SERIES UC-NRLF *B 3m fi3T if. l HHH U ■ i 1 Q -«*\. .* lj Irwij 3, EDITOR •_ Agric . Educ « 7nc. J m*jM u8sa; i si Qbe IRural ftext^Boofe Series Edited by L. H. BAILEY SOILS AND FERTILIZERS Etje iftural Eext^iSooft Series Edited by L. H. BAILEY Carleton, The Small Grains. B. M. Duggar, Plant Physiology, with special reference to Plant Production. J. F. Duggar, Southern Field Crops. Gay, The Breeds of Live-Stock. Gay, The Principles and Practice of Judging Live-Stock. Goff, The Principles of Plant Culture, Revised. Harper, Animal Husbandry for Schools. Harris and Stewart, The Principles of Agronomy. Hitchcock, A Text -Book of Grasses. Jeffery, Text-Book of Land Drainage. Jordan, The Feeding of Animals, Revised. Livingston, Field Crop Production. Lyon, Soils and Fertilizers. Lyon, Fippin and Buckman, Soils — Their Properties and Management. Mann, Beginnings in Agriculture. Montgomery, The Corn Crops. Morgan, Field Crops for the Cotton-Belt. Mumford, The Breeding of Animals. Piper, Forage Plants and their Culture. Warren, Elements of Agriculture. Warren, Farm Management. Wheeler, Manures and Fertilizers. White, Principles of Floriculture. Widtsoe, Principles of Irrigation Practice. Plate I. "The earth is perhaps a stern earth, but it is a kindly earth." — Bailey. SOILS AND FERTILIZERS BY T. LYTTLETON LYON PROFESSOR OP SOIL TECHNOLOGY IN THE NEW YORK STATE COLLEGE OF AGRICULTURE AT CORNELL UNIVERSITY THE MACMILLAN COMPANY 1921 Ml rights reserved Copyright, 1917, By THE MACMILLAN COMPANY. Set up and elect rotyped. Published August, 191.7* ■ Nortoootf lPr«s J. S. Cushing Co. — Berwick & Smith Co* Norwood, Mass., U.S.A. PREFACE In many of the high schools and other secondary schools into which instruction in agriculture was introduced a few years ago there has been such a development of the subject that one general text is no longer adequate. In these schools some of the more important phases of the subject now re- ceive a degree of attention that calls for specialized texts. This is particularly true of the secondary agricultural schools and the normal schools. It was with the hope of meeting this need, and also of contributing to the demands of short courses in agriculture and of summer courses for teachers, that this book was written. The attempt has been made so to present the subject that the pupil who has no knowledge of chemistry or other natural science will be able to understand it. No chemical symbols or formulae have been used. Use has been freely made of a limited number of names of chemical substances contained in commercial fertilizers which contribute to the nutrition of plants. These, however, are terms with which the pupil can familiarize himself as readily as with the geographical and other names that he has already mastered. Following each chapter are field and laboratory exercises, designed to illustrate in a concrete manner the teachings of the text. There are more of these than any one teacher will probably find it expedient to have his class perform, but the considerable number and variety of exercises will make it possible for any school to afford the necessary facilities for performing some of the demonstrations. v 451794 VI PREFACE It has not been thought necessary to cite authorities on which the statements in the text are based. For these and for more complete discussions of most of the matters treated in this book, teachers and others who may wish to pursue the subject further are referred to the college text on soils by Lyon, Fippin and Buckman. The author is especially indebted to Dr. H. O. Buckman for much assistance and advice. He has contributed prac- tically all of the laboratory exercises. Ithaca, N. Y., June 1, 1917. CONTENTS CHAPTER I PAQEB Soil as a Medium for Plant Growth . . . 1-7 Soil as a mechanical support for plants, § 1 ; Soil as a reservoir for water needed by plants, § 2 ; Uses of water by plants, § 3 ; Soil as a source of plant-food materials, § 4 ; Quantities of plant-food materials in the earth's crust, § 5 ; Soil-forming rocks, § 6 ; Rock- forming minerals, § 7 ; Important minerals, § 8. Questions on Chapter I ...... 7-8 Laboratory Exercises ....... 8-10 Study of soil-forming minerals, I ; Study of soil- forming rocks, II ; To show that plants give off water, III; Conditions for plant growth, IV; Ef- fects of different plant nutrients, V. CHAPTER II Soil Formation and Transportation . . . 11-16 Agencies concerned in soil formation and trans- portation, § 9 ; Action of heat and cold, § 10 ; Ac- tion of frost, § 11 ; Action of water, § 12 ; Action of ice, § 13 ; Action of wind, § 14 ; Action of gases, § 15 ; Action of plants and animals, § 16 ; Powdered rock is not soil, § 17. Questions on Chapter II • 16 Laboratory Exercises ....... 17 Soil formation and transportation, I. CHAPTER III Soil Formations 18-28 Residual soils, § 18 ; Distribution of residual soils, §19; Cumulose soils, §20; Colluvial soils, §21; vii Vlll CONTENTS PAGES Alluvial soils, § 22 ; Character and distribution of alluvial soils, § 23 ; Marine soils, § 24 ; Distribution of marine soils, § 25 ; Lacustrine soils, § 26 ; Glacial soils, § 27 ; ^Eolian soils, § 28. Questions on Chapter III ....... 28 Laboratory Exercises ....... 29 Classification of soils, I ; Use of soil auger in taking samples, II. CHAPTER IV Texture and Structure op Soils .... 30-45 Shape of particles, § 29 ; Space occupied by parti- cles, § 30 ; Mechanical analysis of soils, § 31 ; Me- chanical analysis of some typical soils, § 32 ; Soil class, § 33 ; Some properties of the separates, § 34 ; Chemi- cal composition of soil separates, § 35 ; Soil structure . § 36 ; Relation of structure to pore space, § 37 ; Re- lation of structure to tilth, § 38 ; Conditions and operations that affect structure, § 39 ; Relation of texture to structure, § 40 ; Wetting and drying, § 41 ; Freezing and thawing, § 42 ; Effect of organic matter on structure, § 43 ; Roots and animals, § 44 ; Tillage and structure, § 45 ; Structure as affected by lime, § 46 ; The soil survey, § 47 ; Classification of soils, § 48 ; Information furnished by a soil survey, § 49. Questions on Chapter IV . . . . . . . 45 Laboratory Exercises 46-50 Examination of soil particles, I ; Examination of soil separates, II ; Simple mechanical analysis, III ; Study of soil class and its determination by examina- tion, IV ; Determination of soil class from a mechani- cal analysis, V; Soil structure, VI; Determination of apparent specific gravity of dry sand and clay, VII ; Calculation of pore space, VIII ; A study of the plow, IX. CHAPTER V Organic Matter 51-57 Classes of organic matter, § 50 ; Beneficial effects of organic matter, § 51 ; Porosity of organic matter, CONTENTS . IX § 52 ; Organic matter and drainage, § 53 ; Organic matter and soil color, § 54 ; Organic matter a source of plant-food material, § 55 ; Organic matter and nitrogen, § 56 ; Organic matter and soil microorgan- isms, § 57 ; Organic matter forms acids, § 58 ; In- jurious effect of organic matter, § 59 ; Management of organic matter in soils, § 60 ; Sources of organic matter, § 61. Questions on Chapter V ...... 57 Laboratory Exercises .......' 58-60 Examination of soil — organic matter, I ; Exami- nation of peat and muck, II ; Estimation of organic matter, III; Extraction of decomposed organic matter, IV ; Influence of organic matter on percola- tion through soils, V ; Influence of organic matter on percentage of moisture held in soil, VI ; Influence of organic matter on percentage of moisture held in soil, VII. CHAPTER VI Soil Water 61-85 Forms of water in soils, § 62 ; How the three forms of water differ, § 63 ; Hygroscopic water, § 64 ; Capil- lary water, § 65 ; Capillary water capacity, § 66 ; Movement of capillary water, § 67 ; Effect of tex- ture on capillary movement, § 68 ; Effect of struc- ture on capillary movement, § 69 ; Height of water column and capillary movement, § 70 ; Gravitational water, § 71 ; The water table, § 72 ; Relations of soil water to plants, § 73 ; Ways in which water is useful to plants, § 74 ; Water requirements of plants, § 75 ; Transpiration by different crops, § 76 ; Effect of moisture on transpiration, § 77 ; Effect of humidity, wind and temperature of the air, § 78 ; Effect of soil fertility on transpiration, § 79 ; Quantity of water required to mature a crop, § 80 ; Capillary move- ment and plant requirement, § 81 ; Optimum mois- ture for plant growth, § 82 ; The control of soil mois- ture, § 83; Run-off, § 84; Percolation, § 85; Evap- X CONTENTS PAGES oration, § 86; Mulches for moisture control, § 87; The soil mulch, § 88 ; Frequency of stirring, § 89 ; Depth of mulch, § 90 ; Effectiveness of mulches, § 91 ; Other devices to prevent evaporation, § 92 ; Rolling and subsurface packing, § 93 ; Removal of water by drainage, § 94 ; Benefits of drainage, § 95 ; Soil air, § 96 ; Soil tilth, § 97 ; Available water dur- ing the growing season, § 98 ; Length of growing season, § 99 ; Other results of drainage, § 100 ; Open ditches, § 101 ; Tile drains, § 102 ; Arrangement of drains, § 103 ; Digging ditches and laying tile, § 104. Questions on Chapter VI ....... 85 Laboratory Exercises 85-89 Determination of the percentage of water in a soil, I ; Capillary movement in different soils, II ; Rate of percolation of water through soils, III; Water- holding capacity of soils, IV ; Moisture conservation by means of a soil mulch, V ; Loss of water by tran- spiration, VI ; Review problems Chapter IV and VI, VII; Tile drainage, VIII. CHAPTER VII Plant-Food Materials in Soils . . . . 90-110 Variations in content of plant nutrients in different soils, § 105 ; The total supply of plant-food materials, § 106; Upward movement of plant-food materials, § 107 ; Plant nutrients compose a small part of the soil, § 108; Relation of composition to productive- ness, § 109 ; Available and unavailable plant-food materials, § 110; Conditions that influence avail- ability, § 111; Water-soluble matter in soil, § 112; Relation of water-soluble matter to productiveness, § 113; Chemical analysis of soil, § 114; Absorptive properties of soils, § 115 ; Selective absorption, § 116 ; The availability of absorbed fertilizers, § 117 ; Other forms of available plant-food material in soils, § 118; Loss of plant-food material in drainage water, § 119; CONTENTS XI Quantities of plant-food materials in drainage, § 120 ; Effect of crop growth on loss of plant nutrients in drainage, § 121 ; Effect of fertilizers on loss of plant- food materials in drainage, § 122; Drainage water from different soils, § 123 ; Absorption of good mate- rials by plants, § 124 ; How plants absorb nutrients, § 125; How roots aid in solution of soil, § 126; Pro- duction of carbon dioxide by microorganisms, § 127 ; Solvent action of roots in other ways, § 128 ; Differ- ence in absorptive power of crops, § 129 ; Substances needed by plants and substances merely absorbed, § 130; Quantities of plant-food materials removed by crops, § 131 ; Possible exhaustion of mineral nutrients, § 132. Questions on Chapter VII ...... Laboratory Exercises ....... Soluble matter of soil, I ; Absorptive power of soil for dyes, II ; Selective absorption by soil, III ; Ab- sorptive power of the soil for gas, IV. 110-111 111 CHAPTER VIII Acid Soils and Alkali Soils . . . . . Nature of soil acidity, § 133; Positive acidity, § 134 ; Negative acidity, § 135 ; Ways by which soils become sour, § 136 ; Drainage as a cause of acidity, § 137 ; Effect of plant growth on soil acidity, § 138 ; Effect of fertilizers on soil acidity, § 139 ; Effect of green-manures on acidity, § 140 ; Weeds that flourish on sour soils, § 141 ; Crops adapted to sour soils, § 142 ; Crops that are injured by acid soils, § 143 ; Litmus paper test for soil acidity, § 144; Litmus paper and potassium nitrate, § 145 ; The Truog test, § 146; Alkali soils, § 147; Nature and movements of alkali, § 148 ; Effect of alkali on crops, § 149 ; Tolerance of different plants to alkali, § 150 ; Irriga- tion and alkali, § 151 ; Removal of alkali, § 152 ; Control of alkali, § 153. 112-121 Questions on Chapter VIII 121-122 Xll CONTENTS Laboratory Exercises . . . . Acid soils in the field, I ; Litmus paper with and without potassium nitrate, II ; Litmus paper test, III ; Test for soil carbonates, IV ; Ammonia test for acidity, V ; Zinc sulfide test for acidity, VI ; Incrusta- tion of "alkali" by capillary action, VII. PAGES 122-124 CHAPTER IX The Germ Life of the Soil 125-140 Microorganisms injurious to crops, § 154 ; Germs not directly injurious to crops, § 155 ; Numbers of bacteria in soils, § 156 ; Conditions affecting bacterial growth, § 157 ; Air supply, § 158 ; Moisture, § 159 ; Temperature, § 160 ; Organic matter, § 161 ; Soil acidity, § 162 ; Bacteria in relation to soil fertility, § 163 ; Action on mineral matter, § 164 ; Decom- position of non-nitrogenous organic matter, § 165; Decomposition of nitrogenous organic matter, § 166 ; Ammonification, § 167; Nitrification, § 168; Effect of soil aeration on nitrate formation, § 169 ; Effect of temperature on nitrate formation, § 170; Effect of sod on nitrate formation, § 171 ; Depths at which nitrate formation takes place, § 172 ; Loss of nitrates in drainage, § 173 ; Denitrification, § 174 ; Nitrogen fixation, § 175 ; Nitrogen fixation through symbiosis with higher plants, § 176; Soil inoculation for le- gumes, § 177; Nitrogen fixation by free-living germs, § 178. Questions on Chapter IX ...... 40 Laboratory Exercises . . . . . . . 140-142 Test for nitrates in soil, I ; Test for ammonia in soil, II ; Factors affecting nitrate formation, III ; Examination of legume nodules, IV ; Examination of nodule bacteria, V; Soil inoculation, VI. CHAPTER X Soil Air and Soil Temperature .... 143-152 Soil air contained largely in non-capillary spaces, § 179 ; There may be too much or too little soil air, CONTENTS Xlll § 180 ; Movement of soil air, § 181 ; Movement of water, § 182 ; Diffusion of gases, § 183 ; Composi- tion of soil air, § 184 ; Production of carbon dioxide in soils, § 185 ; Conditions that affect the quantity of carbon dioxide in soils, § 186 ; Usefulness of air in soils, § 187; Oxygen, § 188; Nitrogen, § 189; Car- bon dioxide, § 190 ; Control of the volume and move- ment of soil air, § 191; Soil temperature, § 192; Sources of soil heat, § 193 ; Relation of soil tempera- ture to atmospheric temperature, § 194 ; Factors that modify soil temperature, § 195 ; Control of soil tem- perature, § 196. Questions on Chapter X ...... Laboratory Exercises ....... Movement of soil air as measured by texture and structure, I ; The presence of carbon dioxide in soil air, II ; Production of carbon dioxide by germs, III ; Temperature and soil color, IV ; Slope and soil tem- perature, V; Drainage and temperature, VI. 152 152-154 CHAPTER XI Nitrogenous Fertilizers Relative quantities of the different forms of nitro- gen in soils, § 197 ; Forms in which nitrogen is ab- sorbed by plants, § 198 ; Nitrates as plant-food materials, § 199; Absorption of ammonia by agri- cultural plants, § 200 ; Direct utilization of organic nitrogen by crops, § 201 ; Forms of nitrogen in fer- tilizers, § 202 ; Nitrate of soda, § 203 ; Crops mark- edly benefited, § 204 ; Effect of nitrate of soda on soils, § 205 ; Sulfate of ammonia, § 206 ; Composition of sulfate of ammonia, § 207 ; Action when applied to soils, § 208; Cyanamid, § 209; Composition of cyanamid, § 210; Changes in the soil, § 211; Fer- tilizers containing organic nitrogen, § 212; Vege- table products, § 213; Animal products, § 214; Fish waste, § 215; Guano, § 216; Effects of nitrogen on plant growth, § 217 ; Availability of nitrogenous 155-168 XIV CONTENTS fertilizers, § 218 ; Relative values of organic and inorganic nitrogenous fertilizers, § 219. Questions on Chapter XI ....... Laboratory Exercises ....... Influence of nitrogen on plant growth, I ; Exami- nation and identification of nitrogen fertilizers, II; Comparison of fertilizer effects on plant growth, III. 168 168-170 CHAPTER XII Phosphoric Acid Fertilizers 171-176 Bone phosphate, § 220; Mineral phosphates, § 221 ; Basic slag, § 222 ; Acid phosphate, § 223 ; Com- position of acid phosphate, § 224 ; Reverted phos- phoric acid, §,225; Absorption of acid phosphate by soil, § 226 ; Relative availability of phosphoric acid fertilizers, § 227 ; Rock phosphate versus acid phos- phate, § 228 ; Effect of phosphoric acid on plant growth, § 229 ; Plants particularly benefited by phosphoric acid, § 230. Questions on Chapter XII 176-177 Laboratory Exercises ....... 177-178 Influence of phosphoric acid on plant growth, I; Examination and identification of phosphate fer- tilizers, II; Comparison of fertilizer effects on plant growth, III. CHAPTER XIII Potash and Sulfur Fertilizers Stassfurt salts, § 231 ; Wood ashes, § 232 ; Insolu- ble potash fertilizers, § 233 ; Effects of potash on plant growth, § 234 ; Sulfur as a fertilizer, § 235 ; Experiments with sulfur as a fertilizer, § 236 ; Quantities of sulfur contained in crops, § 237 ; Quantities of sulfur in soils, § 238 ; Quantities of sul- fur in drainage water, § 239 ; Sulfur contained in fer- tilizers, § 240. 179-185 CONTENTS XV Questions on Chapter XIII ...... Laboratory Exercises ....... Influence of potash on plant growth, I ; Examina- tion and identification of potash fertilizers and sulfur, II ; Comparison of fertilizer effects on plant growth, III. 185 185-186 CHAPTER XIV Lime Forms of lime, § 241 ; Absorption of lime by soils, § 242 ; Lime requirement of soils, § 243 ; Effect of lime on tilth, § 244 ; Effect of lime on bacterial action, § 245 ; Liberation of plant-food materials, § 246 ; Effect on plant diseases, § 247 ; The use of magnesian limes, § 248 ; Caustic lime versus ground limestone, § 249 ; Fineness of grinding limestone, § 250; Gypsum or land plaster, § 251. Questions on Chapter XIV Laboratory Exercises ....... A study of the forms of lime, I ; Fineness of ground limestone, II ; Effect of lime on biological action, III; Flocculation by lime, IV; Flocculation by lime, V ; Lime and the rotation, VI ; Forms of lime to apply, VII. 187-192 192 193-195 CHAPTER XV The Purchase and Mixing of Fertilizers Brands of fertilizers, § 252 ; High- and low-grade fertilizers, § 253 ; Fertilizer inspection and control, § 254 ; Trade values of fertilizer ingredients, § 255 ; Computation of the wholesale value of a fertilizer, § 256 ; Home mixing of fertilizers, § 257 ; Fertilizers that should not be mixed, § 258 ; Calculation of a fertilizer mixture, § 259 ; How to mix the ingredients, § 260. 196-205 Questions on Chapter XV 205-206 XVI CONTENTS Laboratory Exercises Fertilizer inspection and control, I ; Laboratory mixture of fertilizers, II ; Home mixture of fertilizers, III. CHAPTER XVI The Use of Fertilizers Fertilizers for different crops, § 261 ; Small grains, § 262 ; Grass crops, § 263 ; Leguminous crops, § 264 ; Root crops, § 265 ; Vegetables, § 266 ; Orchards, § 267 ; Fertilizer mixtures for different crops, § 268 ; Fertilizers for different soils, § 269 ; Calcula- tion of results of fertilizer experiments, § 270 ; Fer- tilizing the rotation, § 271 ; Methods of applying fer- tilizers, § 272 ; The limiting factor, § 273 ; The law of diminishing returns, § 274 ; Conditions that influ- ence the effect of fertilizers, § 275 ; Response of sandy and of clay soils to fertilizers, § 276 ; Cumulative need of fertilizers, § 277. Questions on Chapter XVI ...... Laboratory Exercises ....... Fertilization of standard rotations, I; Fertiliza- tion of home-farms, II ; Fertilizer practice in the community, III; Fertilizer experimentation, IV. PAGE3 206 207-219 219 219-220 CHAPTER XVII Farm Manures Solid and liquid manure, § 278 ; Chemical compo- sition of manures, § 279 ; Farm manure an unbal- anced fertilizer, § 280 ; Quantities of manure voided by animals, § 281 ; Effect of food on composition of manure, § 282 ; Commercial evaluation of manures, § 283 ; Agricultural evaluation of manures, § 284 ; Deterioration of farm manure, § 285 ; Fermentations of manure, § 286 ; Leaching of farm manure, § 287 ; Protected manure more effective, § 288 ; Reinforcing manure, § 289 ; Methods of handling manure, § 290 ; Covered barnyard, § 291 ; Application of manure to 221-232 CONTENTS XVll land, § 292 ; Place of farm manure in crop rotation, §293. Questions on Chapter XVII . . . . . Laboratory Exercises ....... Study of farm manure, I ; Experiments with farm manure, II ; The value of manure produced on the home farm, III ; Reinforcement of farm manure, IV; Building of a compost pile, V. 232 233-234 CHAPTER XVIII Green-Manures 235-240 Protective action of green manures, 294; Mate- rials supplied by green manures, § 295 ; Transfer of plant-food materials, § 296 ; Crops used for green- manuring, § 297 ; When green-manures may be used, § 298 ; Handling green-manure crops, § 299 Questions on Chapter XVIII . Laboratory Exercises .... Study of green-manure in the field, manure and the rotation, II. I ; Green- 240 240-241 CHAPTER XIX Crop Rotation, ........ Crop rotation and soil productiveness, § 300 ; Root systems of different crops, § 301 ; Nutrients re- moved from soil by different crops, § 202 ; Some crops or crop treatments prepare nutriment for other crops, § 303 ; Crops differ in effect on soil structure, § 304 ; Certain crops check certain weeds, § 305 ; Plant diseases and insects, § 306 ; Loss of plant-food material between crops, § 307 ; Produc- tion of toxic substances from plants, § 308 ; Manage- ment of a crop rotation, § 309 Questions on Chapter XIX .... Laboratory Exercises ..... Crop rotations, I ; Fertilizing the rotation, 242-247 248 248 II. LIST OF ILLUSTRATIONS facing facing facing facing facing facing Frontispiece Rock disintegration by heat and cold Wearing action of water on rock Plants as soil formers Glacial soil and alluvial soil . Stratification of rock and soil Auger for taking soil samples Relative sizes of soil particles Graphic statement of mechanical analyses of soils . Scheme for determining soil class (after Whitney) . Ideal arrangement of soil particles .... Section showing structure of loam soil in good tilth Plowed land, showing good and poor tilth Apparatus for simple mechanical analysis of soil . Apparatus for the determination of the apparent specific gravity of soil A walking plow and its attachments Cross sections of furrows turned at different angles Apparatus for the estimation of organic matter in soil Apparatus for estimating rate of percolation and water-holding capacity Soil particles and surrounding films of hygroscopic and capil lary water Erosion of soil by water and by wind . . . facing Section of soil with and without a mulch Systems of laying out tile drains . Drain tile outlets facing Sections of land showing locations of tile drains and water . tables Diagrammatic explanation of water control in a humid region Apparatus for moisture measurement . . . facing Apparatus for demonstration of effectiveness of mulches in conserving soil water Apparatus for observation of transpiration of water from * plants xix 6 12 16 25 29 29 31 33 35 38 39 42 47 49 50 56 58 59 63 72 77 82 83 84 84 86 87 88 XX LIST OF ILLUSTRATIONS PAGE Surface soil and subsoil facing 92 Relative quantities of potash, lime, phosphoric acid and nitrogen in a soil ........ 94 Equipment for making the litmus paper test .... 123 Apparatus for making the zinc sulfide test .... 124 Relative sizes of bacteria and soil particles . . . . 128 Appearance of some soil bacteria (after Lohnis) . . . 131 Diagrammatic representation of the nitrogen cycle . . 139 Apparatus for estimating the relative rate of air movement through soils 153 Apparatus to demonstrate the presence of carbon dioxide in soil air .......... 153 Apparatus to demonstrate the formation of carbon dioxide in soil 154 Effect of certain fertilizer constituents on plant growth facing 156 Extent to which fertilizers are used in the several states . 197 Tag representative of the kind often used on bags of fertilizer 201 Plan for fertilizer experiments 212 Field plat experiments facing 212 Influence of soil moisture on the effectiveness of fertilizers facing 218 Composition of farm manure 223 Storage of farm manure facing 226 Movements of plant-food materials between soil, air and plant 237 Cover crops which are also green manures . . facing 238 SOILS AND FERTILIZERS SOILS AM) FERTILIZERS CHAPTER I SOIL AS A MEDIUM FOR PLANT GROWTH The farmer's interest in the soil is due chiefly to what it contributes to plant production. In this respect it per- forms several functions : (1) it acts as a mechanical support for plants by furnishing a foothold comprising many open- ings through which plant roots ramify and hold the plant in place; (2) it- serves as a receptacle in which water is held in a convenient way for roots to appropriate ; (3) it is composed, in part, of substances that dissolve in the water which it holds and are absorbed from solution by roots, and utilized by plants as food material ; (4) its porous nature allows air to circulate within it, thus supplying plant roots witl), air. These are the contributions that soils make to plant growth. Before proceeding with a more detailed study of soil it will be desirable to consider briefly the needs of the plant as supplied by the soil. 1. Soil as a mechanical support for plants. — Land plants need anchorage, for they must have some permanent supply of water and other food material, which is not to be had from the atmosphere. The soil serves, at once, as anchor- age and food reservoir. One property of soil that adapts b 1 ' 2 SOILS AND FERTILIZERS it especially for the growth of roots is its permeable structure, which furnishes innumerable channels through which roots may ramify ; another property is its compressibility, which makes it possible for the roots to grow in thickness by forcing together the surrounding particles. The compacting thus effected may be noted in a field of mangels or other large roots at harvest. The firmness of this anchorage is illustrated by the resistance that large trees offer to heavy winds. 2. Soil as a reservoir for water needed by plants. — The leaves of land plants thrive without being in contact with water, but their roots must have a nearly constant supply. This the soil helps to maintain by catching and holding more or less of the water that falls as rain. The water thus held is in contact with the small roots and root-hairs of plants, and may readily be absorbed by them. 3. Uses of water by plants. — Plants require moisture for several reasons : (1) Water acts as a solvent for substances that are essential to plant growth, and these substances can be absorbed by plants only when they are in solution. (2) Water is itself a plant-food material and it either becomes a part of the cell without change, or is decomposed and its component parts are used in forming new substances. (3) The cells, of which plants are composed, are kept filled and the plant is more or less firm and erect when its cells are extended with water. When not so filled, the plant wilts. (4) Nutri- tive substances and substances formed from them in the plant tissues are transferred from one part of the plant to another, as occasion requires, by water in the plant. (5) The evaporation of moisture from leaves (transpiration) causes a reduction of temperature in plants, as does evaporation of perspiration from animals. 4. Soil as a source of plant-food materials. — Plants re- quire for their growth certain nutrient substances, of which SOIL AS A MEDIUM FOR PLANT GROWTH 3 some are derived from the air and some from water, but the larger number must be obtained from soil. They may be classified thus : Substances obtained from air or water : Carbon Hydrogen Oxygen Nitrogen Substances obtained from soil : Nitrogen Phosphoric acid [phosphorus] * Potash [potassium] Lime [calcium] Magnesia [magnesium] Iron Sulfur All these substances are essential to the normal devel- opment of farm crops. Carbon, oxygen and nitrogen are found in air. Hydrogen and oxygen are in water. Plants obtain their carbon from the air; their oxygen from both air and water; their hydrogen from water; their ni- trogen, in the case of certain plants only, from the air. The other substances are found in all arable soils, from which plants obtain them after they have become dissolved in the soil water. While arable soils contain all these substances, the fact that they must be in solution before plants can use 1 This list of plant-food materials gives the names commonly used. Thus the terms phosphoric acid, potash, and lime are the ones used in con- nection with fertilizers. Nitrogen is sometimes spoken of as ammonia by fertilizer manufacturers, but the most general term is nitrogen. The words in brackets following the unbracketed words indicate other names some- times found, but not used in this book. All the substances in this list are capable of uniting with certain other substances to form various combinations. When present in the soil they are not likely to be in the same combinations as when present in plants. When, therefore, phosphoric acid in soil or in a plant is spoken of, nothing is implied regarding the form in which it exists. 4 SOILS AND FERTILIZERS them sometimes leads to a deficiency in the available supply. This is either because they are not present in sufficient quantity, or because they are not readily dissolved by the liquids with which they come in contact. Many things tend to influence the quantity of these substances that plants may obtain. Among these are tillage, decaying vegetation, drainage and the kind of plant grown. It is the nitrogen, phosphoric acid, potash and possibly sulfur that are most likely to be deficient in the solution to which plants have access, and commercial fertilizers usually con- tain one or more of these substances. The kind of fertilizer that it will be desirable to apply depends, in part, on the so-called availability of each of the nutrient substances contained in the soil, availability in this case meaning the readiness with which the plant can appropriate these food materials. But some plants require more of certain of these substances than they do of others. Hence the needs of the plant must also be taken into con- sideration in deciding what fertilizer to use on a given soil. 5. Quantities of plant-food materials in the earth's crust. — As all of the food materials that plants draw from soil, with the exception of nitrogen, came originally from rocks, it is of some interest to know what the proportions of these substances are in the entire crust of the earth. As stated by Clarke they are present in the following percentages : Oxygen 47.17 Potash . 3.00 Iron ........ 4.44 Sulfur 0.11 Lime 4.79 Phosphoric acid .... 0.25 Magnesia 3.76 Nitrogen does not appear in this list because it does not occur as a constituent of the rocks forming the earth's crust. The nitrogen that soil contains is derived from the atmos- phere by processes that will be described later. Most of the constituents of soil have, however, been formed from SOIL AS A MEDIUM FOR PLANT GROWTH 5 rock, and hence soil may be expected to have a somewhat similar composition to that of the earth's crust. It will be seen that two of the important nutrients, as far as plants are concerned, namely phosphoric acid and sulfur, are present in relatively small quantities. Potash, magnesia, lime and iron are present in much larger proportions. This is somewhat the relation in which we are likely to find them in soils, and emphasizes the probable need of phosphoric acid and sometimes sulfur for the maximum production of crops. Potash, in spite of its greater quantity, is often not available in sufficient amount and must be applied as a soluble fertilizer. Lime, being easily soluble in soil water, has frequently been leached out of soils in such quantities that it must be replaced. Magnesia is less soluble and hence is rarely lacking. 6. Soil-forming rocks. — As the earth, which was once a molten mass, cooled, the crust became solid and this solidi- fied material formed igneous rocks, so called to distinguish them from rocks that were formed in other ways. Some examples of igneous rocks are granite, syenite and basalt. Other kinds of rocks, called sedimentary, have been formed from material derived from igneous rock by solution and sedimentation, and later solidified into rock, often under pressure. Limestone, dolomite, shale and sandstone repre- sent some rocks of sedimentary origin. The first two are quite readily soluble in soil water, having been deposited from solution in the process of their formation. Shale is a more or less hardened clay. Sandstone, as its name implies, consists of sand grains cemented together. Metamorphic rocks have been formed by heat, pressure, solution and other processes acting on either igneous or sedi- mentary rocks. These forces have frequently produced rocks quite unlike those originally involved in the process. 6 SOILS AND, FERTILIZERS Gneiss, marble and slate are among the rocks so formed. Gneiss somewhat resembles granite, from which it is formed, but unlike granite has a layered structure, the result of the pressure to which it was subjected. Marble has been formed from limestone or dolomite by heat and pressure, which have caused crystallization. It is not, therefore, so readily soluble as limestone. Slate has been formed from shale by heat and pressure. 7. Rock-forming minerals. — Most rocks are not homo- geneous, but are made up of a number of different materials. An examination will frequently show grains of different sizes, colors and hardness. The grains are minerals and they differ from each other in their composition as they do in their appearance. But each mineral always has a more or less well-defined composition, so that when we have a certain mineral we know something of the quantity of potash or lime or other base that it contains. The quan- tity of potash or other plant-food material in a rock will depend on the proportion of minerals containing those sub- stances that compose the rock. 8. Important minerals. — There are a few minerals that it will be well to mention : (1) because they or their products occur in very large quantity in soil and influence its physical properties; (2) because of the plant-food material that they contain. Quartz and feldspar are examples of the class first mentioned. Quartz is found in almost all soils, and may form from 85 to 99 per cent of their composition. It is particularly prevalent in sandy soils. It usually occurs as a large grain, called sand, is hard and insoluble and con- tributes no plant-food material. A soil with a great deal of quartz is usually a light, easily worked soil. On weathering feldspar contributes to soils a mass of very finely divided matter known as clay, the smallest of the soil particles. It, therefore, forms part of the clay in Plate II. Soil Formation. — Heat, cold, and frost have been largely instrumental in fracturing the rocks in the upper figure, and in produc- ing the rock debris and soil in the lower. Note that vegetation has already well started on the slope. SOIL AS A MEDIUM FOR PLANT GROWTH 7 soils and adds to their plasticity, and in addition, this very fine material is an absorbent, holding the soluble plant-food materials of fertilizers in a form that prevents them from leaching from the soil, and yet gives them up to plants rather easily. As examples of the second class we again have the feld- spars as they furnish lime, magnesia and potash; calcite, which contains lime ; hematite, which consists largely of iron ; dolomite, which contains both lime and magnesia ; apatite, which furnishes phosphoric acid and lime, and gyp- sum, which is a combination of lime and sulfur. These minerals and the plant-food materials contained in them may be reviewed in tabular form thus : Mineral Plant-food Material Feldspars Potash, lime, magnesia Calcite Lime Dolomite Lime, magnesia Hematite Iron Apatite Phosphoric acid, lime Gypsum Sulfur, lime Quartz Silica (not a plant-food material) As these minerals are widely distributed in rocks from which soils are formed, they are found in almost all soils, and thus it is that all the substances required by plants are to be found in most soils. QUESTIONS 1. What are the properties of soil that make it well adapted to furnish a mechanical support for plants? 2. What relation does soil have to the needs of plants for water? 3. Describe the reasons why plants need water. 4. Name the elemental substances that plants derive from soil. 5. What elemental substance do plants obtain from soil that is not present in rocks from which soil is formed? 6. What two substances necessary to plant growth are contained in the earth's crust in the smallest quantities ? 8 SOILS AND FERTILIZERS 7. In what way were igneous rocks formed ? Sedimentary rocks ? Metamorphic rocks ? Name examples of each. 8. Name a mineral containing potash, a mineral containing lime, a mineral containing magnesia, a mineral containing phosphoric acid, a mineral containing sulfur, a mineral containing iron. LABORATORY EXERCISES The following exercises are designed to suggest possible experi- ments and demonstrations that may be carried out in connection with the various chapters. Some may be performed by the student if adequate facilities are at hand, some are only possible as demon- strations, while others are field studies and depend on local condi- tions. Enough suggestions are made with each chapter to give the teacher a range of choice according to his conditions and facilities. It is not considered possible or advisable that all the experiments and demonstrations listed be carried out. Exercise I. — Study of soil-forming minerals. (The teacher will find an elementary text in mineralogy of great aid in this experi- ment.) Materials. — Small specimens of quartz, potash-feldspar, mica, calcite, apatite, gypsum and hematite. Also a piece of a glass, a knife, dilute muriatic acid, a hand-lens and flame (gas or alcohol). Procedure. — Study the specimens according to the following outline, with a view to identifying the minerals unlabeled. Use hand lens where possible Hardness. — Determine hardness by the following scale. Hardness Mineral Scratched by finger nail GypsumN>Mica Cut by knife Calcite / Scratched with difficulty with knife . . Apatite Scratches glass Feldspar — Hematite Scratches glass very easily Quartz Color. — Observe color and luster of the various specimens and determine if it is characteristic and useful in identifying the mineral. Cleavage and fracture. — Do specimens split easily in certain direc- tions or do they fracture ? What effect do these characters have upon the appearance of the mineral ? Form. — Do the specimens seem to have any crystal form that is characteristic and useful in identification ? SOIL AS A MEDIUM FOR PLANT GROWTH 9 Action of acid. — What is the result if the specimen is treated with a few drops of acid ? Explain. Flame. — Hold a small fragment of each mineral in the flame. Observe fusibility and change of color. Is the flame given any color which is characteristic ? Exercise II. — Study of soil-forming rocks. Materials. — Small specimens of granite, basalt, shale, slate, limestone, sandstone and quartzite. Procedure. — Study the color, texture, and structure of each sample. Identify the minerals present and from this determine the plant-food materials carried by each rock. Be prepared to identify unlabeled samples in laboratory and field. Exercise III. — To show that plants give off water. Materials. — Plant growing in small pot, a tumbler. Procedure. — Place a tumbler over a small plant and observe the condensation of moisture on the sides. Where does this mois- ture come from ? What was its original source ? How do plants give off water? Explain uses of water to the plant. Exercise IV. — Conditions for plant growth. Materials. — Small flower pots, rich soil, oat seed. Procedure. — Fill four small flower pots with a rich garden loam. Moisten well and plant with oat seeds. When seedlings are a week old, thin to desired number of plants. Grow for a few weeks under optimum conditions and then subject them to the following condi- tions : Pot 1. — Sunshine and optimum water. Pot 2. — Sunshine and minimum water. Pot 3. — Cold, shade, and optimum water. Pot 4. — Dark and optimum water. Observe results and explain. More pots with other conditions may be tried at the pleasure of the teacher. , Exercise V. — Effect of the different plant nutrients. Materials. — One-gallon flower pots, very poor sandy soil, nitrate of soda, acid phosphate, muriate of potash, barley seed. Procedure. — Fill five flower pots to within an inch of their tops with poor sandy soil. It is essential to the success of the experiment that the soil be poor, and also that it shall be surface soil and con- 10 SOILS AND FERTILIZERS tain some plant food material. Weigh the soil that is placed in each pot, mixing with it fertilizer in the following proportions : Pot 1, nitrate of soda one part to five thousand parts of soil. Pot 2, acid phosphate, one part to five thousand parts of soil. Pot 3, muriate of potash, one part to ten thousand parts of soil. Pot 4, all three of these carriers, each at the rate specified above. Pot 5, no fertilizer. Mix the fertilizer and soil thoroughly before placing in the pots. Plant a dozen or more barley seeds in each pot. Add water in sufficient quantity to make the soil moist but not too wet. Place the pots in a place that is moderately warm during the day, where they will not freeze at night, and where there is abundant light. When seedlings are a week old, thin to ten. Allow plants to grow for use in laboratory exercises in Chapters XI, XII and XIII. Observe growth in each pot. CHAPTER II SOIL FORMATION AND TRANSPORTATION Side by side are to be seen rock and soil. On the rock no vegetation is growing except a few lichens and other minute plants. On the soil there is a luxuriant growth of multitudinous plants. Soil is derived from rock. Evi- dently there must have been a profound change to cause such a difference in their relations to plant growth. In some regions of the earth there is much rock and little soil, while often on the prairie one sees no large rocks, and may plow all day and perhaps not strike even a small boulder. It may be surmised that in connection with the process of soil formation there has been a large transporta- tion of material from one place to another. All this was brought about by natural agencies, most of which are still operating to form more soil and to increase the productive- ness of soil already under cultivation. The process of soil formation is, however, extremely slow, and it must be remembered that thousands and tens of thousands of years have elapsed while the operation has been in progress. 9. Agencies concerned in soil formation and transporta- tion. — The agencies that have brought about these trans- formations may be listed as follows : Heat and cold Ice Frost Wind Water Gases Plants and animals 11 12 SOILS AND FERTILIZERS 10. Action of heat and cold. — Rocks, as we have seen, are mixtures of different minerals. These minerals have different rates of expansion when heated. Exposed rock will suffer great changes in temperature in twenty-four hours, especially if it be located in a region of high altitude and cloudless weather. A block of marble one hundred feet long will expand one-half inch with a change of 75° Fahren- heit, and this is frequently of diurnal occurrence in an arid climate. Because the minerals composing rock expand and contract at different rates, they tend to tear apart, thus producing crevices that may fill with water, and this water acts still further to disintegrate the rock. 11. Action of frost. — One reason that building stones are more likely to disintegrate in a cold moist climate than in a dry or warm one is that the small pores and cracks on their surfaces fill with water, which, when it freezes, exerts an enormous pressure. The expansive power of freezing water amounts to about 150 tons to a square foot, which is equivalent to a column of rock a third of a mile in height. The rock surface becomes chipped off by repeated freezing and even great masses of rock are detached by the freezing of water in larger cracks, as may be seen beneath rock ledges in the spring of the year. An interesting example of the effect on rock disintegration of a cold moist climate as compared with a dry one is found in the difficulty that has been experienced in preserving the obelisk, now in Central Park, New York, which had pre- viously stood for many hundreds of years in the Egyptian desert without great damage. It has been found necessary to cover the entire surface of the stone with paraffine in order to preserve the hieroglyphics carved on its surface. 12. Action of water. — Water has another effect on rock. It is a solvent, weak but universal. It acts on all minerals, dis- solving slight quantities of some, considerably more of others. Plate III. Water Erosion. — The wearing action of water is slow but constant, and is leveling the surface of the earth at the rate of an inch in several hundred years. SOIL FORMATION AND TRANSPORTATION 13 It is as a transporting agent that water is most active. From the time when raindrops beat down on the surface of the soil, while they are gathering into rivulets and the rivulets are becoming rivers that discharge into the ocean, they are engaged in moving particles of rock debris and soil. It is estimated that the United States is being planed down at the rate of one inch in seven hundred and sixty years. This is rapid enough if it were applied at one point to dig the Panama Canal in seventy-three days. The carrying power of water has resulted in the formation of the rich river valley soils that have been deposited by the streams flowing through them. The coastal soils and lake soils have also been transported by water. 13. Action of ice. — In former times a considerable part of the northern United States was covered by huge masses of ice, known as glaciers. These ice masses were of enormous vol- ume and moved slowly in a southerly direction. The great thickness of the ice mantles, amounting to several thousand feet at some places, caused them to cover hills, valleys and mountains, and their enormous weight ground rock surfaces, pushed forward heaps of soil and transported huge boulders. The southern limit of the glaciers corresponded roughly to the lines now marked by the Ohio and Missouri rivers, and again extended farther southward along the Pacific coast. It met the Atlantic coast at about the present location of New York. Changes of climate caused an alternate reces- sion and extension of the ice sheets several times, and during all this period soil was being formed and worked over by the ice and the water that melted from it. When the glacier melted, stranded ice masses remained .behind. These formed lakes in which soil was reworked and shifted, and as the lakes finally drained off, the reworked soil was left behind. These glacial soils are, as a rule, productive, because of the thorough pulverization and mixing they have received. 14 SOILS AND FERTILIZERS 14. The action of wind. — That wind has been an active factor in the transporation of soil is evident to any one who has lived in an arid or semi-arid region, where dust storms are not infrequent. In a humid region the move- ment of soil by wind is not so patent, but even there, espe- cially along the seacoast, there is some movement of this kind. There is also an erosive action produced by wind, but this has not been very important. However, in arid regions the sand-bearing wind has been instrumental in wearing away large surfaces of rock, the eroded portions of which have helped to form soil. The most important result of wind action has been the production of loessial soils, which are found in parts of Wis- consin, Illinois, Iowa, Missouri, Nebraska and Kansas, also in the valley of the Rhine and in parts of China. An- other result is the production of adobe soils, which are found in mountain sections of western and southwestern United States. While these soils do not owe their present location entirely to the action of wind, that element has played a large part in removing them from other regions and depos- iting them where they now are. 15. Action of gases. — Of the gases that compose the normal atmosphere, oxygen and carbon dioxide are instru- mental in decomposing rock and soil. They unite chemi- cally with some of the substances composing rocks, and when the new compound thus formed is more soluble than the original substance, the resistance of the rock to water is decreased. This is a very constant operation, and as air penetrates deeply into soil and into the pores of rock its action is widespread. 16. Action of plants and animals. — Some of the lower forms of plants, of which lichens are a notable example, are able to live on the bare surfaces of rock, fastening them- selves to the small crevices and pores and in the process of SOIL FORMATION AND TRANSPORTATION 15 their growth causing the rock to decay and organic matter to accumulate in the crevices. These plants are followed by higher vegetation, the roots of which are larger ; when these roots extend themselves into cracks in the rock they exert a prying action when wind gives the plant a swaying motion. After rock becomes sufficiently pulverized to produce soil, plants are active agents in decomposing soil particles by the solvent action of the acid secreted by their roots and formed by their decay. Very small plants, included among the microorganisms because they are too small to be seen without a microscope, are also concerned in rock decay. Their action is exerted principally in. soil, and is due to the production of acids even stronger than that secreted by the roots of higher plants. 17. Powdered rock is not soil. — We have seen that in the process of soil formation the rock is pulverized, but the process of weathering to which nature resorts is different in its result from merely grinding rock in a crusher or mortar. At the same time that the particles are becoming smaller, certain chemical changes are going on that produce a ma- terial having a different composition from the original rock. One result of the transition is the removal of a part or some- times all of the more soluble constituents of the rock. The percentage loss of some of the constituents of granite and of limestone in the process of forming a clay is as follows : Table 1. — Percentage Loss of Plant-Food Materials in Granite and Limestone in Process of Soil Formation Constituents Percentage of Loss Granite Limestone Phosphoric acid Potash Lime 0.00 83.52 100.00 74.70 68.78 57.49 99.83 Magnesia 99.38 16 SOILS AND FERTILIZERS This table represents merely two cases, and is not meant to imply that these losses always occur in just these propor- tions whenever rocks of this type are converted into soil. It will be noticed that some of the most valuable plant-food materials are lost in large quantities. For instance, practi- cally all the lime has been lost, as has also a large propor- tion of the magnesia and potash. Phosphoric acid shows great variation in respect to loss. Other changes that occur in weathering include the forma- tion of extremely fine particles that give plasticity to soils, and that have the property of absorbing certain substances, like fertilizers, from solution and holding them in a condition in which they do not leach readily from the soil, and yet in a form in which roots may make use of them. As these particles are very small, we find a relatively large propor- tion of them in a clay soil, but a very small proportion in a sand. Another operation that accompanies soil formation is the incorporation of vegetable matter or animal remains — together called organic matter — with the soil particles. This adds greatly to the crop-producing power of a soil, for as the organic matter decays it makes more soluble the inorganic constituents. QUESTIONS 1. Name the agencies concerned in soil formation and trans- portation. 2. In what way do heat and cold act to decompose rock ? 3. What is the action of frost on rock ? 4. How does water aid in the transportation of soil ? 5. What part did the great glaciers play in soil formation ? 6. Has wind been more potent as a soil former or as a trans- porter ? 7. Describe the ways in which roots aid in the decomposition of rocks. 8. Explain the difference between powdered rock and soil. Plate IV. Plants as Soil Formers. — Plants are active agents in the decomposition of rock. In the upper figure lichens may be seen beginning the disintegration, and in the lower, large tree roots are forcing themselves into the cracks in the rock. SOIL FORMATION AND TRANSPORTATION 17 LABORATORY EXERCISES Exercise I. — Soil formation and transportation. This exercise is based on observations in the field and its value depends on examples available. Use Chapter II as a basis for the field observations. If rock outcrops can be found in the neighborhood, a visit to them would be worth while. Examples of wind action, heat and cold, frost, and plant and animal influences in forming or transporting soil should easily be found. The erosive and carrying power of streams should also be studied in relation to soil formation. An examination of weathered rock of various kinds should be made in order to illustrate the chemical phase of soil formation. The rusting of iron could be used as an example of the effect of gases. The iron of rocks rusts in the same way. This, together with the assumption of water and a loss of soluble materials, brings about the decay of the rock. Remember, however, that the physical and chemical agencies work hand in hand and that these agencies are as active upon the soil as upon the original rocks. An examination in the spring of fall-plowed land would permit a study of the effect of weathering on soil structure. CHAPTER III SOIL FORMATIONS From the preceding description of the processes of soil formation, it will be seen that the operation may involve the transfer of soil from one place to another, or that it may take place in one locality, leaving the resulting soil where the parent rocks stood. The latter soils are called sedentary, the former transported. These may again be subdivided as follows : a , f Residual — formed in place Sedentary \ ~ , . • I Cumulose — plant remains Colluvial — gravity deposits Alluvial — stream deposits Marine — ocean deposits Lacustrine — lake deposits Glacial — ice deposits . iEolian — wind deposits Transported 18. Residual soils. — Soils of this formation are geologi- cally old, that is, they were formed at an earlier period than any of the other arable soils. They always bear more or less resemblance in composition to the rocks underlying them, although, on account of their great age they have lost much of the more readily soluble constituents of the original rock. This is also of agricultural significance, because many of these soluble constituents are of great importance 18 SOIL FORMATIONS 19 in the growth of plants. The following table shows the partial composition of an Arkansas limestone and of the clay soil formed from it, also the percentage of each of the constituents lost in the process : Table 2. — Partial Composition op Limestone Rock and Its Residual Clay Constituents Percentage Composition Rock Soil Lost Potash Lime Magnesia Iron Silica 0.35 44.79 0.30 2.35 4.13 0.96 3.91 0.26 1.99 33.69 66.36 98.93 89.38 89.56 0.00 It will be seen from the above table that lime, magnesia and potash have disappeared in large quantities, as has also iron, but that silica has lost little or none of what was orig- inally present, and now constitutes by far the larger part of the soil. Silica although not of great importance as a plant nutrient is, nevertheless, of value in crop production, because it contributes to the formation of the absorptive compounds before mentioned. The great age of residual soils has also led to changes in the composition of iron compounds, producing usually those of a red or yellow color, these colors being characteristic of residual soils. The long period of weathering has frequently resulted in wearing down the particles to such a degree of fine- ness that heavy soils of the nature of clay, clay loam or silt are produced. Analyses of two typical residual soils from Virginia, that have been formed from gneiss and limestone respectively, are given in the following^table : 20 SOILS AND FERTILIZERS Table 3. — Percentage Composition op Typical Residual Soils from Virginia Constituents Original Rock Gneiss Limestone Phosphoric acid Potash Lime 0.47 1.10 trace 0.40 12.18 45.31 0.10 4.91 0.51 Magnesia Iron 1.20 7.93 Silica 57.57 A striking feature is their low lime content, which is characteristic of soils that have been long subjected to leaching. Such soils would require applications of lime for the profitable production of most crops. The low content of lime in the soil derived from limestone illustrates the fact that such an origin does not insure a satisfactory supply of lime. 19. Distribution of residual soils. — These soils are widely distributed in the United States, being found in four great provinces — the Piedmont plateau along the eastern slope of the Appalachian mountains, the Appalachian moun- tains and plateaus, the limestone valleys and uplands be- tween and west of these mountains, and the Great Plains west of the Mississippi and Missouri rivers. 20. Cumulose soils. — Unlike residual soils, cumulose soils are of very recent origin. They have been formed by the growth of vegetation in and around lakes, ponds and marshes, many of which were left by the retreating glaciers. As the plants die they become immersed in water, which shuts off the supply of air, and thereby arrests decomposi- tion. The partly decomposed plant remains accumulate SOIL FORMATIONS 21 until the surface of the water is reached, when larger plants take root, and it is not uncommon to find large forests covering soil formed in this way. Cumulose soils, as may be expected from their mode of formation, contain a very large proportion of organic matter. On the basis of the degree of decomposition of the organic matter they have been divided into two classes — peat and muck. In peat the stem and leaf structure of the original plants may still be detected. In muck, however, decomposition has gone so far that the organic matter forms a more or less homo- geneous mass, and is mixed with a larger proportion of min- eral matter than in peat. Peat is used extensively as fuel in some European coun- tries, but is not of much value for agricultural purposes. The degree of decomposition reached by the organic matter determines its usefulness for both these purposes. Muck cannot profitably be used for fuel, but some muck lands are highly prized for market-gardening and other of the more intensive agricultural operations. The following table shows the composition of some typical cumulose soils : Table 4. Percentage Composition of Some Cumulose Soils Constituents Percentage Composition Muck Muck Marsh Mud Mineral matter Organic matter Nitrogen Phosphoric acid Potash 31.60 68.40 2.63 0.20 0.17 24.79 67.63 2.03 0.19 0.15 80.40 15.77 0.15 0.65 1 Not determined. 22 SOILS AND FERTILIZERS Many muck soils are underlaid by deposits containing lime derived from shells of aquatic organisms that inhabited the bodies of water in which the muck was formed. This adds materially to the value of the land, as lime is a valuable soil amendment, particularly on muck land. It is well to keep this in mind when examining muck land. The percentage of potash is much lower than in any other kind of soils, and a potash fertilizer is usually of great benefit to crops planted on muck. 21. Colluvial soils. — On all steep slopes there is a gradual downward creep of soil particles due to the effect of gravity assisted by rainfall, freezing and thawing, the movements of animals, in fact any agency that starts the particles in motion, after which their direction is almost invariably downward. This soil formation is not extensive, nor in any sense important. Such soils are confined largely to the bases of mountains. They are usually shallow and stony. 22. Alluvial, soils. — A stream flowing through its valley will erode its bed if very steep and will deposit sediment if nearly level, but under most circumstances it both erodes and deposits soil. As the upper reaches of a river are usually of steeper grade than the lower, it often happens that con- siderable material is picked up by the stream near its source, and as the current becomes slower farther down, this material is deposited. Alluvial soil is, therefore, found most largely along rather slowly flowing streams. It is estimated that water flowing at the rate of three inches a second will carry only fine clay, but if this rate is increased to twenty-four inches a second, pebbles the size of an egg will be moved along the stream bed. It is quite customary for streams flowing through a flat region both to erode and deposit soil. Such streams are likely to be sinuous in their course, the curves gradually becoming more angular as the current erodes the soil from SOIL FORMATIONS 23 the concave bank and deposits it on the convex. Finally the curve becomes so great that the stream breaks through the banks and straightens its course. In this way a broad valley may gradually be covered by sediment deposited by the stream. Changes in velocity of a stream, as when in flood after heavy rains or melting snows, cause a change in its canying power. Much material will be picked up by a stream in flood that must be deposited as the flood subsides. A stream may build up its bed so that the surface of the water is higher than is the land at some distance on either side. Such is actually the case in the lower Mis- sissippi valley. 23. Character and distribution of alluvial soils. — Allu- vial soils may be sands, loams or clay, depending on the veloc- ity of the stream and the nature of the eroded material. It is likely to be the case that the alluvial deposits along the upper stretches of a stream will be sandy, and that the material deposited will become finer as the stream proceeds. Soils of this formation have no very distinctive composition. Naturally this character depends on the nature of the ma- terial farther up the stream, and this, of course, varies in different parts of the country. Even along any one stream there may be a wide diversity of material picked up and hence an alluvial soil is likely to be a heterogeneous one. The content of organic matter is usually high, as this is carried and deposited with the other matter. Alluvial soil is generally regarded as rich soil, but there are many exceptions. When situated along slowly flowing streams, the land is likely to need drainage. Alluvial soils are naturally confined to the margins of streams, but they are found along small as well as large ones, and consequently the aggregate area of alluvial land is large. The Mississippi valley and its branches contain 24 SOILS AND FERTILIZERS the largest area of alluvial soil found anywhere in the United States. Rivers flowing through the coastal plain are all well lined with alluvial soil adjacent to their banks. 24. Marine soils. — Soils of this formation have been made by material carried by rivers and deposited in the ocean, whence they afterwards emerged by elevation of the sea bottom. They, therefore, resemble alluvial soil that has been worked and reworked by sea water. They are generally sandy soils, as the solvent action of water and the pulverizing force of waves has disposed of most of the min- erals except quartz. They are light not only in texture, but also in color. They are nearly always deficient in organic matter. Their sandy nature fits them particularly well for trucking, and it is to that industry that a large area of marine soil is devoted. 25. Distribution of marine soils. — A fringe of land aver- aging many miles in width along the Atlantic coast from Long Island southward and including all of Florida is com- posed of marine soil. This fringe then turns westward and extends along the Gulf coast in a wide band as far west as the Rio Grande. The alluvial plain of the Mississippi river cuts through the belt, but at this point the marine soil extends as far north as Tennessee. In the aggregate the marine soils constitute a large area of important agricultural land producing cotton, corn and other farm crops, as well as truck crops for which they are especially adapted. The following is a statement of the analysis of a typical marine soil from the coastal plain in Maryland : Table 5. — Percentage Composition of a Typical Marine Soil Phosphoric acid . . . 0.05 Magnesia 0.35 Potash 0.70 Iron 0.91 Lime . 0.41 Silica 92.30 Plate V. Soil Formation. — The upper figure shows a glacial till soil, the lower an alluvial soil. SOIL FORMATIONS 25 A striking peculiarity of this soil is the high percentage of silica, due to the fact that quartz is highly resistant to the constant working to which the particles have been subjected and which has removed much of the phosphoric acid, potash, lime and magnesia. Soils of this particular type contain little fertility, but respond well to fertilization. 26. Lacustrine soils. — These soils have been formed in the beds of lakes both ancient and comparatively modern. The older ones were formed in the glacial lakes, and both are soils that have been worked over by water. They constitute good agricultural soils and are found from New England westward along the Great Lakes, and spread out in a wide area in the Red River valley. 27. Glacial soils. — - The tremendous grinding to which rocks have been subjected by glacial action has resulted in a large proportion of very fine particles, and consequently these soils and subsoils are likely to be rather heavy. The particles are jagged instead of having the rounded appear- ance found in older soils and soils that have been worked over by water for longer periods. Owing to the fact that this process of soil formation has employed mechanical rather than chemical agencies the soils resemble the parent rock very closely. Unlike residual soils, glacial soils when formed from limestone are generally rich in lime. If, on the other hand, glacial soils are formed from rocks poor in lime, they have a small lime content. The hill soils of southern New York (Volusia series) are derived from shales poor in lime and the soils share this quality, while certain glacial soils of the Mississippi valley (Miami series) that are formed from limestone and sandstone are rich in lime. In the following table are shown analyses of residual and glacial soils from Wisconsin, the original rocks from which they were formed having been largely limestone : 26 SOILS AND FERTILIZERS Table 6. — Percentage Composition op Residual and Glacial Clays from Wisconsin Constituents Residual Glacial 1 2 3 4 Phosphoric acid .... 0.02 0.04 0.05 0.13 Potash 1.61 1.61 2.36 2.60 Lime 0.85 1.22 15.65 11.83 Magnesia 0.38 1.92 7.80 7.95 Iron 5.52 11.04 2.83 2.53 Silica 71.13 49.13 40.22 48.81 It will be seen that of the substances important for their plant-food value phosphoric acid and potash are somewhat more abundant in the glacial soils, that lime and magnesia are very much more abundant, while the less consequential substances are present in large quantity in the residual soil. This is because the residual soil has been subjected to more leaching. 28. JEolisLTi soils. — Following the retreat of the glaciers there ensued a period of aridity, especially in the southwest section of the territory now a part of the United States. Into these regions there had been washed a large quantity of fine glacial till, and during the dry period this was blown, by high westerly winds, into a large area in the Mississippi and Missouri valleys, where it is now found. It has been given the name of loess and on account of its wide area and great fertility it is an important agricultural soil. These soils are frequently of great depth, their texture is favorable to the maintenance of good tilth and in prairie regions their long period in grass, before they were placed under cultivation, has given them a good supply of organic matter. The following table contains a statement of analysis of soils from different sections of the loessal area : SOIL FORMATION 27 Table 7. — Percentage Composition of Loess Location of Soil, Iowa Mississippi Missouri Wyoming Phosphoric acid .... 0.23 0.13 0.09 0.11 Potash 2.13 1.08 1.83 2.68 Lime 1.59 8.96 1.69 5.88 Magnesia 1.11 4.56 1.12 1.24 Iron 3.53 2.61 3.25 2.52 Silica 72.68 60.69 74.46 67.10 All of the important plant-food materials, particularly lime, are abundant in these soils. They rarely need liming, and up to the present time commercial fertilizers have been used but little on them. Adobe is the name applied to another seolian soil similar to loess in its physical qualities, but differing somewhat in its mode of formation. It is supposed to be a mixture of loess with debris from the mountain slopes and has been formed under arid conditions. The soils thus formed are extremely fertile when placed under irrigation, which is usually necessary for their cultivation, because they are found in Colorado, Utah, southern California, Arizona, New Mexico and arid portions of Texas. The composition of two typical soils is given below : Table 8. — Percentage Composition of Two Adobe Soils Constituents Phosphoric acid . . Potash Lime Magnesia .... Iron ...... Silica 0.94 1.71 13.91 2.96 5.12 44.64 28 SOILS AND FERTILIZERS These soils show a remarkably high content of phosphoric acid and an abundant supply of the other substances needed by plants. Sand dunes and volcanic dust are two other forms of seolian soils but nowhere are these soils of much agricultural importance. QUESTIONS 1. How may soils be divided with respect to the localities in which they have been formed ? 2. What common plant-food materials have been lost in great- est quantities by residual soils ? Why are these soils likely to have a large proportion of clay ? 3. In what four regions of the United States are residual soils found to be predominant ? 4. What is the characteristic constituent of cumulose soils ? For what agricultural purposes are muck soils largely used ? In what important plant nutrient are they likely to be deficient ? 5. How is the velocity of a stream likely to affect the nature of a soil with respect to its proportion of sand and clay ? What kinds of streams form little alluvial soil ? 6. Why are marine soils characteristically sandy ? For what agricultural industry are they frequently used ? 7. Are marine soils usually rich or poor in plant-food materials ? Why? 8. State over what areas in the United States lacustrine soils are found. 9. Why do glacial soils resemble chemically the rocks from which they were formed ? What is a characteristic difference between residual soil and glacial soil when both are formed from rocks rich in plant-food materials ? 10. Describe the mode of formation of the two principal kinds of seolian soils in the United States. Are they characteristically rich or poor in plant-food materials, and in what one particularly ? 11. Using any map of the United States as a base (preferably a colorless map showing the state boundaries and river courses), draw lines tracing roughly the regions occupied by residual, alluvial, marine, glacial, and seolian soils. These areas may then be shaded or colored differently and a soil map of the United States thus be made. Plate VI. Stratification. — The upper figure illustrates stratifica- tion of rock, the lower stratification of soil. This shale rock has at one time been soil. The soil may sometime be rock. SOIL FORMATION 29 LABORATORY EXERCISES Exercise I. — Classification of soils. A study of the various kinds of soils must nec-v, essarily be made in the field. No one locality affords examples of all the different kinds of soil listed in Chapter III. In some places only one or two classes may be available. In any case make all possible use of the materials, studying each soil as to origin, parent rock, color, depth, sub- soil, organic matter, drainage, general fertility and crop adaptability. Exercise II. — Use of the soil auger in taking soil samples. Material. — Soil auger and jars or bags for samples. Procedure. — Explain the construction of a soil auger and then proceed with the taking of a sam- ple of the first eight inches of soil, removing the soil in two portions. Then clean out a hole larger than the auger worm to prevent contami- nation of later samples and take the second eight inches in the way already described. Place sam- ples in bags or jars for future reference or exhibi- tion. Be sure that the samples are representative ger for taking soil of the soils to be studied. samples. (A) These samples may be used later in the tests handle, (B) joint, for organic matter, acidity, water retention, and modified^utTing other demonstrations according to directions in the edge, laboratory exercises to be found elsewhere in the book. Au- CHAPTER IV TEXTURE AND STRUCTURE OF SOILS As a result of the grinding to which rock is subjected in the process of soil formation, there are to be found in soils particles of all sizes, from gravel and coarse sand down to particles so minute that they cannot be seen with the highest power microscope, to say nothing of the unassisted eye. In all but very sandy soils, particles are generally gathered into clusters or granules. Texture is a term used in refer- ence to the size of the particles in a soil ; the term struc- ture refers to the arrangement of particles into granules. 29. Shape of particles. — There is no universal shape for soil particles. They vary from spherical to angular, and are sometimes rather elongated, but the occurrence of anything like needle shape is not common. Soils formed by erosion and wave action are likely to have rounded particles, as are also soils formed from limestone. 30. Space occupied by particles. — The number of par- ticles in a given volume of soil can only be estimated, their minute size precludes an actual enumeration. It has been estimated that the number of particles in a gram of soil of certain different kinds is as follows : Early truck 1,955,000,000 Truck and small fruit ....... 3,955,000,000 Tobacco 6,786,000,000 Wheat 10,228,000,000 Grass and wheat 14,735,000,000 Limestone 19,638,000,000 30 TEXTURE AND STRUCTURE OF SOILS 31 If all the particles were spheres, it is estimated that each cubic foot of soil would have a surface area on its particles amounting to from two to three and one-half acres. 31. Mechanical analysis of soils. — A separation of the particles of a soil into groups, each of which comprises particles whose sizes fall within certain definite limits, is -Firm gravel •COARSE 5AHD -MEDIUM - -FINE VERTHME;'' SILT CL/T/ Fig. 2. — Relative sizes of soil particles in the various grades into which a mechanical analysis separates a. soil. All are enlarged many times. Par- ticles of fine gravel may vary in size from the largest circle to the next largest ; coarse sand from the second to the third ; medium sand from the third to the fourth, and so on. The dot in the center represents the largest clay particles ; the smallest cannot be shown in a figure of this magnification. called a mechanical analysis of the soil. The size limit of these groups is a purely arbitrary matter, consequently it is desirable that a universal system shall be adopted. The classification in general use in this country is one pro- posed by members of the Bureau of Soils of the United States Department of Agriculture. It provides for groups of the following sizes : 32 SOILS AND FERTILIZERS Diameters of Particles Millimeters Inches Fine gravel . . Coarse sand . . Medium sand Fine sand . * Very fine sand . Silt Clay .... 2-1 1-0.5 0.5-0.25 0.25-0.10 0.10-0.05 0.05-0.005 less than 0.005 0.08-0.04 0.04-0.02 0.02-0.01 0.01-0.004 0.004-0.002 0.002-0.0002 less than 0.0002 32. Mechanical analysis of some typical soils. — When soils are analyzed according to the mechanical separation just described, there are shown to be great differences between some of them, and soils that are adapted to certain crops are found to have a somewhat characteristic composi- tion. It must be remembered, however, that such dis- tinctions are always limited by climate. The following table, based on the work of the Bureau of Soils and the Minnesota Experiment Station, contains a statement of the mechanical analyses of a number of typical soils : Table 9. Mechanical Analyses of Soils and Subsoils Adapted to Certain Crops Coarse Sand Me- dium Sand Fine Sand Very Fine Sand Silt Clay Garden truck soil, Norfolk, Virginia 1.42 28.27 38.25 7.51 21.04 7.15 Garden truck soil, Jamaica, Long Island .... 19.06 24.91 9.65 10.08 17.39 7.25 Grass soil, Hagerstown, Md. 0.08 0.13 0.53 10.94 23.69 51.75 Wheat and grass subsoil, Kentucky 0.00 0.15 0.25 2.34 39.92 51.77 Corn subsoil, Nebraska 0.00 0.00 0.10 25.83 57.00 9.49 Potato soil, Minnesota . . 0.00 59.04 5.60 28.40 4.05 Wheat soil, Minnesota . . 0.00 0.00 6.18 30.60 57.00 TEXTURE AND STRUCTURE OF SOILS 33 sSOIL-, MO. 1 FINE COARSE 6 RAVEL 5AN0 FINE SAND VERY FINE SAND CLAY vSOIL-, TSDO . a. fftf 1- flW o 70 s 60 fe tfO UJ 40 an UJ ?<0 ll 1 W Cl 0 FINE COARSE. MEDIUM GBAVEL SAND S/4ND FINE. 5AM D VERY FINE SAND 5ILT CLAY Fig. 3. — Graphic statement of mechanical analyses of two soils. No. 1 is a very sandy soil, and it will be noted that the bulk of its particles consist of medium and fine sand. No. 2 is a heavy clay and its particles belong mainly to the silt and clay divisions. 33. Soil class. — The terms " sandy soil," "loam soil," " clay soil " and the like have been in such general use and are so convenient that attempts have been made to devise a sys- tematic classification on this basis. A soil class is made 34 SOILS AND FERTILIZERS up of particles of various sizes, but the proportion of the large, medium or small particles determines the class to which it belongs. The following table published by Whitney will show what percentages of soil separates are contained in an average sample of each of the soil classes. Table 10. — Mechanical Composition OF VA rious Soil Classes Based on Averages of Many Analyses Fine Gravel Coarse Sand Me- dium Sand Fine Sand Very Fine Sand Silt Clay Coarse sands . . . 12 31 19 20 6 7 5 Sands 2 15 23 37 11 7 5 Fine sands . . . 1 4 10 57 17 7 4 Sandy loams . . . 4 13 12 25 13 21 12 Fine sandy loams . 1 3 4 32 24 24 12 Loam 2 5 5 15 17 40 16 Silt loams .... 1 2 1 5 11 65 15 Sandy clays . . . 2 8 8 30 12 13 27 Clay loams . . . 1 4 4 14 13 38 26 Silty clay loams . . 0 2 1 4 7 61 25 Clays 1 3 2 8 8 36 42 There must be a certain amount of variation in the per- centages of the separates that go to make up a soil class. In order to determine the class to which a soil belongs when its mechanical analysis is known, the diagram in Fig. 4 may be used. If, for instance, a soil contains 40 percent of silt and 15 percent of clay, lines are drawn from the point marked 40 percent silt and 15 percent clay, the lines being parallel to the sides of the right angle formed at 0. It will be found that these lines intersect in the space marked loam, which is the class to which the soil belongs. If a soil has 20 percent silt and 10 percent clay, the intersection of the lines drawn from these points falls in the space marked sandy loam, and the soil belongs to that class.. TEXTURE AND STRUCTURE OF SOILS 35 ci^r 34. Some properties of the separates. — In addition to differences in their size, there are other distinctions that are more or less characteristic of these separates. A mechanical analysis, therefore, tells us something about several of the properties of a soil. Clay particles, by reason of their mi- nute size, tend to make a soil plastic and may cause it to become hard, com- pact and cloddy when dry. Silt does this to a much less degree. The extent to which a soil exhibits these properties depends on its content of clay or silt. Soils containing much clay or silt must not be plowed when wet or they will puddle. Both clay and silt serve to increase the water-holding power of a soil, and clay especially increases the difficulty of tillage. The sand separates have the opposite properties of clay, and in the order of their greater size of particles. Sandy soils are more easily worked, are not likely to puddle or to form clods, and do not hold a large amount of water, but on the contrary have a tendency to become dry. Sandy soils are termed " light " soils because they are easy to till ; clay soils are called " heavy " because they make a heavy draft on the plow. The absolute specific gravity, or weight of the particles as compared with the weight of the volume of water which Fig. 4. — Plan by which the soil class may be ascertained from a mechanical analysis. 36 SOILS AND FERTILIZERS these particles would displace if they were immersed in it, does not necessarily correspond to these terms. Particles of greater and less specific gravity are scattered through both " light " and " heavy " soils and if we are to find the specific gravity of a soil we must have in the sample to be tested enough particles to give an average of all in the soil. 35. Chemical composition of soil separates. — The fact that one kind of mineral wears down to a small particle more easily than does another indicates that there would be a preponderance of resistant minerals, like quartz, among the coarse particles and a large proportion of the more easily decomposed minerals, like the feldspars, among the fine particles. This is actually the case, and it indicates a chemical difference in the separates. Analyses of sepa- rates made by the Bureau of Soils of the United States De- partment of Agriculture bring out these differences, as shown by the following table : Table 11. — Chemical Composition of Some Soil Separates Soils Percentage op Phosphoric Acid Percentage op Potash Percentage op Lime Sand Silt Clay Sand Silt Clay Sand Silt Clay Crystalline residual . Limestone residual . Coastal plain . . Glacial and loessial . Arid . . .07 .28 .03 .15 .19 .22 .23 .10 .26 .24 .70 .37 .34 .86 .45 1.60 1.46 .37 1.72 3.05 2.37 1.83 1.33 2.30 4.15 2.86 2.62 1.62 3.07 5.06 .50 12.26 .07 1.28 4.09 .82 10.96 .19 1.30 9.22 .94 9.92 .55 2.69 8.03 It will be noted from this table that, in general, the smaller particles are richer in 'phosphoric acid, potash and lime than TEXTURE AND STRUCTURE OF SOILS 37 are the larger ones, the only exception being the lime in the limestone residual. The arid soils do not show as great differences as do the others, because they have not been subjected to the same amount of solvent action and tritura- tion. 36. Soil structure. — By soil structure is meant the ar- rangement of the particles of which the soil consists. These particles may be separated so that each is free to move independently of any other, which is usually true of a dry coarse sand. Such an arrangement is known as the separate grain structure. On the other hand the particles may be arranged in small groups or granules, these being so firmly combined that the granule acts like a separate particle. The latter condition is termed the granular or crumbly structure. When applied to loams and clay soils, these arrangements of the particles have a relation to the condi- tion popularly known as tilth. Good tilth in clays and loams implies a granular structure, poor tilth a separate grain structure. The granular structure is not to be confused with a cloddy condition of the soil. In fact clods have the separate grain structure, because the soil has been worked when wet until the granules are broken down and the particles move easily over each other owing to the lubrication of the moisture. 37. Relation of structure to pore space. — The arrange- ment of the soil particles determines to a considerable degree the amount of free or pore space within the soil, especially in loams and clays. Merely for the purpose of illustrating this let us suppose that the soil particles are perfect spheres of equal size, which, of course, they are not. There would be two arrangements possible, if each sphere were independent of every other: (1) in columnar order, in which each particle is touched on four places by its neighbors ; (2) oblique order, in which each particle is in contact with six of its 38 SOILS AND FERTILIZERS neighbors. The calculated pore space in the first arrange- ment is 47.64 percent. That in the second case is 25.95 percent. (See Fig. 5.) It is not actually the case, however, that soil particles are of the same size in any natural soil. Consequently small particles fit in between large ones, thus decreasing greatly the actual pore space. These three cases, of which only the last may occur in nature, illustrate pore space Fig. 5. — If all soil particles were spheres they could be arranged as shown above, in which case the pore space would vary in volume as ex- plained in the text. when the separate grain structure obtains, as in a dry sand or a puddled loam or clay. The granular structure is the one most likely to be found in nature, although all of the particles may not be in gran- ules. The granules being of irregular form, with many angles, there is likely to be a large amount of space between them. It would be possible under this arrangement for a soil to have a pore space of 72 percent. The weight of a given volume of soil, including the pore space, as compared with an equal volume of water is termed the apparent specific gravity. This it will be seen is not the same as the absolute specific gravity because the amount of pore space is the important factor in determining the ap- parent specific gravity. Neither do the terms " light " soil and " heavy " soil bear any definite relation to the apparent specific gravity. A knowledge of the apparent specific TEXTURE AND STRUCTURE OF SOILS 39 gravity of a soil is useful because it is an indication of the amount of pore space. 38. Relation of structure to tilth. — The term " tilth" is commonly used to denote the condition of a soil with refer- ence to plant growth. When the physical condition of a soil is favorable to plant growth, the soil is said to be in good tilth ; when the physical condition is unfavorable, it is said to be in poor tilth. A loam or clay soil to be in good tilth must have the greater number of its particles in a granular condition. The more sandy a soil the less the necessity for a highly granular structure in order that it shall be in good tilth. The greater the proportion of clay in a soil, the more necessary is the granular structure. One of the great ob- jects in soil management is to produce and maintain the granular structure. 39. Conditions and operations that affect structure. — So far as the structure of a soil is concerned, something de- pends on the inherent quali- ties of the soil and something on its treatment by the weather and by man. These factors may be enumerated as follows : (1) texture,. (2) wetting and drying, (3) freezing and thaw- ing, (4) addition of organic matter, (5) tillage, (6) roots and animals, (7) lime. 40. Relation of texture to structure. — A coarse sand admits only of the separate grain structure. There is not sufficient cohesion to hold the particles in granules, and there is no plasticity. With a decrease in the size of the partieles, there is a greater tend- ency to the formation of the granular structure, other con- Fig. 6. — Structure of a loam soil in good tilth. (A) sand particle, (B) pore space, (C) granule com- posed of silt and clay particles. 40 SOILS AND FERTILIZERS ditions being equal. This does not mean that a clay soil is easier to keep in good tilth than is a loam soil, but under favorable conditions the small particles have greater plastic- ity and cohesion and hence form granules more readily. 41. Wetting and drying. — As a soil becomes dry there is a contraction of volume in which process lines of cleavage or cracks occur and clods are formed. If these clods be again wetted and partly dried without working, they will separate into smaller clods and finally a granular structure will be produced. This is illustrated by the greater ease with which clods may be worked down after a rain and partial drying, than when they remain perfectly dry. Land in need of drainage is usually in poor tilth, while after drain- age this condition gradually improves. 42. Freezing and thawing. — The " heaving " of roots during winter is an indication that frost has a disrupting action on the solidarity of the soil. Roots are pried out because the surface of the soil rises when freezing occurs and sinks when melting takes place. Water that is held between soil particles freezes when the temperature of the surrounding soil falls below the freezing point. As water freezes it expands, the effect of which is to force the particles farther apart. The pressure applied by the freezing water is very unevenly distributed. Around the larger water- holding spaces the particles are moved farther than are those adjacent to smaller spaces, because the larger the body of water the greater the expansion when it freezes. The uneven crowding of the particles causes a breaking up of the soil into more or less separate masses and as this pro- ceeds with repeated freezing and thawing there is a pro- nounced formation of granules in a clay or loam soil. Fall-plowed land, if left unharrowed, or if too cloddy to work down to a good tilth, will generally be mellow by spring, provided there is much freezing weather during the winter. TEXTURE AND STRUCTURE OF SOILS 41 43. Effect of organic matter on structure. — The quantity of organic matter in a soil is frequently the deciding factor in determining its structure. Partially decomposed organic matter has a loose, spongy structure and at the same time a plastic quality. The latter causes the soil particles to cohere, and the former gives to the organic matter the property of swelling when the soil becomes wet and shrink- ing when it becomes dry. These changes in volume facilitate the formation of granules as previously explained. Large areas of land in this country have deteriorated in productivity and have become compact and difficult to work on account of the gradual loss of organic matter. Naturally clay and heavy loam soils have suffered more in this way than have lighter soils. Where marked decrease in crop returns has occurred during the time that soils have been under cultivation, the difficulty can generally be traced to loss of organic matter more than to any other factor in plant growth. Compact soil, with consequent poor tilth, is one of the most common conditions in poor farming regions, and is usually associated with a low content of organic matter. 44. Roots and animals. — In some way not very well understood roots exert more or less influence on soil struc- ture. Shallow, fibrous-rooted plants, among which are the grasses, wheat, barley, millet and buckwheat, have the most favorable action in granulating soil. More deeply rooted, and especially tap-rooted plants, have this property to a less extent. In fact, a crop of beets may help to com- pact a soil already in bad condition. In establishing a rotation it is desirable that some fibrous-rooted plants form one or more of the courses. Various forms of animal life help to granulate soils. Of these, earthworms are the most notable. The soil particles that they excrete from the digestive tract may amount to 42 SOILS AND FERTILIZERS several tons in an acre in the course of a year, while their bur- rows ramify through the soil in all directions. The move- ment of soil particles that results is an appreciable factor in changing soil structure. Insects and other burrowing creatures affect soil structure in a similar way. 45. Tillage and structure. — The ordinary operations of tillage are designed to improve soil structure, and are effective if these operations are conducted at the proper time and in the best way. Plowing, which is the most fundamental of all tillage operations, may improve soil structure or may injure it, depending on the condition of the soil at the time of plowing. It is a matter of common knowledge that working a soil saturated with water will cause it to puddle, or in other words, to assume the separate grain structure. Plowing when the soil is very dry may have the same effect, although not usually to the same extent. However, when a soil is mod- erately moist, plowing aids greatly in effecting a granular structure. This it does by the peculiar twisting action that the curved moldboard gives to the furrow slice. The soil in immediate contact with the plow surface is retarded by friction, and the layers above tend to slide over one another much as do the leaves of a book when they are bent. The soil is thus broken up into masses of aggregates correspond- ing to the location of the lines of weakness. If a soil has been strongly compacted, so that there are few lines of weak- ness, the clods will be large when the soil is plowed. Plow- ing helps to improve the tilth of the soil, but it will not over- come entirely a bad physical condition. 46. Structure as affected by lime. — One of the properties possessed by lime is that of flocculating clay. This may be readily observed by stirring a spoonful of clay in a tumbler of water and then adding a quarter of a spoonful of burnt lime. It will be noticed that the soil settles much more quickly after the lime has been added than before. Sandy Plate VII. Tillage. — Good tilth is a response to good soil manage- ment. The upper figure is an illustration of poor, the lower of good, tilth. TEXTURE AND STRUCTURE OF SOILS 43 soils are not flocculated to the same extent by lime, but are thus affected in proportion to the quantity of clay they possess. Of the different forms of lime, quick-lime and water- slacked lime are more active in producing a granulated struc- ture of soil than is ground limestone, marl or air-slacked lime. This is one reason why the burned lime is superior to ground limestone for use on heavy clay soils, on which there may be a pronounced difference in the effect of the two kinds of lime on crop production. Warington reports a statement of an English farmer to the effect that by the use of large quantities of lime on heavy clay soil he was enabled to plow with two horses, while three were necessary before applying lime. 47. The soil survey. — The purpose of a soil survey is to classify and map the soils in a given area according to their crop relations and their physical properties, and to correlate these soils with those in other areas. The soil unit, or what may be termed the soil individual, is the type, and on a soil map each type is given a different color. Every soil type has a certain peculiar and characteristic appearance and certain inherent properties that distinguish it from every other type. When the type is known some practical infor- mation regarding its texture and its amenability to tillage and to drainage may be predicted, and something in regard to its productiveness and the crops to which it is adapted may also often be inferred. 48. Classification of soils. — In order to distinguish between soils, and to give a basis on which to separate them into the types to which reference has been made, a form of classification has been adopted in this country that takes into consideration much of what is known of their history and their properties. Thus the first large division into which a soil falls is known as the soil province, which is based, in a general way, on the process of formation. A 44 SOILS AND FERTILIZERS province may represent residual soil, like the Piedmont province, or glacial soil, or marine soil, or soils of other processes of formation. The next smaller division is the series. A soil series has been defined as"a group of soils having the same range in color, the same character of subsoil, particularly as regards color and structure, broadly the same tj^pe of relief (topog- raphy) and drainage, and a common or similar origin." The last of these properties is due to the fact that soils of the same series must fall within the same province. The final division is the class, which has been described in paragraph 33. A soil class is not limited in its occurrence to a soil province, but the same class may be found in all provinces. In this respect it differs from a series, any one of which occurs only in a single province. A soil type represents a soil of a single province, a single series and a single class, and represents the features of each. The following is an example : Province Piedmont Series . . . Cecil Class Clay Type Cecil clay 49. Information furnished by a soil survey. — The method of arriving at the identification of a soil type involves a history of the soil, and that may tell something about its probable chemical composition, as may be judged from the tables of analyses of soils of different formations (§§ 18-28). The series we have already found to signify something in regard to the working qualities of the soil, as does also the class. These distinguishing features are much more marked in some types than in others ; in the case of certain types considerable definite information is available when the soil type is known, while in the case of others less knowledge is afforded. Some types always represent a defective soil due TEXTURE AND STRUCTURE OF SOILS 45 perhaps to lack of lime, or poor drainage, or they may be characteristically deficient in phosphoric acid or even in potash. Again a type is often indicative of the kind of crops to which a soil is adapted, but as climate is a large factor in determining the success of any crop, conclu- sions of this nature are not of universal application. The working qualities of a soil may usually be gauged with some degree of certainty when the type is known. It is, however, as a foundation for a further study of soils that the survey is probably of greatest usefulness. QUESTIONS 1. To what does the term " texture " refer when used with refer- ence to soils ? 2. Name the groups into which soils are divided by a mechanical analysis. 3. What characterizes the difference in mechanical composition of soils adapted respectively to wheat, corn and potatoes ? 4. What is meant by class as applied to soils ? 5. In what class does soil belong that contains 20 percent clay and 20 percent silt ? One that contains 40 percent clay and 30 per- cent silt ? One that contains 25 percent clay and 35 percent silt ? 6. How do soils containing a high percentage of clay or silt be- have when wet ? How is their water capacity likely to compare with that of a soil high in sand ? 7. How do coarse and fine particles usually differ with respect to their content of phosphoric acid, potash and lime ? 8. What is meant by soil structure ? 9. Distinguish between separate grain structure and granular structure. Which permits of the greater amount of pore space ? 10. Describe the relation of tilth to structure. 11. Explain relation of structure to texture. 12. Explain relation of structure to wetting and drying of soil. 13. Explain relation of structure to freezing and thawing of soil. 14. Explain relation of structure to organic matter. 15. Explain relation of structure to roots and animals. 16. How is structure affected by lime ? 17. How is structure affected by tillage ? 46 SOILS AND FERTILIZERS LABORATORY EXERCISES Exercise I. — Examination of soil particles. Materials. — Samples of soil, hand lens, high power microscope. Procedure. — Examine various sizes of soil particles under the hand lens and later under the microscope. Observe shape and color. If possible measure size of particles. Try to distinguish between silt, clay and sand particles. Exercise II. — Examination of soil separates. Materials. — The seven separates into which a soil is divided in making a mechanical analysis. Procedure. — As a soil is made up of the seven grades of parti- cles in varying amounts, the characteristics of the grades will determine the characteristics of the soil. Observe the cohesion and plasticity of each grade. The finer grades are usually richer in plant food. Therefore try to imagine the physical and chemical properties of different mixtures. Study the separates with a view to identification if presented unlabeled. Exercise III. — Simple mechanical analysis. Materials. — Sandy loam well pulverized, 8 oz. bottle, funnel with filter paper, torsion balance, ammonia. (See Fig. 7.) Procedure. — Place 50 grams of a dry and well-pulverized sandy loam in a bottle of about 8 ounces capacity. Add a few drops of ammonia and fill two-thirds full of water. Shake five minutes to break up all granules. Then allow sample to stand until the various grades of sand have settled to the bottom, after which de- cant the silt and clay. Add water and repeat this until the water clears as soon as the sands have settled. Then wash the sands out into a weighed filter paper held in a funnel. Allow sands to drain. Then dry sands and filter paper thoroughly and weigh. This weight, less the weight of the filter, will give the weight of the sands. Fifty grams, less the weight of the sands, will give the weight of the silt and clay. Calculate the percentages of sand and of silt and clay respectively in the sample of sandy loam. Exercise IV. — Study of soil class and its determination by examination. Materials. — Hand lens, a number of different soil classes (sand, sandy loam, clay loam, loam, silt loam, muck, etc.) labeled for study and a set of unknown specimens for identification. TEXTURE AND STRUCTURE OF SOILS 47 Procedure. — Examine the texture of each of the labeled soils both under the hand lens and by the feel. Observe the color and estimate the amounts of organic matter by the darkness of the color. Be able to identify samples if unlabeled. Observe the plasticity and cohesion of each soil when enough water has been added to develop maximum plasticity. Make small marbles of sand, clay and muck respectively when each is at its maximum plasticity. Dry and observe relative cohesion and plasticity. Be able to state the relation of texture, moisture and or- 9 CLAY SAND5 APPARATU5 FOR FILTERING 5AND3 Fig. 7 — Apparatus for a simple mechanical analysis of soil. Shaker bottle, funnel, filter, beaker and stand. ganic matter to cohesion and plasticity. What is the practical im- portance of texture and class ? Obtain set of unlabeled samples for identification of class. If possible, pupils should also identify samples in the field. As mois- ture variations and tillage operations often make great differences in the general appearance of a soil, skill in quickly and accurately determining the class of any soil in the field is a valuable asset in all agricultural work. Exercise V. — Determination of soil class from a mechanical analysis. Materials. - — Figure on page 35. 48 SOILS AND FERTILIZERS Procedure. — By the use of the chart determine the class of the following soils and describe their probable characteristics. Soil Fine Gravel Coarse Sand Medium Sand Fine Sand Very Fine Sand Silt Clay 1 1 5 6 5 3 70 10 %^ 2 2 3 10 18 12 45 10 X- 3 1 2 14 18 25 30 10S~i 4 2 3 25 14 16 30 10 5 3 7 25 30 20 10 5 6 2 3 12 19 24 10 30 7 1 4 9 11 10 40 25 8 2 2 3 4 4 60 25 9 1 2 7 6 4 20 60 10 2 1 3 2 2 50 40 u fr* Be ready to explain the practical value of a mechanical analysis. Exercise VI. — Soil structure. Materials. — Puddled and granular soils. Procedure. — Examine under hand lens a granular and a puddled soil. Describe each and make drawings. Discuss each as to prob- able relation to air and water movement, penetration of plant roots, ease of making seed bed, etc. Be ready to suggest practicable reme- dies for poor structure. Exercise VII. — Determination of apparent specific gravity of a dry sand and clay. (See Fig. 8.) Materials. — Torsion balance, dry soils and a 100 c.c. graduated cylinder. Procedure. — Apparent specific gravity is the weight of dry soil compared to the weight of the same volume of water. Weigh the 100 c.c. graduate in grams, then fill to the 100 c.c. mark with loose sand. Weigh and calculate the weight of the sand in grams. The weight of the sand divided by 100 (the weight of 100 c.c. of water in grams) will give the apparent specific gravity of the loose sand. Now compact the sand as much as possible by jarring and read volume. Divide the weight of the sand by this volume to obtain the apparent specific gravity of the sand compact. TEXTURE AND STRUCTURE OF SOILS 49 Determine in the same way the apparent specific gravity of the clay when loose and when compact. Compare the figures from each soil and explain the reasons for the differences observed. Calculate the weight per cubic foot and acre foot of the sand and clay when loose and when compact. Fig. 8. — Equipment for the determination of the apparent specific gravity of soil, consisting of a balance, a set of weights and a 100 c.c. gradu- ated cylinder. Exercise VIII. — Calculation of pore space. Materials. — Data from Exercise VII. Procedure. — Using 2.7 as the absolute specific gravity of soils and the data from the preceding exercise, calculate the pore space on loose and compact clay and sand respectively by means of the following formula. % pore space = 100 - ["ap-sp-gr. x l^Ql ■ Labs. sp. gr. 1 J Be ready to explain the reasons and significance of the results obtained. 1 Ap. sp. gr. means apparent specific gravity. Abs. sp. gr. means absolute specific gravity. E 50 SOILS AND FERTILIZERS Exercise IX. — A study of the plow. Material. — Garden plow and team. Procedure. — Study the plow by following the diagram in Fig. 9. Locate the mold board, point, share, landside, shin, heel beam, coulter and clevis. Adjust the plow to various widths and depths of furrow slice, trying out each adjustment by throwing several furrows. Be sure that with each adjustment the plow operates properly. h—?^L^ Fig. 9. — A walking plow and its attachments, (a) clevis, (6) beam clevis, (c) bridle, (d) beam, (e) mold board, (/) depth wheel, (g) rolling coulter, (h) jointer, (i) standard, (j) share point, shin above, (k) landside. Study the inversion of the furrow slice and be ready to explain how and why a plow is a good pulverizing agent. The pupils should hold the plow as much as possible in the various tests. If a sod plow is available, a study of this form would be of value, comparing it with the garden plow above. A comparison of a walk- ing plow with a sulky plow would also be worth while. A visit to an implement dealer for the purpose of looking over the various makes of plows might be a profitable exercise. The manufacturer's and the dealer's viewpoint is as valuable as that of the farmer. CHAPTER V ORGANIC MATTER A very important constituent of soil is the more or less decomposed organic matter that has become incorporated with it. Organic matter is found in larger quantity in sur- face-soil than in subsoil because it comes largely from vege- table matter that has fallen on the surface and there decayed, or that has been plowed under. Animal remains and lower forms of plant life also contribute to the supply. The roots of dead plants are one source of organic matter, and as these generally penetrate into the subsoil they deposit a limited quantity of organic matter in that part of the soil. 50. Classes of organic matter. — Organic matter that is incorporated with soil gradually decomposes, forming substances that are very different in their properties from the original material. The process may be roughly divided according to the degree of decomposition into three classes, viz : (1) undecomposed matter, (2) partially decomposed matter, (3) final products. The substances representing each of the stages in the process have different properties and differ in their effect on soil. Undecomposed organic matter is of use in making less compact a heavy soil ; on the other hand, it may make too loose a naturally light soil and may cause it to dry out to such an extent that its productiveness will be curtailed. For instance, a stand of oat stubble or of corn stalks that would be of much benefit to a heavy soil in a humid region might injure seriously a light soil in a semi-arid region. 51 52 SOILS AND FERTILIZERS Partially decomposed organic matter is of benefit to soils in a number of ways and it may also be injurious. These properties will be discussed later. The term " humus" has been somewhat loosely used with reference to the sub- stances of this class. It will not be used in this book. Organic substances represent a wide range of intermediate products of decomposition. They profoundly affect the properties of soils and are always present in arable soils. Final products of decomposition of organic matter are water and gases. The latter may unite with some of the inorganic matter of the soil to form purely inorganic sub- stances, and these are as a rule readily available to plants. They differ from the substances of the other two classes in that none of them is injurious to crop production. 51. Beneficial effects of organic matter. — There are many ways in which organic matter may benefit soils, either directly or indirectly. Soils differ somewhat in the effect that organic matter may have on some of their properties. An example of this has been cited in the effect of organic matter on a heavy soil in a humid region as compared with its results in a light soil in a semi-arid region. Another example is to be found in the results that follow the plowing under of green-manures. In some soils and under certain conditions this may be temporarily injurious, although it is usually a very beneficial practice. An enumeration of the beneficial effects of organic matter in soil is necessarily open to criticism on account of the dif- ferent responses of different soils, but with some modifications the following will hold. (1) It increases the tendency towards the formation of granular structure. (2) On account of the porous nature of organic matter the pore space of the soil is increased and aeration improved. (3) It increases the water-holding capacity of soils. ORGANIC MATTER 53 (4) It improves drainage by reason of the properties stated under (1) and (2). (5) It increases the extent of root growth for the same rea- sons. (6) By making the soil darker, it facilitates heat absorp- tion. (7) It is a source of plant-food material. (8) It furnishes energy for the growth of bacteria. (9) Its decomposition produces carbonic acid gas and other acids that help to render plant-food materials soluble. 52. Porosity of organic matter. — The way in which or- ganic matter promotes a granular structure in soils has already been described, as has also the relation of soil struc- ture to tilth. In addition to this effect on soils, organic matter also serves to make soil more porous by reason of its own porosity. It may be compared to a sponge in its ability to hold air or water. A peat soil, for instance, will hold more water than its own weight of dry matter. Or- ganic matter extracted from a peat soil was found to carry twelve times its own weight of water. It may readily be seen that the porous nature of this organic matter may greatly increase the water-holding capacity of a soil. At the same time it may increase the capacity of the soil for air. 53. Organic matter and drainage. — By reason of the greater porosity due to the presence of organic matter, the movement of water through soils is facilitated and thus the soil is better drained. The advantages of good drainage will be discussed more fully later, but an important one of these is a greater growth of roots, which increases their opportunity for securing food and thus increases the size of crop. 54. Organic matter and soil color. — Partly decomposed organic matter generally gives a dark color to a soil. A dark soil absorbs heat more readily than does a light-colored 54 SOILS AND FERTILIZERS one, and as warmth is an important factor in plant growth, especially in the spring, a dark soil usually has an advantage over a light-colored one. 55. Organic matter a carrier of plant-food material. — In its relation to the supply of plant-food material, organic matter is the storehouse in which nitrogen is held in a form in which it cannot be leached from the soil in large amounts and yet from which it gradually becomes available to plants. Certain inorganic plant nutrients are likewise held in such condition that they readily become useful to plants. In the process of rotting, combinations are formed between organic matter and certain inorganic plant nutrients, removing the latter from the very insoluble minerals of the soil. On further decomposition the inorganic substances are left in a form readily usable by plants. 56. Organic matter and nitrogen. — The relation of organic matter to the nitrogen supply is of particular inter- est because it is as organic matter that practically the entire supply of nitrogen enters the soil. All soil nitrogen has been secured from the air and the process is still going on. This is done largely by the lower forms of plant life known as bacteria, fungi and molds. These organisms living in the soil, or in the roots of higher plants, feed on the non-nitrog- enous organic matter of the soil and plants, and upon the nitrogen of the atmosphere that passes into the pores of the soil. The non-nitrogenous organic matter and the atmos- pheric nitrogen are thus combined to form the tissues of these lower plants, which soon die and finally add to the soil the nitrogen they have accumulated. 57. Organic matter and soil microorganisms. — We have just seen how the nitrogen-fixing organisms use non-nitrog- enous organic matter in their growth. They use it as a source of energy, as do animals. Many other forms of lower plant life use organic matter, both nitrogenous and non- ORGANIC MATTER 55 nitrogenous. As the growth of these organisms is very- necessary in making the various sorts of plant nutrients available, the supply of organic matter for this purpose is of great importance. 58. Organic matter forms acids. — Finally, organic matter in its very last stages of decomposition continues to serve the plant by producing carbonic acid gas, which, dissolved in soil water, is an excellent solvent for many mineral sub- stances needed by plants. It is estimated that in an acre of soil sixteen inches deep, sixty-eight pounds of carbon dioxide are produced annually from the decomposition of organic matter when present in ordinary quantity. There are also other organic acids formed by the rotting of or- ganic matter that serve to dissolve the inorganic matter of soils. The combinations of these organic acids with min- eral substances form readily available plant-food materials. Another final product of nitrogenous organic matter is nitrate, which is the most 'available form of nitrogen for many plants. 59. Injurious effect of organic matter. — The injury that organic matter may cause is probably not of very frequent- occurrence and is unimportant as compared with its benefi- cial action. Two effects have been noted : (1) Undecomposed organic matter may cause a soil to dry out quickly by preventing it from settling sufficiently to establish water connection with the subsoil and by leav- ing large air spaces that allow a rapid movement of air through them which dries out the soil. (2) Partially decomposed organic matter may form prod- ucts that are poisonous to some agricultural plants or that interfere with the operations of those microorganisms that are beneficial to plant growth. 60. Management of soil with respect to organic matter. — The first step in the control of organic matter in soil is to 56 SOILS AND FERTILIZERS bring about decomposition, which operation is performed by bacteria, fungi and molds. It has already been pointed out that unrotted organic matter has very little useful- Fig. 10. — The upper figure represents a furrow slice laid too flat for the most rapid decay of organic matter when present in large quantity. The lower illustration shows a better furrow angle. ness and may be injurious. The conditions that favor the rapid and desirable rotting of organic matter are the fol- lowing : (1) An amount of moisture that will not fill all of the pore spaces, but that will provide water required by the organisms that decompose the organic matter. The soil moisture content most favorable for plant growth is about the same as that most favorable for rotting organic matter. (2) The soil should be loose enough to allow air to pene- trate readily, but not so loose as to leave large air spaces. Air is necessary to the activity of those organisms that pro- duce a desirable kind of decomposition. A compact soil, or a very wet soil delays the rotting process and favors the growth of organisms that form products poisonous to agri- cultural plants. ORGANIC MATTER 57 (3) The soil should not lack lime, as the presence of lime in a readily soluble form favors the development of many forms of life that decompose organic matter, and it also prevents the poisonous action of certain substances pro- duced in the process. 61. Sources of organic matter. — In addition to the natural supply of organic matter referred to in the first part of this chapter, there are other sources from which the farmer may obtain a supply by outright purchase or by means of their production on the farm. Among these are farm manure, grass and clover sod, green-manures, peat and muck, crop residues, like straw, cornstalks and leaves, dead animals, certain commercial products, like cottonseed meal and dried blood, and finally weeds, which are sometimes used for that purpose in orchards. These various materials and their use in contributing to the supply of organic matter in soils will be discussed later under the respective heads (1) farm manure, (2) green- manures and (3) commercial fertilizers. QUESTIONS 1. Into what three classes may the organic matter of the soil be divided ? . 2. What is the effect of organic matter on the water-holding capacity of soil ? 3. What is the effect of organic matter on drainage ? 4. How does organic matter contribute to the availability of plant nutrients in soils ? 5. In what general way does organic matter affect the growth of bacteria in soils ? 6. How do the final products in the decomposition of organic matter increase the availability of plant-food materials in soil ? 7. In what two ways may organic matter be injurious to soils ? 8. What are the soil conditions that favor a rapid and desirable decomposition of organic matter ? 9. Name the sources of organic matter that may serve to increase the supply in soils. 58 SOILS AND FERTILIZERS LABORATORY EXERCISES Exercise I. — Examination of soil for organic matter. Materials. — Samples of clay soils respectively low and high in organic matter, hand lens, flame. Procedure. — Examine a soil rich in organic matter under the hand lens. Observe character of the organic matter, its color and its effect on structure. Compare the structure of the soils high and low in organic matter. What effect does the organic matter ap- pear to have upon granulation ? How should the organic matter influence the ease of preparing a seed bed? How does organic matter influence percolation of water through a soil ? How does it affect its water capacity ? Place a small portion of the soil rich in organic matter in the flame. Observe and explain the results. Exercise II. — Examination of peat and muck. Materials. — Samples of peat and muck, hand lens, flame. Procedure. — Examine samples under lens and describe and make drawings. What is the origin of the materials, their structure, com- position and degree of decay ? What is the value of peat and muck ? Place a small portion of each in the flame. Observe and explain results. What is shown regarding the composition of peat and muck ? Exercise III. — Estimation of organic matter. Materials. — Soil samples, cru- cible, stirring wire, flame, tripod, clay triangle, balance. Procedure. — Place a five-gram sample of dry soil in a weighed crucible. Ignite with frequent stirrings at a low red heat over a flame until original dark color has disappeared. Cool and weigh. The loss has been largely organic matter. Calculate the percentage based on the original sample. Find in this way the percentage of organic matter present in several different soils. Fig. 11. — Apparatus for the esti- matiqn of organic matter in soil. (A) crucible, (B) clay covered tri- angle, (C) tripod, (D) Bunsen burner. ORGANIC MATTER 59 Exercise IV. — Extraction of partly decomposed organic matter. Materials. — Muck, dilute hydrochloric acid, ammonia, hydrate of lime, filter paper and funnel. Procedure. — Place about a gram of moist muck on a filter paper in a funnel. Treat the muck with a few drops of dilute hydrochloric acid. Wash out the acid with 50 c.c. of distilled water. Discard this percolation. Now treat the soil with ammonia. After allow- ing it to stand a few minutes wash with distilled water and catch percolate. The percolate should be black, showing the presence of partly de- composed organic matter. This is the material seen escaping from manure piles. It is the most valuable portion of the organic matter. Treat a portion of this soluble organic matter with hydrate of lime. Note the flocculating effect, which prevents the leaching of organic matter from the soil. Exercise V. — Influence of organic matter on rate of percola- tion of water through soils. Fig. 12. — Apparatus for studying the influence of the addition of organic matter to a soil on the rate of percolation and percentage of water holding capacity. Materials. — Clay or clay loam soil finely pulverized, moist muck, lamp chimneys, torsion balance and weights, cheesecloth. Procedure. — Divide the soil in two portions. To one add 10 per- cent of the moist muck. Mix thoroughly. Place equal and definite 60 SOILS AND FERTILIZERS weights of the two portions of soil in respective lamp chimneys, having previously tied cheesecloth neatly over the bottoms to keep the soil in place and yet to allow drainag3. Compact the soils to uniform height. Weigh each chimney plus its portion of soil. Set the chimneys in such a position as to allow free drainage. Pour equal amounts of water on each and observe the rate of percolation of the water through the two soils. Explain results and show the practical bearing of the experiment. Exercise VI. — Influence of organic matter on percentage of moisture held in soil. Materials. — Same as Exercise V. Procedure. — After observing the rate of percolation in the above exercise, saturate the soils, and allow them to drain freely until all gravity water has disappeared. Now weigh each chimney plus its soil. The increased weight over that of the original sample is water retained. Calculate the percentage of water thus re- tained, based on the weight of the original dry sample. Explain the practical importance of the results. CHAPTER VI SOIL WATER Of the great number of factors that influence the growth of crops none is of more importance, or possibly of as much importance, in its effect on the yield of crops as water. A soil may contain too much water for the best growth of crops, or it may have too little. On the one hand, we approach swamp conditions, and on the other the desert state. Even in the same locality and with equal rainfall one field may have too much moisture and another too little. While the volume of water contained in a soil depends more or less on the rain- fall, it is not controlled entirely by it; for within a wide range of atmospheric precipitation soils of the same type may not vary greatly in their moisture content. This is because there are other factors beside rainfall that serve to regulate the supply of soil water. 62. Forms of water in soils. — It has already been pointed out that in every soil there are spaces between the particles, or aggregates of particles and that the size and total volume of these spaces vary with different soils. These spaces may be completely filled with water or they may be nearly empty. When the pore spaces are entirely filled with water, three forms of water are found to be present : (1) hygro- scopic, (2) capillary and (3) free or gravitational. These forms differ in their relation to the soil particles. 63. How the three forms of water differ. — No soil in a natural state, that is as it exists in the fields or woods, is ever perfectly dry. No matter how small the rainfall or how 61 62 SOILS AND FERTILIZERS parched the crops, there is always a thin film of moisture surrounding each particle or aggregation of particles, al- though plants may not be able to obtain it. The thin film that is absorbed from the air and condensed on the surfaces of the particles, when no other source of supply is at hand, is termed hygroscopic water. If the film becomes somewhat thicker by reason of another supply like rainfall or under- ground water, the additional supply is termed capillary water. These two forms are much alike, both being held as a film around the particles, partly by the attraction of the soil for the water and partly by the attraction of the particles of the water for each other, which prevents the film from breaking and running away. One other difference between hygroscopic water and capillary water is that the former is always stationary, while the latter may move. A further increase in the quantity of water in a soil gives rise to the third form — gravitational or free water. With the advent of more water, the films become so thick that the attraction by which they adhered to the particles is overcome by gravity and there is a downward movement through the pore spaces, or else the pore spaces are com- pletely filled and the soil becomes saturated by reason of the inability of the water to escape from the soil. 64. Hygroscopic water. — From a practical viewpoint, hygroscopic water is not of much importance because plants cannot use it. A plant may die for want of water when the soil in which it grows contains its maximum of hygroscopic moisture. The forces that hold the water in the soil are greater than those that tend to draw it into the plant. The quantity of hygroscopic moisture that a soil will hold depends largely on its texture and on the quantity of partially decomposed organic matter that it contains. Fine particles have a greater absorptive power for water than do SOIL WATER 63 coarse ones. Clay has a large absorptive capacity and the presence of certain compounds increases immensely the content of hygroscopic moisture. 65. Capillary water. — The essential difference between capillary water and hygroscopic water is that the former is capable of motion and most of it may be used by plants. The fact that the capillary film is thicker causes it to be less firmly held by the soil particles, in consequence of which the water near the outer surface of the film can move in response to certain forces, and the absorptive ac- tion of roots is sufficient to withdraw FlG 13 _ Diagram_ it, Until the film becomes SO thin that matic drawing of soil par- very little except hygroscopic water £^ ™^! remains. The difference between hy- lary water, (s) soil parti- groscopic water and capillary water is ^^^^ ^ illustrated in Fig. 13. 66. Capillary water capacity. — Comparatively large quantities of water may be held in soils by capillarity. In fact by far the major portion of water used by crops is ob- tained from the capillary form. The quantity present varies with different soils and at different times in the same soil. The conditions that tend to increase the capillary moisture content of soil are the following : LA fine-grained texture, or in other words a large pro- portion of small particles. Thus in a test of a fine sand, a sandy loam and a clay soil they were found to contain respectively 10, 15 and 20 percent of capillary water in addition to the hygroscopic water. 2. A soil structure that gives a maximum effective sur- face exposure within the soil. For this reason the granula- tion of a clay soil, or the compacting of a coarse sand will cause a rise in its capillary capacity. 64 SOILS AND FERTILIZERS 3. A large amount of partially decomposed organic matter. Thus a muck soil may contain a greater weight of capillary water than the weight of the dry soil itself. Farm manure or green-manures are valuable for this purpose. 4. A low soil temperature, if it is above the freezing point. 5. A strong soil solution, such as is produced by proper manuring and good tillage. 6. The absence of oily material produced by decay of organic matter. The conditions that are favorable to a large crop pro- duction are, in general, helpful in increasing the capillary water capacity of a soil. The effect of temperature, and of oily material formed by decay of organic matter, are excep- tions to this. Much may be done by tillage, drainage and manuring to increase capillary water capacity. 67. Movement of capillary water. — The movement of capillary water is from particle to particle within the water film, the film being continuous from one particle to the other. The movement is always from the thicker part of the film to the thinner part, because there is a tendency for the film to assume the same thickness throughout. Capillary move- ment may, therefore, be upward or downward or lateral. Following a shower of rain the movement is downward, as there is more moisture at the surface than below. Generally the movement during the growing season is from the lower soil towards the surface, because the roots and surface evapo- ration continually remove water from the upper part of the soil and this is replenished from the wetter soil below. The lateral movement is usually slight. The factors that deter- mine the rate of movement of capillary water are much the same as those that influence its quantity. They are (1) texture, (2) structure, (3) height of water column, and to a less extent the other factors that influence the quantity of capillary water. SOIL WATER 65 68. Effect of texture on capillary movement. — The finer the texture of a soil, other things being equal, the slower is the movement of capillary water, but the water will eventually rise higher in the soil of fine texture. This is illustrated by the experimental data contained in the fol- lowing table : Table 12. — Effect of Texture on Rate and Height of Capillary Rise from a Water Table through Dry Soil Soil 1 Hour 1 Day 2 Days 3 Days 4 Days 5 Days inches inches inches inches inches inches Sand . . . . . 3.5 5.0 5.9 6.8 6.8 6.9 Clay .5 5.7 8.9 10.9 12.2 13.3 Silt 2.5 14.5 20.6 24.2 26.2 27.4 One can see from the above data that although water rises most rapidly in the sand, it does not rise as high as in the other soils. This experiment was not continued long enough to obtain the maximum rise in clay. Some experimenters have been able to obtain a rise of water to a height of twenty- six feet in a clay soil. 69. Effect of structure on capillary movement. — Soil structure by affecting the size of the pore spaces also affects the rate of capillary movement. In general the condition most favorable for plant growth is also best adapted to capillary movement. Good tillage, tile drainage, farm manure and lime all help to hasten the movement of water in a soil. A very loose soil does not admit of capillary move- ment and consequently cultivation of the surface prevents water from coming to the surface of the ground from whence it escapes into the air. Rolling, or otherwise compacting the soil aids capillary movement and thus causes loss of moisture from the surface soil. 66 SOILS AND FERTILIZERS 70. Height of water column and capillary movement. — Gravity opposes the upward movement of water and conse- quently the higher water rises the more slowly it moves. This has been demonstrated by measuring the quantity of water that evaporated from the surface of columns of sand of different heights, the rate of loss by evaporation indicat- ing the degree of rapidity of movement. Table 13. — Evaporation from the Surface of Sand Columns of Different Heights, their Bases being in Contact with Free Water Height of Column in Inches Daily Evaporation at Surface in Pounds per Acre 6 25,872 25,191 18,155 7,716 4,312 12 18 24 30 This has a practical significance in dry weather when the moisture supply for plants is drawn largely from the water stored in the lower soil. The lower the water level becomes, the more slowly does the moisture rise to the surface soil where are to be found the larger part of the roots of many plants. Fortunately, however, as the soil dries out, the roots go some- what deeper, so that they in part overcome this difficulty. 71. Gravitational water. — It has already been said that gravitational, or free water, is the water in excess of the cap- illary water and is constantly moving downward, thus pre- venting the soil from becoming saturated owing to the inability of the water to escape. It is very desirable that the gravitational water shall not remain in that part of the soil in which plants have their roots. A saturated condition of the surface soil is very injurious to most agri- cultural plants. In this respect there is a great difference SOIL WATER 67 between gravitational water and capillary water, and while it is desirable to have as much capillary water as possible in the soil at all times, it is equally important that the gravi- tational water shall be removed. The factors that determine the rate of flow of gravitational water in soil are texture, structure, and cracks and openings produced by freezing, by drying, by roots and by the bur- rowing of sundry forms of animal life, like worms and insects. Another, and very important factor, is the means for the escape of water from the subsoil, since without that a soil will become saturated no matter how favorable the conditions may be for escape of water from the surface soil. For this purpose tile drainage must often be used. A sandy soil allows the escape of gravitational water more rapidly than does a loam or clay soil. Soil in good tilth is better in this respect than is compact soil. It is better that water should run through a soil than that it should run off the surface. The latter generally causes erosion with the loss of much good soil, and may leave the subsoil too dry. For this reason a loam or clay soil should always have a loose surface when no crop is on the ground. 72. The water table. — The gravitational water that passes through the ground accumulates, in humid regions, in the lower depths of soil, or possibly in underlying sand or gravel, which it saturates. The surface of this mass of water is called the water table, the depth of which below the surface of the ground varies from a few inches to a great many feet, depending on the opportunity it has to escape. This is the water that furnishes the supply for shallow wells and for springs. In some places the water table is sufficiently near the surface to be of use to plants owing to its capillary rise during dry periods. 73. Relations of soil water to plants. — The quantities and movements of the several forms of water in soils are of 68 SOILS AND FERTILIZERS the greatest importance in the growth of plants. There are certain more or less definite relations that obtain, so that for any given condition of the water supply certain results in crop growth may be expected. As we shall see later, these conditions of water supply are, within certain limits, subject to the control of man and consequently the growth of crops may be regulated to some extent by these means. 74. Ways in which water is useful to plants. — In many indirect ways water contributes to plant growth, as for instance in aiding in the disintegration of rocks, in the pro- motion of decay of organic matter and in numerous other ways, but it is with the use of water as it occurs in soils and as taken up by plants that we are now concerned. The functions that water thus serves may be listed as follows : 1. Water is a direct source of food material, for it either becomes a part of the plant substances without change (about 90 percent of most plants is water), or it is decomposed and its elements are used in building plant tissue. 2. Water acts as a solvent and carrier of plant-food ma- terials, taking up these substances in the soil and transferring them to the plant, where they are utilized in the formation of plant tissue. 3. Water in the plant serves to keep the cells expanded, to regulate the temperature and to carry in solution sub- stances from those portions of the plant in which they are formed, to the places where they are needed, as for instance, to transport soluble matter from the leaves of the potato, where the starch is formed, to the tuber, where it is stored. 75. Water requirements of plants. — Most of the water that enters the roots passes on through the plant and evapo- rates from openings in the leaves. A large crop will, other things being equal, require more water for its production than a small crop. The ratio of the quantity of water used, to the quantity of dry matter that the plants contain, is SOIL WATER 69 called the transpiration ratio, because the water given off by the leaves of the plants is said to be transpired. The quantity of water required to produce a pound of dry matter varies from 200 to 500 pounds in humid regions to almost twice that amount in arid regions. There are a number of factors that influence the transpiration ratio. Among these are the following : 1. The kind of plant. 2. The quantity of water in the soil. 3. The humidity, wind and temperature of the air. 4. The natural fertility and manurial treatment of the soil. 76. Transpiration by different crops. — Some kinds of plants require much more water to produce a pound of dry matter than do others. Oats, rye, peas and potatoes are crops that have a high transpiration ratio. Wheat and barley have medium ratios and corn and millet low ratios. This, in a way, is a guide to the adaptability of these crops to growth on dry soils. 77. Effect of soil moisture on transpiration. — An increase in the water content of any soil usually results in an increased transpiration ratio for any crop grown on it. This is well brought out by an experiment in which corn was grown in soil contained in pots to which different quantities of water were added and so maintained during the entire period of growth of the plants. The results are expressed in the following table : Table 14. — Effect of Soil Moisture on Transpiration Soil Moisture Transpiration Percentage op Total Capacity Ratio 100 290 80 262 60 239 45 229 35 252 70 SOILS AND FERTILIZERS The most economical utilization of water was secured by a medium water supply. 78. Effect of humidity, wind and temperature of the air. — A dry atmosphere and a high temperature increase the transpiration ratio. For this reason crops require a large amount of water in arid regions and in regions of high summer temperatures. A high and constant wind movement also tends to raise the transpiration ratio. In parts of the country requiring irrigation the economical use of water must be considered. Such a region is likely to have much sun- shine associated with high temperatures and dry atmosphere. 79. Effect of soil fertility on transpiration. — A soil high in available plant-food material has, in general, the property of producing crops with a small unit expenditure of water. Experiments in Nebraska gave the following results : Table 15. — Relative Water Requirements of Corn on Different Types of Nebraska Soils Soil Dry Weight of Plants in Grams per Pot Transpiration Ratio Poor • 113 184 270 549 Medium Fertile 479 392 80. Quantity of water required to mature a crop. — A rough estimate of the quantity of water required to bring to maturity a crop of wheat may be calculated as follows : Assuming the yield to be forty bushels or about two tons of dry matter in straw and grain and the transpiration ratio to be 400, the quantity of water actually used by the plants would be 800 tons to the acre, or equivalent to about 7 inches rainfall. In addition to this there would be an equal or larger quantity of water evaporated directly from the SOIL WATER 71 soil. The annual amount of rainfall required for crop- production is brought to a much higher figure by the loss due to run-off and percolation. 81. Capillary movement and plant Requirement. — We have seen that there is a capillary movement of water from the more moist to the less moist soil. As water is absorbed by plants, the moisture content is reduced in the soil sur- rounding the root-hairs by which the moisture is taken up. Immediately a movement begins to establish equilibrium in the water films and during the time the roots continue to absorb moisture, the movement of capillary water goes on. During the blooming period, plants must have very large quantities of water if they are to develop fully and produce large yields of grain. Capillary movement is necessarily slow, especially in heavy loam and clay soils. It is often impossible for the capillary movement to carry moisture fast enough, except for short distances, to supply plants adequately and the crop suffers for want of moisture. In a dry season the capillary capacity of a soil is likely to be of more importance than the rate of capillary movement, as the supply is more easily available. Hence, in time of drought a loam soil in good tilth is better than a sandy soil. 82. Optimum moisture for plant growth. — Plants wilt for want of water at a moisture content somewhat higher than that represented by hygroscopic moisture. They show the pale color characteristic of too much moisture when a soil is saturated. Before either of these well-known signs of distress is shown, the plant may have too much or too little water to allow of its maximum growth. The optimum moisture content lies somewhere within the range of capillary moisture. It is variously stated by different experimenters to lie between 60 and 90 percent of the water capacity of soils. Probably it varies with different soils. 72 SOILS AND FERTILIZERS The range is doubtless greater for a soil in good tilth than for one in poor condition, and the wider the range of optimum moisture content the less likely is a crop to suffer from either extreme. 83. The control of soil moisture. — Since there may be too much or too little water in a soil for its most effective crop production, the problem of moisture control is to remove the excess and to conserve the remainder, attempting to maintain the supply within the range of the optimum mois- ture content. In heavy soils there is likely to be a surplus of water in the spring and in sandy soils a deficit in midsum- mer. The excessive water content in the spring is also objectionable because it delays plowing, planting, and germi- nation of seed as well as the early growth of crops. The ways in which water leaves soil are by (1) run-off over the surface ; (2) percolation ; (3) evaporation ; (4) absorption by plants. The last of these is to be encouraged, at least when it is economically accomplished. Run-off should generally be prevented. Percolation and evaporation should be con- trolled within certain limits. 84. Run-off. — Removal of water in this way is objection- able because the rivulets carry with them the fine particles, which are frequently the most valuable part of a soil, and gullies are formed that may interfere with the working of the land. In regions in which the rainfall is large, and particularly where it falls in torrential showers, more than half of the precipitation may escape in this way. The water so removed is, of course, entirely lost so far as its utilization by plants is concerned. The proportion lost by run-off is greater on slopes than on level land, and on com- pact soil than on sandy soil or on soil in good tilth. The removal of excess water by means of open ditches is, to some extent, a utilization of run-off to drain land, but it is not so desirable a method as tile drainage. It is better Plate VIII. Forms of Erosion. — Erosion of soil by water in upper figure. Erosion by wind in lower. SOIL WATER 73 to have the moisture pass into the soil and this is encouraged by any of the operations and conditions that favor the main- tenance of good tilth. Fall plowing and early spring plow- ing also serve this end. In arid and semi-arid regions run- off is usually not of any moment. Terracing a hillside is often resorted to as a preventive of run-off, especially in the south Atlantic states where the rainfall is often tor- rential. 85. Percolation. — Water that enters a soil is either retained by the capillary spaces or eventually percolates into the subsoil. The percolate is lost to crops, except that part which remains in the subsoil and is later raised by capillarity to within reach of roots. The chief consideration is to maintain the soil in good tilth, which gives a large capillary capacity, thus storing within easy reach of the roots a maximum quantity of the descending water. The more rapidly the gravitational water is disposed of the better, because its presence prevents aeration of the soil together with those beneficial processes that good ventilation encour- ages. One of the most frequent causes of saturation of soil is lack of facility for the water to escape from the lower depths. This difficulty is best relieved by tile drainage. 86. Evaporation. — It has been concluded from experi- ments conducted at Rothamsted, England, that with an annual rainfall of twenty-eight inches, one-half is lost by percolation. The quantity of water required to produce an average crop in a humid region is about seven inches, which is one-half of the water retained by the soil. The other half is presumably lost by evaporation. A rough estimate of the disposition of rain water in a humid region would there- fore be one-half lost by percolation, one-fourth by evapora- tion and one-fourth used by the growing crop. The ratio of quantity lost by evaporation to quantity used by crop may vary by reason of a number of factors, among which is 74 SOILS AND FERTILIZERS the ease with which evaporation may take place. Moisture saved from evaporation is at the immediate disposal of the crop. 87. Mulches for moisture control. — Any material ap- plied to the surface of a soil primarily to prevent loss by evaporation may be designated as a mulch. It may at the same time fulfill other useful functions, like keeping down weeds and maintaining a uniform soil temperature. The mulch ordinarily used for fallow land is produced by stirring the surface soil. Mulches may be formed of straw, leaves, flat stones, cloth, sawdust and various other materials, but the most practical material is soil. 88. The soil mulch. — The soil mulch is made by stirring the surface of the soil with some one of the ordinary tillage implements. For fallow land a disk harrow, straight, or spring tooth harrow may be used. For intertilled crops numerous forms of cultivators are made for the special pur- pose of going between the rows of plants. For small grain a weeder or spike-tooth harrow, with the teeth slanted back- ward, is frequently used while the grain is young. This practice has much to recommend it in an arid or semi-arid region. In making a soil mulch the object is to destroy the capil- larity near the surface soil and thus to prevent the move- ment to the surface of water from the portion of the soil below the mulch. Stirring may accomplish this by breaking up the cohesion of particles to such an extent that moisture cannot pass from one to the other. 89. Frequency of stirring. — Some kinds of soil re- quire more frequent stirring than others. For instance, a sand will maintain a mulch longer than a loam or clay. The latter becomes moist from below and will gradually allow moisture to reach the surface. Rain will also compact a mulch and unless it is soon restored there may be more SOIL WATER 75 moisture lost than was received as rain. While it is not possible to make a definite rule for frequency of stirring a mulch, it may be said that a mulch should never be allowed to remain in a compact condition. However, in arid regions the surface of the soil sometimes becomes completely dry so quickly, even when compact, that capillary connection is destroyed and loss of moisture is prevented. 90. Depth of mulch. — In considering the depth that a mulch should have, several facts should be kept in mind. The deeper the mulch the more effective it will be, but as it must be perfectly dry, roots cannot obtain nourishment in the zone occupied by the mulch. The surface soil, from which plants derive a large part of their material, is frequently only eight to ten inches deep in humid regions and the deeper the mulch the less top soil remains for roots. In arid regions plants obtain food materials from greater depths and mulches may be made deeper, which is fortunate since they need to be deeper in regions where evaporation is greater. Another consideration is the disturbance of roots in the process of cultivation. Here, again, there is less occasion to cultivate shallow in an arid region, as roots are generally found at greater depths in such soils. A good depth for a mulch in humid regions is about three inches, becoming somewhat less during the last cultivations of corn. In irrigated regions a mulch of ten to twelve inches is frequently used, especially in orchards, in which it is often not necessary to renew the mulch, as the rainfall is usually light. 91. Effectiveness of mulches. — That mulches are effec- tive in conserving moisture and increasing crop yield has lately been called in question by certain writers who claim that corn is not more benefited by tillage than by the removal of weeds without tillage, and by some experi- menters who find that fallow land contains as much moisture 76 SOILS AND FERTILIZERS when weeds are removed by scraping the surface of the ground as when the soil mulch is maintained. It seems possible that the latter result may occur only in those regions in which conditions are such that a natural mulch is formed by the rapid drying of the surface soil, in which process moisture is removed so quickly that the capillary column is broken and further loss of moisture is stopped. This would confine it to semi-arid and arid regions of high summer temperatures. The failure of the soil mulch to conserve moisture in corn land has been explained on the supposition that the corn roots ramifying through the upper soil absorb so much water that they cut off the upward movement as effectually as does a mulch. The results of some experiments in semi-arid Montana indicate a high degree of usefulness for the mulch. Table 16. — Moisture Content op Mulched and Unmulched Eastern Montana Soils. Average of Three Years Depth op Sample Percent Moisture in Soil on Oct 6. Mulched Unmulched Firstfoot 16.8 10.8 Second foot 16.4 9.4 Third foot 13.2 9.5 Fourth foot 10.1 8.9 Fifth foot 9.6 8.5 Average 13.2 9.4 The investigator comments on these results as follows : " If the wilting point of this soil is 6 percent, the mulched area contains more than twice as much available moisture. This 3.8 percent of available moisture by which the mulched soil excels the unmulched is equivalent in a five-foot depth to about 250 tons of water, enough to increase the crop by a ton of dry matter." SOIL WATER 77 92. Other devices to prevent evaporation. — Plowing in the early spring or immediately after taking off a crop of small grain is a means of preventing evaporation. In regions e&capino moisture: 3 1 f 1 »l(SO Mpl NO MULCH Fig. 14. — The effect of a soil mulch is to break up the capillary spaces within the mulch itself and thus to prevent the upward movement of water through it. Water, therefore, remains in the lower soil instead of evaporat- ing from the surface. This condition is shown in the right-hand column. When no mulch is maintained the soil dries at the surface and then cracks, which allows it to dry more rapidly below. in which grain crops suffer for moisture in the early spring, it is not uncommon for farmers to harrow the small grain, following the drill rows with a spike-tooth harrow with its teeth turned backwards. This practice is likely to be very beneficial. 78 SOILS AND FERTILIZERS Windbreaks are effective in decreasing evaporation by lessening the velocity of the wind. King found that evapora- tion from a moist soil was twenty-four percent less at a dis- tance of twenty to sixty feet from a black oak grove than it was about three hundred feet distant. 93. Rolling and subsurface packing. — These operations are resorted to in order to bring moisture to the surface or upper layer of soil. Rolling compacts the superficial layer of soil and thus establishes capillary connection with the moist soil below. This may be desirable in order to bring moisture in contact with seeds, but although germination is hastened loss of moisture results. Subsurface packing is designed to make more compact a naturally loose soil by running wedge-rimmed wheels through it. If the soil is too loose for capillary movement of water to proceed effectively, this operation promotes it. Its use is confined to arid or semi-arid regions. 94. Removal of water by drainage. — Land drainage is any condition, natural or artificial, that enables the surplus water to escape from soils. A soil may be highly productive when drained, but worthless before draining. This is but another illustration of the many factors affecting soil pro- ductiveness. Where natural drainage is poor, artificial drainage is general^ a profitable investment. It may be accomplished either by surface ditches or by underground drains. 95. Benefits of drainage. — There are many ways in which good drainage benefits soils and crops. The need of drainage may be very evident in the yellow color and poor growth of young, plants, or it may be less readily detected, and yet may be sufficiently needed to make it a profitable invest- ment. Good drainage is the first requisite in enabling a soil to reach its maximum productiveness. The principal ways in which drainage benefits the soil and crop are as follows : SOIL WATER 79 1. Enlargement in the supply and movement of soil air. 2. Improvement in tilth. 3. More available water throughout the growing season. 4. Longer growing season. 96. Soil air. — Drainage increases the supply and move- ment of soil air by allowing the gravitational water to run off and thus to be replaced by air. With each fall of rain there is a movement of air through the soil. The increased air supply is of benefit in the following ways : 1. It furnishes air to roots which require it for the proper performance of their functions. 2. It facilitates the decomposition of organic matter of all kinds, thus disposing of the vegetable matter incorporated with the soil, and permitting the most beneficial kind of de- composition (see §§ 59, 60). 3. It furnishes the conditions necessary for the trans- formations of nitrogen in the soil which prepare that sub- stance to be used by plants (see §§ 116-168). 97. Soil tilth. — Alternate drying and wetting of soil is one of the processes that causes the formation of granular structure and consequent improvement of tilth. A soil that is constantly saturated or very wet when worked in the spring assumes a compact condition. The larger air space reduces heaving by allowing expansion of freezing water within the soil, and diminishes the tendency to erosion, by allowing water to sink quickly into the soil, instead of running over the surface. 98. Available water during the growing season. — A soil in need of drainage is often in need of moisture in midsummer, because when it does dry out its water-holding capacity is low, on account of its compact condition. Furthermore, plants form shallow roots in a saturated soil, and if the weather becomes dry later in the season, the roots do not then go to the depth necessary to reach the water supply. 80 SOILS AND FERTILIZERS It frequently happens, therefore, that plants suffer much from lack of moisture on a soil that has been saturated with water during the early part of the growing season. 99. Length of growing season. — Drainage increases the length of the growing season in two ways : (1) The soil can be worked much earlier than on poorly drained land. (2) The soil becomes warm earlier, because it is easier to heat soil particles than it is to heat water. Then too the evaporat- ing moisture causes a lowering of the soil temperature. Seeds germinate more quickly and uniformly and plants make a more rapid growth on account of the warmer soil. 100. Other results of drainage. — All of these improved conditions unite to produce larger yields of crops and more uniform growth. Drainage eliminates the continually wet or swampy portions of fields that interfere with tillage operations and necessitate working the field in sections. There is, accordingly, an economy in operation. In meadows and pastures the kinds of forage plants that grow on a well- drained soil make better feed than those kinds that grow on wet land. 101. Open ditches. — Excess water is sometimes removed by means of open ditches of size and depth necessary to drain water from the land and carry it to some waterway. Such ditches sometimes merely follow a depression or swale in the land and thus carry off the worst of the excess water, especially that which comes from higher land, or they are sometimes laid out in a more systematic way. Level fields may be plowed in lands with dead furrows every twelve to twenty feet apart, and with a larger ditch run through lower ground for the dead furrows to empty into. This affords only surface drainage, but is better than nothing. Larger ditches should have grass planted along the sides for several feet from the ditch. Weeds must be mowed and trash, dirt and stones removed at intervals. SOIL WATER 81 Open ditches require much labor to keep them in order, they do not remove the water so thoroughly as do tile drains, and they not only occupy a considerable area but they inter- fere with the cultivation of much land on account of the space along the ditches required for turning the teams in cultural operations. Only under exceptional conditions may open ditches be profitably used instead of tile drains. 102. Tile drains. — These drains are composed of baked clay or hardened concrete cylinders with open ends, their length being about one foot and their diameter varying from three inches to eight or more. These tiles are laid end to end on the bottom of ditches two to four feet in depth, having a fall sufficient to carry off the water and prevent the tiles from becoming clogged with soil particles. Tile should not be made of clay that contains particles of lime, as the lime when baked is converted into quicklime, which causes the tile to crumble when buried in the soil. It is not necessary that tile shall be permeable to water, as it is through the openings between the ends of the tile that water enters, and not through the pores. Vitrified tile may well be used, as they are less likely to be injured by freezing than are porous tile, because expansion of ab- sorbed water on freezing causes the latter to disintegrate. Concrete tile are often used and these may be made on the farm, with forms constructed for the purpose. Silt and fine sand may enter the tiles through the open- ings between them, and to guard against this collars are sometimes placed over the joints, but with proper grades this is not necessary. Sometimes tile are hexagonal on the outside, for the purpose of preventing settling of the tile in places, with a consequent stoppage with silt. However, if the bottom of the ditch is carefully made, round tile are not likely to deviate from alignment and they are more easily laid. 82 SOILS AND FERTILIZERS 103. Arrangement of drains. — In laying out a system of drains certain rules must be regarded. A main drain usually follows a depression in the land, rising with the natural grade, or if that does not give a sufficient rise, becoming shallower as it ascends. Some- times this will be sufficient to re- move the surplus water, but more often lateral drains will be nec- essary. These are of smaller tile and are usually paral- lel to each other and from twenty to a hundred feet apart. This ar- rangement is called the herring bone system. (See Fig. 15.) There may also be submains branch- ing off of the main drain, and laterals running into the submains. This is known as the gridiron system. (See Fig. 15.) Sometimes the laterals are run across the slope, but usually it is better to run them down. A lateral should not enter a main drain at a right angle, Fig. 15. — The upper drawing illustrates the her- ring bone system of laying tile drains. The lower represents the gridiron system. Plate IX. Drainage. — The drain outlet is often poorly constructed and easily clogged, as shown in the upper figure. The lower one is well protected. SOIL WATER 83 but an acute angle should be formed between the two streams above the point of contact; otherwise the flow of water will be impeded. For the same reason two laterals should not enter a main drain opposite to each other. It is desirable to have as few main drain outlets as possible, for the outlet is likely to be the weakest point in a drainage system. If it becomes clogged, the entire system is put out of action. It is more likely to be injured by freezing than is the underground tile, and unless well protected it affords an opening into which small animals may crawl and clog the system. The quantity of water removed by tiles of various sizes, and laid at certain distances and grades as well as other operations that cannot be treated here, may be ascertained from the books that deal exclusively with the subject of land drainage. 104. Digging ditches and laying tile. — The depth of ditches for tile drainage varies from two to four feet. Three feet is the usual depth. The closer together the laterals, the shallower the drains may be laid. A compact soil, through which water moves very slowly, will require the use of shallow drains. A lighter soil underlaid by hardpan will also require shallow drains. The shallower the drains in any soil, the closer together they must be laid, the cus- tomary range being from twenty to a hundred or more feet. Surplus water enters the drains from the soil immediately surrounding them. As the larger pore spaces become partly empty, water enters them from surrounding soil, and in this way drainage gradually extends. The soil mid- way between the drains is the last to lose its surplus water, and the water table is always higher between drains than over them. The distance between drains must be small enough to allow the water table to descend promptly to a point where 84 SOILS AND FERTILIZERS it will not interfere with root growth. The more permeable the soil and the deeper the drains, the further apart they may 3 bM O dw8 Fertilizer 'S < 22 S 3 ft J £ j a 3« s 6^ 1 , 2 d 8T OF P )RTH OF Hands RMER 2 'E o 01 c3 a ^a o g« Sod o < So«i * 3 °£ 4 < ^ ^ *5 MHfr Wo o£S£ £ PM dH >SQ High grade . $26.30 #38.93 $12.63 $0.48 28 5.7 6.3 67.6 Medium grade 18.22 30.00 11.78 0.65 31 6.3 7.0 60.6 Low grade 13.52 27.10 13.58 1.00 38 7.6 8.5 50.0 In mixing fertilizers in a factory, it is customary to incor- porate with the carriers of plant nutrients more or less material that has no influence on plant growth, but that serves to di- lute the mixture and to prevent it from becoming damp by the absorption of moisture, and also to prevent the chemical interaction of the constituents. This material is called a filler. 254. Fertilizer inspection and control. — Most of the states have enacted legislation providing for the inspection and control of the sale of commercial fertilizers. Each brand of fertilizer, that sells for $5.00 or more a ton, must pay a state license fee and each bag must bear a tag stating the guaranteed percentage of nitrogen, phosphoric acid and potash that the fertilizer contains, and giving some informa- tion in regard to their solubility. There is little uniformity in the requirements of the dif- ferent states. In some states a very detailed statement of the composition of the fertilizer and the solubility of its constituents is required. The following information is called for by some of the states. Percentage of nitrogen in the following forms : 200 SOILS AND FERTILIZERS In nitrates and ammonium salts. These are generally present in nitrate of soda and sulfate of ammonia. Their availability has already been discussed (see § 218). Water-soluble organic nitrogen. This is probably not so readily available as the two former kinds, but differs little from them in this respect. Active water-insoluble organic nitrogen. Although not directly available this becomes so quickly enough for the crop to which it is applied to obtain part of it. Inactive water-insoluble organic nitrogen is that part of the organic nitrogen that is of little value for immediate plant growth. Percentage of phosphoric acid in the following forms : Water-soluble phosphoric acid, which is readily available (see § 227). Reverted phosphoric acid. Not so readily available (see § 227). Available phosphoric acid. This usually consists of the sum of the two forms mentioned above. Sometimes when this term is used no distinction is made between the water- soluble and the reverted, but this is not so satisfactory. Insoluble phosphoric acid. This is slowly available, but in animal products, such as bone, tankage and other slaughter house waste, it becomes available more quickly than if present in rock phosphate. However, the analysis does not distin- guish between the organic and inorganic carriers. Percentage of potash in the following forms : Soluble in water. Present as chloride. 255. Trade values of fertilizer ingredients. — In the states having fertilizer inspection laws, it is customary for the officers in charge of the inspection to adopt each year a schedule of trade values for nitrogen, phosphoric acid and potash in each of the carriers ordinarily found in fertilizers. THE PURCHASE AND MIXING OF FERTILIZERS 201 These vrlues are based on the whulesale market reports for six months preceding March 1 of each year, to which is added about 20 percent of the price, to cover cost of handling. Potato Manure "A" without Potash 1916 Nitrogen - * A • 4.1 1 to 4.94 per cent. Equal to Ammonia ^^k 5. to 6. " Soluble Phosphoric Acid ^^A 4. to 5. Reverted Phosphoric Acid ^^^^L 4. to S. Available Phosphoric Acid - M ^^L 8. to 10. Insoluble Phosphoric Acid - MgJ^^L 1. to 2. Total Phosphoric Acid '^^^^^^L 9' to ,2, MANUFACTURED BY >C - Y- Z - FERTILIZER COMPANY Fig. 30. —Tag representative of the kind often used on bags of fertilizer to state the percentages of their constituents. The following values are for the year 1914. Trade Values of Plant Nutrients in Raw Materials Value per Pound in Cents Nitrogen in nitrates 18.5 Nitrogen in ammonium salts 18.5 Organic nitrogen in dried and finely ground fish, meat and blood '. . 20.0 Organic nitrogen in finely ground bone and tankage . . 19.0 Organic nitrogen in coarse bone and tankage .... 15.0 Organic nitrogen in castor pomace and cottonseed meal . 20.0 Phosphoric acid, water soluble 4.5 Phosphoric acid, reverted 4.0 Phosphoric acid in fine bone, fish and tankage .... 4.C Phosphoric acid in cottonseed meal and castor pomace . 4.0 Phosphoric acid in coarse fish, bone, tankage and ashes . 3.5 Phosphoric acid in mixed fertilizers, insoluble .... 2.0 Potash as high-grade sulfate, in forms free from muriate, in ashes, etc 5.25 Potash as muriate 4.25 Potash as castor pomace and cottonseed meal .... 5.0 202 SOILS AND FERTILIZERS These values may be used by the consumer to calculate the wholesale cost of a fertilizer of guaranteed composition, which he can then compare with the retail price asked by the retail dealer. He may also compare the relative values of brands of similar composition offered for sale by different manufacturers. 256. Computation of the wholesale value of a fertilizer. — Suppose that we have the following statement of the analysis of a fertilizer. Per Cent Nitrogen in nitrate of soda 1 Nitrogen in dried blood 2 Phosphoric acid, water soluble 6 Phosphoric acid, reverted 2 Potash, as muriate 10 The number of pounds of each constituent to a ton of fertilizer is then found by multiplying the weight of a ton of fertilizer by the percentage of the constituent, thus : Nitrogen, as nitrate .01 X 2000 = 20 pounds per ton. Nitrogen in dried blood .02 x 2000 = 40 pounds per ton. Phosphoric acid, water-soluble .06 X 2000 = 120 pounds per ton. Phosphoric acid, reverted .02 X 2000 = 40 pounds per ton. Potash, muriate .10 X 2000 = 200 pounds per ton. The trade values, as published by the fertilizer inspection officers, are then applied to the several constituents. Nitrogen as nitrate 20 X $.185 = $ 3.70 Nitrogen in dried blood 40 x $.20 = 8.00 Phosphoric acid, water-soluble 120 X $.045 = 5.40 Phosphoric acid, reverted 40 x $.04 = 1.60 Potash, muriate 200 X $.0425 = 8.50 $27.20 Such a fertilizer will cost the consumer more than the fig- ure derived in this way, because the entire cost of mixing and retailing must be added to it. It may serve as a basis for ascertaining whether it would not be more profitable THE PURCHASE AND MIXING OF FERTILIZERS 203 for a group of consumers to purchase the fertilizer ingredients in car-load lots and do the mixing themselves. It must also be remembered that this is the commercial value and not necessarily the agricultural value, which latter is determined by the profits from its use, and will depend on many factors. . 257. Home mixing of fertilizers. — There is a large margin between the trade value of fertilizer ingredients and their retail price as sold by the dealer. The cost of the raw ma- terials often doubles in the process of mixing and retailing, with the necessary transportation. It has been demon- strated that the raw materials may be purchased from the wholesale dealer and mixed by the consumer at a consider- ably lower cost than if purchased mixed from the retail dealer, and that the results are fully as satisfactory. Other advantages from home mixing are that it permits the farmer to use exactly the proportion of the several con- stituents that he desires, and that it makes unnecessary the handling of a large amount of inert materials frequently contained in mixed fertilizers. It is thus possible for him to ascertain, by field tests, the best proportions of the various fertilizer constituents to use on his own land for each of the crops he is growing. This knowledge makes it possible to decrease greatly the expenditure for fertilizers. 258. Fertilizers that should not be mixed. — Because fertilizers consist of chemicals, some of which react on each other to form compounds different from those in the original substances, it is unwise to mix certain of these carriers. The result may be to convert soluble nutrients into insoluble ones, or to cause the loss of some constituent in the form of gas. If one is to mix his own fertilizers he must know what materials should not be brought in contact. The fol- lowing are some of the common carriers that should not be mixed : 204 SOILS AND FERTILIZERS Caustic lime 1 f. ., , , .■ ■■ iT7 j i_ .lL Acid phosphate Wood ashes > with < ^. f . \ -„ . , Dissolved bone Basic slag Cyanamid Caustic lime Wood ashes Basic slag with ' Sulfate of ammonia Slaughter house waste containing ni- trogen Farm manure The following mixtures should be applied immediately : )f Nitrate of soda with < Muriate of potash [ Kainit Acid phosphate with Nitrate of soda or ground limestone. Cyanamid should not be mixed with acid phosphate if there is more than one part of the former to ten of the latter. 259. Calculation of a fertilizer mixture. — In deciding on the composition of fertilizers the best and simplest way is to consider them according to the percentage of each of the three constituents, nitrogen, phosphoric acid and potash, they contain, /if we decide to use a 3-8-5 fertilizer, the next step is to calculate how many pounds of each of the carriers of these substances must be used for each ton of the complete fertilizer, and how much filler must be added. Suppose we have on hand the following carriers : Nitrate of soda containing 15 percent nitrogen Acid phosphate containing 14 percent available phosphoric acid Muriate of potash, containing 50 percent potash > The first step is to calculate the number of pounds of nitrogen, of phosphoric acid and of potash in a ton of a 3-8-5 fertilizer. To do this we merely multiply the num- ber of pounds in a ton by the percent of each plant-food material. THE PURCHASE AND MIXING OF FERTILIZERS 205 2000 x .03 = 60 pounds nitrogen per ton 2000 X .08 = 160 pounds phosphoric acid per ton 2000 X .05 = 100 pounds potash per ton The next step is to calculate the number of pounds of the carrier required to furnish the quantity of plant-food material that has just been found. This is done by dividing the weight of the plant-food material required by the percent of this particular plant-food material in the carrier that is to be used. 60 •*- .15 = 400 pounds nitrate soda 160 ■¥■ .14 = 1143 pounds acid phosphate 100 + .50 = 200 pounds muriate of potash 1743 pounds of the three carriers The weights of the different carriers are then added, giving in this case 1743 pounds needed for every ton of fertilizer. The remainder of the ton (2000 - 1743 = 257 pounds) is then made up with a filler, consisting of sand, dry earth, muck, peat, sawdust or something of the kind. 260. How to mix the ingredients. — A smooth tight floor is needed on which each carrier is spread in turn to break down the lumps. It is then passed through a coarse screen. A weighed quantity of the filler or principal carrier is then spread out in uniform depth and on top of it another carrier, until all are represented. Then the pile is shoveled over and over, and finally leveled and the process repeated until the ingredients are thoroughly mixed. This lot of fertilizer is then put in sacks and the operation repeated with another quantity until a sufficient amount is prepared. There should always be two hundred pounds or more of filler in each ton to give a more uniform distribution of the carriers. QUESTIONS 1. In what parts of the United States are fertilizers used in greatest quantities ? 2. What is meant by a brand of fertilizer ? 206 SOILS AND FERTILIZERS 3. What is a high-grade in distinction from a low-grade fertilizer ? 4. Explain what is meant by a filler. 5. What, in a general way, does a report on the inspection of a fertilizer show ? 6. How are trade values of plant nutrients evaluated ? 7. What are the advantages to be derived from the home mixing of fertilizers ? LABORATORY EXERCISES Exercise I. — Fertilizer inspection and control. Fertilizer laws are designed to protect the honest manufacturer as well as the farmer. Obtain the laws of your state which have to do with fertilizer inspection and control. Analyze them step by step with this point always in mind. Decide whether or not the law does really regulate and protect in the way that it should. A study of fertilizer bags and tags could also be made with profit. Exercise II. — Laboratory mixture of fertilizers. Materials. — Sodium nitrate, dried blood, acid phosphate, muriate of potash, sulfate of potash, balances, dry soil as a filler. You must have the guaranteed composition of each carrier. Procedure. — Make 2000-gram lots of the following mixtures. Fertilizers must be dry and fine. Put through sieve if necessary. No. 1. — Make up 2 kilos of a 3-7-10 fertilizer, using sodium nitrate, acid phosphate and muriate of potash. Add filler as nec- essary. No. 2. — Make up a fertilizer as above, using dried blood, acid phosphate and sulfate of potash. Allow these mixtures to stand for some weeks and compare. Also compare them as to physical condition with a ready mixed fertilizer of a similar guarantee. Exercise III. — Home mixture of fertilizers. If possible cooperate with some farmer in the mixing of fertilizers. Allow the pupils to check all calculations and to aid in the actual mixing of the goods. The pupils should also understand the pro- cedure of selecting and ordering the fertilizer carriers in order that every step in the process may be familiar to them. The educational value of a study of the crop, soil, fertilizer and rotation is a strong point in favor of home mixing. CHAPTER XVI THE USE OF FERTILIZERS We have seen that a very considerable economy in the purchase of fertilizers may be effected through a knowledge of their composition. There is still further opportunity for both economy and profit through a study of their use. 261. Fertilizers for different crops. — It has already been pointed out that there is a difference in the ability of plants of different kinds to extract nutriment from the soil. Some crops are able to draw abundant nourishment from soils from which others derive but little. This may be due, in part, to (1) a deficiency in the soil of the particular sub- stance most greatly needed b,y the crops, or (2) the inherent ability of one crop to make available plant-food materials, while another crop may possess that quality in much less degree. There are therefore two ultimate considerations in the selection of fertilizers : (1) the nature of the soil ; (2) the kind of crop. The second of these will be discussed first. 262. Small grains. — Most of the small grains, like wheat, rye, oats and barley, need the principal part of their nitrogen early in the season, before the soil has warmed sufficiently to induce the germs that produce nitrates to lay up an abun- dant supply. Consequently the application of nitrate of \ soda, when growth begins in the spring, is very beneficial to these crops. Wheat in particular needs such an appli- cation. Since it is a " delicate feeder " it grows best after fallow, or a cultivated crop, and when it follows oats, as is 207 208 SOILS AND FERTILIZERS the usual custom, it needs a complete fertilizer. Rye is a " stronger feeder " and does not have the same need of fertilization. Oats and barley, when spring sown, find more nitrates in the soil, because they are later than winter wheat in starting growth, and, as they can make better use of the soil fertility, they do not require so much fertilizing. Corn is a " strong feeder," and, while it removes a very large quantity of plant-food materials from the soil, it does not require that these be added in a soluble form. Farm manure and slowly acting fertilizers may well be used for the corn crop. The long growing period required by the corn plant gives it opportunity to utilize nitrogen as that sub- stance becomes available during the summer, when nitrate formation is most active. Phosphoric acid is the substance usually most needed by corn. 263. Grass crops. — Meadows and pastures are greatly benefited by fertilizers. The grasses are less vigorous feed- ers than the cereals, have shorter roots, and, when left down for a year or more, the formation of nitrates is much curtailed. There is usually a more active fixation of nitrogen in grass land than in cultivated land, but nitrogen thus acquired becomes available very slowly. Different soils and different climatic conditions necessitate different methods of manur- ing for grass. The use of nitrate is almost always attended with much success, even when used alone, but in most situa- tions a complete fertilizer is profitable. 264. Leguminous crops. — Most of the leguminous crops are deep-rooted and are vigorous " feeders." Their ability to acquire nitrogen from the air makes the use of that sub- stance unnecessary except in the form of nitrate, which is often very effective in starting a young seeding of alfalfa. The nitrate probably serves to carry the young crop through the period preceding the development of tubercles. Potash salts are almost always profitably used on legumes, and THE USE OF FERTILIZERS 209 phosphoric acid is also likely to be effective. For such crops as clover and alfalfa there should always be an ample supply of lime, without which these crops cannot be prof- itably grown. 265. Root crops. — Most of the root crops remove very large quantities of plant-food materials from the soil, when these are present in available form. Like corn they have a long growing season and the slowly acting fertilizers or farm manure are well adapted to their use. A complete fertilizer in rather large quantity will usually bring a response in yield. For sugar beets the proportion of potash should be high, and for table beets and carrots there should be more nitrogen than for the other roots. 266. Vegetables. — In raising some kinds of vegetables, the object is to produce a rapid growth of leaves and stalks rather than fruit or seeds, and with these kinds growth should often be made in the early spring. Therefore, for crops like lettuce, radishes and asparagus a soluble form of nitro- gen is very desirable. For crops that are raised later in the season a smaller proportion of nitrogen may be used, and for the more slowly growing kinds of vegetables the less soluble fertilizers may be applied. For all vegetables farm manure or other organic manure should be generously used, as it keeps the soil in a mechanical condition favorable to retention of moisture, which vegetables require in large quantities, and it also supplies needed fertility. The very intensive culture employed in the production of vegetables necessitates the use of much greater quantities of fertilizers and farm manure than are used for field crops, and the great value of the product justifies the practice. 267. Orchards. — In manuring orchards, it is the aim to maintain a continuous supply of nutrients available to the plants, but not sufficient for stimulation, except during the early life of the tree, when rapid growth of wood is 210 SOILS AND FERTILIZERS desired. During the first few years after setting out, there should be a liberal supply of nitrogen. An acre of apple trees in bearing removes as much plant-food material from the soil in one season as does an acre of wheat. Green- manures may be used to advantage in orchards, as by plant- ing these crops in midsummer, moisture is removed from the soil and the wood of the trees is thereby hardened and thus prepared to withstand the low temperatures of winter. The green-manures also hold snow on the ground, if allowed to stand over winter, and may then be plowed under in the spring. 268. Fertilizer mixtures for different crops. — On ac- count of the large number of factors that enter into the pro- cesses of crop production, it is obviously impossible to pre- scribe accurately the proportion and quantity of fertilizer carriers that should be applied. Some rough approximation can, however, be arrived at on the basis of the peculiarities of the various classes of crops that have just been enumerated. It must be remembered that different soil conditions may materially change the proportions of the fertilizer ingredi- ents that should be applied. The following proportions of nitrogen, phosphoric acid and potash for different classes of crops have been proposed and have been found a fairly useful guide in the home mixing of fertilizers. Table 43. — Fertilizer Formulas for Different Crops Crops Percentage of Nitrogen Percentage of Phosphoric Acid Percentage of Potash Legumes (young) .... Small grains Vegetables Grass Orchard Roots 1 3 4 5 4 3 8 8 8 4 8 8 10 5 10 4 6 7 THE USE OF FERTILIZERS 211 A fertilizer based on the first percentages would be called a 1-8-10 fertilizer ; one based on the second a 3-8-5 ferti- lizer, and so on. In making up these formulas the carriers to use are indicated in the previous discussion. The quan- tities that it is desirable to use will depend so much on the natural productiveness of the soil that it is not possible to prescribe for soils in general. On soils of about average productiveness, however, a certain range for each of the classes of crops may be suggested. Legumes . . 100 to 200 pounds per acre Small grains 100 to 300 pounds per acre Vegetables 500 to 1000 pounds per acre Grass 200 to 500 pounds per acre Orchards 200 to 600 pounds per acre Roots . 300 to 800 pounds per acre 269. Fertilizers for different soils. — The best way to ascertain what fertilizers are needed for a particular soil is to test it with different kinds and quantities of fertilizing ma- terials. It will thus be possible to estimate whether the three substances, nitrogen, phosphoric acid and potash are all needed, and in about what quantities they should be applied. A practical way is to select a level and apparently uniform part of a field and on it lay off plats of land eight rods long and one rod wide, giving an area of ^ of an acre. These plats should lie parallel on their long side, but should have a space of at least three feet between them. The arrange- ment is shown in Fig. 31 on the next page, which also in- dicates the quantity of fertilizing substance that each plat should receive. The fertilizer used in this experiment is designed for small grains, the mixture being 3-8-5 if the carriers contain about 15 percent nitrogen, 14 percent phosphoric acid and 48 per- cent potash respectively. If a legume or grass crop is 212 SOILS AND FERTILIZERS used in the test the fertilizer should be adjusted to suit the crop, as stated in Table 43. If grass is the most important No fertilizer Nitrate of soda 5 pounds Acid phosphate 15 pounds Nitrate of soda 5 pounds Muriate of potash 2\ pounds No fertilizer Acid phosphate 15 pounds Muriate of potash 2\ pounds Nitrate of soda 5 pounds Acid phosphate 15 pounds Muriate of potash 2| pounds No fertilizer Nitrate of soda 2\ pounds Acid phosphate 1\ pounds Muriate of potash 1 pound Fig. 31. — Plan for a fertilizer experiment with small grains. Plats of land 8 rods long and 1 rod wide, giving an area of fa acre in each plat. The rate of application to the acre would therefore be twenty times the quantities given in the diagram. crop the test should be made with special reference to it, and so with any other important crop. In any case a ro- Plate XIII. Crop Work. — The upper figure shows a plat of timothy the left-hand side of which has been properly fertilized. The right-hand side has received no fertilizer. Note the thick stand of daisies on the latter. The lower figure illustrates the method of laying off plats for tests of fertilizers. THE USE OF FERTILIZERS 213 tation should be followed and the system of fertilization should be adjusted to the rotation as explained in § 271. In order that the kind and quantity of fertilizer shall be a con- trolling factor, the plats should be well drained and well tilled and should not be in need of lime, which may be ascertained by either of the tests described in §§ 145, 146. 270. Calculation of the results. — Each test plat has, on one side of it, a plat that has not been fertilized. The non- fertilized or check plats will not all give the same yield be- cause the soil differs in various parts of the field. If the variations in yield between check plats are not greater than one bushel to the acre, they may be considered as being equal. If a greater difference exists, the yield from each check plat must be subtracted from the yields of the test plats beside it and the result may then be considered to be the increase due to the fertilizer application. If the yield is as good, or nearly as good, on a check plat as it is on the corresponding test plat that lacks one of the fertilizing constituents, it may be concluded that the use of that constituent would not be a profitable investment. On the other hand, the very beneficial substances will be indi- cated by the increased yields wherever they are used. Fi- nally the desirable quantities will be indicated by a compari- son of the rates of increase on the plats receiving the full quantity and those receiving the half quantity of complete fertilizer. The tests should be continued for a period of three to five years in order that they shall be indicative of the fertilizer needs of the soil, and a rotation of crops should be used, with an adjustment of the fertilizer treatments to suit the different crops. 271. Fertilizing the rotation. — In a rotation of crops fertilizers need not be applied every year. For instance a rotation consisting of hay, two or three years, corn, oats and wheat would probably not receive any fertilizers on 214 SOILS AND FERTILIZERS one or two of the courses. It is desirable to make the rela- tively heaviest applications for the crops having the greatest money value. If the hay crop represents the largest pos- sible returns, the crop should be well fertilized. Another reason for giving liberal applications to the hay crop is that the sod is thereby increased and furnishes a larger supply of organic matter to be plowed under (see § 204). Corn is the crop of greatest importance in some localities, in which case it should be well fertilized. Farm manure is usually the best fertilizer for corn, but farm manure should be supplemented by phosphoric acid either in the form of acid phosphate, basic slag or floats. Oats will seldom give a profitable response to fertilizers which may be dispensed with for that crop, but should be applied in the fall in prep- aration for wheat. It is hardly necessary to say that winter wheat should have the nitrogen applied in the spring in the form of nitrate of soda, while the phosphoric acid and potash should be harrowed in before planting. 272. Methods of applying fertilizers. — The distribution of fertilizers by means of machinery is much more satis- factory than is broadcasting by hand, because the former method gives a more uniform distribution. Cereal and other crops are now usually planted with a drill, or a planter provided with an attachment for dropping the fertilizer at the same time that the seed is sown, the fertilizer being, by this method, placed under the surface of the soil. Broad- casting machines are also used, which leave the fertilizer uniformly distributed on the surface of the ground, thus per- mitting it to be applied and harrowed in a sufficient time before the seed is planted to prevent injury to the seed through the chemical activity of the fertilizer. Corn-planters with fertilizer attachment deposit the ferti- lizer beneath the seed, so as not to bring the two in contact. Grain drills do not do this and if the quantity of fertilizer THE USE OF FERTILIZERS 215 exceeds 300 or 400 pounds to the acre, it is better to apply it before seeding. Grass seed and other small seeds should be planted only after the fertilizer has been mixed with the soil for several days. 273. The limiting factor. — Attention has been called to the important influence that any condition unfavorable to plant growth is sure to exercise in curtailing yield of crops. If poor drainage is the difficulty, crop yields may be reduced to almost nothing, while if this be corrected a very productive piece of land may result. The same principle holds true when there is a deficiency of any one of the fertilizing sub- stances. There may be present in a soil an abundant supply of available phosphoric acid and potash, but if nitrogen is deficient the crop yield is limited to the size of crop that the quantity of available nitrogen present will produce. Each of the essential plant-food materials exercises this control. It is, therefore, a requisite in the economical use of ferti- lizers to have a well-balanced mixture of plant nutrients. The balance must be adjusted to the needs of each partic- ular soil, and to each kind of crop. Of course it is impossible to work out any fertilizer mixture that will fit these condi- tions exactly. These relationships are best worked out by field tests with fertilizer mixtures (see § 269). 274. The law of diminishing returns. — A small applica- tion of fertilizer usually effects a greater percentage increase of crop than does a larger application. This is unfortu- nate, because it means that there is a limit to the profit- able use of fertilizers, for although the cost of the fertilizer rises in direct proportion to the quantity used, the rate of yield decreases after a certain point has been reached, and consequently the value of the product finally becomes less than the cost of the fertilizer. This law of diminishing returns may be illustrated by an experiment in which floats were applied in several different quantities to plats of land, 216 SOILS AND FERTILIZERS each of which plats also received an application of farm ma- nure at the rate of 15 tons an acre. The applications of floats were at the rate of 200, 400, -800 and 2400 pounds to the acre respectively. In the following table are stated the increased yields over the check plats receiving the same quantity of farm manure but no floats. The values of the crops and cost of floats are reckoned on the same basis. Table 44. — Increased Yields and Values op Corn Resulting from Application of Farm Manure and Floats Fertilizer Treatment per Acre Grain BU. Value Cost of Floats Difference 15 tons of manure + 200 lbs. floats 7.0 $4.62 5.48 6.73 8.38 $ 0.90 1.80 3.60 10.80 $3.72 15 tons of manure + 400 lbs. floats 8.3 3.68 15 tons of manure + 800 lbs. floats 10.2 3.13 15 tons of manure + 2400 lbs. floats 12.7 2.42 loss It may be seen that the increase from the use of the first 200 pounds of floats was greater than from the additional 200 pounds, and from the next 400 pounds the increase was at a still lower rate. This is best shown by a curve, which may be seen in the upper part of Fig. 32. From the direction taken by the curve it may be seen that finally a point will be reached when there will no longer be any increase from larger applications of fertilizer. Long before that point is reached, however, the use of the ferti- lizer ceases to be profitable. This may be shown by another diagram containing curves for the value of the grain and the cost of the fertilizer. (See lower diagram in Fig. 32.) This diagram as well as the last column of Table 44 shows that the difference between the value of the product and the THE USE OF FERTILIZERS 217 cost of the fertilizer decreases after the lowest application, and that for the very heavy application there is an actual loss. 275. Conditions that influence the effect of fertilizers. — The extent to which fertilizers are utilized by crops depends is 44 \o sc o /z 6b Ye>oo zooo Z440 POUHDS OF FLOATS APPLIED PER. X7CRE pounos 800 /200 OF PLOPT5 APPLIED /600 2000 PER PCR.E 34W Fig. 32. — In the upper diagram the heavy line shows how the yields of corn were increased by graduated applications of phosphoric acid in floats. It will be seen that the increases in yields were proportionately much greater for small applications than for large. The lower diagram illustrates the rate at which the cost of the fertilizer approaches and finally passes the value of the product as the size of the appli- cation increases. on the presence or absence of certain conditions. The entire amount of any constituent of a fertilizer is never recovered by a crop in any one year. This is a very important consideration in the manuring of land, for under conditions as they fre- quently exist, the use of fertilizers is wasteful and extravagant. 218 SOILS AND FERTILIZERS The factors, within the control of man, that affect the availability of fertilizers are the following : (1) the kind of crops ; (2) soil moisture content ; (3) soil acidity ; (4) tilth of the soil ; (5) organic matter in the soil. An undesirable condition of any one or more of these factors is a very common occurrence, and yet fertilizers are expected to produce profitable returns, in spite of these adverse conditions. It must be remembered that the supply of nutrients is only one of the conditions that influence plant growth. Furthermore, an economical use of fertilizers requires that they merely supplement the natural supply of plant nutrients in the soil, and that the latter should fur- nish the larger part of the nutrient material used by the crop. Finally, most fertilizers are rendered less readily soluble by the absorptive properties of the soil, and the re- lease of these substances for plant use depends to a great extent on the conditions enumerated above. 276. Response of sandy and of clay soils to fertilizers. — It is generally recognized that a sandy soil responds more promptly to the application of fertilizers than does a clay soil. There are probably two reasons for this : (1) Absorp- tion may not be so complete both on account of the particles being larger, and because in many sandy soils the particles are largely composed of quartz, which does not have the property of forming combinations with bases, as does clay; (2) Drainage and aeration are likely to be better, as are most of those conditions that make plant-food materials more available. For these reasons, a sandy soil generally makes a greater response to fertilizers the first year, but shows less effect in subsequent years unless the treatment is repeated. On the other hand, less fertilizing material is lost from a clay soil by leaching. 277. Cumulative need for fertilizers. — It is often re- marked that on land habitually fertilized there is a gradually } , i Si— : : s | J 1- 1 l l « i 1 J 1 X \, "■'/ /|Hj iy • iiv- fixi ,w%nk :m$k [Hu \ ^^^J Wm H A sufficient supply of moisture makes a fertilizer more effective. Note the greater response to fertilization in the vessels having more moisture. Vessel 45. Moisture 30 per cent, Vessel 49. Moisture 15 per cent, Vessel 58. Moisture 30 per cent, Vessel 64. Moisture 15 per cent, Vessel 69. Moisture 30 per cent. Vessel 78. Moisture 15 per cent, no fertilizer, no fertilizer, complete fertilizer, complete fertilizer, more fertilizer, more fertilizer. Plate XIV, — A soil may contain too much or too little moisture. The best crop is in the vessel having next to the largest quantity of water. Vessel 20. Moisture 11 per cent. Vessel 26. Moisture 25 per cent. Vessel 22. Moisture 13 per cent. Vessel 28. Moisture 38 per cent. Vessel 24. Moisture 20 per cent. Vessel 32. Moisture 45 per cent. THE USE OF FERTILIZERS 219 increasing need for greater quantities of fertilizers. This is doubtless the case in many instances, and arises from neglect of other factors affecting soil productiveness. As we have seen, certain fertilizers cause the soil to lose lime, which results in soil acidity. Organic matter is allowed to decrease, and this causes the soil to become compact and poorly aerated, and thus, one bad condition leads to another and crops be- come poorer in spite of increased applications of fertilizer. QUESTIONS 1. Why are some crops able to draw abundant nourishment from soils on which other crops yield poorly ? 2. How do wheat and corn differ in their need of plant-food materials ? 3. Why is nitrate of soda particularly beneficial to grass ? 4. What two fertilizer materials are generally useful on legumes ? 5. What fertilizer material is required in large amounts by most root crops ? 6. What plant nutrient is especially needed by vegetables that are expected to make a rapid and succulent growth ? 7. In what ways are green-manures of use in orchards ? 8. Plan a fertilizer test similar to that shown in Pig. 31, but to be used with a crop of timothy instead of small grain. 9. To what crops in a rotation of corn, oats, wheat, and grass would you apply fertilizers ? 10. Explain what is meant by the limiting factor in plant growth with respect to the use of fertilizers. 11. What is meant by the law of diminishing returns ? 12. Name five soil factors within the control of man that influ- ence the availability of fertilizers. 13. Give two reasons why a sandy soil responds more promptly to fertilizers than does a clay soil. 14. Explain why soils sometimes demand an increasing use of fertilizers to maintain their productiveness. LABORATORY EXERCISES Exercise I. — Fertilization of standard rotations. The fertilization of the rotation is the ultimate and final consider- ation of any systematic use of fertilizers. While the fertilization as 220 SOILS AND FERTILIZERS to amounts and mixtures is generally different for different farms, the place of fertilizers in a standard rotation is more or less fixed. Take a number of good practical rotations and indicate where in the succession of crops the fertilization should occur. Also suggest what should be the formula of each mixture used, the fertilizer compounds which should be carried and the amounts that might be applied to a given soil. Exercise II. — Fertilization of home-farms. Encourage the pupils to bring in data regarding the fertilization on their home farms. Tabulate, discuss and criticize such data in a practical way. If any of the pupils have home project gardens, the fertilization of such gardens should be made a special problem for them. Exercise III. — Fertilizer practice in the community. A fertilizer survey of the township could be made with profit by the teacher, visiting each farmer and making inquiry adequate for the purpose in view. The pupils could aid not only in the col- lection of such data but also in such compilation and interpreta- tion as would later be necessary. Taking the class to visit a farmer whose system of farming and fertilization is a practical success is to be advocated. The economic use of fertilizers is attained not only by scientific knowl- edge, but also by good sound experience and practice. Exercise IV. — Fertilizer experimentation. The measurement in crop yield of the effects from fertilizer use is the only true means of gauging fertilizer needs and fertilizer prac- tice. Whether a certain fertilizer pays is the ultimate question. Jjay out plans for fertilizer experimentation as suggested in the text with the idea of taking careful data as to crop yield from the various treatments used and the calculation of the net returns. The fertilizer needs of the soil for nitrogen, phosphoric acid, potash and lime may be determined by the use of the various fer- tilizer carriers both alone and in combination. Different ready mixed fertilizers may also be compared. The amount of any particular fertilizer that may most economically be used can be tested by vary- ing the applications of the same mixture. The relation of lime, farm manure and time of application to the effectiveness of any particu- lar fertilizer may also be made a subject of experimentation. CHAPTER XVII FARM MANURES The use of animal manure to enrich the soil antedates written history, and it is still the most commonly and widely used fertilizer. It is produced on nearly every farm. Mar- ket-gardeners, who usually keep few animals, buy large quan- tities of horse manure from cities. Its use constitutes a way of returning to the land a part of the plant nutrients taken up by crops, as well as replacing some of the or- ganic matter destroyed by cultivation. Farm manure con- tains nitrogen, phosphoric acid, potash, lime and the other ingredients removed from soils, and hence is a direct ferti- lizer. In addition to these it contains a large quantity of organic matter, which by its influence on tilth, moisture and absorptive properties is a valuable soil amendment, and finally it favors, in a number of ways, a vigorous bacterial activity that does much to bring plant nutrients into an available condition. 278. Solid and liquid manure. — Farm manure is made up of the solid excreta of animals, the urine, which is usually largely absorbed by the solid ingredients, and the litter used for bedding the animal. As these constituents differ greatly, not only in composition but also in physical proper- ties, their proportions must appreciably affect the agri- cultural value of the manure. Litter usually does not have as high a fertilizer value as do the solid and liquid excreta. Of the excreta the larger part is solid and the smaller is urine. The ratios may be found in Table 45. The propor- 221 222 SOILS AND FERTILIZERS tion of litter is variable, depending on the extent to which bedding is used. 279. Chemical composition of manures. — From what has already been said regarding the variable nature of ma- nure, it will be understood how difficult it is to give a state- ment of the composition of a representative sample of ma- nure. The following table gives the results of an analysis that may be considered fairly representative of mixed fresh manure from several different classes of animals. Table 45. — Pounds of Water and Plant-Food Materials in One Ton of Solid Excreta, One Ton of Liquid Excreta and in One Ton of Entire Excreta of Several Different Classes of Animals Percentage op Solid and Liquid Parts of Excrement {Solid, 80 percent Liquid, 20 percent Entire excreta . {Solid, 70 percent Liquid, 30 percent Entire excreta . {Solid, 67 percent Liquid, 33 percent Entire excreta . {Solid, 60 percent Liquid, 40 percent Entire excreta . Pounds in a Ton Water 1500 1800 1560 1700 1840 1720 1200 1700 1360 1600 1940 1740 Nitro- gen 11 27 14 8 20 12 15 27 19 11 8 10 Phos- phoric Acid 6 trace 5 4 trace 3 10 1 7 10 2 7 Potash 8 25 11 2 27 9 9 42 20 8 9 8 This table shows that the solid excrement constitutes by far the larger part of the total. It also shows that a ton of liquid excreta is generally richer in nitrogen and potash than FARM MANURES 223 is an equal quantity of solid excrement, but in the case of swine there is little difference between the solid and liquid excreta in this respect. TOTAL NITROGEN 0.5% PHOSPHORIC ACID 0.5% POTASH 0.6% Fig. 33. — A farm manure containing 0.5 percent nitrogen, 0.3 percent phosphoric acid and 0.6 percent potash will, on the average, have these constituents divided between the solid and liquid parts of the manure in the proportions shown above. 280. Farm manure an unbalanced fertilizer. — A mix- ture of horse and cow manure, with an ordinary quantity of straw litter will have a composition somewhat as follows : 224 SOILS AND FERTILIZERS Constituents Water Dry matter Nitrogen Phosphoric acid Potash Pounds Per Ton 1460 540 10 5 12 Assuming that one-half of the nitrogen, one-fifth of the phosphoric acid and one-half of the potash are readily avail- able, twenty tons of mixed manure would be equivalent to one ton of a 5-1-6 fertilizer. Comparing this with any ordinary fertilizer, it is evident that it is high in nitrogen and very low in available phosphoric acid. This suggests that for its most effective use farm manure should be sup- plemented by some form of phosphoric acid. As an illustra- tion of the advantage of supplementing farm manure by phosphoric acid see Table 52. 281. Quantities of manure voided by animals. — An idea of the quantity of excreta, solid and liquid, produced by different animals may be obtained from the following table : Table 46. Excreta from Various Farm Animals to the 1000 Pounds Live Weight Animal Pounds per Day Tons per Year Horse 50 70 40 85 34 9.1 Cow 12.7 Steer 7.3 Swine . 15.5 Sheep 6.2 282. Effect of food on composition of manure. — The richer the food in nitrogen and other plant-food materials, the more of these there will be in the manure. This has FARM MANURES 225 been demonstrated by a number of experiments, from which the following have been selected. Table 47. — Effect of Food on Composition of Animal and Poultry Manure Pounds per Ton of Manure Ration Nitrogen Phosphoric Acid Potash Fed to steers Corn and mixed hay Corn, oil meal and hay .... Corn, oil meal and clover . . . Fed to fowls Nitrogenous ration Carbonaceous ration 29.80 31.00 33.60 16.00 13.20 10.53 10.99 11.91 18.78 14.65 26.64 24.48 24.96 6.48 5.04 283. Commercial evaluation of manures. — As a means of comparing manures, they may be evaluated in a manner similar to that used with commercial fertilizers. This, however, fails to place any value on the organic matter, which is undoubtedly of much benefit to the soil. In the following table are given the values of manures produced by different animals based, in part, on the composition given in Table 45 when the nitrogen is considered to be worth ten cents a pound, the phosphoric acid two and one-half cents and the potash four cents. Table 48. — Value of Excreta Produced by Several Farm Animals « Animal Value per Ton Swine excreta $1.50 Cow excreta 1.64 Horse excreta 1.97 Sheep excreta 2.87 Poultry excreta 4.80 226 SOILS AND FERTILIZERS If the mixed horse and cow manure together with litter, similar to that referred to in section 280, be made the basis of the calculation, the evaluation would be $1.60. Dilu- tion of the plant-food materials due to the litter tends to reduce the value. 284. Agricultural evaluation of manures. — The com- mercial value may be quite different from the agricul- tural value, which is calculated from the increased crop production resulting from the use of the manure. This will vary with different soils, but even on similar soils it will vary with different manures. The following table gives the results of an experiment in which treated and untreated manures were evaluated commercially and were then applied to the land. The value of the increased crops in a three years' rotation was then calculated in terms of financial return to the ton of manure applied : Table 49. — Commercial and Agricultural Evaluation op Manures Manure Commercial. Value Agricultural Value Yard manure untreated .... Yard manure plus floats . -. . . Yard manure plus acid phosphate . Yard manure plus kainit . . . Yard manure plus gypsum . . . $1.41 2.04 1.65 1.45 1.48 $2.15 3.31 3.67 2.79 2.76 285. Deterioration of farm manure. — There is always a loss in the value of farm manure on standing. The ways in which this is brought about are: (1) fermentation; (2) leaching. The first of these is a natural process, common to all farm manure on standing, and not occasioned by any outside agencies. The second is due to the running off of Plate XV. Manures. — Farm manure is becoming relatively more scarce every year. Its protection is becoming more essential to success- ful farming. FARM MANURES 227 the liquid portion of the manure, and to the exposure of the manure to rain. 286. Fermentations of manure. — The mixture of solid and liquid excreta together with litter used as bedding con- stitutes a wonderfully favorable material for the growth of bacteria, the number of which frequently amounts to many billion in a gram of manure. This is many times more than are found in soil. It is then small wonder that fer- mentations proceed at a prodigious rate in a manure heap. These fermentations are produced both by bacteria requiring oxygen for their activity and by those that need little. The fermentations on the outside of the heap are different from those on the inside, where air does not readily penetrate, but as fresh manure is thrown on the pile from day to day, most of the manure first undergoes fermentation in the pres- ence of air and afterwards without air. It is through the action of germs on the nitrogenous com- pounds of manure that loss of value through fermentation occurs. In the presence of air ammonia is formed, and this being in a volatile form, is likely to escape. The drier the heap, the more likely the ammonia is to escape. The fermentations in the interior of a moist manure heap are, in the main, favorable to the production of readily available plant-food material. It is desirable to keep the heap as compact as possible, and to prevent it from becom- ing dry by the application of water in amounts sufficient to keep the heap moderately moist without leaching it. In the arid and semi-arid parts of the country, this is an im- portant precaution to be taken in the preservation of farm manure. 287. Leaching of farm manure. — When water is allowed to soak through a manure heap and to drain away from it, there is carried off in solution, and to some extent in sus- pension, more or less of the organic matter and plant-food 228 SOILS AND FERTILIZERS materials that are soluble in water and that consequently represent the most valuable part of the manure. As about one-half of the nitrogen and two-thirds of the potash of farm manure is in a soluble condition, the possibility of loss by leaching is very great. Even phosphoric acid may thus be removed. It is rather difficult to distinguish between the losses due to fermentation and those caused by leaching. In an experi- ment conducted in Canada a carefully mixed quantity of farm manure was divided into two parts, one of which was placed in a bin under a shed, the other was exposed to the weather outside, in a similar bin. After a year the two por- tions were analyzed and the losses thus computed are stated in the following table. Table 50. Losses by Fermentation Alone and by Fermen- tation and Leaching Combined Constituent Lost Percentage Loss Organic matter Nitrogen . Phosphoric acid Potash . . . 288. Protected manure more effective. — Over a period • of fourteen years, in a three year rotation of corn, wheat and hay at the Ohio Experiment Station, stall manure gave an average yield of 30 percent more than did equal quantities of yard manure. This gives a fair basis on which to cal- culate whether it would pay to protect the manure when the expense of doing so, and the quantity of manure produced, are considered. FARM MANURES 229 289. Reinforcing manure. — Various substances are in- corporated with animal manures, either in the stall or in the heap, for the purposes of : (1) curtailing loss by leaching and fermentation, and (2) balancing the manure in order to better adapt it to the needs of most crops. The latter has been mentioned in section 280. The materials commonly- used for these purposes are gypsum, kainit, acid phosphate and floats. Experiments at the Ohio Experiment Station indicate that the conserving effect is slight, but that the benefit due to reinforcing is considerable when acid phosphate or floats are used. To ascertain the conserving properties of several substances, each was mixed with the manure at the rate of 40 pounds to the ton, and the loss of fertilizing value was computed from analyses after the mixtures had stood from January to April. The results are shown in the following table : Table 51. Effect of Reinforcing Materials on Conserva- tion of Fertility in Farm Manure Materials Used Value of Ton of Manure Percentage In January In April Loss None Gypsum Kainit - . . . Floats Acid phosphate $2.19 2.05 2.24 2.81 2.34 $1.41 1.48 1.45 2.04 1.65 36 38 35 24 29 The actual agricultural value of the reinforced manure was ascertained from tests covering a period of fourteen years in a rotation of corn, wheat and hay, of which the results were as follows :, 230 SOILS AND FERTILIZERS Table 52. — Financial Results of Reinforcing Farm Manure Value of Net In- creased Yield to the Ton of Manure Manure alone .... Manure plus gypsum . . Manure plus kainit . . . Manure plus floats . . . Manure plus acid phosphate $3.31 3.56 3.71 4.49 4.82 It has already been remarked that farm manure is deficient in available phosphoric acid, and this experiment demon- .strates the benefit to be gained by reinforcing it with a phos- phoric acid fertilizer. 290. Methods of handling manure. — The least oppor- tunity for deterioration of farm manure occurs when it is hauled directly to the field from the stall and spread at once. Manure may even be spread on frozen ground or on snow, provided the land is fairly level and the snow is not too deep. However, it is not always possible to follow this method and manure must sometimes be stored. In the storage of ma- nure the two important conditions are a sufficient but not an excessive supply of moisture, and a well-compacted mass. Water draining away from a manure heap, and a fermenta- tion producing a white appearance of the manure under the surface of the pile (" fire fanging "), are both sure indications of unnecessary loss in its fertilizing value. 291. Covered barnyard. — The best method of storing manure is in a covered yard in which the cattle are allowed to exercise and thus to trample and compact the mixed manure from the barn. The advantage to be gained from the tram- pling is brought out by some Pennsylvania experiments in which the losses of fertilizing constituents were compared when the covered manure was trampled and when it was not. FARM MANURES 231 Table 53. — Loss of Fertilizing Constituents from Farm Manure in Covered Sheds when Trampled and when Not Trampled Percentage Loss of Treatment of Manure Nitrogen Phosphoric Acid Potash Covered and trampled Covered and not trampled . . ■. . 5.7 34.1 5.5 19.8 8.5 14.2 292. Application of manure to land. — In applying farm manure to the field, it is customary either to throw it from the wagon in small heaps, from which it is distributed later, or to scatter it as evenly as possible immediately on hauling it to the field. The use of the automatic manure-spreader accomplishes the latter procedure in an admirable manner. As between these two methods, the advantage, so far as the conservation of fertility is concerned, is with the practice of spreading immediately. When piled in small heaps, fer- mentation goes on under conditions that cannot be controlled, and that may be very unfavorable. The heaps may dry out, and thus lose much of their nitrogen, or they are likely to leave the field not uniformly fertilized because of the leaching of some of the constituents of the manure into the soil directly under and adjacent to the heap. On the other hand, when spread immediately, little fermentation takes place, as the manure does not heat, and the soluble sub- stances are leached quite uniformly into the soil. Plowing should follow as closely as possible the spreading of the manure, except when it is intended for a top dressing. 293. Place of farm manure in crop rotation. — When a crop rotation includes grass or clover as one of the courses, the application of farm manure may well be made at that time as a dressing. It can thus be spread at times when cultivated land would not be accessible, and the crop of hay 232 SOILS AND FERTILIZERS will profit greatly. Sod, when plowed under, is frequently planted to corn — a crop that is rarely injured by farm ma- nure. Experiments in Illinois indicate the great response of clover to farm manure, as compared with oats and corn. Table 54. — Increased Crop Yields and Values When Manure Was Applied to Corn and Oats and to Clover Percentage Increase in Yield Percentage Value of Increase Treatment Corn and Oats Clover Corn and Oats Clover Manure Manure, lime and phosphate 11 30 92 141 $ 7.53 12.21 $10.08 15.48 QUESTIONS 1. What plant nutrients does farm manure contain, and what indirect fertilizing material ? 2. In what ways is the organic matter of farm manure beneficial to soils ? 3. Which is richer in plant-food materials, liquid or solid manure ? 4. What constituent should farm manure have added to it in order that it should be a well-balanced fertilizer ? 5. What farm animal produces the largest quantity of manure for every 1000 pounds of live weight ? 6. Which produces the more valuable manure, a ration rich in plant-food materials, or one poor in these substances ? 7. Which of the farm animals furnishes a manure having the greatest commercial value a ton ? , 8. In what two ways does farm manure suffer loss on standing ? 9. How is nitrogen likely to be lost by fermentation, and what condition is likely to bring this about ? 10. What substances are lost by the leaching of manure ? What materials are used for conserving manure ? Is it better to store manure, or to haul it directly to the land ? 11. 12. Why? 13. Discuss the place of manure in the crop rotation. FARM MANURES 233 LABORATORY EXERCISES Exercise I. — Study of farm manure. In one or more trips through the community the class may study in a practical way the following points regarding farm manure and its utilization. 1. Enter a horse stable where fresh manure is lying in the stalls. Observe the odor of ammonia. Explain the reason for such an odor and its significance. 2. Compare horse manure and cattle manure as to weight, struc- tural condition and amount of water. What relation may these characteristics have to fermentation and to the handling of the manures ? 3. In the same way compare swine, sheep and poultry manures. 4. Examine the teachings from an exposed manure pile. What is the color of such liquid and what plant-food materials does it prob- ably contain ? 5. Study the various ways of handling manure that are in vogue in the community. List and discuss their good and poor points, remembering that the method that would entail the least loss of plant-food material may not always be practicable, due to lack of capital or to the press of the season's work. The common ways of handling manure are : hauling directly to the field and either (1) spreading or (2) leaving in piles for later distribution, (3) stor- ing in a covered barnyard, (4) storing in a manure pit, (5) allowing manure to be tramped down behind the animals or (6) storing in piles either under cover or exposed. 6. Study the mechanism and operation of a manure-spreader. An efficient spreader should run easily and yet distribute the manure evenly and in a finely divided condition. Exercise II. — Experiments with farm manure. Plat experiments similar to those suggested in Exercise IV, Chap- ter XVI might be carried out with profit with farm manure. The effect of different amounts of manure, the relative returns of manure from different classes of animals, the influence of lime on the return from the application of manure, and the residual influence of manure are only a few of the possible tests that might be made. Tests as described in Exercise III, Chapter XI might be carried out with manure as well as with commercial fertilizers and lime if plats of soil are not available. 234 SOILS AND FERTILIZERS Exercise III. — The value of manure on the home-farm. From the data in the text, have each student calculate the probable quantity of manure produced on his home-farm. Have him calculate the commercial value of this manure. Then from the way in which the manure is handled have him estimate the loss which occurs to this manure. Now discuss the probable agricultural value of the manure as compared with its original commercial value. Exercise IV. — Reinforcement of farm manure. In cooperation with some near-by farmer, reinforce some farm manure, allowing the pupils to aid not only in the actual work, but in the determination of the kind and amount of reinforcing materials to use. Calculate from the quantities used and their composition as given in the text, the probable composition of the manure after the treatment and determine whether it has become a properly balanced material. The reinforced manure should be spread in the field so that its influence on the succeeding crop may be com- pared with untreated manure. Reinforcements with different ma- terials may even be compared under actual field conditions. Exercise V. — Building of a compost pile. Farm manure in a compost pile supplies the organisms which bring about the decay of the sod, leaves or other plant materials which are to be reduced to simple compounds. Composted mate- rials are of especial value in greenhouses and gardens in supplying organic matter to the soil, that a good structure may be maintained. Choose a level spot on which to locate the compost pile. First put down a layer of sod, moistening if necessary until optimum con- ditions are attained. Next apply a thin layer of fine, well-rotted manure, then sod and so on till the pile is complete. The pile may be as large as necessary or convenient and should be level on top to prevent the rainfall from running off the surface. If the interior of the pile is moist to begin with, it will stay moist through the period given to fermentation. Six months or a year are necessary for effective composting. Other materials than sod may be placed in a compost heap, such as leaves, vines of all kinds, rotted vegetables, garbage, small sticks, etc. It is a good practice also to add lime to the pile to keep it sweet. If the material is to be used as a fertilizer as well as to condition the soil, acid phosphate may also be added. CHAPTER XVIII GREEN-MANURES Crops that are grown primarily for the purpose of being plowed under to improve the soil are called green-manures. They may benefit the soil in one or more of four ways : (1) By utilizing soluble plant-food material that would otherwise leach from the soil ; (2) by incorporating vegetable matter with the soil ; (3) leguminous crops, when used, add to the available nitrogen of the soil ; (4) plant-food materials from the lower soil may be brought tfcrthe surface soil. A large number of crops may be used for this purpose, while the climate determines to some extent which crops should be used. Crops that can be planted in the fall to grow during the cool weather may be utilized when otherwise the land would frequently lie bare. Leguminous crops have the great advantage of acquiring nitrogen from the air. Deep- rooted crops usually accumulate a large amount of nutriment from the soil and considerable from the lower depths. They are therefore useful in bringing plant-food material to the upper layers of soil. Succulent crops decompose easily, and dry out the soil less, when plowed under, than do woody crops. Crops with extensive root- systems prevent loss of soluble matter more thoroughly than do plants with small root systems. 294. Protective action of green-manures. — It has been shown in section 121 that the growth of crops on land may prevent a large loss of plant-food material, especially nitrogen 235 236 SOILS AND FERTILIZERS and lime, in drainage water. If, therefore, green-manure crops cover the soil, when otherwise nothing would be growing on it, they exercise a protective action. In the case of orchards a green-manure crop saves much nutriment as compared with clean cultivation. A catch-crop, like rye, that is sown in the fall after a summer crop has been harvested and is plowed under in the spring, saves some plant-food material. 295. Materials supplied by green-manures. — Probably the most beneficial effect exerted by green-manures is the ad- dition of organic matter to soil. Practically the only source of organic matter is in the form of farm manure or of plant residues. Farm manure is yearly becoming more scarce and expensive. Some substitute must be found. In an average crop of green-manure, from five to ten tons of material is turned under. Of this, from one to two tons is dry matter, and from four to eight tons is water. This would correspond to a dressing of four to eight tons of farm manure, so far as the organic matter alone is concerned. Legumes add nitrogen as well as organic matter. The nitrogen contained in a ton of the green crop, when in a con- dition to plow under, is as follows : Table 55. — Quantities of Nitrogen in Some Leguminous Green-Manure Crops Crop Red or mammoth clover Crimson clover . Alsike clover .... Alfalfa Cowpeas Soy beans Canada field peas . . Nitrogen per Ton, Pounds Probable Yield per Acre, Tons 10 6 9 6 10 5 14 8 8 6 10 6 11 5 Nitrogen per Acre, Pounds 60 54 50 112 48 60 55 GREEN-MANURES 237 Not all of the nitrogen contained in these crops is taken from the air. On soils rich in nitrogen, a considerable pro- portion may be obtained from the soil. On poor soils, the proportion derived from the atmosphere is considerably larger. Soils needing nitrogen most are those that benefit most largely from its application. 296. Transfer of plant-food materials. — There is a trans- fer of plant nutrients in a double sense : (1) removal of these L055 LAR6ELY ORGANIC * WITH SOME NITROGEN AND PHOSPHORIC ACID ANIMAL TO MARKET LARGE L055 OF 0R6ANIC * MATTER, NITROGEN, PHOS- PHORIC ACID AND POTASH GREEN MANURE Fig. 34. — Movements of plant-food materials. After absorption by the plant they may be returned in whole or in part to the soil. If grain and straw or hay are sold nothing but the stubble and roots are returned. If fed to animals, part may be returned in the manure. If plowed under as green-manure, all are returned. substances from combination with other minerals and their conversion into combinations with organic matter; (2) re- moval from lower soil by absorption by roots and the deposi- tion of this material in the upper layer of soil when the plant dies and is plowed under. The first of these transfers results in an improved condition of the plant nutrients, because in the combinations with organic matter they are in general more available to plants than when in combinations with 238 SOILS AND FERTILIZERS inorganic matter. By the second form of transfer the nutri- ents in this available form are deposited in the upper soil from which most crops draw the larger part of their nutriment. 297. Crops used for green-manuring. — The following table contains a list of the plants commonly used as green-manures both in cultivated fields and in orchards, together with some information as to the season of the year when they may be used and whether adapted to northern or southern conditions. Table 56. Crops Used as Green-Manures Legumes (annual) Canada field pea Hairy vetch Crimson clover Peanut Velvet bean Soy bean Cowpeas Legumes (biennial or perennial) Red or mammoth clover . . . Alsike clover Alfalfa Sweet clover Non-Legumes Rye Oats Buckwheat Cowhorn turnips Mustard Rape Season summer winter winter summer summer summer summer one year at least one year at least one year at least one year at least winter fall or early spring fall and summer summer summer summer and fall Region Northern states Northern and southern states Middle and southern states Middle and southern states Middle and southern states Middle and southern state3 Southern states Northern states Northern states Northern and southern states Northern and southern states Northern and middle states Northern and middle states Northern states Northern states Northern states Northern states A soil that has become less productive under cultivation, and that must be improved before profitable crops can be grown, receives more benefit from the use of legumes than from any other crop. The legume to use is naturally the one best adapted to the region in which the soil is located. The perennial or biennial legumes are too slow of growth really to be considered green-manure crops. They are like Plate XVI. Soil Covers. — Cover-crops may consist merely of weeds allowed to grow voluntarily, as shown in the upper figure, or of grain or other planted crops, as shown in the lower. GREEN-MANURES 239 timothy and other grasses and can well be grown for hay, only the sod being plowed under. Only in the case of very much run down soils are these crops plowed under. Crimson clover is an annual, and in the central and southern states may be sown in the fall and plowed under in the late spring, thus making use of a period of the year when the ground is least likely to be occupied by a crop. Cowpeas, soy beans and field peas must be raised during the summer months. Vetch promises to be a satisfactory green-manure for winter use in the northern states, when the cost of seed becomes less than it is at present. Where it is desired to keep a crop on the soil during the autumn, winter and spring, for the purpose of utilizing the soluble plant-food material, the cereals, especially rye, are useful. Buckwheat, on account of its ability to grow on poor soil, is adapted to use as a green-manure, but it must be grown in the summer or early fall. 298. When green-manures may be used. — The most economical way to use green-manures is between the regular crops, rather than to lose a crop for the purpose of applying green-manure. Between a small grain crop and a spring- planted crop, there is usually opportunity for some green- manure to be raised, even in the northern states. This crop may be rye, vetch, buckwheat or rape and in the southern states may be added crimson clover, which is perhaps best for that region. In the South, however, there is much more opportunity for the use of green-manure crops on ac- count of the longer season. Where timothy and red clover grow successfully, it is probably best to rely on the sod of these crops to furnish green-manure rather than to attempt any system that would necessitate dropping a crop from the rotation. By a judicious fertilization of the hay crops, a heavy sod may be produced, thus utilizing the inorganic matter of the fertilizer to produce organic matter in the sod. 240 SOILS AND FERTILIZERS It is probably where special crops are produced that green- manures will reach their greatest usefulness. Their use in orchards is well established. For this purpose they are plowed under in the spring and planted in midsummer. Potato-growers and even market-gardeners are using green- manures in increasing quantity. ^ 299. Handling green-manure crops. — The stage of growth at which green-manures should be plowed under has a rather important bearing on their effect on the soil. In order that they shall decompose readily, they should be succulent when incorporated with the soil. If plants that have fully ripened are plowed under, they decompose very slowly and interfere with the formation of nitrates. An acid soil is unfavorable to the decomposition of green-manures and to the formation of nitrates ; hence it is desirable that lime be applied before planting the manure crops unless the soil is already well supplied with lime. QUESTIONS 1. Describe what is meant by green-manure crops. 2. State four ways in which they may be beneficial to the soil. 3. What two substances are prevented from being leached from soil in large quantities by the growth of green-manure crops ? 4. How do legumes differ from other green-manures in con- tributing to soil fertility ? 5. In what two ways is there a transfer of plant nutrients brought about by the use of green-manures, and how do they benefit the soil ? 6. Name five leguminous green-manure crops and state the time of year in which they are generally planted in your locality. 7. Give the same information regarding five non-legumes. 8. What is the disadvantage of plowing under green-manure crops when they are fully ripe ? LABORATORY EXERCISES Exercise I. — Study of green-manure in the field. Plan a field trip to some farm where a crop is being turned under for green-manure. Determine whether the time is most favorable GREEN-MANURES 241 for the operation. Study the action of the plow which is being used and see if the depth of the plowing, the inclination of the furrow slice, and the covering of the green material is as it should be. Calculate the weight of the crop being turned under and with this as a basis, figure the pounds of water, dry matter, nitrogen, phosphoric acid and potash being placed in the soil per acre. If the crop is a legume, make a guess as to the probable gain of the soil in nitrogen. Is this nitrogen available or unavailable ? Exercise II. — Green-manure and the rotation. Take a number of good practical rotations and indicate where, in the succession of crops, a green-manure might be introduced. Encourage the pupils to bring data from their home farms for this study. Tabulate such material and study it in the class room. Also bring up the question in relation to gardening and trucking. Discuss the necessity, advisability and ways of introducing a green- manure under such conditions. CHAPTER XIX CROP ROTATION Early in the development of agriculture, it was understood that a succession of different crops on any piece of land gave better returns than did one crop raised continuously. The practice of changing the crops raised each year thus became customary, and the prevalence of the method among European peoples shows that its benefits are widely appre- ciated. In Great Britain and some of the countries of Europe, crop rotations have been most systematically and effectively developed . S uch development has been stim- ulated by the diminishing productiveness of the soil, con- sequent upon long-continued cultivation, coupled with an increasing and progressive population. Regions having undepleted and uninfested soil, as was formerly the case in the prairie region of the United States, and countries that have an unprogressive people, like those of India, have done little with crop rotation. Another condition that discourages the use of crop rotation is the suitability of a region to the production of some one crop of outstanding value, combined, perhaps, with a rela- tively cheap supply of fertilizing material. These conditions obtain in the cotton belt of the United States. The abun- dant use of fertilizers may postpone for a long time the recourse to crop rotation. 300. Crop rotation and soil productiveness. — There are many benefits to be derived from a proper rotation of 242 CROP ROTATION 243 crops that are not directly concerned with soil productive- ness, and of these this book does not treat. In a number of ways crop rotation may directly affect the soil, and these will be discussed under several different heads. 301. Root systems of different crops. — Some crops have roots that penetrate deeply into the subsoil, while others are only moderately deep-rooted and still others very shallow- rooted. Among the deeply rooted plants are alfalfa, clover, certain of the root crops and some of the native prairie grasses. Among those having moderately long roots are oats, corn, wheat meadow iescue and a few other grasses, and among those having shallow roots are barley, turnips and many of the cultivated grasses. As plants draw their nourishment from those portions of the soil into which their roots penetrate, the deeper soil is not called upon to provide food material for the shallow-rooted crops, and the deep-rooted crops remove relatively less of their nutrients from the surface soil. It, therefore, happens that a rotation involving the growth of deep and shallow- rooted plants effects, by utilizing a larger area of the soil, a more economical utilization of plant nutrients than would a continuous growth of either kind. 302. Nutrients removed from soil by different crops. — Some crops require large amounts of one fertilizing constit- uent, while others take up more of another. For instance, wheat crops are able to utilize the potassium and phosphorus of the soil to a considerable degree, but have less ability to secure nitrogen. They are usually much benefited by the application of a nitrate fertilizer and leave in the soil a con- siderable residue of nitrogen that may be available to other plants. A number of other crops, as, for example, beets and carrots, can utilize this residual nitrogen. Grasses remove comparatively little phosphoric acid. Potatoes remove very large quantities of potash. A rota- 244 SOILS AND FERTILIZERS tion of crops is, therefore, less likely to cause a deficiency of some one constituent than is a continuous growth of one crop, and it utilizes more completely the available nutrients. 303. Some crops or crop treatments prepare nutriment for other crops. — It is quite evident that leguminous crops not only leave in the soil an accumulation of organic nitrogen transformed by bacteria from atmospheric nitrogen, but that they leave part of the nitrogen in a form readily available for use by other plants. The presence of a grass crop on the land for several years favors the action of non-symbiotic nitrogen-fixing bacteria. The grass crops also leave a very considerable amount of organic matter in the soil, which by its gradual decomposition contributes both directly and indirectly to the supply of available nutrients. Stirring the soil at intervals during the summer greatly facilitates decomposition, and leaves a supply of easily avail- able food material. The introduction of intertilled crops in the rotation thus serves to prepare nutriment for those that receive no intertillage. 304. Crops differ in their effect on soil structure. — Plants must be included among the factors that affect the arrangement of soil particles. The result of root growth is usually to im- prove the physical condition of soil. In general, crops with rather shallow and very fibrous roots are most beneficial, at least to the surface soil. Millet, buckwheat, barley and to a less extent, wheat leave the soil in a friable condition. It is on heavy soils that this property is most beneficially exercised. Tap-rooted plants, and others with few surface roots, do not exhibit this action. Alfalfa and some root crops are likely to leave the soil rather compact as compared with the crops mentioned above. The effect of sod is nearly always bene- ficial to heavy soils, and this is one of the reasons for using a grass crop in a rotation. CROP ROTATION 245 305. Certain crops check certain weeds. — By rotating crops the weeds that nourish during the presence of one crop on the land may be greatly checked by succeeding crops. Some weeds are best destroyed by smothering, for which purpose small grain, and notably corn or sorghum grown for fodder are effective. Other weeds are most injured by til- lage, to accomplish which the hoed crops are needed ; while others can best be checked by the presence of a thick sod on the ground for a number of years. In the warfare against weeds that must be waged wherever crops are raised, the use of different crops involving different methods of soil treat- ment is of great service. 306. Plant diseases and insects. — Many plant diseases and many insects spend their resting stages and larval exist- ence in the soil. A continuous growth of any one crop on the soil favors the increase of these species by providing each year the particular plant on which they thrive. A change of crops, by removing the host plants, causes the disappearance of many diseases and insects through their inability to reach their host plants. A long rotation, such as is frequently used in Great Britain, is particularly effective in eradicating those diseases that persist in the soil for a number of years. In the case of diseases that affect more than one species of plant, as does the beet and potato scab, there is need for special care in arranging the rotation. Such considerations may make it desirable to change the plan of a rotation. Another feature of the relation of crop-rotation to plant dis- eases is that the more thrifty growth obtainable under rota- tion assists the crop to withstand many diseases. 307. Loss of plant-food material between plantings. — Many systems of crop rotation permit a more constant use of the land than is possible with continuous growth of most annual crops. As a soil bearing no crop on it always loses more plant-food material in the drainage water than does one on 246 SOILS AND FERTILIZERS which plants grow, it is thus possible, by a well-chosen rotation, to save plant-food material that would otherwise be lost. 308. Production of toxic substances from plants. — Tl^at soil sometimes contains organic substances that exert an injurious effect on the growth of certain plants is indicated by- recent experiments and was surmised by some early writers on the subject. De Candolle was probably the first to ad- vance the idea in 1832. He suggested that at least some plants excrete from their roots substances that are injurious to the growth of the plants themselves and others of their species, although the excreta may be harmless or even bene- ficial to other plants. This he considered one of the reasons for the failure of many crops to succeed when grown contin- uously, while the same soil may be productive under a rota- tion of crops. Of recent years this subject has been investigated exten- sively in the United States and to some extent in Europe. There appears to be no doubt that toxic substances of an organic nature sometimes occur in soils, and there is evi- dence that some of them are connected with the growth of certain crops to which they are injurious. In most soils containing toxic substances the injurious effect is exerted on a large number of plants rather than only on those that have been previously grown. It is still a question to what extent excretion from roots or partial decomposition of plant residues are responsible for the poor growth that results from the continuous growth of crops on the same soil. 309. Management of a crop rotation. — The advantages of a crop rotation are so apparent and are connected so closely with the profits to be derived from farming that there can be no doubt regarding the advisability of practicing a rotation, even when some one crop may be much more profitable than any others that can be grown. Thus even in regions and on CROP ROTATION 247 soil particularly favorable to the production of any one crop, like tobacco, cotton, hay, corn or wheat, it will seldom be ad- visable to raise one crop to the exclusion of others, but the most rational practice will generally provide for some system of crop rotation. There are three classes of crops that should, so far as possi- ble, have a place in any rotation. These are legumes, sod crops or grasses and intertilled crops. The value of legumes as nitrogen gatherers has already been discussed. It is partic- ' ularly on poor land that legumes are of most benefit, and if some of the tops, as for instance, the second growth of clover, be plowed under, their value will be greater. Sod crops are of great value in furnishing organic matter to the soil. The larger the hay crop, the more sod produced, which is a double incentive to the use of fertilizers and farm manure on this crop (see § 204). Sod also forms a favorable condition for the fixation of nitrogen. Legumes appear to have one advantage over sod crops as nitrogen gatherers, in that the nitrogenous matter remaining in the soil is more available to some crops, at least, and is more readily converted into nitrates. In each course of a rotation there should be, if possible, one intertilled crop, like corn, cotton, potatoes or cabbage. The intertilled crop should follow the sod crop, or the legume, because the cultivation given the soil throughout the summer produces a condition favorable to the decomposition of the organic matter furnished by the sod. Except where the con- servation of moisture is an important factor, the use of an intertilled crop is preferable to a clean fallow, as it is more economical of the nitrogen and lime supply, and appears to result in better crops the year following. Other crops to be used in the rotation will be determined by the climate, soil, market and convenience in handling. Fertilization of the rotation is discussed in section 271. 248 SOILS AND FERTILIZERS QUESTIONS 1. What advantage is gained by alternating deep-rooted with shallow-rooted plants in a rotation ? 2. Why is a rotation of crops less likely to cause a deficiency in some one constituent of the soil than is the continuous growt^L of one crop ? 3. In what ways do some crops and some crop treatments pre- pare available nutriment for other crops ? 4. How may soil structure be affected by crop rotation ? 5. Explain the relation of crop rotation to weeds. 6. Explain the relation of crop rotation to plant diseases and insects. 7. How may plant nutrients be prevented from leaching by the use of the proper rotation ? 8. What three classes of crops should have a place in any rota- tion and why ? LABORATORY EXERCISES Exercise I. — Crop rotations. Study standard crop rotations from different parts of the United States as to crops grown, climate, markets, fertility of the soil, fertilization, etc. Try to find the reason for the use of each rotation under its particular conditions. , With the aid of the pupils, obtain a number of the rotations used in the community or county. Study these from all standpoints, and, if possible, suggest improvements. A rotation survey of the community might be made in order that data valuable to the farmers, as well as to the pupils, shall be obtained. The students should aid in this as well as in the tabulation and interpretation of the data. Exercise II. — Fertilizing the rotation. Under given conditions have the pupil work out the fertilization of a standard rotation for the locality. This means not only the kinds and quantities of fertilizer to apply, at what point in the rotation to add them and at what time of year to put on the soil, but also the use of lime, green manure and farm manure. Such a study should be a summation of many of the practices and principles of good soil management. INDEX Absolute specific gravity, of soil Air of soil, oxygen in, 146 particles, 35. and "heavy" soil, 35. and "light" soil, 35. Absorbed fertilizers, 100. Absorption, of lime by soils, 188. of gases, test for, 111. selective, 99. selective, test for, 111. Absorptive power of different crops, 107. Absorptive properties of soils, 99. Acid phosphate, absorption by soil, 173. manufacture and composition, 172. vs. rock phosphate, 174. Acid soils, described, 112. causes of, 113. crops adapted to, 116. crops injured by, 116. effect of drainage on, 113. effect of fertilizers on, 114. effect of green manures on, 115. effect of plant growth on, 114. litmus paper test for, 117. relation to bacteria, 129. tests for, 122, 123. Truog test, 118. weeds that nourish on, 115. Adobe, composition of, 27. distribution of, 27. iSColian soils, described, 26. adobe, 27. loess, 27. Air of soil, composition, 145. control of movement, 148. control of volume, 148. demonstration of movement, 152. in relation to drainage, 79. movements, 144. nitrogen in, 147. quantities present, 143. relation to pore space, 143. relation to water, 144. usefulness of, 146. Alkali and irrigation, 120. control of, 121. effect of crops on, 119. movements of, 118. removal of, 120. tolerance of different plants to, 119. Alkali soils, nature of, 118. Alluvial soils, character of, 23. described, 22. distribution of, 23. formation of, 22. Ammonia, absorption by plants, 156. test for, in soil, 141. Ammonification, 132. Animals, effect on structure, 41. Apatite, plant-food materials in, 7. Apparent specific gravity, and "heavy" soil, 38. and "light" soil, 38. of soil particles, 38. Auger for sampling soil, 29. Available plant-food materials, 94. Availability, conditions that in- fluence, 95. of nitrogenous fertilizers, 166. Bacteria, action on mineral matter, 129. ammonification caused by, 132. conditions affecting growth, 128. decomposition of nitrogenous organic matter, 131. decomposition of non-nitrogenous organic matter, 130. examination of nodules for, 142. 249 250 INDEX Bacteria, in relation to air supply, 128. in relation to lime, 189. in relation to moisture, 128. in relation to organic matter, 129. in relation to soil acidity, 129. in relation to soil fertility, 129. in relation to temperature, 129. nitrification caused by, 132. numbers in soils, 127. Basic slag, 172. Calcite, plant-food material in, 7. Capillary capacity, test for, 87. Capillary movement, test for, 86. Capillary water, 63. Carbon dioxide, conditions that affect quantity, 146. demonstration of formation in soil, 154. demonstration of presence in soil, 153. functions in soil, 147. percentage in bare and planted soil, 106. percentage in soil air, 145. production by microorganisms, 107. production in soils, 145. Chemical analysis of soil, 98. Chemical composition, of various soils, 91. relation to productiveness, 93. Class, the soil, defined, 33. in soil survey, 44. method for determination, 34. Classification of soils in survey, 43. Colluvial soils, described, 22. formation of, 22. Compaction of soil due to root growth, 2. Compost, building of a pile, 234. Crop rotation, 242. Crops, relation to soil texture, 32. Cumulose soils, composition of, 21. described, 20. formation of, 20. Cyanamid, changes in the soil, 162. composition of, 161. manufacture of, 161. Denitrification, 135. Dolomite, plant-food materials in, 7. Drainage, and length of growing season, 80. and available water, 79. benefits from, 78. by open ditches, 80. * defined, 78. in relation to soil air, 79. in relation to tilth, 79. Drainage water, composition of, 103, 104. Drains, arrangement of, 82. concrete, 81. tile, 81. Evaporation, prevention of, 74-77. proportion of rainfall lost by, 73. Feldspars, plant-food materials in, 7. Fertility of soil in relation to bac- teria, 129. Fertilizer constituents, trade values, 200. experiments, plan for, 212. formulas for different crops, 210. ingredients, how to mix, 205. mixture, calculation of, 204. Fertilizers, brands of, 196. computation of wholesale value, 202. conditions that influence effect of, 217. consumption of, in U. S., 196. cumulative need of, 218. effect on soil acidity, 114. for different crops, 207. for different soils, 211. for grasses, 208. for leguminous crops, 208. for orchards, 209. for root crops, 209. for small grains, 207. for vegetables, 209. high and low grade, 198, home mixing of, 203. inspection and control, 199. law of diminishing returns, 215. methods of applying, 214. nitrogenous, 155. nitrogenous, forms of nitrogen in, 157. phosphoric acid, 171. INDEX 251 Fertilizers, phosphoric acid, tests for, 177. potash, 179. potash, tests for, 185. response of soil to, 218. tests for nitrogenous fertilizers, 169. that should not be mixed, 203. the limiting factor, 215. the purchase and mixing of, 196. use of, 207. Fertilizing the rotation, 213. Formation of soil, agencies concerned, 11. Formations of soil, 18. Freezing and thawing of soil, effect on structure, 40. Frost, effect on rock disintegration, 12. Gases, diffusion of, 144. effect on rock disintegration, 14. Germs, injurious to crops, 125. in soil, kinds of, 125. not directly injurious to crops, 126. Glacial soils, composition of, 26. described, 25. distribution of, 26. formation of, 25. Glaciers, effect on rock disintegra- tion, 13. Grains, fertilizers for, 207. Granite, losses during soil formation, 15. Grasses, fertilizers for, 208. Gravitational water, 67. Green manures, crops used for, 238. effect on soil acidity, 115. handling, 240. materials supplied by, 236. nature of, 235. protective action of, 235. when to use, 235. Guano, 165. Gypsum, plant-food material in, 7. use on land, 192. Heat and cold, effect on rock disin- tegration, 12. Heat of soil, sources of, 149. "Heavy" soil, and absolute specific gravity, 35. "Heavy" soil, and apparent specific gravity, 38. Hematite, plant-food material in, 7. Hygroscopic water, 61. Ice, effect on rock disintegration, 13. Igneous rocks, 5. Inoculation of soil for legumes, 138. Iron, proportion in earth's crust, 4. Irrigation for removal of alkali, 120. Lacustrine soils, described, 25. formation of, 25. Law of diminishing returns, 215. Legumes, fertilizers for, 208. Leguminous plants as nitrogen fixers, 137. "Light" soil, and absolute specific gravity, 35. and apparent specific gravity, 38. Lime, absorption by soils, 188. as a soil amendment, 187. caustic vs. ground limestone, 191. demonstration of flocculation by, 194.. effect on bacterial action, 189. effect on plant diseases, 190. effect on tilth, 189. fineness of grinding limestone, 191. forms of, 189. in relation to structure, 42. liberation of plant-food materials, 190. magnesium, 190. proportion in earth's crust, 4. requirements of soils, 188. tests for, 193. Limestone, effect of fineness of grind- ing, 191. ground vs. caustic lime, 191. losses during soil formation, 15. Limiting factors in plant growth, 215. Loess, composition, 27. distribution, 26. Magnesia, proportion in earth's crust, 4. Manure, cow, partial composition of, 222. effect of food on composition of, 224. 252 INDEX Manure, farm, 221. farm, agricultural evaluation of, 226. farm, an unbalanced fertilizer, 223. farm, application to land, 231. farm, chemical composition of, 222. farm, commercial evaluation of, 225. farm, covered barnyard for, 230. farm, deterioration of, 226. farm, experiments with, 233. farm, fermentations of, 227. farm, leaching of, 227. farm, methods of handling, 230. farm, place in crop rotation, 231. farm, protected more effective, 228. farm, reinforcing, 229. farm, solid and liquid, 221. green, crops used for, 238. green, materials supplied by, 236. green, handling, 240. green, nature of, 235. green, protective action, 235. green, when to use, 239. horse, partial composition of, 222. quantities voided by animals, 224. sheep, partial composition of, 222. swine, partial composition of, 222. value from different animals, 225. Marine soils, composition of, 24. described, 24. distribution of, 24. formation of, 24. Mechanical analysis of soil, 31. determination of class from, 34. method for, 46. of some typical soils, 32. relation of crops to, 32. size of separates, 32. Mechanical composition of various soil classes, 34. Metamorphic rocks, 5. Minerals, from which rocks are formed, 6. soil-forming, laboratory exercise, 8. plant-food materials in, 7. relation to soil, 6. Moisture, see water. Muck, origin, 21. relation to lime and potash, 22. Mulch, depths of, 75. Mulch, effectiveness of, 75. frequency of stirring, 74. of soil, nature and use, 74. Mulches, for moisture control, 74. test for conservation of water by, 87. Nitrate formation, depths of occur- rence, 135. effect of aeration on, 132. effect of lime on, 189. effect of sod on, 134. effect of temperature on, 133. Nitrate of soda, effect on soils, 159. sources and composition, 157. Nitrates, as plant-food material, 156. crops markedly benefited by, 158. loss in drainage water, 135. test for, in soil, 140. Nitrification, 132. Nitrogen, animal products contain- ing, 163. availability in fertilizers, 166. effects on plant growth, 165. fixation, nature of, 136. fixation by free living germs, 139. fixation by plants, 137. forms in fertilizers, 157. forms in which used by plants, 156. in fertilizers, 155-170. in soils, quantities of different forms, 155. organic, direct utilization by plants, 156. organic, fertilizers containing, 162. vegetable products containing, 163. Nodules, examination for, 142. on leguminous plants, 137. Orchards, fertilizers for, 209. Organic matter, and drainage, 53. and formation of acids, 55. and nitrogen, 54. and plant-food material, 54. and soil color, 53. and soil organisms, 54. benefits of, 52. effect on structure, 41. effect on availability of plant nu- trients, 102. estimation of, 58. INDEX 253 Organic matter, examination of soil for, 58. extraction of, 59. influence on rate of percolation, 59. influence on water held by soils, 60. injurious effect, 55. in soil, description, 51. in soil management, 55. kinds of, 51. porosity of, 53. sources of, 57. Oxygen, proportion in earth's crust, 4. Packing, subsurface, 78. Particles of soil, examination, 46. number per gram, 30. relative sizes, 31. shape of, 30. space occupied by, 30. Peat, origin, 21. Percolation, test for rate of, 86. Plant constituents, obtained from air or water, 3. obtained from soil, 3. Plant-food materials, available and unavailable, 94. essential to growth, 3. absorption by plants, 105. in apatite, 7. in calcite, 7. in drainage water, 102. in dolomite, 7. in farm manure, 222. in green manures, 236. in gypsum, 7. in hematite, 7. in liquid excreta, 222. in minerals, 7. in soils, 90. in solid excreta, 222. laboratory exercise, 9. liberation by lime, 190. movement of, 93. obtained from air or water, 3. obtained from soil, 3. possible exhaustion, 109. proportion in soils, 93. quantities in earth's crust, 4. removed by crops, 108. total supply in soils, 92. variations in soils, 90. Plan* growth, conditions of, labora- tory exercise, 9. Plant nutrients, laboratory exercise, 9. Plant roots, aid in solution of soil constituents, 106. solvent action, 107. Plants, effect on rock disintegration, 14. substances essential to growth, 3. uses of water by, 2. Phosphate, bone, 171. mineral, 171. Phosphoric acid, effect on plant growth, 175. Phosphoric acid, plants benefited by, 176. proportion in earth's crust, 4. reverted, 173. Phosphoric acid fertilizers, 171. availability of, 174. Pore space, its determination, 49. relation to structure, 37. Potash, effect on plant growth, 181. proportion in earth's crust, 4. Potash fertilizers, sources, 179. wood ashes, 180. Province, the soil, in soil survey, 44. Quartz, substance of which composed, 7. Residual soils, composition, 20. described, 18. distribution of, 20. loss during formation, 19. Rock, changes in soil formation, 15. disintegration by heat and cold, 12. disintegration, effect of gases on, 14. disintegration, effect of glaciers on, 13. disintegration, effect of ice on, 13. disintegration, effect of plants on, 14. erosion by wind, 14. expansion by heat, 12. relation to soil, 15. Rocks, from which soil has been formed, 5. igneous, 5. 254 INDEX Rocks, losses during soil formation, 15. metamorphic, 5. sedimentary, 5. soil-forming, laboratory exercise, 9. Rolling land, 78. Root crops, fertilizers for, 209. Root systems of different crops, 243. Roots of plants, effect on structure, 41. Rotation of crops, 242. and soil productiveness, 242. management of, 246. nutrients removed by, 243. Sedentary soil, 18. Sedimentary rocks, 5. Separates of soil, 32. chemical composition of, 36. examination, 46. properties of, 35. Series, the soil, in soil survey, 44. Soil, as a mechanical support for plants, 1. as a reservoir for water, 2. as a source of plant-food material, 2. changes during formation from rock, 15. Soil class, in classification for surveys, 44. method lor its determination, 47. Soil formation, agencies concerned, 11. and transportation, laboratory exercise, 17. Soil formations, 1, 18. Soil-forming minerals, laboratory exercise, 8. Soil-forming rocks, laboratory exer- cise, 9. Soil mulch, nature and use, 74. Soil province, in classification for surveys, 44. Soil, relation to rock, 15. Soil series, in classification for sur- veys, 44. Soil survey, described, 43. classification of soil for, 43. information furnished by, 44. Soil type, in classification for surveys, 44. Soils, residual, 18. sedentary, 18. transported, 18. Specific gravity, apparent, its deter, mination, 48. of soil, apparent, 38. of soil particles, absolute, 35. of soil particles, apparent, 38. Structure, of soil, as affected by freez- ing and thawing, 40. as affected by lime, 42. as affected by organic matter, 41. as affected by plant roots and animals, 41. as affected by tillage, 42. as affected by wetting and drying, 40. conditions that affect, 39. granular or crumbly, 37. defined, 37. relation to pore space, 37. relation to texture, 39. relation to tilth, 39. operations that affect, 39. separate grain, 37. Subsurface packing, 78. Sulfate of ammonia, action when applied to soils, 160. composition, 160. sources, 159. Sulfur, as a fertilizer, 182. contained in crops, 182. contained in drainage water, 183. contained in fertilizers, 184. contained in soils, 183. proportion in earth's crust, 4. Temperature, control of, 151. demonstration of effect of slope on , 154. factors that modify, 150. of soil and atmosphere, 149. of soils, relation to plant growth, 148. Texture, of soil, described, 30. relation to crops, 32. relation to structure, 39. Tile, concrete, 81. drains, 81. laying, 83. Tillage in relation to structure, 42. INDEX 255 Tilth, as affected by lime, 189. in relation to drainage, 79. relation to structure, 39. Toxic substances and crop rotation, 246. Transpiration, as affected by soil moisture, 69. by different crops, 69. conditions affecting, 70. ratio, 69. relation to soil fertility, 70. test for loss by, 88. Transported soil, 18. Type, the soil, in soil survey, 44. Vegetables, fertilizers for, 209. Water, as a soil transporting agent, 13. capillary, capacity of soils, 63. capillary, definition, 62. capillary, effect of structure on movement of, 65. capillary, effect of texture on movement of, 65. capillary, height of column and movement, 66. capillary movement and plant re- quirement, 71. capillary, movement of, 64. capillary, properties of, 63. carrying power for rock debris, 13. control of soil content, 72. effect on rock disintegration, 12. evaporation from soil, 73. Water, expansive power in freezing, 12. forms in soils, 61. gravitational, definition, 62. gravitational, movement, 67. gravitational, properties of, 66. hygroscopic, definition, 61. hygroscopic, properties of, 62. in soil, determination of per cent, 85. optimum content for plant growth, 71. percolation through soil, 73. quantity required to mature a crop, 70. relation to plants, 67. - requirements of plants, 68. run-off, 72. solvent action on rock, 12. test for capacity of soil for, 87. test for capillary movement, 86. test for conservation by mulch, 87. test for loss by transpiration, 88. test for rate of percolation, 86. uses by plants, 2. ways in which useful to plants, 68. Water-soluble matter in soil, 96. test for, 111. Water table, 67. Weeds that flourish on acid soils, 115. Wetting and drying soil, affect on structure, 40. Wind, action in transporting soil, 14. erosive action on rocks, 14. Windbreaks, to decrease evaporation, 78. Printed in the United States of America. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS mmmm NOV 131940 — mv-±^m [N0V15 1941 -g#*et^- ?<>1 * D LD 21-l00m-8,'34 YB 51414 y 454794 UNIVERSITY OF CALIFORNIA LIBRARY