of the fertility status of the soils on which the experimental work has been conducted in conjunction with response

SOIL TESTS

243

data is the basis of interpreting the soil tests on samples taken from farmers’ fields. Data obtained from testing a number of soils from experimental fields make it possible to make recommendations for the various conditions encountered in the farmers’ fields.

1. Objectives of Soil Testing Information gained from soil testing is used in many ways. Some of the more important objectives include: a. To group soils into classes for the purpose of suggesting fertilizer and lime practices. The amount of plant nutrients needed is related to the crop to be grown and the levels of available nutrients in the soil. b. To predict the probability of getting a profitable response to the application of plant nutrients. In the efficient production of crops information is needed on the possibility of getting a suitable return above the cost of the treatment. c. To help evaluate soil productivity. The organic matter content, level of nutrient elements, and pH of the soil have been found to be good guides in estimating the potential productivity of soils. d. To determine specific soil conditions which may be improved by addition of soil amendments or cultural practices. Alkaline and saline soil conditions can be detected with soil tests, and recommendations made for im’provement. 2. General Trends in Extent of Testing

a. United States. Chemical soil tests are now widely accepted in the United States. All the states but one have central laboratories. Ten of the states have regional laboratories and nine have county laboratories. The state not having a central laboratory has several regional laboratories. In addition to the state-operated laboratories there are a number of commercial laboratories. Fifteen states reported an increase in the number of commercial laboratories during the last few years, but the number remained about the same in the remaining states. Large numbers of soil samples have been tested. In 1950 approximately 1,223,700 samples were analyzed (Table I). This was increased to 1,830,100 in 1954, which is almost a 50 per cent gain during the four-year period. The greatest intensity of soil testing is in the North Central Region, where the highest percentage of land is under cultivation. The largest percentage increase during the four years was in the Southern Region, where the number of samples tested was about doubled. b. Other Countries. Soil testing has expanded in many countries, including the Netherlands, Denmark, Ireland, England, Germany, France, and Scotland. For example, in each of the four countries, the

2M

J. W. FITTS A N D WERNER L. NELSON

TABLE I Approximate Numbers of Soil Samples Tested in the Four Major Regions of the United States in 1950 and in 1954' 1950 Samples tested North Central Northeastern Southern Western

880,000 85.000 255,000 19,700

One soil sample for each% 260 acres 590 acres 1,000 acres 5,050 acres

l,%P3,700

1954 Samples One soil sample Increase, tested for each% % 1,205,000 105,000 500,000 20,100

190 acres 510 acres 510 acres 2,080 acres

57 a4 96 46

1,830,100

1 Personal 3

communication. Expressed on acreage in crops and pasture.

Netherlands, Denmark, Ireland, and England, more than 100,000 samples are tested annually. Hence, soil analyses are now widely used as a guide in liming and fertilizing.

3. Phases of Soil Testing There are four major phases of soil testing: calibration of the test with crop response, the securing of representative samples, chemical testing procedures, and interpretations and recommendations. These various phases are discussed along with a consideration of soil test summaries in the following sections.

11. CALIBRATION OF SOILTESTS The successful use of soil tests depends upon careful calibration of the tests with the increases in crop yields from applications of fertilizers and lime. Many factors other than fertility level influence the response obtained. These include climatic conditions, soil properties, crop varieties, thickness of stand, cultural practices, insects, and diseases. Interaction in the soil between chemical elements, both essential and nonessential, may be expected. Most of the variable factors can be more readily controlled in greenhouse experiments than in field studies. A majority of the calibrations, however, have been based on field studies. Since the calibration of soil tests has not been the primary purpose of many of these field studies, the data are often inadequate to cover all situations. In experiments designed for calibration of soil tests a group of soils are selected which range from low to high in content of the nutrient

245 being studied. The crop is grown, and growth, yield, and/or nutrient uptake measurements taken. Several different chemical methods may be used in analysis of the soil. A study is then made to determine which method will best predict response. Samples of the soil from such experiments are generally saved for future studies. New methods and techniques which may aid in interpreting results are continually being developed. Some countries, among them the Netherlands and Denmark, may have hundreds of soil samples on which yield responses are known. When new extractants are to be tested these samples are analyzed. The results are then calibrated with the known yield responses and the most efficient extractant determined. The calibration of the soil tests may be accomplished in several ways. The most common procedure is the correlation of soil test values with per cent yield of plant material or total uptake of the nutrient element from treated and untreated areas. The “A” values (the amount of soil phosphorus that is as available to plants as the phosphorus in the phosphate fertilizer which has been mixed with the soil), as developed by Fried and Dean (1952), have been used to correlate soil test values also. Yield of nutrient curves have promise in estimating the amount of nutrients available to the plant from the soil and hence may be important in standardizing soil tests. Dean (1954) has used this technique for phosphorus. He applied increasing rates of the nutrient in question and plotted the amount of nutrients absorbed by the plants. This curve extrapolated back to the x-axis gave a measure of available soil phosphorus and approximated the “A” value. SOIL TESTS

1. Field and Greenhouse Studies A large number of soil samples from both field and greenhouse studies are needed for calibration purposes to cover the range of conditions encountered in testing. The National Soil Test Work Group report (1956) indicates that higher correlation between soil tests and percentage yields can be obtained in greenhouse studies than in field studies. This should be expected, since a number of uncontrolled factors such as rainfall and temperature, or factors more difficult to control, such as insects, diseases, weeds, and cultural practices, may affect plant growth more in the field than in the greenhouse. For this reason, a better comparison of testing procedures can be made through use of greenhouse studies. After the procedure to follow has been determined, however, it is essential to calibrate it with field trials. Under such circumstances, the frequency distribution or probability methods may be used as a v i d e in making fertilizer and lime recommendations.

J. W. FITTS A N D WERNER L. NELSON 246 The difference in results between greenhouse and field studies is well illustrated in the National Soil Test Work Group report (1956). Of the 74 field experiments conducted with phosphorus, significant yield increases were obtained at only 25 locations. In the greenhouse studies with surface samples from the same locations, a significant increase was obtained from 45 fields. The difference can be attributed to better control of moisture, temperature, and other growth factors. Of course another important point is the difference in the volume of soil occupied by the plant roots. The greenhouse pots contained only surface soil, whereas roots of plants in the fields penetrated the subsoils, which may have been higher in available phosphorus. This contribution of the lower horizons to the nutrient supply of these plants represents a problem needing much further study. Since samples are taken only from the plow layer, it may be necessary to group soils by soil associations or origin as to possible contributions from lower horizons. Pratt et al. (1955) found certain soil series higher than others in phosphorus in the lower horizons. In Iowa the loessial soils have been found to contribute considerable subsoil potassium to growing crops and recommendations are modified accordingly on these soils.

2. Correlation Studies The correlation coefficient, r, is often used to present the results of the relationship between per cent yields, “A” values, etc., and soil test values. The correlation coefficient is a simple index for expressing the degree of linear relationship between two variables when the scatter diagram for the sample consists of a cluster of points which is roughly elliptical in shape. The value of r varies between +l and -1. Positive values for r indicate on the average that an increase in one variable is accompanied by an increase in the other. Negative values indicate that an increase of one variable is accompanied by a decrease of the other. The correlation coefficients of soil tests are expected to have a positive value. The coefficient of determination is rz X 100. It is a measure of the percentage variation in one variable that is associated with variation in the other variable. A correlation coefficient r = 0.80 would have a coefficient of determination of 64 per cent. This indicates that 64 per cent of the variation in per cent yield or “A” value can be predicted or accounted for by the concomitant variation in soil testing results. Conversely (1 - r2) X 100 or 36 per cent is the amount of variation not accounted for. By correlating a large number of per cent yields and soil test values a value for r may be obtained which is statistically significant. This means that relationship between the two variables is not due to chance.

247

SOIL TESTS

It is possible to have statistical significance and still have a method of little value in predicting the nutrient status of the soil. An I value of 0.5 might be statistically significant. The value of r2 would be 0.25 and only 25 per cent of the variation would be explained. In many instances the relationship between response and soil test value is curvilinear rather than linear. For example in Fig. 1 showing soil test values for available phosphorus as related to per cent yield the relationship is not linear but curvilinear. Reporting a correlation value

o C/A C/&. .CIA) 0

( 1.1

1.2-2.0 2.1

FIG. 1. The relation between phosphorus extracted and per cent yield (Soil Test Work Group report, 1956).

for such data would result in a much lower I value than would be obtained by transforming the data to logarithms to obtain a linear scale. Hence the relationship must be observed carefully before determining correlation procedures. Statistically significant I values in correlation of soil tests may be somewhat misleading in evaluating the merits of the test. Soil test results are usually grouped into classes such as very low; low; medium; and high. A testing procedure may accurately place the results in a given class without having a high correlation in that range of the scale. For example, a procedure for determining phosphorus colorirnetrically may employ ammonium vanadate instead of stannous chloride. The ammonium vanadate procedure is not as sensitive in low concentrations

J. W. FITTS A N D WERNER L. NELSON 248 of phosphorus and although it may place the samples in the low class, the soils may not be placed in the same order by the ammonium vanadate as by the stannous chloride. Hence the correlation coefficient may be lower for the former method even though the samples are placed in the proper class. Bray ( 1948) has made extensive studies in plotting percentage yield values against soil test values for phosphorus and potassium. The curve closely coincided with a typical Mitscherlich growth curve. Mitscherlich’s equation for the curve was modified to fit as follows:

log (100 - y ) = log 100 - C l b l , where 100 = the LPK yield of corn, y = the percentage yield for the LP or LK plots, b, = the potassium or phosphorus test value on the untreated plot, and c1 = the proportionality constant. 3 . Frequency Distribution

In soil testing one of the objectives is to group the soils into classes relative to the level of nutrients for the purpose of suggesting fertility and lime practices. Similar fertilizer recommendations are generally made for all soil samples falling within a given class. The soils may be divided into classes in which the untreated soil yields less than 25 per cent, 26 to 50 per cent, 51 to 75 per cent, 76 to 90 per cent, and over 90 per cent of the yield obtained with the addition of the plant nutrient. Unfertilized fields yielding less than 25 per cent of the fertilized fields could be designated as very low, those yielding 26 to 50 per cent as low, and so on. Of course, other percentage ranges could be selected for very low, such as less than 35 per cent, or a low value given to all yields less than 50 per cent. The interpretation made for each class will determine to some extent the range to be assigned. Upon selection of the percentage ranges for the various classes, the soil test values can be selected to conform to these percentage yields. It is helpful to determine the frequency distribution of soil test values grouped together according to percentage yield. An example of this for phosphorus is shown in Table 11, which is taken from the National Soil Test Work Group report (1956). The 74 soil samples were separated into five classes, those yielding less than 25 per cent, 26 to 50 per cent, 51 to 76 per cent, 76 to 90 per cent, and over 90 per cent without the addition of phosphorus. Soil test results are shown for six laboratories using different extraction solutions. Four classes relative to level of phosphorus were established for each extractant. In general, greatest response would be expected in the lower classes and least response in the upper classes. Of the 15 samples having a yield less than 25 per cent, all the laboratories placed a majority

249

SOIL TESTS

TABLE I1 Frequency Distribution of Samples According to Per Cent Yield and Soil Test

Ib. PzOs/acre

Per cent yield

96-50

51-75

76-90

over DO

Number of samples in each group 0.095 N HCI and 0.03 N NH4F

<90 91-35 36-50 >50

14 1 0 0

5

6 4 0 0

0

a

a

1

1 7

0

1

a a 26

0.1 N HCI and 0.03 N NH4F <75 76-193

1as-aoo

>200

11 1 1

a

4

0 3 1 4

9 9 9

0 0 3 7

0 0 4

27

0.05 N HCI and 0.085 N HzSO4 <75 76-190 191-200

>zoo

13

1 0 1

9 1 0 0

5 1 0

a

0 3 1% 16

a

2 2 4

9

a

3

1 3 4

10 19

3 0

5 7

Morgan’s (Na Acetate) <8 9-14 1545 >25

19 0

<100

13 0 0

8 0 2

9

0

15 0 0 0

9 1 0 0

9

1

7 0 2 1

a 1

1 1

0.3 N HC1

101-150 151-190 > 190

3 2 1 2

2

6

5

15

9 4

9

a 0

3

6 9

0

0

7

coz < 10 11-15 16-95 >25

6

of the samples in tho lowest class, with very few if any in the upper classes. Four of the six procedures placed most of the samples yielding over 90 per cent in the higher classes. Most of the laboratories encountered the greatest difficulty in proper placement of soils in the 76 to 90 per cent yield range and the next greatest difficulty in the 51 to

J. W. FITTS A N D VlrERNER L. NELSON 250 76 per cent range. This should be expected, since factors other than fertility exert a proportionately greater influence upon the yields at the higher fertility level. It must be kept in mind that various interactions are likely to be encountered between elements which may influence the soil test values for given classes. For example, the values for magnesium in the various classes will be different at a low potassium level than the values at a high potassium level.

nol

600

500 INCREASE LBSIACRE COTTON

400

I

IN-PKI- (N-P-01 K.40 TO 120 LBS K,O

PER ACRE

*

. 0

-50

.03

FIG.2.

.07

K

.II

.I5

EXTRACTED

.I9 M.E./IOO

.23

.27

.31

GRAMS

The response to potash by cotton on soils of different potassium levels (Fitts, 1955).

4. Probability Another method of predicting lime and fertilizer response is the “probability” approach as suggested by Fitts (1955). The probability of obtaining a profitable increase in yield for a given fertilizer treatment is plotted against soil test results. The probability is actually the percentage of fields within a given range of soil test values that respond profitably to application of fertilizer. In Fig. 2 are yield data from North Carolina on response of cotton to application of potassium. Of the seven fields testing less than 0.05 me. K, six increased the yield more

SOIL TESTS

25 I

than 250 pounds per acre, which is quite profitable. The probability would be 0.86 or 86 times out of 100 that a profitable increase might be expected. This does not indicate the magnitude of the response, as shown by the increase in yield ranging from 260 pounds to more than 700, but all were profitable. No doubt, factors other than fertility influenced the responses, In the range of 0.07 to 0.15 me. K, six of nine fields, 0.67 or 67 times out of 100, gave a profitable increase, but none exceeded 200 pounds per acre. This range could be classed as low. The 0.15 to 0.30 me. K range might be classed as medium, since there was an even chance of getting a profitable yield. More field tests are needed in this range to delineate the boundaries more precisely. No data were available for a high category. The 150 pounds per acre increase on a soil having 0.30 me. K per 100 g. of soil was on a very high-yielding field. The better farmers are more likely to get a profitable response at higher soil test values than the average farmer, since management practices will be better and general yield levels will be higher. The range for the classes will vary with different soils and crops and separate charts have to be prepared for each crop or soil, or group of crops or soils. For some crops there may not be a sufficient number of field studies to permit more than three class separations. In some instances it might even be desirable to make only two, those likely to respond and those not likely to respond. A problem frequently encountered is that a majority of field experiments are conducted on soils known to be low in fertility, leaving only a few, if any, results for calibration in the high or very high ranges. This is well illustrated in Fig. 2. In the “probability” approach, the odds are against receiving a profitable increase from fertilization on fields testing in the high classes. This does not preclude the possibility of getting a response, however, when all other factors influencing crop yield are optimum. In LLgood” years then all classes may tend to shift upward and in poor years, downward. The data presented in Fig. 2 illustrate the probability of response for only one element. Response surfaces can be constructed, however, on two or three planes with two or three elements. Contour lines can be located for various yield responses and the probability of getting such an increase determined.

5 . Soil and Plant Characteristics Affect Calibrations Soil characteristics influence the availability of nutrients. McLean and Adams (1954), Mehlich (1953b), Brown (1955), and many others have shown the effect of type of clay mineral on cation absorption.

252

J. W. FITTS AND WERNER L. NELSON

Workers in the United Kingdom have pointed out the importance of the parent material of the soil in evaluating the supply of available nutrients. Soil aeration and temperature also have been demonstrated to have an important influence on nutrient requirements. The interaction among plant nutrients and ion activities are bportant in determining availability. Schuffelen (1952), Wiklander (1952), Elgabaly (1952), Bondorff (1952), Woodruff (1955), and Van Der Paauw (1952) have emphasized the need for control of these interactions insofar as possible. Several investigators have stressed the importance of root characteristics in absorption of nutrients (Gray et al., 1953; Mehlich, 1953b, McClean and Adams, 1954). Fried (1953) and others have demonstrated the difference among plants in feeding power for phosphates. These differences among plants and soils emphasize the importance of fully characterizing the conditions under which calibrations are attempted. It is becoming of great importance that a wide range of soils and crops be evaluated as more complete calibration studies are attempted.

111. REPRESENTATWE SOILSAMPLES The soil samples submitted for testing should be representative of the area on which information is desired. Taking representative samples is undoubtedly one of the most important phases of soil testing, since a poorly taken sample may lead to completely erroneous recommendations. Some of the problems encountered in soil sampling include: the size of an area to sample, the depth of sampling, and the number and distribution of cores for a composite sample. Moisture content of the soil when samples are taken, season of the year, frozen soils, influence of growing crop, and handling of the samples preparatory to testing are also important factors that must be considered. The National Soil Test Work Group (1951) encountered many variations in sampling techniques when surveying the status of soil testing in the United States. A large number of different agencies was found to be involved in taking soil samples. Almost all the agencies recommended taking a composite sample, but the suggestions for doing so varied considerably. Very little research has been conducted on taking soil samples from fields for soil test analyses. Furthermore, much of the information that has been obtained has not been published. A survey of existing data was made by Reed and the National Soil Test Work Group (1953). The report of this Work Group provides detailed instructions for taking samples. The error in soil analyses consists of the error encountered in sam-

253

SOIL TESTS

pling plus the analytical errors in the laboratory. This is illustrated in the following equation:

Vf +-. Vd v; = f

d

V ; is the variance of the mean; Vfis the combined variance in taking samples; and V d is the combined variance in the laboratory procedures. The symbols f and d are the number of cores and the number of replicate determinations, respectively. Cline (1945) found that the error in sampling a field is generally greater than the error in laboratory analyses. Rigney (1955) points out V; may be reduced by reducing the contributions from either(Vf/f), (Vd/d), or both. The obvious choice would be to take the one that costs the least. The ratio of field to laboratory effort which will give a desired accuracy for a minimum cost is:

where Cf is the cost of taking additional borings and Cd is the cost of running additional replicates of laboratory determinations. A few extra borings for a composite sample is likely to be the cheapest means of reducing the overall error. Using the variances reported by Rigney and Reed (1945) and Reed and Rigney (1947) for phosphorus and potassium tests, the optimum number of field borings to take per laboratory determination under the conditions studied would be: Optimum borings per lab determination Phosphorus Potassium Uniform areas Nonuniform areas

6 21

7 23

The general recommendations of 10 to 20 cores per composite sample would appear to fit most conditions. 1. Area to Sample

In most instructions for taking soil samples the area to be sampled is designated as a field. Frequently the instructions suggest that a separate composite sample be taken for every 5 to 10 acres, which restricts the size of the field. Judgment in selecting the area to be sampled usually is based on visual inspection of differences in topography, degree of erosion, drainage, past management, etc. From a practical standpoint it may be maintained that little is to be gained by dividing a field for sampling if the field is to be fertilized or limed as a unit. Small

254

J. W. FITTS AND WERNER L. NELSON

areas within the field that are obviously different should be sampled separately or omitted. A few cores from a problem spot mixed with cores from the remainder of the field may greatly influence the results of the tests. In sampling the small areas, approximately as many cores are needed for a composite sample as on the larger areas (up to 5 or 10 acres). Cline (1944) has called attention to the fact that variations in both horizontal and vertical dimensions should be considered in determining the area to be sampled. In the accuracy of predictions studies by Reed and Rigney (1947), the equation

T.'"

=

vp

-

P

Vf + vs +I'a +f

3

a

is based on the assumption that each operation represents a random choice. This means that every boring has an equal chance of occurring anywhere in the field regardless of where any other boring is placed. The requirement of random distribution of borings of a soil sample does not mean that samples should be uniformly distributed over the area. It is difficult to obtain completely random distribution of borings over the area to be sampled, and in practice it is doubtful if it is the most efficient method that can be used. Haynes (1948) studied four patterns of locating soil samples:

1. Random method 2. Stratified random

3. Random grid 4. Zigzag

His results indicate that the stratified random and zigzag methods are superior to random distribution. The superiority was especially pronounced at low rates of sampling as compared with high rates, meaning that the accuracy of the stratified o r zigzag patterns is greater than would be indicated by the equations given above.

2. Depth of Sampling In soil sampling for routine chemical tests most of the emphasis is placed on taking samples from the plow zone or to a depth of 5 or 6 inches. Without question, the nature of the soil profile below the plow layer will influence the growth of plants and the eventual yield that will be obtained. Other than in the plow layer, however, the fertility conditions of the soil profile do not change materially from one year to another under most farming conditions. Neither phosphate nor lime moves much in the soil and if added they are usually retained in the top few inches. Welch and Fitts (1956) found a marked gradient in fertility patterns in the upper 9 inches of soil taken from both row crops and sod

255 crops. Greatest concentration of the phosphorus and potassium was found in the surface 3 inches, with a gradual decrease to a depth of 9 inches. Although the 0- to 6-inch depth was lower in nutrient elements than the 0- to 3-inch layer, the difference was not as great as might be anticipated by comparing the 0- to 3- and the 3- to 6-inch layers with the 0- to 6-inch depth. Where lime and fertilizer have been broadcast on the surface of the ground there is evidence that a better relationship exists between analysis of the upper 2 inches of soil and the plant nutrient requirement than can be obtained by testing a 0- to 6-inch soil sample. For this reason the instructions from many laboratories restrict the sample to the upper 2 inches for permanent pastures or lawns. On some soils deep application of lime and fertilizer once every four or five years may be desirable to extend the feeding zone of plant roots. Under such circumstances it would be necessary to extend the depth of soil sampling to correspond to the placement of the fertilizer. This would still be sampling the plow zone, however, where greatest changes take place due to management. SOIL TESTS

3. Sampling Tools A great variety of equipment is used for sampling soils and this will probably continue, since some tools are better adapted for certain soil conditions than others. Reed (1953) describes the “ideal” soil sampling tool as one which should: a. Be relatively easy to use in the field to provide fairly rapid sampling. b. Take a small enough volume so that 15 or 20 borings can be placed in shipping containers. c. Be easy to clean and rust-resistant. d. Be adaptable to dry sandy soil as well as to fairly moist sticky soils. In addition, two more requirements might be mentioned: one, the tool should take a uniform slice from the surface to as deep as the tool is inserted, and two, uniform volumes of soil should be taken from each spot. Welch and Fitts (1956) found that satisfactory samples could be obtained equally well with a soil tube, spade, trowel, or auger. The important factor was to obtain a uniform core or slice of soil to the desired depth of each spot in the field. This could be done with each of the tools if properly handled. There was a tendency for the surface inch of soil to be lost from the auger, especially under dry conditions. Under most soil conditions the soil tube is the tool which is easiest to use correctly.

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J. W. FITTS A N D WERNER L. NELSON

4 . Time of Sampling There are few published data on the effect of moisture level or season of the year upon soil samples. Most laboratories recommend taking samples whenever the soil is in a physical condition that it can be plowed or cultivated. This is important in the mixing of the cores for the composite sample if for no other reason. It is known that pH, available phosphorus, and potassium determinations vary throughout the year, but factors responsible for these variations have not been fully appraised. The soluble salt concentration TABLE I11 Effect of Time of Sampling and Soil Moisture on Soil Test Values on Sassafras Sandy Loam' Date of % Water sampling in soil 5/29/50 6/12/50 6/26/50 7/10/50 7/24/50

18.7 7.2 4.7 14.0 10.7

l0/30/50 11/13/50

8.2 7.7

11/27/50 12/11/50 1/%/51

14.6 16.4 15.3

I 1

8

Condition of soil Soggy wet Dry on top Very dry Very wet Moist, excellent condition to cultivate Moist, dry on top Moist, have had extended dry period Too wet to cultivate Too wet to cultivate Too wet to cultivate

pH

Phos- Potas- Niphorusz &ma trate2

Salt conc.8

15.9 12.8

92 51 276 59 56

55 91 100 17 63

73 120 116 48 73

5.4 5.4

18.9 21.6

1eo 145

108 125

130 120

5.4 5.6 5.6

19.5 20.1 19.2

150 145 124

136 33 50

125 55 73

5.6 5.5 5.5 5.6 5.5

20.6 17.0 20.8

Duntou d d.(1964). Parta per million in air dry soil. Micromhos (specific conductance) with a soil-water ratio of 1 :1.

in soils varies throughout the year and may influence pH. The higher the salt concentration, the lower will be the pH reading on acid soils. The presence of CO, may influence pH values also, especially on neutral soils. The equilibrium between slowly available and exchangeable potassium as influenced by crop removal and soil conditions may be important. Release of nutrient elements such as phosphorus from organic matter as influenced by temperature and moisture must be considered also. The activity of soil microorganisms is an important factor that must be reckoned with, not only because of the release of phosphorus from organic matter but because of the influence on the availability of other elements. T h e results in Table I11 were obtained in a sandy Coastal Plain soil to which no fertilizer was applied and on which no crop was growing.

SOIL TESTS

25 7

The rather marked differences in phosphorus and potassium tests from one sampling to another are attributed to the movement of soluble salts. There apparently was an accumulation of fertilizer salts in this soil. This condition represents a rather extreme case, however.

5 . Frequency of Sampling Soil tests furnish information relative to the fertility status of the soil. Under ordinary management practices the fertility and acidity level of soils does not change rapidly. Most soil testing laboratories recommend taking soil samples only once every three to five years. This should be sufficient to indicate the trend in fertility and acidity levels and to develop a good management program for the cropping system followed. Under specialized types of farming and under some soil conditions more frequent sampling may be desirable.

6. Soil Containers Most laboratories have found it desirable to furnish containers for submitting soil samples. An adequate amount of soil is then usually received for testing and the samples can be more readily handled in the laboratory. The I-pound or pint size folding cartons are the most widely used containers. Information relative to taking samples and mailing instructions and a place for identification are usually printed on the cartons. The half-pint carton and heavy paper bags are also being used successfully.

IV. CHEMICALTESTING PROCEDURES Methods for testing soils chemically have been under investigation for a considerable period of time. In general efforts have been made to develop procedures that are accurate, rapid, and adaptable to large-scale testing. In recent years this goal has been largely attained, particularly in central and regional laboratories, where the accuracy approaches that of the accepted “long” methods customarily employed in analyzing soils. Tests f o r pH and/or lime requirement, phosphorus, and potassium are most common and these tests are made in practically all soil-testing laboratories. Many other tests are also made either on a routine basis or on special samples. 1. Drying In almost all laboratories the soils are air-dried before analysis. This facilitates crushing and thorough mixing of the soil samples before analysis. Drying is accomplished at room temperatures in most instances and sometimes is speeded up by forced air. A limited amount

258

J. W. FITTS A N D WERNER L. NELSON

of heat is used in some laboratories but high temperatures are avoided because of possible effects on availability of nutrient elements. Under some conditions, particularly in certain parts of the North Central Region of the United States, the soils are air-dried for about 10 days. Illite-type minerals are present which may release potassium on drying and time is required for the soil to equilibrate. Much work has been done on the release of potassium from nonexchangeable forms and an extensive review has been prepared by Reitemeier et al. (1951). Bray and DeTurk (1938) demonstrated the tendency for the forms of soil potassium to attain equilibrium. The effect of drying apparently is related to the potassium status of the soil (Attoe, 1946). Evidence obtained by Luebs et al. (1956) indicates that potassium uptake by plants is better correlated with the exchangeable potassium of undried rather than of air-dried samples. Determining potassium on moist samples presents a number of problems in a large-scale testing program but these should not be insurmountable. 2. Crushing The crushing of all the large lumps in the soil sample is essential in order that complete mixing may be accomplished. Most laboratories pass ,the samples through either 10- or 20-mesh screens. Mechanical crushers or mills facilitate crushing, insure more uniform treatment, and are now used in a number of laboratories (National Soil Test Work Group, 1951) .

3 . Volume us. Weight in Measuring Samples The quantities of soil constituents generally are expressed as pounds per acre to plow depth, usually considered to be 6% inches. It is recognized that this volume of soil will vary considerable in weight, depending upon whether the soil is a sand, loam, clay, or muck, but it still represents the same volume €or root growth. Samples for soil analysis usually are measured rather than weighed. This permits more rapid handling of samples. Measuring cups or spoons containing up to 25 g. are used. Uniform methods of filling, including striking off the excess soil, result in reproducible amounts of soil. 4. p H The determination of soil acidity was one of the first routine soil tests and still is the determination most widely used. Perhaps pH tells more about the fertility status of the soil than any one other single measurement. The definition of pH is the negative logarithm of the hydrogen ion

SOIL TESTS

259

concentration of a system, and it is viewed as a reflection of the acidity of a soil. Actually in a heterogeneous system such as a soil, the H-ion concentration indicated by its pH often is a very small fraction of the total acidity. Since the ions responsible for soil acidity are concentrated at the surface of the soil particles, the relationship between pH and total acidity is not a simple one, though some generalizations can be made. a. Methods. There are two general methods for determination of soil reaction, electrometric and colorimetric (Reed and Cummings,

1945). The glass electrode has made pH a simple measurement and this instrument is standard equipment in most laboratories. Either battery or line-operated instruments are satisfactory, with the line instruments requiring less maintenance. Values are usually reported to the nearest 0.1 pH. Color indicator dyes are employed in some county laboratories and in field kits but must be used by relatively experienced operators and the results checked with pH meters periodically if reliable results are to be obtained. Mason and Obenshain (1938) found that the better methods gave deviations of 0.2 to 0.4 pH unit. b. Some Factors Afecting the p H Value. The pH value of a given soil may be influenced by several factors including the soil-water ratio. In general, pH determinations are made at as low a dilution as practical, since wide dilutions tend to result in high values. Very narrow ratios may not be feasible, however, because of improper mixing and difficulty in rinsing the electrodes between samples. Ratios of 1: 1 or 1 :2 are generally used. Because soil pH depends on the soil-water ratio, it is essential that the soil be kept suspended during measurement (Bailey, 1943).This can be accomplished best by stirring. In finer textured soils stirring just before measurement is usually satisfactory, as the soil stays in suspension for a sufficient length of time for the reading to be made. Stirring and mixing assemblies operating in close proximity to the glass electrode have been developed to increase efficiency of the operation (National Soil Test Work Group, 1951). When soils have a pH above 7.0 a knowledge of the presence of calcium carbonate may be helpful in identifying certain problems. Dilute HCl added to the soil will cause effervescence in varying degrees depending on the amount of free lime.

5 . Lime Requirement A measurement of the concentration of hydrogen ions in solution (pH) does not indicate the amount of soil acidity but when related to base saturation may serve as a useful guide in lime recommendations.

260

w.

r,. NELSON Mehlich (1942) showed that a relationship exists between the percentage base saturation and pH for given soil types. The amount of organic matter and the amount and type of clay largely determine the percentage base saturation at a certain pH value. In most of the soil-testing laboratories the amount of organic matter and clay is considered along with the pH in making lime recommendations. A more direct and rapid method for determining soil acidity was proposed by Brown (1943). He used neutral normal ammonium acetate and measured the depression in pH when mixed with soil to estimate exchangeable hydrogen. He also added normal acetic acid to a soil and used a rise in pH as a measure of exchangeable bases. Using a similar technique, Woodruff (194713) developed a solution composed of paranitrophenol, calcium acetate, and sodium hydroxide which was buffered at pH 7.0. The depression in pH of a mixture of soil and solution is used as a guide to lime requirement. Greatest accuracy with this procedure is in the range of 1.0 to 4.0 tons per acre of limestone. The method has not been satisfactory for use on low exchange capacity soils which can be easily overlimed for certain crops. In order to obtain greater sensitivity, Mehlich has proposed the use of barium chloride-triethanolamine and barium acetate buffered at pH 8.0. A change in pH of 0.4 is equivalent to about 1000 pounds of limestone, which is about twice the sensitivity of the other proposed methods. J.

FITTS AND WERNER

6. Phosphorus Nelson et al. (1953) made a rather complete review of the background of soil tests for phosphorus. In addition Kurtz (1953) reviewed the status of inorganic phosphorus in acid and neutral soils, Olsen (1953) the status in alkaline and calcareous soils, and Black and Goring (1953) the status of organic phosphorus in soils. For many years soil chemists have attempted to evaluate that portion of the soil phosphorus that would be available during the growing season. The availability of phosphorus is complicated by the fact that it is retained in the soil in various forms, including complexes or compounds of calcium, iron, and aluminum. Pratt et al. (1955) show some difference among soils in the effect of pH on availability of phosphorus. They state that the calcium phosphates and apatite forms are soluble in alkali and the Fe and A1 phosphates are soluble in acids. The phosphorus availability picture is further complicated by the fact that phosphorus is released from plant residues and soil organic matter and this release is affected by factors affecting microbial activity. Because of the many forms in which phosphorus can exist in the soil, any soil-testing procedure for measuring phosphorus availability is empirical.

26 1 a. Extractants. A number of different kinds of extractants are being used including water, carbon-dioxide-satura ted water, acids, bases, salts, and buffered solutions. Electrodialysis is also employed in one laboratory (Purvis and Hanna, 1949). The method outlined by Bray and Kurtz ( 1945) involves extractants combining dilute HCl and NH,F. It removes a proportionate amount of easily soluble and replaceable phosphorus. The P, test procedure employs 0.025 N HC1 and 0.03 N NH,F, while the P, test employs 0.1 N HCl and 0.03 N NHaF. The National Test Work Group (1956) found the Bray P, test best correlated with percentage yield and “A” values. Thompson and Pratt (1954) found that the PI test gave the best correlation with plant available phosphorus. Lawton et al. (1947) found the weak acid extractants superior to the stronger acid extractants in Michigan soils. More recently a method was proposed by Olsen et crl. (1954) using 0.5 M NaHCO, at pH 8.5 as the extractant. This solution increases the calcium phosphate as the result of lowering the Ca++ activity in solutions and because of its alkaline reaction also dissolves phosphorus from iron and aluminum complexes or compounds. Smith et al. (1956) found Bray’s PI more satisfactory than this method for predicting yield response from fertilizer application. Strongly buffered acidic salt solutions, such as sodium acetate adjusted to about pH 4.8 with acetic acid (Morgan, 1941), are used in a number of laboratories, particularly in the Northeastern Region. The National Soil Test Work Group (1956) reported such extractants to be rather poorly correlated with percentage yield and “A” values. Semb and Uhlen (1955) found calcium lactate buffered at pH 3.7 to be superior to other methods. Dilute acids (HCl, HNO,, H,SO,, citric) are used, particularly on acid soils. Because it complexes Fe, Al, and Ca, citric acid is somewhat more effective than dilute mineral acids in dissolving phosphorus from such soils. Van Der Paauw et al. (1951) found this extractant most effective on soils of pH 5.5 to 6.2. In Germany, Riehm (1952) reports the lactic acid method to be the most satisfactory of 12 methods compared on 1000 soil samples from long-term field experiments. In general the amount of phosphorus extracted with water is rather low and a clear extract may not be obtained. Hence, it may be difficult to measure the phosphorus accurately. Thus little use is being made of this extractant. Carbon-dioxide-saturated water has been in use for some years in the alkaline and calcareous soils of the western part of the United States. Although this method has been used extensively and has been considered to be reasonably satisfactory, it gradually is being replaced by more satisfactory methods. There are distinct differences in the value of different extractants SOIL TESTS

262

J. W. FITTS AND WERNER L. NELSON

depending on the origin and nature of the soil. In Scotland, Williams et al. (1952) found Truog’s method best for slate and basic igneous rocks, acetic acid for granitic soil, and NH,F for old red sandstone soils. The National Soil Test Work Group (1956) also found that the correlation coefficients varied with different groups of soils. The variation was greater for some extractants than others. b. Measurement. The intensity of blue color produced in the ammonium molybdate-stannous chloride procedure or the yellow color in the ammonium molybdate-ammonium vanadate procedure is measured with electric photometers in almost all soil-testing laboratories in the United States. Readings are made visually by matching with standards in the soil-testing kits.

7 . Cation-Exchange Capacity and Percentage Base Saturation Cation-exchange capacity refers to the sum of all the exchangeable cations. Percentage base saturation refers to the percentage of the exchange capacity which is made up of exchangeable base including ammonia but exclusive of hydrogen and aluminum. Very few laboratories report cation-exchange capacity and percentage saturation. However, in Missouri cation-exchange capacity is reported (Graham, 1950; Smith, 1954). Missouri workers feel that the percentage saturation with calcium, magnesium, and potassium is important, with the approximate optimum value for calcium being 75 per cent, for magnesium 10 per cent, and for potassium 2.5 to 5.0 per cent. The higher value for potassium is applicable to the soils with lower exchange capacity. This appears to be a desirable approach especially in areas with soils having a relatively wide range in type oE colloid and exchange capacity. 8 . Potassium

In determining “available” potassium, most laboratories use chemical methods that remove an amount approximating the exchangeable portion. Most of the soil potassium occurs in silicate minerals and these minerals generally break down too slowly to release potassium in amounts necessary for growing crops. The conversion from nonexchangeable to exchangeable forms is constantly taking place but soils differ greatly in ability to release potassium. A number of workers including Reitemeier et al. (1947), Reitemeier (1951), Reitemeier et al. (1951), and Kolterman and Truog (1953) have proposed methods of measuring release of this nonexchangeable potassium. Recently Hunter and Pratt (1956) developed a method using H,SO,, which compares favorably with the boiling nitric acid method but is more rapid. Pratt

263 and Morse (1954) found that in Ohio soils the release of nonexchangeable potassium was more characteristic of the soil type and soil area than the exchangeable K values. Pratt (1951) studied eight characteristic soil types in Iowa and found that the best single criterion for predicting potassium removed by alfalfa was the determination of exchangeable potassium before cropping. a. Extractants. Ammonium acetate has long been considered to be the standard extracting reagent for potassium and many laboratories are using this reagent. A number of states, particularly those with county laboratories, employ a concentrated solution of Na salts such as 25 per cent NaNOJ. Other laboratories use dilute acids or sodium acetate. With these two latter extracting solutions phosphorus and other cations can be determined on the same extract, thus simplifying the analyses. In correlating exchangeable potassium with Neubauer values for available potassium, the National Soil Test Work Group (1956) reported that best results were obtained with ammonium as the replacing ion. Sodium, hydrogen, and sodium plus hydrogen followed in the order listed as next most effective. Semb and Uhlen (1955) working on Swedish soils found the boiling nitric acid method to give the most satisfactory agreement with crop yields. b. Measurement. Almost all central or regional laboratories use the flame photometer to determine the amount of potassium in the extract. Although there is a difference in flame photometer operators (Mehlich and Monroe, 1952), greater consistency of results and speed of operation are obtained by this method of measurement. In most instances the lithium internal standard is not used because as it is felt that the increase in accuracy does not justify the extra time. In other instances the sodium cobaltinitrite method is used and the turbidity measured. Photometers are employed in most laboratories but in some the measurements are made visually. Temperature control is extremely important in this method. SOIL TESTS

9. Calcium and Magnesium Almost one-half of the laboratories in this country analyze for calcium and magnesium on a routine basis. Some of the other laboratories include these elements in their “special” analyses. Calcium and magnesium may be determined in an aliquot of most of the extractants that are used for potassium analysis. The sum of exchangeable calcium, magnesium, potassium, and the exchange acidity gives a good estimate of the cation-exchange capacity, from which the percentage saturation of each element can be ascertained. In calcareous soils a determination of free carbonates is of more value than a determination of exchangeable calcium. The excess free

264

J. W. FITTS A N D W E R N E R L. N E L S O N

carbonates may serve as a guide to nutrient deficiencies such as those of phosphorus or iron. Calcium may be determined by means of a flame photometer but more generally it is determined turbidimetrically as the oxalate. In many soils only a small portion of the total magnesium is present as the exchangeable cation. Some of the salt solutions and acids used in extractants remove appreciable quantities of nonexchangeable magnesium. This may not be serious in estimating “available” magnesium since plants probably use some of these forms. As an estimate of its percentage saturation, however, the error could be large. In general, the determination of magnesium is somewhat less accurate than that of other elements usually determined in soil-testing laboratories. Magnesium may be determined with a flame photometer where efforts are made to obtain greatest sensitivity. Usually it is determined colorimetrically with thiazol yellow. Mehlich ( 1956) suggests the addition of sodium polyacrylate in the thiazol yellow procedure to stabilize the color lake over a wide range of magnesium concentration. The solubility of calcium and magnesium from recently applied limestone may be appreciable in some of the extractants. Several investigators, including Mehlich (1953a) and Bower (1955), have developed methods to reduce this error. Barium chloride-triethanolamine buffered at pH 8.15 or normal sodium acetate buffered at pH 8.2 dissolves only small amounts of calcium and magnesium from the carbonates. 10. Organic Matter Organic matter content is determined in about one-third of the state laboratories. Organic matter furnishes a part of the exchange groups in soils, and also releases nitrogen and other nutrients as it decomposes. The primary purposes of this determination are first to obtain a better measure of the exchange capacity, and second, to obtain an idea as to the amount of nitrogen which may be released. In soil-testing laboratories the “easily oxidizable organic matter” usually is determined. This involves the use of the wet combustion method, in which the less resistant fractions are oxidized with sulfuric acid and potassium dichromate. In most instances unreduced dichromate is titrated with a reducing agent. In some laboratories, however, the system is filtered and the intensity of color measured with a photometer. 11. Nitrogen The increasing awareness of the importance of nitrogen in crop production has emphasized the need for evaluating the capacity of soils and cropping systems to supply nitrogen. Nitrate production in normal

SOIL TESTS

265

soils takes place under conditions permitting aerobic microbiological activity. Fitts et al. (1955) state: “Many complex factors such as quantity and quality of organic matter, nature and quality of residue from preceding crop, moisture and temperature fluctuation patterns, nature of soil microflora, aeration, soil reaction, mineral nutrient status and other biotic properties of the soil all have an influence on the rate of field nitrate production.” Hence, a meaningful determination of nitrogen availability is not simple. a. Methods. As was mentioned in the previous section, the amount of organic matter may be used to infer potential nitrogen availability. A systematic interpretation of nitrogen release as related to soil type has been worked out in Missouri (Woodruff, 1947a; Smith, 1954). Soil organic matter contains about 5 per cent nitrogen. Under Missouri conditions for corn and other summer cultivated crops the breakdown of organic matter is said to release from 1.25 to 6 per cent of the soil nitrogen in the course of a growing season. The amount of nitrate produced is greater in sandy soils. The release of nitrogen for small grains will be about one-half these amounts and for nonleguminous meadows about three-fourths that of small grains. A method employing chemical extraction of a fraction of the soil nitrogen has been developed at Wisconsin and is used in the soil-testing program there (Truog et al., 1955). The soil is boiled with potassium permanganate and anhydrous sodium carbonate for 5 minutes in a Kjeldahl flask under carefully controlled conditions relative to time required to bring to boiling. The distilled ammonia is determined with Nesseler’s solution. This method is rapid but does not measure the nitrogen in fresh organic matter. T o correct for this when alfalfa or clover sods are plowed under, 100 pounds of nitrogen is added to that obtained in the soil test. A third method involving the biological mineralization of nitrogen during controlled incubation of soil samples has received much attention in Iowa (Fitts et al., 1953, 1955; Stanford and Hanway, 1955; Hanway and Dumenil, 1955), and is being used in the soil-testing program. A 10-gm. sample of soil is incubated for two weeks at 3 5 O C. and leached with water. The nitrate is determined by adding phenoldisulfonic acid and reading in a colorimeter. Automatic pipettes, special shakers, and filtration racks make this method adaptable to soil testing. In the nitrate production method of evaluating nitrogen requirement the results from a given field will provide a reliable indication as to the potential nitrogen-supplying power of the soil which should hold over a period of a few years. The interpretation will vary depending upon the previous crop and the crop to be grown. Nitrate nitrogen is often determined on greenhouse soils by leach-

266

J. W. FITTS AND WERNER L. NELSON

ing out the nitrate and analyzing the leachate. The actual amount of nitrate nitrogen will vary considerably from one time to another. 12. Minor Elements

Most soil-testing laboratories do not include tests for minor elements except on special samples. A few commercial laboratories report values as part of the regular analysis. So far there is little information as to the relationship between the amounts of these elements found and the needs of crops. The pH of the soil is often used as a guide to minor element deficiencies or toxicities. In neutral to alkaline soils, iron, zinc, and manganese are frequently deficient. In contrast molybdenum is more likely to be deficient in acid soils. “Available” boron in soils can be measured fairly reliably by determining water-soluble boron according to the method of Berger and Truog (19M). The soil in suspension in hot water is refluxed for 5 minutes and after development of color the intensity is read with a photometer or by visual comparison with a set of standards. Exchangeable or easily reducible manganese may be determined as a guide to availability. Exchangeable manganese may be determined in solutions used for exchangeable cations. The easily reducible form is determined by the use of a reducing agent such as hydroquinine in the extracting solution. Zinc and copper occur in very small amounts in soils, and it is difficult to determine these elements with precision in most routine laboratories. Wear and Sommers (1947)related acid-extractable zinc to zinc deficiency symptoms in corn. Camp (1945)has utilized salt solutions to extract zinc. Tucker and Kurtz (1955) found that 0.1 N HCl, EDTA, and dithizone gave results for zinc that were significantly correlated with bioassay values. Davis (1952) used the Aspergillus method for determining copper availability. Continued use of copper in fertilizers or as a spray may result in an excess of this element, especially on sandy soils. Spencer (1954) developed a rapid test for excess copper using 1 N HCl as a leaching solution and treating with a carbamate reagent. Sulfur deficiency in soils is becoming more widespread but as yet few tests are made by laboratories in the United States for this element. Malavolta ( 1951 ) adapted the Aspergillus niger method for determining sulfur availability in soils of Brazil. The growth obtained followed the Mitscherlich equation. Spectrographic analysis is being used to some extent, especially in some commercial laboratories where tests are desired for several elements. Greatest use of the spectrograph has been in plant analysis in

26 7 surveys of nutrient deficiencies. McClung et al. (1956) used this technique in determining fertility problems in peach orchards. Whittles (1952) reports the spectrograph is used in Scotland for suspected cases of minor element deficiencies. In trace element surveys in New Zealand chemical analyses are made for boron, molybdenum, and cobalt. SOIL TESTS

13. Soluble Salts

In some soil conditions it is desirable to determine the amount of soluble salts present. This is often helpful in greenhouse soils or soils that have been overfertilized. Soluble salt determinations also are made to determine saline-alkali conditions. In Nebraska, for example, soluble salt determinations are made on all samples having a pH of 8.0 or more as well as where an excessive amount of sodium is detected in the flame during the potassium test (Knudsen, 1955). A solu-bridge is used for soluble salt determination in most instances. The conductivity of the saturated soil paste or the water extract of the soil may be measured. The readings are recorded directly in mhos conductivity or in ohms resistance and converted to per cent soluble salts or to parts per million (Magistad et al., 1945). 14. Soil Solution Ratio The ratio of the soil to the solution affects the results of a determination. Since most laboratories use an equilibrium procedure rather than leaching for removal of nutrients, a more complete extraction should be obtained with wider ratios. The more dilute solutions (wider ratios) allow the correlation curve to “stretch out” and make it easier to group the results into the various classes. Smith and Cook (1953) found that in measuring adsorbed phosphorus using Bray’s P, method a ratio of 1:50 gave a better correlation with plant yield response than did the usual 1: 10 ratio. Changing the ratio had no effect on the results of the Bray P, method, however. The authors felt that in the case of Bray’s PI method a more complete measurement of adsorbed phosphorus was provided with the wide ratio. In the pH determination ratios wider than about 1:2 tend to give too high values. 15. Labor-Saving Devices Soil testing on a service basis means handling relatively large numbers of samples. A few seconds saved on each of several manipulations is extremely important. Labor-saving equipment that will aid in handling the large volume of work rapidly yet accurately is essential. In most instances accuracy is considerably improved with special equipment. If an operation is made easier and more routine with such equipment

268

J. W. PITTS AND WERNER L. NELSON

the laboratory technician is less subject to fatigue and hence less subject to errors. Drawings of some of this equipment are given in the report of the National Soil Test Work Group (1951). It has also been described by other workers including Constable and Miles (1941), Miles and Reed (1948), Hester (1948), Wormley (1951), and Carpenter (1953). Many laboratories are rapidly adopting this type of special equipment.

FIG. 3. Dr. E. W. Constable, State Chemist, North Carolina Department of Agriculture, views the original dispenser which he developed in 1940 for adding extracting solution to 12 bottles at one time. The dispenser has been in constant use since then and has set the pattern for dispensers used in many other soil testing laboratories.

Mechanical crushers have been developed to facilitate preparation of the samples. Soil is measured out by volume with a scoop into bottles assembled in racks holding 10 to 12 bottles. Specially built dispensers are used to add the desired quantity of extracting solution to all bottles in each rack at one time (Fig. 3). Automatic hand-operated pressure bulb pipettes delivering 1 to 5 ml. are used to transfer aliquots of the filtrate to vials for testing. Electrically powered automatic pipettes dispensing 1 to 3 ml. or more with each stroke are used to add reagents to the samples and this speeds up analyses considerably. An automatic balancing type of photometer to

269 determine color intensity saves adjustments and in some instances the meter is calibrated to read directly in pounds per acre. Washing glassware is a tedious, time-consuming job. A washer designed to wash glassware without removal from racks is used in a number of laboratories. The trays are inverted over a pipe with 10 or 12 nozzles (one for each bottle or tube) and the soil washed out. A special stirring and rinsing assembly may be used to facilitate the pH determination. For example, the rinsing assembly is composed of a perforated tube bent in a ring around the electrode and connected to the distilled water source. A small pan connected with the drain serves to take away the rinse water. This gives brief mention of some of the types of special equipment which have been developed. A study of the individual problems in each laboratory is helpful in developing schemes to make the operations more efficient and hence more economical. SOIL TESTS

V. INTERPRETATION AND RECOMMENDATIONS After the soil test analyses are obtained, the results must be interpreted in terms of fertility levels or possible responses. This is a critical step in any soil-testing program. 1 . Reporting Results The results may be classified as very low, low, medium, high, and very high and/or in terms of pounds per acre of such elements as phosphorus and potassium in reports sent to persons submitting the samples. It will be noted in Table IV that there is considerable difference in the method of reporting among the various sections of the country. It TABLE IV Method of Reporting and Recommendink

Region Southern (1%states) Northeastern (1% states) North Central (1% states) Western (9 states)

States reporting2 P and K as

States recommending*

Low, medium, high Lb. per acre

Lb. of N, Material or Pz05, and K20 grade and rate

9

6

10

11

3

10

5

5

lQ

8

8

9

8

8

9

3

7

9

3

5

Personal communication. states report or recontrue~ldboth. 8 All or part. I

'1 Some

County agents recommend8

270

J. W. FITTS A N D WERNER L. NELSON

is felt in some states that pounds per acre is a more exact method of reporting and many states report pounds per acre as well as low, medium, and high levels. Advantages given by some soil-testing directors for reporting low, medium, and high are: the farmer has some basis for knowing what the report means, and three to five levels is detailed enough to report the phosphorus and potassium level of the soil. Disadvantages are given as: crops vary in requirement and what is low for a crop such as potatoes might be high for a crop such as small grain; and what is low for a soil such as a clay loam may be high for another such as a sandy loam. Differences exist in the meaning associated with the various classes, but this should be expected, since the objectives of soil-testing programs vary. Some laboratories regard soils classified as “high” as those on which no fertilizer should be applied. Soils requiring only a maintenance application are classed as “medium.” The “low” soils need larger amounts of fertilizers. Other laboratories regard the “high” classification as the one at which optimum production is attained and recommend the addition of maintenance fertilizers on these soils. Heavier applications of fertilizer are recommended on the lower classes. No doubt differences in the concepts may be associated with testing programs in regions where soils are inherently fertile as compared to regions where virgin soils are low in some of the nutrient elements.

2. Recommendations Many states are recommending pounds of N, P,O,, and K,O per acre along with examples of different fertilizer materials or grades and rate to meet the recommendations (Table IV). In the Western Region all of the states reporting, are giving recommendations in pounds per acre. The need for recommending pounds has become more important in recent years. There are a large number of nitrogen materials available and there are often several grades of the same ratio. For example, in the 1:4:4 ratio there may be 3-12-12, 4-16-16, 5-20-20, and 6-24-24 available in a state. In several states a table accompanies the report to convert from pounds of one grade or material to pounds of another.

3 . Familiarity with Local Conditions Although the soil tests may indicate the fertility status of the soil, the predictions of crop responses to lime and fertilizer applications must be made in terms of productivity, of which fertility is only one part. In order that the lime or fertilizer will be used most efficiently, full use must be made of all sources of information. The problem of proper use of fertilizers and lime includes not only determining what nutrients

271 are needed for best plant growth as related to local soil conditions but also making sure that the recommendations are understood and can be followed. Satisfactory machinery and other equipment must be available for proper fertilizer applications and for good cultural practices. The correct grades of fertilizer for the area must be available also. Personal contact by someone well trained in soils is of untold value in a soil-testing program. Local agricultural leaders, usually county agents, have taken or are taking over the soil test recommendations in many states. This is particularly true in the Northeastern and North Central Regions (Table IV). Definite advantages are: the county agent is familiar with local soil conditions and with the farmer; it encourages the county agent to think more about the fertility needs in his county; and his position of leadership in the county is improved since the soil is the basis for farming. Basic training in soil fertility and plant nutrition is essential for the interpretation of soil test results. In the states where county agents are making the recommendations much effort is spent in training schools for the agents. Tables giving the suggested amounts of plant nutrients at the various test levels are made available to the county agents. The location of the laboratory is of little consequence as long as the tests are accurately performed and the results returned to the sender within a reasonable period of time. SOIL TESTS

4 . Information Sheets Almost all soil-testing laboratories require information sheets to be submitted with soil samples. The information requested is designed to acquaint the person making fertilizer and lime recommendations with the conditions other than fertility that will influence the crop yield and the response to fertilizer application. Depth of surface soil, nature of subsoil (sometimes obtained from soil survey maps when locations of farms are given), drainage condition, erosion, past fertilization and liming, cropping system, level of crop yields, and management practices in general are among the questions asked. Recently applied lime usually is not detected by most soil-testing procedures for lime requirement, so this information is pertinent. Provisions for information on several samples on one sheet reduces the amount of writing required and is helpful to the person making the recommendations. Many information sheets carry sampling instructions on the back for simplicity. Printed sheets with simple diagrams illustrating the various phases of sampling are the most attractive and are more likely to be read and followed.

272

J. W. FITTS AND WERNER L. NELSON

5 . Liming and Fertilizing Soils In making fertilizer and lime recommendations a decision must be taken as to the quantities to be applied. Lime recommendations are reasonably well standardized. Since lime is relatively inexpensive, quantities are usually suggested that will bring the soil up to the optimum pH level for the rotation to be followed. With phosphorus and potassium the situation is different. For the most economical returns, should phosphorus and potassium be applied only for the immediate crop (fertilizing the crop) or in larger amounts to build the fertility level of the soil (fertilizing the soil)? Several factors must be considered in endeavoring to answer this question. Landlord-tenant contracts often complicate the problem. Yields anticipated or desired are important. Fixation of the elements into less available forms by the soil, leaching losses, and luxury consumption must be considered also. On soils classed as low or very low in an element, the lack of fertility usually is the limiting factor in the crop yield. Increasing the level of the element to medium or high, where good yields can be obtained if other factors are satisfactory, generally should be the most profitable undertaking. Information is needed as to the amounts of phosphorus and potassium to change the various soil types from low to medium or high, however. Fixation of phosphorus may be so great on some soils that it is not economically feasible to do this except for high-return crops. Leaching losses of potassium on low exchange soil, fixation, or luxury consumption by some crops may limit the amount of potassium fertilizers that should be applied at any one time. After the fertility level has been increased to a desired point (either medium or high), maintenance application of phosphorus and potassium must be applied to keep the level that has been attained. The amounts required for maintenance will depend upon crop removal, losses by leaching, fixation, or erosion, and amounts released by the soil. Small amounts of readily available nutrients, particularly phosphorus, often are essential for young seedlings and the need may have little relationship to the fertility level of the soil. Soil tests cannot be used satisfactorily to predict “starter effect” from fertilizer applications. In many instances these fertilizers applied at planting can be applied in sufficient quantities to serve for maintenance. The method used for nitrogen recommendations is of course considerably different from that used for phosphorus and potassium. Nitrogen does not accumulate to any extent in the soil. Hence, recommendations are made from year to year and are influenced greatly by the rotation employed. Fertilizing and liming soils for a whole rotation or cropping system

273

SOIL TESTS

should be considered. Soil tests will furnish information which can be used as a good guide for applicatioii of fertilizers and lime for a period of three to six years. Residual effects usually will be noted for more than one year. The length of time will be influenced by rates of application, soil characteristics, and yield of crops. Fertilizing a crop for a succeeding crop may be very profitable. An example is the application of potassium on corn preceding peanuts. Corn responds well to direct applications of potassium, whereas peanuts do not. Peanuts, on the other hand, respond to general increases in fertility level. The prescription method for making recommendations is being used in several states. This is based on the idea that plants can secure certain TABLE V Estimated Percentages of Nitrogen, Phosphorus, and Potassium in Soil, Manure, and Fertilizer Available to a Crop Such as Corn during One Season' Percentages obtained during one season Source of N,

PzO,,and KzO

Soil (available) Manure (total) Fertilizer (available) 1

N

Pz05

KzO

40 30

40 30 30

40 50 50

60

Berger (1054).

percentages of the nitrogen, phosphorus, and potassium contained in the soil, manure, and fertilizer. An example of the system used in Wisconsin is shown in Table V. When the approximate pounds per acre required to produce a given yield are known the amount of supplemental manure and/or fertilizer is calculated. It is recognized that this method has limitations. However, it does serve to point out very well the nutrient needs of crops and the fact that higher yields will demand greater quantities of plant nutrients.

6. Soil Tests and Soil Surveys The nature of the soil profile, particularly the depth of the topsoil and the nature of the subsoil, greatly influences the crop yield that will be obtained. Smith (1954) points out that soil surveys enumerate and classify readily visible soil differences. Great differences will develop, however, on the same soil type after several years of differential management. Aside from the plow layer, the fertility and acidity conditions

274

J. W. FITTS A N D WERNER L. NELSON

of the soil profile do not change materially from one year to another under most farming conditions, however. Routine soil tests are concerned largely with testing the surface soil. This zone may show an accumulation of an element over the virgin soil condition if heavy applications of fertilizer or lime have been applied periodically. It may also show a decline where fertilizer practices have been inadequate. In the calibration of the tests for making lime and fertilizer recommendations, it is essential that the characteristics of the soil in the plant root zone be known. For optimum results it probably will be necessary to increase the phosphorus status of the plow zone to a higher level on soils that are low in available phosphorus in the subsoil, as compared to soils that are high. In the latter instance, only enough phosphorus to start the plant may be necessary. When the subsoil contains very little available phosphorus, the plant will have to rely largely on added phosphorus in the plow zone. The same relationship exists with respect to liming soils that have acid or neutral subsoils. Since only surface soils are analyzed it would be very helpful in interpreting soil tests if the fertility status of the lower profile of all major soil associations was characterized. The availability of various nutrient elements in the soil below plow depth and extending to root depth (or the upper few feet) could be determined. The nature of the clays in the soil profile may be readily estimated by determining the cation-anion ratio and pH values (Mehlich, 1953a). Bawngardner (1955) found a definite difference between imperfectly and very poorly drained profiles in the correlation of the phosphorus test and per cent yield but little effect on the correlation for potassium. Drainage had a marked effect on the relationship between uptake of K by plants and soil test. General maps could be prepared showing the characteristics of the lower profile relative to nutrient availability and to acidity. This would eliminate the necessity for getting subsoil samples in routine analyses. These maps would be of great value in making fertilizer and lime recommendations in a soil-testing program. It is essential, of course, for the person submitting a sample to give the location of the area from which it was taken. Sometime in the future, characterization of lower soil profiles for fertility purposes might be included with soil survey reports. VI. SOILTESTSUMMARIES The inherent characteristics of soil type and past fertilizer and lime practices are largely responsible for variations in fertility levels. The primary purpose of most soil-testing programs is to furnish the individual farmer with dependable information about the fertility status

SOIL TESTS

275

of each of his fields. In addition to this individual service, summaries of soil test results such as prepared by Mosher (1952), Bishop (1951), Welch and Nelson (1951), Miles and Gholston (1950), and Bohannon (1954) are of great value to educational agencies, research workers and commercial companies. In the North Central Region, for example, all the states have some kind of a summary of soil tests. Many soil test summaries consist of tables in which the percentages of samples testing very low, low, medium, high, or very high are recorded. For educational purposes Tennessee (1951) used a circular or pie diagram. A diagram was prepared for each element in the area for which the summary was prepared. I . Areas for Preparing Summaries In most states a county is the smallest unit for which it is desirable to prepare summaries. Usually the number of samples tested for areas smaller than this is insufficient to give a representative picture of the soil conditions. It is even questionable if satisfactory summaries can be prepared on a county basis when the number of samples taken has not been large or if they have come mostly from one part of the county. Since local agricultural agencies frequently operate on a county basis, county summaries are desirable. Summaries of soil tests prepared for larger areas than counties, such as soil association areas, cropping regions, or states, are of more interest to persons engaged in research or to the fertilizer and lime industries. Welch and Nelson (1951) , Giddens ( 1954), and Bohannon (1954) have prepared summaries on an area basis. Welch and Nelson (1951) also separated the soil test results into the various categories, very low to very high, for the more common crops grown in North Carolina. This separation was particularly useful in studying the build-up of nutrient elements due to heavy fertilization of certain crops. In North Carolina 70 per cent of the fields growing tobacco, cotton, or Irish potatoes were high in phosphorus, The reverse was true of forage crops, with about 65 per cent of the fields low in phosphorus. 2. Two-way Tables In determining the ratio of fertilizers needed for a given area it is very important to know the relationship between at least two elements such as phosphorus and potassium. Information as to the relative amounts of each ratio of fertilizer for an area is helpful not only to educational agencies but to commercial companies in preparation and distribution of materials. Fitts and Nelson (1953), Fitts (1954), and Fitts et a2. (1956) have shown how phosphorus and potassium when summarized together give a good indication of the ratio of fertilizers

976

J. W. FITTS A N D WERNER L. NELSON

needed most. The two-way summary tables can be prepared for any size area such as a county or region and for specific crops such as corn. The size of the unit to use in preparation of summaries for a given crop will be influenced by the number of samples tested. It is useless to attempt a summary unless a sufficient number of samples has been TABLE VI The Percentage Distribution of the 1951 Phosphorus and Potassium Soil Test Results for Corn in Cropping Area I1 and Suggested Fertilization'

A. Distribution of Soil Tests-Potassium Very high, % Very high P High P Medium P Low P Very low P Total potash, % (read across)

High, %

1.1 2.8 5.7 5.7 2.8

0.6

18.1

Medium, %

Low, %

Total Very low, phosphorus, % % (read down)

7.5 6.4

0.8 1.3 5.7 9.7 8.2

0.0 0.7 5.3 11.0 9.7

0.0 0.5 0.8 4.0 1.7

22.5

25.7

26.7

7.0

1.8

6.2

2.5 7.1 23.7 37.9 28.8

B. Suggested Fertilization-Potassium Very high P

High

20-20-20

High P

(250 Ib. 8-8-8)

Medium low

Very low

20-20-40 (350 Ib. 64-12)

20-20-80 (350 lb. 6-6-12 75 Ib.

._.___..._....... ...... ..................... .................... ......_.......... ..._.___ __ ................... ............. .......... .... Medium P Low P Very low P

20-40-20 (350 lb. 6-12-6)

+

muriate)

20-40-40

20-40-80

(400 lb. 5-10-10)

(400 Ib. 5-10-10

+ 70 lb. muriate)

Note: In addition to the nitrogen in the mixed fertilizer extra nitrogen is suggested as follows: corn following nonlegume 80 Ib. N per acre 40 lb. N per acre corn following legumes turned under 1

Fitts and Nelson (1964).

taken to give a fairly representative picture. An example of a twoway summary table and how it may be used to predict the relative proportions of various fertilizer grades needed for the area is shown in Table VI. By adding up the percentage of samples tested in each group it is possible to determine the grades most likely needed. Such information is helpful in preparing general fertilizer recommendations for the

277 area. The widespread distribution of the results, however, shows the great need for testing each field for the most reliable information rather than just relying upon general recommendations. SOIL TESTS

3. Nutrient Index In order to compare soils of one area with soils of another, it is necessary to obtain a single value for each nutrient. To do this Parker et al. (1951) introduced the nutrient index concept. The percentage of samples in each of five classes from very low to very high is multiplied by 1, 2, 3, 4, and 5, respectively. The sum of the figures thus obtained is divided by 100 and gives the index or weighted average. The index permits a ready comparison of various conditions within a given region. Welch and Nelson (1951), Graham and Sheldon (1951), and Fitts (1954) used this technique to present soil test summaries for North Carolina, Missouri, and Iowa, respectively. In North Carolina, where commercial fertilizers have been used for many years, past management is clearly indicated from a nutrient index map of the state. The phosphorus levels can be related to the distribution of tobacco, cotton, and truck crops and subsequent heavy applications of fertilizers high in phosphorus. The content of potassium in the soils was more closely related to the soil association than to past fertilization. The sandy soils of the Coastal Plains were found to be lower in available potassium and more acid than soils of the Piedmont or Mountain regions. The index maps of Missouri indicated that almost half of the soils tested were low in organic matter (less than 2 per cent), and nitrogen requirements for crops such as corn would be high. The available phosphorus was low on 87 per cent of the upland soils of the state. The highest potassium level was found in the northwest part of the state, where loess soils predominate. A remarkably close relationship was found between the nutrient index maps and soil association areas in Iowa, where use ol commercial fertilizers on a large scale is a relatively new practice. Potassium deficiency was found to be more prevalent in the older more weathered soils of the northeastern and southeastern regions of the state. Potassium was high in the loessial soils of the western part of the state. The maps indicated areas where more field studies were needed on phosphorus and potassium application and where greater emphasis should be placed on a liming program. The nutrient index maps may serve many useful purposes but should not be used as a guide to general fertilizer or lime recommendations. The results are weighted averages and give no indication of what individual farms may need. The nutrient index for a given county

J. W. FITTS A N D WERNER L. NELSON 278 might be high but individual fields would range from very low to very high. 4. Accuracy of Summaries

The soil test summaries will have some bias because the more progressive farmers will make the greatest use of the service. Some samples will be taken from “trouble areas,” too, and the proportion of these samples may not be representative of the relative acreage involved. A higher percentage of samples from a given region also may come from one or two crops in relation to other crops. For example, more samples may be taken from crops such as tobacco and cotton than from pastures in the same region. An extensive soil-sampling study was reported by McCollum and Nelson (1954) in which results from soil samples sent in by farmers in Duplin County, North Carolina, were compared with approximately 1200 samples taken by the authors. Briefly, it was found that the pH and potassium were somewhat higher in the farmers’ samples but the phosphorus was somewhat lower. The differences were small in magnitude, however, and the study demonstrated that summaries of soil tests for a given area will give a good picture of the fertility levels of the cultivated fields. A fairly large number of samples must be tested to obtain consistent results. Both North Carolina and Iowa have found the summaries do not vary much from year to year when more than 40,000 samples are tested, but when only 10,000 samples were tested per year there was considerable variation. VII. FUTURE TRENDS IN SOILTESTING Although soil testing has been practical for a number of years the greatest advances have been made during the past ten years. During the ensuing years even greater advances are anticipated. As more information is gained through research concerning the factors influencing the availability of nutrient elements, improved testing procedures will be developed. The advent of new instruments and better equipping of laboratories will help reduce variability in results obtained. Good equipment helps to reduce the human error in analyses. During the past few years several states have initiated research programs for the primary purpose of calibrating soil tests. More of such studies are needed and should be forthcoming. Cooperative studies in regional programs offer a good opportunity greatly to increase the information on comparable soil conditions in several states. Such programs will also aid in the selection of fewer extracting solutions and testing procedures. This should create more uniformity in the interpre-

279 tation of soil test results and in recommendations for use of lime and fertilizers . More follow-up studies to determine the effectiveness of recommendations based on soil tests are needed. This may include observations of the growing plants, tissue tests, or yield measurements. There is more interest in plant analyses and tissue tests in conjunction with soil test calibration studies. One of the major problems in interpreting soil tests and in making recommendations is the interaction between essential elements in respect to soil and climatic conditions. The ability of plants to obtain one element may vary with the amount of another present. This interaction is particularly noticeable in minor elements as reported by Moore et al. (1955). The treatment combinations were chosen using a cube plus an octahedron as a model. This permitted a greater range in treatments (5 levels each of 3 elements) without having a cumbersome number of plots. This study in conjunction with that of Hader et al. (1955) presents a technique for studying interactions which should furnish valuable information for the calibration of soil tests. Interpretation of the results will be more difficult but greater accuracy in making recommendations will be possible. Intensive studies are being made of climatic patterns and frequency of occurrence of droughts. A more complete knowledge of the probability of weather conditions should help in interpretation and recommendations. Research in soil fertility generally is largely concerned.with factors affecting the availability of nutrient elements and the response that is likely to be obtained from application of soil amendments. In making recommendations for use of lime and fertilizers based on soil test results, consideration should be given to the economics involved. Development of economic response data in respect to application of nitrogen, phosphorus, and potassium is very important. Studies which should give valuable information on this subject to soil-testing programs are under way in Iowa, Virginia, and North Carolina, as well as in other states. The large increase in the number of samples tested during the past ten years should continue. The participation of fertilizer dealers in taking samples for the farmer to send to official laboratories should grow. Farmers must have as much information about their land as possible in the efficient use of plant nutrients and in the production of crops. Greater use will be made of soil tests in specialized types of farming and under special conditions. Some companies processing truck crops are using soil tests several times a season as a guide in fertilization to obtain quality products. With the increase in soil-testing proSOIL TESTS

J. W. FITTS A N D WERNER L. N E L S O N 980 grams more emphasis is needed on the personal contact between local agricultural leaders and persons submitting soil samples for testing. These leaders can give invaluable service in obtaining more representative soil samples and in guiding the farmers with recommendations.

REFERENCES Attoe, 0. J. 1946.Soil Sci. SOC.Am. Proc. 11,145-149. Bailey, E. H. 1943.Soil Sci. 55, 143-146. Baumgardner, M. F. 1955.M. S. Thesis, Purdue Univ. Berger, K. C. 1954. Farm Chemicals 1 1 7, 47-50. Berger, K.C., and Truog, E. 1944.Soil Sci. 57,25-36. Bishop, W. D. 1951.Tennessee Agr. Ext. Circ. 375. Black, C. A., and Goring, C. A. I. 1953. In “Agronomy Monographs” (A. G. Norman, ed.), Vol. 4, pp. 123-152. Academic Press, New York. Bohannon, R. A. 1954. Kansas Agr. Ext. Circ. 1-137. Bondorff, K. A. 1952. Trans. Intern. SOC.Soil Sci. 1, 290-299. Bower, C. A. 1955. Soil Sci. SOC.Amer. Proc. 19, 40-42. Bray, R. H. 1948. I n “Diagnostic Techniques for Soils and Crops” (H. D. Kitchen, ed.), Chapter 2, pp. 53-85. American Potash Institute, Washington, D. C. Bray, R. H., and DeTurk, E. E. 1938.Soil Sci. SOC.Amer. Proc. 3, 101-106. Bray, R. H., and Kurtz, L. T. 1945.Soil Sci. 59, 3945. Brown, D. A. 1955. Soil Sci. SOC.Amer. Proc. 19,296-300. Brown, I . C. 1943.Soil Sci. 56, 353-357. Camp, A. F. 1945. Soil Sci. 60, 157. Carpenter, P. N. 1953. Maine Agr. Expt. Sta. Misc. Publ. 623. Cline, M. G. 1944. Soil Sci. 58,275-278. Cline, M. G. 1945.Soil Sci. 59, 3-5. Constable, E.W., and Miles, I. E. 1941. J . Am. SOC.Agron. 33, 623-631. Davis, E.B. 1952. Tram. Intern. SOC.Soil Sci. 1, 167-179. Dean, L.A. 1954.Soil Sci. SOC.Amer. Proc. 18,462467. Dunton, E. M., Taylor, M. E., and Hall R. B. 1954.Betier Crops with Plani Foods 38, NO. 11, 13-15. Elgabaly, M. M. 1952. Trans. Intern. SOC.Soil Sci. 1, 195-204. Fitts, J. W.1954. Better Crops with Plant Food 38, No.1, 13-17. Fitts, J. W.1955. Better Crops with Plant Food 39, No. 3, 17-21. Fitts, J. W.,and Nelson, W. L. 1953. Plant Food I. 7, No. 4, 6-8. Fitts, J. W., Bartholomew, W. V., and Heidel, H. 1953. Soil Sci. SOC. Amer. Proc. 17, 119-122. Fitts, J. W., Bartholomew, W. V., and Heidel, H. 1955. Soil Sci. SOC.Amer. Proc. 19, 69-73. Fitts, J. W., Welch, C. D., and Nelson, W. L. 1956. Soil Sci. SOC.Amer. Proc. 20, 36-41. Fried, M. 1953.Soil Sci. SOC.Amer. Proc. 17,357-359. Fried, M., and Dean, L. A. 1952. Soil Sci. 73,263-271. Giddens, J . 1954. Better Crops with Plant Foods 38, No. 3, 11-13. Graham, E.R. 1950. Missouri Agr. Ezpt. Sta. Circ. 345, 1-22. Graham, E. R., and Sheldon, V. L. 1951. Missouri Agr. Expt. Sta. Bull. 552, 1-27. Gray, B., Drake, M., and Colby, W. G. 1953. Soil Sci. SOC.Amer. Proc. 17,235-239. Hader, R. J., Harward, M. E., Mason, D. D., and Moore, D. P. 1955. Unpublished

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manuscript presented before Section IV, Soil Sci. Soc. Amer. meeting, Davis, California. Hanway, J., and Dumenil, L. 1955. Soil Sci. Soc. Amer. Proc. 19, 77-80. Haynes, J. D. 1948.M. S. Thesis, North Carolina College. Hester, J. B. 1948. In “Diagnostic Techniques for Soils and Crops” (H. D. Kitchen, ed.), Chapter 4, pp. 105-135. American Potash Institute, Washington, D. C. Hunter, A. H., and Pratt, P. F. 1956. Soil Sci. SOC.Amer. Proc. 20. In Press. Knudsen, D. 1955. Univ. Nebraska Agron. Dept. Mimeo. pp. 1-7. Kolterman, D. W., and Truog, E. 1953. Soil Sci. SOC.Amer. Proc. 17,347-351. Kurtz, L. T. 1953. In “Agronomy Monographs” (A. G. Norman, ed.), Vol. 4, pp. 59-88. Academic Press, New York. Lawton, K., Robertson, L. S., Cook, R. L., and Rood, P. J. 1947. Soil Sci. SOC.Amer. Proc. 12, 353-358. Luebs, R. E., Stanford, G., and Scott, A. D. 1956. Soil Sci. SOC. Amer. Proc. 20, 45-50. Magistad, 0. C., Reitemeier, R. F., and Wilcox, L. V. 1945. Soil Sci. 59, 65-75. Malavolta, E. 1951. Universidade de SBo Paula (Brasil) Separata No. 137. Mason, D. D., and Obenshain, S. S. 1938. Soil Sci. SOC.Amer. Proc. 3, 129-137. McLean, E. O.,and Adams, D. 1954. Soil Sci. SOC.Amer. Proc. 18,273-276. McClung, A. C. 1956. Soil Sci. SOC.Amer. Proc. 20, 10-15. McCollum, R. E., and Nelson, W. L. 1954. Soil Sci. SOC.Amer. Proc. 18, 287-292. Mehlich, A. 1942. Soil Sci. SOC.Amer. Proc. 7, 167-174. Mehlich, A. 1953a.J. Assoc. Ofic. Agr. Chemists 36, 445-457. Mehlich, A. 1953b.Soil Sci. Amer. Proc. 17, 231-234. Mehlich, A. 1956.J. Assac. Ofic. Agr. Chemists 30. In Press. Mehlich, A., and Monroe, R. J. 1952.J . Assoc. OEc. Agr. Chemists 35, 588-596. Miles, I. E.,Gholston, L. E. 1950.Mississippi Agr. Ezt. Circ. 140. Miles, I. E.,and Reed, J. F. 1948. In “Diagnostic Techniques for Soils and Crops” (H. B. Kitchen, ed.), Chapter 3, pp. 87-104. American Potash Institute, Washington, D. C. Moore, D. P., Harward, M. E., Mason, D. D., Lott, W. L., and Jackson, W. A. 1955. Unpublished manuscript presented before Section IV, Soil Sci. SOC.h e r . meeting, Davis, California. Morgan, M. F. 1941. Connecticut Agr. Ezpt. Sta. Bull. 450,579-628. Mosher, P. 1952. Maine Agr. Ezt. Circ. 1-8. National Soil Test Work Group. 1951. National Soil and Fertilizer Research Committee. National Soil Test Work Group. 1956. National Soil and Fertilizer Research Committee. North Carolina Agr. Ezpt. Sta. Tech. Bull. 121, 1-36. Nelson, W. L., Mehlich, A., and Winters, E. 1953. In “Agronomy Monographs” (A. G. Norman, ed.), Vol. 4, pp. 153-188. Academic Press, Inc., New York, New York. Olsen, S. R. 1953. In “Agronomy Monographs” (A. G. Norman, ed.), Vol. 4,pp. 89122. Academic Press, New York. Olsen, S. R., Cole, C. V., Watanabe, F. S., and Dean, L. A. 1954. U . S.Dept. Agr. Circ. 939. Parker, F. W., Nelson, W. L., Winters, E., and Miles, I. E. 1951. Agron. J . 43, 105-1 12. Pratt, P. F. 1951.Soil Sci. 72, 107-117. Pratt, P.F.,and Morse, H. H. 1954.Ohio Agr. Ezpt. Sta. Bull. 747. Pratt, P. F.,Holowaychuck, N., and Morse, H. H. 1955. Ohio Agr. Research Circ. 27.

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PurVis, E. R., and Hanna, W. J. 1949.Soil Sci. 67,47-52. Reed, J. F. 1953.Better Crops w'th Plant Food 37, 13-19. Reed, J. F., and Cummings, R. W. 1945.Soil Sci. 59, 97-104. Reed, J. F., and Rigney, J. A. 1947. J . Am. SOC.Agron. 39,26-40. Reitemeier, R. F. 1951. Advances in Agron. 3,113-164. Reitemeier, R. F., Brown, I. C., and Holmes, R. S. 1951. U.S. Dept. Agr. Tech. Bull.

1049. Reitemeier, R. F., Holmes, R. S., Brown, I. C., Klipp, L. W., and Parks, R. Q. 1947. Soil Sci. SOC.Amer. Proc. 12, 158-162. Riehm, H. 1952. Trans. Intern. SOC.Soil Sci. 1,261-273. Rigney, J. A. 1955. Unpublished paper read at A.I.B.S. meetings, North Carolina State College, Raleigh, North Carolina. Rigney, J. A,, and Reed, J. F. 1945.Soil Sci. SOC.Amer. Proc. 10,257-259. Schuffelen, A. C. 1952. Trans. Intern. SOC.Soil Sci. 1, 180-188. Semb, G., and Uhlen, G. 1955. Acta Agr. Scand. 1, 4.4-68. Smith, F.W., and Cook, R. L. 1953. Soil Sci. SOC.Amer. Proc. 17,2630. Smith, F. W., Ellis, B. G., and Graves, J. 1956. Soil Sci. Soc. Amer. Proc. 20. In Press. Smith, G. E. 1954. Better Crops with Plant Food 38, No. 8,643. Spencer, W. F. 1954.Florida Agr. Expt. Sta. Bull. 544. Stanford, G., and Hanway, J. 1955. Soil Sci. SOC.Amer. Proc. 19, 74-77. Thompson, L. F., and Pratt, P. F. 1954.Soil Sci. SOC.Amer. Proc. 18,467470. Truog, E., Hull, H. H., and Shihata, M. M. 1955. Univ. Wisconsin Mimeo. pp.

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Tucker, T. C., and Kurtz, L. T. 1955.Soil Sci. Soc. Amer. Proc. 19,477481. Van Der Paauw, F. 1952. Trans. Intern. Soc. Soil Sci. 1,207-221. Van Der Paauw, F., and DeLaLande Cremer, L. C. N., and Ris, J. 1951. Verslag Landbouwk. Onderzoek. No. 57.1 5, 1-67. Wear, J. F., and Sommers, A. L. 1947.Soil Sci. Soc. Amer. Proc. 12, 143-145. Welch, C. D.,and Fitts, J. W. 1956.Soil Sci. SOC.Amer. Proc. 20, 5457. Welch, C. D., and Nelson, W. L. 1951.North Carolina Dept. Agr. Bull. 1-123. Whittles, C. L. 1952. Trans. Intern. SOC.Soil Sci. 2,379-390. Whittles, C. L.,and Little, R. C. 1950. J . Sci. Food Agr. 1, 323-326. Wiklander, L. 1952. Trans. Intern. SOC.Soil Sci. 1, 189-194. Williams, E. G., Reith, J. W. S., and Inkson, R. H. E. 1952. Trans. Intern. SOC.Soil Sci. 2, 8491. Woodruff, C. M. 1947a. Soil Sci. SOC.Amer. Proc. 14,208-212. Woodruff, C. M.1947b.Soil Sci. SOC.Amer. Proc. 12, 141-142. Woodruff, C. M. 1955.Soil Sci. SOC.Amer. Proc. 19,36-40. Wormley, G. W. 1951. What's N e w in Crops and Soils 3, 1618.

Tall Fescue J. RITCHIE COWAN Oregon State College, Corvallis, Oregon'

I. Introduction . . . . 11. Production and Utilization

. . . . . . I. Adaptation . . . . , . 2. Palatability . . . . . . 111. Cultural Practices . . . . . . 1. Establishment . . . . . 2. Fertilization . . . . . . 3. Management . . . . . . IV. Genetics and Cytology . . . . V. Varieties . . . . . . . . 1. ALTA . . . . . . . 2. KENTUCKY 31 . 3. Other Varieties .

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VI. Breeding Behavior . 1. Mode of Reproduction 2. Genetic Variability a. Seed . . . . b. Forage . . . c. Quality . . . VII. Seed Production . . . VIII. Fescue Poisoning . . . IX. Diseases . . . . X. Future of Tall Fescue . References . . .

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I. INTRODUCTION Tall fescue was probably introduced from Europe over a century ago. It assumed only minor significance until Oregon and Kentucky released simultaneously the two varieties ALTA and KENTUCKY 31. Botanically it closely resembles meadow fescue and as a result remained somewhat in oblivion because of confusion which existed relative to the distinguishing differences between these two species. Although a native of western Europe, it was considered of little value. This may have been Miscellaneous Paper 21, Oregon Agricultural Experiment Station. 283

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due to the fact that in many cases it was found growing in low swampy areas. It was brought into this country by early settlers as a crop having possibilities of wide adaptation and use, similar to timothy, orchardgrass, red clover, and others. This did not prove to be so for almost a hundred years, following the first reports of its being observed and grown in this country. It was not until the late nineteen-thirties that its value was recognized. From 1940 until 1953 it enjoyed continuous and rapid growth in popularity. During this period, there were many enthusiastic press releases relative to its potentialities. These probably overrated it in some cases. By some it was severely criticized. However, during this period it has established itself as one of our important agricultural crops. In recent years there has probably not been any one crop which has prompted so much controversy as to its potential value in our agriculture. Some early American writers believed that tall fescue was a native of this country. It was known by several names such as “Reed fescue,” “Randall,yyand “Evergreen” grass. Vinall (1909) states that meadow fescue was introduced into North America from England in the eighteen-seventies, after which commercial seed production flourished in Kansas until 1907. The earliest specimen of tall fescue recorded by the United States National Herbarium was collected in Oregon in 1886. Also specimens from New York and Washington were collected in 1890, from Michigan and Utah in 1895, and the District of Columbia in 1897. It is presumed that most of these were grass garden specimens. It is difficult to determine when the first importation of tall fescue was made to the United States, since it was considered as being similar to meadow fescue in the early days. Sutton (1891) mentions that Festuca pratensis was known in Tennessee and North Carolina. It is believed that this grass was tall fescue since many local and isolated populations had been shown by Crowder (1952) to be of the tall fescue type. Tabor (1952a) and Crowder (1952) give quite a complete history of tall fescue. It has been confused with meadow fescue by botanists and agronomists. In 1753 Linnaeus included the Festuca genus in his classification. At this time, he listed both meadow and tall fescue as Festuca elatior. In 1771 Schreber recognized a more robust type and called it Festuca arundinacea. Hackel’s monograph in 1882 became the botanical authority which was followed by most Europeans. Festuca elatior L. ssp. typica var. genuina Hack. (meadow fescue) ssp. arundinacea (Schreb.) Hack. var. genuina Hack. (tall fescue) Hitchcock (1935) regarded meadow fescue as F. elatior L. and tall fescue as F . elatior var. arundinacea (Schreb.) Winn. In 1950 the two

285 were given specific rank for the first time in North America and were listed by the following binomials according to the international rules of botanical nomenclature: TALL FESCUE

F. elatior L. (meadow fescue) F . arundinacea (Schreb.) (tall fescue) The difficulties encountered by taxonomists in separating these two species has retarded to some degree the recognition of tall fescue as an agricultural crop of some value. Crowder (1952) made an extensive study of morphological and cytological comparisons between tall fescue and meadow fescue. No distinct or easily discernible differences could be established between these two species for the following characters: coleoptile measurements, tillering, number and size of upper and lower stomates, and seed weight. Chase (1950) separates meadow and tall fescue primarily by the abstract description termed “robustness.” When a study of tiller diameter and leaf width was undertaken to arrive at some indication of robustness, no dependable criteria could be developed (Crowder, 1952). I n general tall fescue plants had fewer but larger tillers and wider leaves than meadow fescue. However, it was noted that individual plant measurements overlapped within and between species. Thus, it is quite possible that the two species could be confused on an individual plant basis if these characteristics were used as the sole criteria of classification. They can be distinguished by somatic chromosome counts, meadow fescue 2n = 14 chromosomes and tall fescue 2n = 42 chromosomes (Myers and Hill, 1947; Crowder, 1953a). Kreitlow and Myers (1947) and Crowder (1952) reported meadow fescue to be susceptible to the pathogen Puccinia coronata Cda. which causes crown rust, whereas tall fescue was immune or highly resistant. One distinguishing morphological characteristic has been noted on the auricle (Crowder, 1953b). Tall fescue has a number of small hairs or cilia which are visible to the naked eye, whereas no such outgrowth is found on meadow fescue. These studies readily illustrate why there has been considerable difficulty in the past in separating these two species. The high potential production of tall fescue was first reported by the Duke of Bedford on his estate at Woburn Abbey, England. In a test of 23 grasses and 3 legumes carried out in 1824, yields were taken at the time of blossoming, in seed stage, and aftermath. Alfalfa led in total yield and nutrient matter per acre, with tall fescue second. These results were widely used in the United States for the next 60 years. The temporary popularity which tall fescue enjoyed in the early eighteen hundreds, when it was first introduced from Europe, was very short-lived. The release of the two varieties ALTA and KENTUCKY 31, originating over 2000 miles apart, one developed as an ecotype selection

286 J. RITCHIE COWAN by a plant breeder and the other by natural selection, were responsible for the tremendous growth and interest in this particular crop. In the 15-year period from 1940 to 1955 this crop, which was grown on 40,000 acres in 1940, has increased to more than 4-million acres (Cowan, 1954, unpublished). The peak seed production during this period was reached in 1952 with a national production of 50 million pounds. During this particular year, domestic consumption was only 24 million pounds. AS a result of the efforts and foresight of two agronomists, Mr. H. A. Schoth in Oregon and Dr. E. N. Fergus in Kentucky, tall fescue during the last 15 years has moved into a position of an important grass crop in the agriculture of the United States. 11. PRODUCTION AND UTILIZATION Tall fescue as a crop has shown itself to be adapted to widely varying conditions. Except in the more arid sections of the Great Plains, the dryland area of the West and Southwest, and the Lower Coastal Plains of South Carolina, Georgia, Florida, and the Gulf Coast, this grass has become established as a major species in the United States (Wheeler and Hill, 1957). Under certain conditions, the growth of the forage is tough and less palatable than of many other species. However, when properly managed and fertilized, it is palatable and nutritious. Its limited use in some areas has been chiefly due to the complaint of its lack of palatability. Buckner and Fergus (1951) point out that a general and unqualified criticism of this nature is not justified. A more palatable variety might increase the forage value of this particular crop. Data are presented which show that there is a great deal of selective grazing among populations of tall fescue plants. Its adaptability to nonirrigated land depends to a large degree on the supply of available soil moisture (Hafenrichter et al., 1949). It is affected more by moisture than by temperature. Under irrigation it grows well from the hot interior valleys of Arizona and California to the high mountain valleys of Colorado. Where the annual rainfall is 18 inches or more and where the elevation is under 5000 feet, tall fescue seems to be well adapted for forage production. In the Gulf States it is usually not recommended for uplands in areas of less than 35 inches of rainfall (Bailey, 1951). It has been shown to give excellent performance as a pasture grass by a number of workers across the country (King et al., 1953, South Carolina; Brooks, 1950a, northern Georgia; Sell and Crowder, 1949, Sell, 1950, central Georgia; Leasure, 1952, Tennessee; Fergus and Johnstone, 1948, Kentucky; Marlowe et al., I95 1, Mississippi; Hodson, 1951, Arkansas; Thompson et al., 1955, Missouri; Rampton, 1950, Oregon). In every case it has been pointed out that this grass provides very satisfactory and palatable forage when grown in combination with

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a legume, particularly ladino clover. There has, on the other hand, been some definite opposition registered as to its potential value. Pratt and Haynes (1950) point out that in Ohio this grass has been most unsatisfactory for dairy production purposes. In New Zealand, Saxby (1945) describes tall fescue as one of the worst weeds in the high-fertility swamp country. It is referred to as having poor quality, and although eaten to a certain extent by cattle, affords little more than a maintenance diet. Cattle grazing in New Zealand on this grass have suffered from a condition referred to as “fescue foot.” This condition if permitted to become quite severe can be fatal to the animal.

1. Adaptation It is a crop with wide adaptation. Tall fescue is tolerant of poor drainage, particularly in the winter. At Klamath Falls, Oregon, the variety ALTA has thrived on alkaline soil with a pH of 9.5 (Cowan, 1952, unpublished). On another site near Astoria, Oregon, plants have been showing good growth on a strongly acid soil with a pH of 4.7 (Rampton, 1950). It does well on mountainous slopes and serves as an excellent soil conserving plant (Fergus, 1952; Brooks, 1950b). Initially ALTA tall fescue was selected because of its ability to produce forage during the long dry season peculiar of the Willamette Valley in western Oregon. On the other hand, the appealing feature of KY 31 was that it would produce forage during the winters in southern Kentucky, when other grasses had gone dormant. These features of the two leading varieties have been responsible for their wide acceptance and popularity. Throughout the intermountain region and western states where irrigated pastures are used extensively, tall fescue has become one of the common grass constituents. In the Southeast, owing to its ability to grow in the cool, moist conditions of the winter, tall fescue has become an important grass for winter grazing. Under irrigated conditions, difficulties have been encountered in getting the most efficient and satisfactory use of a pasture in which this grass was one of the main constituents, if it has not been properly managed. With additional fertility and continuous availability of moisture, as is true of irrigated pastures, it grows very rapidly and rank. Frequently it will smother out the legume entirely, and difficulties are encountered in keeping a desirable grass-legume balance. Where it is used as a winter grazing grass with considerable degree of satisfaction, frequently difficulty has been encountered in carrying it through the summer, since it could not persist under the high temperatures experienced in those areas during the summer season. Tall fescue is probably the best grass available for poorly drained soils which are in irrigated pastures. It is used in mixtures in irrigated

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pastures from southern California to northern Washington. Its ability to grow on wet soils, its tolerance of alkalinity and salinity, and its ability to produce heavy turf, make it an excellent grass for these sites. For winter grazing, it is necessary to have a strong sod which will not be broken through by the trampling of the animals. A study by Crowder and Sell (1952) showed that tall fescue provided a stronger sod than other grasses. A one-year-old fescue sod was found to be the most resistant to breaking through in winter grazing in comparison with four other sods. In southern Illinois extensive trials have shown tall fescue to have an important place (McKibben, 1955, personal correspondence). Solid stands have largely replaced cereals for fall, winter, and early spring pasture. This has been due in part to the excellent manner in which it prevents trampling of the fields in comparison with cereals. Marlowe et al. (1951) carried out extensive studies in Mississippi to determine the value of fescue-ladino when compared as winter, summer, and year-round grazing. The winter period lasted from November 21 to May 18. This particular mixture was compared with ryegrasscrimson clover and oats-red clover. On November 21, all paddocks were stocked with beef animals. It was necessary to remove steers from the ryegrass on Thanksgiving owing to a freeze and it was not possible to return them until February 28. All steers were removed from the oat and red clever paddocks on December 19 for the same reason. The oats did not recover. Steers grazed continuously on fescue and ladino from November 21 to August 9, with the exception of January 29 to March 6, owing to an ice sheeting. The ladino-fescue yielded 209 pounds of beef to 137 pounds on the ryegrass-crimson clover, or gave a return of $58.00 per acre versus $19.00. It has been the experience of the Central Station in Mississippi to lose stands of oats, two years out of every six. Fescue-ladino pasture was inferior when compared with Dallis grass and white clover f o r summer pasture. On the year-round basis for grazing, a profit of $92.00 per acre was made on the fescue-ladino mixture. Thompson and Holdaway ( 1954), reporting on dairy grazing trials in Virginia for the years 1950, 1951, and 1952, found that fescue-ladino was superior in the first year to other mixtures used. The following two years this mixture was not significantly better than other mixtures in the trial. At Knoxville, Tennessee, tall fescue grows whenever the mean weekly temperature is above 40° F. (Leasure, 1952). In 1950 and 1951 tall fescue was never completely dormant when the mean weekly temperature dropped to 34O F. Orchardgrass grew very little unless the mean weekly temperature was above 50° F. and was found to be completely dormant around 40° F. Ladino in mixtures with tall fescue and orchardgrass began growth two to three weeks earlier than when it was

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grown alone. It was found that light intensities were similar in both orchardgrass and tall fescue sods. Tall fescue produced more than 7000 pounds of roots in the surface acre 8 inches in six years on class I11 land at Pullman, Washington (Hafenrichter et al., 1949). Plots which were clipped at three-week intervals produced more than 5000 pounds of roots. The roots of tall fescue were tough and coarse, which enabled them to produce a good sod. It was the best among five grasses studied in the amount of roots produced. Bailey and Scott ( 1949) reported that the extensive deep-root systems were ideal for holding steep Class VI land and for pastures on Class IV land in the southeastern states. The combination of tall fescue and subterranean clover has more than doubled the carrying capacity of pastures on western Oregon hill lands (Rampton, 1950). Brooks (1950b) reported that ladino-tall fescue had given excellent results in the northern mountainous area of Georgia. His observations would indicate that phosphate, potash, and lime were needed for best results. With the advent of KY 31, a means was available by which much hill land of Kentucky which was being eroded and which was of poor fertility, could be brought into productive use. Some enthusiasts referred to this grass as the “wonder grass.” Tall fescue is generally better suited for pasture than for hay because of its numerous basal leaves. However, excellent hay yields have been reported (Rampton, 1949; Fergus, 1952; Cowan, 1955a). It will give high-yielding hay crops particularly on fertile bottom lands where leaf growth is extremely heavy. The aftermath even under dry conditions is usually rather productive. It is not uncommon after seed harvest to use the stover for a roughage. 2. Palatability One of the chief criticisms of this particular grass has been its lack of palatability (Pratt and Haynes, 1950). Contributing factors which govern palatability might be the age of the leaves, the fertility of the soil in which it is grown, the season of the year, the genetic variation, and perhaps the kind of pasture and feed to which the animal has been previously accustomed. It appears to be somewhat less palatable than most other pasture grasses, yet livestock sometimes graze it as readily as most other grasses. Usually it is more palatable if kept grazed rather close or clipped to prevent accumulation of old leaves and if it is grown with legumes or supplied with generous quantities of nitrogen fertilizer. Chemical analysis of samples taken throughout the growing season show that tall fescue compares favorably with other grasses in protein and mineral nutrients if grown on good soil (Fergus, 1952). In Arkansas, Hodson (1951), when comparing tall fescue with ryegrass and oats

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as pasture grasses, found that tall fescue produced much more total protein annually than either of the other two crops. King and Lamaster (1950) reported tall fescue-ladino silage to be as palatable as corn silage. A study was conducted over a 16-week continuous period, feeding fescue-ladino clover silage and corn silage. The daily consumption of corn silage was 45.6 pounds as compared to 47.8 pounds of fescue-ladino silage per animal. The daily production was 34.9 pounds of milk for corn silage and 34.6 pounds of milk for fescueladino silage. The carotene content of the corn silage was 62 p.p.m. and that of the fescue-ladino silage was 240 p.p.m. Fonville (1952) reported the protein content of orchardgrass-ladino as 16 per cent and that of tall fescue-ladino as 19.5 per cent. Protein yield per acre was the same for both grasses without clover, but 1174 pounds per acre for orchardgrass and 1374 pounds per acre for fescue when the clover was present. Extensive work by King et al. (1953) in South Carolina showed that dairy cattle would do very well on mixtures of tall fescue and ladino clover. Comparisons were made between the varieties KENTUCKY 31 and ALTA. No significant difference was found. It was observed that the cows would readily graze pure clover stands and mixtures of tall fescue and clover, but were reluctant to consume tall fescue alone. The grazing habits of milking cows in the results of these experiments indicated the necessity of maintaining high proportions of ladino clover with tall fescue. Similar results have been reported by Brooks (1950a), Sell and Crowder ( 1949), Marlowe et al. (1951) , and Rampton (1950). Rampton (1950) reports a case in western Oregon'where a 12-acre pasture carried 50 milking cows and heifers during the pasture season from March until late December. This production was carried on over a ten-year period. In 1948 this herd averaged 526 pounds of butterfat per milking animal. Several cows produced well over 800 pounds of butterfat during the same 12-month period. The original pasture mixture was ALTA tall fescue, perennial ryegrass, orchardgrass, and ladino clover and was established in the spring of 1943. A rotational grazing system of 2-acre blocks was used. Irrigation water was applied with a portable sprinkler. The fertilizer program involved top-dressing with barnyard manure, superphosphate, ammonium nitrate in early spring, and a summer application of ammonium nitrate with irrigation water and a fall top-dressing o€ ammonium phosphate. In a few years this 12-acre pasture soon became chiefly tall fescue and ladino clover. Similar success has been reported by many other investigators (Brooks, 195Oa,b; Hodson, 1951; Bailey, 1950; Tabor, 1952a). It is evident that this grass is acceptable and palatable to animals when properly managed and grown on soil of good fertility.

29 1 The nutritional adequacy of ALTA tall fescue pasture for wintering pregnant ewes was studied by Thompson et al. (1955) in Missouri. It was found to be quite satisfactory for this purpose, where tall fescue was the sole ration. Beef animals grazing KY 31 tall fescue and ladino in Virginia made lower gains than those on orchardgrass and ladino mixtures (Blaser et al., 1954). The presence of ladino improved feed quality of both orchardgrass and tall fescue. When pure grass stands were treated with nitrogen higher carrying capacity was obtained from KY 31 tall fescue and orchardgrass. Since tall fescue is better adapted to tolerate dry and warm weather it makes more growth than orchardgrass. Likewise the carrying capacity of tall fescue-ladino pastures had been higher than that for orchard-ladino pastures. KY 31 tall fescue made better summer growth than any other grass but nutritionally pastures with tall fescue appeared inferior when compared with other grasses. KY 31 pastures seemed better for maintaining than fattening cattle. In southern Illinois cows have wintered very satisfactorily on tall fescue without supplemental feeding and calved normally with calves of average and above-average weight at birth (McKibben, 1955, personal correspondence). Ewes have been handled in a similar manner, but are usually brought into winter quarters about January 1. If the ewes are to lamb during January and February supplemental grain feeding is usually found to be advisable for the last 20 days of December, but the tall fescue continues to furnish all the necessary roughage. It is possible to alter the nutrient value of this particular crop by selection (Buckner and Fergus, 1951; Cowan, 1954, 1955). Studies carried on in Kentucky in 1950 with 2750 two-year-old plants of KENTUCKY 31 grazed in April, July, September, and November by beef animals showed some rather striking differences. Thirty-six per cent of these plants were grazed closely once. Nine per cent were grazed closely twice, 1 per cent three times, and 0.18 per cent four times. This selective grazing by animals would indicate variability of nutritive value and palatability in a population of plants of this particular variety. It was also noted that of plants grazed in April, 16 per cent were grazed twice again, 4 per cent three times, and 3 per cent four times. In Oregon 20 clonal lines studied intensively over a three-year period (1953, 1954, and 1955) showed a wide range in ability to produce crude protein. These analyses showed as high as 10 per cent difference in protein at any one time when harvested under the same conditions and the same stage of maturity. Therefore, it would appear quite possible to effect improvement in palatability and nutrition by plant breeding. TALL FESCUE

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111. CULTURAL PRACTICES

I. Establishment The most uniform stands have resulted when tall fescue is planted on well-prepared firm seedbeds. Usually for best soil preparation plowing is required. The land should be plowed and harrowed several weeks prior to planting. In this way the soil has an opportunity to become settled by at least one or more rains in areas where natural precipitation is available. Under irrigation it is necessary to make sure that adequate moisture is available near the surface of a good firm seedbed. Cultipacking or any other seedbed preparation method which effects firming of the soil has been found to be most advantageous in getting a good stand. In general, seedling establishment is somewhat slow. Although this plant is a vigorous one after it has been established, it does not in general demonstrate such vigor in the early stages of growth. Consequently, as a result of the slow initial growth, a clean seedbed is most desirable for rapid establishment. For fall plantings spring-plowed, summer-fallowed land may be used but the most common procedure is to prepare a seedbed on land that has grown a cultivated crop or a spring-sown grain crop. This practice assists in the elimination of weeds which are extremely competitive with the slow-growing fescue seedlings. Land which has considerable amounts of logs, stumps, slash, brush, or weeds may be put into a seedbed shape for planting by burning, if cultivation is impossible. Burning and subsequent seeding in ashes is usually best done in the fall (Rampton, 1949). When it is impossible to prepare a seedbed by burning or by the use of machinery, successful stands are usually not insured. Broadcasting of fescue seed on unprepared seedbeds usually results in very poor stands. On soil of low fertility and under rather dry conditions, Tabor (1952b) obtained good results when seeding tall fescue in rows 30 to 36 inches apart, and interseeding between rows with white clover. This seemed to aid in the persistence and establishment of both crops under adverse weather, particularly drought. Good stands were obtained in Kentucky when sown between corn rows in August (Bailey and Scott, 1949). Similar success was obtained in the coastal plains area of Georgia and South Carolina when seeded in November. Drilling seems to be preferable to broadcasting because of the more uniform stands which are more readily obtained (Rampton, 1949; Fergus, 1952). Success has been obtained by broadcasting the seed evenly and following this operation with a light harrowing. The depth of planting should be such that the seed is placed not more than 1 inch

293 in depth. Recommended rates of seeding vary all the way from 2 pounds to 16 pounds per acre. These various rates are influenced to some degree by the other components of the mixture. It has been found that lighter rates are quite satisfactory for seeding on well-drained land where a large proportion of legumes is desired. Heavier rates are recommended for wet land, especially if it is to be pastured during the winter. This provides for a more dense sod in a shorter time. When developing terrace outlets, waterways, roadsides, and turf, seeding rates are much higher. For such purposes seeding rates usually range from 20 to 30 pounds per acre. In some cases for the development of turf, seedings have been as high as 75 to 100 pounds per acre. Tall fescue can be seeded either late in the summer or in early spring. When seeded late in the summer it produces a cover crop for the winter holding of erodible soils and furnishes some winter pasture. Late summer seeding also occasionally permits harvesting of a seed crop, if so desired, the following year. Spring seedings produce considerable grazing during the first season, where adequate soil moisture is available. On the Pacific Coast late summer planting is usually practiced except on cultivated hill soils that heave badly during the winter o r early spring. Three months of five rates of seeding of alfalfa-tall fescue were studied over a four-year period on Cecil sandy loam near Raleigh, North Carolina (Chamblee and Lovvorn, 1953). Comparisons were made between alternate-row, mixed-in-the-row, and broadcast methods of seeding. Spacing between the rows was 6 inches. Rates of seeding ranged from 10 to 20 pounds of alfalfa and 5 to 15 pounds of tall fescue. Reductions in total yields were obtained from plots seeded at high rates of tall fescue. Alternate-row plots produced less total forage than the broadcast or mixed-in-the-row plots. Tall fescue suppressed the growth of alfalfa much more than did orchardgrass. After four years growth stand counts showed that only 10 per cent of the original alfalfa plants remained. 2. Fertilization TALL FESCUE

Tall fescue is a crop that has thrived on soils varying in pH from 9.5 to 4.5. This wide soil adaptation has resulted in wider utility than for most other grasses. It grows well at elevations from sea level to 5000 feet. Within this range of conditions it has adapted itself quite well to most soil types. However, it is similar to other crops and will do much better on soils of high fertility than on those of low fertility. I t has the faculty of successfully establishing itself under a rather adverse soil condition. It responds readily to high applications of nitrogen. The lack of nitrogen may cause a condition referred to as “sod binding,” in solid

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stands. Richardson (1951) found nitrogen to be the key fertilizer element in the stimulation of increased growth in tall fescue which had become “sod bound.” Once the nitrogen requirements of the plant were met, applications of phosphorus and lime to “sod bound” stands were effective in increasing yields. The application of fertilizers was found to be only a partial answer to overcoming the “sod bound” condition. Usually where desirable balance of grass-legume has been retained, the “sod bound” condition is not experienced. Good tall fescue can be grown in pure stands if enough nitrogen fertilizer is used, although it is better to sow it with one or more legumes. The legumes not only supply nitrogen needed by the grass for rapid, vigorous growth but also apparently improve the nutritive value of the fescue (Fergus, 1952; Sell and Crowder, 1949). Ladino clover, lespedeza, alfalfa, red clover, alsike, sweet clover, and birdsfoot trefoil have all been found to grow successfully with tall fescue. Application of 200 to 300 pounds of complete fertilizer, such as 4-12-4 or 8-8-8, at seeding time usually more than pays for itself in encouraging initial growth. A pure stand of tall fescue generally responds well to later applications of nitrogen such as 100 to 150 pounds of ammonium nitrate or equivalent per acre. Nitrogen fertilizers should be applied in early spring before rapid growth has started. In general it is advisable to apply 500 to 1000 pounds of 20 per cent superphosphate or the equivalent of other phosphate fertilizer per acre. Since tall fescue is usually grown with a legume, lime and fertilizer requirements for the legume must be met. Vigorous well-fed legumes usually stay well in mixtures with tall fescue. Weak starved legumes fade out early or are low producers. Gill and Jones (1951) working in Mississippi at three locations observed very marked responses in establishment when fertilizer applications were made. Wherever no phosphorus was applied there was no clover and very little fescue. Sixty-four pounds of nitrogen per acre on lime-treated soil hastened the establishment. Ninety-six pounds of nitrogen per acre was required to effect good establishment in the seedling year. It was noticed that the nitrogen and potassium content of tall fescue was much higher when it was grown with a legume than when grown alone (Gill and Jones, 1951). The protein per cent of tall fescue when grown without nitrogen application or ladino clover was 0.8 per cent less than that of orchardgrass (Fondle, 1952). When both orchardgrass and tall fescue were grown with ladino the protein content of fescue was 3.5 per cent higher than that of orchardgrass. Chamblee and Lovvorn (1953) found tall fescue to be more competitive with alfalfa for potassium than orchardgrass.

TALL FESCUE

295

3 . Management New stands are often weakened after planting by overgrazing and trampling during the first winter while the ground is wet. In the south, tall fescue seeded in early September often grows to a height of 5 inches or more before the middle of the winter. Light grazing while the ground is dry and firm does no serious damage to these new stands. Close grazing and heavy trampling before a good sod develops, retards root development and reduces plant vigor. The plant should develop a good root system and have about 5 to 6 inches of top growth before grazing is commenced (Hodson, 195I ) . In order to assure ample succulent forage for desirable grazing, close grazing on well-established stands is a good management practice. Even though tall fescue withstands heavy grazing for short periods, it may be injured severely by continuous close grazing. Under irrigation, where a rotational system of grazing is practiced and where the forage is grazed back quickly and closely, it recovers very well. If it is given a rest period of two to three weeks, a new growth that is succulent and desirable will be available for the next cycle of grazing. It is generally agreed that tall fescue should not be grazed more closely than 2 to 4 inches of top growth at all times for best production and longevity. Bailey (1950) feels that grazing is an important factor in maintaining a balance between fescue and ladino or other legumes. It has been observed that in seasons when either plant tended to be dominant, grazing appeared to reduce the competition and helped to retain the sod in a desirable balance. It has been observed, also, that if the fescue tends to become too tall and coarse, clipping is a useful practice to induce new, succulent, nutritious growth. Where tall fescue is to be used for winter pasture, late summer grazing is not advisable. Tall fescue will remain green during cold weather and provides considerable forage which is readily eaten by livestock. Growth is reduced when the temperatures go below 65O F. If stock are removed in late summer, tall fescue in a mixture with a good stand of clover or with application of nitrogen fertilizer should have at least 8 to 10 inches of leafy growth by the time cold weather begins in the southern parts of the country.

N. GENETICSAND CYTOLOGY Tall fescue is a polyploid. It belongs to the tribe Festuceae which has a basic chromosome number of 7. The diploid chromosome number of 14 has been reported for European and American F . elatior material. The literature dealing with work along this line has been covered very completely by Crowder (1952). The hexaploid number of 42 has been

296

J. RITCHIE COWAN

recorded for F. arundinacea material (Peto, 1934; Myers and Hill, 1947; Crowder, 1952, 1953a). The varieties ALTA and KENTUCKY 31 have been classified as hexaploids having 42 chromosomes (Myers and Hill, 1947; Crowder, 1953a). Crowder (1953b) found a supernumerary chromosome occurring in three plants, under study. Otherwise, the meiotic chromosome behavior in tall fescue resembled that of other alloploids, except for a low incidence of multivalent association. Significant plant differences existed with respect to the number of microsporocytes with the chromosomes paired as bivalents at metaphase one, but averages of selections did not differ. Of ten 150 metaphase I cells observed 85 per cent possessed twenty-one bivalents, 11 per cent had twenty bivalents and two univalents, and 4 per cent showed mostly bivalents with occasional univalerits and multivalents. On a chromosomal basis 99 per cent of the chromosomes occurred as bivalents, 0.7 per cent as univalents, and 0.3 per cent as multivalents. These results would indicate that tall fescue behaves as an alloploid with little or no homology between chromosomes of different genomes. Myers and Hill (1947) found that quadrivalents were quite common at metaphase I in tall fescue. Sexivalents at diakinesis, univalents at metaphase I, laggards at anaphase I, and micronuclei in quartets were also observed. Evidence of considerable homology between chromosomes of different genomes of the tall fescue seems to be provided by the high incidence of pairing at metaphase I in F, hybrids with meadow fescue ( F . elatior). It has been suggested that autoploids may play an important role in the origin of new forms. Tall fescue as observed by Myers and Hill ( 1947) and Crowder (1952) does not appear to behave cytologically as an autohexaploid. Pairing between chromosomes of different genomes was not complete. As a result, if this hexaploid race arose originally as an autohexaploid the pairing relationships of its chromosomes evidently have been altered during the course of development since that time. Considerable homology was observed between the chromosomes of the different genomes of the hexaploid. The results would indicate that there might be some relationship between F. elatior and F. arundinacea. Extensive studies by Jenkin (1933) reported several successful interspecific and intergeneric hybrids between F. arundinacea and other Festuca species and the Lolium genus. There has been considerable interest in such wide crosses. It does provide an opportunity, when interspecific crosses are made and the homology of their chromosomes studied, to assist in ascertaining the possible evolution of tall fescue. Tall fescue as a crop has had some undesirable characteristics such as coarseness and lack of palatability. Such a species as Lolium multiflorum

TALL FESCUE 297 Lam. thrives well and is more nutritious but being an annual is not especially desirable for hay or grazing. If possible the incorporation of some of the desirable characteristics of this species into tall fescue might result in a more valuable forage and pasture crop. Swayne published a treatise in 1790 suggesting that Festuca loliacea might be of hybrid origin (Jenkin, 1933). An artificial cross of this nature has been made successfully. Pet0 (1934) observed several F. arundinacea x L. perenne progenies showing pairing between Festuca and Lolium chromosomes and among Festuca chromosomes. Bivalents, multivalents, and unpaired chromosomes were seen at metaphase I. There seemed to be a degeneration process occurring which resulted in male sterility of the F,. Crowder (1953a) obtained information which indicated that perhaps two or more of the genomes of F . arundinacea might be homologous with Lolium. Twelve seedlings having 21 chromosomes were obtained when crossing h l i u m perenne L. by a tetraploid Festuca elatior L. (Carnahan and Hill, 1955). These triploid hybrids were treated with colchicine to induce autoallohexaploids. These triploids were unusually vigorous and leafy. Since several workers have crossed diploid Lolium and diploid Festuca with hexaploid F . arundinacea, it suggested the possibility of crossing these hexaploids with the productive and widely adapted, but frequently unpalatable, hexaploid tall fescue. It may be a means for introducing more desirable forage characteristics into the tall fescue crop. Many workers have attempted successful interspecific crosses between Festuca elatior and Festuca arundinacea to attempt a better understanding of the evolution of F . arundinacea and also to determine the possibilities of introducing some of the more desirable forage characteristics of F . elatior into F . arundinacea. I n 1882, Hackel classified a plant as intermediate between meadow and tall fescue and called it a hybrid (Crowder, 1952). Other natural crosses have been reported and it is believed that many may exist which have escaped notice. Jenkin (1933, 1955a, b, c) made this interspecific cross reciprocally and obtained very good seed set. The caryopsis development appeared normal and several weak plants were established. Nilsson in Sweden and Crowder in the United States have reported the occurrence of natural hybrids and have produced them artificially using meadow fescue as the female (Crowder, 1952). The F, was morphologically intermediate between the parents and was cytologically irregular. Observation of 3 F, plants revealed mainly 7 bivalents and 14 univalents with an occasional multivalent. Myers and Hill (1947) bagged together panicles of diploid and hexaploid fescue plants which were practically self-sterile in an effort to obtain interspecific progeny. No seeds were produced on

298 J. RITCHIE COWAN the tall fescue plants but a small number were set on those of meadow fescue. Meiotic observations of the resulting F1 plants revealed that bivalents were usually formed with some multivalent pairing and with some chromosomes left unpaired. Crowder (1953a) obtained several Fl derivatives which were rather vigorous and possessed certain characteristics which were agronomically more desirable than those of Festuca arundinacea. The F, hybrids were less coarse and the foliage was not as harsh as that of the F. arundinacea parent. All progenies were infertile. Many attempts to obtain back crosses resulted in a stimulation of 10 caryopses one of which germinated, but the seedling died. Crowder (1953a) suggests that chromosome doubling of the F, hybrids offers a possibility for obtaining fertility. Difficulties encountered in making successful hybrids between these two species would suggest that natural intercrossing would not be common. Also, if such crossing did take place the hybrids would be highly sterile but yet not so completely sterile as to exclude the possibility of further breeding, particularly with F. arundinacea. The possible production in later generations of fertile types still showing some of the influence of the F. elatior is also indicated (Jenkin, 1955a). Heritability studies on tall fescue by Burton and DeVane (1953) have shown wide variability existing for certain characters. The opportunity for selecting superior genotypes with higher forage and seed production and drought and disease resistance than those now available seemed to be very good. V. VARIETIES

1. ALTA ALTA is one of the two varieties of tall fescue which has made a very substantial contribution towards the evolution of this species into an important agricultural crop in the United States. It was an ecotype selection developed cooperatively by the Oregon Agricultural Experiment Station and the Forage and Range Section of the Agricultural Research Service of the United States Department of Agriculture. H. A. Schoth of the Forage and Range Section observed tall fescue introductions growing in a nursery and on the farm of Max Heinricks at Pullman, Washington, in 1916. These tall fescues were characteristic in their ability to produce green forage under rather adverse summer conditions. The climatic pattern in the Willamette Valley of western Oregon is such that it is not uncommon to have very low precipitation from late May until late September. It had been the practice to use ryegrasses as the common constituent of pastures. These are low forage producers during this long dry period. It appeared to Schoth that tall

299 fescue might have some possibilities as a summer grazing grass if it could withstand the long dry period usually experienced in western Oregon. In 1918 some of the more promising lines of tall fescue were established on the Oregon Experiment Station at Corvallis, Oregon. The seed was obtained from Max Heinricks, Pullman, Washington. Three lines, P.I. 19728, P.I. 24838, and P.I. 25206 were used. Two of these three plant introductions made available by the Plant Introduction Section are known to have had their origin in Germany. P.I. 19728 was received January 24, 1907, from the A. LeCoq and Company, Darmsteadt, Germany. P.I. 24838 was from a commercial lot of about 500 pounds purchased from the J. C. Peppard Company, Kansas City, Missouri, March 1, 1909 (probably the present-day Peppard Seed Company). P.I. 25206 was from a lot of seed presented by Dr. George Bitter, Director of the Botanic Garden, Bremen, Germany. This lot was received by the Plant Introduction Section, March 26, 1909. The two lots from Germany come from the almost extreme northern and southern parts of that country. It is not known from what country or part of the world P.I. 24838 was obtained. This material was planted in the spring of 1918. It was noted to have made exceptionally fine growth during the first season. It was of sufficient interest to receive special mention in annual reports during 1919, 1920, 1921, and 1922. In the winter of 1922-1923 it suffered severe winter killing. The surviving plants were put together and became the source of seed for Selection No. 7 of tall fescue. Selection No. 7 was planted in a small increase block for observation and seed production purposes. In 1955, after 32 years, this particular planting still remains quite vigorous with an excellent stand (see Fig. I ) . This is an indication of its ability to persist. In 1927 the designation of Selection No. 7 was changed to F.C. 29366. It remained under this particular Selection Number until it was given the name ALTA in 1940. It was registered by this name by the Committee on Varietal Standardization and Registration of the American Society of Agronomy on November 15, 1944, and has the distinction of being one of the first forage crop varieties to receive such a certificate. Considerable interest was expressed in this selection during its early years of experimental observation because of its ability to remain green during the dry summers experienced in western Oregon and because of the high yields of forage it produced. The first seed increase was harvested in 1932 on the Oregon Agricultural Experiment Station. The initial commercial seed harvest took place in 1936 (Rampton, 1949). Its use has expanded continuously since that time. Owing to the wide adaptation of ALTA, it is grown under many varTALL FESCUE

300 J. RITCHIE COWAN ied conditions. It soon spread throughout the Pacific Northwest and into California and Arizona. With the advent of irrigated pastures it became one of the main constituents of such pastures because of its ability to produce high quantities of forage. In 1940, the value of ALTA tall fescue as a seed crop in Oregon was about $31,000. It reached a peak in 1951 of almost 2% million dollars. The growing of ALTA tall fescue seed became an important enterprise in Oregon and throughout the Pacific Northwest. By 1949, 90 per cent of the ALTA fescue seed produced in Oregon was being shipped to other parts of the country. As a result it

FIG. 1. H. A. Schoth standing in November, 1955, on original planting of tall fescue from which the variety ALTA was developed. This plot was seeded in 1923. (Oregon Experiment Station photo.)

became widely used throughout the other parts of the country, particularly in the Southeast. The seed production program for this variety is on a generation basis in Oregon. The breeder’s seed is maintained cooperatively by the Oregon Experiment Station and the Forage and Range Section of the U. S. Department of Agriculture.

31 KENTUCKY 31 has quite a different history from that of ALTA. It is a natural selection. There are several versions of its possible origin. E. N. Fergus, Agronomist of the Kentucky Experiment Station, was responsible for appreciating its potential and initiating experimental work with it in 1931. It has been frequently referred to as Suiter’s grass, by virtue of the fact that the original seed was obtained from a planting on William Suiter’s farm in Menifee County in eastern Kentucky. 2.

KENTUCKY

30 1 I n 1931, Fergus was invited to Frenchberg, Kentucky, the county seat of Menifee County, to judge a sorghum show. During the course of this show, Fergus learned of a grass being grown on the farm of William Suiter which stayed green all winter. Such performance was of real interest and arrangements were made to observe this particular planting. Fortenbery (1948) gives a very interesting account of what transpired subsequent to this visit and leading up to the introduction of KY 3 1 to American agriculture (see Fig. 2). TALL FESCUE

FIG.2. This is the hillside where William Suiter established tall fescue, probably about 1890. (Photo courtesy of Farm Quarterly, 1948.)

There are at least two versions of how tall fescue initially was planted at this particular site in eastern Kentucky. One has it that seed was brought in by William Suiter's father from Virginia. The other indicates that the seed was possibly carried in by birds and dropped at this particular location. However. some 40 years prior to the visit of Fergus a few plants of tall fescue had been observed by William Suiter to be able to withstand drought and cold weather and still stay green. Seed was saved from these particular plants and gradually over a period of years a steep hillside was planted entirely to this grass. Tabor (1952a) reports that tall fescue had been favorably recognized as early as 1884 along with subsequent similar reports in 1857, 1875, and 1888. It is quite possible that these favorable reports had to do with plantings

302

J. RITCHIE COWAN

made by early immigrants to the eastern part of the country. Such material possibly was the source of seed which was transported one way or another into southern Kentucky about 1887 and through survival of the fittest resulted in what was used to form the breeder seed stock of KENTUCKY 31 in 1931. It was tested at the Kentucky Experiment Station, Lexington, Kentucky, for some seven years or so before it was actually considered as a useful crop for Kentucky agriculture. Johnstone, Field Agent in Agronomy for the Kentucky College of Agriculture, came upon this planting of tall fescue in Menifee County in the fall of 1938. Being particularly interested in the value of fall-seeded grain crops for winter grazing and soil conservation, this block of green in an otherwise fall brown countryside was startling. Upon inquiry of the County Agent in this area it was learned that some seven years previously seed had been sent back with Fergus to be tested by the experiment station. Results of experimental work by this time indicated that it was grass of some promise. The experiment station did not have adequate seed for widespread tests and seed was obtained from Suiter for some of the initial testing throughout Kentucky. I n 1946 Kentucky had 30 seed growers harvesting about 75,000 pounds. Two years later over 950 growers harvested seed producing nearly 4 million pounds. An organization known as the Kentucky 31 Fescue Association with offices at 929 South Limestone Street, Lexington, Kentucky, was organized. This organization had the services of a full-time secretary whose job it was to promote the use of this particular grass. Its use soon became quite widespread throughout the Southeast because of its winter growing characteristic and ability to provide considerable grazing throughout the mild winter of the southeastern states. In recognition of the contribution which KY 31 has made to grassland agriculture, a monument has been erected to it on the roadside of William Suiter’s farm. It is perhaps the only memorial of this kind ever made to a grass.

3 . Other Varieties GOAR is another variety of much lesser importance than ALTA or KENTUCKY 31. It too has an interesting backpound different from that of these other two varieties. W. Southworth in the Field Husbandry Department of the University of Manitoba, Winnipeg, Canada originally obtained seed from a Dr. Dagon, Budapest, Hungary. I n trials in southern Manitoba it was found that this grass grew quite well but was extremely variable. It gave good crops and survived the extreme droughts in the southern counties. The hay was not of the best quality.

303 Seed of this particular source received by Southworth from Hungary was sent to P. B. Kennedy, University of California, March 22, 1926. This material was grown in a grass garden both at Davis and Berkeley for a number of years. It was carried under the accesssion number T.O. 899. Seed of this accession was sent forward to L. G. Goar at the El Centro Experiment Station in the Imperial Valley, California, in 1941. Here it was grown and reselected. It is grown widely in southern California and eastward to Texas, where daytime temperatures are high. It has a very vigorous seedling. Hafenrichter (1953) found that it performed well on alkaline lands in California. There are other varieties of tall fescue but these are of little importance currently when compared to the above. S.170 is a selection made at the Welsh Plant Breeding Station, University College, Wales, Aberystwyth, Wales. OTTAWA 39 was developed by the Forage Division of the Experimental Farm Service, Ottawa, Ontario, Canada. H-144 was selected by the Lilly Seed Company out of ALTA. Several naturalized strains have been found in Kentucky. TALL FESCUE

VI. BREEDINGBEHAVIOR

I . Mode of Reproduction In 1949 an extensive breeding program was initiated on tall fescue at the Oregon Agricultural Experiment Station, Corvallis, Oregon. Among the studies set up on breeding behavior, many of the earlier had to do with its mode of reproduction. Detailed investigations were made on flowering habit. The degree of self-fertility was determined by studying 1500 plants over a three-year period (1951-53). Another study was made on the feasibility of vegetative reproduction. The intervals between the different stages of inflorescence, emergence, and actual flowering are quite consistent. About 10 days are required after the panicles have emerged from the boot stage before there is any indication of flowering. The panicles on the culms in the center of the plant are the first to appear. Flowering does not take place under cool, cloudy, and moist conditions. After a prolonged cool wet period during which the plant has developed to the physiological stage for flowering, its flowering will be most profuse on the first clear, warm, day. Detached culms were placed in water in the laboratory to study the flowering pattern within a single panicle. It was noted that the time involved for a panicle to complete flowering in the laboratory was practically the same as in the field. It took approximately 3 days for one panicle to complete flowering. Flowering started at the top of the panicle on the tip ends of the branches and worked inward to the center of the panicle and downward in a systematic fashion.

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J. RITCHIE COWAN

Although the actual time of flowering was rather specific, the time of initiation and subsequent interval was influenced by the environment. Flowering usually commenced at 2:OO P.M. and continued until about 6:OO P.M., reaching its peak around 4:OO P.M. One year it was

noted that the flowering was much later in the afternoon and continued until sundown. Occasionally some flowering was observed just at sunrise. However, it discontinued flowering as soon as the sun was up a couple of hours or so. Temperature and humidity seem to have a very marked effect on the time of day of flowering. A selection grown at Tifton, Georgia, which produced practically no inflorescence whatsoever, has flowered profusely under conditions at the Corvallis Experiment Station in Oregon during 1954 and 1955. Apparently this plant is TABLE I Frequency Distribution of Tall Fescue Plants on the Basis of Their Self-Fertility

Year

1-10

11-20

1949 1950 1951 1959 1953

42 57 735 719 1337

42 47 297 201 19

Class intervnls in per cent self-fertility 21-30 31-40 41-50 51-60 61-70 22 23 79 61 1

12 8

31 21 0

71-80

81-90

Total

9 2 4 0 0

la8 148 1181 1031 1364

6 3 16 14

-

a

-

4 19

2

2

2 4 7 0

9 3 9 0

6

influenced in its flowering pattern by length of day and possibly temperature. There is a complete range in self-fertility from highly self-sterile plants to highly self-fertile plants. Self-fertility measures were determined by using seed yield. Details of the procedure are described by Cowan ( 1952, unpublished). The formula used was as follows:

% Self-fertility

Yield of self-pollinated scetl by weight Yield of open-pollinated seed by weight

= __-

x

100

This criterion gave quite uniform and consistent results over the threeyear period used in this study. An indication of the range in self-fertility in this study is shown in Table I. When 10 highly self-sterile plants were crossed in all 45 possible combinations seed set was obtained from all crosses (Cowan, 1953b). Since there was apparently good cross-fertility between all 10 self-sterile lines, it is possible that self-incompatibility may be a cause of the selfsterility. There was positive and highly significant correlation between years for self-fertility. Where some form of male-sterility is to be employed in a hybridization program, it is important to have some knowl-

305 edge of asexual propagation of the species. Several studies were carried out in this connection on tall fescue. In a siudy using 40 two-year-old plants, it was found that 200 propagules could be obtained readily from each of them. If these were established in August in the greenhouse and transplanted to the field in October, each clonal plant could produce at least 40 more propagules in the subsequent August. Thus, within a twoyear period, it is possible to multiply one plant vegetatively into approximately 8000 clonal plants. It is possible to make up these propagules from a very small portion of the basal stem which has only one node and a part of two internodes, and to have them readily established themselves. Chopped up rhizomes also establish well. There is no advantage in using plant growth hormones. It was found that clonal material established from plants lifted in February produced many more tillers than those lifted in September or December. TALL FESCUE

2 . Genetic Variability a. Seed. The potential for increasing seed production by selection is great. The amount of seed produced per panicle appears to be a better indication of the seed production of a plant than the number of culms it contains. It is possible to select for high seed yield and high forage yield at the same time (Cowan, 1955a). A three-year study using 20 lines selected from 135 lines, 10 of which were selected on the basis of high seed yield and 10 on the basis of low seed yield and which were handled for hay, pasture, and seed production, showed no direct correlation between seed yield and forage production. Some high seed yielders were low in forage production, whereas some low seed yielders were high in forage production and still other high seed yielders were high in forage production. The results of this study clearly indicated that it was possible to select for high performance both in seed production and forage production in the same genotype. Burton and DeVane (1953), when estimating heritability in tall fescue, observcd that seed yield was not correlated with any other character studied. There were indications of being able to select for superior individuals with high seed yield. These investigators felt that if selection pressure was exerted for high seed production, it would be acquired at the expense of some forage yield. Over a three-year period, 1951 to 1953 inclusive, three 4-panicle samples of seed were harvested from some 1500 individual plants. The results of this study showed very little variation, if any, between samples within a plant. However, the variation in seed-producing ability between plants was very high. Table I1 indicates the range in seedproducing potential. There is a range here of those plants having the

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J. RITCHIE COWAN

ability to produce as much as 19 g. of seed per 12 panicles and those plants that produced less than 1 g. of seed per 12 panicles. The average individually spaced plant produces from 250 to 400 panicles. There is a wide range in seed size. Some genotypes produce seed which hull or leave only the groats after threshing much more so than others. b. Forage. Forage characteristics vary widely in this species. Some plants produce an upright type of growth. Others produce a lax type of leaf that drops to the ground readily. One particular selection had leaves as long as 18 inches. These lax types appear to be much more suceptible to leaf diseases. The edges of the leaves on some plants are very scabrous and harsh to the touch. Others are very smooth and soft. Some TABLE I1 Frequency Distribution of a Number of Tall Fescue Plants per Weight of Seed Class Yield of seed in grams of 3 four-panicle samples per plant Year 0

1

2

3

4

5

6

7

8

9

Plant

10 11 12 13 14 15 16 17 18 19 total

1951 6 4 18 53 99 150 180 178 133 135 8% 53 40 2% 8 6 195% - 8 41 196 179 209 173 128 77 5 1 %4 11 1 2 ‘ 1 1953 36 66 113 195 195 175 155 154 108 64 50 60 3% 15 11 6

2

-5

% 1 - 1175 1 - - 103% % 1 1 1364

have extremely wide leaves while others are quite narrow. The narrow ones tend to “rope up” under the duress of moisture shortage. Visual ratings were made on some 1500 plants as to their forageyielding capacity, over the three-year period, 1951 to 1953 inclusive, in March, August, and September. These observations provided an opportunity to determine the type of forage produced at these three seasons. The rainfall pattern at the Corvallis Experiment Station is such that very little precipitation is experienced from late May to the middle of September. Since no irrigation was available, these plants were essentially growing under dryland conditions. There was found to be no correlation between the performance of the plants in March, August, and October. It would not be possible to select plants in March and predict their performance in August and September. The same 1500 plants were also classified as to leaf texture or width. Five different classes were set up with 0 being very narrow and 5 being quite wide. It will be noticed in Table I11 that there were plants fitting into all these classifications in each of the three years observed, with the exception of the very fine selection in 1951 and 1952. Therefore, it would be possible to select for width of leaf, if this seemed to be an important factor in producing a desirable type of forage. Chase (1950) described tall fescue as being a plant without rhi-

307

TALL FESCUE

zomes. In a group under study plants have been found that vary all the way from those without any rhizomes to those with rather aggressive rhizomatous development. Some plants will spread very slowly, whereas others will make a solid mat even to the distance of I foot within a year's time. A heritability study indicated that forage yields in south Georgia could be increased by at least 50 per cent (Burton and DeVane, 1953). This would be a substantial advance. It is suggested that if an efficient means of vegetative propagation could be developed such an advance could be realized by selecting superior individuals within a given population. It was noted that the highest yielding plants were in general the more disease-resistant. Apparent advances in yield of up to 40 per cent TABLE I11 Frequency Distribution of Tall Fescue Plants on the Basis of Texture

Year

0

1

2

3

4

5

Total

1951 1952 1953

-

14 94 2

140 224 81

436 618 749

544 92 510

48 4 15

1182 1032 1364

7

were also evident if selections were possible for heat and drought tolerance. An introduction from Constantine, North Africa, collected in the Altlan Mountains shows a very striking characteristic of winter growth under western Oregon conditions. This particular selection produces practically no forage during the summer; in fact it appears to be practically dead during this dormant period. I n October or November, as soon as the fall rains start, growth is initiated. During December, January, and February considerable growth is produced (Cowan, 1955b). A similar performing selection has resulted from material obtained about 1923 from the Museum of Natural History in Paris by the Botanic Gardens in Canberra, Australia. This material has been under experimentation at the Armidale Experiment Station in New South Wales, Australia. McTaggart (1937, 1941) first reported the potential of this introduction. This material was introduced from France under the name of Festuca mairei. It is now known as Demeter fescue. It has been found to produce considerable forage under the rather adverse weather conditions prevailing in winter. During the winter of 1955 (March to October) in combination with white clover, it gave better live weight gains for sheep than any other grass with the same clover. c. Quality. The most severe criticism of tall fescue has been its lack

308 J. RITCHIE COWAN of palatability. It has been possible to alter the acceptability or palatability of this grass by growing it in association with a legume, by adding fertilizer, by keeping all old growth clipped back, and by encouraging new succulent growth. It appeared that it should be possible also to effect some improvement by selection. If this is so, then some criteria must be found to measure this particular characteristic. In 1950, some studies were set up in the tall fescue breeding program at the Oregon Experiment Station to see if a microtechnic might be devised which would be reliable for selection on the basis of quality. In order to determine whether any such method could be devised, it was necessary to employ certain nutritional techniques first to determine whether differences might be distinguished between individual plants. It has been generally accepted that crude protein is an indicator of the nutritional value of a forage. Therefore, because of the simplicity of this particular analysis and the rapidity with which it can be carried out, which permits a large number of analyses to be made within a reasonably short time, this particular method was employed first as an indicator of some of the nutritional differences, if any, that might exist between tall fescue plants. Dry matter production is also an indicator of potential feed value. This particular measure was employed as well. Ninety individual plants which were clipped over a period of one year everytime they reached the height of 8 inches, showed a wide range in ability to produce crude protein (Cowan, 1953a). There was a range of as much as 10 per cent in protein between individual plants in this particular survey. It was also observed that the number of days required to produce 100 g. of dry matter from one plant ranged all the way from 41 days to 256 days. Following the above study, two more detailed studies were set up. One was designed so that frequent regular clippings might be made everytime the forage attained a height of approximately 8 or 9 inches. The other was designed so that the forage might be harvested at different stages of maturity up to the seed stage (June), and the aftermath at monthly intervals throughout the following eight months. Green weight, dry weight, and protein per cent were determined on every plot in this study. There were some 4500 measurements made per year and the study was carried on for three years. Twenty different clonal selections having rather strikingly different phenotypic appearances were used. During one year one clonal selection produced 6789 g. of dry matter per plot and 736 g. of protein, while another produced 8231 g. of dry matter per plot and 720 g. of protein per plot, respectively. Here were two selections producing approximately the same amount of protein, but one was producing a far greater bulk of material than the other. If crude protein is an indicator of nutritive value then the second

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would not carry nearly as much concentrate per bulk as the first. It would appear that there is some possibility of selecting on a quality basis in this particular crop. Reid et al. (1950) reported on a method which he called the “chromogen” technique as a laboratory indicator of digestibility in forages. This method was devised primarily for nutritional studies of pasture mixtures. This technique is being employed to determine whether it may have a n y possibility as a plant breeding tool. Preliminary results to date indicate that there are differences between tall fescue plants in their “chromogen” content (Cowan et al., 1955). It has also been observed that genetic variation exists in the ability or ease of extraction of the “chromogen” in the laboratory. The extraction of “chromogen” is much more difficult from some clonal lines than others. Buckner ( 1955) has conducted extensive investigations of the feasibility of measuring palatability of individual plants and their progenies with the grazing animal. Previous work had shown that the animal’s choice varied considerably with the season, but some plants were consistently grazed. Some of the plants which had been consistently grazed were selfed and also intercrossed. Three subsequent generations were studied. The grazing of individual plants was not found to be a n entirely satisfactory criterion. It could be used as a primary test in screening. However, it should be followed by a grazing of the best lines (clones) in a replicated clonal plot. For the most critical evaluation of the progeny, the grazing should be done during the second year following establishment. Age of the plant apparently influenced its palatability. There was great variation in palatability at different grazing dates in both first and second generations. In some cases certain clones were well grazed at all dates. When the inbred material was compared with the open-pollinated lines on the basis of vigor, prior to grazing a noticeable reduction was observed as a result of inbreeding. In the first generation 35 per cent reduction was noted and in the second generation, 50 per cent. There was some relationship shown between low fiber, high moisture content. and palatability. Some well-grazed lines were also high in protein. Some progress was made in improving palatability by selection within subsequent generations of crosses between well-grazed clones. Greater progress, however, was made by selection within subsequent inbred generations of clones which had been well grazed. These studies would indicate that there is ample opportunity through plant breeding for developing varieties much improved in nutritive value and palatability as coml)ared with those now available.

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VII. SEEDPRODUCTION

Seed production was largely a by-product of farm operation until the last 20 or 25 years. During this recent period the production of forage crop seed has become a main farm enterprise in many areas and in some cases practically the sole enterprise. This type of farming was pioneered largely by the farmers of the western irrigated areas. Tall fescue is a relatively high seed-yielding crop per acre. It contributed greatly towards the success of this new type of farming. Wheeler and Hill (1957) have dealt in considerable detail with the various aspects of tall fescue seed production. The production of seed went from a million pounds in 1945 to slightly over 50 million pounds in 1952. There was a very decided drop in 1953 to some 27 million pounds. The very rapid increase over a short period of time was reflected by high prices, a good demand, and relatively good yields of seed per acre. The average United States yield of tall fescue seed for more than ten years has been over 200 pounds per acre. During the five-year period ( 1948-1 952) the average yields of the two important seed-producing states were: Oregon, 261 pounds, and Kentucky, 223 pounds per acre. In 1952, the three states of Oregon, Idaho, and Washington averaged over 350 pounds per acre of the variety ALTA. The five largest KENTUCKY 31 producing states, Kentucky, South Carolina, Tennessee, Mississippi, and Alabama, averaged 190 pounds per acre. The price has ranged all the way from $5.00 a pound to $0.08 a pound. Hyer et al. ( 1949), in making a survey of the cost of production in producing ALTA seed in western Oregon in 1948, estimated that it was approximately $0.12 per pound. Production of seed of this crop has undergone some rather radical changes in the short time that it has been grown commercially. Initially most of the seed was produced from meadows that were not used for pasture purposes. This still remains true in many of the seed-producing areas. However, experience of seed growers and results of research on seed production have shown that it is much more profitable to grow the plants in rows if seed is desired. Although tall fescue will remain in a solid stand for many years the seed production capacity declines rather rapidly after the first two or three years. It takes on a condition that is frequently referred to as “sod bound.” This condition can be temporarily remedied by various renovation practices. Solid stands can be renovated by “skin” plowing, which is plowing with a sod plow at about 4 inches. When plowed in the fall, a fair stand will be re-established by the following spring. No seed crop will be produced until the next year. The second year after such renovation as much R S I100 pounds of seed have been harvested

31 1 from plots which had previously been yielding less than 100 pounds per acre (Richardson, 1951) . Richardson (1951) found nitrogen to be the most important material for stimulating seed yield on old stands which had become sod bound. The theory was advanced that sod binding possibly was due to an improper balance of nutrients combined with the failure of the plant to form new rhizomes, from which shoots may arise from the nodes. Along this line studies were made as to what renovation effects the applications of chemicals might have on thinning of the stand. Furtick (1952) used TCA (trichloracetate) , IPC (isopropylphenyl carbamate), Shell DD, and Ammate (ammonium sulfamate). It was concluded that no renovation practice of this nature would be successful in producing a profitable seed crop without the application of nitrogen fertilizer. However, nitrogen fertilizer alone did not give satisfactory results. It appeared that it was necessary to have a combination of nitrogen with some form of periodic stand reduction before satisfactory seed yields could be produced. Rampton (1945) reported on studies conducted over a six-year period showing that row cultures were much more satisfactory for producing high yields of seed over a long period of time than were solid stands. Similar results were reported in Kentucky by Spencer (1950). It was also noted that low rates of seeding of 2 and 3 pounds per acre were much superior to higher rates of seeding in row plantings. The row widths varied from 2 feet to 4 feet. I n commercial practice this width is regulated largely by the available cultivation equipment. Usually it is necessary to cultivate only once, and not more than twice, in the spring. Following the second cultivation sufficient growth has been made to compete readily with any weed growth that may develop. Cleaner seed is usually grown when row culture is used. Ryegrass is one of the more serious weeds in seed production. Also in some areas rattail fescue (Festuca rnyuros) is quite a problem. Both of these are exceptionally difficult, if not impossible, to clean out of the seed; therefore it is necessary to attempt their eradication in the field. Considerable success has been obtained in selectively removing these weedy grasses by certain chemical sprays (Freed et al., 1952; Bayer, 1953; Furtick and Chilcote, 1955). Compounds which have been used successfully are IPC (isopropylphenyl carbamate), 3 Chloro IPC (isopropyl-3-chlorophenyl carbamate), and Karmex DW. Care must be exercised in making the applications of these sprays a t the right time of year; otherwise serious damage may be done to the subsequent seed crop. Applications can be made in October in Oregon without any reduction in seed yield and yet provide effective control of such weedy grasses as ryegrass, rattail fescue, and velvet grass in the seedling stage. In 1952 Oregon entered for certification 4,964,113 pounds of ALTA, of TALL FESCUE

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which only 2,193,757 pounds or 44 per cent was eligible for the blue tag which denotes top quality. The remainder failed to reach this standard because of excessive amounts of ryegrass, rattail fescue, and chess. The removal of these weeds by chemical spray aids in producing higher quality of seed and economic returns. Bayer (1953) showed that the time of application of chemical sprays for weed control was extremely critical. There was a marked reduction in seed yield during the subsequent year if 3-Chloro-IPC or IPC was applied after the first of November. Similar to many other grasses, seed of tall fescue shatters readily as the plants ripen. Severe wind storms or rain at the time the seed is ready to harvest can result in very heavy losses. Harvesting has been done by two methods, either the binder or the combine. When the seed was selling for a high price, it was found profitable to harvest with the binder, placing especially built pans under various points of the binder where shattered seed might normally fall on the ground. However, as the price of seed dropped and more efficient harvesting operations became necessary, direct combining became the popular method for harvesting. I n the case of solid seedings, windrowing has been found to be quite effective. The stand is cut somewhat on the immature side, and the heads finish maturing in the windrow. This has resulted in seed of high germinability and very little shattering. However, this particular method has to be used with caution because there is a very great possibility of picking up many undesirable weed seeds, which normally would not be taken into the harvesting equipment if direct combining was done. Also, such a practice is not too satisfactory where row cultures are used. When combining direct, it is necessary to harvest as much as possible while the seed is still tough. This necessitates thorough drying before storing large quantities in bulk. The present methods of harvesting seed are far from satisfactory. It has been estimated by Hill and Harmond (1955) that 35 to 40 per cent of the total seed crop is lost owing to shattering ahead of the combine, regardless of whether the crop is combined directly or picked up in the swath. Care of the seed fields following harvest is extremely important. If the stover and stubble are not removed, a decided reduction in seed yield the following year can be anticipated. It is usually the practice to mow the stover and remove it by various methods. Sometimes it is baled and used as a roughage feed. Some growers will rotovate it back into the soil. In other cases it will be burned. There has been some question as to whether burning might have some effect on the new seed crop. A study of the seed head primordia development by Whitesides (1947) would indicate that there is no danger of this as long as the burning is completed fairly early in the fall. It must be a quick fire;

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burning too long in one spot can be damaging to the subsequent seed crop. In cleaning the seed it is almost impossible to remove such other crop seeds as orchardgrass, tall oatgrass, ryegrass, and chewings fescue. Tall fescue seed usually weighs between 22 and 27 pounds per bushel. There are approximately 225,000 seeds per pound. VIII. FESCUE POISONING During the eighteen hundreds tall fescue was introduced into New Zealand from Europe with the hope that it might be a useful species to plant on some low wet areas which otherwise were of little or no value for grazing purposes. It established itself readily and spread rapidly under the prevailing moist soil conditions. It was soon noted that livestock which fed on this grass for extended periods of time became quite lame. If this lameness was not stopped by removing the stock from these areas, it would become so acute as to permit a type of gangrene to set in which in some cases would result in the loss of extremities such as hoofs. The symptoms were quite similar to those found when the animals consumed toxic quantities of ergot (Clauiceps purpurea), a fungus disease that attacks many species of grains and grasses, including tall fescue. Cunningham (1948) produced conclusive proof from his experimental work to show that “fescue foot” was not due to ergotism. Lameness develops 10 to 14 days after the cattle first eat tall fescue (Cunningham, 1948). The left hind limb is usually the first to be affected, though occasionally both hind limbs may be affected. There is local heat and swelling with severe pain; later, the pain diminishes somewhat and there is some reduction in swelling. This stage is accompanied by drying and hardening of the skin and by the extremities’ becoming cold and numb. An indented line forms a t the junction of the necrotic and normal skin and here the warm and cold regions are sharply separated. The line may be at various points on the leg, and it is at this point that the peripheral portion of the limb may be shed. It was concluded that the leaves must contain some toxic substance. It affected cattle most and was not too serious in sheep. Horses did not seem to be affected in any manner. Pulsford (1950) working in South Australia found that a similar situation existed there. It was first drawn to his attention in 1946 when cattle became lame grazing on “Williams grass.” This particular grass was tall fescue which had been introduced from New Zealand as a winter and spring forage. Unlike the situation in New Zealand, there was marked seasonal incidence. It seemed to be most prevalent during the winter, that is, the period from May to October. It was rarely seen in the summertime. In contrast to the

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difficulty experienced in South Australia, very successful use has been made of tall fescue in the state of New South Wales in the region of Armidale. An introduction from France known as Demeter tall fescue has provided very satisfactory winter grazing, with no apparent difficulties as far as poisoning is concerned. On the Hauraki Plains of New Zealand tall fescue has become an extremely serious weed, owing to its poisoning effect causing “fescue foot.” It smothers out useful pasture species and is particularly difficult to control on poorly drained land. Banfield (1953) recommends various practices for eradication. It is suggested that it be replaced as soon as eradicated by Harding grass (Phalaris tuberosa). Some of the suggestions for eradication are improvement of the drainage, and deep plowing followed by summer fallow. New pastures should be grazed with sheep for the first six months. This close grazing with sheep tends to eliminate any tall fescue plants that might recover or volunteer. It is suggested that remaining plants be dug out and roadsides and ditchbanks cleared of any escapes. “Fescue foot” seems to be very closely associated with the growth of this crop on low, wet, poorly drained areas. Tall fescue appears to thrive under these conditions. Similar examples have been reported in the United States (Goodman, 1952). However, in relation to the extent of the use of this crop, the number of cases reported are extremely few. In many instances reports have proved to be nebulous when an attempt has been made to determine exactly whether tall fescue was responsible for an ailment reportedly suffered by the livestock. There have been reports from Colorado, Tennessee: Florida, Missouri, and California, where tall fescue definitely seems to be the primary source, if not the source, of lameness and loss of extremities by cattle. It has been noted, however, in one case in California, that uptake of selenium in toxic quantities by tall fescue was largely responsible for difficulties encountered by grazing cattle on this particular stand. Some of the most severe cases and most extensive difficulties have been encountered in western Colorado. Cunningham (1948) placed three cows on tall fescue hay for a period of time. One became very lame within two weeks, the second showed slight signs of lameness for a short period, and the third was unaffected after a month’s feeding. There would seem to be some indication in this case of genetic variation among the animals in susceptibility to this particular difficulty. I n Colorado no success has been attained so far in attempting to reproduce the disease experimentally with small numbers of trial animals. However, most of these trials were carried out in relatively mild winters in Colorado, and most of the severe cases had occurred in very cold winters. Observations in

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Colorado are similar to those that are reported from New Zealand, where this difficulty seems to be particularly severe when it occurs on areas well supplied with moisture. There is little information as to differences between varieties. The only report of variety comparisons comes from a trial in Australia, where it is stated that KENTUCKY 31 appeared to be the worst offender among the tall fescue varieties tested.

IX. DISEASES Diseases on this crop have not been particularly serious to date. They have been confined primarily to areas of high humidity and high temperature. In general, little or no difficulty has been experienced in the irrigated areas of the West. The two most serious diseases have been caused by Helminthosporium and Rhizoctonia. Wells and Allison (1952) observed that tall fescue could carry the net blotch fungus Helminthosporium dictyoides. This net blotch will cause severe leaf blighting of seedlings. A number of lots of southeastern seed and ALTA were planted. H . dictyoides was obtained from 3 to 5 per cent of all viable seeds of the southeastern grown lots but on none from the ALTA seed. It would appear either that the ALTA variety carried some resistance to this particular disease or that it was grown in an area where the disease was not prevalent, and thus did not have an opportunity to become a carrier. Atkins (1950) found Helminthosporium on KENTUCKY 31 in mid-January in Louisiana. After midFebruary grazing most symptoms disappeared. Luttrell (1951) in a disease survey carried on in Georgia in 1949 and 1950 indicated that fescue was subject to net blotch attacks during the winter and early spring. In summer, leaf blotch seemed to be by far the most serious. However, in 1953 Luttrell (1953) reports that Helminthosporium satiuitm did not cause any lesions on tall fescue. Kreitlow et al. (1950) report that tall fescue was susceptible to both H . dictyoides and H . sativurn. There appeared to be no resistance among varieties when three varieties were inoculated and observed for symptoms. Hardison (1945b) reported a new leaf spot on tall fescue in Kentucky, caused by a species of Cercospora. This particular disease was later reported by Whitehead and Holt (1950) in Texas. Hardison had reported the disease to be rather mild in Kentucky. At College Station, Texas, in the summer of 1949, one-year-old seedlings of KENTUCKY 31 were affected 10 per cent while those of ALTA were affected 30 per cent. These workers also offered an amended description and drawings of this organism. Resistance to crown rust was reported by Kreitlow and Myers (1947). Hardison (1945a) had observed tall fescue to be highly resistant

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to crown rust in Kentucky in September, 1942. ALTA, NY2659, and KY 31 were all inoculated with crown rust by Kreitlow and Myers. All varieties proved to be immune and highly resistant to crown rust. Varieties of meadow fescue varied in their degree of susceptibility. One selection from Maine was immune. Allison et al. (1949) found Rhizoctonia solani to cause a disease on ALTA. It was a limiting factor in the seedling establishment and persistence of this particular variety. Luttrell (1951) reported white mold (Sclerotium rolfsii), several Basidiomycetes, Curuularia, Fusarium species, Trichoderma, Thielauia, and Aspergillus also on tall fescue.

X. FUTURE OF TALL FESCUE Tall fescue has become of age and is now a major forage crop in the United States. From 1884 to 1930 favorable opinions were expressed by several agricultural writers of its potential value, but it was unable to replace such crops as timothy, orchardgrass, tall oatgrass, and redtop. With the simultaneous release of the two varieties ALTA and KY 31 in 1940, it was destined to become a major crop. Its growth in popularity during the last 15 years has been phenomenal, and possibly the fastest of any forage crop in the history of the country. Domestic consumption of seed went from a few thousand pounds in 1940 to 35 million pounds in 1954. This rapid rise to prominence has not been without errors. Enthusiastic promoters have referred to it as a “wonder grass.” It has been considered by some to be the means towards an end oE solving our pasture, silage, and conservation problems. Its shortcomings are no more numerous, when weighed against its virtues, than those of any other grass. It has been overpromoted and many of the criticisms leveled towards it have been justified. In spite of this, however, it has established itself as an integral component of forage crop programs in many sections of the country. It is classified as a cool season grass. It has produced considerable forage under the mild conditions of southern winters. However, it appears that when the species is more carefully studied it will be possible to make selections giving even greater winter growth. Such selections or unique varieties will have a real place in providing an almost year around pasture program throughout the southern part of the country as well as in certain areas of the Pacific Coast. Many desert areas being brought under cultivation are extremely alkaline. Tall fescue has shown itself to be a crop which can tolerate and produce readily in soil with a high pH. Survey work indicates that it has a great deal of promise in this connection. Further, it has shown considerable adaptability on saline areas typical of many of the intermountain grazing regions.

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It was introduced into western agriculture originally as a crop which would provide green grass through the long dry periods of summer. With the advent of irrigated pastures it soon became a n important and in many cases a major constituent of these pastures. It has not always been successful inasmuch as very dense luxuriant growth has been experienced under high fertility and with ample supplies of water. In many cases, owing to poor management of such luxuriant growth, ranchers and farmers have become critical of its value. There is a vast area of research which needs to be done by irrigation pasture specialists in order that this grass may be used to best advantage in this type of cropping practice. It is quite possible that the plant breeder will have to develop varieties particularly adapted for irrigation purposes. T h e toughness of this grass, its drought resistance, and dense deep sod, make it a n ideal cover for airports, playgrounds, athletic fields, and other areas where a durable, firm, wear-resistant turf is essential. It has been used with a reasonable amount of success in this manner. T h e variability w h k h exists between individuals in most tall fescue plant populations would indicate untold possibilities of selection for a more desirable turf type, than would be obtained by using either the varieties ALTA or KENTUCKY 31. It would be important to have a selection which would be aggressive and spreading i n nature and yet not too tall in overall growth. It should be reasonably easy to procure such selections once the plant breeders give this problem their attention. Its deep penetrating root system and rather rapid sod development make it a n excellent soil conserver. It has been used very successfully on waterways, eroding hillsides, gulleys, levies, and other areas where a long-lived tenacious deep-rooted grass is needed. It has been shown to be particularly valuable in some cases as a means of biological control of perennial weeds. This has been demonstrated i n Kentucky where wild onion, dock, and other pernicious weeds have been greatly reduced after tall fescue has been established. I n Oregon it has been noted that it will compete readily and practically eliminate in some cases wild onion, Canada thistle, wild morning glory, and quackgrass. Its potential in the field of conservation has hardly been tested. An ample supply of high-quality reasonable priced seed will insure stability of this crop. Seed production as a n enterprise must guarantee the producer a reasonable margin of profit. If the price is to be lowered so that the consumer can profitably plant the crop and expect reasonable returns per acre, the seed producer must be efficient and secure high seed yields. Tremendous losses have been experienced in the harvesting and processing methods of this particular grass as well as of others. There is need for research on this subject in order that the efficiency of seed harvesting and handling m a y be improved to a much

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higher degree than at present. The use of fertilizer, rates of seeding, length of stands for seed production, and many other cultural practices need to be explored more thoroughly. Plant breeders have already shown that seed yields well over 2000 pounds of seed per acre are not beyond the realm of possibility. Since 1950 more concern has been expressed over tall fescue poisoning or “fescue foot.” Although not too many reports have been forthcoming in the United States, it still is of grave concern to those investigators working with this particular crop. Many reports had been found to be extremely nebulous when an investigation has been attempted. However, the fact still remains that this is a characteristic of at least some type of tall fescue which certainly cannot be overlooked. The problem is of such a nature that veterinarians, livestock men, biochemists, agronomists, and plant breeders must give serious attention to it in the future. Tall fescue has been severely criticized by its critics for lack of palatability. This ciifficulty has been overcome to a measurable degree by certain management practices. There still remains much to be learned about the species in this connection. This will also be an everchanging area of study as new varieties become available, because they will probably react in different ways to various management practices. It appears evident at present that substantial improvement may be made by plant breeders in improving the palatability and the nutritional qualities of this particular crop. Therefore, it can be anticipated that the varieties of the future will have a higher degree of palatability and be more nutritious and more acceptable to the animal, so aiding the livestock man in more efficient production of milk, beef, and mutton. Tall fescue is a crop which has remained practically in oblivion throughout the rest of the world. In the United States it has proven itself and its future looks bright. Moreover, it offers a real challenge to agronomists if it is to remain an important integral part of our forage production program.

REFERENCES Allison, S. L., Sherwin, H. S., Forbes, I., Jr., and Wagner, R. E. 1949. Phytopathology 39, 1.

Atkins, J. G. 1950. Plant Disease Reptr. 34, 157. Bailey, R. Y. 1950. Better Crops with Plant Food 34 (9), 6 1 3 , 4.3. Bailey, R. Y. 1951. In “Forages.” (H. D. Hughes, M. E. Heath, and D. S. Metcalfe, eds.), pp. 327-334. Iowa State College Press, Ames, Iowa. Bailey, R. Y., and Scott, L. B. 1949. US.Dept. Agr. Leaflet No. 254. Banfield, G. L. 1953. New Zealand J . Agr. 07,433,435-436. Bayer, D.E. 1953. M.S. Thesis, Oregon State College.

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Blaser, R. E., Taylor, T. H., Griffith, W. L., and Hammes, R. C. 1954. Virginia Agr. Expt. Sta. Forage Crop Rept. No. 5. Brooks, 0. L. 1950a. Georgia Agr. Expt. Sta. Press Bull. 593 (revised). Brooks, 0. L. 195Ob. Proc. Assoc. Southern Agr. Workers 47, 184. Buckner, R. C. 1955. Ph.D. Thesis, University of Minnesota. Buckner, R. C., and Fergus, E. N. 1951. Proc. Assoc. Southern Agr. Workers 48, 65-66. Burton, G. W., and DeVane, E. H. 1953. Agron. J. 45,478-481. Carnahan, H. L., and Hill, H. D. 1955. Agron. J. 47,258-261. Chamblee, D. S., and Loworn, R. L. 1953. Agron. I. 45, 192-196. Chase, A. 1950. U.S. Dept. Agr. Misc. Publ. 200. Cowan, J . R. 1951. Agron. Abstr. 4. Cowan, J. R. 1952. Ph.D. Thesis, University of Minnesota. Cowan, J. R. 1953a. Rept. 7 t h Western Grass Breeders Work Planning Conf. p p . 3s35. Cowan, J. R. 1953b. Agron. Abstr. 82. Cowan, J . R. 1954. Rept. 8th Western Grass Breeders Work Planning Conf. p. 14. Cowan, J. R. 1955a. Rept. 9th Western Grass Breeders W o r k Planning Conf. pp. 2630. Cowan, J. R. 1955b. Oregon’s Agr. Prog. 3 ( l ) , 6 7 . Cowan, J. R., Weswig, P. H., Johnson, J. R., and Schubert, J. R. 1955. Agron. Abstr. 49.

Crowder, L. V. 1952. Ph.D. Thesis, Cornell University. Crowder, L. V. 1953a. Am. J. Botany 40, 348-354. Crowder, L. V. 1953b. Agron. I. 45, 453-454. Crowder, L. V. 1953c. J. Heredity 44, 195-203. Crowder, L. V., and Sell, 0. E. 1953. Crops and Soils 5 (I), 12-13. Cunningham, I. J. 1948. N e w Zealand J . Agr. 77 (5), 519. Fergus, E. N. 1958. Uniu. Kentucky Circ. No. 497. Fergus, E. N., and Johnstone, W. C. 1948. Proc. Assoc. Southern Agr. Workers 45, 29-3 I. Fondle, W. J. 1952. J. Soil Water Conservation 7, 177-183. Fortenbery, B. W. 1948. Kentucky Farmer 84 (3), 6-7,39. Freed, V. H., Bayer, D. C., and Furtick, W. R., 1952. Oregon Agr. Expt. Sta. Circ. Information No. 514. Furtick, W. R. 1952. M.S. Thesis, Oregon State College. Furtick, W. R., and Chilcote, D. 0.1955. Oregon Agr. Expt. Sta. Circ. Information No. 551. Gill, J. B., and Jones, U. S. 1951. Proc. Assoc. Southern Agr. Workers 48, 45. Goodman, A. A. 1952. J. Am. Vet. Med. Assoc. 121 (907), 289-290. Hafenrichter, A. L. 1953. westland Pasture 4 (4). Hafenrichter, A. L., Mullen, L. A., and Brown, R. L. 1949. U.S. Dept. Agr. Misc. Publ. No. 678. Hardison, J. R. 1945a. Plant Disease Reptr. 29, 76-85. Hardison, J. R. 1945b. Mycolgia 37 (4), 492-4439. Hill, D. D., and Harmond, J. E. 1955. Crops and Soils 8 (I), 27. Hitchcock, A. S . 1935. U.S. Dept. Agr. M i x . Publ. No. 200. Hodson, E. A. 1951. Better Crops with Plant Food 25 (4), 21-24,39. Hyer, E. A., Becker, M. H., and Mumford, D. C. 1949. Oregon Agr. Expt. Sia. Circ. Information No. 462. Jenkin, T. J. 1933. J . Genet. 28, 205-264.

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Jenkin, T. J. 1955a. J . Genet. 53, 81-93. Jenkin, T. J. 1955b. J . Genet. 53,94-99. Jenkin, T. J. 1955c. J . Genet. 53, 100-104. King, W. A., and Lamaster, J. P. 1950. J. Dairy Sci. 33, 389. King, W. A,, Lamaster, J. P., and Mitchell, J. H. 1953. South Carolina Agr. Expt. Sta. Bull. No. 410. Kreitlow, K. W., and Myers, W. M. 1947. Phytopathology 37, 59-63. Kreitlow, K. W., Sherwin, H. S., and LeFebure, C. L. 1950. Plant Disease Reptr. 34, 189-190. Leasure, J. K. 1952. Proc. Assoc. Southern Agr. Workers 49, 177-178. Luttrell, E. S. 1951. Plant Disease Reptr. 35, 83-85. Luttrell, E. S. 1953. Plant Disease Reptr. 37, 150-151. Luttrell, E. S., and Sell, 0. E. 1950. Proc. Assoc. Southern Agr. Workers 47, 178. Marlowe, T. J., Leveck, H. H., and Horn, L. 1951. Mississippi Farm Research 14 ( l o ) , 1, 8. McTaggart, A. 1937. J . Council Sci. Ind. Research 10 ( l ) , 17-27. McTaggart, A. 1941. J. Council Sci. Ind. Research 14 (2), 215-218. Myers, W. M., and Hill, H. D. 1947. Bull. Torrey Botan. Club 74, 19-111. Osborn, H. 1954. Oregon Agr. Ext. Circ. No. 573. Peto, F. H. 1934. J . Genet. 28, 113-157. Pratt, A. D., and Haynes, J. L. 1950. Ohio Farm and Home Research 35 (262), 10-11. Pulsford, M. F. 1950. Australian Vet. J . 26, 87-88. Rampton, H. H. 1949. Oregon Agr. Expt. Sta. Bull. No. 427. Rampton, H. H. 1950. Crops and Soils 2 ( 7 ) , 18-19,25. Reid, J. T., Woolfolk, P. G., Richards, C. R., Kaufman, R. W., Loosli, J. K., Turk, K. L., Miller, J. I., and Blaser, R. E. 1950. J . Dairy Sci. 33, 60-72. Richardson, G. L. 1951. Ph.D. Thesis, Oregon State College. Saxby, S. H. 1945. N e w Zealand Dept. Agr. Bull. No. 427. Sell, 0. E. 1950. Georgia Agr. Expt. Sta. Press Bull. No. 625. Sell, 0. E., and Crowder, L. V. 1949. Georgia Agr. Expt. Sta. Press Bull, No. 601. Spencer, J. T. 1950. Kentucky Agr. Expt. Sta. Bull. No. 554. Sutton, M. J. 1891. “Permanent and Temporary Pastures.” Simpkin, Marshall, Hamilton, Kent and Co. Ltd., London. Tabor, P. 1952a. Crops and Soils 4 (a), 9-1 1. Tabor, P. 1952b. Soil Conservation 18, 3 9 4 0 . Thompson, N. R., and Holdaway, C. W. 1954. I . Dairy Sci. 37, 666. Thompson, G. B., Dyer, A. J., and Guyer, P. Q. 1955. I . A n i m l Sci. 14, 1241. Vinall, H. H. 1909. U . S. Dept. Agr. Farmers Bull. No. 361. Wells, H. D., and Allison, J. L. 1952. Proc. Assoc. Southern Agr. Workers 49, 177. Wheeler, W. A., and Hill, D. D. 1957. “Grassland Seeds.” Van Nostrand, New York. Whitehead, M. D., and Holt, E. C. 1950. Phytopathology 40, 1023-1026. Whitesides, W. J. 1947. M.S. Thesis, Oregon State College.

The Mineral Nutrition of Corn US Related to Its Growth and Culture LEWIS B. NELSON

United States Department of Agriculture. Beltsuille. Maryland

I. Introduction . . . . . . . . I1. Nutrient and Water Absorption by Corn 1. The Corn Root System . . . a . Zone of Absorption . . . b . Influence of Soil Moisture . c. Influence of Soil Fertility . 2. Forms of Nutrients Absorbed .

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3. Effect of One Ion on the Uptake of Another 4. Effect of Environmental Factors . . . . 5. Effect of Inheritance . . . . . . . . I11. Foliar Absorption of Nutrients . . . . . . . IV. Growth and Accumulation of Dry Matter . . . . V Accumulation and Movement of Elements within the 1. Translocation during Growth . . . . . . 2. Elemental Composition and Protein Content . a . Mineral Composition of the Mature Plant b . Protein Quantity and Quality of Grain . c. Composition of Leaves . . . . . . d . Plant Tissue Tests . . . . . . . e. Expressed Fluids and Sap . . . . . VI . Symptoms of Nutritional Disorders . . . . . VII . Effect of Fertilizers on Nutrition and Growth . . 1. Localized Placement at Planting . . . . . 2 Application of Large Amounts of Fertilizer . 3. Effect of Liming . . . . . . . . . VIII . Influence of Plant Population . . . . . . . I X. Effect of Soil Moisture on Nutrition and Growth . I As Influenced by Soil Fertility . . . . . 2 As Influenced by Moisture Stress . . . . Acknowledgment . . . . . . . . . . . References . . . . . . . . . . . . .

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I. INTRODUCTION Corn. Zea mays. L., ranks as one of the most important agricultural crops of the world . About 220 million acres are devoted to its produc321

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tion. The United States, which produces over 50 per cent of the world‘s crop, plants annually over 80 million acres. It is grown on over twothirds of all farms and occupies about 25 per cent of all crop land in this country. As might be expected with a crop of such great economic importance, a tremendous research effort has been expended and a very large body of scientific literature has accumulated. It is the purpose of this review to attempt to bring together and examine the more pertinent literature dealing with the field of mineral nutrition and growth of corn, particularly as it relates to various cultural aspects of corn production. The nutrition of corn first received attention by the American Indians, probably well in advance of the introduction of the plant into Europe. Not only did the Indians develop varieties adapted to various climatic and soil conditions as well as for special purposes (Weatherwax, 1923; Erwin, 1949), but they recognized the value of soil amendments. The latter is evidenced by this statement attributed to Captain John Smith (Carrier, 1923): “In Virginia they never manure their overworne fields . . . but in New England they doe, sticking at every plant of come a herring or two.” Rapid adoption of this practice by the settlers of New England is indicated by an observation in 1632 (Carrier, 1923): “There is a Fish that at the spring of the year . . . are taken in such maltitudes in ever river . . . that the inhabitants dung their ground with them . . . an acre thus dressed will produce and yield so much corne as 3 acres without fish . . . . Earliest investigations with corn dealt not with mineral nutrition and growth but primarily with the water, starch, ash, gluten, zein, sugar, fat, gum, and fiber contents of corn grain. Large numbers of varieties were analyzed and compared. The first report appears to be that of Gorham (1821) of Harvard University. Other early American investigators were Salisbury (1848) of New York, and Atwater (1869) of Yale. European investigators were numerous and included Boussingault (1836), Horsford (1846), Polson (1855), Poggiale (1856), Steph (1859), and Fresenius ( 1859). Boussingault made determinations of the nitrogen content and pointed out the possibility of variations in the chemical constituents of the grain as being due to climatic factors. Weiske (1879) included determinations of phosphorus and sulfur in his feed analyses of corn. In the light of present knowledge, these early investigations are of historical interest only. Modern investigations on mineral nutrition of corn apparently originated with Hornberger of Germany (1882). Probably one of the most comprehensive studies ever published upon the accumulation and movement of various organic and inorganic materials in the developing corn plant is his 164-page treatise. It would appear that this work rep9,

323 resents the first great forward step in advancing our knowledge of the nutrition of corn. Hornberger’s investigations initiated a line of research that has been actively pursued to the present. A goodly portion of the extensive scientific literature on corn has been indexed in the Maize Bibliography of the Iowa Corn Research Institute (Iowa Agricultural Experiment Station, 1941, 1948, 1951). MINERAL NUTRITION O F CORN

FIG.1. Root systems of 6-weeks-old corn; A, dry land; B, lightly irrigated; and C. fully irrigated. Note the predominantly lateral growth at this stage, and the greater development under dry conditions. Reprinted from Jean and Weaver (1924).

11. NUTRIENT AND WATER ABSORPTION BY CORNROOTS The uptake of nutrients and water by corn roots is influenced by many factors ranging from the rate of growth and location of the roots in the soil to the influence of one ion upon the entry of another. Many interrelationships and interactions exist between the various factors, all of which influence: directly or indirectly, the ability of the corn plant to absorb the nutrients and water essential to its growth. 1 . The Corn Root System The nutrients and water absorbed by the corn plant are dependent in many ways upon the extent and character of the root system. The

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latter may vary greatly between varieties, and with the conditions under which the plant is grown. The fertility, moisture content, aeration, texture, structure of the soil, the placement of fertilizers, and the effect of root diseases may all influence the absorptive efficiency of the roots. a. Zone of Absorption. The zone occupied by the corn root system is related to the stage of development of the plant (see Figs. 1 and 2).

FIG.2. The root system of a maturing corn plant showing the large zone from which the roots may absorb moisture and nutrients. Reprinted from Weaver et al. (1922).

Until the plant has its seventh or eighth leaves, the roots take a course parallel or almost parallel to the surface of the soil and seldom penetrate more than a foot in depth (Hays, 1889; Ten Eyck, 1889; Weaver et at., 1922; Hall et at., 1953). In fact, most of the roots occur in the layer from 3 to 6 inches from the surface. Thus, fertilizer placed on either side of the seed and slightly below will be in direct line of growth and should be available for earlier absorption than fertilizer placed directly below or above the seed (Millar, 1930, 1933). By the time the plants are about 4 feet high, the lateral roots may

325 have extended to a distance of 2 to over 3 feet from the base of the stalk, where they usually turn down rather abruptly. Penetration of these roots may range from 1.5 to over 4 feet. A number of younger roots run almost vertically downward or spread laterally a few inches and turn downward. These may have penetrated to a depth of 4 or 5 feet a t this stage (Weaver et al., 1922). As the corn approaches maturity, the roots tend to branch and grow deeper. The maximum spread of the main roots at maturity often is about 3.5 feet in all directions from the stalk, while the maximum penetration may range from 5 to 8 feet under favorable soil conditions (Hays, 1889; Ten Eyck, 1889; Weaver et al., 1922). King (1893) found at tasseling that corn roots “have fully occupied the upper 3 feet of soil in the entire field.” The depth of penetration and the pattern of root growth is dependent upon the characteristics of the soil. Friable well-drained soils favor greater penetration than compact or poorly aerated soils. For example, Fehrenbacher and Snider ( 1954) observed penetration in a friable Muscatine silt loam to a depth of 7 feet. In an Elliot silt loam underlaid at 24 to 28 inches by a silty clay loam glacial till of high volume weight, poor structure, and low aeration, there was little penetration below about 28 inches except through a few cracks. Dry matter weights of roots in the Muscatine soil was 2008 pounds per acre, 70.7 per cent of which was in the upper 10 inches, 19.5 per cent from 10 to 30 inches, 7.5 per cent from 30 to 48 inches, and 2.3 per cent from 48 to 72 inches. In the Elliot, there were 2224 pounds of roots per acre with 55.5 per cent in the upper 8 inches, 41.5 per cent from 8 to 28 inches, 3.0 per cent from 28 to 48 inches, and none below. Russell et al. (1940) studied the pattern of moisture extraction in the field and noted that corn roots first absorbed moisture at a shallow depth directly beneath the corn hills. Then, the zone of absorption extended laterally until most of the moisture at that depth was depleted. As the growing season progressed, the moisture absorption occurred at successively lower depths. Howe and Rhoades (1955) also observed the increased depth of moisture removal as the season advances. On a permeable fine sandy loam irrigated to field capacity before planting, 35 per cent of the available water remained in the upper 6 inches of soil on July 4, at which time the plants were about 36 inches high. All the available water was removed from the surface 6 inches by July 14, from the upper 30 inches by July 31, and from 42 inches by October 13. Weaver et al. (1922) found that the absorption of water and nitrates at the various depths is directly correlated with the abundance of roots and the time the roots were present and active at the various levels. Their investigations showed clearly that in studies of soil ferM I N E R A L N U T R I T I O N O F CO RN

326 LEWIS B. NELSON tility more than the surface soil must be taken into account. Millar (1930, 1933) also noted that the lower root system of corn can absorb available nutrients when present. He obtained inferior growth of corn on subsoils but this was due largely to the lack of available nutrients. Woodruff and Smith (1946) obtained small but significant yield increases from applying lime and fertilizers in mechanically shattered claypan subsoils. Hall et al. (1953), using a technique for studying root distribution and activity by injecting radiophosphorus into the soil at various depths and distances from the plant, found that phosphorus placed at a depth of 3 inches contributed half of the plant’s supply of fertilizer phosphorus through the first 7 weeks and over one-third throughout the growing season. Phosphorus placed at a depth of 8 inches contributed about one-third, and the remaining third came from that placed at 13 to 18 inches. On the basis of their data, they conclude that corn can draw upon a large volume of soil for nutrients and moisture, and that ordinary methods of shallow fertilizer placement are relatively insignificant except during early growth. Also, it appeared that cultivation may cause root injury and reduce nutrient uptake, and that later side-dressing applications of fertilizers do not have to be placed at any particular location between the rows for greatest efficiency. b. Influence of Soil Moisture. Corn grown under conditions of relatively low soil moisture conditions has a larger root system with a greater absorbing surface than that grown under more nearly optimum conditions (Kiesselbach, 1910; Jean and Weaver, 1924; Miller and Duley, 1925). Also, under drier conditions, the root laterals are more abundant, longer, and more profusely branched, and there is a tendency for them to turn downward faster. Corn roots, like those of most crop plants, cannot readily penetrate a layer of very dry soil, even though a satisfactory moisture supply may exist below (Shantz, 1927). The corn root system apparently can absorb moisture from a zone of moist soil and exude it into a zone of very dry soil, thus causing a moisture build-up to the point where some growth and nutrient absorption can take place in the dry soil. Brezeale (1930) observed moisture transfer from moist to dry soil by the brace roots of corn. Volk (1947) divided the corn root system between soil dry to near the permanent wilting point and soil adequately supplied with moisture and noted some moisture translocation and root growth into the dry soil. The roots in the dry soil were able to absorb nitrogen and potassium but little if any phosphorus. Hunter and Kelley (1946) grew corn for 30 days in tar-paraffin pots filled with moist soil and surrounded with dry soil below the wilting point. The roots penetrated into the dry soil and

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a build-up of moisture occurred therein. However, the moisture level in the dry soil never reached values as high as the wilting point. Although radiophosphorus was present in the dry soil, none could be detected in the plant. Where the surface soil is of higher than optimum moisture content, the corn plant roots may be largely confined to the surface foot of soil. The roots tend to develop more horizontally, the lateral spread is less, and branching is much less pronounced (Jean and Weaver, 1924). Davis (1940) found that a newly developing corn plant extracts the available moisture from the soil near its base and, as the wilting percentage in this area is approached, the plant is maintained by the extension of its roots into moist soil. I n uniformly moistened soil, roots of established plants absorbed moisture first near the plants and later farther from them. The growing roots also extracted water below the wilting percentage in the vicinity of the plant, while 2 to 4 feet away the roots were absorbing moisture at a level midway between wilting percentage and field capacity. The distant water, however, was eventually absorbed. c. Influence of Soil Fertility. Where corn roots come in contact with a fertilized layer in the soil they generally develop more abundantly and branch more profusely (Nobbe, 1862; Weaver et al., 1922). Haveler (1892) grew corn plants in containers with alternate layers of sand and fertile soil. The roots in the fertile soil branched profusely but in the sand little branching occurred. Pettinger (1933) found that fertile soils were more favorable to corn root development than infertile soils, and that corn grown in rotation with other crops had a greater root growth than corn grown continuously. He also found that applications of both phosphorus and potassium exerted a beneficial effect upon the root development and anchorage of corn grown on a soil deficient in these elements. Superphosphate was much more effective than rock phosphate in this respect. Fehrenbacher and Snider (1954) observed that liming, fertilizing, and turning under of legumes induced root penetration and development into lower soil horizons. Plants on comparable untreated plots, however, were much smaller. Corn is unable to attain maximum absorption of nutrient elements through only a portion of its roots, even though the absorptive capacity of those roots in contact with the nutrients may be greatly increased. This has been demonstrated clearly by experiments performed by Gile and Carrero (1917, 1921). In one experiment they grew corn with half the roots maintained in a complete nutrient solution and half in a nitrogen-free solution. These plants made noticeably less growth than normal plants having all of their roots in a complete nutrient solution and absorbed only three-fourths as much nitrogen. The portion of the

328 LEWIS B. NELSON roots in the complete solution, however, absorbed 1.48 times more nitrogen per gram of roots as the normal plants. Total plant growth and assimilation of nutrients were roughly proportional to the extent the nutrients were restricted to separate portions of the roots. Spencer (1937) also noted a lack of growth when he divided the roots of monthold corn into three parts and supplied nitrogen, phosphorus, and potassium to them in separate compartments. On the basis of the above observations, one might doubt the desirability of localized application of fertilizers in soils extremely deficient in nutrients. 2. Forms of Nutrients Absorbed

Undoubtedly a considerable portion of the nitrogen absorbed by field-grown corn is in the form of nitrates, since nitrification usually takes place at a fairly rapid rate in most soils. Corn, however, apparently can absorb and use appreciable amounts of ammonium nitrogen. Viets et al. (1946) grew corn plants, previously depleted in soluble nitrogen compounds and showing nitrogen deficiency symptoms, upon a complete nutrient solution containing ammonium sulfate. The plants absorbed the ammonium nitrogen and continued to increase in weight. Although the plants increased in amino nitrogen, they did not synthesize protein appreciably, suggesting that some nitrate nitrogen may be necessary. Pantanelli and Severini (1910, 1911) believed that the potential nutritive value of ammonium salts was superior to nitrates, inasmuch as these could be utilized more easily in the synthesis of organic nitrogen compounds. Evidence that significant amounts of the ammonium ion can be absorbed and utilized also has been found by Hoerner and DeTurk (1938). The proportion of nitrate to ammonium nitrogen absorbed varies with the conditions of the substrate. Loo (1931) noted that much more ammonia than nitrate nitrogen was absorbed by corn seedlings in nutrient solutions containing relatively high amounts of ammonium nitrate. At low ammonium nitrate concentrations, more nitrate than ammonium nitrogen was absorbed. Mevius (1928) found that corn supplied with ammonium salts grew well if the culture solution pH was maintained between 3.5 and 7.0, but above this range the internal solution of the plant became alkaline, excessive quantities of ammonia were absorbed, and growth was depressed. Naftel (1931 ) and Wadleigh et al. (1937) have observed that young corn plants absorb the ammonium ion more readily than the nitrate ion and that nitrate is absorbed more readily by older plants. Best growth of the plants, however, resulted when both were present. That nitrites can be absorbed and utilized by corn is demonstrated by experiments of Mwius and Dikussar (1930). In these, sweet corn

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was able to utilize nitrites i n neutral and alkaline solutions. An increase of nitrates by two- to threefold in the nutrient solution caused only a slight increase in the nitrogen content of the plant. Increasing the nitrite nitrogen, however, resulted in a rapid assimilation and increase in the nitrogen content. Brigham (1917) believed from his work that corn may be able to assimilate directly and take part of its nitrogen from a number of organic sources including asparagine, casein, cottonseed meal, hemoglobin, linseed meal, uric acid, peptone, guanine, alanine, urea, creatine, malt, and glycine. Whether sterile conditions were maintained throughout the experiment, however, might be open to question. Results of numerous field experiments in which different sources of nitrogen fertilizer have been compared indicate only small differences in the efficiencies of the various sources (Krantz and Chandler, 1954; Chandler, 1952; Williamson et al., 1927). Even though the original chemical forms may differ greatly in their composition, nitrification proceeds rather rapidly under favorable soil and temperature conditions. Thus, the chemical form in which the nitrogen is applied usually does not influence growth materially or consistently. The corn plant apparently absorbs and utilizes phosphorus largely i n the form of inorganic phosphates. In contrast to alfalfa or the clovers, it is incapable of obtaining much of its phosphorus from relatively insoluble inorganic phosphorus carriers. Bauer (1921 ) grew corn in quartz sand with rock phosphate and obtained only 42 per cent of the dry weight produced with mono-calcium phosphate. The percentage of phosphorus in the plants was much higher where the soluble phosphate was used. Dickman and DeTurk (1940) found that plants grown on gravel cultures made up entirely of rock phosphate were limited in growth and their phosphorus composition was about half that of plants having a soluble phosphorus source. Hall et a2. (1949) observed that the percentage of phosphorus i n the corn plant derived from application of alpha-tricalcium phosphate was lower than from either superphosphate or calcium metaphosphate. There has been some evidence presented indicating that corn can utilize certain organic phosphorus compounds to a limited extent. Rogers et al. (1940) report that both phytin and lecithin were absorbed directly from nutrient solutions by corn. The rate of uptake of phytin approached that of KH,PO,, but lecithin was absorbed more slowly. They believed that neither of these two compounds was hydrolyzed by enzymes occurring on the exterior of the plant roots. Nucleic acid, nucleotides, and calcium glycerophnsphate were decomposed when placed in contact with corn roots in nutrient solutions, yielding inorganic phosphorus. Sodium and potassium salts of phytic acid, nucleic

330 LEWIS B. NELSON acid, and glycerophosphate, as well as the calcium salts of hexose monoand diphosphates, have been indicated by Weissflog and Mengdehl (1933) as available to corn grown in acid nutrient solutions under sterile conditions. Eid et al. (1954), on the basis of their research, believe that soil organic phosphorus is of little or no value in the phosphorus nutrition of corn and that it becomes of value only when changed to the inorganic form. Potassium is easily absorbed by the corn root system from soluble and easily replaceable inorganic sources. Tyner (1935) noted that corn is a poor feeder on feldspathic potassium, a material of low solubility. Studies by Leonard and Bear (1950), Truog et al. (1953), Larson and Pierre (1953), and Cope et al. (1953) show that corn absorbs very little sodium even when this element is present in the substrate in appreciable quantities. As a general rule, sodium salts do not materially increase the growth of corn, nor does there appear to be any notable substitution of sodium for potassium within the plant. Sodium applications on some soils may result in small growth increases but this probably results from the sodium replacing potassium in the soil through cation exchange which increases the concentration of potassium in the soil solution. The corn plant seems capable of absorbing certain soluble carbohydrates through its root system and then utilizing these materials in its metabolism. Laurent (1904) and Mazd and Perrier (1904) all found that corn could absorb and utilize glucose. Experiments conducted by Knudson (1916) indicate that glucose, fructose, saccharose, and maltose increased the dry weight of corn in the order listed. Robbins and Maneval (1924) observed that excised corn roots grew well in the dark in a solution containing minerals and glucose and fructose. Without the sugars, they made little growth. Knudson and Lindstrom (1919) carried out experiments with albino corn plants and obtained a sustained growth on a 0.2 M sucrose solution in addition to Pfeffer’s solution over a 55-day period. Plants growing on the mineral solution alone perished at the end of 30 days. Although the plants growing in the sugar solution died at the end of 55 days, their roots remained alive for several months after all the check plants had perished. Mazd and Mazd (1939) found that corn could absorb considerable sucrose from a 1 per cent solution, but very little from 2 to 4 per cent solutions. Duley and Miller (1921 ) observed that corn plants seem incapable of absorbing excessive amounts of calcium and magnesium even when there is a large supply. Taylor (1954), however, was able to increase the magnesium absorption several-fold through increasing the magnesium level of nutrient solutions. Liming of soils has been found to increase the calcium and magnesium absorption only slightly (Weeks

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and Fergus, 1946; Weeks et al., 1940; Stubblefield and DeTurk, 1940). Eisenmenger and Kucinski (1941) found that magnesium was more easily introduced into the plant tissue than was calcium when additional amounts were added to the soil.

3 . Effect of One Ion on the Uptake of Another

A number of ion relationships affecting the absorption of nutrients have been demonstrated with corn. Beckenbach et al. (1938) showed that the nitrate ion concentration in the substrate directly affected the calcium content of the corn tissues, high calcium in the tissues being associated with high nitrates in the substrate and low calcium with low nitrate. Magnesium uptake, also, appears directly affected by variations in the nitrate ion concentration (New Jersey Agricultural Experiment Station, 1938). Wadleigh and Shive (1939) noted that the ammonium ion depressed calcium and potassium absorption and, to a lesser degree, magnesium absorption. Tyner and Webb (1946) also observed a lowered potassium content in the leaves of field grown corn following application of ammonium sulfate fertilizer. Phosphorus absorption appears relatively unaffected by variations in the concentration of other ions in the substrate (Beckenbach et al., 1938; New Jersey Agricultural Experiment Station, 1938; Tyner and Webb, 1946; Glover, 1953b). Potassium interferes competitively with the absorption of a number of ions. Wadleigh and Shive (1939) and Thomas and Mack (1939) found that high potassium absorption depressed the absorption of calcium and magnesium. Stanford et al. (1941) added potassium to a soil high in calcium and magnesium carbonates and observed lowered calcium and magnesium uptake. Tyner and Webb (1946) noted that potassium fertilization depressed the nitrogen level in the leaves and intensified nitrogen deficiency symptoms. Dumenil and Nelson ( 1948) obtained a lowered corn yield response from ammonium sulfate fertilizer on a soil high in potassium when potassium fertilizer was also applied. DuToit (1947) obtained somewhat similar results in South Africa, and Ohlrogge ( 1944) noted that potassium additions intensified nitrogen deficiency symptoms on corn growing on nitrogen-deficient soils. Glover (1953a), on the other hand, found no interference between potassium and nitrogen nutrition in sand cultures with potassium levels ranging from 5 to 45 p.p.m. Boron and potassium absorption appear closely related, according to Reeve and Shive (1943). They observed that boron absorption increased as the potassium concentration in the substrate was increased. Also, they

332 LEWIS B. NELSON noted that the boron concentration had little influence on the total amount of calcium absorbed. Sulfur absorption is inversely related to variations in the concentrations of calcium and nitrate ions in the substrate, high sulfur content of corn tissues corresponding to low concentrations of calcium and nitrate, and low sulfur to high calcium and nitrate (Beckenbach et al., 1938; New Jersey Agriculture Experiment Station, 1938). Taylor (1954) found that increasing the magnesium content of the substrate decreased the uptake of sulfur. Barbier (1936) observed that increasing the potassium concentration of the nutrient medium favored sulfur absorption. A phosphate-manganese relationship was noted by Snider (1943). He found that applications of phosphate fertilizer increased the manganese content of the corn plant. Superphosphate was more effective in this respect than rock phosphate. Viets et a2. (1953) observed that applications of phosphorus did not induce zinc deficiency symptoms or restrict zinc uptake as shown by leaf analysis. Zinc-deficient plants were found to be high in phosphorus, potassium, copper, and frequently manganese, but this resulted from a high external supply of these elements in relation to the restricted plant growth induced by the zinc deficiency. The unequal absorption of cations and anions by the corn plant is brought out by the work of Redfern (1922). She grew corn plants in tap water and then transferred them to various solutions of calcium chloride. Her data show that absorption of calcium is considerably in excess of the absorption of the chloride. The difference in rate of absorption of the two ions was found to lessen as the solution became more dilute, becoming almost nil in solutions of %ooo N . Unequal absorption of the ions in ammonium nitrate, ammonium chloride, and ammonium sulfate has been observed by Rllazk et al. (1935). The ratio of cation to anion varied also with different concentrations of the salts. 4 . Effect of Environmental Factors Limited research, as reviewed by Richards et al. (1952), indicates that soil temperatures influence the absorption of nutrients by plant roots and that the temperature effects vary between plant species. Only one study was found dealing with corn. Zamfirescu (1936, 1937) grew corn in sand cultures maintained at temperatures ranging from 40 to 490 C. He found that the effect of temperature is different for the optimum absorption of nitrate nitrogen than for ammonium nitrogen. Below 1 8 O and above 4 4 O C., the nitrate was absorbed more easily than the ammonium nitrogen, whereas the latter was absorbed more rapidly between 1 8 O and 4 4 O C. Potassium was found to penetrate the plant

333 with a n intensity 9 times as strong at 32O as at 4O C. Phosphorus was 8 times as strong and calcium twice as strong. Brewer and Bramley (1940) report that plants stunted in their early growth by a nutrient deficiency took up very little sodium or phosphorus from the substrate owing to an impairment which began in the root system and gradually extended up the stalk. Absorption of sodium and phosphorus was very low when the plants were in the dark but increased rapidly on exposure to light. Low temperatures and an atmosphere of carbon dioxide decreased the uptake. Hayward and Spurr (1943) observed that the water intake was reduced between 79 to 82 per cent when the osmotic pressure of the nutrient solution was increased from 0.8 to 4.8 atmospheres. Soil aeration has a marked effect upon nutrient absorption by corn. Lawton (1945) found that decreasing the total pore space in the soil occupied by air by increasing either the soil moisture or the degree of soil compaction resulted in the following order of reduction of nutrient absorption: K > Ca > Mg > N > P, and forced aeration greatly increased the amount of potassium absorbed, the order being K > N > Ca > Mg > P. Lawton states “ . . . the conditions of soil aeration present during the growing season may limit the growth and absorption of potassium by corn. These conclusions would explain why large field response to potash fertilizers is obtained on poorly-drained soils which contain a relatively high level of exchangeable potassium.” Bower et al. (1944), observing nutrient uptake of corn under different tillage practices, noted decreased potassium absorption under tillage conditions conducive to poor aeration. MINERAL NUTRITION O F CORN

5 . Effect of Inheritance There is considerable evidence indicating a relationship between nutrient absorption and inheritance. The relationship, except for size of root system, seems far from being well defined. DeTurk et al. (1933) studied the response of two corn hybrids on a phosphorus-deficient soil to treatments with and without superphosphate. One hybrid exhibited a pronounced response to phosphate fertilizer, whereas the other failed to respond appreciably. Where phosphate was not applied, the nonresponsive cross maintained a higher total phosphorus concentration in the plant during active vegetative growth than did the responsive cross, indicating a greater ability to absorb phosphorus from the limited supply available. Kurtz et al. (1949) compared two single crosses in alternate rows on plots having different treatments of fertilizer and water. One hybrid yielded poorly under unfavorable levels of nitrogen and water, but under adequate levels, both yielded equally well.

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LEWIS B. NELSON

Smith (1934), with nutrient solutions, and Lyness ( 1936), with sand cultures, studied the behavior of a large number of inbred lines and hybrids to varying supplies of nutrient.s. Greater differential responses were found among corns grown with varied phosphorus concentration than with varied nitrogen concentration. Burkholder and McVeigh (1940) observed differential response between lines and hybrids to higher increments of nitrogen in sand cultures. All hybrids exceeded either one or both inbred parents in dry matter produced under conditions of high nitrogen. Sayre (1952b) noted fivefold differences or more in the amounts of mineral elements in the leaves of different corns, especially inbred lines. Some inbreds failed to accumulate enough of certain elements to prevent deficiency symptoms even when grown under average soil fertility conditions. The importance of a large root system in the absorption of phosphorus from nutrient solutions has been variously noted (Shank, 1945; Kiesselbach and Weihing, 1935; Rabideau et al., 1950; and others). Kiesselbach and Weihing found, upon hybridization, that .the depth of penetration, the combined length of all main roots, and their diameter increased materially in the first generation, while in the second they were intermediate. Evidence of the influence of long-continued selection on the type of root system is indicated by observations of Collins (1914). He found a type of corn grown by Indians in New Mexico and Arizona which was peculiarly adapted for survival in extremely arid regions. The corn developed a greatly elongated mesocotyl which permitted deep planting in order to contact moist soil. It also produced a single seminal root or radicle which was capable of descending rapidly to moist subsoil in order to supply water during the critical seedling stage. Miller et al. (1950) report that Mexican corns are capable of yielding under more adverse soil fertility conditions than are encountered in the United States. They believe that the process of selection for low soil fertility conditions in Mexico has probably resulted in survival of corn varieties which will produce ears (however small) under low nutrient conditions where American corns would become barren. Fertilizer response data obtained would indicate that the Mexican corns are not capable of utilizing high levels of available nutrients.

111. FOLIAR ABSORPTION OF NUTRIENTS Corn plants can utilize nitrogen from urea solutions applied to the leaves as spray; however, all but small amounts cause burning. Hinsvark et al. (1953) reported marginal leaf burn from solutions containing as little as 4 to 6 pounds of urea per 100 gallons of water. Shubeck

335 and Caldwell (1949), Foy et al. (1953), and Chesnin and Shafer (1953), using solutions of 20 pounds or more of urea per 100 gallons, all obtained burning, the severity of which increased with concentration. Mixing sucrose with the solution and increasing the drop size reduced burning to some extent. I n no instance, however, was it possible to apply nominal rates of from 20 to 40 pounds of N per acre without injury. Neither did urea sprays produce a yield benefit over the same amounts of nitrogen applied to the soil as side-dressings. Limited data indicate that corn may be about intermediate among crops in sensitivity to injury from urea sprays. Hinsvark et al. (1953) found cucumber leaves more susceptible to injury than bean, tomato, and corn, while celery and potato were less susceptible. They believed that utilization of urea nitrogen by leaves results from hydrolysis of the urea by the enzyme urease to give ammonia and CO,. The foliage injury appears to be due to rapid hydrolysis, possibly induced by high urease activity, resulting in a toxic accumulation of ammonia. Using (?,-labeled urea and the evolution of the radioactive C14 as a measurement of urease activity, they noted that hydrolysis of urea on sweet corn leaves was complete within a few hours after application. Boynton (1954), however, questions the urease hydrolysis hypothesis of Hinsvark et al. as follows: “This is a plausible conjecture but direct evidence on urease activity and ammonia concentration is needed before it can be taken seriously.” Although the use of other nitrogen carriers as foliar sprays for corn has not been investigated, most of them are known to cause leaf injuries at concentrations below that of urea (Boynton, 1954). Phosphorus also can be absorbed through the foliage and utilized by the corn plant. Oliver ( 1952), using irradiated superphosphate on month-old plants, found that the phosphorus was readily absorbed and translocated into all parts of the plant, being greatest in the rapidly growing parts. Wittwer and Lundahl (1951) observed that corn leaves were efficient organs in the absorption of phosphorus, particularly the leaf sheaths. Silberstein and Wittwer ( 195I) observed growth increases from several phosphorus compounds under greenhouse conditions. Ortho-phosphoric acid at 25 mM. per liter was one of the best treatments; however, it was not as effective as phosphorus added to the nutrient medium and absorbed by the roots. Spray applications of 0.5 per cent ZnSO, solutions applied to the foliage have been found to overcome chlorosis and restore vegetative growth on calcareous soils in central Washington (Viets, 1951; Viets et al., 1953). Grain yields were not increased, inasmuch as plants affected during early growth frequently produced normal plants regardMINERAL NUTRITION OF CORN

336

LEWIS B. NELSON

less of treatment. ZnSO, applied to the calcareous soil was much less effective in overcoming the deficiency, even though large amounts of zinc were absorbed by the plants. Boynton (1954)suggests certain criteria for determining the feasibility of nutrition by foliar application: “The usefulness of foliar application of nutrients depends on the following circumstances: ( a ) The existence of special problems that may not be coped with as well by application of the fertilizer to the soil or by soil management. (b) Satisfactory plant responses to the nutrient spray. These are mostly determined by the amount of the nutrient required by the plant, the efficiency of foliar absorption and use, and the tolerances of the leaves to the nutrient compounds available for use. (c) Economic materials and methods of application.” Of the three elements studied on corn, only zinc applied to corn growing on calcareous soils would meet Boynton’s specifications.

IV. GROWTH A N D ACCUMULATION OF DRYMATTER The accumulation of dry matter in the corn plant tends to follow the characteristic sigmoid-shaped curve (Bair, 1942).Dry matter production is slow immediately following seedling emergence and then accelerates rapidly until the end of the first 40 or 50 days. For the next 50 to 60 days, dry matter accumulates rather uniformly, but drops off rapidly as maturity is approached. Jordan et al. (1950) observed that dry matter elaboration approached linearity when large amounts of nitrogen fertilizer were applied. Sayre (1948) in Ohio found the maximum rate of dry matter production between July 26 and August 4, during which time tasseling and silking took place and increase in height had ceased. At tasseling and silking, approximately one-half of the final dry weight of the plant had been produced. The maximum weight of the leaves and stalks was reached about August 22, although the maximum leaf area had occurred earlier. After grain formation started, all of the dry matter produced passed into the grain with only a little loss from the other tissues of the plant except the husks. Sayre’s data for dry matter production are shown graphically in Fig. 3. Miller (1943) in Kansas noted, during the first week following emergence, that leaves accounted for almost 100 per cent of the dry matter of the plant. During the second week, the stem began to contribute a larger proportion of the weight and between the eighth and ninth week the stem and the leaves comprised an equal portion of the total dry weight. During the next five weeks, the dry weights of the stems increased rapidly, much faster than the leaves. The ear reached

337 its maximum dry weight at the end of the 14th week, while the husks attained this maximum at the close of the 13th week. As maturity was approached, leaves accounted for 20.5 per cent, the stem 34 per cent, and the ear 32 per cent of the total dry weight. Kiesselbach (1950) found that leaf area increased in a sigmoid-shaped curve from emergence until about silking, after which leaf growth stopped abruptly. He observed that total leaf area in typical corn fields with two plants per 42-inch spaced hills averaged 1.64 acres of leaf area per acre. Plant height and root growth tend to parallel each other. Kiesselbach's (1950) measurements showed height growth to follow the characteristic sigmoid curve during the vegetative period, while Sayre MINERAL NUTRITION OF CORN

JUNE

JULY AUGUST SEPT. SAMPLING DATES 3-DAY INTERVALS FIG.3. The height and dry matter production of corn at Wooster, Ohio, in 1940. (After Sayre, 1948.)

-

(1948) observed that it followed practically a straight line. Both reported an abrupt ending of height growth at about tasseling and silking. Root growth apparently is most rapid in the period preceding tasseling and silking. Loomis (1935) reported that plants developing normally made comparatively little root growth after this time. Weihing (1935) observed that the full number of functional roots were attained at tasseling; however, the length and depth of penetration of the main roots increased to maturity. The growth of the corn plant can be divided into four cycles, according to Pearl and Surface (1915). The first, or root cycle, is marked by a rapid increase in the root system, the second by a rapid increase in leaf area, the third by the development of the reproductive organs, and the last by the development of the ear and its maturation.

338

LEWIS B. NELSON

V. ACCUMULATION A N D MOVEMENT OF ELEMENTS WITHIN

PLANT The corn plant requires large amounts of the major nutrients (N, P, K, Ca, Mg, S ) for its development plus smaller but equally important amounts of a number of minor elements (Mn, Fe, B, Cu, Zn, Mo). The THE

approximate quantity of each element required, the pattern of its translocation within the plant during growth, and the final effects upon the composition and quality of the crop all have an important bearing in the determination of the nutrient needs of the crop and in developing and evaluating fertilizer and management practices.

1. Translocation during Growth Buckner (1915) found that approximately two-thirds of the mineral elements in corn seed were translocated into the roots and above ground portions of the seedling. These were sufficient to sustain growth for 23 days following germination, after which the seedlings began to etiolate. There were no very striking differences between the percentages of phosphorus, calcium, magnesium, and silica translocated from the seed; however, the translocation of potassium was in excess of the others. The curve for nitrogen accumulation in the whole plant parallels, or slightly precedes, the curve for dry matter production until sometime following tasseling and silking (Hornberger, 1882; Jones and Huston, 1914; Radu, 1937; Sayre, 1948). Sayre, for example, reported that onemonth-old plants contained about 3.5 pounds of nitrogen per acre. Ten days later, when the dry matter production was increasing rapidly, the plants had accumulated 15 pounds per acre. At about silking time, during most rapid dry matter production, they were accumulating 4.0 pounds of nitrogen per acre per day. Following tasseling and silking, the pattern of nitrogen uptake is not clear-cut and apparently depends upon the supply available in the soil and upon other factors affecting absorption. Sayre noted that nitrogen accumulation in the whole plant, after reaching a peak about silking time, continued for another four weeks and then stopped somewhat abruptly. Jones and Huston observed that the silking peak was followed by a decreased rate which again became high at about the time the kernels began to glaze. Ince (1916), Hopper ( 1925), Ladd ( 1890), Duley and Miller ( 1921) , Whitehead et al. (1948), and Jordan et al. (1950) all observed accumulation until maturity. Hornberger’s data showed a continued accumulation until ripening and then an actual loss. Glover (I 95313) , using sand cultures, found nitrogen absorption decreased during the setting and ripening of the grain, quickly falling off to a very low level before harvest. Nitrogen accumulates rather rapidly in the grain until maturity. This is accomplished in large part through movement and depletion

339

M I N E R A L N U T R I T I O N OF CORN

from other plant parts (Hornberger, 1882; Jones and Huston, 1914; Sayre, 1948; Jordan et al., 1950). For example, some nitrogen moves out of the cob, leaves, and stem, and a considerable amount from the husks (Fig. 4). Whitehead et al. (1948) observed during growth that the total nitrogen contents of leaves, sheaths, shanks, and tassels reached a maxima and then decreased, the net loss being attributable to gain in the ears. Phosphorus accumulates in the whole plant at a fairly continuous rate until maturity (Hornberger, 1882; Jones and Huston, 1914; Radu, 1937; Sayre, 1948; Jordan et al., 1950; and Glover, 1953b). As with ACCUMULATION OF NITROGEN

JUNE

JULY SAMPLING DATES

AUGUST

- 3- DAY INTERVALS

SEPT.

FIG. 4. The accumulation of nitrogen in the growing corn plant and its various parts at Wooster, Ohio, in 19M.(After Sayre, 1948.)

nitrogen, the period of most rapid accumulation occurs at silking. Hornberger's data, however, differ somewhat by showing a slowing up for about three weeks after the silking peak and then another period of rapid absorption. The greatest rate of phosphorus accumulation usually parallels the period of most rapid dry matter production. As pollination approaches, phosphorus starts to migrate into the developing but yet seedless ear (Earley and DeTurk, 1944; DeTurk et al., 1933), and then accumulates rapidly in the grain until maturity. The leaves, stalk, husk, and cob lose phosphorus to the grain (Fig. 5 ) . With the approach of the reproductive period, DeTurk et al. (1933) observed a much greater transfer of phosphorus from roots to tops than the amount of phosphorus actually absorbed from the soil. Also, throughout the period of growth preceding pollination, a gradual decrease in phosphorus concentration

340 LEWXS B. NELSON was noted in the tops owing to more rapid production of plant tissue as compared with the rate of phosphorus uptake from the soil. Translocation of inorganic phosphorus absorbed either through the roots or foliage may be quite rapid, as evidenced by studies with radiophosphorus. Brewer and Bramley ( 1940) detected radiophosphorus in the second leaf of 12-inch plants 5 minutes after their transfer to nutrient solutions containing radiophosphorus. Moore ( 1949) observed labeled ions in all parts of the plant within 2 hours after adding radiophosphorus to the nutrient medium. Wittwer and Lundahl (1951) noted translocation to the roots and to nontreated leaf portions of corn ACCUMULATION OF PHOSPHORUS

SAMPLING DATES

- 3-DAY INTERVALS

FIG.5. The accumulation of phosphorus in the growing corn plant and its various parts at Wooster, Ohio, in 1940. (After Sayre, 1948.)

seedlings within 2 hours after radiophosphorus was applied to the base of leaf sheaths. Reports on distribution of the absorbed radiophosphorus, however, are somewhat conflicting. Brewer and Bramley ( 1940) found that radioactivity was more intense in the bottom leaf than the top leaf, and decreased from the base to the tip of the leaf during the initial period following transfer to the nutrient solutions containing radiophosphorus. Final distribution became quite uniform except for the tips of the leaf blades which remained low. Rabideau et al. (1950), on the other hand, noted the radiophosphorus accumulation was always greatest in those regions of the plant where growth was most rapid, including the tips of terminal leaves. Sayre (1952a) obtained no difference in radiophosphorus accumulation anywhere in the leaf. Potassium translocation and accumulation differ in several respects from nitrogen and phosphorus. Most striking is the actual loss of po-

341

M I N E R A L N U T R I T I O N O F CORN

tassium from the corn plant as maturity is approached (Hornberger, 1882; Jones and Huston, 1914; Sayre, 1948). This loss occurs chiefly from the leaves, stalks, and husks, and is not surprising inasmuch as most of the potassium in the plant is in water-soluble form (Morris and Sayre, 1935; Wadleigh and Shive, 1939). Sayre reports a loss of potassium amounting to about 16 pounds per acre, and Jones and Huston report a loss of 12 pounds. Notable also is the lack of potassium accumulation in the grain. Sayre (1948) found the potassium accumulation in the whole plant reached a maximum about three weeks after silking, followed by a loss ACCUMULATION OF POTASSIUM I-

W

z

W

2 0 26 2 JUNE

8

14 2 0 26

I

JULY SAMPLING OATES-

13 19 25 31 6 12 AUGUST SEPT 3 - D A Y INTERVALS 7

18

FIG.6. The accumulation of potassium in the growing corn plant and its various parts at Wooster, Ohio, in 1940. (After Sayre, 1948.)

to maturity (Fig. 6). Hornberger (1882) and Jordan et al. (1950) show accumulation until four weeks after silking. Jones and Huston (1914) noted very rapid absorption in the two-week period preceding tasseling and silking followed by a period of relatively slow absorption and then a period of rapid absorption at the time of greatest starch formation in the grain. Calcium and magnesium accumulation, according to Hornberger (1882), do not follow the curve for total dry matter production. Instead, he found the rates of uptake highest at tasseling and silking, and by that time the plant had accumulated most of its calcium and magnesium. Sayre (1952b) noted that magnesium continued to accumulate somewhat after tasseling and silking as contrasted with little o r no increase in calcium. Duley and Miller (1921) observed that the total calcium in the leaves increased as the plant grew older-an observation in conflict with Hornberger's leaf data. Sayre (I 952a), using radioautographs, found calcium to accumulate evenly in all parts of the leaf blade.

342

LEWIS B. NELSON

Translocation of sulfur in the whole plant apparently has been studied only by Hornberger (1882). He noted the highest rate of uptake at tasseling. Relatively large amounts moved into the tassels and ears, and later into the cobs and kernels. Sayre’s (1952a) radioautographs showed the leaf veins to be lower in sulfur than the tissue between them. Zinc accumulates in the upper, younger leaves to a greater extent than in the older, lower leaves, according to Viets et al. (1953). They believed this to be an indication of ready mobility of zinc and that it is translocated from older to younger leaves. Radioautographs by Stout and Pearson (Ulrich, 1952) showed that zinc accumulated in the growing points and in the nodes. Shaw (1952) also found high concentrations of radiozinc at the node locations. Shaw et al. (1954) observed that zinc translocated from the seed furnished an important part of the zinc needs of the plant. They also obtained evidence indicating that zinc was not readily translocated within the plant, particularly when the soil was adequately supplied with zinc. A number of investigators have noted iron and aluminum accumulation in the nodal tissues during growth. Hoffer and Cam (1923) first observed the phenomenon which produced a purplish-brown discoloration of the nodal tissues followed by disintegration. Later, Hoffer and Trost (1923) suggested that the accumulation was related to root rots in that it disrupted the translocation of carbohydrates from the leaves to the roots. The roots, thus weakened, were thought to be more subject to attack by root organisms. They also noted an inverse relationship between iron accumulation in the nodes and the amount of potassium in the plant sap. The latter observation led to the development of a qualitative tissue test for an insufficiency of available potassium in the soil (Hoffer, 1930). Welton et al. (1926), however, found the relationship between accumulated iron and potassium deficiency not close enough for use in predicting potassium fertilizer needs. Salter and Ames (1928) also observed considerable variation in the percentage of total iron in nodal tissues among different corn plants. Sayre (1930) noted further that iron accumulated only at the nodal plates of corn stems, and only in the bundle sheath and outer layers of pith cells around the bundle. There is evidence that ions absorbed by roots on one side of the plant will not be evenly distributed through the plant. Spencer (1937) observed half-leaf injury and other symptoms of malnutrition in plants where the roots were segregated into different nutrient compartments. The injury was most marked on the lower leaves. Gile and Carrero (1917, 1921), using a similar technique, found that the absorbed ions were only slowly translocated within the plant. Apparently there is a migration of certain nutrients from the plant

343 back into the soil or nutrient culture. Redfern (1922) noted that potassium and magnesium diffused out of corn roots in appreciable quantities. Brewer and Bramley (1940) found a considerable diffusion of sodium out of the plant, but only small losses of phosphorus. Moore (1949) also noted a slight efflux of phosphorus. As reported previously, several investigators have observed a loss of potassium as the plant approaches maturity; however, it is conceivable that part or all of the potassium losses might have occurred from leaching with rain or dew. MINERAL NUTRITION O F CORN

2. Elemental Composition and Protein Content

A vast amount of literature exists upon the elemental composition of the corn plant. Investigations show that the amount of essential as TABLE I Mineral Composition of the Corn Plant'

Element Calcium Phosphorus Potassium Sodium Chlorine

0.02% 0.28% 0.28% 0.01%

Sulfur

O.l%% 0.10%

Magnesium Iron Manganese Copper 1

Grain (dent)

Composition Stover (ears removed)

0.06%

0.003% 5 . 7 p.p.m. 4 . O p.p.m.

o.29yo

0.05% 0.67% 0.0670 0.28% 0.150/,

0.22% 0.020% 122.8 p.p.m. 4 . 6 p.p.rn.

Morrison (1951).

well as nonessential elements found in the plant depend upon many factors. These include the variety, its age and stage of development, the physical and chemical nature of the soil, kinds and amounts of soil amendments applied, methods of cultivation, soil moisture conditions, climate, and plant population. The influence of a number'of these factors is discussed at various places throughout the review. a. Mineral Composition of the Mature Plant. Probably the most comprehensive data on the average composition of mature corn are provided by Morrison (1951). Some of his data are summarized in Table I. Beeson (1941 ) also has compiled data from several hundred sources. Examples of the percentage composition of the various plant parts are given by Latshaw and Miller (1924) and reproduced in Table 11. These data are for a single variety grown at Manhattan, Kansas,

344

LEWIS B. NELSON

during a single season and thus have definite limitations. In addition to the elements listed in Table 11, sodium, boron, copper, barium, strontium, lead, tin,nickel, cobalt, chromium, zinc, and molybdenum have been variously reported as present in the corn plant. At maturity, the corn grain contains over half of the total nitrogen in the plant and about three-fourths of the phosphorus. Calcium and silicon are largely concentrated in the leaves with very little occurring in the grain. Magnesium, on the other hand, occurs in some quantity in TABLE I1 Elemental Composition of the Leaves, Stem, Grain, Cob, and Roots of Corn Grown at Manhattan, Kansas'

% of element, dry basis Element

Leaves

Stems

Grain

Roots

Cob

Carbon Oxygen Hydrogen Nitrogen Phosphorus Potassium Calcium Magnesium

41.27 43.86 5.86

44,51 43.90 5.90 0.84 0.089 1 .23 0.17 0.16 0.16

44.72 45.30 6.96 2.15 0.34 0.42 0.025

42.31 43.58 5.73 1.97 0.12 0.48 0.61 0.17 0.26 0.52 4.44

45.75 45.89 6.36 1 .38 0.94 0.46 0.022 0.11 0.021 0.025 1 .33 0.05 0.122 0.031

Sulfur Iron Silicon Aluminum Chlorine Manganese

1 .so

0,207 1.48 0.47 0.21 0.24 0.070 e.59 0.074 0.222

0,043

0.052

0.42 0.013 0.224 0.017

0.20

0.14 0.043 0.016 0.003 0,033 0.037

0.98

0.11 0.066

Total dry matter distribution: Leaves. 98.10%; stem, 44.04%; grain, 31.48%:cob, 9.37%: and roots, 7.95%. Plants analyzed wben grain was fully dented and in late dough stage. The leaves were all intact. 1 Latehaw and Miller (1994).

the grain as well as in the leaves and stem. About one-fourth of the potassium and one-fourth of the sulfur is found in the grain and most of the remainder in the stem and leaves. Copper is about equally divided between the-grain and the stem and leaves. As a general rule, the grain is less subject to variations in elemental composition than is the stover, since both organic and inorganic reserves are diverted to the grain. Furthermore, the grain is quite selective in the elements it accumulates. In the case of plants with poorly filled ears, Brunson and Latshaw (1934) found the nitrogen content uniformly higher than that of plants with well-filled ears. The increase of nitrogen was greatest in the cob. In barren plants, the total nitrogen content was 20 to 40 per cent higher in the stalks and leaves. Loomis (1937) found that the increase in nitro-

345

MINERAL NUTRITION O F C O R N

gen in such plants is mostly in the nitrate form and has not been synthesized to amino acids or proteins. b. Protein Quantity and Quality of Grain. Numerous references indicate that applications of nitrogen fertilizers usually increase the total protein content of corn grain, whereas phosphorus and potassium applications usually have little influence. Data provided by MacGregor (1954) can be referred to as an illustration of this. An interesting example of increasing increments of nitrogen fertilizer upon the total protein is provided by Hunter and Yungen (1955) and is shown in Table 111. TABLE I11 Effect of Increasing Rates of Nitrogen Fertilizer upon the Yield, Ear Weight, Total Protein of Corn, Grain, and the Percentage of Applied N Recovered in the Grain' N, Ib./acre

Yield, bu./acre

Ear weight, Ib./ear

%

0 40 80 100 120 140 160 180

64.6 90.4 118.2 132.4 140.7 141 .O 146.8 141 . 2 147.1 145.8 147.8 143.6

0.28 0.35 0.45 0.49 0.53 0.59 0.56 0.57 0.53 0.56 0.54 0.54

6.92 7.27 7.86 8.06 8.45 8.46 8.74 9.00 9.30 9.17 9.55 9.58

400 240 280 320 1

N recovered in grain, Lh./acre %

Protein

211 310 199 504 569 564 606 602 647 639 665 650

39.6 45.5 46.7 46.6 40.0 39.4 34.8 34.7 28.0 25.8 21.9

Hunter and Yungen (1955).

Note particularly that the protein content of the grain continues to increase even when the effect of the fertilizer upon yields becomes negligible. In some instances on extremely nitrogen-deficient soils, the f i s t increment of nitrogen may have little effect on the total protein content or the protein content may actually decrease. This is always associated with a marked increase in the dry weight of the grain (Earley and DeTurk, 1948; Zuber et al., 1954; Krantz and Chandler, 1954). Also, on soils well supplied with nitrogen, nitrogen fertilizer may increase the protein content somewhat without an appreciable grain yield increase. Increasing plant population tends to decrease the total protein content of the grain (Earley and DeTurk, 1948; Jordan, 1951; Zuber et nl., 1954; Shubeck and Caldwell, 1955).

346

LEWIS B. NELSON

Corn grain traditionally has been known to contain an "unbalanced" protein which influences its nutritive value as an animal feed. This is due to its low content of the critical amino acids particularly tryptophan and lysine (Osborne and Mendel, 1914; Sauberlich et al., 1953a, 1953b). Thus, the effect of fertilizer and management practices is important not only upon the quantity of protein but also upon its quality. Determinations of the various amino acid and protein fractions have been employed mostly in characterizing genetic factors. Generally, these studies have shown that the protein in high-protein varieties contains a larger proportion of zein and a smaller proportion of tryptophan and lysine than that in low-protein varieties; also, that marked varietal differences exist as to content of both the different amino acids and proteins (Showalter and Carr, 1922; Frey, 1949, 1951; Hansen et al., 1946; Sauberlich et al., 1953a; Miller et al., 1952). Feeding trials with animals usually indicate an inferior quality in the protein of highprotein corn (Dobbins et al., 1950; Mitchell et al., 1952; Sauberlich et al., 1953b). A limited amount of research has been conducted on the effects of management factors upon amino acid content. Sauberlich et al. (1953a) compared samples of corn grain from plots receiving 24 pounds of N per acre with those receiving 84 pounds of N per acre. The protein content for the low-nitrogen treatment ranged from 6.8 to 8.2 per cent and for the high-nitrogen treatment ranged from 9.3 to 12.0 per cent. The higher rate of nitrogen caused a marked increase in the content of all 18 amino acids when expressed as a per cent of a given amino acid in the whole corn grain. The increases of each amino acid, however, did not necessarily correlate directly with increases in the per cent of the total proteins present in the grain. For example, the content of leucine, alanine, phenylalanine, and proline in the total protein became greater as the percentage of total protein in the grain increased. On the other hand, the content of arginine. glycine, lysine, and tryptophan, and to some extent, threonine and valine, became smaller. Prince ( 1954) determined total proteins, zein, tryptophan, leucine, and isoleucine in samples of grain from plots receiving varying rates of nitrogen application and of plant population. Increasing the rate of nitrogen increased the total proteins, the zein fraction, and the leucine in the corn grain. Leucine was increased also in the total protein. No pronounced effects were apparent in either tryptophan or isoleucine; however, there was a tendency for the tryptophan percentage of the protein to decrease with nitrogen application. Also, the ratio of zein to total protein increased at a faster rate than the total protein as the rate of nitrogen increased. Increasing the plant population per acre decreased the percentage of crude protein, zein, and leucine.

M I N E R A L N U T R I T I O N OF CORN

347

Corn grown under conditions of high soil nitrogen was found by Schneider et al. (1952) to be higher in zein as compared with corn grown with low soil nitrogen. Earley et al. (1952) reported an increase in total protein and thiamine and a decrease in nicotinic acid from a high application of nitrogen and phosphorus. Hamilton et al. (1951), studying the effects of long-term fertilization and rotation practices, found that corn grain from the better practices contained 30 per cent higher total protein than that from unfertilized continuous corn plots. However, the quality of protein was poorer from the better treatments because of higher zein content and lower lysine and tryptophan contents. C. Composition of Leaves. Determination of total N, P, and K in corn leaves has received considerable emphasis in recent years, particularly as a diagnostic procedure. Following Tyner’s ( 1946) work, investigators have more or less standardized upon the selection of the sixth leaf from the base taken during the period of full silk for leaf analysis. Tyner listed four reasons for his selection: (1) the stage is easily recognized and described, (2) all varieties mature in about the same number of days once silking and tasseling occur, ( 3 ) the weight of vegetative parts is at or near its peak at this time, and ( 4 ) this is a period when nutrient demands by the plant are very high. In most studies, the supply of limiting nutrient was varied in the substrate while the others were kept nonlimiting to growth. Most investigators have found high positive correlations between the level of the nutrient element in the leaf, the rate of nutrient application or its available level in the soil, and the yield of the corn grain (Tyner, 1946; Krantz and Chandler, 1951; Bennett et al., 1953; Andharia et al., 1953; Viets et al., 1954). An example of this relationship is given in Table IV. Some effort has been made to establish critical leaf concentrations above which doubtful or rapidly diminishing growth responses would result from further nutrient applications to the soil. Tyner (1946) arrived at 2.90 per cent N, 0.295 per cent P, and 1.30 per cent K as being the critical concentrations under the conditions of his studies. Bennett et al. (1953), although questioning the existence of a definite critical percentage for nitrogen, found that the critical percentages in a series of experiments ranged somewhere between 2.8 and 3.0 per cent N. Viets et al. (1954), however, found little evidence of a critical nitrogen percentage in their experiments. The high positive correlations found between leaf N and grain yield has led to calculation of regression equations in an attempt to establish some quantitative relationships. Tyner (1946), in West Virginia, found for each change of 0.1 per cent N, P, and K in the sixth leaf at silk, that grain yields varied 4.43, 25.3, and 2.05 bushels per acre, respectively.

348

LEWIS B. NELSON

I n Iowa each change of 0.1 per cent N was related to a yield change of 3.19 bushels (Bennett et aZ., 1953). In Washington each 0.1 per cent N corresponded to 5.53 to 6.99 bushels of corn (Viets et al., 1954). These investigators caution that the existence of many uncontrollable and variable factors which influence final yields makes the widespread use of such quantitative interpretations questionable. Correlations have been made also between the elemental composition of the sixth leaf and that of the mature grain (Krantz and Chandler, 1951; Bennett et al., 1953). As might be expected, there is a definite relationship between the N percentage of the leaf at silking and the TABLE IV Relationship between Rate of Nitrogen Application, Yield, Time of Leaf Sampling, and Composition of Leaves' Sampling date and composition __

N from NHlNOJ

Yield

June 174

July 9'

Lb./acre

Bu./acre

%N

%N

%N

%P

0 40 80 160

76 107 133 156

9.05 3.08

1.85

2.33

3.0% 3.05

9.45 2.56

1.01 1.31 1.62 1.95

0.124 0.145 0.163 0 .'242

~

1

August 5'

~~

Viets ct al. (1054). h w e s t expanded leaf. Fully developed lenf near center of plant. Second leaf below upper ear on plnnta in s ilt.

N percentage of the grain at maturity. Nitrogen differences resulting from fertilizer treatments however are wider in the leaf than in the grain. I n the case of P and K, differences in leaf content usually are not reflected in the mature grain. The leaf analysis studies by the various investigators show that as nitrogen fertilizer is applied to soils low in available nitrogen, both the N and P contents of the leaf usually are increased (Table IV). The effect upon the K content apparently varies with local conditions and the chemical form in which the nitrogen is applied. The possible effects of one element upon another thus can exert a profound influence upon the interpretation of leaf analysis data. d. Plant Tissue Tests. Semiquantitative colorimetric determinations of nitrates, inorganic phosphorus, and potassium in the green tissue of corn have received much emphasis as an index of the current nutrient status of the plant (Thornton, 1932; Thornton et al., 1939; Scarseth, 1943; Goodall and Gregory, 1947; Krantz et nl., 1948; Ohlrogge, 1952).

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Nitrates usually are determined by adding a nitrate reagent directly to a cut portion of the plant stem, whereas phosphorus and potassium are determined on a measured amount of green plant sample (leaves or stem) after a brief period of extraction. The nutrient levels are expressed as high, medium, or low, on the basis of predetermined critical values. Many workers, however, have preferred to compare the composition of the test plants with the composition of healthy, vigorous plants grown in the same field. Advantages usually ascribed to tests are ( I ) the analyses are inexpensive and can be performed quickly and in the field, and (2) the unelaborated forms in which the nutrients are determined provide a sensitive index of the current nutrient status of the plant. Numerous examples are available which demonstrate the application of tissue tests to field problems (Cook, 1941; Ohlrogge, 1941; Olson, 1941; Drake, 1944). The amounts of the different nutrient fractions present in the tissue vary with the stage of growth and the plant part sampled. Nitrates are highest in the early stages of growth when the demands for nitrogen by the plant are low. During the period of vegetative growth, the concentration is highest at the base of the stem and lessens progressively from bottom to top of the plant as meristematic activity increases. Inorganic phosphorus has been reported highest in the main stem just below the tassel during the period between tasseling and silking. Whether some other fraction of the nonprotein nitrogen in the corn tissue might be equally or more satisfactory than nitrates apparently has not been determined. I n this respect, Hoerner and DeTurk (1938), using 88-day-old corn plants grown in nutrient solutions containing sodium nitrate, found that the total nitrogen was about equally divided between water-soluble and water-insoluble forms. The water-soluble forms consisted to the greatest extent of amino nitrogen and secondary protein derivatives, followed in turn by nitrates. There were only low concentrations of ammonia- and amide-nitrogen, indicating that these were transient forms subject to conversion as rapidly as they were produced. The inorganic phosphorus contained in the vegetative parts of corn may range between 30 and 40 per cent of the total phosphorus (Weeks and Walters, 1946). Data obtained by Montouliac (1941) indicate that the proportion of inorganic phosphorus remains high throughout the season. With potassium, little difference would be expected between an extracted fraction and total potassium, since it is present in the corn plant largely in water-soluble or easily extractable form. e. Expressed Fluids and Sap. The chemical composition of expressed plant tissue fluids or juices and of exuded sap of corn was the subject of a number of investigations from about 1925 to 1935. These studies

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LEWIS B. NELSON

were aimed largely toward relating the composition of the juice and sap to the nutrient status of the soil. No great use appears to have been made of them for diagnosing nutrient deficiencies, and more recent efforts have been directed toward leaf analysis and plant tissue tests. Fluids expressed from ground parts of the green corn plant were studied by Gilbert (1926), Gilbert and Hardin (1927), Gilbert et al. (1927), Pettinger (1931), and Pettinger and Thornton (1934). Methods varied somewhat in that Gilbert and his co-workers used low pressures to express the juices and determined only the phosphate phosphorus, whereas Pettinger used a pressure of 6500 p.s.i. and determined total phosphorus. Both groups noted that the nitrate, phosphorus, and potassium contents of the expressed tissue fluids paralleled the levels in the soil, and both suggested a series of tentative critical values. The large fluctuations encountered in the nutrient contents, however, would make the use of these values questionable. It has also been noted by others that the composition of expressed fluids varies greatly with small variations in pressure during expression. Pettinger (1931) found that the total phosphorus in the expressed juice increased as the plant aged, whereas the potassium remained fairly constant. The phosphorus content remained high when the grain production was subnormal, and low when it was normal or above normal. Nutrients in the juices were higher when growing conditions were unfavorable and where there was a deficiency of one nutrient element, the concentration of other nutrients increased. The exuded sap technique consisted of collecting sap from the cut ends of live stems. Proponents of the method believed it offered advantages over the expressed juice procedure in that the sap was easier to collect and analyze and not subject to variable contamination from protoplasmic material. Pierre and Pohlman (1933) found the sap to contain about 3700 p.p.m. of total solids, of which approximately onethird was in the inorganic form. Total phosphorus ranged from 150 to 400 p.p.m. of PO, of which the inorganic form made up about twothirds of the total. Silica averaged about 250 p.p.m., calcium 80 p.p.m., and chlorides 90 p.p.m., while nitrates ranged from a trace to 344 p.p.m. Phosphorus and silica were much higher in the sap than in displaced soil solution, chlorides and calcium were in considerably lower concentrations, and nitrates were higher in some instances and lower in others. Sabinin and Kolotova (1929) observed an accumulation of cations in the sap of corn grown in nutrient solutions having high pH values and of anions in solutions of low pH values. Lowry et al. (1936) observed that the phosphorus and potassium content of the sap reflected the fertilizer treatments used whereas the nitrogen content did not. Pohlman and Pierre (1933) noted a good correlation between PO,

351

MINERAL NUTRITION OF CORN

TABLE V The Influence of Superphosphate Fertilization on the PO, Concentration of the Soil Extract and of the Plant Sap of Corn Grown in Pots’ 1.b. phosphate per acre

Dry wt. of corn 5 grams

None 1500 3000 6000

27.3 33.2 35.3

20% super-

15.9

p.p.m. PO, in sap Inorganic 80 191 232 314

Total

p.p.rn. PO, in soil

129

0.29

218

1.35 3.75 8.54

21.6 369

Pohlman and Pierre (1938).

content of the sap and the water-soluble phosphorus content of the soil. Some of their data are given in Table V. VI. SYMPTOMS OF NUTRITIONAL DISORDERS The corn plant exhibits characteristic symptoms of most of the common nutrient deficiencies. These usually are easy to recognize and identify, particularly when the deficiency is pronounced. Excellent color plates showing the more common deficiencies are available from several sources, including Hoff er and Krantz ( 1949), Wallace ( 1951 ) , Cook and Millar (1949), and Olson (1950). As a rule, mild deficiencies do not produce recognizable symptoms and some other method such as soil and plant analysis or pot and field trials must be relied upon for their identification. I n some instances, insect, fertilizer, or mechanical injury may produce symptoms which may be confused with nutritional deficiencies. I n the case of at least one element, zinc, differing intensities of the deficiency appear to produce somewhat differing symptoms. It is also conceivable that more than one deficiency symptom may appear on the same corn plant; however, the reviewer found no reports in the literature describing such an occurrence. Nitrogen deficiency symptoms are by far the most prevalent and are observed in most localities where corn is grown. The symptoms are striking. As described by Hoffer and Krantz ( I 949), young plants have a stunted and spindly growth and light yellowish-green foliage. Older plants develop definite leaf symptoms. Yellowing occurs first in the older leaves, starting at the leaf tip and progressing backward along the mid-vein in a V-shaped pattern. Later the whole leaf turns yellow and the process proceeds up the plant leaf by leaf. A few days after the leaf tissue yellows it dies or “fires” and turns brown. Glover (1953a) has found that an unbalance hetween nitrogen and phosphorus was

352

LEWIS B. NELSON

important in bringing out the deficiency symptoms. For example, if both nitrogen and phosphorus were low and the plants grew slowly, nitrogen deficiency symptoms did not appear. On the other hand, if additional phosphorus was present, characteristic symptoms appeared. Nitrogen deficiency symptoms are sometimes confused with drought symptoms, inasmuch as nitrogen deficiencies frequently appear during drought periods. This results because the upper soil layers contain most of the available nitrogen and, as these layers dry out, an important supply of nitrogen is lost to the plant. Phosphorus deficiency symptoms are sometimes difficult to identify. According to Hoffer and Krantz (1949), young corn plants deficient in phosphorus are characterized by slow, stunted growth and a dark-green color. The leaves and stems have a tendency to become reddish or purplish in color, with the intensity greatest at the tips or along the margins of the leaves. The coloration apparently results from an accumulation of sugars which is related to the formation of anthocyanin (DeTurk, 1941). Some varieties of corn are more subject to purpling than others, and insect injury to the roots, leaves, or stem, earless plants, or mechanical injury will often result in similar coloration. Phosphorus deficiency may result in delayed maturity which is particularly noticeable at the time of silking and tasseling. The ears frequently show irregular rows of kernels and immaturity. Sayre (1952a), using radioactive phosphorus, found that phosphorus in phosphorus-deficient leaves decreased uniformly over the leaf blade as the deficiency progressed. He concluded that the pattern of development of the red or purple pigment at the tips and along the margins was a secondary effect of the general lowering of the phosphorus level in the plant. Glover (1953a) observed, as in the case of nitrogen, that when both nitrogen and phosphorus levels were low, visual phosphorus deficiency symptoms failed to appear. Correcting the nitrogen deficiency, however, resulted in the appearance of the usual symptoms. Potassium deficiency symptoms appear first as a diminution of growth of the seedlings and young plants followed by definite leaf symptoms (Hoffer and Krantz, 1949). The edges and tips of the leaves become dry and appear scorched. Similar leaf symptoms may appear on older plants and in severe cases the entire lower leaves may die. The tip ends of the ears are poorly filled and the kernels are loose and chaffy. Deficient plants are often dwarfed and may lodge badly because of defective root systems. The appearance of potassium deficiency symptoms, however, does not always indicate a low available potassium level in the soil. Soils containing large amounts of calcium and magnesium salts interfere with normal potassium absorption by the plant, even though the soil may be relatively well supplied with potas-

MINERAL NUTRITION O F CORN

353

sium (Bower and Pierre, 1944). Poor soil aeration may also limit the plant’s ability to absorb potassium (Lawton, 1945). This reviewer has also observed that application of some of the newly introduced weed sprays as well as the application of fertilizer salts in sprinkler irrigation water may cause leaf symptoms indistinguishable from potassium deficiency symptoms. Calcium deficiency symptoms are most distinct in young plants (DeTurk, 1941; Marsh and Shive, 1941; Stubblefield and DeTurk, 1940). The tips of the unfolding leaves gelatinize and as the plants continue to grow, the leaf tips may stick together. Occurrence of calcium deficiencies pronounced enough to produce the characteristic symptoms are extremely rare under field conditions. The only reported instance found in the literature was that of Melsted (1953). He noted typical symptoms on corn growing in southern Illinois on soils of pH 4.5 or lower and containing less than 2 milliequivalents of calcium per 100 grams of soil. Whole plant samples taken on July 15 contained less than 0.2 per cent calcium. The deficiency appeared where large amounts of NPK fertilizer had been applied. Magnesium deficiencies of field grown corn have been reported in Massachusetts by Jones (1939), in North Carolina by Garner et al. (1922), and in South Carolina by Cooper et al. (1933). Jones (1939) observed that about two weeks after the corn emerged, the intervascular tissue showed a light-green color while the vascular tissue remained a deep green. As the season progressed, the light-green color of the intervascular tissue continued to fade, leaving white streaks extending the entire length of the leaves. I n extreme cases, both the vascular and the intervascular tissues lost their green color, turned brown, and dried prematurely. Another symptom frequently noted is the bronzing and reddening of the leaves. The bottom or older leaves are affected first and most severely. Sulfur deficiency symptoms on corn apparently have not been described in the literature nor have there been instances reported where field applications of sulfur resulted in increased growth. Iron deficiency symptoms have been described by Olsen (1935, 1938) as alternating dark-green and chlorotic stripes extending the entire length of the leaves. The green first disappears between the vascular bundles and later even this tissue may lose its green color. The younger leaves may be almost white. No reports were found of iron responses from field-grown corn. Manganese deficiency is described by Pettinger et al. (1932) as the appearance of white or chlorotic spots on the leaves of three-week-old plants. As the plants grow older these coalesce into elongated chlorotic streaks. The tissue in the middle of the chlorotic areas then turns brown

354

LEWIS B. NELSON

and becomes necrotic, and the dead tissue sometimes falls out of the leaf leaving a number of holes. Manganese deficiency in corn has been reported on overlimed soils in Rhode Island by Pettinger et al. (1932) , on calcareous soils in Florida by Gilbert and McLean (1928), and in South Carolina by Skinner and Ruprecht (1930). Copper deficiency on field-grown corn was described by Nelson et al. (1955) as follows: “The youngest leaves became light yellowish green near the base of the leaf, the tips become necrotic. If the deficiency is less severe and the plants reach 4 to 8 feet in height, a necrosis appears along the margins of the upper leaves, usually near the base of the leaf but sometimes extending to the tip. These necrotic areas appear similar to potassium deficiency but differ in that they are narrower, particularly at the leaf tip and appear only on the upper leaves.” Copper has been noted to exert beneficial effects upon the growth of corn in Florida by Allison et al. (1927); in Maryland, Pennsylvania, Delaware, and Virginia by Russell and Manns (1933, 1934); in Wisconsin by Berger and Truog (1948) and Nelson et al. (1955) ; and in western Australia by Teakle and Burvill ( 1941) . Zinc deficiency was found the cause of the “white bud” disease in Florida (Barnette and Warner, 1935; and Barnette et al., 1936). The first deficiencies may occur within a week after emergence. Lightyellow streaks appear between the veins of the older leaves followed by rapid development of white necrotic spots. The unfolding leaves are often white to a very light yellow in color, giving rise to the term “white bud.” Before the older leaves die, they develop a number of dead areas ranging in color from light slate to dark brown, often merging until the whole leaf dies. Wets (1951) and Wets et al. (1953, 1954) describe zinc deficiency symptoms in Washington as being somewhat similar to those observed by Barnette and his co-workers, except that the unfolding leaves were seldom white or very light yellow but were greener than any others on the plant. Interveinal chlorosis and chlorosis of the lower leaves occurred and the internodes were short. In the case of extreme zinc deficiency, no ears were produced but there was vegetative growth. Plants often recovered from the deficiency. I n California, Reed and Beck (1939) observed that the deficiency curtailed production of cobs and kernels more than that of stalks, leaves, and husks. Berger and Truog (1948) have reported zinc responses on sweet corn in Wisconsin. Lack of boron, according to French (1937), results in almost complete cell disorganization in the older leaves. The new leaves fail to uncurl and the apical portion dies, followed in turn by the dying back of all new growth. Schropp and Arenz (1938) reported a general check to growth, derangements in emergence of the tassel, distortion of the

355 spikelets, and an absence of anthers. The leaves showed long, white, transparent stripes and the leaf tissue suffered marked changes. Eltinge (1936) observed chlorosis of older leaves, failure of the newer leaves to develop normally, disintegration of the parenchyma cells, failure of certain leaf cells to differentiate, hypertrophy of cells of the lower epidermis, root tip injury, and disintegrating cells in the stem tip. The above deficiency symptoms all have been developed on nutrient and sand cultures. Nusbaum (1948) has reported boron deficiency symptoms and a yield response to boron in field grown corn. MINERAL NUTRITION O F CORN

VII. EFFECTOF FERTILIZERS O N NUTRITION AND GROWTH According to data reported by the Fertilizer Work Group of the National Soil and Fertilizer Research Committee (1954), 25 per cent of all commercial fertilizer nutrients consumed in the United States during 1950 were applied for corn. This was more than for any other crop, and amounted to a total consumption of 286,600 tons of N, 442,800 tons of P,O,, and 291,700 tons of K,O. However, the average use per planted acre was relatively low, averaging 7 pounds of N, I1 pounds of P,O,, and 7 pounds of K,O, and only 46 per cent of the planted acres were estimated as receiving fertilizer. Thus, although fertilizers are playing an important role in the total corn production in the United States, much more could be used advantageously if greater corn production appeared desirable. Relatively large amounts of N, P, and K are required to produce a high-yielding crop of corn. For example, a corn crop yielding 100 bushels per acre would require about 140 pounds of N, 30 pounds of P, and 98 pounds of K (Sayre, 1948). Frequently half or more of the total nitrogen required by the corn crop must be supplied through fertilizers (Scarseth et al., 1944; Krantz and Chandler, 1954; and others). Usually enough nitrogen is available in the soil from legume, starter fertilizers, and other sources to supply early requirements of the crop and only when the corn is well along in its grand period of growth does the need for additional nitrogen become markedly apparent. The need is greatest on sandy, eroded, and low organic matter soils, and under farming systems involving few legumes and limited applications of manure. Second- and third-year corn invariably suffers more than first-year corn from lack of nitrogen. Lack of phosphorus often limits corn production but the deficiency is by no means universal. The large build-up of residual phosphorus in soils from applications of phosphate fertilizers and manure, the existence of available native phosphorus in the soils, and the widespread use of starter fertiliiers all contribute toward supplying the phosphorus needs of the crop. Lack of phosphorus usually is most apparent during

356

LEWIS B. NELSON

early growth when the root system is small and in contact with only a limited volume of soil. This is evidenced by the high proportion of total phosphorus absorbed by the young plant which is derived from fertilizer (Stanford and Nelson, 1949; Nelson et al., 1947; and others), and also by the marked early growth response to phosphorus. Corn response to potassium fertilizer is practically nonexistent in the subhumid and arid regions of the United States, on many of the soils derived from water-laid sediments of the Mississippi and Missouri rivers, as well as on soils derived from most loessial deposits in the corn belt states. Potassium responses, on the other hand, are widespread throughout much of the humid region, being greatest on sands and other low exchange soils. Deficiencies of other nutrient elements, as pointed out in Section VI, are not widespread, usually being associated with some local soil condition. Corn fertilizer recommendations vary somewhat in different parts of the country. I n the northern states, the usual recommendation is to apply 100 to 200 pounds per acre of a low-nitrogen mixed fertilizer such as 3-12-12 or 3-18-9 in bands near the seed at planting time (commonly referred to as “starter” fertilizer), plus a separate application of 40 to 80 pounds of nitrogen either before or after planting. I n the southern states, from 200 to 600 pounds per acre of a mixed fertilizer is broadcast and plowed under or otherwise incorporated into the soil before planting and supplemented by a separate nitrogen application. In the western and Great Plains states, nitrogen often is the only nutrient applied. It is a general practice throughout the country to vary the formula of the mixed fertilizer according to the available levels of N, P, and K in the soil as determined by soil tests and past management. Nitrogen applications are based upon the expected needs of the crop after making allowances for the amounts of nitrogen contributed by the soil, past legume crops, and manure applications.

I . Localized Placement at Planting Placement of comparatively small amounts of fertilizer in bands near the seed at planting time has received much attention (Dumenil and Shaw, 1952; Burson and Rost, 1953; and many others) and for years was the most widely accepted method for fertilizing the corn crop. Usually the fertilizer is applied with a corn planter fertilizer attachment about 1 inch to the side and 1/2 inch below the seed. The fertilizer so placed is within the early absorptive range of the roots (see Section 11, l a ) and, as a result, growth of the young corn plant may be markedly accelerated. The corn crop generally will derive a greater benefit

MINERAL NUTRITION O F CORN

357

from localized placements than from broadcast applications (Sabinin and Manina, 1935; Nelson et al., 1949; Pesek and Dumenil, 1953). Frequently, 200 pounds of fertilizer applied in the row is as effective in increasing corn yields as 400 pounds broadcast. Location of the fertilizer with respect to the young corn roots largely determines its effectiveness as a starter fertilizer. Stanford and Nelson (1949), in this respect, found that drilling radioactive phosphate fertilizer in bands at seed level resulted in markedly greater utilization of the applied phosphorus than did either banding above the seed level or 3 inches below the seed level. Nelson et al. (1949) noted greater utilization of the fertilizer phosphorus when small amounts were placed close to the seed rather than in bands 3 inches out from the seed; Krantz and Chandler ( 1954) observed greater early response to phosphate placed alongside the seed than 10 inches below the seed; and Truog et al. (1925) found that most rapid growth of the young plant resulted when the fertilizer was applied as near the seed as possible without interfering with germination. Reduction in germination may result if the fertilizer comes in direct contact with the seed (Truog et al., 1925; Smith, 1927; Coe, 1926; Collier, 1954). For fertilizers localized in the hill and in direct contact with the seed, Coe found a retardation of germination when the acre rates of application reached 60 pounds of 16 per cent superphosphate, 60 pounds of 2-12-2, 30 pounds of sodium nitrate, and 40 pounds of ammonium sulfate. For fertilizers drilled in the row and in contact with the seed, decreases in germination began with 250 pounds of 16 per cent superphosphate, 50 to 75 pounds of sodium nitrate, and 50 to 75 pounds of muriate of potash. Increased rates of application caused even greater retardation of germination. Rock phosphate at 600 pounds per acre had no effect upon germination. The degree of fertilizer injury is influenced by other factors, including the salt content of the soil, the moisture level and the pattern of the moisture movement in the soil, and the texture and exchange capacity of the soil. Several beneficial effects other than yield have been ascribed to starter fertilizers (Truog et al., 1925; Smith and Harper, 1926; Gerdel, 1931; Olson and Walster, 1934; Dumenil and Shaw, 1952; Krantz and Chandler, 1954). Better weed control is possible, inasmuch as taller corn is easier to cultivate and competes with the weeds. The size of the root system of the young plants is increased more rapidly, thus increasing the absorptive zone. Silking may be hastened from 2 to 10 days, and the time required for maturing the crop reduced correspondingly. The latter is of major importance in northern corn-growing areas, where danger from fall frost damage is serious and where high moisture content of the grain is a problem.

358

LEWIS B. NELSON

Starter fertilizers exert some influence upon frost effects. Magistad and Truog (1925) found that application of starter fertilizer increased the osmotic pressure of the sap of young corn plants, which in turn lowered the freezing temperature of the plant from l o to 2 O C. They concluded that this is often sufficient to prevent spring frost damage. Dumenil and Shaw (1952) also noted that in areas where corn was killed by frost before maturity, starter fertilizer increased the shelling percentages from 2 to 5 per cent and the bushel weight from 2 to 4 pounds. The beneficial effects of starter fertilizers upon early growth are not always reflected in the final corn yield (Lowrey and Ehlers, 1954; Krantz and Chandler, 1954). This is particularly apparent in the South and during warm seasons in the North. The effectiveness of starter fertilizers thus appears greatest where the spring season is cool and wet and where early frost damage may be a problem in the fall. Ohlrogge et al. (1943) and Rhoades and Lowrey (1954) have observed that whereas a small amount of nitrogen applied at planting stimulates early growth, it may not materially influence the yield of corn if the plant is short of nitrogen at tasseling time. In fact, DeTurk (1941) cites an example where the starter fertilizer actually reduced the yield below that of the unfertilized check. However, addition of nitrogen in midJuly completely overcame any adverse effects of the starter fertilizer. 2. Application of Large Amounts of Fertilizer Large applications of nitrogen fertilizer often increase corn yields markedly (Krantz and Chandler, 1954; Rhoades et al., 1954; Dumenil, 1952; MacGregor, 1954; Hunter and Yungen, 1955; Ohlrogge et al., 1943). Yield responses to increasing increments of nitrogen usually follow the Mitscherlich-type curve, providing the levels of other nutrients and moisture are not limiting. On soils extremely deficient in nitrogen, near-maximum yields are obtained from applications of about 160 pounds of N per acre (see Table 111). However, under soil nitrogen levels most frequently encountered in the field, near-maximum yields are usually obtained from applications ranging from 40 to 80 pounds of N per acre. The percentage recovery of the applied nitrogen decreases as the rate of nitrogen application increases, is less under dry surface soil conditions and where the nitrogen-supplying power of the soil is high, and may be low in soils receiving large amounts of undecomposed lownitrogen crop residues. Recovery also is low where leaching occurs during the growing season. Krantz and Chandler (1954) reported 68 per cent recovery in the grain from a 110 pound per acre application of

359 nitrogen, 54 per cent from a 160 pound rate, and 50 per cent from a 180 pound rate. Scarseth et al. (19M) and Hunter and Yungen (1955) reported recoveries ranging mostly from 20 to 50 per cent. Some of the nitrogen remaining in the soil after the crop is harvested normally is recovered in subsequent crops. A number of investigations have been directed toward determining the best time to apply nitrogen (Rogers, 1932; Fitts et al., 1946; Lang, 1946; Dumenil, 1950; Robertson and Ohlrogge, 1952; Rhoades and Lowrey, 1954; and others). Most studies indicate that other than providing a few pounds of nitrogen positionally available for the small plant, the major application should be made to provide an adequate supply when the nitrogen requirement of the plant becomes high (see Section V, 1). Thus, nitrogen applied as side-dressings when the corn is 2 to 3 feet tall has generally proven more effective than either earlier or later applications. Nitrogen applied at tasseling is too late to meet the requirements of the plant during the period of rapid vegetative growth. Except on very sandy soils where leaching losses may be high, two or more side-dressings are seldom superior to applying the nitrogen as a single side-dressing. The position in which side-dressed nitrogen is placed with respect to the distance from the corn row does not seem to make a great deal of difference (Robertson and Ohlrogge, 1952). This would be expected in that the corn root system rapidly extends across the entire space between rows (see Section 11, 1a ) . The depth to apply nitrogen is by no means clear-cut and appears to vary with the moisture content of the soil through the season and the pattern of moisture movement. Many of the studies involving depth of placement are confounded with time of application and their interpretation is difficult. Krantz and Chandler (1954) in North Carolina, for example, found greater yield responses from side-dressing applications than from plow-sole applications made before planting. There was some evidence of greater leaching losses under the deep placement and yields were generally inferior where the nitrogen was applied at depths of 10 to 16 inches. Yoder et al. (1943) in Ohio, Scarseth et al. (1944) in Indiana, and Pitner (1946) in Mississippi all found evidence favoring plow-sole applications. Krantz and Chandler (1954) observed that nitrogen increased the grain weight three to four times as much as the stover weight. On nonitrogen plots, about 3 pounds of stover were produced for each pound of grain, whereas on plots receiving from 160 to 180 pounds of nitrogen per acre, only about 0.8 to 0.9 pound of stover was produced per pound of grain. MacGregor (1954) noted some delay in maturity from nitrogen MINERAL NUTRITION O F CORN

360

LEWIS B. NELSON

side-dressings and suggested that further investigation should be made. Effects of nitrogen fertilizers upon the composition and quality of the crop are discussed under Section V, 2. On phosphorus-deficient soils, large applications of phosphorus fertilizer are required. However, except on soils where phosphorus fixation is a serious problem, the major phosphorus applications are made earlier in the rotation usually either on or preceding the legume hay or pasture crop. Inasmuch as a considerable portion of the phosphorus applied earlier in the rotation remains residually available for the following corn crop, this ha5 become a major practice for overcoming low phosphorus levels. Where a soluble phosphorus fertilizer is applied directly to the corn crop, the amount of response is closely related to the available phosphorus level in the soil, providing other nutrients or factors are not limiting. Krantz and Chandler (1954),for example, report yield increases ranging from 0 to 35 bushels per acre, depending upon the phosphorus status of the soil. Where large additions of soluble phosphorus are applied directly to the corn crop, it seems desirable to incorporate it or place it in the soil at depths sufficient to avoid dry surface soil and to make it positionally available for absorption by the plant’s root system. Scarseth et al. (19M), for example, found that banding in the plow sole was more effective than broadcasting and plowing under, and considerably more effective than broadcasting on the surface after plowing. Hall et al. (1953) observed that a major portion of the plant’s seasonal uptake of fertilizer phosphorus came from 8- to 13-inch depths. Where summer moisture deficiencies are pronounced, deeper placement has been shown to be advantageous (Puhr and Worzella, 1947; Millar et d.,1946, 1947). On well-managed lands in the northern states, the 20 to 50 pounds of P,O,per acre normally applied in starter fertilizers will satisfactorily provide the additional phosphorus needed for a high-yielding crop. However, under conditions of low phosphorus supply, starter fertilizers cannot be depended upon solely to supply the major requirements of the crop. Reasons for this are twofold: ( I ) the plant recovers less than 15 per cent of the applied fertilizer phosphorus (Nelson et al., 1947; Stanford and Nelson, 1949),and (2) the starter fertilizer is localized near the surface and, since phosphorus does not move appreciably in the soil, it remains in an area unfavorable for absorption during periods of even minor droughts (Hall ei al., 1953;Scarseth, 1943). Large amounts of potassium are usually applied broadcast and plowed under, banded in the lower part of the plow layer before planting, or put on as a side-dressing while the corn is growing. Washko (1945) applied muriate of potash as side-dressings at 40, 59, and 73

MINERAL NUTRITION O F CORN

361

days after planting. Greatest effectiveness resulted from the 40-day application, although some response was obtained from the 73-day application. Lang ( 1946) observed that broadcast application after plowing was more effective than broadcasting and plowing under, Scarseth et al. (1944) favored banding in the plow sole, and Yoder et al. (1943) concluded that all potassium should be banded regardless of depth of placement. Since potassium is fairly mobile in most soils, it would appear that exact placement, other than for starter effect, would not be a major consideration. Poor aeration in some soils, however, may reduce its effectiveness. As has been indicated in Section 11, 3, proper nutrient balance is essential for optimum growth. The work of Glover (1953a) is of particular value in pointing up this requirement. For example, his studies showed that when lack of nitrogen restricted growth, providing an excess of phosphorus beyond that required to balance the nitrogen supply was of little or no value in increasing growth; or conversely, if phosphorus restricted growth, then more nitrogen than was required to balance it was of little value. Fertilizers have been found to influence the degree of lodging. Krantz and Chandler (1954), in one experiment, found that lodging was decreased 17 per cent and corn yields were increased 47 bushels per acre by 120 pounds of K,O per acre on a soil deficient in potassium. However, adding potassium influenced neither lodging nor yield on soils well supplied with potassium. In their studies, nitrogen had only a slight tendency to increase lodging. Plant population must be carefully adjusted in order to realize maximum efficiency from applied nutrients (see Section VIII) , and adequate soil moisture is necessary to realize maximum return from fertilizers (see Section IX, 1).

3 . Effect of Liming Numerous field experiments have been conducted in which liming and soil pH variables have been introduced. As a general rule, liming acid soils has a pronounced beneficial effect upon the growth and yield of corn. Salter and Barnes (1935) in Ohio report step increases in yield from a n average minimum of about 15 bushels per acre on unlimed soil of pH 5.0 to about 36 bushels on soil limed to pH 6.8. However, corn is grown successfully on soils with pH of around 5.0 in the humid region to soils with pH well above neutral in some of the western states. T h e beneficial effect of the liming upon corn growth probably is associated indirectly with an increase in the availability of the soil phosphorus, addition of more nitrogen to the soil from increased growth of legumes under limed conditions, and a host of other side effects. As

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LEWIS B. NELSON

pointed out in Section VI, calcium and magnesium deficiencies sometimes occur. Application of these elements through liming undoubtedly exerts some direct beneficial effects upon the corn crop. On the other hand, overliming may make certain of the minor elements less available and result in deficiencies of these. VIII. INFLUENCE OF PLANT POPULATION The number of corn plants per acre resulting either from varying the planting rate within the row or the distance between rows has a marked influence upon nutrition and growth. The data on this are voluminous and only a portion of the references can be quoted. The efficiency of fertilizer use is closely correlated with the thickness of stand (Stringfield and Thatcher, 1947; Seem and Huber, 1947; TABLE VI Interrelation between Plant Population and Fertilizer Application upon the Yield of Corn in North Carolina' Yield, bushels per acre Plants2 per acre

20 lb. N/acre

70 lb. N/acre

120-170 lb. N/acre

4,000 7,000 10,000 13,000

39 39 41 36

58 73 71 73

63 84 92 92

* Krantz and Chandler (1954). :Prolific or +?-ear liybrirl.

Nelson and Dumenil, 1947; Larson et al., 1950; Jordan, 1951; Long, 1953; Krantz and Chandler, 1954; Duncan, 1955; Shubeck and Caldwell, 1955). A typical example of this is given in Table VI. It is generally found that the rate of planting has little influence on grain yields at low levels of soil fertility. As fertility increases, higher yields are produced from increasingly higher rates of planting until a maximum is reached at around 10,000 to 12,000 plants per acre for multiple-ear hybrids and 16,000 to 18,000 for single-ear hybrids. Under the dry conditions of the Great Plains, maximum populations for single-ear hybrids are about 8000 plants per acre. At any given soil fertility level, increasing the population decreases the size and weight of the ear. Mediumsized ears, having an air-dry weight of 0.5 to 0.6 pound, usually are found associated with maximum yields. Most investigators consider that a large ear is an indication of a plant population too low to make most efficient use of the available nutrients.

MINERAL NUTRITION O F CORN

363

Almost exactly the same relationship exists between population and soil moisture (Carreker and Liddell, 1948; Larson et al., 1950). Some of Carreker and Liddell’s data are given in Table VII, showing the three-way effect of population, moisture, and fertility. Under extremely arid conditions, where moisture is a seriously limiting factor, much lower plant populations are required than elsewhere (Brandon, 1937). Shubeck and Caldwell (1955) noted significantly less soil moisture under thick stands than under thin stands. In addition to influencing the grain yield and ear size, increasing the population increases the tendency for barren stalks and nubbins, decreases the number of ears per stalk in multiple-ear varieties, increases lodging, and may delay the silking date from 2 to about 5 days (Stringfield and Thatcher, 1947; Long, 1953; Krantz and Chandler, 1954; Shubeck and Caldwell, 1955). Population differences apparently have little or no effect on shelling percentages (Nelson and Dumenil, 1947; Shubeck and Caldwell, 1955). Observations by Eisele (1938) showed that variations in population of corn planted in hills had no appreciable effect on plant height, but did affect the total leaf area. The maximum leaf area per plant was 8900, 7908, and 6573 sq. cm. for hills containing 1, 3, and 5 plants, respectively. Also, the average cross-sectional area of stalks at maturity was 60 per cent as large in 3-plant hills as in 1-plant hills, and only 40 per cent as large in 5-plant hills as l-plant hills. Shubeck and Caldwell (1955) also observed no effect on plant height; however, Brandon (1937), working under dryland conditions, found differences in height some years. Various ways of spacing the plants have been attempted. Stringfield and Thatcher (1947) observed no difference in grain yields at equal populations between several plants in a hill versus single plants in the row. Dungan ( 1946) and Bryan et al. ( 1940), however, obtained data indicating that thick planting in hills results in overcrowding, and that spacing plants singly and equidistant in all directions might be most advantageous for the plants.

IX. EFFECT OF SOILMOISTURE ON NUTRITION AND GROWTH Lack of adequate soil moisture is one of the major limiting factors in corn production not only in the arid and subhumid regions but also in the humid eastern states. As a result, many of the practices adopted by the corn grower have been either developed or adjusted to make best use of the existing soil moisture. These include practices involving irrigation, thickness of planting, row spacing, fertilizing, and tilling. Irrigation has been a long-standing practice in arid regions as a means

364

LEWIS B. NELSON

of overcoming moisture deficiencies, and it is coming into wider use in subhumid and humid regions. Successful use of irrigation not only involves many problems in the application and timing of the individual irrigations but also requires careful integration with other cultural practices. Experimental results presented in Table VII will serve to illustrate the latter. Rhoades et al. ( 1954) and Rhoades and Nelson (1955) also have discussed corn irrigation from the standpoint of related practices. The amount of water needed to produce a corn crop (consumptive use or evapo-transpiration) naturally varies with the locality, weather TABLE VII The Effect of Nitrogen Level and Plant Spacing upon the Yields of Irrigated and Unirrigated Corn in Georgia'

Rate of nitrogen

Lb.per acre 20 60 100 Average 1

Irrigated

Unirrigated

Hill spacing in row 18 in. 84 in.

12 in. 18 in. 84 in.

18 in.

Bu. per acre 85 113

77 93

194

95

107

88

Hill spacing in row

Bu. per acre 66 84 80 77

76

57

81

64

84 80

70 64

55 68 69

68

Carreker and Liddell (1048).

conditions including temperatures, soil conditions, and the cultural and soil management practices followed. Scrutiny of a large amount of data, largely from unpublished U. S. Department of Agriculture sources, indicates that the crop ordinarily needs from 16 to 25 inches, although amounts vary between extremes of 12 to 33 inches. Consumptive use varies with the season and stage of growth. Maximum daily consumptive use data obtained by Harrold and Dreibelbis (1951) at Coshocton, Ohio, were 0.20 inches during May, 0.23 during June, 0.28 during August, 0.09 during September, and 0.06 during October. Rhoades et al. (1954) reported that the average daily consumptive use in Nebraska was 0.30 inches per day over 15- to 20-day intervals during the last of July and throughout August. Consumptive use during some 5- to 7-day intervals was as high as 0.40 inches per day during hot, windy weather. Land and Carreker (1953) in Georgia report an average rate of 0.22 inches for irrigated corn during the period of June 10 to July 26, with a maximum of 0.28 inches per day and a minimum of 0.15 inches per day. During the same period, unirrigated corn averaged 0.1 1 inches per day.

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365

1. As Influenced by Soil Fertility The use of fertilizers and manures and the level of soil fertility have an important bearing on the amount and efficiency o€ water use by the corn plant. In general, the water requirement of corn is lower on soils of high fertility or on soils where amounts of manure or fertilizer were added in sufficient quantities to affect growth. This relationship was brought out first in early investigations involving determination of water requirement under different environmental conditions in which plants were grown in sealed containers. The water requirement values thus determined, expressed as the amount of water required to produce a unit amount of dry matter, usually represent transpiration losses plus the relatively small amount of water retained by the plant. On an infertile soil, Montgomery and Kiesselbach (1912) found a water requirement of 550 and where manure was applied the water requirement was lowered to 350. On a fertile soil, the water requirement was 392 without manure and 347 with manure. Widtsoe (1909) reduced the water requirement from 908 to 613 through application of manure, and even more through use of nitrogen fertilizer. Data reported by Smith (1954) from field studies in Missouri showed that highly fertilized land produced 79 bushels of corn per acre and required 16 inches of water, i.e., some 5600 gallons of water were required to produce a bushel of corn. Corn grown without soil treatment produced 18 bushels per acre and required about 14 inches of water, or some 21,000 gallons of water per bushel of corn. Rhoades et nl. (1954) give several sets of data showing the influence of nitrogen fertilizer upon the efficiency of water use. At Arapahoe, Nebraska, for example, they found that 10 inches of irrigation water produced 108 bushels per acre where an adequate supply of nitrogen fertilizer was applied, and only 68 bushels per acre without nitrogen. Similar data are quoted by Singleton et al. (1950) and by Larson et al. (1950) in the Columbia Basin. During the drought years of 1953 and 1954, considerable emphasis was placed upon the use of fertilizers as a means of increasing the efficiency of limited supplies of soil moisture. In many instances, however, results were disappointing. In localities where the subsoil moistures were depleted and where the rainfall was extremely limited, moisture was so deficient that yields were no different regardless of fertility level. 2 . As Influenced by Moisture Stress The level of soil moisture, or soil moisture stress, exerts considerable influence upon the efficiency of water use and also upon the nutrient

366 LEWIS B. NELSON uptake and growth of the corn plant. Corn appears particularly sensitive to high moisture stress (low moisture) at about the tasseling and silking period (Smith, 1914; Miller and Duley, 1925; Wallace and Bressman, 1937; Robb, 1934; Davis and Palleson, 1940; Robins and Domingo, 1953; Howe and Rhoades, 1955). The classical experiment of Miller and Duley (1925) on varying moisture supply deserves special mention. They grew corn in large potometers with varying amounts of water during three consecutive 30-day periods of growth. Optimum (28 per cent) and minimum (13 per cent) soil moisture levels were maintained in all possible combinations with the three periods of growth on a soil having a wilting coefficient of 7.6 per cent. They found that the moisture supply during the second 30-day period, or from the time the plants set their ninth leaves until tasseling, had the greatest effect upon the total dry weights of the plants. Plants stunted by lack of moisture during the first 30-day period were able to recover if moisture conditions were favorable during the last two periods, but the time for maturing was prolonged. Minimum moisture during any period gave a greater root growth to tops than did optimum moisture. Leaf growth responded more readily to changes in soil moisture than any other part of the plant. Ear production was influenced most by moisture level during the third period (after tasseling), being somewhat less during the second period,. and least during the first period. Further insight on the relation of moisture deficits at different intervals and growth periods is shown by the work of Robins and Domingo (1953) and Howe and Rhoades (1955). Robins and Domingo found that depletion of moisture throughout the root zone to the wilting point for periods of 1 to 2 days during tasseling reduced yields 22 per cent, and for 6 to 8 days reduced yields 50 per cent. The yield reductions were due in part to reduced ear size and in part to a reduction in fertilization from nonreceptive silks. A moisture deficit also delayed tasseling and silking by 4 to 5 days. Howe and Rhoades obtained a maximum yield of 153 bushels per acre with six irrigations which maintained the soil in a relatively moist condition (low stress) throughout the growing season. Three irrigations timed to keep the soil moist before tasseling and through silking produced 144 bushels per acre, and more widely spaced irrigations or fewer irrigations resulted in lower yields. Optimum ear development required moist soil during the period of growth before tasseling and through silking as well as an adequate moisture supply after silking until maturity. Where a dry soil was irrigated during the tasseling period, there was a marked recovery in ear development. Lack of irrigation before tasseling delayed development of tassels and silks by 2 or 3 days.

367 Miller and Duley (1925) , Robins and Doming0 (1953) , Howe and Rhoades (1955) , and others also show that lack of moisture reduces the length of the internodes, depresses the stalk weight, encourages root growth, and decreases leaf growth. Leaf growth, more than any other plant part, responds most readily to changes in moisture. The stress with which the soil moisture is held in the soil influences its availability to the corn plant. Davis (1940), Haynes (1948), and Howe and Rhoades (1955) observed a decrease in the growth rate of corn as the soil moisture stress increased within the range between field capacity and permanent wilting. Some of the earlier workers reported data to support the view that the water requirement of corn increases as the moisture content of the soil approaches either dry or wet extremes (Widtsoe, 1909; Kiesselbach, 1910; Kiesselbach and Montgomery, 1911 ) . Briggs and Shantz (1913), however, pointed out that this view was not justified, in that nutrient deficiencies limiting plant growth occur in dry soils and lack of soil aeration undoubtedly becomes a factor in wet soils. Thus, the e€fect of soil moisture extremes on water requirement is an indirect rather than a direct effect. More recent investigations add credence to Briggs and Shantz’s criticism. Soil moisture conditions influence the nutrient accumulation in the plant. Richards and Wadleigh (1952) make these observations for plants in general: “ . . . it is well established that when growth of plants is limited by soil moisture supply, nitrogen tends to accumulate within the plant because rate of entry is approximately maintained in conjunction with the decreased rate of utilization in growth processes. The general tendency for potassium content to be relatively low in plants on the drier soils show that rate of entry of potassium decreases to a greater degree than does rate of utilization in these slower growing plants, . . . the effect of soil moisture on phosphate nutrition is far less consistent than is observed for nitrogen and potassium . . . . The available evidence consistently shows magnesium to be relatively high in plants growing under restricted moisture supply . . . . Since entry of calcium and magnesium in plants tends to vary reciprocally, it could be inferred that the characteristically low potassium content of plants with inadequate moisture supply would be accompanied by a relatively high content of calcium.” Specific studies with corn have been limited. Miller and Duley (1925) ,however, found that corn grown under minimum moisture conditions contained a higher percentage of nitrogen and phosphorus. They noted little effect of minimum moisture on calcium accumulation and a variable effect on potassium and magnesium. Greaves and Nelson (1925) , with corn grown on a highly calcareous soil, observed a decrease in nitrogen content of the kernels with irrigaMINERAL NUTRITION O F CORN

368

LEWIS B. NELSON

tion which they assumed was due to the nitrogen’s being leached out of the root zone. The ash, calcium, phosphorus, and potassium contents of the kernels were increased with irrigation. MacGillivray (1949) noted that sweet corn kernels obtained from low moisture plots had higher percentages of dry matter, sugars, and nitrogen. Woodworth et al. (1952) in Illinois found extremely high grain protein contents during drought years. ACKNOWLEDGMENT An earlier unpublished version of this review was prepared in 1949 while the author was a staff member of the Department of Agronomy, Iowa State College. Much of the more pertinent material of that review is incorporated herein.

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Larson, W. E., and Pierre, W. H. 1953. Soil Sci. 76, 51-64. Latshaw, W. L., and Miller, E. C. 1924. J . Agr. Research, 27, 845-861. Laurent, J. 1904. Reu. gin. botan. 16, 1 4 4 8 . Lawton, K. 1945. Soil Sci. SOC.Amer. Proc. 10, 263-268. Leonard, C. D., and Bear, F. E. 1950. N e w Jersey Agr. Expt. Sta. Bull. 752. Long, 0. H. 1953. Tennessee Agr. Expt. Sta. Bull. 232. Loo, T. L. 1931. J . Fac. Agr. Hokkaido I m p . Uniu. 30, 1-118. Loomis, W. E. 1935. Iowa State Coll. I . Sci. 9, 509-520. Loomis, W. E. 1937. I. Am. SOC.Agron. 29, 697-702. Lowrey, G. W., and Ehlers, P. L. 1954. Nebraska Agr. Expt. Sta. Dept. Agron. Outstate Testing Circ. 35. Lowry, M. W., Forrest, L. A,, and Huggins, W. C. 1936. Georgia Agr. Expt. Sta. Bull. 193. Lyness, A. S. 1936. Plant Physiol. 11, 665-686. MacGillivray, J. H. 1949. Proc. A m . SOC.Hort. Sci. 54, 33&338. MacGregor, J. M. 1954. Minnesota Agr. Expt. Sta. Misc. Rept. 22. Magistad, 0. C., and Truog, E. 1925. I . Am. SOC.Agron. 17, 517-526. Marsh, R. P., and Shive, J. W. 1941. Soil Sci. 51, 141-151. MazB, P., and Maze, P. J., Jr. 1939. Compt. rend. SOC. biol. 132, 377-378. Mazk, P., Ma&, P. J., Jr., and Anxionnaz, R. 1935. Compt. rend, SOC. biol. 120. 693695.

Mazk, P., and Perrier, A. 1904. Ann. inst. Pasfeur 18, 721-747. Melsted, S. W. 1953. Soil Sci. SOC.Amer. Proc. 17, 52-54. Mevius, W. 1928. 2. Pflananzenerniihr. Dung. u. Bodenk. 10,208-218. Mevius, W., and Dikussar, I. 1930. Jahrb. wiss. Botan. 73, 633-703. Millar, C. E. 1930. I. Am. SOC.Agron. 22, 868-874. Millar, C. E. 1933. I . A m . SOC.Agron. 25, 4 1 M 2 6 . Millar, C. E., Cook, R. L., Cumings, G. A., Hansen, C. M., Hulburt, W. C., and Robertson, L. S. 1947. Proc. Natl. Joint Comm. Fertilizer Application 23, 129-133. Millar, C. E., Cook, R. L., Cumings, G. A., Hulburt, W. C., Robertson, L. S., Rood, P. J. 1946. Proc. Natl. Joint Comm. Fertilizer Application 22, 168-179. Miller, E. C. 1943. Kansas Agr. Expt. Sta. Tech. Bull. 54.

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Miller, E. V., Pitner, J. B., Romo, C., and Villa, R., 1950. Soil Sci. SOC.Amer. Proc. 14, 270-275.

Miller, M. F., and Duley, F. L. 1925. Missouri Agr. Ezpt. Sta. Research Bull. 76. Miller, P. A., Brimhall, B., and Hurst, T. L. 1952. Agron. 1.44, 343-345. Mitchell, H. H., Beadles, J. R., and Hamilton, T. S. 1952. 1. Nutrition, 48, 461476. Montgomery, E. G., and Kiesselbach, T. A. 1912. Nebraska Agr. Ezpt. Sta. Bull. 128. Montouliac, G. 1941. Compt. rend. acad. agr. France 27, 778-796. Moore, J. F. 1949. Am. 1.Botany 36, 166169. Morris, V. H., and Sayre, J. D. 1935. Plant Physiol. 10, 565-568. Morrison, F. B. 1951. “Feeds and Feeding,” 21st ed., pp. 1154-1157. Morrison Publishing, Ithaca, New York. Naftel, J. A. 1931. 1.Am. SOC.Agron. 23, 142-158. Nelson, L. B., and Dumenil, L. 1947. Iowa Farm Sci. 1, No. 10,3-5. Nelson, L. G., Andries, H. J., and Berger, K. C. 1955. Soil Sci. SOC.Amer. Proc. 20, 69-72.

Nelson, W. L., Hall, N. S., Krantz, B. A., and Welch, C. D. 1949. Soil Sci. 68, 137144. Nelson, W. L., Colwell, W. E., Dean, L. A., Hawkins, A., Krantz, B. A., MacKenzie, A. J., Rubins, E. J., and Woltz, W. G. 1947. Soil Sci. SOC.Amer. Proc. 12, 113-118.

New Jersey Agricultural Experiment Station. 1938. 59th Ann. Rept. p. 88. Nobbe, F. 1862. Landwirtsch. Vers.-Sta. 4, 212-224. Nusbaum, C. J. 1948. Victory Farm Forum 31, 5-6. Ohlrogge, A. J. 1941. Proc. Natl. Joint Comm. Fertilizer Application 17, 40. Ohlrogge, A. J. 1944. Soil Sci. Soc. Amer. Proc. 8, 196200. Ohlrogge, A. J. 1952. Purdue Uniu. Agr. Expt. Sta. Bull. 584. Ohlrogge, A. J., Krantz, B. A., and Scorseth, G. D. 1943. Soil Sci. SOC.Am. Proc. 8, 196-200.

Oliver, W. F. 1952. Sci. Agr. 32, 427-432. Olsen, C. 1935. Compt. rend. trau. lab. Carlsberg Shr. chim. 21, 15-52. Olsen, C. 1938. Compt. rend. trau. lab. Carlsberg Sir. chim. 21, 301-313. Olson, L. C. 1941. Soil Sci. SOC.Am. Proc. 6, 238-242. Olson, L. C. 1950. Georgia Agr. Expt. Sta. Circ. 165. Olson, P. J., and Walster, H. L. 1934. 1. Am. SOC.Agron. 26, 205-213. Osborne, T. B., and Mendel, L. B. 1914.1. Biol. Chem. 18, 1-6. Pantanelli, E., and Severini, G. 1910. Staz. sper. agrar. ital. 43, 449-544. Pantanelli, E., and Severini, G. 1911. Staz. sper. agrar. ital. 44, 873-908. Pearl, R., and Surface, F. M. 1915. 2.Indukt. Abstam. u. Vererbungsl. 14, 97-203. Peseb; J., and Dumenil, L. 1953. Iowa Farm Sci. 7, No. 10,3-6. Pettinger, N. A. 1931. J. Agr. Research 43. 95-119. Pettinger, N. A. 1933. Virginia Agr. Ezpt. Sta. Tech. Bull. 46. Pettinger, N. A., and Thornton, S. F. 1934. J . Am. SOC.Agron. 26, 547-561. Pettinger, N. A., Henderson, R. G., and Wingard, S. A. 1932. Phytopathology 22, 33-51.

Pierre, W. H., and Pohlman, G. G. 1933.1. Am. SOC.Agron. 25, 144-160. Pitner, J. B. 1946. Mississippi Agr. Ezpt. Sta. Seruice Sheet 400. Pogialle, M. 1856. J . Pharm. Chim. [3], 30, 255-269. Pohlman, G. G., and Pierre, W. H. 1933.1. Am. Soc. Agron. 25, 160-171. Polson, A. 1855. Chem. Gaz. 13, 211. Prince, A. L. 1954. Agron. 1. 46, 185-186. Puhr, L. F., and Worzella, W. W. 1947. South Dakota Agr. Expt. Sta. Circ. 68.

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Rabideau, G. S., Heimsch, C., and Whaley, W. G. 1950. Am. I . Botany 37, 93-99. Radu, I. F. 1937. Bodenkunde Pflanzenerniihr. 2, 351-383. Redfern, G.1922.Ann. Botany (London) 36, 167-174. Reed, H.S., and Beck, J. V. 1939.Growth 3, 1-7. Reeve, E.,and Shive, J. W. 1943.Better Crops with Plant Food 27, 1616,4548. Rhoades, H. F., and Lowrey, G. W. 1954. Nebraska Agr. Erpt. Sta. Quart. 1954, 2, No. 4, 7-8. Rhoades, H. F., and Nelson, L. B. 1955. I n U. S. Dept. Agr. Yearbook, 1955 (A. Stefferud, ed.), pp. 394-400. Supt. of Documents, Washington, D. C. Rhoades, H.F., Bondurant, J. A., Hamilton, F. B., and Howe, 0. W. 1954. Nebraska Agr. Expt. Sta. Bull. 424. Richards, L. A., and Wadleigh, C. H. 1952. I n “Agronomy Monographs (A. G. Norman, ed.), Vol. 2, pp. 73-251. Academic Press, New York. Richards, S. J., Hogan, R. M., and McCalla, T. M. 1952. In “Agronomy Monographs” (A. G. Norman, ed.), Vol. 2, pp. 303-4430.Academic Press, New York. Robb, A. D. 1934. Monthly Weather Reu. 62, 286289. Robbins, W. J., and Maneval, W. E. 1924.Botan. Gaz. 70, 424-432. Robertson, W.K., and Ohlrogge, A. J. 1952. Agron. I . 44, 170-172. Robins, J. S., and Domingo, C. E. 1953.Agron. J . 45,618-621. Rogers, H. T., Pearson, R. W., and Pierre, W. H. 1940. Soil Sci. SOC. Amer. Proc. 5, 285-291. Rogers, W. B. 1932.South Carolina Agr. Erpt. Sta. Bull. 203. Russell, M . B., Bair, R. A., and Davis, F. E. 1940. I. Am. SOC.Agron. 32, 92g930. Russell, R., and Manns, T. F. 1933. Trans. Peninsula Hort. SOC.47th Annual Meeting 23, 51-57. Russell, R., and Manns, T. F. 1934. Trans. Peninsula Hort. SOC.48th Annual Meeting 24, 97. Sabinin, D. A., and Kolotova, S. S. 1929. Proc. Intern. Society Soil Sci. 4, 81-82. Sabinin, D. A., and Manina, H. 1935.2. Pflanzenerniihr. Dung. u. Bodenk 40, 1-48. Salisbury, J. H.1848. Trans. New York State Agr. SOC.0, 678-874. Salter, R. M., and Ames, J. W. 1928.J. Am. SOC.Agron. 20, 808-836. Salter, R. M., and Barnes, E. E. 1935. Ohio Agr. Expt. Sta. Bull. 553. Sauberlich, H. E.,Chang, W., and Salmon, W. D. 1953a.I . Nutrition 51, 241-250. Sauberlich, H.E.,Chang, W., and Salmon, W. D. 1953b.I . Nutrition 51, 623-635. Sayre, J. D. 1930. Plant Physiol. 5, 393-398. Sayre, J. D. 1948. Plant Physiol. 23,267-281. Sayre, J . D. 1952a.Ohio Agr. Expt. Sta. Research Bull. 723. Sayre, J . D. 1952b.Proc. Natl. Joint Comm. Fertilizer Application 28, 1626. Scarseth, G.D. 1943. Soil Sci. 55, 113-121. Scarseth, G. D., Cook, H. L., Krantz, B. A., and Ohlrogge, A. J. 1944. Purdue Uniu. Agr. Expt. Sta. Bull. 402. Schneider, E. O., DeTurk, E. E., and Earley, E. B. 1952.Agron. I. 44, 161-169. Schropp, W., and Arenz, B. 1938. Phytopathol. 2. 11, 58g606. Seem, B. L.,and Huber, L. L. 1947.Pennsylvania Agr. Expt. Sta. Bull. 400,Suppl. 3. Shank, D. B. 1945.I . Agr. Research 70,365-367. Shantz, H. L.1927.Ecology 8, 145-157. Shaw, E. 1952.Soil Sci. 74,479480. Shaw, E., Dean, L. A., and Menzel, R. G. 1954.Soil Sci. 77,205-214. Showalter, M. F.,and Carr, R. H. 1922.I . Am. Chem. SOC.44.2019-2023. Shubeck, F. E.,and Caldwell, A. C. 1949. Proc. Nail. Joint Comrn. Fertilizer Applicarion 25. 94-95.

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Steph, J. 1859. J. prakt. Chem. 76, 88-96. Stringfield, G. H., and Thatcher, L. E. 1947. I. Am. SOC.Agron. 39,995-1010. Stubblefield, F. M., and DeTurk, E. E. 1940. Soil Sci. Soc. Amer. Proc. 5, 120-124. Taylor, G. A. 1954. Plant Physiol. 29, 87-91. Teakle, L. J. H., and Burvill, G. H. 1941. I. Dept. Agr. W . Australia 18, 125-132. TenEyck, M. A. 1889. North Dakota Agr. Ezpt. Sta. Bull. 36. Thomas, W., and Mack, W. B. 1939. I. Agr. Research 58, 477491. Thornton, S. F. 1932. Purdue Univ. Agr. Ezpt. Sta. Bull. 355. Thornton, S. F., Conner, S. D., and Fraser, R. R. 1939. Purdue Univ. Agr. Expt. Sta. Circ. 204 (Revised). Truog, E., Attoe, 0. J., and Berger, K. C. 1953. Soil Sci. 76,41-50. Truog, E., Harper, H. J., Magistad, 0. C., Parker, F. W., and Sykora, J. 1925. Wisconsin Agr. Expt. Sta. Research Bull. 65. Tyner, E. H. 1935. Soil Sci. 39, 405422. Tyner, E. H. 1946. Soil Sci. Soc. Amer. Proc. 11, 317-323. Tyner, E. H., and Webb, J. R. 1946. J. Am. SOC.Agron. 38, 173-185. Ulrich, A. 1952. Ann. Rev. Plant Physiol. 3, 207-228. Viets, F. G., Jr. 1951. Agron. I . 43, 150-151. Viets, F. G., Jr., Crawford, C. L., and Nelson, C. E. 1954. Soil Sci. SOC,Amer. Proc. 18, 297-301.

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Organic Soils J . E . DAWSON New York State College of Agriculture. Cornell University. Ithaca. New York Page I. Introduction . . . . . . . . . . . . . . . . . . 378 I1. Organic Soil Materials . . . . . . . . . . . . . . . 378 1 . Peat and Fibrous Peats . . . . . . . . . . . . . 378 2.Muck . . . . . . . . . . . . . . . . . . 380 3.Gyttja . . . . . . . . . . . . . . . . . . 380 4 . D y . . . . . . . . . . . . . . . . . . . 380 5. M a r l . . . . . . . . . . . . . . . . . . . 380 6. Diatomaceous Earth, Volcanic Ash, and Pumice . . . . . . 381 I11. Stratigraphy of Organic Soils . . . . . . . . . . . . . 381 1 . Marl-Gyttja Sequence . . . . . . . . . . . . . . 381 2. Gyttja-Fibrous Peat Sequence . . . . . . . . . . . 382 3 . Fibrous Peat-Fibrous Moss Peat Sequence . . . . . . . . 382 4. Diatomaceous Earth-Gyttja or Gyttja and Fibrous Peat Mixture Sequence . . . . . . . . . . . . . . . . . 382 5 . Sequences Including Muck as a Layer . . . . . . . . . 382 6. Sequences Including Dy as a Layer . . . . . . . . . . 382 7. Profiles Including Sedimentary Layers . . . . . . . . . 383 8. Profiles Not Including Sedimentary Layers . . . . . . . 383 9 . Profiles Involving Regressive Development . . . . . . . . 383 10. Causes of Variety in Organic Soil Profiles . . . . . . . . 383 IV. Rate of Formation of Peat Soils . . . . . . . . . . . . . 384 I. Rate for Organic Layers from Pollen Distributions . . . . . 384 2. Rate for Organic Layers from Radiocarbon Dates . . . . . . 384 3 . Effect of Plant Nutrients on Rate of Formation . . . . . . 384 4. Rate of Marl Layer Formation . . . . . . . . . . . 385 V. Subsidence of Organic Soils . . . . . . . . . . . . . . 385 1. Rate of Subsidence . . . . . . . . . . . . . . . 385 2. Effect of Depth to Water Table on Rate of Subsidence . . . . 385 3. Effect of Organic Matter Content on Rate of Subsidence . . . . 386 4. Effect of Time after Drainage on Rate of Subsidence . . . . . 386 5. Causes of Subsidence . . . . . . . . . . . . . . . 386 VI . Some Chemical Properties of Organic Soils of Significance in Crop Production . . . . . . . . . . . . . . . . . . . . 387 1 . Soil Tests as a Measure of Fertility Status . . . . . . . . 387 2. Lime Deficiency . . . . . . . . . . . . . . . 388 3. Zinc Toxicity . . . . . . . . . . . . . . . . 390 4. Manganese Deficiency . . . . . . . . . . . . . . 390 377

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Pap VII. Recent Chemical Work on Peat Soils and Related Materials . . . . 390 1. Formation of Humus and Humic Acids . . . . . . . . . 390 a. By Browning Reaction . . . . . . . . . . . . . 391 b. By Microorganisms . . . . . . . . . . . . . 3w c. Specific Effects and Humic Acids . . . . . . . . . 393 2. Inorganic Composition of Organic Soils . . . . . . . . . 394 a. Trace Element Content . . . . . . . . . . . . 394 b. Vivianite and Siderite . . . . . . . . . . . . . 394 . . . . . . . . . . . . . . . . . 395 c.sulfur 3. Functional Groups of Peat Soils . . . . . . . . . . . 395 4. Solubility of Humic Acids, Peat, and Coal . . . . . . . . 396 5. Titration Curves for Humic Acids . . . . . . . . . . 397 6. Amino Acid Content of Organic Soils . . . . . . . . . 397 VIII. Some Problems in Stratigraphy, Formation, Subsidence and Chemistry of Organic Soils . . . . . . . . . . . . . . . . . . 398 References. . . . . . . . . . . . . . . . . . . 399

I. INTRODUCTION The literature dealing with peat is extensive, particularly with respect to a number of subjects not related to the utilization of peat as a soil or medium for supporting plant growth. Publications related to utilization of peat as a soil are not too numerous if those publications primarily of local interest are eliminated. This review will deal with those agricultural publications that are in the opinion of the writer of rather general interest. First, a number of older papers will be reviewed to the extent that they help to indicate the materials found in organic soils and their stratigraphy. Second, publications dealing with the rate of formation of peat soils will be discussed. Third, publications on the subsidence of organic soils will be reviewed. Fourth, some of the chemical properties of these soils of significance in crop production will be considered. Fifth, a number of papers dealing with chemical work on peat and related materials will be reviewed. 11. ORGANICSOILMATERIALS The materials composing organic soils have been extensively described as accumulations of the plant remains by Auer (1933), Dachnowski-Stokes (1933), and Rigg (1940).As soil materials, these deposits have been described as consisting of peat and muck.

I . Peat and Fibrous Peats Peat is usually defined as any partially decomposed plant material that has accumulated in water or in a water-saturated soil where plant growth and deposition have exceeded decomposition. The kind of peat has usually been specified in terms of identifiable remains. Such terms

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as reed and sedge, woody, tule, and moss peat are in common usage. These terms are often appfied when the portion of the soil that can be identified as derived from the plant in question is rather small. In the case of the fibrous peats the diluent of the identifiable plant remains is often finely divided organic matter derived from such plants as those of the algae and lemnae groups. Thus, fibrous peats are often a mixture of fibrous and sedimentary material. It should also be noted that fibrous peat itself is sometimes stratified and has been called spalter peat in this case. I t has long been recognized that there are peats rich in calcium and nitrogen, eutrophic peats, and peats poor in these elements, oligotrophic peats. Dachnowski-Stokes (1933) indicates that Webber first used these TABLE I Distribution of Nitrogen Values for Peat Soils Analyzed by Wilson and Staker (1932) and Feustel and Byers (1930) Nas % organic matter 0 -0.49 0.50-0.99 1 .00-1.49 1.50-1.99 2 . 00-2.49 a . 50-2.99 3.00-3.49 3.50-3.99 4 .00-4.49 4.504.99

Number of samples 0 12 4

12 15 25 35 29 5 0

terms. Fibrous peats of the latter group are usually derived from the Sphagnum mosses and associated plants. Most other plants that form fibrous peats, those usually not growing in association with the Sphagnum mosses, produce eutrophic peat. The extent to which these groups merge into one another is shown by the data in Table I. These data indicate that two kinds of fibrous peat should be recognized from a chemical point of view. The color of fibrous peat samples is mixed, i.e., there are relatively dark-colored small particles and lighter colored fibers. The hue may be 5YR, 7.5YR, or 1OYR. The value may vary from 2 to 8 and the chroma from 2 to 6. The higher chroma and value numbers are for fibers and the lower numbers are for the small particles. The acidity of Sphagnum moss peat is often less than pH 5 and that of other fibrous peat greater than pH 5. There are, of course, exceptions in both types of fibrous peat.

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J. E. DAWSON

These peats usually have low solubilities in saturated sodium pyrophosphate solution.

2. Muck When the degree of decomposition of an organic soil material becomes high enough to prevent identification of the plant from which it was derived the material is called muck. All of the kinds of organic materials found in organic soils decompose into mucks. This decomposed material is more than finely divided. Some of it is rather low in molecular weight. This low molecular weight material forms true solutions in the presence of some salts, for example, sodium pyrophosphate. Also, it will diffuse through cellophane membranes. It is in part humic acid and some of its salts are insoluble. The color of muck is variable. The hue is usually IOYR, the value is often 2 or 3, and the chroma varies from 0 to 3. Muck has acidity values varying from less than pH 4 to more than 7.5. Samples having pH values of 6 or above may contain free calcium carbonate. 3 . Gyttja Ruttner (1953) in reviewing publications on limnology also included gyttja as an organic soil material. Gyttja is peat derived from plankton and deposited on the bottoms of bodies of water by sedimentation. When deposited in deep bodies of water it is usually stratified. When stratified it has a low vertical permeability to water and often drys into hard horizontally laminated lumps. Dry sedimentary peat is difficult to rewet. The color of gyttja is variable. The hue varies from 2.5Y to 5YR to IOYR. The chroma varies from 1 to 4 and the value is usually 2 or 3. The acidity of gyttja is also variable. Suspensions of it may have pH values at least as low as 4.5 or they may contain free calcium carbonate. Gyttja, incidentally, has a very low solubility in saturated sodium pyrophosphate solution. 4. D y Ruttner (1953) also included dy as an organic soil material. Dy muck is composed of insoluble salts of humic acids. The calcium and the iron and aluminum salts of humic acids are common. The color of dy is usually IOYR 2/4. Its solubility in saturated sodium pyrophosphate is very high. The acidity of dy shows the same variations as does the acidity of gyttja.

5 . Marl Some organic soils contain a layer, or layers, of bog marl, calcium carbonate precipitated in bodies of water as a result of carbon dioxide

381 and bicarbonate ion utilization by plankton in photosynthesis. Marl usually is mixed with sedimentary peat derived from the plants that precipitated the marl. The color of marl of high carbonate content is usually near 5Y 6/2. It approaches the color of gyttja as it is diluted with this material. ORGANIC SOILS

6 . Diatomaceous Earth, Volcanic Ash, and Pumice Dachnowski-Stokes ( 1933) has described layers of diatomaceous earth, volcanic ash, and pumice in the organic soils of the Pacific Northwest. The diatomaceous earth layers are genetically a part of organic soil profiles in the same sense as are marl layers. This relation of diatomaceous earth to organic soil genesis will be discussed in following paragraphs of this section. Volcanic ash and pumice layers are not genetically a part of organic soil profiles. They are comparable to layers in alluvial mineral soils. The particles of diatomaceous earth and volcanic ash are too small to be seen with a hand lens in the field. Volcanic ash often contains grit which can be detected by rubbing the material between the fingers. Diatomaceous earth is usually free of such grit. Pumice is a porous volcanic glass that can be observed in the field with a hand lens. 111. STRATIGRAPHY OF ORGANIC SOILS Organic soil profiles may include layers of muck, fibrous moss peat, other fibrous peats, gyttja, diatomaceous earth, volcanic ash, pumice, dy, and marl. Studies of the stratigraphy of organic soils and of processes by which these soils are formed have shown that certain sequences of two or more of these layers are common. These sequences are spoken of as progressive if as they develop the bog changes from a wet toward a dryer state. The profile of an organic soil is made up of one or more of these sequences. Discussions of some of the more common sequences and profiles follow. 1. Marl-Gyttja Sequence One of the common sequences develops as peat formation fills a lake. Gyttja develops on top of and mixed with marl. Photosynthesis carried on by plants suspended in lake water uses up carbon dioxide and bicarbonate ions and displaces the calcium carbonate solid phasecalcium bicarbonate solution equilibrium toward calcium carbonate, (Ruttner, 1953). Also, certain plants of the Characeae group precipitate calcium carbonate in the egg wall after fertilization, while some plants of the Myxophyceae group precipitate it in the mucilage cell envelope. There is a tendency, according to Ruttner (1953), for calcium carbonate precipitated near the surface of deep water to be redissolved be-

382 J. E. DAWSON fore settling to the bottom. This sometimes causes deposits of marl to he thicker in the shallower than in the deeper parts of bogs. Such a process usually results in the formation of gyttja layers over marl layers. 2. Gyttja-Fibrous Peat Sequence A second common sequence is fibrous peat, other than moss, over gyttja peat. As a lake or other body of water is filled it becomes shallow enough for plants to grow in water with roots in the sedimentary peat. Plants that form gyttja peat usually will be present in the water. Thus, mixtures of fibrous and gyttja peats are common layers over relatively pure gyttja layers. Marl may or may not be present under the gyttja.

3 . Fibrous Peat-Fibrous Moss Peat Sequence A third common sequence frequently observed in northern organic soils is fibrous moss peat over a layer of some other kind of fibrous peat, which may be mixed with sedimentary material. Other layers of peat may or may not occur underneath this sequence of layers. 4 . Diatomaceous Earth-Gyttja or Gyttja and Fibrous Peat Mixture Sequence

A fourth sequence was observed in Oregon by Dachnowski-Stokes (1933). It consists of gyttja or gyttja and fibrous peat mixture over diatomaceous earth which is a sedimentary siliceous material formed by diatoms, blue-green algae. It should be noticed that other members of the blue-green algae group of plants form gyttja and participate in precipitation of calcium carbonate. Thus, the formation of these diatomaceous earth and marl layers is dependent upon plants which grow in open bodies of water.

5 . Sequences Including Muck as a Layer Oxidation resulting from a lowering of the water table into or below an organic soil can convert any of the above organic layers into muck. Sequences such as muck over fibrous peat, fibrous moss peat, gyttja, marl, or diatomaceous earth layers have been observed.

6. Sequences Including D y as a Layer Humic acids from oxidized peat and/or from mineral soils surrounding a bog may be precipitated (Ruttner, 1953), as dy by ions entering the bog from limestone. These layers are sometimes found as the bottom ones of organic soils over sand.

ORGANIC SOILS

383

7. Profiles Including Sedimentary Layers Organic soil profiles formed by the filling of relatively deep lakes may have a basal layer of marl, diatomaceous earth, or gyttja. Profiles progressively and completely developed on a basal layer of either marl or diatomaceous earth often consist, from bottom to top, of layers of gyttja, fibrous peat-gyttja mixture, and muck. Profiles progressively and completely developed on a basal layer of gyttja are often the same as the corresponding part of the preceding profile. All possible incompletely developed profiles of this group, with and without surface layers of muck, have been observed by Auer (1933), Dachnowski-Stokes (1933), and Rigg (1940a, b). In addition, profiles have been observed with a basal layer of both marl or gyttja that have surface layers of fibrous moss peat. 8 . Profiles Not Including Sedimentary Layers Organic soil profiles formed either on dry land or by filling shallow bodies of water may have a basal layer of fibrous peat-gyttja mixture, fibrous moss peat, or dy. Profiles progressively and completely developed on a basal layer of dy will consist, from bottom to top, of layers of fibrous peat-gyttja mixture, fibrous moss peat, and muck. Similarly developed profiles on a basal layer of fibrous peat-gyttja mixture will consist, from bottom to top, of layers of fibrous moss peat and muck. Some profiles are fibrous peat throughout. Many of the possible incompletely developed profiles in this group have been described by Auer ( 1933) ,Dachnowski-Stokes ( 1933), and Rigg ( 1940a, b) .

9. Profiles Involving Regressive Development In addition to the progressively developed and rather simple soil profiles described in Sections 111, 7 and 8, there are others that involve regressive development. About one-fourth of the profiles described by Dachnowski-Stokes (1933) were of this type. These profiles may consist of as many as seven or eight layers and may include the sequence, marl under gyttja over fibrous reed and sedge peat which is normally the next layer above the marl-gyttja sequence. This particular regressive change obviously resulted from a considerable and sudden increase in bog water depth. I n fact, regressive development often does involve large and sudden changes in bog water depth.

10. Causes of Variety in Organic Soil Profiles It can be seen from the material presented in this section that different organic soil profiles result from three causes. First, different profiles are observed because of variations in the completeness of

384 J. E. DAWSON development of the soil. Second, different profiles are observed because of variations in initiation of these formations. Third, different profiles are observed because of regressive development. OF PEAT SOILS IV. RATEOF FORMATION

I. Rate for Organic Layers from Pollen Distributions Flowering plants produce pollen grains which are covered with a chitinous layer that is very resistant to decomposition. Each year, pollen grains typical of the plants of the year have settled on peat bogs and been preserved. In the course of time, there have been several marked changes in the pollen grains deposited on peat each year. It is possible to recover pollen grains from peat, to identify them, and thus to observe these changes as a function of depth of peat. Godwin (1934a) has published dates at which certain of these changes took place. Using Godwin’s (1934a) dates and pollen curves from Godwin (1934b, 1941), Godwin and Mitchell (1938), Hardy ( 1939), and Hyde (1940), Dawson (1950) has shown that peat accumulation has occurred at a rate of 0.0021 f 0.0006 foot per year. 2. Rate for Organic Layers from Radiocarbon Dates Since Dawson’s publication, a number of radiocarbon dates have become available for peat from Arnold and Libby (1951), Libby (1951, 1954), and Preston et al. (1955). These data show a n average rate of formation of 0.0021 -1- 0.0013 foot per year. These data indicate that the average time for formation of 1 foot of peat is about 500 years. Deevey et al. (1954) have called attention to the incorporation of old nonradioactive carbon from limestone into water plants growing in hard water lakes. Radiocarbon data on sedimentary material were not included in the above average for this reason.

3 . Eflect of Plant Nutrients on Rate of Formation

For peat formation to take place at the above rate over long periods of time on continuously waterlogged sites, large amounts of inorganic elements must be transported into bogs from outside sources. Dawson (1950) has reviewed this situation. The data he presented show that rain water is an adequate source of sulfur for peat formation. They show that much larger drainage areas or watersheds are required to supply the nitrogen than are required to supply any other element. In the case of oligotrophic peats which may contain I per cent or less of nitrogen, the difference between the watershed required for nitrogen and phosphorus is not great. These data show that if availability of any

385 element determines the rate of peat formation or determines whether eutrophic or oligotrophic peat forms, nitrogen is the most likely element. 4 . Rate of Marl Layer Formation Portner (1951) has published an article on the mechanism and rate of marl deposition in lakes. He found marl to be formed at a rate of 0.0020 0.0007 foot per year. Both Portner (1951) and Ruttner (1953) have indicated that formation of marl is a result of plants absorbing carbon dioxide and/or bicarbonate ion, thereby displacing the calcium carbonate solid-calcium bicarbonate in solution equilibrium toward calcium carbonate. Thus, marl is usually a mixture of calcium carbonate and sedimentary peat formed from the plants that precipitated the carbonate. Sedimentary peat formation usually follows marl formation in profile development. Sedimentary peat formation, on the other hand, is not necessarily accompanied or preceded by marl formation. V. SUBSIDENCE OF ORGANICSOILS ORGANIC SOILS

*

1. Rate of Subsidence Organic soils subside, or decrease in elevation, when the water table is maintained below the soil surface. Subsidence is rapid enough to be reliably measured over a period of a few years. Measurements of subsidence have been made at regular intervals since 1922 by Weir (1950) on the San Joaquin delta area in California. Measurements have also been made several times since 1914 by Clayton (1936, 1937) along a number of subsidence lines on the Everglades peat area in Florida. In California, the average annual subsidence increment was 0.25 +- 0.04 foot, and the annual increment for the last period, 1948 to 1955, was 0.19 & 0.05 foot. I n Florida, according to Clayton (1936, 1937), the annual increment for the last period was 0.14 -t 0.03 foot. These large differences probably are not primarily a result of errors in subsidence measurement, but they are instead variations in subsidence due to variations in variables controlling subsidence. 2. Effect of Depth to Water Table on Rate of Subsidence Roe (1936) has shown that subsidence in Minnesota increases as depth to water table increases. These data show an annual subsidence increment per foot of soil above the water table of 0.07 f 0.03 foot for water table depths of 1.2 to 4.3 feet. Jones (1948) has also obtained data from Florida relating depth of water table to subsidence, The annual subsidence increment per foot of soil above the water table that he obtained was 0.040 0.007 foot for water table depths of 1 to 3 feet.

*

386 J. E. DAWSON Depth to water table fluctuated significantly in areas on which both Weir and Clayton measured subsidence, and these variations undoubtedly contributed to the differences between and the variations in their measurements,

3. Effect of Organic Matter Content on Rate of Subsidence Subsidence on soils high in organic matter has also been observed to exceed subsidence on soils lower in organic matter (Weir, 1950). Variations in subsidence with organic matter content has caused the soil surface to develop a slope toward the center of the islands in the San Joaquin delta area investigated by Weir (1950). In addition, a former slough way filled many years ago is now several feet higher than the surrounding soil of higher organic matter content. This reversal of topography has sometimes been described in the literature as inverted profiles. 4 . Effect of Time after Drainage on Rate of Subsidence The subsidence rate immediately following drainage has been observed to be faster than the rate several years after drainage. The difference between Weir’s average and final subsidence increments involved this factor. Clayton’s (1936, 1937) data show an especially large initial annual subsidence increment, 0.8 & 0.3 feet per year, for an average period of 1.5 & 0.5 years.

5 . Causes of Subsidence At least five causes of subsidence, oxidation, fire, compaction, shrinkage, and wind erosion, have been suggested. Both Clayton (1936, 1937) and Weir (1950) have suggested that oxidation is the major cause of subsidence. This conclusion is deduced rather than observed. It is based upon the following facts. First, subsidence is proportional to depth to water table. Second, the volume weight of the surface layer of most drained organic soils is only about two times the volume weight of deeper layers of soil. Third, subsidence has occurred along lines crossing areas that had not been burned. Fourth, cultivation has not been observed to increase subsidence by more than a trivial amount. These combined observations indicate that fire, compaction, and wind erosion have not been important as causes of subsidence, The very high initial rates of subsidence involve oxidation and shrinkage. Since Clayton et al. (1942) did not observe the increase in volume weight of surface soil mentioned above on uncultivated areas that had been drained, it is presumed that shrinkage may not be an important cause of the high initial rate of subsidence already mentioned.

387

ORGANIC SOILS

VI. SOMECHEMICALPROPERTIES OF ORGANICSOILS OF SIGNIFICANCE IN CROPPRODUCTION

2. Soil Tests as a Measure of Fertility Status Virgin organic soils are of low fertility level with respect to phosphate and potassium. To obtain high yields of intensively cultivated crops on these soils over long periods of time, it is necessary to fertilize them heavily with both these elements. Soil-testing methods have been extensively applied to these soils in Michigan by Bigger et al. (1953), in Florida by Forsee and Hoffman (1950, 1951), Forsee (1945) and Forsee et al. (1954), and in New York by Lathwell and the author. TABLE I1 Relations of Soil Test Values for Phosphorus and Potassium to Phosphate and Potash Applied, Respectively Extracting solution 0.10 N HCl and 0.0s N NHlF 0.155 N HCI 0.018 N CHaCOOH 1.4 N CHaCOONa CHaCOOH to pH 4.8 Morgan's solution

+

89%

NaNOa

0.155 N HCI 0.018 N CHsCOOH 1.4 N CHaCOONa CHaCOOH to pH 4.8 Morgan's solution

+

Regression line'

+

P

= l.Ol(P~0s) 11 P = l.l2(P206) - 88 P = 0.86(PzOa)- S . 8

P = 1.58(PzOa) - 15

K K K

+ 76 + 88 + 88

= 1.15(KzO) = l.lO(Kz0) = 0.63(K20)

K = 4.26(&0)

- 184

Correlation coefficient 0.986 0.915 0.967 0.959 0.64 0.67 0.67 0.948

* Soil test P and K values are expressed in p.p.m. of soil except for Morgan's (1957) solution values obtained in New York. These values are in pounda per 2 million pounds of soil. Pro, and L O values are all expressed in pounds per acre of soil.

Bigger et al. (1953) have analyzed samples from the Michigan fertility experiment involving ten fertilizer mixtures applied annually from 1941 to 1950. They found that both phosphorus and potassium by soil tests are linearly related to the amount of these elements applied annually in the fertilizer treatments for all extracting solutions used. Samples from this experiment have also been taken, analyzed, and correlated by Davis, Lathwell, and Dawson, respectively, and similar relations were observed between fertilizer applied and soil test values. A summary of these data are presented in Table 11. It shows that soil tests for phosphorus and potassium are highly correlated with fertilizer practices. Samples from Florida fertility experiments have been analyzed by Forsee et al. (1954) in Florida and by Lathwell and Dawson in New York. Forsee et al. (1954) used water as extractant for phosphorus and

388 J. E. DAWSON 0.5 N acetic acid as extractant for potassium. Lathwell and Dawson used Morgan's solution (1937) as extractant. Forsee et al. (1954) expressed their results as pounds per acre 6 inches of soil. Straight lines were obtained when Florida soil test values per unit volume were plotted against New York values per unit weight. Variations in volume weight caused different lines to be obtained for different areas of soil. Despite this fact, both weight and volume are still being used to express the soil test results on organic soils. Good correlations have been obtained by Forsee et al. (1954) between crop yields and soil test values and also between crop composition and soil test values. Bigger TABLE I11 Relation of Organic Soil pH Values to Soil Test Aluminum Soil test aluminum, in lb. per 2 million lb. of soil pH of soil suspension <4.6

4.6-4.9 6 .O-6.1 6 .P-6.S 6.4-6.6 6.6-6.7

6.8-6.9 6.0-6.4 >6.4

0-19

QO-39

40-69

60-79

20 46 74 137 166 164 137 61 39

6 36 66 66

6 44 60 98

77 49

86 36

38

19

2% 16 9

6

37 1s 11

1%

6

6

a

a

3

a

1

1

0

4

21 10

3%

Se99

0 17 16 11 19 9

100-149

160-%99 >a99

16

as

60

10% 38

46 63

aa 14 12 1 0 0

a1

sa

9 P 1 1 0 0 0

et QZ. (1953), on the other hand, were unable to establish optimum levels for phosphorus and potassium for maximum yields of crops. This was because of the limited number of fertilizer analyses and rates of application in their experiment, seasonal variations in plant composition, and differential response of crops to fertilizer treatments and fertility level as measured by soil tests.

2. Lime Deficiency Nygard (1954)'has published data on the identification of lime-deficient peat soils. His study included trials on 37 peats. On 22 of these peats, growth of four lime-sensitive crops for three seasons showed that lime was required for normal crop growth. Two to three tons of calcium carbonate per acre of soil produced good growth without a substantial decrease in acidity. The calcium oxide contents of these soils ranged from 0.37 to 0.74 per cent on a n ash-free dry matter basis. On 15 of these 37 peats, growth of crops was satisfactory. The calcium oxide contents of these soils ranged from 0.78 to 3.67 per cent on an

389 ash-free dry matter basis. Nygard also reported that azotobacter was present in only one of the 22 lime-deficient peats. Vegetation on uncultivated bogs and p H were found not to be reliable indicators of limedeficient bogs. Poor crop production on acid organic soils containing more than 0.70 per cent calcium oxide is more common than Nygard’s ORGANIC SOILS

TABLE IV Relation of Organic Soil pH Values t o Soil Test Iron Soil test iron, in lb. per 2 million lb. of soil p H of soil suspension <4.5 4.5-4.9 5.0-5.1 5.2-5.3 5.4-5.5 5.6-5.7 5.8-5.9 6.W3.4 >6.4

0-19

20-39

40-59

60-79

80-99

100-149

31 130 193 318 339 959

3 56 58

8 43 20 19 11 3 1 0 0

4 17 4 11 7 4 1 1 0

5 17 11 4 5

5 34 7 7

1 1 0

0

38 40

14 19 3 1

205

84 35

s

150-299 >a99

4 6

15 29 23 11 5

29 40 11 3 0

4

1 0 0 0

0 0 0

0 0

TABLE V Relation of Soil Test Values for Aluminum and Phosphorus Soil test aluminum, lb. per 2 million lb. of soil 19 39 59 79 80- 99 100-149 150 -999 >999 0204060-

Soil test phosphorus, in Ib. per 2 million lb. of soil 0-39 40-79 80-119 190-179 180-239 240-299 300-359 360-419 >419 36

60

8

23

28 10 8 49 120 57

53 24 36 116 85 8

91 61 69 40 15 52 11 0

266

134 164 38 19 14 0 0

127 55 34 5 0 1 0 0

76 19 17 0 0 0 0 0

102 25 8

2 1 0 0 0

90

2 1 0 0 0 0 0

46 4 1 0 0 0 0 0

data indicate. Some, but not all, of these soils have high soil test values, using Morgan’s solution (1937) as extractant, for aluminum and low values for phosphorus. Data available from New York are presented in Tables 111, IV, V, and VI. These distributions indicate that pH exercises some control over soluble iron and aluminum and soluble iron and aluminum exercise even more control over soluble phosphorus. Vivianite, a ferrous phosphate mineral, has been found in organic soils by

390

J. E. DAWSON

TABLE VI Relation of Soil Test Values for Iron and Phosphorus Soil test iron, lb. per 2 million lb. of soil 0- 19 20- 59 40- 69 60- 79 80- 99 100-149 150-999 >299

Soil test phosphorus, in lb. per 2 million lb. of soil 0-39 40-79 80-119 120-179 180-289 240-299 500-559 560-419 >419

74 24

59 19 2% 29 51 65

145 65 46 18 19

so 56 19

255 47 21 10 4 2

586 46 4 1 1

0

1

0 0

0

119 0 0 0 0

154 1 1 0 0

0

0

0

0 0

0

0

215 6 1 0 1

95

0

0 0 0 0 0 0

51 0 0 0 0 0 0

0

0

0

Bushinskii (1946) and Prokopowicz (1947), and its presence is a further indication of iron control of phosphate solubility.

3. Zinc Toxicity Staker and Cummings (1941) and Staker (1944) have reported the presence of toxic concentrations of zinc in organic soils. The toxicity of zinc occurs after drainage as a result of oxidizing zinc sulfide present in undrained bogs to zinc sulfate. The source of the zinc deposited in the bogs studied by Staker is sphalerite occurring in a dolomite formation underlying the area. The author has found one other bog in which zinc toxicity occurs. In this case, the zinc was transported into the bog by a stream from higher lying mineral soils. 4 . Manganese Deficiency Organic soils having pH values of 6.0 or above and containing free calcium carbonate tend to be manganese-deficient when crops sensitive to this deficiency are grown. Similarly, when organic soils having pH values of 6.0 or more are treated with 2 tons or more oE lime, manganese deficiency is often induced in sensitive crops. These two points are illustrated by the data in Tables VII and VIII.

WORK ON PEAT SOILSAND RELATEDMATERIALS VII. RECENTCHEMICAL I . Formation of Humus and Humic Acids Organic soils often contain highly decomposed organic matter of low chroma and color value, some of which is soluble in alkali hydroxide solutions from which some is precipitated by acids. These materials

39I

ORGANIC SOILS

that form soluble alkali salts and that precipitate upon the addition of acids are called humic acids. The formation of humic acids has been studied by many people. Some of these investigations of this process are reviewed below. a. By Browning Reaction. Maillard (1917) published a paper in which he claimed that the brown material, melanoidin, formed by heating amino acids with reducing sugars, is similar to naturally occurring humic acids. The reaction is called the browning reaction. Enders and Fries (1936) again called attention to the similarity of humic acids and TABLE VII Onion Production in Relation to Lime Applied to Soils Having pH Values Greater than 5.9 (Data for 1946-1954) Lime applied (tons per acre) Onion production Satisfactory Unsatisfactory

Q tons or more

Less than Q tons

1

67 56

PO

TABLE VIII Onion Production in Relation to Presence or Absence of Free Calcium Carbonate (CaC03) in Soils Having pH Values Greater than 5.9 (Data for 1946-1954) Calcium carbonate Onion production

Present

Absent

Satisfactory unsatisfactory

IS

44

49

so

melanoidin. Enders and Marquardt ( 1941) suggested that methylglyoxal is an intermediate in the process. Enders and Sigurdsson (1947) showed that methylglyoxal will react with amino acids under physiological conditions to form humic acids. They also determined methylglyoxal in soil and found it in the extracts of 5 out of 16 soils. In food technology, this reaction has been investigated extensively and a review prepared by Hodge (1953). The reaction course as outlined by Hodge does not necessarily involve methylglyoxal, although this material when present reacts readily. According to Hodge, the initial stage of the browning reaction includes the formation of a sugar amine by condensation of a reducing sugar with an amine and an Amadori rearrangement of the sugar amine to an N substituted 1-amino-I -deoxy-2-

398

J. E. DAWSON

ketose in keto form. The intermediate stage of the reaction involves three reactions of which any, or perhaps all, may occur. First, the sugar moiety may be dehydrated. Second, amino acid (Strecker) degradation may occur. Third, fragmentation of the sugar moiety may occur. All these intermediate reactions produce aldehydes or ketones. Hodge (1953) suggested that the aldehydes and ketones produced in the intermediate stage form melanoidin by aldol condensation. Hodge (1953) indicated that sugar recovery by hydrolysis ceases after the Amadori rearrangement and that only half of the amino acid can be recovered at this point. Work dealing with the melanoidins has been reviewed by Langer (1951). He did not report a successful degradation of melanoidins to identifiable compounds by either acid or basic hydrolysis, oxidation¶ or reduction. Schuffelen and Bolt (1950) prepared Enders and Sigurdsson (1947) browning polymers from methylglyoxal and glycine. They compared their C:N ratios and their titration curves with soil humic acids. Hayes and Dawson obtained a sample of the Enders and Sigurdsson (1947) polymer prepared by Schuffelen and Bolt (1950) and compared it by electrophoresis with Maillard (1917) polymer synthesized from glucose and glycine and also with brown material from an organic soil. Both the Enders polymer and the Maillard polymer had lower mobilities than the soil material. This difference in mobility was large enough for a mixture of the Enders polymer and soil material to be resolved into two zones by column electrophoresis. Enders et al. (1948) have noted that melanoidin has a lower exchange capacity than natural humic acid. This difference in exchange capacity and the difference in mobility observed by Hayes and Dawson (to be published) are consistent. b. By Microorganisms. The browning reaction is not a process carried out by microorganisms, although they may contribute reactants. Many microbiological studies have been made recently under conditions that lead to humic acid formation. For example, pigments and fruiting bodies from several organisms have been converted into humic acids. Kiister (1952) started with a pigment from Aspergillus niger and one from a Streptomyces. Dark brown end products were obtained from cultures containing these two pigments after 55 and 28 days, respectively. Plotho (1951) exposed a pigment from an Aspergillus and one from an Actinomyces to atmospheric oxidation. He obtained humic acids in both cases. Humic acids have also been produced by growth of a variety of organisms in nutrient solutions. I n these studies, the effect of carbon and nitrogen sources and p H of cultural solution have been investigated. Plotho (1950) observed that Aspergillus and Fusarium could use sodium nitrate as a nitrogen source, Fusarium, Actinomyces, and

393 several bacteria could use glutamic acid, and Penicillium could use ammonium salts. Flaig et al. (1952) observed that Streptomyces grown in a medium containing glycerol and one amino acid produced humiclike substances when some 14 but not all of .32 amino acids were used. Flaig (1952) and Laatsch et al. (1952) grew streptomycetes and Spicaria elegans, respectively, in a medium containing peptone and obtained humic acids. Scheffer et al. (1950) grew eight strains of Actinomyces and observed that the yield of humus depended upon the carbon and the nitrogen source. These authors also observed that brown substances were formed by autolysis. Kiister (1950) observed that Aspergillus niger produced heterocyclic nitrogen compounds in the course of autolysis. The distribution of nitrogen in fungus humus between amide, amino, and heterocyclic nuclei was similar to that of soil humus. Pochon and Wang (1950) reported that metabolism of benzoic acid by azotobacter produced a black substance related to humus. Kiister ( 1953) reported production of polyphenoloxidases by the azotobacter, aspergilli, and basidiomycetes. He suggested that polyphenoloxidases are concerned in humus formation. Both chemically and microbiologically produced brown materials have been very superficially compared with the brown components of soils in the above publications. This statement is not a criticism of these authors since few, if any, of the above substances have been definitely characterized. Data on electrophoretic mobility, intrinsic viscosity, functional group content, numbers of acidic groups, and their intrinsic association constants would improve the above situation. c. Specific Effects and Humic Acids. In the last few years, a number of observations have been made, some of which may be specific effects. However, none of these observations has been exploited as specific effects usually are exploited in biological chemistry. Pochon and de Barjac (1952) reported aqueous extracts of peat to inhibit strongly all bacteria found in normal soils and to be especially effective in inhibiting cultures of Azotobacter chroococcum. Alfoldy (1949) reported an inhibition of Escherichia coli by sterilized peat. The active fraction was the humic acid one and the authors believed the active substance to be acidic hydrogen. Volkova and Shinkarenko (1946) reported that the bactericidal power of Tainbukan mud persists after sterilization and therefore is not due to bacteriophages or antibiotics. The active component can be extracted with ethanol containing hydrochloric acid or citric acid, and it is more toxic to staphylococci than 0.25 per cent sulfanilamide. A Japanese patent was issued to Oshima (1946) for extraction of a germicide from peat. On the other hand, both Kudrina ( 1951) and Tarovderov (1950) have contended that sterilized humic acid and peat have no bactericidal power. ORGANIC SOILS

394

J. E. DAWSON

2. Inorganic Composition of Organic Soils

a. Trace Element Content. Articles by Gordon (1952), Malyuga (1945), and Salmi (1950) have appeared recently on the trace element content of organic soils. Salmi (1950) analyzed a number of organic soil samples for copper, zinc, cadmium, nickel, lead, manganese, and cobalt. In discussing these data, he observed that peat bogs act as collectors of trace elements and that copper contents greater than 0.1 per cent, zinc contents greater than 0.6 to 1.0 per cent, and nickel contents greater than 0.06 to 0.1 per cent of peat probably indicate ore deposits within the watershed of the bog. The high zinc soils near Elba, New York, described by Staker (1944) and Staker and Cummings (1941) are an especially striking example. The zinc content of these soils is high because of the occurrence of sphalerite in dolomite underlying the bog. Oxygen carrying ground water has converted some of the sphalerite to zinc sulfate and transported it into the bog where the sulfate has been reduced to sulfide and reprecipitated zinc as the sulfide. Zinc contents of organic soils in this area range up to 8 per cent zinc. Upon drainage, soils containing excessive amounts of zinc have been shown to produce poor crop growth because of zinc toxicity. In view of this situation, the trace element content of both organic soils and the waters of rivers and lakes in their watersheds are of interest in connection with organic soil formation and composition. Malyuga (1945) has published data on the latter and Gordon (1952) on the former. b. Vivianite and Siderite. Bushinskii (1946) has published a paper on the formation of siderite, vivianite, and brown iron ore in the peat bogs of White Russia. He indicates that when the drainage area of a bog is acid, the waters entering the bog from this area are acid and contain iron, manganese, and phosphorus among other elements. When such a bog also receives alkaline spring water and when mixing of these waters occurs within the bog, lenses of vivianite, white to blue ferrous phosphate, and siderite, gray ferrous carbonate, will be formed in the pH range 7.2 to 7.4. Marl will be formed in the pH range 7.5 to 8.0. He also suggested that brown bog iron ore results from oxidation of siderite. Prokopowicz (1947) has also published on the origin of vivianite peat. He has suggested that the phosphorus of vivianite arises as a result of decomposition of bog material and that the iron in vivianite comes from ground water. He has indicated that the peat plays no essential role in the formation of vivianite beyond maintenance of satisfactory pH values and reducing conditions. Publications by Baranov and Novitskaya (1949a, b) , S t r m ( 1948), and Szalay (1954) have reported accumulation of uranium and/or radon in peat muds and brown coal. These accumulations were associ-

ORGANIC SOILS

395

ated with granitic rocks in the watershed of higher than average uranium contents, according to S t r m ( 1948) and Szalay (1954). c. Sulfur. Sugawara et al. (1953, 1954) and Tadashiro and Sugawara (1953) in a series of papers on the forms of sulfur in lake mud flooded at high tide by ocean water observed sulfate, sulfide, free sulfur, and a solid phase of iron pyrite, ferrous sulfide. It should be pointed out that this is the third crystalline iron compound reported in peat in this review. Kreulen (1952) has studied the Rosa coal of Istria and found it to contain a low percentage of oxygen and 11 per cent sulfur, a large part of which occurs in ring structures. Oxidation of the coal produces humic acids containing 8 per cent sulfur. H e also reported that both coal and humic acid have large absorbing capacities for hydrogen sulfide. Articles by Larsen (1952) and Stirka (1949, 1951) dealing with organisms appearing in marine and lake sediments that participate in sulfur transformations have been published. Campbell and Skilling (1950) have studied the absorption of hydrogen sulfide by peat in the presence of ammonia. They postulate oxidation of sulfide to free sulfur as the mechanism of absorption. Thode (1954) has found that the sulfur isotope 34 is a lower percentage of total sulfur in peat than in the original sulfur source.

3. Functional Groups of Peat Soils A number of studies of the functional groups of humic acids from coal have been made. Dragunov et aZ. (1948) determined carboxyl and phenolic OH groups by methylation procedures. Kukharenko (1950) determined these groups and methoxyl groups. Syskov and Kukharenko (1947) determined phenolic OH and carboxyl groups by a titration procedure. He reacted humic acid with barium hydroxide and titrated the excess to determine the amount reacting with phenolic OH and carboxyl groups. He determined carboxyl groups by reacting the humic acid with calcium acetate and titrating the acetic acid form. Kukharenko and Borozdina (1949) studied the nature of the exchange reaction between humic acid and calcium acetate as a function of temperature, 20° to looo C., and concentration of calcium acetate. The final amount of acetic acid liberated was independent of temperature but it was increased with increasing concentrations of calcium acetate. The authors concluded that calcium acetate reacts with carboxyl but not with phenolic OH groups. This conclusion is important in connection with exchange capacity determinations on peat soils. It means, if it is true, that the exchange capacity of the peat measured by leaching with an acetate salt will not correspond to the point at which free base appears in the peat suspension upon titration with alkali hydroxides. Kukharenko (1946) has observed cupric acetate to react with both carboxyl and

396 J. E. DAWSON phenolic OH groups in humic acids, except for one OH group. I n exchange capacity determinations, barium acetate rather than cupric or calcium acetate is usually the replacing solution. Data obtained by the author in a frontal analysis chromatography (Tiselius, 1952) run involving the reaction of barium acetate with hydrogen peat are presented in Fig. 1 to illustrate this point. The data show the expected reaction of barium acetate with the carboxyl groups of the peat and they show an incomplete reaction with weaker acidic groups. When the peat had

Fraction number, 2.07 ml.

FIG. , 1. Exchange reaction of barium acetate with hydrogen-saturated peat by frontal analysis chromatography.

been exhaustively leached with barium acetate, a frontal analysis chromatography run was made using hydrochloric acid as replacing solution. The data show that exhaustive leaching with barium acetate does cause reaction with all acids of the peat sample, since the same value for exchange capacity was obtained by titration with alkali hydroxide.

4 . Solubility of Humis Acids, Peat, and Coal Studies have been made of the solubility of humic acids and coal by Dragunova ( 1954), Dryden ( 195 1) , Fromel ( 1945, 1948), and Herbert et al. (1948). Dryden (1951) observed that the better solvents for coal had either an oxygen or a nitrogen atom with an unshared pair of electrons. These solvents probably deserve more attention in organic soils work than they have received in the past so as to reduce degrada-

ORGANIC SOILS

397

tion during extraction. Since studies of humic acids by Flaig and Beutelspacher (1951), Gorbunov (1947), and Riley (1949) have shown the organic matter to be noncrystalline, solubility cannot be used as a means of determining numbers of components. Such changes in the slope of solubility curves as are observed may merely correspond to changes in a solid solution phase rather than to saturation with respect to a component.

5 . Titration Curves for Humic Acids Okuda and Shiro (1952) titrated humic acid with a positively charged colloid, chitosan-HC1, or methylated chitosan, using an indicator, toluidine blue, that shows metachromatic colors. They added a n excess of chitosan-HC1 or methylated chitosan and titrated the excess with a negative colloid, the sulfuric acid ester of potassium polyvinyl alcohol. The pH was controlled during titration with hydrochloric acid and sodium hydroxide. The procedure was originally suggested by Terayama ( 1952). Cameron (1952) titrated hydrogen-saturated peat with sodium hydroxide and at each point on the titration curve determined the pH and conductivity of both the suspension and the filtrate. He also titrated the acid and salt dissolved in the filtrate. The base of the latter was titrated in alcoholic solution with hydrochloric acid. These data show four times as much acid and nine times as much salt in solution at pH 6.37 as at pH 4.02. Cameron also found that the difference in pH between filtrate and suspension was not significant, presumably because of the solubility and low molecular weight of the peat solute. Dawson et al. ( 1 950) studied the exchange of calcium for hydrogen in the same peat Cameron studied. They found high calcium ion activities in the suspensions of this soil above 20 per cent saturation with calcium. Marshall and Patnaik (1953) measured “ionization” of salts and hymatomelanic acids by use of membrane electrodes and found high metal ion activities in their suspensions. Jones (1947) and Allaway (1945) have compared the availability of potassium from potassium humate and calcium from calcium peat with the availability of exchangeable potassium and calcium, respectively, in mineral soil and clays, respectively. These ions are more available to plants in the organic systems.

6 . Amino Acid Content of Organic Soils Kojima (1947a, b) and Bremner (1949, 1950a, b, 1952) have determined the amino acid contents of a few organic soils. Bremner (1952) has published the most comprehensive data and Kojima ( 1947b) has probably published the most quantitative data. Bremner

398 J. E. DAWSON (1952) identified 20 amino acids by paper chromatography from 10 different soils including fen and peat soils. or-c-Diaminopimelic acid was one of the 20 acids he identified. This is of interest since this substance, so far as is known, is peculiar to bacteria. This suggests that a part of the amino acids obtained from organic soils are derived from hydrolysis of microbial proteins. VIII. SOMEPROBLEMS IN STRATIGRAPHY, FORMATION, SUBSIDENCE, AND CHEMISTRY OF ORGANIC SOILS A taxonomic system of classifying peat soils that clearly brings out the similarities as well as the differences between these soils is needed. The present system being used in the United States by soil survey specialists does less than is needed. There are several difficulties inherent in the present system. In the f i s t place, too much emphasis is placed on surface layers, which are the layers most subject to change. In the second place, sedimentary peat, gyttja, has been described as muck or as mucky peat when mixed with fibrous peat. Yet, these sedimentary materials are not highly decomposed as are the small particles of muck. Methods of formation of organic soils have been discussed by Auer (1933). In general, these methods of formation produce many of the sequences of layers of organic soil materials discussed in this review in Section 111, “Stratigraphy of Organic Soils.” A system of classification of these soils could and should be developed based on organic soil materials and the sequences of these materials that occur. Work completed to date on the subsidence of organic soils needs to be expanded especially in areas of lower temperature than Florida and California. This work should be done on areas where water table control is practiced. Chemical work on organic soils of several kinds is needed. In the first place, very few analyses for inorganic elements have been published for adequately described profiles of organic soils. Work of this type would help considerably in setting up a system for classifying these soils. Second, the reviewer does not consider the nature of humus, the brown material of organic soils, to be a satisfactorily settled problem. For example, if humus were a lignin-protein complex, as is often suggested in soils publications, it would not dialyze through cellophane membranes. It does, however, dialyze through these membranes. It has also been suggested that humus is a browning polymer. Since neither polymer has been adequately characterized, this suggestion is premature. A degradation reaction has not yet been found that will yield identifiable simple molecules when applied to humus. It has also been found that certain microorganisms produce brown materials when grown for long

ORGANIC SOILS

399

periods in media containing a suitable carbon and nitrogen source. Autolysis of microbial tissue probably is important in some media in this process. Since degradative products of these brown materials cannot be used to characterize them, it seems that there are only two choices. First, characterize the brown particles as they occur and second, continue the search for a degradative reaction applicable to them. In characterizing these brown particles modern quantitative analytical methods for functional groups should be used. More detailed and accurate titration curves should be published, if they are resolved into numbers and types of acidic groups of various association constants. Electrophoretic data on these brown materials would be helpful, but one should note that the low molecular weight of peat humus and the dark colors of all these substances will make work in this field difficult. Third, there is a need for work on the interaction of ions such as iron, aluminum, manganese, and copper with humus. Dialysis, however, cannot be used as in similar protein studies because of the diffusion of humus through cellophane membranes. There are many other problems that could be mentioned, but these are certainly some of those that are or should be under investigation.

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400

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Dawson, J. E. 1950. I n “Agricultural Chemistry” (D. E. H. Frear, ed.), Vol. I, pp. 778-797.Van Nostrand, New York. Dawson, J. E., Danielson, R. E., and Cameron, D. M. 1950. Soil Sci. SOC.Amer. Proc. 15, 292-297. Deevey, E. S., Jr., Gross, M. S., Hutchinson, G. E., and Kraybill, H. L. 1954. Proc. Natl. Acad. Sci. U.S. 40,285-288. Dragunov, S. S., Zhelokhoutseva, N. J., and Strelkova, E. I. 1948. Pedology (U.S.S.R.) 1948, 409420. Dragunova, A. F. 1954.Doklady Akad. Nauk S. S. S. R. 96,77-79. Dryden, I. G. C. 1951. Fuel 30, 39-44. Enders, C., and Fries, G. 1936. Kolloid-2. 76,289-291. Enders, C., and Marquardt, H. 1941. Naturwissenschuften 29,46. Enders, C., and Sigurdsson, S. 1947. Biochem. Z . 31 8,4446. Enders, C., Tschapek, M., and Glnne, R. 1948. Kolloid-Z. 1 1 0 , 240-244. Feustel, I. C., and Byers, H. G. 1930. U.S. Dept. Agr. Tech. Bull. 214. Flaig, W . 1952.Z . Pflanzenerniihr. Dung. Bodenk. 56 (IOI),63-67. Flaig, W., and Beutelspacher, H. 1951. 2. Pflanzenerniihr. Dung. Bodenk. 52 (97), 1-21. Flaig, W.,Kiister, E., Segler-Holzweissig, G., and Beutelspacher, H. 1952. Z . Pflanzenerniihr. Diing. Bodenk. 57 (102),42-51, Forsee, W.T., Jr. 1945. Soil Sci. SOC.Florida Proc. 7,75-81. Forsee, W.T., Jr, and Hoffman, J. C. 1950. Soil Sci. SOC.Amer. Proc. 15, 297-299. Forsee, W.T., Jr., and Hoffman, J. C. 1951.Proc. Amer. SOC.Hort. Sci. 56, 261-265. Forsee, W. T., Jr., Green, V. E., Jr., Webster, R. H. 1954. Soil Sci. SOC.Amer. Proc. 18, 7679. Fromel, W. 1945. Bodenkunde u. Pflanzenerniihr. 36, 92-104. Fromel, W.1948.Kolloid-Z. 1 1 1, 166-174. Godwin, H.1934a.N e w Phytologist 33,278-305. Godwin, H. 1934b. N e w Phytologist 33, 325-358. Godwin, H. 1941.N e w Phytologist 40, 108-132. Godwin, H., and Mitchell, G. F. 1938.N e w Phytologist 37,425-454. Gorbunov, N. I. 1947. Pedology (LJ.S.S. R.) 1947,240-249. Gordon, M. 1952.Torfnachrichten 3, 12. Hardy, E.M. 1939. N e w Phytologist 38, 364-396. Herbert, S. A., Charmbury, H. B., and Kinney, C. R. 1948.Fuel 27, No. 5, 168-169. Hodge, J. E.1953.Agr. Food Chem. 1,928-943. Hyde, H. A. 1940. N e w Phytologist 39, 226233. Jones, L. A. 1948. Florida Agr. Ezpt. Sta. Bull. 442 (in cooperation with U. S. Dept. Agr. S. C. S.). Jones, U. S. 1947.Soil Sci. SOC.Amer. Proc. 12, 373-378. Kojima, R. T. 1947a.Soil Sci. 64, 157-165. Kojima, R. T. 1947b.Soil Sci. 64,245-252. Kreulen, D. J. W. 1952.Fuel 31, 462467. Kudrina, E. S. 1951. Trudy Pochvennogo Inst. im. V . V . Dokuchaeua Akad. Nauk S. S. S.R. 30. 185-253. Kukharenko, T. A. 1946. J . Appl. Chem. ( U . S. S. R.) 19, 187-195. Kukharenko, T. A. 1950. Torfyanaya Prom. 27, No. 12,23-26. Kukharenko, T. A., and Borozdina, L. A, 1949.Kolloid, Zhur. 11, 244-250. Kiister, E. 1950. Arch. Mikrobiol. 15, 1-12. Kiister, E. 1952. 2. Pflanzenerniihr. Dung. Bodenk. 57 (102),51-57. Kiister, E. 1953. Zentr. Bakteriol. Parasitenk. 160,207-213.

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40 1

Laatsch, W., Hoops, L., and Bieneck, 0. 1952. Z. Pflanzenerniihr. Dung. Bodenk. 58 ( 103), 258-268. Langer, A. W. 1951. Ph.D. Thesis, Ohio State University. Larsen, H. 1952. I . Bacteriol. 64, 187-196. Libby, W. F. 1951. Science 114,No.2960,291-296. Libby, W. F. 1954.Science 120, No. 3123, 733-742, Maillard, L. C. 1917. Ann chim. 7, 11S152. Malyuga, D. P. 194,5.Compt. rend. acad. sci. U . R. S. S.48, 113-116. Marshall, C.E.,and Patnaik, N. 1953. Soil Sci. 75, 153-156. Morgan, M.F. 1937. Connecticut Agr. Expt. Sta. Bull. 392. Nygard, I . J. 1954. Soil Sci. SOC.Amer. Proc. 18, 188-192. Okuda, A., and Shiro, H. 1952. Bull. Research Inst. Food Sci. Kyoto Univ. No. 9, 24-32. Oshima, K. 1946. Japanese Patent 172,573 (April 30). Plotho, 0. V. 1950. Z Pflanzenerniihr. Dung. Bodenk. 51 (96),212-224. Plotho, 0.V. 1951.2.Pflanzenerniihr. Dung. Bodenk. 55 (loo), 151-169. Pochon, J., and de Barjac, H. 1952. Ann. inst. Pasteur 83, 196-199. Pochon, J., and Wang, T. L. 1950. Compt. rend. 230, 151-152. Portner, C. 1951. Geol. Rundschau 39, 212-216. Preston, R. S., Preston, E., and Deevey, E. S., Jr. 1955.Science 122, No.3177,954-960. Prokopowicz, N. 1947. Z. Naturforsch. 2b, 404-406. Rigg, G.B. 194Oa. Botan. Rev. 6,666693. Rigg, G.B. 1940b.Am. J . Botany 27, 1-14. Riley, H.L. 1949. 1. Soil Sci. 1, 104-111. Roe, H.B. 1936. Minnesota Agr. E r p t . Sta. Bull. 330. Ruttner, F. 1953. (Translated by Frey, D. G., and Fry, F. E. J.) “Fundamentals of Limnology.” 2nd ed. University of Toronto Prcss. Salmi, M. 1950. Geol. Tutkimuslaitos 51, 20. Scheffer, F., Plotho, 0. V., and Welte, E. 1950. Landwirtsch. Forsch. 1, 81-92. Schuffelen, A. C., and Bolt, G. H. 1950. Ouerfruk Uit Het hndbouwkundig Tijdschrift 62 ste Jaargang No. 4/5. Staker, E. V. 1944.Soil Sci. SOC.Amer. Proc. 8 , 345. Staker, E. V.,and Cummings, R. W. 1941. Soil Sci. SOC.Amer. Proc. 6, u)7-213. Stirka, J. 1949. Casopis CeskLho Lgkdrnictva 62, 100-103. Stirka, J. 1951.Biol. Listy 32, 108-118. Strram, K.M. 1948.Nature 162, 922. Sugawara, K.,Koyama, T., and Kozawa, A. 1953. J . Earth Sci. Nagoya Univ. 1, 1 7-23. Sugawara, K., Koyama, T., and Kozawa, A. 1954. J . Earth Sci. Nagoya Univ. 2, 1 4 . Syskov, K. I., and Kukharenko, T. A. 1947.Zauodskaya Lab. 13, 25-28. Szalay, S. 1954. Acia Geol. Acad. Sci. Hung. 2, 299-311. Tadashiro, K.,and Sugawara, K. 1953. J . Earth Sci. Nagoya Uniu. 1,24-34. Tarovderov, L. N.1950. Veterinuriya 27, No. 10,40-43. Terayama, H.1952.J . Polymer Sci. 8 . 243-253. Thode, H. G. 1954. Can. Mining Met. Bull. 507,463-465. Tiselius, A. 1952. Endeavour 1 1 , No.41,5-16. Volkova, 0.Y.,and Shinkarenko, A. L. 1946. Mikrobiologiya 15, 319-324. Weir, W. W.1950. Hilgardia 20, 37-56. Wilson, B. D., and Staker, E. V. 1932.Cornell Agr. Expt. Sta. Bull, 537.

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Author Index Numbers in italic indicate the pages on which the references are listed. A

Adams, A. F. R., 168, 177, 186,202 Adams, D.,251, 252,281 Adams, M.W.,142,159 Adams, W.L.,350, 370 Agarwala, S. C., 171, 174, 180, 199, 200,

201

Ahlgren, H. L., 211,239 Akerberg, E.,141, 159 Akerman, A., 143, 159 Moldy, Z.,393, 399 Allaway, W.H.,359,369, 397, 399 Allen, 0.N.,153,160 Allison, F.E.,100,123,195,201 Allison, J. L.,315, 320 Allison, R. V.,354, 368,386,399 Allison, S. L.,316, 3f5 Allison, S. S., 3, 59 Ames, J. W., 342, 373 Anderson, A. J., 164, 165, 166, 167, 168,

Arnon, D.I., 164,171, 172, 195,199 h o t , R. H., 168, 190, 194,199 Atkins, I. M.,205,236 Atkins, J. G.,315,318 Attoe, 0.J., 209, 211, 239, 258, 280, 330,

374 Atwater, W. O., 322,368 Atwood, S. S., 130,151,159,160 Auer, V.,378,383,398,399 Ausemus, E.R., 210,217,224,236 Ayers, A. D.,76, 124 B

Bailey, E. H., 259, 280 Bailey, R. Y.,286, 289, 290, 292, 295, 318 Bair, R. A., 325,336, 368, 373 Baker, G.O.,20,22,59 Baldwin, M.,9, 59 Bamberg, R. H., 210,217,224,236 169, 170, 174, 175, 176, 177, 178, Banfield, G.L.,314,318 179, 180, 182, 183, 184, 185, 186, Banfield, W.G.,136,162 187, 188, 189, 190, 191, 192, 193, Baranov, V. I., 394,399 Barber, S. A., 335,369 194, 195,196,197,198,199,201 Anderson, J. A,, 207, 233, 238 Barbier, G.,332, 368 Anderson, J. H., 324,326,360,370 Barnes, E.E.,361,373 Anderson, K. L.,206,237 Barnett, F. L.,137,160 Anderson, 0.E., 70, 72, 73, 76, 77, 98, Barnette, R. M.,354, 368 Barrie, N.,167, 202 123 Barshad, I., 178, 185, 189, 190, 197, 199 Andharia, R. M., 347,368 Bartholomew, W.V.,265, 280 Andrew, W.D.,168, 198,199 Andrews, W.B., 67, 68, 71, 74, 76, 80, Bauer, F.C.,329, 368 Baumgardner, M.F.,274, 280 81, 83, 84, 114,115, 123,124 Bayer, D.C.,311, 319 Andries, H. J., 354, 372 Anxionnaz, R., 332,371 Bayer, D.E.,311, 312, 319 Bayles, B. B., 205,238 Appleton, W.H., 329, 375 Arakeri, H.R.,205, 223,236 Beacher, R. L.,107, 108, 124 Beadles, J. R., 346, 372 Arenz, B., 354, 373 Bear, F. E.,170, 174, 178, 180, 189, 190, Armiger, W.H.,181, 191,202 192, 196, 200,330, 371 Armstrong, J. M.,141,159 Beard, D.F.,156, 157,160 Arnold, J. R., 384,399

403

404

AUTHOR INDEX

Beatty, D. W., 212, 236 Beaudry, J. R., 140, 160 Beck, J. R., 33, 59 Beck, J. V., 354, 373 Beckenbach, J. R., 328, 331, 332, 368, 374 Becker, J., 218, 224, 236 Becker, M. H., 310, 319 Beddows, A. B., 142, 160 Beeson, K. C., 343, 368 Belehradek, J., 204, 236 Bell, F. G., 25, 59 Bell, R. W., 226, 236 Bennett, N., 208, 236 Bennett, W. F., 347, 348, 368 Berger, K. C., 266, 273, 280, 330, 354, 368, 372, 374 Bertrand, D., 178, 197, 199, 200 Betty, R. C., 178, 201 Beutelspacher, H., 393, 397, 400 Bianchi, W. C., 106, 124 Bieneck, O., 393, 401 Bigger, T. C., 387, 388, 399 Bingefors, S., 141, 159 Birsch-Hirschfeld, L., 164, 200 Bishop, J. C., 106, 124 Bishop, W. D., 275, 280 Bjorkman, S. O., 136, 140, 160 Black, C. A., 260,280,330,369 Blake, M. A., 219, 237 Blanch, G. E., 31, 59 Blaser, R. E., 211, 236, 291, 309, 319, 320 Blcdgett, E. C., 21, 59 Blomfield, P. D., 169, 176, 183, 184, 200 Blue, W. G., 74, 75, 76,124 Boawn, L. C., 21, 60, 332, 335, 342, 354, 374 Bobko, E. V., 164, 200 Bock, R. M., 172, 201 Bohannon, R. A., 275,280 Bolt, G. H., 392, 401 Bondorff, K. A., 252,280 Bondurant, J. A., 358,364,365, 373 Borozdina, L. A., 395,400 Bortels, H., 164, 169, 188, 195, 200 Bosemark, N. O., 138, 160 Botting, G. W., 200 Boussingault, J., 322, 368 Bowden, W. M., 206,236 Bower, C. A., 264, 280,333, 353, 368

Boyle, W. S., 140, 160 Boynton, D., 335, 336, 368 Bradfield, R., 330, 369 Brady, N. C., 211,236 Bramley, A., 333, 340, 343,368 Brandon, J. F., 363,368 Bray, R. H., 248, 258, 261, 280, 333, 371 Breen, A. V., 181, 191,202 Bremner, J. M., 397, 398, 399 Bressman, E. N., 366, 374 Brewer, A. K., 333,340, 343, 368 Brezeale, J. F., 326, 368 Brierley, W. G., 216, 217, 236 Briggs, D. R., 210, 226, 230, 234, 238 Briggs, L. J., 367, 368 Brigham, R. O., 329,368 Brimhall, B., 346, 370,372 Brink, R. A., 205,236 Brooks, 0. L., 286,287, 289, 290, 319 Brough, 0. L., Jr., 25, 26, 60 Brown, D. A., 251,280 Brown, G. F., 128,160 Brown, I. C., 258, 260,262, 280,282 Brown, R. L., 286,289, 319 Browning, G. M., 333,368 Brunson, A. M., 344,368 Bryan, A. A., 363, 368 Bryan, 0. C., 354, 368 Buckner, G. D., 338, 368 Buckner, R. C., 286,291, 309, 319 Bula, R. J., 227,236 Bunakov, D. J., 213,236 Burema, S. J., 194, 200 Burk, D., 164, 195,200,201 Burkhart, L. F., 348,371 Burkholder, P. R., 334, 368 Burlison, W. L., 207, 237 Burnett, W. T., Jr., 172, 202 Burson, P. M., 356, 368 Burton, G. W., 130, 131, 133, 142, 151, 155, 156, 160, 161, 233, 236, 298, 305, 307, 319 Burvill, G. H., 354, 374 Buskinskii, G. I., 390, 394, 399 Byers, H. G., 379, 400 C

Caldwell, A. C., 335, 345, 362, 363, 373, 374 Cameron, D. M., 397, 399,400 Camp, A. F., 266,280

405

AUTHOR INDEX

Camp, J. P., 354, 368 Campbell, J. R., 395, 399 Cardwell, A. B., 226, 227, 236 Carnahan, H. L., 297,319 Carpenter, P. N., 268, 280 Carr, R. H., 342,346, 370, 373 Carreker, J. R., 363,364, 368, 371 Carrero, J. O., 327, 342, 370 Carrier, L. E., 227,229,236,332, 368 Carroll, J. C., 151, 160, 211, 236 Carter, J. F., 153, 154, 160 Carter, J. N., 347, 369 Caveness, E. W., 115,123 Celarier, R. P., 138, 160 Chamblee, D. S., 293, 294, 319 Chandler, W. V., 324, 326, 329, 345, 347, 348, 355, 357, 358, 359, 360, 361, 362, 363, 369, 370, 371 Chang, W., 346, 373 Chapman, H. D., 67,124 Charmbury, H. B., 396,400 Chase, A., 285, 306, 319 Chesnin, L., 335, 369 Chilcote, D. O., 311, 319 Chilton, S. J. P., 205, 238 Ching, C. B., 143, 145, 162 Chippendale, F., 168, 172, 174, 202 Church, G. L., 140,160 Clausen, J., 140, 160 Clayton, B. S., 385, 386, 399 Clements, L. B., 67, 124 Cline, M. G., 253, 254, 280 Clore, W. J., 365, 374 Coe, D. G., 357, 369 Coffman, F. A., 205,236 Colby, W. G., 252, 280 Cole, C. V., 261, 281 Collier, J. W., 357, 369 Collins, G. N., 334, 369 Colwell, W. E., 356, 360, 372 Comar, C. L., 172, 202 Comstock, R. E., 148, 158, 160, 162 Conner, S. D., 348, 374 Constable, E. W., 268, 280 Cook, H. L., 355, 359, 360, 361, 373 Cook, R. L., 261, 267, 281, 282, 349, 351, 360, 369, 371 Cooper, H. P., 353, 369 Cooper, J. P., 152, 160 Cope, J. T., Jr., 330, 369 Cormack, M. W., 212,214, 236

Cornelius, D. R., 134, 160 Corns, W. G., 206, 236 Cowan, J. R., 286, 287, 289, 291, 304, 305, 307, 308, 309, 319 Crandall, B. M., 223, 239 Crawford, C. L., 21, 60, 332, 335, 342, 347, 348, 354, 374 Crist, J. W., 324, 325, 327, 374 Crofts, F. C., 169, 200 Crowder, L. V., la, 160, 284, 285, 286, 288, 290, 292, 295, 296, 297, 298, 319, 320 Cullen, N. A., 168, 183,191, 192, 200 Cumings, G. A., 360, 371 Cummings, R. W., 259, 282, 390, 394, 401 Cunningham, I. J., 313, 314, 319 Curtis, 0. F., 230, 239 Cushman, H., 23,26, 59 Cutler, G. H., 210,211, 232, 239 D

Dachnowski-Stokes, A. P., 378, 379, 381, 382, 383, 399 Dale, T., 128, 160 Danielson, R. E., 397, 400 Datta, N. P., 171, 202 Davidson, 0. W., 219, 237 Davies, E. B., 165, 168, 171, 181, 191, 192, 195,200,266,280 Davis, C. H., 327,367,369 Davis, F. E., 325, 366, 369, 373 Davis, J. F., 387, 388, 399 Davis, W. E., 136, I 6 0 Dawson, J. E., 384, 397, 400 Dayton, W. A., 129, 161 Dean, L. A., 245, 261, 280, 281, 329, 342, 356, 360,370 372, 373 de Bajac, H., 393, 401 Deevey, E. S., Jr., 384, 400, 401 De La Lande Cremer, L. C. N., 261,282 Dermott, W., 172, 201 De Turk, E. E., 258, 280, 328, 329, 331, 333, 339, 345, 347, 349, 352, 353, 358,369, 370, 373, 374 De Vane, E. H., 298,305,307, 319 Dexter, S. T., 205, 209. 211, 212, 213, 215, 216, 217, 223, 224, 225, 226, 227,228 229,232,233,236 Dick, A. T., 172, 173,200

406

AUTHOR INDEX

Dickman, S. R., 329,369 Dickson, J. G.,153,154,160 Dikussar, I., 328,371 Dillman, A.C.,207,236 Dmitriev, K. A.,164, 196,200 Dobbins, F. A., 346, 369 Domingo, C.E.,365,366,367,373,374 Donaldson, R. W., 21 I, 237 Doneen, L.D., 106,124 Dragunov, S. S., 395, 400 Dragunova, A. F., 396, 400 Drake,F. R.,169,171,180,200 Drake, M., 252,280,349,369 Dreibelbis, F. R.,364, 370 Dreier, A. F., 88,124 Dryden, I. G.C.,396,400 Duley, F. L., 326, 330, 338, 341, 366, 367, 369, 372 Dumenil, L.,88, 124, 265, 281, 331, 347, 348, 356, 357, 358, 359, 362, 363, 368, 369, 372 Duncan, E. R., 362,369 Dungan, G.H., 363,369 Dunham, H.W., 67,124 Dunne, T.C.,171,200 Dunton, E. M.,256,280 Du Toit, J. J., 331, 369 Dyer, A.J., 286,291,320

Enden, C., 391,392,400 Eno, C. F.,74, 75,76,124 Erlanson, C. O.,129, 161 Ermilov, G.B.,218,236 Erwin, A. T.,322, 369 Evans, H. J., 168, 170, 174, 178, 180, 181, 189, 190, 192,196,200 F

Fang, C. T., 153,160 Fawcett, R. G., 167, 187, 192, 201, 202 Fehrenbacher, J. B., 325,327,369 Fejer, S. O.,152,160 Fergus, E. N.,286, 287, 289, 291, 292, 294, 319, 331, 374, 375 Ferguson, D. D., 336,338,339,341,370 Ferguson, W. S., 167,200 Ferres, H.M.,167,200 Feustel, I. C.,379, 400 Fielding, A. H.,181, 201 Filinger, G.A.,226,227,236 Fireman, M.,22,59 Fitts, J. W., 250, 254, 255, 265, 275, 276, 277,280,282, 359, 369 Flaig, W., 393, 397,400 Fondle, W.J., 290, 294, 319 Forbes, I., Jr., 316, 318 Forrest, L.A.,350,371 Forsee, W.T.,Jr., 387, 388, 400 E Fortenbery, B. W., 301,319 Fox, E. I . , 18, 19, 60,62,125 Eades, J. A., 219,236 Earley, E. B., 339, 345, 346, 347, 369, Foy, C.D., 335,369 Frandsen, K.J., 148, 160 373 Fraser, R. R., 348,374 Eck, H.V.,101,124 Freed, V. H.,311, 319 Eckhardt, R. C.,363,368 French, R. B., 354, 369 Ed&, A. H.,172,200 Fresenius, R.,322, 369 Edgington, G.,181, 191,202 Edwards, F. E., 67, 68, 71, 76, 80, 114, Frey, K. J., 346, 369 Fricke, E.F., 167, 172, 192,200 123, 124 Fried, M.,!?A6, 252, 280 m e n , P.L.,88,124,358,371 Fries, G.,391, 400 Eid, M.T.,330,369 Froier, K., 143, 159 Eisele, H.F., 363, 369 F’riimel, W.,396, 400 Eisenhart, C.,205, 236 217,218,219,224,236 Esenmenger, W. S., 211, 237, 331, 369 Fuchs, W.H., Fuelleman, R. F., 206,238 &wand, H., 214,236 Furtick, W. R., 311,319 Elgabaly, M.M.,252,280 Elliott, F. C.,137, 139,160 0 Ellis, B. G.,261,282 Eltinge, E. T.,355,369 Gall, 0. E., 354, 368 Emmert, F. M.,222,226,227,236 Gammon, N.,172, 200

AUTHOR INDEX

Garber, R. J., 154,162 Garner, W.W., 353,369 Gehenio, P.M., 204,237 Gehrke, C.W., 346,375 Gerdel, R. W., 342,357,369,375 Gholston, L.E.,275,280 Giddens, J., 275, 280 Gilbert, B. E.,350,354,369,370 Gile, P.L.,327,342,370 Gill, J. B., 294, 319 Glane, R., 392, 400 Glover, J., 331,338,351,352,361, 370 Godwin, H., 384, 400 Goforth, F.,204, 237 Good, J. M.,75, 76,124 Goodall, D.W., 348,370 Goodman, A.A.,314,319 Gorbunov, N.I., 397, 400 Gordon, M.,394, 400 Gorham, J., 322,370 Goring, C.A. I., 260,280 Gorman, L.W., 134,160 Graber, L. F., 156, 162, 206, 207, 211, 212, 213, 215, 217, 225, 226, 228, 229, 236, 237, 238 Graham, E. R., 262, 277,280 Grandfield, C. O.,21 1, 227,237 Graumann, H. O.,150, 160 Graves, J., 261, 282 Gray, B., 252,280 Greathouse, G. A,, 209, 227, 228, 233, 237 Greaves, J. E., 367, 370 Green, D.E.,172, 195,201, 202 Green, V.E.,Jr., 387,388,400 Gregor, J. W., 134, 160 Gregory, F. G., 348,370 Griffith, W.L.,291, 319 Griffiths, D.J., 147, 160 Grigg, J. L.,181, 200 Groeneveld, M.H. H., 25, 26, 60 Gross, M.S., 384, 400 Griin, P.,138,160 Gupalo, P.I., 218, 237 Guttay, J. R., 98, 105,125 Guyer, P.Q.,286, 291,320 H

Hader, R. J., 279,280 Hafenrichter, A. L.,130, 160, 286, 289, 303, 319

407

Hagle, B. J., 106,124 Hall, N. S., 324, 326, 329, 357, 360, 370, 372 Hall, R. B., 256, 280 Hamilton, B. C.,347, 370 Hamilton, F.B., 358,364,365,373 Hamilton, T.S., 346,347,369,370,372 Hammes, R. C.,291, 319 Hammons, J. G., 67,80,123,124 Hanna, W.J., 261, 282 Hansen, C.M.,98, 105,125,360,371 Hansen, D.W., 346,370 Hanson, A.A.,147,161 Hanway, J., 265, 281, 282 Hardin, L. J., 350,369 Hardison, J. R.,315,319 Hardy, E. M.,384,400 Harlan, J. R., 132, 134, 135, 138, 142, 160 Harmond, J. E., 312,319 Harper, H. J., 357,374 Harrison, C. M.,21 I, 238 Harrold, L. L.,364, 370 Harston, C. B.,28, 60 Hartridge, F.,167, 202 Harvey, P.H., 152, 158,160,162 Harvey, R. B.,204,216,227,237 Harward, M.E.,279,280, 281 Haskell, G., 207, 237 Haveler, W.,327, 370 Hawk, V. B.,143, 144, 145,160,162 Hawkins, A.,356,360,372 Hayes, H. K.,130,142,143,160 Haynes, J. D.,254,281 Haynes, J. L.,287, 289, 320,367,370 Hays, W.M.,324,325,370 Hayward, H.E.,333, 370 Heidel, H.,265, 280 Heimsch, C.,334,340,373 Hein, M.A.,129,161 Heinrichs, D.H., 146,150,154,160 Helms, H. B., 329,375 Henderson, D.W., 106,124 Henderson, R. G., 353,354,372 Henkel, P. A,, 231, 237 Herbert, S. A.,396, 400 Hester, J. B., 268, 281 Heusinkvelt, D.,213, 237 Hewitt, E. J., 166, 170, 171, 174, 179, 180, 194, 200, 201 Highsmith, R. M.,Jr., 5, 6,8, 34, 59

4Q8

AUTHOR INDEX

Hill, D. D., 286, 310, 312, 319, 320 Hill, H. D., 137, 143, 160, 161, 285, 296, 297, 319, 320 Hinsvark, 0. N., 334, 335, 370 Hitchcock, A. S., 284, 319 Hittle, C. N., 148, 160 Hoagland, D. R., 164, 166, 201 Hodge, J. E., 391, 392,400 Hodgman, C. D., 114,124 Hodson, E. A., 286, 289, 290, 295, 319 Hoerner, I. R., 328, 349, 370 Hoffer, G. N., 342,351, 352, 370 Hoffman, J. C., 387, 400 Hogan, R. M., 332, 373 Holbert, J. R., 207, 237, 333, 339, 369 Holdaway, C. W., 288, 320 Holland, D. M., 164, 201 Hollowell, E. A., 156, 157, 160, 213, 237 Holmes, G. A., 168, 192, 200 Holmes, R. S., 258, 262, 282 Holmgren, A. H., 140,160 Holowaychuck, N., 246,260,281 Holt, E. C., 315, 320 Hoops, L., 393, 401 Hoover, M. M., 129,161 Hopper, T. H., 338, 370 Horn, L., 286,288,290, 320 Hornberger, R., 322, 338, 339, 341, 342, 370 Horner, C. K., 195,201 Horner, G. M., 25, 59,99,124 Homing, T., 26, 59 Horsford, E. N., 322, 370 Hosking, J. S., 76, 124 Howe, 0. W., 325, 358, 364, 365, 366, 367, 370, 373 Howk, B. W., 333, 369 Howlett, F. S., 222, 226, 227, 228, 236, 238 Hoyert, J. H., 84,125 Huber, L. L., 362, 373 Huggins, W. C., 350, 371 Hughes, R., 134, 161 Hulburt, W. C., 360,371 Hull, H. H., 265, 282 Hunter, A. H., 262, 281 Hunter, A. S.,21, 59, 326, 345, 358, 359, 370 Hunter, J. H., 354, 368 Hurst, T. L., 346, 372 Huston, H. A., 338, 339, 341,370

Hutchinson, G. E., 384, 400 Hyde, H. A., 384,400 Hyer, E. A., 310, 319 I

Iljin, W. S., 213, 229, 232, 237 Immer, F. R., 130, 142,160 Ince, J. W., 338, 370 Inkson, R. H. E., 262, 282 Ireland, J. C., 210, 232, 237 Ivanoff, S. S., 231, 237 Ivanov, V. V., 207,212,237 J

Jackson, T. L., 99, 124 Jackson, W. A., 279, 281 Janssen, G., 226, 237 Japha, B., 218, 224, 236 Jean, F. C., 323, 324,325, 327, 370, 374 Jenkin, T. J., 140, 161, 296, 297, 298, 320 Jenny, H., 76, 124 Jensen, H. L., 169, 178, 195, 201 Jensen, M. C., 20, 59 Johnson, A. G., 207,237 Johnson, B. C., 347, 369, 370 Johnson, B. L., 139, 161 Johnson, C. M., 169, 170, 172, 174, 175, 177, 178, 179, 181, 182, 185, 189, 194, 197, 198, 201,202 Johnson, I. J., 143, 144, 148, 150, 161, 162, 204, 237 Johnson, J. R., 309, 319 Johnston, J. F. W., 67,124 Johnstone, W. C., 286,319 Jones, E. W., 171, 174, 179, 180, 200, 201 Jones, F. R., 211, 212, 237 Jones, J. D., 172, 201 Jones, J. P. 353, 370 Jones, K., 138,161 Jones, L. A., 385, 400 Jones, L. T., 171,200 Jones, U. S., 294, 319, 397, 400 Jones, W., 229, 238 Jones, W. J., Jr., 338, 339, 341, 370 Jordan, H. V., 336, 338, 339, 341, 345, 362, 370 Jugenheimer, R. W., 368,375 Jiihl, H., 138, 161 Juhl-Noodt, H., 141, 161

409

AUTHOR INDEX

Kurtz, L. T., 260, 261, 266, 280, 281, 282 Kurtz, T., 333, 371 Kiister, E., 392, 393, 400 Kuykendall, R., 89,125

Julen, G., 134, 158, 161 Jurjev, V., 225, 237 K

Kabanov, P. G., 225,237 Kaiser, V. G., 25, 26, 60 Kalmykov, K. F., 231, 237 Kalton, R. R., 135, 147, 151, 161 Karraker, P. E., 331, 375 Kaufman, R. W., 309, 320 Kehoe, J. K., 169, 171, 180,200 Keller, W., 130, 149, 150, 151, 161, 236 Kelley, 0. J., 326, 370 Kellogg, C. E., 9, 59 Kelly, J. B., 331, 374 Kempthorne, O., 330, 369 Kernkamp, M. F., 146,162 Kiesselbach, T. A., 224, 227, 239, 334, 337, 365, 367, 370,371, 372 Kinebacker, E. J., 208,237 King, F. H., 325, 371 King, W. A., 286,290,320 Kinney, C. R., 396, 400 Kipps, E. H., 167, 202 Kline, C. H., 168, 189, 201 Klipp, L. W., 262, 282 Kneebone, W. R., 145,161 Knobloch, I. W., 137, 161 Knowles, R. P., 135, 147, 150, 161 Knudsen, D., 267, 281 Knudson, L., 330, 371 Kojima, R. T., 397, 400 Kolotova, S . S., 231, 237, 350, 373 Kolterman, D. W., 262, 281 Kostjucenko, I. A., 205, 231, 237 Koyama, T., 395, 401 Kozawa, A., 395, 401 Kramer, H. H., 151,161 Kramer, P. J., 229, 237 Krantz, B. A., 329, 345, 347, 348, 352, 355, 356, 357, 358, 359, 361, 362, 363, 370,371, 372,373 Krassilnikova, A. J., 164, 201 Kraybill, H. L., 384, 400 Kreitlow, K. W., 285, 315, 320 Kreulen, D. J. W., 395,400 Krider, J. L., 346, 369 Kucinski, K. J., 211, 237, 331, 369 Kudrina, E. S., 393, 400 Kukharenko, T. A., 395,400,401

1

205,

326,

351, 360,

Laatsch, W., 393, 401 Ladd, E. F., 338, 371 Laird, K. C., 336, 338, 339, 341, 370 Lamaster, J. P., 286, 290, 320 Lamb, C. A., 212,214,233,237 Land, W. B., 364, 371 Landon, R. H., 217,236 Lang, A. L., 359, 361,371 Langer, A. W., 392,401 Larsen, H., 395, 401 Larson, C. A., 21, 60, 362, 363, 365, 371, 374 Larson, W. E., 330, 371 Latshaw, W. L., 343,344-, 368,371 Laude, H. M., 207, u)8,237 Laurent, J., 330, 371 Law, A. G., 206, 237 Lawton, K., 261, 281, 333, 353, 371, 387, 388, 399 Learner, R. W., 362,363, 365, 371,374 Leasure, J. K., 286, 288, 320 Leavitt, F. H., 67, 119, 124 Lebedev, A. M., 230,238 Lebsock, K. L., 135, 151,161 Leeper, G. W., 180, 201 Le Febure, C. L., 315, 320 Leffel, R. C., 147, 161 Leggett, G. E., 99, 125 Leng, E. R., 368, 375 Leonard, C. D., 172, 182, 191, 202, 330, 371 Leveck, H. H., 286,288,290,320 Levitt, J., 204, 210, 213, 218, 227, 230, 233, 234, 235, 237,238 Lewis, A. H., 167, 188, 189,200,201 Lewis, G. C., 20, 59 Libby, W. F., 384, 399,401 Liddell, W. J., 363, 364, 368 Lindstrom, E. W., 330,371 Little, R. C., 282 Livingston, J. E., 207, 237 Lobb, W. R., 168, 169, 172, 174, 175, 182, 183, 191, 192, 196, 198,201

410

AUTHOR INDEX

McMillen, R. W., 206,238 McMurtey, J. E., 353,369 McTaggart, A., 307,320 McVeigh, I., 334, 368 Magistad, 0. C., 267, 281, 357, 358, 371, 374 Mahler, H. R., 172, 195,201,202 Maillard, L. C., 391,392,401 Malavolta, E., 266, 281 Malyuga, D. P., 394, 401 Maneval, W. E., 330, 373 Manina, H., 357, 373 Manns, T. F., 354, 373 Marlowe, T. J., 286, 288, 290, 320 Marquardt, H., 391, 400 Marsh, R. P., 353,371 Marshall, C. E., 397,401 Mason, D. D., 259,279,280, 281 Maximov, N. A., 204,230,235,237 Mad, P., 330,332,371 Ma&, P. J., Jr., 330, 332, 37f Meader, E. M., 219, 237 Meagher, W. R., 169, 170, 174, 177, 178, 179, 181, 182, 185, 189, 194, 198, 201, 202 Mech, S. J., 22, 60 M Megee, C. R., 210, 224, 227, 229, 232, 233, 234, 238 McCall, A. G., 25, 59 Mehlich, A., 251, 252, 260, 263, 264, McCalla, T. M., 332, 373 274, 281 McClelland, C. K., 205, 235 Mehring, A. L., 63, 124 McClung, A. C., 267,281 Melsted, S. W., 333, 353, 371 McClure, J. T., 359,361,375 Mendel, L. B., 346,372 McCollum, R. E., 278,281 Mengdehl, H., 330, 375 McCormick, L. L., 88,124 Menzel, R. G., 342, 373 McCubbin, E. N., 172,200 Menzies, J. D., 365, 374 MacDonald, H. A., 151,160 Merkle, F. G., 96, 124 McElroy, W. D., 179, 201 Mevius, W., 328, 371 McGee, H. A., 353,369 Meyer, D., 187, 192, 201 MacGillivray, J. H., 368, 371 MacGregor, J. M., 87, 89, 124, 345, 358, Middleton, G. K., 206,238 Miles, I. E., 268, 275, 277, 280, 281 359, 371 Millar, C. E., 324, 326, 351, 360, 369, McHenry, J. R., 359, 369 371 MacIntire, W. H., 67, 124 Miller, E. C., 336, 343, 344, 371 Mack, W. B., 331,374 Miller, E. V., 334, 372 McKay, M. C., 23, 60 Miller, J. I., 309, 320 MacKenzie, A. J., 356,360,372 Miller, M. F., 326, 330, 338, 341, 366, Mackler, B., 172, 201 367, 369, 372 McLachlan, K. D., 167, 168, 185, 186, Miller, P. A., 346, 372 199, 201 Milligan, R. T., 168, 198,199 McLean, E. O., 251,252,281 Millikan, C. R., 172, 194,201 McLean, F. T., 350, 354,370

Lohnis, M. P., 194,201 Loneragan, J. F., 187, 192,201 Long, 0. H., 362,363,371 Loo, T. L., 328,371 Loomis, W. E., 208,236, 337,344,371 Loosli, J. K., 309, 320 Lorenze, A. O., 106,124 Lott, W. L., 279,281 Loughlin, M. E., 154,161 Love, A., f61 Love, R. M., 137, 138, 139, 141, 158,160, 161 Loworn, R. L., 293,294,319 Lowe, C. C., 142,161 Lowrey, G. W., 88, 124, 358, 359, 371, 373 Lowry, M. W., 350,371 Luebs, R. E., 258,281 Lundahl, W. S., 335, 340,375 Lunn, W. M., 353,369 Luttrell, E. S., 315, 316, 320 Luyet, B. J., 204,237 Lynch, P. B., 168, 192, 195,200,201 Lyness, A. S., 334, 371

41I

AUTHOR INDEX

Minenkov, A. R., 164; 201 Minges, P. A., 106,124 Mitchell, G. F., 384, 400 Mitchell, H. H., 346, 347, 370, 372 Mitchell, J. H., 286, 290, 320 Mitchell, K. J., 171, 201 Mogen, C. A., 22, 59 Monroe, R. A., 172, 202 Monroe, R. J., 263, 281 Montenegro, G., 335, 369 Montgomery, E. G., 365, 367, 371, 372 Montouliac, G., 349, 372 Moore, C. W. E., 195,202 Moore, D. P., 279, 280, 281 Moore, J. F., 340,343,372 Morgan, M. F., 261, 281, 387, 388, 389, 401 Morris, V. H., 341, 342, 372, 375 Morrison, F. B., 343, 372 Morrison, K. G., 21, 60 Morse, H. H., 246,260,263,281 Mosher, P., 275, 281 Moss, E. G., 353, 369 Moss, W. A., 23, 60 Moxon, A. L., 328, 338, 339,374,375 Moye, D. V., 174, 175, 192, 193, 199 Mulder, E. G., 172, 176, 178, 179, 180, 181, 183, 184, 186, 188, 194, 195, 198, 199, 201 Mullen, L. A., 286, 289, 319 Mumford, D. C., 310, 319 Miintzing, A., 138,161 Murphy, H. C., 205,238 Murphy, R. P., 142, 145, 146, 159, 161 Musser, H. B., 130, 161 Myers, W. M., 130, 137, 143, 160, 161, 205,238,285,296,297,315,320 N

Naftel, J. A., 79, 124, 328, 372 Nason, A., 179, 180, 201 Neely, J. A., 67, 71, 76, 80, 114,124 Neenan, M., 168, 181, 196,202 Neller, J. R., 386, 399 Nelson, C. E., 21, 60, 332, 335, 342, 347, 348, 354, 365, 374 Nelson, D. H., 367, 370 Nelson, L. B., 331, 356, 357, 360, 362, 363, 364, 369, 372, 373, 374

Nelson, L. G., 354, 372 Nelson, W. L., 99, 125, 260, 275, 276, 277, 278, 280, 281, 282, 329, 348, 356, 357,360, 370,371,372 Newman, R. J., 167, 176, 184, 191, 192, 201 Newton, R., 207, 233, 238 Newton, W., 229, 238 Nicholas, D. J. D., 179, 180, 181, 201 Nielsen, E. L., 135, 137, 139, 142, 161 Nilsson, F., 142, 161 Nizenjkov, N. P., 233, 238 Nobbe, F.,327, 372 Nordenskiold, H., 136, 137, 161 Norton, R. A., 333,368 Novitskaya, A. P., 394, 399 Nusbaum, C. J., 355, 372 Nygard, I. J., 388, 401 Nygren, A., 138, 161 0

Oakes, J. Y., 88,124 Oakley, R. A., 223,238 Obenshain, S. S., 259,281 Obraztzova, A. A., 164,201 Oertel, A. C., 167, 169, 176, 177, 178, 186, 187, 188, 189, 190, 191, 195, 196, 199, 201, 202 Ohlrogge, A. J., 109, 125, 331, 348, 349, 355, 358, 359, 360, 361, 372, 373 Okuda, A., 397, 401 Oldemeyer, D. L., 147, 161 Oliver, W. F., 335, 372 Olsen, C., 353, 372 Olsen, S. R., 260, 261,281, 365, 374 Olson, L. C., 349, 351, 372 Olson, P. J., 357, 372 Olson, R. A., 100, 124 OMoore, L. B., 168, 181, 196,202 Orchiston, H. D., 168, 177, 186,202 Osborn, H., 320 Osborne, T. B., 346, 372 Oshima, K., 393, 401 Owen, C. R., 152,161 P

Pack, M. R., 84, 124 Palleson, J. E., 366, 369

412

AUTHOR INDEX

Pantanelli, E., 328, 372 Parbery, N. H., 167, 192, 201 Parker, F. W., 277, 281,357,374 Parks, R. Q., 20, 60,262,282 Patnaik, N., 397, 401 Pawson, W. W., 25,26, 60 Pearl, R., 337, 372 Pearson, G. A., 172, 175, 177, 178, 179, 181, 185, 189, 194, 197, 198, 201, 202 Pearson, R. W., 329, 373 Peech, M., 330, 369 Peltier, G. L., 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 229, 238, 239 Perrier, A., 330, 371 Pesek, J., 357, 372 Peterson, N. K., 95, 124 Peto, F. H., 296, 297, 320 Pettinger, N. A., 327, 350, 353, 354, 372 Phillips, T. G., 154, 161 Pickett, R. C., 154, 155, 162 Pierre, W. H., 329, 330, 331, 350, 351, 353, 368, 371, 372, 373, 374 Piper, C. S., 164, 201 Pitner, J. B., 89, 125, 334, 359, 372 Plant, W., 172, 178, 184, 195, 201 Platt, A. W., 218, 238 Plotho, 0. V., 392, 393, 401 Pochon, J., 393, 401 Pogialle, M., 322, 372 Pohlman, G. G., 350, 351,372 Polson, A., 322, 372 Pope, A., 30, 60 Portner, C., 385, 401 Possingham, J. V., 180, 181, 201 Powers, W. L., 30, 60 Pratt, A. D., 287, 289, 320 Pratt, P. F., 246, 260, 261, 262, 263, 281, 282 Prescott, J. A., 195, 201 Preston, E., 384, 401 Preston, R. S., 384, 401 Prince, A. L., 346, 372 Prokopowicz, N., 390, 394, 401 Puhr, L. F., 360, 372 Pulsford, M. F., 313, 320 Pumphrey, F. W., 88, 124 Purvis, E. R., 166, 168, 170, 174, 178, 180, 181, 189, 190, 192, 196, 200, 201, 261, 282

0

Quisenberry, K. S., 205, 221, 222, 238, 239 R

Rabideau, G. S., 334, 340, 373 Rachie, K. D., 216,223,238 Radu, I. F., 338, 339, 373 Rampton, H. H., 286, 287, 289, 290, 292, 299, 311, 320 Rather, H. C., 21 1,227,238 Redfern, G., 332, 343, 373 Reed, H. S., 354, 373 Reed, J. F., 252, 253, 254, 255, 259, 268, 281, 282 Reeve, E., 331, 373 Reid, J. T., 309, 320 Reid, P. H., 324, 326, 360, 370 Reimer, F. C., 33, 60 Reisenauer, H. M., 99,124, 125 Reitemeier, R. F., 258, 262, 267, 281, 282 Reith, J. W. S., 262, 282 Reviakina, E. Y., 164, 201 Rhoades, H. F., 325, 358, 359, 364, 365, 366, 367, 370, 373 Richards, C. R., 309, 320 Richards, L. A., 22, 60,367, 373 Richards, S. J., 332, 373 Richardson, G. L., 294,311, 320 Richert, D. A., 172,201 Riehm, H., 261, 282 Rigg, G. B., 378, 383, 401 Rigney, J. A., 253, 254,282 Riker, A. J., 153, 160 Riley, H. L., 397, 401 Ris, J., 261, 282 Robb, A. D., 366, 373 Robbins, W. J., 330, 373 Robbins, W. R., 328, 374 Robertson, L. S., 98, 105, 125, 261, 281, 360, 371 Robertson, W. K., 109,125,359,373 Robins, J. S., 366, 367, 373 Robins, W. R., 67,125,331,332, 368 Robinson, H. F., 148, 158, 160,162 Robinson, W. O., 181, 191, 196, 202 Rodenhiser, H. A., 205, 236 Rodger, J. B. A., 216,231,238 Roe, H. B., 385, 401

AUTHOR INDEX

Rogers, H. T., 329, 373 Rogers, W. B., 359, 373 Rogler, G. A,, 139, 161, 206, 238 Rohde, G., 211, 238 Rollins, H. A., Jr., 228, 238 Romo, C., 334, 372 Rood, P. J., 261, 281,360, 371 Rosen, H. R.,205, 238 Rosenstiel, K. V., 218, 236 Rossiter, R. C., 167, 168, 187, 202 Rossman, E. C., 207, 238 Rost, C. O., 356, 368 Routley, D. J., 155,162 Rubins, E. J., 356, 360, 372 Rudorf, W., 205, 207, 224,238 Ruprecht, R. W., 354, 374 Russell, M. B., 325, 373 Russell, R.,354, 373 Ruttner, F., 380, 381, 382, 385, 401

S Sabinin, D. A., 350, 357, 373 Salisbury, J. H., 322, 373 Salmi, M., 394, 401 Salmon, S. C., 215, 217, 218, 219, 221, 222, 223, 225, 238, 239 Salmon, W. D., 346, 373 Salter, R. M., 342, 361, 373 Sarina, N. A,, 209,238 Sauberlich, H. E., 346, 373 Sawina, A. G., 164, 200 Saxby, S. H., 287, 320 Sayre, J. D., 334, 336, 337, 338, 3 4 , 341, 342, 352, 355, 359, 372, 373, 375 Scarseth, G. D., 348, 355, 358, 359, 361, 372, 373 Scarth, G. W., 210, 213, 227, 229, 234, 235, 237, 238 Schaepman, H., 148, 162 Schaller, F. W., 347, 368 Scheffer, F., 393, 401 Schmid, A. R., 143, 160, 205, 216, 236, 238 Schneider, E. O., 347, 373 Scholl, W., 18, 19, 60, 62, 125 Schoth, H. A., 130,161 Schropp, W., 354, 373 Schubert, J. R.,309, 319 Schuffelen, A, C., 252, 282, 392, 401

220,

339, 361, 360, 230,

223,

413

Schultz, H. K., 206, 238 Schulz, G. E., 218, 238 Scott, A. D., 258, 281 Scott, L. B., 289, 292, 318 Seem, B. L., 362, 373 Segler-Holzweissig, G., 393, 400 Sell, 0.E., 286, 288, 290, 294, 319, 320 Semb, G., 261,263,282 Sergeev, L. J., 230,238 Seth, J., 206, 238 Severini, G., 328, 372 Shafer, N., 335, 369 Shank, D. B., 334,373 Shantz, H. L., 326, 367,-368, 373 Shaw, E., 342, 373 Shaw, N. H., 167,202 Shaw, R. H., 356,357,358,369 Shearon, W. H., 65, 125 Sheldon, V. L., 277, 280 Sherman, M. S., 195, 201 Sherwin, H. S., 315, 316, 318, 320 Shihata, M. M., 265,282 Shinkarenko, A. L., 393, 401 Shirlow, N. S., 171, 183, 202 Shiro, H., 397, 401 Shive, J. W., 331, 332, 341, 353, 368, 371, 373, 374 Showalter, M. F., 346, 373 Shubeck, F. E., 334, 345, 362, 363, 373, 374 Shug, A. L., 195,202 Sigurdsson, S., 391, 392, 400 Silberstein, O., 335, 374 Silkett, V. W., 227, 238 Siminovitch, D., 210, 226, 229, 230, 234, 238 Singleton, H. P., 20, 60, 365, 374 Singleton, W. R.,207, 237 Skazkin, F. D., 231, 238 Skilling, W. J., 395, 399 Skinner, J. J., 354, 374 Slykius, J. T., 212,238 Smith, D., 156, 162, 205, 206, 211, 213, 223, 227, 233,236, 237, 238 Smith, D. C., 130, 142, 154,160,162 Smith, D. D., 326, 365, 374, 375 Smith, F. B., 357,374 Smith, G. D., 9, 60 Smith, G. E., 70, 71, 73, 88, 90, 96, 125, 262, 265, 273, 282, 345, 375 Smith, F. W., 261, 267, 282

414

AUTHOR INDEX

Smith, J. W., 366, 374 Smith, S. N.,334,374 Snider, H.J., 325, 327,332, 369, 374 Snyder, L.A.,136, 138,160,162 Sommers, A. L.,266, 282 Sorensen, E. L.,138,162 Spencer, D.,167, 168, 169, 174, 175, 176,

178, 179, 180, 186, 187, 188, 193, 194, 195,199,201,202 Spencer, J. T., 311,320 Spencer, V. E.,328,342,374 Spencer, W.F.,266,282 Sprague, A. F.,363,368 Sprague, G.F.,346,370 Sprague, M.A.,207,213,238 Sprague, V. G.,154, 161, 206, 207, 211, 229, 237, 238 Spurr, W.B., 333,370 Stace, H.C.T., 196,201 Staker, E.V.,379,390,394,401 Stanfield, K.E.,195, 202 Stanford, G., 258, 265, 281, 282, 331, 347,348,356,357,360,368,374 Stanley, F.A.,70, 71, 73,125 Stirka, J., 395, 401 Stebbins, G.L.,135, 136, 139,162 Steinberg, R. A.,164, 171, 188,202 Steinmetz, F. H.,210, 215, 217, 232, 233, 238 Steph, J., 322, 374 Stephens, C.G.,167, 169,202 Stewart, B. A.,101, 124 Stewart, I., 172, 182,191, 202 Stoez, A. D.,130,160 Stout, P.R., 164, 169, 170,171, 172, 174, 175, 177, 178, 179, 181, 182, 185, 189, 194, 195, 197, 198, 199,201,202 Straib, W., 218,222, 239 Strang, J., 168, 202 Strelkova, E.I., 395, 400 Stringfield, G.H.,362,363,374 Strem, K.M.,394, 395,401 Stuart, N.W., 209,227,233,237,239 Stubblefield, F.M.,331, 353,374 Stuckey, I. H.,136,162,230,239 Sugawara, K.,395, 401 Sullivan, J. T., 154, 155, 16i, i62 Suneson, C. A., 207, 219, 224, 225, 227, 229, 239 Surface, F. M., 337, 372 Sutton, M. J., 284, 320

Swinbank, J. C., 207,237 Swingle, C. F.,227, 239 Sykora, J., 357, 374 Syskov, K. I., 395, 401 Szalay, S., 394, 395, $01 t

Tabor, P., 284,290,292,301,320 Tadashiro, K.,395, 401 Takahashi, M., 168, 184,202 Tarovderov, L. N.,393,401 Tartar, H.V.,33,60 Taylor, G.A.,330,332, 374 Taylor, J. W., 205, 236 Taylor, L.H.,144, 150, 162 Taylor, M.E.,256, 280 Taylor, T. H., 291,319 Teakle, L.J. H., 167,202,354, 374 Tedin, 0..143, 159 Ten Eyck, M.A., 324,325,374 Terayama, H.,397, 401 ter Meulen, H., 197,202 Terrill, S. W., 346,369 Tesar, M.B.,211, 239 Thatcher, L.E.,362,363,374 Thode, H.G.,395,401 Thomas, H.L.,146,162 Thomas, M.P., 166, 167, 168, 169, 174,

179, 186,187, 197,198,199

Thomas, W., 331,374 Thompson, G.B., 286,320 Thompson, H.L.,65,125 Thompson, L. F.,261,282 Thompson, N.R.,288,291,320 Thornton, S. F.,348, 350,372,374 Thorp, J., 9, 59, 60 Tiedjens, V. A.,67, 125 Timmons, F. L.,218,220,223,239 Timofeeva-Tjulina, M.T.,205, 231, 239 Tiselius, A., 396, 401 Tonnesson, R. D.,109, 125 Tossell, W.L.,152,162 Totter, J. R.,172,202 Tottingham, W. E., 215, 217, 225, 226,

228, 236

Tregubenko, M. J., 211,239 Tremblay, F. T., 28, 60 Trost, J. F.,342, 370 Trumble, H.C.,f 67,200

AUTHOR INDEX

Truog, E., 209, 211, 239, 262, 265, 266, 280, 281, 282, 330, 354, 357, 358, 368, 371, 374 Tschapek, M., 392,400 Tsiang, Y. S., 144; 162 Tucker, T. C., 266, 282 Tukey, H. B., 334,335,370 Tumanov, J. J., 204, 211, 215, 216, 229, Wl, 239 Turk, K. L., 309, 320 Tyner, E. H., 330,331, 347, 374 Tysdal, H. M., 212, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 233, 238, 239 U

Uhlen, G., 261,263,282 Ulrich, A., 106, 124, 342, 374 V

Vaarama, A., 139, 162 van Bavel, C. H. M., 324, 326, 360, 370 Vander Meulen, E., 214,239 Van Der Paauw, F., 252,261,282 Van Doren, C. A., 227,239 Vanselow, A. P., 171, 202 Vetukova, A., 233, 239 Viets, F. G., 365, 374 Viets, F. G., Jr., 21, 60, 328, 332, 335, 338, 339, 342, 347, 348, 354, 362, 363, 365, 371, 374, 375 Villa, R., 334, 372 Vinall, H. H., 284, 320 Volk, G. M., 172,200,326,374 Volkova, 0. Y., 393, 401 von Stieglitz, C. R., 168, 172, 174, 202 W

Wade, D. L., 219, 236 Wade, G. C., 169, 184,202 Wadleigh, C. H., 328, 331, 341, 367, 373, 374 Wagner, R. E., 316, 318 Walker, R. B., 172,202 Walker, T. W., 168, 177, 186,202 Wallace, H. A., 366, 374 Wallace, H. M., 18, 19, 60, 62, 125 Wallace, T., 174, 202,351,374

415

Walsh, T., 168, 181, 196, 202 Walster, H. L., 357, 372 Walters, A., 349, 375 Wang, L. C., 209,211,239 Wang, T. L., 393, 401 Wang, Shih-Chung, 109, 125 Waring, E. J., 171, 179, 183, 202 Warington, K., 194, 202 Warner, J. D., 354, 368 Washko, J. B., 360, 374 Wassom, C. E., 147, 161 Watanabe, F. S., 261, 281 Watson, P. J., 134, 160 Watson, S. J., 167, 200 Waynick, D. D., 67, 119,125 Wear, J. F., 266,282 Weathenvax, P., 322, 374 Weaver, J. E., 323, 324, 325, 327, 370, 374 Webb, J. R., 331, 374 Webster, R. H., 387,388, 400 Weeks, M. E., 330,349,374,375 Weetman, L. M., 205,238 Weibel, R. O., 221, 222, 239 Weihing, R. M., 334, 337,371,375 Weimer, J. L., 210,224, 232, 233, 239 Weir, R., 167, 202 Weir, W. W., 385, 386, 401 Weiske, H., 322, 375 Weiss, M. G., 144, 147, 150, 161, 162 Weissflog, J., 330, 375 Welch, C. D., 254, 255, 275, 277, 280, 282,329, 357,370, 372 Wells, H. D., 315, 320 Welte, E., 393, 401 Welton, F. A., 211,236, 342, 375 Westerfeld, W. W., 172, 201 Westover, H. L., 223, 238 Weswig, P. H., 309, 319 Wexelsen, H., 142, 162 Whaley, W. G., 334,340,373 Wheeler, W. A., 286, 310, 320 White, W. J., 135, 141,159,161 Whitehead, E. I., 328, 338, 339, 374, 375 Whitehead, M. D., 315, 320 Whitesides, W. J., 312, 320 Whitney, I. B., 172,202 Whittles, C. L., 267, 282 Whyte, R. O., 143,159 Widtsoe, J. A., 365, 367, 375 Wieringa, K. T., 194, 200

416

AUTHOR INDEX

Wiklander, L., 252, 282 Wilcox, L. V., 267, 281 Wilhelm, A. F., 235,239 Williams, A. H., 179, 201 Williams, C. H., 195, 202 Williams, E. G., 262, 282 Williams, S . S., 151, 162 Williamson, J. T., 329, 375 Wilmer, J. A., 207, 239 Wilsie, C. P., 137, 143, 144, 145, 160, 162 Wilson, B. D., 379, 401 Wilson, J. F., 359, 361, 375 Wilson, P. W., 195, 202 Wilson, R. D., 169, 170, 171, 172, 179, 180, 183, 194, 198, 202 Wingard, S. A., 353, 354, 372 Winterberg, S. H., 67, 124 Winters, E., 260, 277, 281 Wit, F., 147, 162 Wittwer, S. H., 334, 335, 340, 370, 374, 375 Wolf, J. J., 84, 125 Woltz, W. G., 356, 360, 372 Wood, J. G., 180, 202

Wood, L. K., 30, 60 Woodruff, C. M., 252, 260, 265, 282, 326, 375 Woodworth, C. M., 368, 375 Woolfolk, P. G., 309, 320 Wormley, G. W., 268,282 Worzella, W. W., 210, 211, 212, 214, 215, 218, 221, 232, 233, 239, 360, 372 Y

Yarwood, C. E., 212, 239 Yoder, R. E., 359, 361, 375 Younge, 0. R., 168, 184,202 Yungen, J. A., 21, 59, 346, 358, 359, 370 2

Zamfirescu, N., 332,375 Zarubailo, T. J., 205, 231, 237 Zhelokhoutseva, N. J., 395, 400 Zimmerman, K., 143, 162 Zobel, M. P., 106, 124 Zoellner, J. A., 330, 369 Zuber, M. S., 345, 375

Subject Index A

crop responses, 79-1 10 distribution, 118-119 early experiments, 67-69 equipment, 110-119 in irrigation water, 67, 106, 107 manufacture, 6S67 nitrification, 75-79 physical properties, 69-70 placement, 109-110 production costs, 67 soil phosphorus release, 73 storage, 110-1 14 synthesis, 65-67 tonnage used, 62-63 Anthocyanin, 147 Anthracnose, 212 Aqua ammonia, 62, 67, 76 Arginine, 346 Arrhenatherum elatius, 56, 143 Asparagine, 329 Aspergillus niger, 181, 392 Austrian winter pea, 45, 53, 59 Avena byzantina, 205 Avena satiua, 91, 205 Azotobacter, 164, 169, 195, 197 Azotobacter chroococcum, 393

"A" value, 245, 246 Agropyron cristatum, 56 Agropyron desertorum, 47 Agropyron elongatum, 56 Agropyron intermedium, 47, 150 Agropyron repens, 14Q Agropyron trachycaulurn, 47, 56, 140 Agrostis alba, 136 Agrostis canina, 136, 140 Agrostis gigantea, 136, 140 Agrostis palusiris, 55, 136, 138 Agrostis stolanifera, 136, 138, 140 Agrostis tenuis, 56, 136, 140 Alanine, 3% Alfalfa, 21, 26, 32, 43-44, 47, 49, 130, 150, 156, 164, 184, 198, 199, 285, 293,294 winter hardiness, 204, 205, 206, 211, 212, 214, 217, 218, 219, 221, 222, 223, 224, 226, 227, 228, 230, 231, 232, 234 Alopecurus pratensis, 56 Alsike clover, 52, 294 Amino acids, 346 Ammate, 311 Ammonia, anhydrous, see Anhydrous B ammonia Ammonium fixation, 70 Bahia grass, 142, 155 Ammonium nitrate, 62, 63, 67, 68, 79, Barley, W 1 , 45, 154 81, 82, 84, 85, 87, 88, 89, 92, 93, 94, Beans, 32, 104, 198 95, 96, 97, 98, 100, 101, 102, 103, Beardless wild rye, 46 104, 105, 106, 108, 290, 328, 332 Beet leaf-hopper, 58 Ammonium phosphate, 290 Bentgrass, 55, 129 Ammonium sulfate, 63, 76, 80, 99, 100, Bermuda grass, 142, 155 106, 107, 187, 328, 331, 332, 357 Big bluegrass, 56 Anabaena, 164, 169 Birdsfoot trefoil, 52, 54, 204, 294 Andropogon scoparius, 134 Boron, 354-355 Anhydrous ammonia, Bromegrass, 131, 132, 135, 137, 143, 144, application, 110-114 145, 146, 147, 150, 151, 152, 153, behavior in soil, 70-79 154 bleeding losses, 114-1 18 Bromus carinatus, 142 417

418

SUBJECT INDEX

Bromus erectus, 139 Bromus inermis, 47, 56, 131, 139 Brornus pumpellianus, 139 Brassica oleracea, 109 Brassica oleracea capitata, 104 C

Cabbage, 104, 105 Calcium nitrate, 99, 100, 109 Carotene, 154, 155 Cauliflower, 165, 171, 172, 174, 183, 191,

195

Cercospora, 315 Chewings fescue, 55, 313 Chitosan, 397 Chlorosis, 21, 175,335,353 Clauiceps purpurea, 313 Clover, 166, 178, 185 Coal, 395, 396 Cold tolerance, see Winter hardiness Copper, 354

Corn, 21, 32, 43, 68, 79, 84-91, 109, 142, 158, 207 acreage in U. S., 321,322 ammonium absorption, 328 calcium deficiency, 353 fertilizer usage, 355-356 growth curves, 336337 mineral composition, 343345, 3473% nitrogen deficiency, 351452 nutrient requirements, 338-343 phosphate absorption, 329-330 phosphorus deficiency, 352 potassium absorption, 330 potassium deficiency, 352-353 protein content, 345-347 response to anhydrous ammonia, 8491 root system, 323-328 water requirement, 364-368 Corn mineral nutrition, 321-368 absorption zone, 324-326 accumulation of elements, 338-343 aeration effects, 333 deficiency symptoms, 351-355 dry matter accumulation, 336337 fertilizer effects, 355-361 foliar absorption, 334-336

forms absorbed, 328-331 history, 321323 ion interactions, 331 moisture effects, 326-327, 363-368 nutrient absorption, 323-334 tissue tests, 348-351 water absorption, 323-334 Corynebacterium sependoricum, 58 Cotton, 68, 79, 81-84 response to anhydrous ammonia, 81-

84

Covered smut, 39 Cow clover, 46 Crested wheat grass, 56 Crimson clover, 52,53, 288 Crown rust, 315,316 Cucumis satiuus, 105 Curly top, 58 Cynodon dactylon, 142 D

Dactylis glomerata, 26, 47, 133, 143 Dallis grass, 103, 104, 142, 152, 288 DD, 311 Defoliation, 21 1 Denitrification, 80 Deschampsia caespitosa, 46 Desert wheatgrass, 47 Diatomaceous earth, 381, 382, 383 Digitaria decumbens, 142 Disk hiller, 70, 113 Drainage, 386 Drought resistance, 151, 232 Dwarf smut, 39 Dy, 380, 382, 383 E

Ehrharta erecta, 135 Elymus canadensis, 140 Elymus glaucus, 136 Erymus interruptus, 140 Etymus macounii, 140 Elymus riparius, 140 Elymus triticoides, 46 Elymus uirginicus, 140 Elymus wieganii, 141) Ergot, 313 Erosion control, 17 Erysiphe graminis, 41

419

SUBJECT INDEX

Eutettii tenellus, 58 Exchange capacity, 395 F

Fertilizer placement, 356-358 Fescue, 101, 102 Fescue foot, 287, 313, 314, 318 Festuca arundinacea, 47, 137, 140, 284, 285,296, 297, 298 Festuca elatior, 101, 137, 284, 285, 295, 296,297,298 Festuca loliacea, 297 Festuca mairei, 307 Festuca myciros, 31 1 Festuca ouina, 140 Festuca pratensis, 138, 140, 284 Festuca rubra, 55, 129, 140 Flame photometer, 263, 264 Flax, 207 Flowrator, 68, 112, 113 Foliar sprays, 334-336 Foot rot, 39 G

Glycerophosphate, 329, 330 Glycine, 329, 346,392 Gossypium hirsutum, 81 Grass breeding, agronomic aspects, 151-152 combining ability, 143-149 crossing techniques, 149-150 cytology, 135-139 disease resistance, 152-154 environmental effects, 134-135 fertility and sterility, 141-142 history, 128-129 hybrid varieties, 150-1 5 1 inbreeding, 142-143 interspecific relations, 139-141 nature of varieties, 131-134 nutritive value, 154-1 56 radiation treatment, 158 variety maintenance, 156158 Gyttja, 380, 381, 382, 383, 398 H

Hairy vetch, 45, 53 Hardening, 151

Harding grass, 314 Helminthosporium dictyoides, 315 Helrninthosporium satiuum, 315 Holcus rnollis, 138 Hop clover, 101 Hordeum brachyantherum, 46 Hordeum jubatum, 140 Hordeum satiuum, 204 Hordeum vulgare, 91 Humic acids, 391, 392, 393, 395, 396, 397 Hymatomelanic acid, 397 Hystrii paiula, 140 I

Intermediate wheat grass, 47, 150 Interpollination, 147-148, 149 Ipomaea batatas, 105 Irrigated pasture, 287-288, 295, 317 Irrigation, 363, 364 in Pacific Northwest, 18, 20-22, 31, 33 sprinkler, 18, 27, 30, 31, 33 Iron, 342, 353 Isoleucine, 346 Isopropyl N-3-chlorophenyl carbamate (Chloro IPC), 311,312 Isopropyl N-phenylcarbamate (IPC), 311, 312

K Karmex, 31 Kentucky bluegrass, 56, 158,211 Kohlrabi, 109 1

Ladino clover, 21, 47, 52, 287, 288, 290, 291, 294, 295 seeding rate, 293 Late blight, 58 Leaching, 80 Leaf rust, 39 Lecithin, 329 Lespedeza, 294 Leucine, 346 Liming, 26!2-263, 361-362 Linum usiiatissimum, 207 Little bluestem, 134 Lolium multiflorum, 140, 296

420

SUBJECT INDEX

Lolium perenne, 47, 133, 134, 140,297 Loose smut, 39,41 Lotus corniculatus, 54,204 Lotus uliginosus, 54 Lupin, 164,198 Lycopersicon esculentum, 105 Lygus bug, 51,52 Lysine, 346

N Naphthalene acetic acid, 206 Nematodes, 58, 75 Nevada bluegrass, 46 Nicotinic acid, 347 Nitrate reductase, 179, 180 Nitrification, 72, 75-79, 95, 101, 109,

110, 180, 328 M

Manganese, 332, 353 Manganese deficiency, 390 Marl, 380-381, 383, 385 Meadow barley, 46 Meadow fescue, 137, 140,283,284, 285 Meadow foxtail, 56 Medicago hispida, 198 Medicago satiua, 43, 198,204 Melanoidin, 391, 392 Melilotw alba, 204 Methylglyoxal, 391, 392 Molybdenum, animal requirement, 172-

173 content in soils, 181-182 crop responses, 167, 184-199 distribution in plants, 178 essentiality, 164, 171 foliage sprays, 182, 184 in fertilizers, 196 nitrogen fixation, 166170 nodulation effects, 175-176, 178, 192-

193 nutrient interactions, 185-187, 194-195 plant metabolism, 170 response by pastures, 164, 165 responses in water culture, 164 toxicity, 167 Molybdenum deficiency, Australia, 167-

168 compound deficiencies, 173-1 74 correction, 182-184 detection, 173-1 74 effect of liming, 189-193 field occurrence, 166173 New Zealand, 168 nitrate accumulation, 179, 180 plant composition, 177-181 symptoms, 174-1 77 Mountain bromegrass, 142 Muck, 380, 382, 398

Nitrogen, forms used by plants, 79-81 Nitrogen fertilizer, 19, 21, 23, 24, 27, 32 Nitrogen fixation, symbiotic, 166, 169,

170, 188, 190

Nitrogen immobilization, 90, 91 Nitrogen mineralization, 265-266 Nostoc, 164, 169 Nucleic acid, 329 Nucleotides, 329 0

Oats, 41-42, 65, 79, 91,92, 93,94, 95 98,

101, 109, 164, 172,205,231 Orchardgrass, 47, 56, 133, 143, leF, 145,

147, 150, 206, 288, 289, 290, 291, 294, 313 Organic soils, amino acid content, 397398 chemical properties, 387-390,398,399 formation of humus, 390-393 functional groups, 395-396 inorganic constituents, 394-395 lime deficiency, 388-390 manganese deficiency, 390 materials, 378-381 nutrient content, 387-388 pollen distribution, 384 profiles, 383-384 radiocarbon dating, 384 rate of formation, 384-385 stratigraphy, 381-384, 398 subsidence, 385-386, 398 zinc toxicity, 390 P

Pacific Northwest crop production, cereals, 37-43 climate, 4 crop zones, 33-37 fertilizer use, 18-19

421

SUBJECT INDEX

forages, 4 3 4 7 irrigation, 18 land forms, 3-4 land use, 7 liming materials, 19 root crops, 5 6 5 8 seed crops, 47-56 silage, 46-47 soil management, 17-33 soil zones, 7-17 water resources, 4-7 Pangola grass, 142 Panicum virgatum, 133 Parsnips, 206 Paspalarn dilatum, 103, 142 Paspalurn notatum, 142 Pastinaca sativa, 206 Pastures, response to anhydrous ammonia, 101-104 Pearl millet, 133 Peas, 26,27, 164, 169,219 Peat, 378 See also Organic soils entrophic, 379, 385 fibrous, 379, 381, 382, 383,398 oligotrophic, 379, 384, 385 spalter, 379 Penniseturn glaucurn, 133 Perennial ryegrass, 47, 54,290 Phalaris arundinacea, 155 Phalaris tuberosa, 185, 314 Phaseolus vulgaris, 104 Phenylalanine, 346 Phleum nodosum, 136 Phleum pratense, 47, 128, 198, 206 Phosphorus accumulation, 339-340 Phosphorus fixation, 30 Phytin, 329 Phytophthora infestans, 58 Pisum sativum, 45, 53, 171, 219 Plasmolysis, 209 Poa alpina, 138, 141 Poa ampla, 56, 141 Poa irrigata, 138 Poa nevadensis, 46 Poa pratensis, 56, 138, 141, 211 Poa scabrella, 141 Polyphenoloxidase, 393 Polyploidy, 135, 138, 158 Potassium accumulation, 340-341 Potato scab, 58

Potatoes, 21, 5658, 212 response to anhydrous ammonia, 1 0 4 106, 109 Proline, 346 Puccinia coronata, 285 Puccinia graminis anenae, 42 Puccinia graminis tritici, 39 Puccinia rubigo-Vera tritici, 39 Pumice, 381 Pyrenophora bromi, 153 0

Quackgrass, 154 R

Radiophosphorus, 326, 340 Rattail fescue, 311 Red clover, 30, 44-45, 47, 51, 164, 167, 198, 212, 227, 294 Red fescue, 129, 133, 145 Reed canary grass, 155 Rhizobium, 170, 176, 182, 193, 198 Rhizoctonia solani, 316 Rice, 79, 106109 response to anhydrous ammonia, 106109 Ring rot, 58 Rock phosphate, 357 Rutabaga, 109 Rye, 4 M 3 , 45, 154,215 S

Saccharum oficinarurn, 104 Saline soils, 22 Sclerotiurn rolfsii, 316 Secale cereale, 91, 215 Seed certification, 129-130 Selenium toxicity, 314 Siderite, 394 Sitanion jubatum, 136 Slender wheatgrass, 47, 56 Small grains, response to anhydrous ammonia, 91-110 Smooth bromegrass, 47, 56 Sodium nitrate, 63, 89, 97, 104, 357 Soil, aeration, 333 aggregates, 72

422

SUBJECT INDEX

erosion, 25 fauna, 74 nitrogen, 264-266 phosphorus, 260-262 profile, 273 structure, 72 Soil sampling, 252-257 errors, 252-253 tools, 255 Soil testing, for lime and fertilizer requirements, area summaries, 274-278 base saturation, 262 calibration, 244-252 cation exchange capacity, 262 chemical procedures, 257-269 field studies, 245-246,248-250 future trends, 278-280 interpretation, 269-271 lime requirement, 259-260, 272 minor elements, 266267 nutrient index, 277-278 objectives, 243 pH determination, 258-259 phosphorus requirement, 260-262, 272, 387-388

potassium requirement, 262-263, 272, 387388

recommendations, 271-273 samples analyzed, 24.3-!M sampling methods, 252-257 Solanurn tuberosurn, 106,212 Sorghum, response to anhydrous ammonia, 104 Sorghum sudanense, 56 Sorghum uulgare, 129 Soybeans, 164 Spicaria elegans, 393 Starter fertilizer, 355, 356,358, 360 Stem rust, 39, 42 Stipa cernua, 139 Stipa lepida, 139 Stipa pulchra, 139 Strawberry clover, 54 Streptornyces scabies, 58 Strip cropping, 17 Stubble mulch, 17,23, 26.99 Subsoil, 273, 274 Subterranean clover, 47, 54, 164, 167, 192, 193, 198

Sudan grass, 56, 129, 154

Sugar beet, 21 Sugar cane, 104 response to anhydrous ammonia, 104 Sulfur, 332,342,353,395 Sulfur deficiency, 175 Supercooling, 208 Superphosphate, 167, 174, 175, 182, 185, 186, 190, 192,327,332,335,357

Sweet clover, 21,26, 47, 54,204, 227,294 Sweet potatoes, 105 Switchgrass, 133, 135, 137 T

Tall fescue, 47, 54, 137, 140 adaptation, 287 breeding, 303-309 cytology, 295-298 diseases, 315-316 establishment, 292-293 fertilization, 293-294 future, 316318 genetic variability, 305-309 genetics, 295-298 introduction, 283-284,299 management, 295 palatability, 289-291, 308, 309, 318 production, 286-291 reproduction, 303-305 seed production, 286,302,310-313 stock poisoning, 313-315 utilization, 286-291 varieties, 298-303 Tall oatgrass, 56, 143, 313 Tall wheatgrass, 56 Thiamine, 347 Tilletia breuaficieus,39 Tilletia caries, 39 Timothy, 47, 52, 128, 134, 136, 151, 154, 155, 206

Tissue tests, 348-351 Tomatoes, 105 Translocation, 338, 340 Trashy fallow, 23,25,26 Trichloracetic acid (TCA), 31I Trifoliurn dubiurn, 101 Trifoliurn hybridurn, 52 Trifolium incarnuturn, 52 Trifolium pratense, 44,213 Trifoliurn repens, 52 Trifoliurn subterramum, 47, 54, 164

423

SUBJECT INDEX

Trifolium uariegatum, 46 Whiptail, 165, 171, 172, 174, 183, 191, Trifolium wormskoldii, 46 195 2,3,5-Triphenyltetrazoliumchloride, 208, White clover, 29, 47,52, 167 229 White-tipped clover, 46 Triiicum satiuum, 204. Wind erosion, 22 Triticum uulgare, 91 Winter barley, 204 Truck crops, response to anhydrous Winter hardiness, ammonia, 104-106 agronomic significance, 204 Tryptophan, 346 artificial hardening, 216217,224-225 Tufted hairgrass, 46 conductivity measurements, 225-229 criteria of injury, 213-214 U effects of fertilizers, 211 field hardening, 21 7-21 8 Urea, 63,329,334,335 field testing, 210-214 Urease, 335 genetic factors, 204-206 Ustilago triiici, 39 ice formation, 208-209, 230 laboratory testing, 214-224 V refrigeration machines, 214-224 seed testing, 230-232 Vernalization, 205 testing methods, 210-235 Vetch, 29, 30,45 theories, 208-210 Vicia satiua, 45 Winter oats, 205 Vicia villosa, 45,53 Vivianite, 394

z

W

Wheat, 22, 23, 24, 25, 26, 27, 3 7 4 , 45,

91,95,96,98,99,100,101, 154 winter hardiness, 204; 207, 211, 213,

21 7,219,222,228,230,232

Zea mays, 84,207,321 Zein, 346,347 Zinc, 332,342,351,354 Zinc deficiency, 21,332,354 Zinc toxicity, 390,394

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