UNITED STATES OF AMERICA. THE CHEMISTRY SOILS AND FERTILIZERS BY HARRY SNYDER, B.S Professor of Agricultural Chemistry, University of Minnesota, and Chemist of the Minnesota Agricultural Experiment Station. EASTON, PA.: THE CHEMICAL PUBLISHING COMPANY. 1899. (All rights reserved.) a) 38465 COPYRIGHT, 1£99, BY EDWARD HART. TWO GOPIE ® NECEIVED. | cat a _. PREFACE For several years courses of instruction have been given at the University of Minnesota to classes of young men who intend to become farmers and who desire information that will be of assistance to them in their profession. In giving this instruction mimeo- graphed notes have been prepared, but the increase in the number of students and the volume of notes have necessitated the publication of this work. In its prep- aration, it has been the aim to give, in condensed form, the principles of chemistry which have a bearing upon the conservation of soil fertility and the economic use of manures. HARRY SNYDER. UNIVERSITY OF MINNESOTA, COLLEGE OF AGRICULTURE, ST. ANTHONY PARK, MINN. April 15, 1899. CONTENTS INTRODUCTION Early uses of manures and the explanation of their action by the alchemists ; Investigations prior to 1800; Work of De Saussure, Davy, Thaer, and Boussingault ; Liebig’s writings and their influ- ence ; Investigations of Lawes and Gilbert ; Contributions of other investigators; Agronomy. Pages I-9. CHAPTER I Physical Properties of Soils. — Chemical and physical properties of soils considered; Weight of soils; Size of soil particles; Clay; Sand; Silt; Form of soil particles; Number and arrangement of soil particles ; Mechanical analysis of soils. Soil types — Potato and truck soils; Fruit soils; Corn soils ; Medium grass and grain soils; Wheat soils. Relation of the soil to water ; Amount of water required for crops ; Bottom water ; Capillary water; Hydro- scopic water; Loss of water by percolation, evaporation, and transpiration ; Influence of cultivation upon the water supply of crops ; Capillary water and cultivation; Shallow surface cultiya- tion ; Cultivation after rains; Rolling; Sub-soiling; Fall plowing; Spring plowing; Mulching; Depth of plowing: Fertilizers and their influence upon moisture content of soils; Farm manures and soil moisture; Permeability of soils; Drainage; Relation of soils to heat ; Heat from chemical reactions within the soil; Heat and crop growth ; Color of soils ; Odor and taste of soils ; Relation of soils to electricity ; Importance of physical properties of the soil. Pages 9-48. CHAPTER II Geological Formation and Classification of Soils. — Geological study of soils; Formation of soils; Action of heat and cold ; Action of water; Glacial action; Chemical action of water; Ac- vi CONTENTS tion of air and gases; Action of vegetation and micro-organisms ; Distribution of soils; Sedentary and transported soils; Rocks and minerals from which soils are derived as quartz, feldspar, mica, hornblende, zeolites, granite, apatite, kaolin, limestone, gypsum ; Chemical composition of rocks. Pages 49-59. CHAPTER III Chemical Composition of Soils. — Elements combine to form minerals; Classification of elements; Combination of elements ; Forms in which elements are present in soils; Acid-forming ele- ments, silicon, double silicates, carbon, sulphur, chlorine, phos- phorus, nitrogen, oxygen, hydrogen; Base-forming elements, alu- minum, potassium, calcium, magnesium, sodium, iron; Classifica- tion of elements for plant-food purposes; Amount of plant food in different forms in various types of soils; How a soil analysis is made; Value of soil analysis; Interpretation of the results of soil analysis ; Use of dilute acids as solvents in soil analysis; Distribu- tion of plant food in the soil; Composition of typical soils; ‘“ Alkali’? soils and their improvement; Organic compounds of soil; Sources ; Classification ; Humus; Humates ; Humification ; Humates produced by ‘different kinds of organic matter; Value of humates as plant food, amount of plant food in humic forms ; Loss of humus by forest fires, by prairie fires, by cultivation ; Humic acid ; Soils in need of humus; Soils not in need of humus; Composition of humus from old and new soils ; Influence of different methods of farming upon humus. Pages 60-IoT. CHAPTER IV Nitrogen of the Soil and Air, Nitrification and Nitrogenous Ma- nures. —Importance of nitrogen as plant food; Atmospheric nitrogen as a source of plant food. Experiments of Boussingault, Ville, and Lawes and Gilbert ; Result of field trials ; Experiments of Hellriegel and Wilfarth and recent investigators ; Composition of root nodules; Amount of nitrogen returned to soil by leguminous crops and importance to agriculture ; Nitrogenous compounds of the soil; Origin ; Organic nitrogen ; Amount of nitrogen in soils ; Removed in crops; Nitrates and nitrites; Ammonium compounds ; : CONTENTS Vil Ammonia in rain and drain waters; Ratio of nitrogen to carbon in the soil; Losses of nitrogen from soils ; Gains of nitrogen to soils; Nitrification ; Former views regarding ; Workings of an organism ; Conditions necessary for nitrification; Influence of cultivation upon these conditions; Nitrous acid organisms, ammonia-produ- cing organisms, denitrification, number and kind of organisms in soils ; Inoculation of soils with organisms ; Chemical products pro- duced by organisms; Losses of nitrogen by fallowing rich prairie lands; Deep and shallow plowing and nitrification ; Spring and fall plowing and nitrification; Nitrogenous manures; Sources ; Dried blood, tankage, flesh meal, fish scrap, seed residue, and uses of each ; Leather, wool waste, and hair; Peat and muck; Legumi- nous crops as nitrogenous fertilizers ; Sodium nitrate, ammonium salts ; Cost and value of nitrogenous fertilizers. Pages 102-137. CHAPTER V Fixation. — Fixation a chemical change, examples of; Due to zeolites; Humus and fixation ; Other compounds of soil cause fixa- tion ; Soils possess different powers of fixation ; Nitrates do not undergo fixation ; Fixation of phosphates; Fixation a desirable property of soils ; Fixation and the action of manures. Pages 138- 140. CHAPTER VI Farm Manures. — Variable composition of farm manures; Factors which influence composition of manures ; Absorbents; Relation of food consumed to manures produced ; Bulky and concentrated foods ; Course of the nitrogen of the food during digestion ; Com- position of liquid and solid excrements ; Manurial value of foods ; Commercial valuation of manure; Influence of age and kind of animal; Manure from young and old animals; Cow manure; Horse manure ; Sheep manure ; Hog manure ; Hen manure ; Mix- ing manures ; Volatile products from manure ; Human excrements . Preservation of manures; Leaching; Losses by fermentation ; Different kinds of fermentation ; Water necessary for fermenta- tion ; Composting manures ; Uses of preservatives ; Manure pro- duced in sheds ; Use of manures ; Direct hauling to field; Coarse manures may be injurious; Manuring pasture land ; Small Vill CONTENTS piles of manure in fields objectionable ; Rate of application ; Most suitable crops to apply to; Comparative value of manure and food ; Comparative value of good and poor manure ; Summary of ways in which manures may be beneficial. Pages I41-I7I. CHAPTER VII Phosphate Fertilizers. — Importance of phosphorus as plant food ; Amount of phosphoric acid in soils, amount removed in crops; Source of soil phosphoric acid ; Commercial forms of phosphoric acid ; Phosphate rock ; Calcium phosphates ; Reverted phosphoric acid ; Available phosphoric acid ; Manufacture of phosphate fertil- izers, acid phosphates, superphosphates; Commercial value of phosphoric acid ; Basic slag phosphates ; Guano ; Bones ; Steamed bone ; Dissolved bone; Bone black ; Use of phosphate fertilizers ; How to keep the phosphoric acid of the soil available. Pages 172- 185. CHAPTER VIII Potash Fertilizers. — Potassium an essential element ; Amount of potash removed in crops ; Amount in soils ; Source of soil potash ; Commercial forms of potash; Stassfurt salts, occurrence of; Kainit ; Sulphate of potash ; Other Stassfurt salts ; Wood ashes, composition of ; Amount of ash in different kinds of wood ; Action of ashes on soils; Ieached ashes; The alkalinity of ashes; Coal ashes; Miscellaneous ashes ; Commercial value of potash ; Use of potash fertilizers; Joint use of potash and lime. Pages 186-195. CHAPTER IX Lime and Miscellaneous Fertilizers. — Calcium an essential ele- ment; Amount of lime removed in crops; Amount of lime in soils; Different kinds of lime fertilizers; Their physical and chemical action; Action of lime upon organic matter and correcting acidity of soils ; Lime liberates potash ; Aids nitrification ; Action of land plaster on some ‘‘alkali’’? soils; Quicklime and slaked lime ; Marl; Physical action of lime; Judicious use of lime ; Miscel- laneous fertilizers; Salt and its action on the soil; Magnesium salts; Soot; Sea-weed ; Strand plants; Wool washings. Pages 196-204. CONTENTS 1X CHAPTER X. Commercial Fertilizers. — History of development of industry ; Complete fertilizers and amendments; Variable composition of commercial fertilizers ; Preparation of fertilizers; Inert forms of matter in fertilizers; Inspection of fertilizers; Mechanical condition of fertilizers; Forms of nitrogen, phosphoric acid, and potash in commercial fertilizers; Misleading statements on fertilizer bags ; Estimating the value of a fertilizer; Home mixing; Fertilizers and tillage ; Abuse of commercial fertilizers; Proper use of ; Field tests ; General principles ; Preliminary experiments ; Verifying results ; Deficiency of one element ; Deficiency of two elements; Will it pay to use fertilizers? Amount to use per acre ; Influence of excessive applications ; Fertilizing special crops ; Com- mercial fertilizers and farm manures. Pages 205-224. CHAPTER XI. Food Requirements of Crops. — Amount of fertility removed by crops ; Assimilative powers of crops compared; Way in which plants obtain their food ; Cereal crops ; General food requirements ; Wheat; Barley ; Oats; Corn; Miscellaneous crops; Flax ; Pota- toes ; Sugar-beets; Roots; Turnips; Rape ; Buckwheat; Cotton ; Hops ; Hay and grass crops ; Leguminous crops. Pages 225-237. CHAPTER XII. Rotation of Crops. — Object of rotating crops ; Principles involved in crop rotation ; Deep and shallow rooted crops; Humus-consu- ming and humus-producing crops ; Crop residues ; Nitrogen-consu- ming and nitrogen-producing crops; Rotation and mechanical condition of soil ; Economic use of soil water; Rotation and farm labor ; Economic use of manures ; Salable crops; Rotations advan- tageous in other ways; Long- and short-course rotations ; Problems in rotations ; Conservation of fertility ; Necessity of manures ; Uses of crops ; Losses of fertility with different methods of farming ; Problems on income and outgo of fertility from farm. Pages 238- 254. References; Experiments; Review Questions; Corrections. Pages 255-272. THE CHEMISTRY OF POLS AND PER TILIZERS INTRODUCTION Prior to 1800 but little was known of the sources and importance of plant food. Manures had been used from the earliest times, and their value was rec- ognized, but the fundamental principles underlying their use were not understood. It was believed that they acted in some mysterious way. ‘The alchemists had advanced various views regarding their action ; one was that the so-called “spirits” left the decaying manure and entered the plant, producing more vigor- ous growth. As evidence, the worthless character of leached manure was cited. It was believed that the spirits had left such manure. The terms ‘spirits of hartshorn’, ‘spirits of niter’, ‘spirits of turpentine’, and many others reflect these ideas regarding the compo- sition of matter. Before the composition of plant and animal bodies was established, it was believed that one substance, like copper, could be changed to another substance, as gold. Plants were supposed to be water transmuted 2 SOELS AND FERTILIZERS in some mysterious way directly into plant tissue. Van Helmont, in the seventeenth century, attempted to prove this. ‘He took a large earthen vessel and filled it with 200 pounds of dried earth. In it he planted a willow weighing five pounds, which he duly watered with rain and distilled water. After five years he pulled up the willow and it now weighed one hundred and sixty-nine pounds and three ounces.”? He con- cluded that 164 pounds of roots, bark, leaves, and branches had been produced by the direct transmuta- tion of the water. It is evident from the preceding example that any- thing like an adequate idea of the growth and compo- sition of plant bodies could not be gained until the composition of air and water were established. The discovery of oxygen by Priestley in 1774, of the composition of water by Cavendish in 1781, and of the réle which carbon dioxide plays in plant and animal hfe by DeSaussure and others in 1800, form the nucleus of our present knowledge re- garding the sources of matter stored up in plants. It was from 1760 to 1800 that alchemy lost its grip and the way was prepared for the development of modern chemistry. The work of DeSaussure, entitled: “‘Recherches sur la Vegetation,” published in 1804, was the first systematic work showing the sources of the com- pounds stored up in plant bodies. He demonstrated, INTRODUCTION 3 quantitatively, that the increase in the amount of carbon, hydrogen, and oxygen, when plants were ex- posed to sunlight, was at the expense of the carbon dioxide of the air, and of the water. of the: soil. “He also maintained that the mineral elements derived from the soil were essential for plant growth, and gave the results of the analyses of many plant ashes. He believed that the nitrogen of the soil was the main source of the nitrogen found in plants. These views have since been verified by many investigators, and are substantially those held at the present time re- garding the fundamental principles of plant growth. They were not, however, accepted as conclusive at the time, and it was not until nearly a half century later, when Boussingault, Liebig, and others repeated the investigations of DeSaussure, that they were finally accepted by chemists and botanists. From the time of DeSaussure to 1835, scientific experiments relating to plant growth were not actively prosecuted, but the scientific facts which had accumu- lated were studied and attempts were made to apply the results to actual practice. Among the first to see the relation between chemistry and agriculture was pict Humphry Davy. In 1813 he: published ‘his ‘Essentials of Agricultural Chemistry”, which treated of the composition of air, soil, manures, plants, and _ of the influence of light and heat upon plant growth. About this same period, Thaer published an important 4 SOILS AND FERTILIZERS work entitled “ Principes Raisonnes d’ Agriculture”. Thaer believed that humus determined the fertility of the soil, that plants obtained their food mainly from humus, and that the carbon compounds of plants were produced from the organic carbon compounds of the soil. This gave rise to the so-called humus theory, which was later shown to be an inaccurate idea re- garding the source of plant food. The writings of Thaer were of a most practical nature, and they did much to stimulate later investigations. About 1830 there was a renewed interest in scientific investigations relating to agriculture. At this time Boussingault became actively engaged in agricul- tural research. He wasthe first to establish a chemical laboratory upon a farm and to make practical inves- tigations in connection with agriculture. This marks the establishment of the first agricultural experi- ment station. Boussingault’s work upon the as- similation of the free nitrogen of the air is reviewed in Chapter IV. His study of the rotation of crops was a valuable contribution to agricultural science. He discovered many important facts relating to the chemical characteristics of foods, and was the first to make a comparative study of the amount of nitrogen in different kinds of foods and to determine the value of foods on the basis of the nitrogen content. His study of the production of saltpeter did much to pre- pare the way for later work on nitrification. The INTRODUCTION 5 work of Boussingault covered a variety of subjects re- lating to plant growth. He repeated and verified much of the earlier work of DeSaussure, and also secured many additional facts relating to the chemis- try of crop growth. As to the source of nitrogen in erops, ue states that: ““The soil furnishes the crops with mineral alkaline substances, provides them with nitrogen, by ammonia and by nitrates, which are formed in the soil at the expense of the nitrogenous matters contained in diluvium, which is the basis of vegetable earth; compounds in which nitrogen exists in stable combination, only becoming fertilizing by the effect of time.” As for the absorption of the gas- eous nitrogen of the air by vegetable earth, he says: “Tam not acquainted with a single irreproachable ob- servation that establishes it; not only does the earth not absorb gaseous nitrogen, but it gives it off.’’? The investigations of DeSaussure and Boussingault, and the writings of Davy, Thaer, Sprengel, and Schtb- ler prepared the way for the work and writings of Liebig. In 1840 he published ‘Organic Chemistry in its Applications to Agriculture and Physiology”. Liebig’s agricultural investigations were preceded by many valuable discoveries in organic chemistry, which he applied directly in his interpretations of agricul- tural problems. His writings were of a forcible char- acter and were extremely argumentative. They pro- voked, as he intended, vigorous discussions upon 6 SOILS AND FERTILIZERS agricultural problems. He assailed the humus theory of Thaer, and showed that humus was not an adequate source of the plant’s carbon. In the first edition of his work he showed that farms from which certain products were sold naturally became less productive, because of the loss of nitrogen. In a second edition he considered that the combined nitrogen of the air was sufficient for crop production. He overestimated the amount of ammonia in the air, and underestimated. the value of the nitrogen in soils and manures. A study of the composition of plant-ashes led him to propose the mineral theory of plant nutrition. De- saussure had shown that plants contained certain mineral elements, but he did not emphasize their 1m- portance as plant food. Ljebig’s writings on the com- position of plant-ash, and the importance of supplying crops with mineral food led to the commercial prepara- tion of manures, which in later years has developed into the commercial fertilizer industry. The work of Liebig was not conducted in connection with field experiments. It had, however, a most stimulating influence upon investigations in agricultural chemistry, and to him we owe, in a great degree, the summari- zing of previous disconnected work and the mapping out of valuable lines for future investigations. Liebig’s enthusiasm for agricultural investigations may be judged from the following extract: ‘I shall be happy if I succeed in attracting the attention of men INTRODUCTION 7 of science to subjects which so well merit to engage their talents and energies. Perfect agriculture ts the true foundation of trade and industry ,; tt ts the foun- dation of the riches of states. But a rational system of agriculture cannot be formed without the applica- tion of scientific principles; for such a system must be based on an exact acquaintance with the means of nutrition of vegetables, and with the influence of soils, and actions of manures upon them. This knowledge we must seek from chemistry, which teaches the mode of investigating the composition and of the study of the character of the different substances from which plants derive their nourishment.” 3 Soon after Liebig’s first work appeared the investi- gations at Rothamsted by Sir J. B. Lawes were under- taken. The most extensive systematic work in both field experiments and laboratory investigations which have ever been conducted have been carried on by Lawes and Gilbert at Rothamsted, Eng. Dr. Gilbert had previously been a pupil of Liebig, and his associa- tion with Sir J. B. Lawes marked the establishment of the second experiment station. Many of the Roth- amsted experiments have been continued since 1844, and results of the greatest value to agriculture have been obtained. The investigations on the non-assimi- lation of the atmospheric nitrogen by crops, published in 1861, were accepted as conclusive evidence upon this much-vexed question. The work on manures, 8 SOILS AND FERTILIZERS nitrification, the nitrogen supply of crops, and on the increase and decrease of the nitrogen of the soil when different crops are produced, has had a most important bearing upon maintaining the fertility of soils. “The general plan of the field experiments has been to grow some of the most important crops of rotation, each separately, for many years in succession on the same land, without manure, with farmyard manure, and with a great variety of chemical manures, the same kind of manure being, as a rule, applied year after year on the same plot. Experiments with different manures on the mixed herbage of permanent grass land, on the effects of fallow, and on the actual course of rotation without manure, and with different manures have likewise been made.”’ 4 In addition to Davy, Thaer, DeSaussure, Bous- singault, Liebig, and Lawes and Gilbert, a great many others have contributed to our knowledge of the chemistry of soils. The work of Pasteur; while it did not directly relate to soils, indirectly had a great influence upon soil investigations. His researches upon fermentation made it possible for Schlosing to prove that nitrification was the result of the workings of living organisms which have since been isolated and studied by Warington and Winogradsky. Many of the more recent investigations relating to the chemistry of soils are reviewed in the following chapters. Our knowledge regarding the chemistry, INTRODUCTION 9 physics, geology, and bacteriology of soils is at the present time far from complete, but many facts have been discovered which are of the greatest value to the practical farmer. Of late years investigations relating to the chemistry of soils and fertilizers have become so extensive that the term ‘agronomy’ has been used to designate that part of agricultural chemistry. In soil investigations it has frequently happened, owing to imperfect interpretation of results and to the presence of many modifying influences, that the results and conclusions of one investigator appear to be directly contradictory to those of another. ‘This is well illustrated in the investigations relating to the assimilation of the free atmospheric nitrogen, in which seemingly opposite conclusions now form a complete theory. CHAPTER PHYSICAL PROPERTIES OF SOILS 1. Soil. — Soil is disintegrated and pulverized rock mixed with animal and vegetable matter. The rock particles are of different kinds and sizes, and are in various stages of decomposition. If two soils are formed from the same kind of rock and differ only in the size of ‘the particles, the difference is imerelee physical one. If, however, one soil is formed largely from sandstone, while the other is formed from lime- stone, the difference is both physical and chemical. Hence it is that soils differ both physically and chem- ically. It is difficult to consider the physical proper- ties of a soil without also considering the chemical properties. The chemical and physical properties of a soil, when jointly considered, determine largely its agricultural value. 2. Physical Properties Defined. — The physical properties of a soil are: TA, Wieigint: 2. Color. Size, form, and arrangement of the soil particles. The relation of the soil to water, heat, and cold. The relation of the soil to electricity. Odor and taste. Obs Me acter PHYSICAL PROPERTIES OF SOILS ae 3. Weight.— Soils differ in weight according to the composition and size of the particles. Fine sandy soils weigh heaviest, while peaty soils are lightest in weight. But when saturated with water, a cubic foot of peaty soil weighs more than a cubic foot of sandy soil. Clay soils weigh less per cubic foot than sandy soils. The larger the amount of organic matter in a soil the less the weight. Pasture land, for exam- ple, weighs less per cubic foot than arable land. Weight is an important property to consider when the total amounts of plant food in two soils are compared. For example, a peaty soil containing 1 per ‘cent,’ of nitrogen and weighing 30 pounds per cubic foot has less total nitrogen than a soil containing 0.40 per cent. of nitrogen and weighing 80 pounds per cubic foot. (1) The weight of soils per cubic foot is approxi- mately as follows :5 Pounds. laps Oilies seeie eee opie et Oa ciate ban ce 70. to 75 BMS SAMMY SOtlwcsisain'. sis os ss, 25 So Sse acter e ees 95 to 110 ES SY2 FEEVIS Co Ria ai ce ORD ae 75 to go EAN SOND salsone Naeio rs Acie: ys aes ee See 25 to 60 MRA RAIL GON om a0 mgd c din lao we ¥ ole toi Se 75 Unienltivated praine soilsc. cc00 se ddes wee ne Bs Figures for the weight per cubic foot or specific gravity of soils are on the basis of the dry soil. When taken from the field the weight per cubic foot varies with the amount of water present. (2) The volume of a soil varies with the conditions 12 SOILS AND FERTILIZERS ® to which it has been subjected. Usually about 50 per cent. of the volume of a soil is air space. A cubic foot of soil from a field which has been well cultivated weighs less than from a field where the soil has been compacted. Hence it is that soils have both a real and an apparent specific gravity. The apparent spe- cific gravity of a soil is sometimes less than half of the real specific gravity. The specific gravity of different soils as given by Shéen is as follows :° Specific gravity. lay Sill ra ereterpa tere eicha = ated tistd atavarwis cela ae eda tin eens 2.65 Satay SSO ree Woeate niche aterm te aren Veloce, woe steer 2.67 Ete SOU ire sores eal Ore Oe bis SEES bb wea eee 2.91 PEMAIS SOUL wvortioGe ce hire Paws we ne eee Toe 25 4. Size of the Soil Particles. — The size of the soil particles varies from those hardly distinguishable with the microscope to coarse rock fragments. ‘The size of the particles determines the character of the soil as sandy, clay, orloam. The term ‘fine earth’ is used to designate that part of the soil which passes through a sieve with holes 0.5 mm. (0.02 inch) in diameter. Coarse sand particles and rock fragments which fail to pass through the sieve are called skeleton. The amount of fine earth and skeleton is variable. Arable soils, in general, contain from 5 to 20 per cent. of skeleton. The fine earth is composed of six grades of soil particles. The names and sizes are as follows: PHYSICAL PROPERTIES OF SOILS 13 Millimeters. Inches. Medium sand...... 0.5 t00.25 0.02 too.oI Finesand.........- 0.25 too.I 0.01 to 0.004 Very fine sand...--. O.I to 0.05 0.004 to 0.002 SoG Jen steex Ser wins Chae lars 0.05 to0o.oI 0.002 to 0.0004 Fine silt........... 0.01 tO 0.005 0.0004 to 0.0002 Clay --..+.e-ee eee 0.005 and less 0.0002 and less Soils are mechanical mixtures of various sized par- ticles. In most soils there is a predominance of one grade, as clay in heavy clay soils, and medium sand in sandy soils. No soil, however, is composed entirely of one grade. The clay particles are exceedingly small; it would take 5000 of the larger ones, if laid in a line with the edges touching, to measure an inch, while it would take but 50 of the larger medium sand particles to measure an inch. 5. Clay. — The term clay used physically denotes those soil particles less than 0.005 mm. (0.0002 inch) in diameter, without regard to chemical composition. As used in a physical sense clay may be silica, feld- spar, limestone, mica, kaolin, or any other rock or mineral which has been pulverized until the particles are less than 0.005 mm. in diameter. Chemically, however, the term clay is restricted to one material, as will be explained in another part of the work. The physical properties of clay are well known. It has the power of absorbing a iarge amount of water, and will remain suspended in water for a long time. The roiled appearance of many streams. and lakes is I4 SOILS AND FERTILIZERS due to the presence of suspended clay particles. The amount in agricultural soils may range from 3 to 50 per cent. Clay soils, if worked when too wet, become puddled; then percolation cannot take place, and the accumulated surface water must be removed by the slow process of evaporation. 6. Silt.—The silt particles are, in size, between sand and clay. Many of the western prairie subsoils, clay- like in nature, are composed mainly of silt. The silt imparts characteristics intermediate to sand and clay. While a clay soil is nearly impervious to water, and when wet works with difficulty, a silt soil is more permeable, but is not as open and porous as a sandy soil. When a soil containing large amounts of clay and silt is treated with water, the silt settles slowly, while the clay remains in suspension. The fine de- posit in ditches and drains, where the water moves slowly, 1s mainly silt. 7. Sand. — There are three grades of sand. The characteristics, as permeability and non-cohesion of particles, are so well known that they do not require discussion. A soil composed entirely of sand would have little, if any, agricultural value. Sandy soils usually contain from 5 to 15 per cent. of clay and silt. The relative sizes of sand, silt, and clay are given in the illustration. 8. Form of Soil Particles. — Soil particles are ex- PHYSICAL PROPERTIES OF SOILS 15 tremely varied in form. When examined with the microscope they show the same diversity as 1s observed in larger stones. In some soils the particles are spher- ical, while in others they are angular. The shape Bio, t. Medimm Sand x 150;) Fig. 2. Fine Sand << 150. Fig. 3. Ver Pine sand, x 156. “Pic. 4. Silt X-325. Fig, 5: Fine Silt < 325. Big. 6. Clay < 325. of the particles is determined by the way in which the soil has been formed and also by the nature of the rock from which it was produced. The form and arrangement of the particles are 1m- portant factors to consider in dealing with the water 16 SOILS AND FERTILIZERS content of soils. In the wheat lands of the Red River Valley of the North, the particles are small and spherical, being formed largely from limestone rock, while the subsoil of the western prairie regions is composed largely of angular silt particles, which are intermingled with clay, forming a mass containing only aminimum of inter soilspaces. The silt particles being angular and imbedded in the clay, the soil has more the character of clay than of silt. While these two soils are unlike in physical composition, the form and arrangement of the particles give each nearly the same water-holding power. On account of a differ- ence in the form and arrangement of the soil particles two soils may have the same mechanical composition, and yet possess materially different physical proper- ties. In some soils to per cent. of clay is of more value agriculturally than in othersoils. Ten per cent. of clay associated with 60 or 70 per cent. of silt, makes a good grain soil, while ro per cent. of clay associated largely with sand makes a soil poorly suited to grain culture. The classification of the soil particles into sand, silt, and clay is purely an arbitrary one. Various authors use these terms in different ways, and when compar- ing soils, reported in different works, one may avoid confusion by omitting the names and noting only the sizes of the particles. A division.has recently been suggested by Hopkins’ in which the square root is PHYSICAL PROPERTIES OF SOILS ity | often taken as the constant ratio between the grades of soil particles. g. Number of Particles per Gram of Soil. — It has been estimated that a gram of soil contains from 2,000,000,000 to 20,000,000,000 soil particles ; soils which contain less than 1I,700,000,000 are unproduct- ive. The number of particles in a given volume of soil varies with their size and form. According to Whitney® the number of particles per gram of differ- ent soil types is as follows : Bathy trek. oiiee clave ane sistem sects oe 1 ,955,000,000* Truck and small fruit .... 6.0.05 000: -* 3,955,000,000 MRO DWACCE oicre kiereial aie werd Sci area pl aha aes tele reMale 6,786,000,000 Watt tains: ia t)-ce Sona tate fat enn topes Sctiareust teeta © 10, 228,000,000 (Grasse ane wihleatea chess loncteleve) ei clclenerecoterions's 14,735,000,000 NSATMICSUOINE.« ort c= Ssis oso e.e oa a. atohae plate oie) os 19,638,000,000 Assuming that the particles are all spheres, it 1s es- timated that in a cubic foot of soil a surface area of from two to three and one-half acres is presented to the action of the roots. 10. Methods Employed in Separating Soil Particles. —Sieves with circular holes 0.5, 0.25, and 0.1 mm. are employed for the purpose of separating the three coarser grades of sand. The sieve a, 0.5mm. size, 1s con- nected with the filtering flask c by means of the tube 6, and the flask is connected at point d@ with a suc- tion-pump. ‘Ten grams of soil, after treatment with * Figures below sixth place omitted and ciphers substituted. 18 SJILS AND FERTILIZERS boiling water, are placed in the sieve. Water is passed through until the washings are clear. All particles larger than 0.5 mm. remain in the sieve, and after dry- ing and igniting, are weighed. The contents of flask ¢, containing the particles less than 0.5 mm., are then passed through a sieve having holes 0.25 mm. in diameter. Finally a o.10 mm. diameter sieve is used. The fine sand and silt are separated by gravity. The fine sand with some silt and clay are read- ily deposited and the water containing the suspended clay is decanted into a second glass vessel. The residue is treated this operation is repeated until the micro- d scope shows the soil particles to be nearly all of one grade. Clay is obtained by evaporating an aliquot portion of the washings or by determining the Figs. Sando. total per cent. of the other grades of particles and the volatile matter and subtracting the sum from 100. This is the Osborne sedimentation method with modi- fications. Hilgard’s’®; elutriator, and the apparatus of Shoen-Mayer are also used for separating the soil particles. @) nti Mes Pigs 7: SOIL TYPES 11. Crop Growth and Physical Properties. —’The SOIL TYPES 19 preference of certain crops for particular kinds of soil, as wheat for a clay: subsoil, potatoes for a sandy soil, and corn for a silt soil, is due mainly to the peculiari- ties of the crop in requiring definite amounts of water, and a certain temperature for growth. These condi- tions are met by the soil being composed of various grades of particles which enable a certain amount of water to be retained, and the soil to properly respond to the influences of heat and cold. In considering soil types, it should be remembered that there are so many conditions influencing crop growth that the crop-producing power cannot always be determined by a mechanical analysis of the soil. . The following types have been found to hold true in a large number of cases under average conditions, but they do not represent what might be true of a case under special conditions. For example a sandy soil of good fer- tility in which the bottom water is only a few feet from the surface, may produce larger graine rops than a clay soil in which the bottom’water.is at a greater depth. In judging the character of. a soil, special conditions must always be taken into consideration. In discussing the following soil types, a normal supply of plant food and an average rainfall are assumed in all cases. | 12. Potato and Early Truck Soils. — The better types of potato soils are those which contain about 60 per cent. of medium sand, 20 to 25 percent. of silt, and 20 SOILS AND FERTILIZERS about 5 per cent. of clay. Soils of this nature when supplied with about 3 per cent. of organic matter will contain from 5 to 12 per cent. of water. The best conditions for crop growth exist when the soil con- tains from 5 to 7 per cent. of water. In a sandy soil vegetation may reduce the water to a much lower point than inaclay soil. On account of sandy soil giving up its water so readily to growing crops nearly all is available, while on heavy clay, crops show the want of water when the soil contains from 7 to 8 per cent., because the clay holds the water so tenaciously. When potatoes are grown on soils where there is an abnormal amount of water the crop is slow in matur- ing. For early truck purposes in northern latitudes, sandy soils are the most suitable because they warm up more readily, and the absence of an abnormal amount of water results in early maturity. Excellent crops of potatoes are grown on many of the silt soils of the west which have a materially different com- position from the type given. A soil may have all of the requisites physically for the production of good potato and truck crops, and still be unproductive on account of some peculiarity in chemical composition. 13. General Truck and Fruit Soils. — For fruit grow- ing and general truck purposes the soil should contain more clay and less sand than for early truck farming. Soils containing from 10 to 15 per cent. of clay and not more than 4o per cent. of sand are best suited for SOIL TYPES Zi growing small fruits. Such soils will retain from ro to 18 per cent. of water. There is a noticeable differ- ence as to the adaptability of different kinds of fruit to different soils. Some fruits thrive on clay land, provided the proper cultivation and treatment are given. There is as much diversity of soil, required for producing different fruit crops as for the production of different farm crops. Asarule, however, a silt soil is most capable of being adapted to the various con- ditions required by fruit crops. 14. Corn Soils. — The strongest types of corn soils are those which contain from 40 to 45 per cent. of medium and fine sand and about 15 per cent. of clay. Corn lands should contain about 15 per cent. of avail- able water. Heavy clays produce corn crops which mature later than those grown on soils not so close in texture. Many corn soils contain less sand and clay, but more silt than the figures given. If the soil contains a high per cent. of organic matter, good corn crops inay be produced where there is less than twelve per cent. of clay. Soils containing a high per cent. of sand are usually too deficient in available water to produce a good crop. On the other hand heavy clay soils are slow in warming up and are not suited to corn culture. The strongest types of corn soils have the proper mechanical composition for the production of good crops of sorghum, cotton, flax, and sugar-beets. How- 22 SOILS AND FERTILIZERS ever, the amount of available plant food required for each crop is not the same. The western prairie soils which produce most of the corn raised in the United States, are composed largely of silt. 15. Medium Grass and Grain Soils. — For the pro- duction of grass and grain a larger amount of water is required than for corn. The yield of both is de- termined largely by the amount of water which the soil contains. For.an average rainfall of about 30 inches, good grass and grain soils should contain about» 15 per cent..of clay and 60 percent, orems, Such a soil ordinarily holds from 18 to 20 per cent. of water. Many grass and grain soils have less silt and more clay. A soil composed of about 30 per cent. each of fine sand, silt, and clay, would also be suitable, mechanically, for general grain production. There are a number of different types of grass and grain soils, with different proportional amounts of sand, silt, and clay. Silt soils, however, form the larger part of the grain soils of the United States. 16. Wheat Soils. — For wheat production, soils of a closer texture are required than for general grain farming. There are three classes of wheat soils. The first (1 in Fig. 10) contains from 30 to 50 per cent. of clay particles, these being mostly disintegrated lime- stone. The soil of the Red River Valley of the North belongs to the first class of wheat-producing soils. The surface soil contains from 8 to 12 per cent. of veg- SOIL TYPES 23 etable matter and the subsoil about 25 per cent. of limestone in a very fine state of division. For the production of wheat the subsoil should contain 20 per cent. of water. A crop can, however, be produced with less water, but a smaller yield is obtained. v4 ogee! Vengeee Fig. 10. Soil types. The second type of wheat soil (2 in Fig. 10) con- tains less clay and more silt. Many prairie subsoils which produce good crops of wheat contain about 20 per cent. of sand, 50 per cent. of silt, and from 20 to 30 percent. of clay. Soils of this class when well stocked with moisture in the spring are capable of 24 SOILS AND FERTILIZERS producing good crops of wheat, but are not able to withstand drought so well as soils of the first class. To the third class of wheat soils (3 1n Fig. 10) belong those which are composed mainly of silt, containing usually 75 per cent., and from 10 to 15 percent. of clay. The high per cent. of fine silt gives the soil clay-like properties. Soils of this class are adapted to a great variety of crops. For the production of wheat on silt soils it is very essential that a good supply of organic matter be kept in the soil so as to bind together the soil particles. The special peculiarities of the different grain crops as to soil requirements will be considered in connection with the food requirements of crops. 17. Sandy, Clay, and Loam Soils. — In ordinary aorieultural literature. the term - ‘sandy, ‘elay, on ‘loam’ is used to designate the prevailing character of the soil. Sandy soils usually contain 90 per cent. or more of silica or chemically pure sand, “Tester light sandy soil is sometimes used to indicate that the soil is easily worked, while the term heavy clay means that the soil offers great resistance to cultiva- tion. Many soils which are clay-like in character are not composed very largely of clay. There are sub- soils in the western states which have clay-like char- acteristics but contain only about 15 per cent. of clay, the larger part of the soil being silt. A loam soil isa mixture of sand and clay; if clay predominates the soil is a clay loam, while if sand predominates it is a sandy loam. | RELATION OF THE SOIL TO WATER 18. Amount of Water Required by Crops. — Ex- periments have shown that it takes from 275 to 375 pounds of water to produce a pound of dry matter in a grain crop. In order to produce an average acre of wheat 350 tons of water are needed. The amount of water required for the production of an average acre of various crops is as follows :” Average amount. Minimum amount. Tons water. Tons water. GlOVe terse cioneusticnee Listeners oe 400 310 OEATOES wictoinle cies Greleceients « 4co 325 WWalite ites sdeteus descents lever oicronone.cacre 350 : 300 VATS? che te eh ete iia lo. ams eens 6090 The rainfall during the time of growth is frequently less than the amount of water required for the pro- duction of a crop. An average rainfall of 2 inches per month during the three months of crop growth would be equivalent to only 369 tons of water per acre, a variable part of which is lost by evaporation. Hence it is that the rainfall during an average grow- ing season is less than.the amount of water required, and in order to produce crops, the water stored up in the soil must be drawn upon to a considerable extent. Inasmuch as the soil’s reserve supply of water is such an important factor in crop production, it follows that 26 SOILS AND FERTILIZERS the capacity of the soil for storing up water and giving it up as needed is a matter to be considered, par- ticularly since the power of the soil for absorbing and retaining water may be influenced by cultivation and manuring. Before discussing the influence of cultivation upon the soil water, the forms in which it is present in the soil should be studied. Water is present in soils in three forms: (1) bottom water, (2) capillary water, and (3) hydroscopic water. 19. Bottom Water is water which stands in the soil at a general level, and fills all the spaces between the soil particles. Its distance from the surface can be told in a general way by the depth of surface wells. Bottom water is of service to growing crops when it is Fig. 11. Water films surrounding soil particles. at such a depth that it can be brought to the plant roots by capillarity, but when near the surface so that the roots are immersed, very poor conditions for crop growth exist. When the bottom water can be brought within reach of the roots by capillarity a crop has an almost inexhaustible supply. In many soils known as old lake bottoms such conditions exist. RELATION OF THE SOIL TO WATER 27, 20. Capillary Water.— The water held in the capillary spaces above the bottom water is known as the capillary water. The capillary spaces of the soil are the small spaces between the soil particles in which water is held by surface tension; that is, the force acting between the soil and the water is greater than the force of gravity. Ifa series of glass tubes of different diameters be placed in water it will be ob- served that in the smaller tubes water rises much higher than in the larger. The water rises in all of K eg Fig. 12. Comparative height to which water rises in glass tubes. the tubes until a point is reached where the force of gravity is equal to the force of surface-tension. In the smaller tubes surface-tension is greater than the force of gravity, and the water is drawn up into the tube. In the larger tubes the surface-tension is less and water is raised only a short distance. There are present in the soil many spaces which are capable of taking up water in the same way as the small glass tubes. The height to which water can be raised by 28 SOILS AND FERTILIZERS capillarity depends upon the size and arrangement of the soil particles. Water may be raised by capillarity to a height of several feet. Ordinarily, however, the capillary action of water is confined to a few feet. The arrangement of the soil particles influences greatly the capillary power of the soil. Usually from 30 to 60 per cent. of the bulk of a soil is air space: by compacting, the air spaces may be decreased; by stirring, the air spaces are increased. In some soils of a close texture an increase in air spaces results in an increase of capillary spaces and of water-holding capacity, while in other soils, as coarse sandy soils, increasing the air spaces decreases the capillary spaces and the water-holding capacity. The best conditions for crop production exist when the soil contains water to the extent of about 40 per cent. of its total capacity of saturation. 21. Hydroscopic Water. — By hydroscopic water is meant the water content of the soil atmosphere. The air which occupies the non-capillary spaces of the soil is charged with moisture in proportion to the water in the soil. Under normal conditions the soil atmos- phere is nearly saturated. When soils have exhausted their capillary water, the water in the soil atmosphere is correspondingly reduced. ‘The available supply in other forms being exhausted, the hydroscopic water cannot contribute to plant growth. 22. Loss of Water by Percolation.— Whenever a soil becomes saturated, percolation or a downward RELATIONS OF ©LHE SOLE TO WATER 29 movement of the water begins. The extent to which losses by percolation may occur depends upon the character of the soil’ and the amount of rainfall. When soils are covered with vegetation the losses by percolation are less than from barren fields. In all soils which have only a hmited number of capillary spaces and a large number of non-capillary spaces, the amount of water which can be held above the bottom water is small. From such soils the losses by perco- lation are greater than from soils which have a larger nuinber of capillary spaces, and a smaller number of non-capillary spaces. In coarse sandy soils many of the spaces are too large to be capillary. If all of the water which falls on some soils could be retained and not carried beyond the reach of crops by percolation, there would be an ample supply for agri- cultural purposes. To prevent losses by percolation, the texture of the soil may be changed by cultivation and by the use of manures. If the soil is of very fine texture, as a heavy clay, percolation is slow, and before the water has time to sink into the soil, evaporation begins; with good cultivation the water is able to penetrate to a depth beyond the immediate influence of evaporation. Compacting an open porous soil by rolling, checks rapid.percolation and prevents the water from being carried beyond the reach of plant roots. In order to prevent excessive losses by perco- lation, the treatment must be varied to suit the re- quirements of different soils. 30 SOILS AND FERTILIZERS ~ 23. Loss of Water by Evaporation. — The factors which influence evaporation are temperature, humidity, and rate of movement of the air. When the air con- tains but little moisture and is heated and moving rapidly, the most favorable conditions for evaporation exist. In semiarid regions the losses of water by evaporation are much greater than by percolation. The dry air comes in contact with the soil, the soil atmosphere gives up its water, and, unless checked by cultivation, the subsoil water is brought to the surface by capillarity and lost. In porous soils, a greater freedom of movement of the air is possible, which 1n- creases the rate of evaporation. When the surface of the soil is covered with a layer of finely pulverized earth, or with a mulch, excessive losses by evaporation cannot take place, because a material of different tex- ture 1s interposed between the soil and the air. 24. Loss of Water by Transpiration. — Losses of water may also occur from the leaves of plants by the process known as transpiration. Helriegel observed that during some years 100 pounds more water were required to produce a pound of dry matter than in other years, because of the difference in the amount of water lost by transpiration. The loss of water by evaporation can be controlled by cultivation, but the loss by transpiration can be only indirectly influ- enced. Hot dry winds may cause crops to wilt be- cause the water lost by transpiration exceeds the amount which the plant takes from the soil. INFLUENCE OF CULTIVATION 31 The three ways in which crops are deprived of water are by (1) percolation, (2) evaporation, and (3) transpiration. With proper methods of cultivation, losses by percolation and evaporation may be controlled, -and losses by transpiration may be reduced. INFLUENCE OF CULTIVATION UPON THE WATER SUPPLY OF CROPS 25. Capillarity Influenced by Cultivation. — The capillarity of the soilis subject to change with different methods of cultivation, as rolling and subsoiling, deep plowing and shallow surface cultivation. The method of cultivation which a soil should receive in order to secure the best water supply for crops must vary with the rainfall, the nature of the soil, and the crop to be pro- duced. It frequently happens that the annual rainfall is sufficient to produce good crops, but is too unevenly distributed. It is possible, to a great extent, to vary the cultivation to meet the water requirements of crops. 26. Shallow Surface Cultivation. — When shallow surface cultivation is practiced, the capillary spaces near the surface are destroyed and the direct connec- tion of the subsoil water with the surface is broken. When the soil particles have been disturbed anda layer of finely pulverized earth covers the surface, there is not that close contact which enables the water to pass from particle to particle. When evaporation takes place there is a movement of the subsoil water to the 32 SOILS AND FERTILIZERS sutface, but if the surface is covered with a layer of fine earth, the subsoil water cannot readily pass through such a medium, and evaporation is checked. Hence shallow surface cultivation conserves the soil moisture. The means by which surface cultivation is accom- plished must, of necessity, vary with the nature of the Bey Lid ae y » | i Mi JA : i ia i 4 Ah i Fig. 13. With surface cultivation. i soil. If a harrow is used the pulverization should be complete. Ifa disk is used the teeth should be set at an angle, and not io ene. so as to prevent, as ip CUAL iF T WA ne i: iH i Fig. 14. Without surface cultivation. suggested by King,” the formation of hard ridges which hasten evaporation. When the disk is set atan angle, a layer of soil is completely cut off, and the capillary connection with the subsoil is broken. Sur- face cultivation should be from two to three inches INELUEPNCE OF CULTIVATION 33 deep, and the finer the condition in which the surface soil is left, the better. Shallow surface cultivation should be resorted to as a means of conserving soil moisture. It can be prac- ticed in connection with deep plowing, shallow plow- ing, subsoiling, or rolling; in fact, it can be combined with any method of preparing the land. Shallow sur- face cultivation does not mean that the soil should not be previously well prepared by thorough cultivation. The following example shows the extent to which shallow surface cultivation may conserve the soil waler.’? Per cent. of water in cornfield. With shallow sur- Without shallow face cultivation. surface cultivation. Soil, depth 3 to 9 inches...... 14.12 8.02 Soil, depth 9 to 15 inches..... L7OE 12.38 27. Cultivation after a Rain. — When evaporation takes place immediately after a rain, not only is there a loss of the water which has fallen, but there may also be a loss of the subsoil water by translocation, if nothing be done to prevent.” The following example shows the extent to which the subsoil water may be brought to the surface.* Per cent. of water. Surface soil. Subsoil. I to 3 inches. 6 to 12 inches. Before the shower..... gheirecuhsets rae 18.22 After the shower....-.....-.- 22.11 16.70 The rainfall was sufficient to have raised the water content of the surface soil to 20.77 percent. The subsoil showed a loss of 1.52 per cent., while the sur- 34 SOILS AND FERTILIZERS face soil showed a gain of 1.34 per cent. in addition to the water received from the shower. If evaporation begins before the equilibrium is reestablished, there is lost, not only the water from the shower, but also the water which has been translocated from the subsoil to the surface. Hence the importance of shallow surface cultivation immediately after a rain. When a subsoil contains a liberal supply of water, and the surface soil a minimum amount, there is after an ordinary shower a movement of the subsoil water to the surface. The soil particles at the surface are surrounded with films of water which thicken at the expense of the subsoil water. Surface-tension is the cause of this movement of the water to the surface, and under the conditions stated it is temporarily greater than the force of gravity. A thin hard crust should never be allowed to form after a rain, because it hastens the losses by evapora- tion, while a soil mulch formed by surface cultivation has the opposite effect. 28. Rolling.— The use of heavy rollers for com- pacting the soil is beneficial in a dry season on a soil containing large proportions of sand and silt. Rolling the land compacts the soil and improves the capillary conditions, enabling more of the subsoil water to be brought to the surface. Experiments have shown that when land is rolled the amount of water in the surface soil is increased. This increase is, however, INFLUENCE OF CULTIVATION as at the expense of the subsoil water.%? Unless rolled land receives surface cultivation excessive losses by evaporation, due to improved capillarity, may result. The use of the roller on clay land during a wet season results unfavorably. In many localities rolling and subsequent surface cultivation are not admissible on account of the drifting of the soil, caused by heavy winds. 29. Subsoiling.— By subsoiling is meant pulveri- zing the soil immediately under the furrow slice. This is accomplished with the subsoil plow, which simply loosens the soil without bringing the subsoil to the surface. The object of subsoiling is to enable the land to retain, near the surface, more of the rainfall. Heavy clay lands are sometimes 1mproved by occasional subsoiling, but its continued practice is not desirable. For orcharding and fruit-growing, it is frequently re- sorted to, but is not beneficial on soils containing large amounts of sand and silt. Rolling and subsoil- ing are directly opposite in effect. Soils which are improved by rolling are not improved by subsoiling. The additional expense involved should be considered when subsoiling is to be resorted to. Experiments have not as yet been sufficiently decisive to indicate the conditions most favorable for this practice. 30. Fall Plowing conserves the soil water, by check- ing evaporation and leaving the land in better condi- tion to retain moisture. Fall plowing should be fol- 36 SOILS AND FERTILIZERS lowed by surface cultivation. Evaporation may take place from unplowed land during the fall, and in the spring the soil contains appreciably less water than plowed land. By fall plowing it is possible to carry over a water balance in the soil from one year to the next. 31. Spring Plowing. — When land is plowed late in the spring there has been a previous loss of water by evaporation, and the soil has not been able to store up as much of the rain and snow as if fall plowing had been practiced." Dry soil is plowed under and moist soil brought to the surface. This moisture is readily lost by evaporation if surface cultivation is not em- ployed; good capillary connection of the surface soil and subsoil is not obtained, and the furrow slice soon becomes dry. Surface cultivation should immediately follow both spring and fall plowing. Per cent. of water in13 Fall plowed Spring plowed April 25 land. land. From 2 to 6 inches...........- 247, 22.4 OS. PAG EAE De Mire Meeker te nye etnias 26.6 24.1 wT In 9 ys ro Wed ee eA ORE TO 28.8 26.5 Average difference ............ 2.27 per Cent: 32. Mulching. — The use of well-rotted manure or straw, spread over the surface as a mulch, prevents evaporation. In forests the leaves form a mulch which is an important factor in maintaining the water supply. In order that a mulch be effectual, it must INFLUENCE OF CULTIVATION 37 be compacted, —a loose pile of straw is not a mulch. In reclaiming lands gullied by water, mulching is very beneficial. A slight mulch may also be used to encourage the growth of grass on a refractory hillside. When land is mulched, evaporation is checked. Sur- face cultivation and mulching may be combined and excellent results obtained.® Per cent. of water in Mulched straw- berry patch. Unmulched. SOUe 2:60.) 5 ACHES snc ast aces = = 18.12 EIT] Bre POnn De ees MSreibcn S crate a we 22.18 18.14 PaO EO Micro Sars \alens o aalas 24.31 21. 1 33. Depth of Plowing. — The depth to which a soil should be plowed in order to give the best results must, of necessity, vary with the conditions. Deep plowing of sandy land is not advisable, particularly in the spring. On clay land deeper plowing should be the tule. The longer a soil is cultivated the deeper and more thorough should be the cultivation. While shallow plowing is admissible on new prairie land, deeper cultivation should be practiced when the land has been cropped for a series of years. The depth of plowing should be regulated by the season. In the prairie regions, and in the northwestern part of the United States, shallow plowing is more generally prac- ticed than in the eastern states. Deep plowing in the fall gives better results than in the spring. It is not a wise plan to plow to the same depth every year. Prof. Roberts says: “If plowing is continued at one 38 SOILS AND FERTILIZERS depth for several seasons, the pressure of the imple- ment and the trampling of the horses in time solidify the bottom of the furrow, but if the plowing 1s shallow in the spring and deep in summer and fall, the objec- tional hard pan will be largely prevented.” In regions of scant rainfall deep plowing of silt soils should be done only at intervals of three or five years. With an average rainfall, deep plowing should be the rule on soils of close texture. The depth of plowing should be varied to meet the requirements of the crop, of the soil and the amount of rainfall. 34. Permeability of Soils.— The rapidity with which water sinks into the soil after a rain depends upon the nature of the soil, and upon the cultivation which it has received. Shallow surface cultivation leaves the soil in good condition to absorb water. When the surface is hard and dry a large per cent. of the water which falls on rolling land is lost by sur- face drainage. Soils of close texture which contain but few non-capillary spaces, offer the greatest resist- ance to the downward movement of water. The term permeable is applied to a soil when it is of such a texture that it does not allow the water to accumulate and clog the non-capillary spaces. Culti- vation may change the texture of even a clay soil to such. an extent as to render it. permeable sees plowing increases permeability. In regions of heavy rains increased permeability is very desirable for good INFLUENCE, OF CULTIVATION 39 crop production on heavy clays. Sandy and loamy soils have a high degree of permeability, and it is not necessary that it should be increased. 35. Fertilizers.— When water contains dissolved salts, it 1s more susceptible to the influence of surface- tension, and is more readily brought to the surface of the soil. In commercial fertilizers soluble salts are present. The beneficial effects of commercial fertili- Fig. 15, Sandy soil without manure. zers upon the moisture content of soils are liable to be overestimated, because the fertilizer undergoes fix- ation when applied, and does not remain in a soluble condition. Fertilizers containing soluble salts exercise a favorable influence upon the moisture content of soils, but the extent of this influence has never been determined under field conditions. 36. Farm Manures. — Well-prepared farm manures exercise a beneficial effect upon the moisture content of soils. When well-rotted manure is worked into a soil, the coarse soil particles and masses are bound together, AO SOILS AND FERTILIZERS and the non-capillary spaces are made capillary. The free circulation of the air which increases evaporation, is prevented when a sandy soil is manured. When Fig. 16. Sandy soil with manure. silt and sandy soils are manured they are capable of retaining more water, as shown by the following ex- ample :73 95 per cent. fine sandy soil. Fine sandy 5 per cent. soil. dry manure. ERericent Per cent. Capacity for holding water...... 25 42 The manure enables the soil to retain more water near the surface and prevents losses by percolation. The difference in moisture content of manured and un- manured land is particularly noticeablein a dry season." Sandy soil Sandy soil well manured. unmanured. Water. Water. Eemeent: Per cent. Soil one to six inches....... 10.50 8.10 Coarse leached manure may have just the opposite effect by producing an open and porous condition of the soil. INFLUENCE OF CULTIVATION AI 37. Drainage.—Good drainage is very essential in order to properly regulate the water supply. If the water which falls on the land is allowed to flow over the surface and is not retained in the soil, there is not sufficient reserve water for crop growth. The object of good drainage is to store up as much water as pos- sible in the subsoil and to prevent surface accumula- tion and losses. Good drainage is accomplished by thorough cultivation, and in regions of heavy rainfall by tile drainage. Well-drained land is warmer in the spring, has a larger reserve store of water, and is in better condition for crop growth. 38. Influence of Forest Regions. — The deforesting of large areas near the source of rivers has an injurious influence upon the moisture content of adjoining farm lands. By cutting over and leaving barren large tracts, less water is retained in the soil. Near forest regions the air has a higher moisture content, due to the water given off by evaporation. Farm lands adjacent to deforested districts lose water more rapidly by evaporation, because the air is so much drier. In Section 24 it was stated that losses of water by trans- piration could be indirectly influenced. ‘This can be accomplished by retaining our forest lands. Good drainage in agriculture means not only good drainage for individual farms, but also good storage capacity in the form of forest lands, for the surplus water which accumulates near the sources of large rivers. RELATION OF THE SOIL TO HEAT 39. The Sources of Heat in soils are (1) solar heat, and (2) heat. resulting from chemical action. Solar heat is the main source for crop produc- tion. The action of heat upon soils has been studied extensively by Schtibler. The amount of heat a soil is capable of absorbing depends upon its texture and moisture content. All dark-colored soils have a greater power for absorbing heat than light-colored ones. From Schubler’s experiments it appears that when dry, there may be as great a difference as 8° C., between light- and dark-colored soils. When one set of soils was covered with a thin white coat of mag- nesia, and another set with lampblack, and exposed under like conditions, the temperatures were :° White coating. Black coating. SAH Geatee eee ee ee aie eae ree A3 50 Gypsum sate, nists Ware ere She iae erst etenelomeratsuete 43 51 STEVIA TU Siavcrrs Vovcnerevere taherers, Sreuehereteeracie thaws 42 49 CTAy occ c eee wees cee ncs wesw scenes AI 48 WE OAT itewterctcpsrare -wilelsns] ssovere, salorere) sav eve jarenene 42 50 The presence of water in the soil modifies the power for absorbing heat. A sandy soil for example retains about 12 percent. of water, while a humus soil retains 35 per cent. The additional amount of water in the humus soil may cause the soil temperature to be lower than that of the sandy soil. While the humus soil absorbs more heat than the sandy soil, the heat is used RELATION OF THE SOIL TO HEAT 43 up in evaporating water. A sandy soil readily warms up in the spring on account of the relatively small amount of water which it contains. The specific heat of a soil is the amount of heat re- quired to raise a given weight 1° C., as compared with the heat required to raise the same weight of water 1°. The specific heat of soils ranges from 0.2 to 0.4. The effect of drainage upon soil temperature is marked. ‘The surface of well-drained land is usually several degrees warmer than that of poorly drained land. Water being a poor conductor of heat it follows that soils which are saturated are slow to warm up in the spring. Ata depth of 2 or 3 feet there is not such amarked difference in the temperature of wet and dry soils. It isto be observed that with proper systems of drainage the surplus water is removed from the sur- face soil and stored up in the subsoil for the future use of the crop, and at the same time the temperature of the surface soil is raised, thus improving the conditions for crop growth. . The relation of drainage to the proper supply of water and temperature for crop growth is a matter which generally receives too little consideration in field practice. 40. Heat from Chemical Reactions within the Soil. — Heat also results from the slow oxidation of the organic matter of the soil. When organic matter decomposes, it produces heat. A load of manure, when it rots in the soil, gives off the same amount of heat as 44 SOILS AND FERTILIZERS if it were burned. Manured land is usually 1° or 2° warmer in the spring than unmanured land; thisis due to the oxidation of the manure. Inanacre of rich prairie soil it has been estimated that the amount of organic matter which undergoes oxidation produces as much heat annually as would be produced from a ton of coal.° In well-drained and well-manured land, the additional heat is an important factor for stimulating crop growth, particularly in a cold, backward spring. The production of heat from manure is illustrated in the case of hotbeds where well-rotted manure is covered with soil; this results in raising the temperature of the soil. When soils are well manured, heat is retained more effectually. In the case of early frosts, crops on well-manured land will often escape. 41. Relation of Heat to Crop Growth. — All plant life is directly dependent upon solar heat as the source of energy for the production of plant tissue. The heat of the sun is the main force at the plant’s dis- posal for decomposing water and carbon dioxide and for producing starch, cellulose, and other compounds. The growth of crops is the result of the transformation of solar heat into chemical energy which is stored up in the plant. When the plant is used for fuel or for food the quantity of heat produced by complete oxida- tion is equal to the amount of heat required for forma- tion. COLOR OF SOILS 42. Organic Matter and Iron Compounds.— The principal materials which impart color to soils are or- ganic matter and iron compounds. Soils containing large amounts of organic matter are dark-colored. A union of the decaying organic matter and the mineral matter of the soil also produces compounds, brown or black in color. When moist, many soils are darker than when dry, and soils in which the organic matter has been kept up by the use of manures are darker than unmanured soils.17 When rich, black, prairie soils lose their organic matter through im- proper methods of cultivation or when the organic matter (humus) is extracted in chemical analysis the soils become light-colored. The red color of soils is imparted by ferric oxide, the yellow by smaller amounts of the same material. The greenish tinge is supposed to be due to the pres- ence of ferrous compounds, such soils being so close in texture as to exclude the oxidizing action of the air. Black and yellow soils are, as a rule, the most produc- tive. Color may serve, to a slight extent, as an index of fertility. The main reason why black soils are so generally fertile is because they contain a higher per cent. of nitrogen. Black soils are occasionally unpro- ductive because of the presence of compounds injurious to vegetation. 46 SOILS AND FERTILIZERS 43. Odor and Taste of Soils. — Soils containing liberal amounts of organic matter have character- istic odors. ‘The odoriferous properties of a soil are due to the presence of aromatic bodies produced by the decomposition of organic matter. In cultivated soils these bodies have a neutral reaction. Poorly drained peaty soils give off volatile acid compounds when dried. The amount of aromatic compounds in soils is very small. The taste of soils varies with the chemical compo- sition. Poorly drained peaty soils usually have a slightly sour taste, due to the presence of organic acids. Alkaline soils have variable tastes according to the prevailing alkaline compound. The taste of a soil frequently reveals a fault, as acidity or alka- limetry. 44. Power of Soils to Absorb Gases. — All soils pos- sess, to a variable extent, the physical power of absorb- ing gases. When decomposing animal or vegetable matter is mixed with the soil the gaseous products given off are absorbed. ‘The absorption is both a chemical* and: a physical. action. ~- The. chemical changes which occur, as the absorption of ammonia, are considered in the chapter on fixation. The organic matter of the soil is the principal agent in the physical absorption of gases; peat, for example, has the power of absorbing large amounts. This action is similar to that of a charcoal filter in removing noxious gases from water. COLOR OF SOILS 47 45. Relation of Soils to Electricity.— There is always a certain amount of electricity in both the soil and the air. The part which it takes in plant growth is not well understood. ‘The action of a strong cur- rent upon the soil undoubtedly results in a change in chemical composition; a feeble current has either an indifferent or a slightly beneficial effect upon crop erowth. In order to change the composition of the soil so as to render the unavailable plant food available, would require a current destructive to vegetation. When plants are subjected to too strong a current of electricity, they wilt and have all of the after-appear- ance of frost. The slightly beneficial action upon plant growth is not sufficient to warrant its use as yet in general crop production on account of cost. The action of a weak current of electricity upon plants is undoubtedly physiological rather than chemical, unless it be in the slightly favorable influence which it exerts upon nitrification. The resistance which soils, when wet, offer to electricity has been taken by Whitney as the basis for the determination of moisture in soils." 46. Importance of the Physical Study of Soils. — From what has been said regarding the physical prop- erties of soils it is evident that such a study will give much valuable information regarding their probable agricultural value. While the physical properties should always be taken into consideration, they should not form the sole basis for judging the character of a 48 SOILS AND FERTILIZERS soil, because two soils from the same locality frequently have the same general physical composition and still have entirely different crop-producing powers, due to a difference in chemical composition. Attempts have been made to overestimate the value of the physical properties of soils and to explain nearly all soil phenomena on the basis of soil physics. Im- portant as are the physical properties of a soil, it can- not be said that they are of more importance than the chemical properties. In fact the four sciences, chem- istry, physics, geology, and bacteriology, are all closely connected and each contributes its part to our knowl- edge of soils. CHAPTER il GEOLOGICAL FORMATION AND CLASSIFICATION OF SOILS 47. Geological Study of Soils.— The geological study of a soil concerns itself with the past history of that soil, the material out of which it has been pro- duced, together with the agencies which have taken a part in its formation and distribution. Geologically, soils are classified according to the period in the earth’s history when formed, and also according to the agen- cies which have distributedthem. Agricultural geology is of itself a separate branch of agricultural science. The principles of soil formation and soil distribution should be understood, because they have such an im- portant bearing upon soil fertility. In this work, only a few of the more important topics of agricultural geology are treated in a general way. 48. Formation of Soils.— Many geologists believe the surface of the earth to have been at one time solid rock. It is now almost universally held that soils have been formed from rock by various agents; as, (1) heat and cold, (2) water, (3) gases, (4) micro-organisms and vegetable life. The disintegration of rock is usually effected by the combined action of these vari- ous agents. The process of soil formation is a slow one and the various agents have been at work for an almost indefinite period. 50 SOILS AND FERTILIZERS 49. Action of Heat and Cold. — The cooling of the earth’s surface, followed by a contraction in volume, resulted in the formation of fissures which exposed a larger area to the action of otheragents. The unequal cooling of the rock caused a partial separation of the different minerals, resulting in the formation of smaller rock particles from larger rock masses. This is well illustrated by the familiar splitting and crumbling of many stones when heated. ‘The action of frost upon rock is also favorable to soil formation. The freezing of water in rock crevices results in breaking up the rock masses, forming smaller bodies. The force ex- erted by water when it freezes is sufficient to detach large rocks. | 50. Action of Water. — Water acts upon soils both -chemically and physically. In its physical action, water has been the most important agent that has taken a part in soilformation. The surface of rocks has been worn away by moving water and in many cases deep ravines and canons have been formed; the pulverized rock, being carried along by the water and deposited under favorable conditions, forms alluvial soil. This is illustrated in the workings of large rivers where the pulverized rock masses are deposited along the river and at its mouth. A large portion of the soil in valleys and river bottoms has been deposited by water. The action of water is not alone confined to the forma- tion of soils along water courses, but is equally impor- CLASSEFICATION OF SOILS oye tant in the formation of soils remote from streams or lakes, as in the case of soils deposited by glaciers. 51. Glacial Action.— At one time in the earth’s history, the ice-fields of polar regions covered much laser areas: than at present.” Chaiees of climate caused a recession of the ice-fields, and resulted in the movement of large bodies of ice, carrying along rocks and frozen soil. ‘The movement and pressure of the ice pulverized the rock and produced soil. This action is well illustrated at the present time where mountains rise above the snow line, and the ice and snow melting at the base are replaced by ice and snow from above moving down the side of the moun- tain. When the glacier receded, stranded ice masses were distributed over the land. ‘These melted slowly and by their grinding action hollowed out places which finally became lakes. The numerous lakes at the source of the Mississippi River and in central Min- nesota are supposed to have been formed by glacial action. ‘The terminal of a glacier is called a moraine and is covered with large boulders which have not been disintegrated. The course of a glacier is fre- quently traced by the markings or scratches of the mass on rock ledges. In glacial soils, the rocks are never angular, but are smooth because of the grinding action during transportation. The area of glacial soils in the northern portion of the United States is quite large. These soils are, as a rule, fertile because of 52 SOILS AND FERTILIZERS the pulverization and mixing of a great variety of rock. 52. Chemical Action of Water.— The chemical action of water has not taken such an important part in soil formation as the physical action. While nearly all rccks are practically insoluble in water there is always some material dissolved, evidenced by the fact that all spring-water contains dissolved mineral matter. When charged with carbon dioxide and other gases, water acts as a solvent upon rocks. It converts many oxides, as ferrous oxide, into hy- droxides. ‘The chemical action of water may result in the formation of new compounds more soluble or readily disintegrated, as deposits of clay, which have been produced by the chemical and physical action of water upon feldspar rock. Limestone is quite readily disintegrated by water, which produces many chemical changes in both rocks and soils. The chemical action of fertilizers known as fixation can take place only in the presence of water. In fact water is necessary for nearly all chemical reactions in the soil. 53. Action of Air and Gases. — The part which air has taken in soil formation has not been as prominent as that taken by water. By theaid of oxygen, carbon dioxide, and other gases and vapors in the air, rock disintegration is hastened. The action of oxygen changes the lower oxides to higher forms. All rock contains more or less oxygen in chemical combination. CLASSIFICATION OF SOILS 53 The carbon dioxide of the air under some conditions favors the formation of carbonates. The disinte- erating action of air, moisture, and frost is illustrated in the case of building stones which in time crumble and form a powder. ‘The combined action of air, moisture, and frost is called weathering. 54. Action of Vegetation.—Some of the lower forms of plants as lichens do not require soil for growth, but are capable of living on the bare surface of rocks, obtaining food from the air, and leaving a certain amount of vegetable matter which under- goes decay and is incorporated with the rock partt- cles, preparing the way for higher orders of plants which take their food from the soil. When this vegetable matter decays it enters into chemical com- bination with the pulverized rock, forming humates.”7 The disintegrating action of plant roots and vegetable matter upon rocks has been an important factor in soil formation. 55. Action of Micro-organisms. — Micro-organisms, found on the surface and in the crevices of rocks, are considered by many as active agents in bringing about rock decay. The nitrifying organisms have taken an important part in rendering soils fertile, and these with others have without doubt aided in soil forma- tion. Some of the organisms found on the surface of rocks are capable of producing carbonaceous matter out of the carbon dioxide and other compounds of 54 SOILS AND FERTILIZERS the air. This action results in adding vegetable matter to the soil. 56. Combined Action of the Various Agents. — In the decay of rocks the various agents named,—water acting mechanically and chemically, heat and cold, air, and vegetation,—have been acting jointly, and have produced a more rapid disintegration than if each agent were acting separately. One of the best evi- dences that soil is derived from rock is that there are frequently found in fields pieces of rock which are actually rotten, and, when crushed, closely resemble the prevailing soil of the field. This is particularly true of clay soils where fragments of disintegrated feldspar are found which, when crushed, resemble the soil in which the feldspar was imbedded. DISTRIBUTION OF SOILS 57. Sedentary and Transported Soils. — The place where a soil is found is not necessarily the place where it was produced ; that is, a soil may be produced in one locality and transported to another. Soils are either sedentary or transported. Sedentary soils are those which occupy the original position where they were formed. ‘They usually have but little depth be- fore rock surface is reached. ‘The stones in such soils have sharp angles because they have not been ground by transportation. Transported soils are those which have been formed in one locality and carried by ROCKS AND MINERALS 55 various agents as glaciers and rivers, to other locali- ties, the angles of stones in these soils being ground off during transportation. ‘Transported soils are divided into classes according to the ways in which they have been formed ; as, drift soils produced by glaciers, and alluvial soils formed by rivers and deposited by lakes. Other agents which have taken a part in soil transportation are wind and volcanic action. Many soils have been either formed or modified by the wind. The denuding action of heavy wind storms upon many prairie soils is well known. Soil particles are carried long distances and then deposited, forming wind-drifted soils. In some localities volcanic soils are found; they are extremely varied in texture and composition—some are very fertile and contain liberal amounts of alka- line salts and phosphates, while others contain so little plant food that they are sterile. ROCKS AND MINERALS FROM WHICH SOILS ARE FORMED 58. Composition of Rock. — Rocks are composed of either a single mineral or of acombination of minerals. Most of the common minerals havea variable range of composition, due to the fact that one element or com- pound may be partially or entirely replaced by another. Most of the common rocks from which soils have been produced are composed of feldspar, mica, hornblende, and quartz. 59. Quartz and Feldspar. — Quartz is the principal constituent of many rock formations. Pure quartz is 56 SOILS AND FERTILIZERS silicic anhydride (Si0,). White sand is nearly pure quartz. A soil formed from pure quartz would be sterile. Feldspar is composed of silica, alumina, and potash or soda. Lime may also be present, and re- place a part or nearly all of the soda. If the mineral contains soda as the alkaline constituent it is known as albite, or if mainly potash it is called potash feld- spar or orthoclase. The members of the feldspar group are insoluble in acids and before disintegration takes place are not ca- pable of supplying plant food. Potash feldspar contains from 12 to 15 percent. of potash, none of which is of — value as plant food. When feldspar undergoes disin- tegration it produces clay. A soil formed from feld- spar is usually wel] stocked with potash. Orthoclase, AIKS1,0,.----. +--+. +06. Potash Feldspar. Albite, AINaSijOg+ +++ eee ee eee Sodium Feldspar. 60. Hornblende.—The hornblende and augite groups are formed by the union of magnesium, calcium, iron, and manganese, with silica. There are none of the members of the alkali family in hornblende. ‘The au- gites are double silicates of iron, manganese, calcium, and magnesium. Quite frequently phosphoric acid is present in chemical combination with the iron. The members of this group are readily distinguished by their color which is black, brown, or brownish green. The hornblendes are insoluble in acids, hence unavail- ROCKS AND MINERALS is ad able as plant food, and when disintegrated do not asa rule form very fertile soils. 61. Mica. — Mica is quite complex in composi- tion, is an abundant mineral, and is composed of sil- ica, iron, alumina, manganese, calcium, magnesium, and potassium. Mica is a polysilicate. The color may be white, brown, black, or bluish green owing to the absence of iron, or to its presence 1n various amounts. The chief physical characteristic of the members of this group is the ease with which they are split into thin layers. It is to be observed that the mica group contains all of the elements of both feld- spar and hornblende. Soils formed from the disintegration of mica are usually fertile owing to the variety of essential ele- iments present. Frequently small pieces of undecom- posed mica are found in soils. 62. Zeolites. — The zeolites form a large group of secondary minerals. ‘They are polysilicates containing alumina and members of the alkali and lime fami- lies, and all contain water held in chemical combina- tion. ‘They are soluble in dilute hydrochloric acid and belong to the group of compounds which are ca- pable, to acertain extent, of serving asplantfood. In color they are white, gray, or red. Zeolites are quite abundant in clay and are an important factor in soil fertility. It is this group which takes such an impor- tant part in the process of fixation. The zeolites, when 58 SOILS AND FERTILIZERS disintegrated, particularly by glacial action, form very fertile soils. 63. Granite is composed of quartz, feldspar, and mica. Itis a very hard rock and is slow to disinte- erate. The different shades of granite depend upon the proportion in which the various minerals are pres- ent. Inasmuch as granite contains so many minerals it usually follows that thoroughly disintegrated granite soil is very fertile. Pure powdered granite before un- dergoing disintegration furnishes no plant food. After weathering, the plant food gradually becomes availa- ble. Gneiss belongs to the granite series but differs from true granite by containing a larger amount of mica. Mica schist contains a larger amount of mica than gneiss. 64. Apatite or Phosphate Rock. — Apatite is com- posed mainly of phosphate of lime, Ca,(PO,),, together with small amounts of other compounds as fluorides and chlorides. This mineral is generally of a green or yellow color. It is present in many soils and 1s of little value as plant food unless associated with or- ganic matter or some soluble salts. 65. Kaolin is chemically pure clay and is formed by the disintegration of feldspar. When feldspar is de- composed and is acted upon by water the potash is re- moved and water of hydration is taken up, forming the product kaolin, which is hydrated silicate of alu- mina, Al (SiO,),.H,O. Impure varieties of clay are col- ROCKS AND MINERALS 59 ored red and yellow on account of the presence of iron and other impurities. Pure kaolin is white, is in- soluble in acids, and is incapable of supplying any nourishment to plants. Clay ‘soils are fertile on ac- count of the other minerals and organic matter mixed with the clay and are usually well stocked with pot- ash because of the incomplete removal of the potash from the disintegrated feldspar. It is to be observed that the term clay used chemically means alu- minum silicate, while physically it is any substance, the particles of which are less than 0.005 mm. in diameter. 66. Other Rocks and Minerals. — In addition to the rocks and minerals which have been discussed, there are many others that contribute to soil forma- tion, as limestone, which is calcium carbonate ; dolo- mite, a double carbonate of calcium and magnesium ; serpentine, a silicate of magnesium ; and gypsum, cal- cium sulphate. CHEMICAL COMPOSITION OF RocKs !” vo - sg 5 ; Eé oC Ete) v Bs 26 g ; Boe ea eo ee he) aaa se > Be DD a BM me a oo. ‘Sete. Fe Quartz ...«.... S100 mates sa a ccan *e wramh ort eiee Feldspar ..... 55-67 20-29 O-I2 I-10 I-II ae AONE 3 6:< 2.5. 46 39 Ae RS ty re RCKO IC biekote Beers 14 : P.O; Apatite ...... aes 5 leans Rees 53 ( = ) WNGaisc es eae AOA, F287 S512. eae ale ne ees oars I-5 Hornblende.. 40-55 0-15 Granite ..:... 60-80 I0-I5 Eg ek Oa ee CHAPTER Il THE CHEMICAL COMPOSITION OF SOILS 67. Elements Present in Soils. — Physically consid- ered, a soil is composed of disintegrated rock mixed with animal and vegetable matter; chemically consid- ered, the rock particles are composed of a large number of simple and complex compounds, each compound in turn being composed of elements chem- ically united. Elements unite to form compounds, compounds to form minerals, minerals to form rocks, and disintegrated rocks form soil. When rocks decom- pose, the disintegration, except ina few cases, is never carried to the extent of liberating the elements, but the process ceases when the minerals have been broken up into compounds. While there are present in the crust of the earth between 65 and 70 elements, only about 15 are found in animal and plant bodies, and of these but 12 are absolutely essential. Only four of the elements which are of most importance are at all liable to be deficient in soils. These four elements are: nitrogen, phosphorus, potassium, and calcium. 68. Classification of the Elements. —’The elements found most abundantly in soils are divided into two classes : CHEMICAL COMPOSITION OF SOILS 61 Acid-forming elements Base-forming elements Oxy CCG (s 2:48." 2. 3a ee Nitrogen ........ 6216) 8:24". TOL96._- 5.02»... 2507 1 O42 = sores Oxygen ----+---- 45.63 34.14 35.97 40.14 40.72 47.07 39-04 MOvale tes ar. 100.00 I00.00 I00.CO 100.00 I00.00 100.00 I00.00 Highest. lowest. Difference. Capon! sais) 57.84 Sugar........ 41.95 Cow manure-.--. 15.89 Hydrogen --. 6.26 Cowmanure- 2.48 Oat straw...... 278 Nitrogen..... 10.96 Meat scraps-. 0.08 Sugar.........- 10.88 Oxygen...... 47.07 Sawdust ..... 24.14 Green clover. .-412793 The differences in composition are noticeable. The humus produced by each material as green clover, oat straw, or sawdust is different from that produced by any other material. The humus from green clover is undoubtedly very complex in nature, because it con- tains both nitrogenous and non-nitrogenous com- pounds, and each class has a different action in humi- fication processes, hence it follows that the humus from the green clover must be a complex mixture of both nitrogenous and non-nitrogenous bodies. The nature of the humus, whether nitrogenous or non-nitrogenous, is important. Humus produced from sawdust and humus from meat scraps may be taken respectively as types of non-nitrogenous and nitrog- enous humus. 101. Value of Humates as Plant Food. — Various opinions have been held regarding the actual value, ORGANIC COMPOUNDS OF SOILS 95 as plant food, of this product from partially decayed animal and vegetable matter. Humus was formerly regarded as composed only of carbon, hydrogen, and oxygen, and inasmuch as plants obtain these elements from water and from the carbon dioxide of the air, no value was assigned to humus. Later investigators added nitrogen to the list but stated that the nitrogen, when combined with the humus and before under- going fermentation, was of no value as plant food. Recent investigations have proved that the phos- phoric acid and other mineral elements combined with the organic matter of soils are of value as plant food,* and it has been demonstrated that crops grown on the black soils of Russia obtain a large part of their mineral food from organic combinations. Cul- ture experiments have shown that under normal conditions plants like oats and rye may obtain their mineral food entirely from humate sources. Seeds when planted in a mixture of pure sand and neu- tral humates from fertile soils, produced normal plants. In order to secure the best conditions for growth, a little lime must be present to prevent the formation of humic acid, and the usual organisms found in fertile fields must also be introduced. ‘The following example is given of oats grown under such conditions : g6 SOILS AND FERTILIZERS NITROGEN AND ASH ELEMENTs.!® In six oat In six mature seeds. plants. Gran. Gram. Nitrogen sroiiesceatateneueratie: cos alist svelte 0.0040 0.0556 OAS ois araseo alc canen eel oe 0.0013 0.0640 SOOTG VR eee Cus oer en 0.0001 1.0079 MRE sate when n eieleneret etme coun: we clene 0.0002 0.0249 Magnesia ».+++.+eeese seen. 0.0005 0.0110 TiO 1A ote etree hetees Sheer Oe a naaeare 0.0064 Phosphoric anhydride...... 0.0016 0.0960 Sulphuric anhydride....... 0.0001 0.0090 STH PY O 1 RRR ts Pera eh ae ad Pe 0.0026 0.7300 The fact that plants feed on humate compounds, and that decaying animal and vegetable matter pro- duce humates from the inert potash and phosphoric acid of the soil, has an important bearing upon crop production, because it indicatesa way by which inert plant food may be converted into more active forms. It also explains that stable manure is valuable because it makes the inert plant food of the soil more available. 102. Amount of Plant Food in Humate Forms.— In a prairie soil containing three and five-tenths per cent. of humus there are present 100,000 pounds of humus per acre. Combined with this humus there are from 1,000 to 1,500 pounds each of phosphoric acid and potash. Soils which have been under long cultivation without the restoration of any humus contain from 300 to 500 pounds each of humic potash and phosphoric acid.*7_ A decline in crop-producing power has in many cases been brought about by the destruction of the humus. ORGANTC COMPOUNDS OF ‘SOILS 97 103. Loss of Humus.— The loss of humus from the soil is caused by oxidation and by fires. Any method of cultivation which accelerates oxidation reduces the humus content. In many of the western prairie soils which have been under continuous grain cultivation for thirty years and more, the amount of humus has been reduced one-half. Summer fallowing also causes a loss of humus. When land is continually under the plow, and no manures are used, the humus is rapidly oxidized, and there is left, in the soil, organic matter which is slow to decay. Forest and prairie fires have been very destructive to the organic compounds of the soil. A soil from Hinckley, Minn., before the great forest fire of 1893 showed 1.69 per cent. humus and 0.12 per cent. nitrogen.77 After the fire there were present 0.41 percent, humuseand -6.02 per cent mitrogen, , “Phe forest fire caused a loss of 2,500 pounds of nitrogen per acre. In clearing new land, particularly forest land, there is frequently an unnecessary destruction of humus materials. Instead of burning all of the vege- table matter it would be better economy to leave some in piles for future use as manure. When all of the vegetable matter has been burned two or three good crops are obtained but the permanent crop-producing power of the land is reduced because of the loss of nitrogen. When the vegetable matter has been only partially removed the crops at first may be 98 SOILS AND FERTILIZERS smaller, but in a few years returns will be greater than if all of the vegetable matter were burned. 104. Physical Properties of Soils Influenced by Humus.— The physical properties of a soil may be entirely changed by the addition or the loss of humus. The influence of humus upon the weight, color, water, and heat of soils, is discussed in the chapter on the physical: properties of soils. Soils reduced in humus content have less power of storing up water and resisting drought. ‘This fact is illustrated in the following table :3° PER CENT. WATER. After 10 hours exposure in In soil. tray, tosun. Soil rich in humus (3.75 per cent.) «+--+ +--+. 16.48 6.12 Adjoining soil poorer in humus (2.50 per cent.) 12.14 3.94 105. Humic Acid.—In the absence of calcium carbonate or other alkaline compounds, the vegetable matter may produce acid products destructive to the growth of some crops. ‘The acidity in such cases may be readily corrected by the use of lime or wood ashes. Studies conducted by the Rhode Island Experiment Station indicate that the areas of acid soils are quite extensive. Acid soils can be distinguished by their action uponred litmus paper. A soil may, how- ever, give an acid reaction and contain a fair amount of lime. The subject of acid soils and liming is consid- ered in Chapter IX: ORGANIC COMPOUNDS OF SOILS 99 106. Soils in Need of Humus.— Sandy and sandy loam soils that have been cultivated for a number of years to corn, potatoes, and small grains, without the use of stable manures or the proper rotation of crops, are deficient in humus. Clay soils, as a rule, do not stand in need of humus so much as loam or sandy sous. The mechanical condition of heavy clays. is, {Carbon Vif Ui y ti, Mj Fig. 21. Humus from new soil. however, improved by the addition of humus-forming material. ‘Alkali’ soils are usually deficient in humus. Its addition to loam or sandy soils is beneficial in pre- venting the soil from drifting because humus binds together the soil particles. There are but few soils, under ordinary cultivation, to which it is not safe to add humus-forming materials. Ordinary prairie soils, for the first ten years after breaking, are usually well 100 SOILS AND FERTILIZERS suppled. Swampy, peaty, and muck soils contain large amounts; in fact, they are often overstocked with humus. 107. Active and Inactive Humus.— When soil has been under long cultivation, and no manures have been used, the nitrogen and mineral matters combined with the humus are reduced. The humus from long cultivated fields contains a higher per cent. of carbon than that from well-manured or new land; it is also less active because of the higher per cent. of carbon which does not readily undergo oxidation.?7 Humus from Humus from new soil. old soil. Percent: Per cent: Car DOM aise se sot rele a2 areeseie sare 4A.12 50.10 yO RCM < leiere tosis « aictsle eal oe = 6.00 4.80 OXyZen --- 2. eee cer eceee sees 35.16 33.70 INpiaec AST WOR oh ween ENA noe 8.12 6.50 PSM a Bio fore laiats (ane ar ellta a eaate iets ated 6.60 4.90 Total humus material.. 5.30 3.38 108. Influence of Different Methods of Farming upon Humus.— The general system of farming has a direct effect upon the humus content and composition of the soil. Where live stock is kept, the manure properly used, and the crops systematically rotated, the crop-producing power of the land is not decreased, as in the case of the one-crop system. The influence of different systems of farming upon the humus con- tent and other properties of the soil may be observed from the following table :3° ww ORGANIC COMPOUNDS OF SOILS per cu. Character of soil. ft Cultivated thirty-five years ; rotation of crops and manure; high state of productiveness. . Originally same as I; con- tinuous grain cropping for thirty-five years ; low state of productiveness-..... Doerace . Cultivated forty-two years ; systematic rotation and ma- nure ; good state of product- iveness .---- st Medina ita! e 4. Originally same as 3; culti- vated thirty-five years; no systematic rotation or ma- nure; medium state of pro- Guctiveness.... cesses secon . lbs. 70 WZ 70 67 Bets cent. 3°32 1.80 3.46 2.45 Ber cent. 0.30 0.26 O22 Phos- phoric acid com- IOI Water- : bined holding Weight Humus. Nitrogen. with humus. capac- ity. Percent Percent. 48 39 59 37 CHAPTER TY NITROGEN OF THE SOIL AND AIR, NITRIFICATION, AND NITROGENOUS MANURES 109. Importance of Nitrogen as a Plant Food. — The illustration (Fig. 22) shows an oat plant which has received no nitrogen, while potash, phosphates, lime, and Big 22. Oat plant grown without nitro- gen. all other essential elements of plant food were liberally supplied. Observe the pe- culiarand restricted growth, with but little root development. The leaves were yel- lowish in color. In the absence of nitrogen a plant j inakes no appreciable growth. With only a limited supply, a plant begins its growth in a normal way but as soon as the avail- able nitrogen is used up, the lower and | smaller leaves begin gradually to die down from the tips, and all of the plant’s energy 1s centered in one or two leaves. J In one experiment when only a small amount of nitrogen was supplied, the plant struggled along in this way for about nine weeks, making a total growth of but six and one-half inches.*° Just at the critical point when the plant was dying of nitrogen starvation, afew milligrams of calcium nitrate were given. In NITROGEN AS A PLANT FOOD 103 thirty-six hours the plant showed signs of renewed life, the leaves assumed a deeper green, a new growth was begun, and finally four seeds were produced. During the time of seed formation more nitrogen was added. but with no beneficial resalt,. ~All- of « the essential elements for plant growth were liberally pro- vided, except nitrogen which was very sparingly sup- pled at first, until near the period of seed formation, when it was more liberally supplied. When plants have reached a certain period in their development, and have been starved for the want of nitrogen, the later application of this element does not produce normal growth, as the energies of the plant have been used up in searching for food. Nitrogen, as well as potash, lime, and phosphoric acid, are all neces- sary while plants are in their first stages of growth. In the case of wheat, nitrogen is assimilated more rapidly than are any of the mineral elements. Before the plant heads out, over eighty-five per cent. of the total nitrogen required has been taken from the soil.%° Corn also takes up all of its nitrogen from four to five weeks before the crop matures. Flax takes up seventy-five per cent. of its nitrogen during the fees fifty days of growth.37 | Nitrogen is demanded by all crops. It forms the chief building material for the proteids of all plants. In the absence of a sufficient amount of nitrogen, the rich green color is not developed; the foliage is of a yellowish tinge. Nitrogen is one of the constituents © 104 SOILS AND FERTILIZERS of chlorophyl, the green coloring-matter of plants, hence with a lack of nitrogen only a limited amount of chlorophyl can be produced. Plants with large, well-developed leaves of a rich, green color are not suffering for nitrogen. Nuitrogenous fertilizers have a tendency to produce a luxurious growth of foliage deep green in color. ATMOSPHERIC: NITROGEN AS A SOURCE OF PLANT FOOD 110. Early Views. — In addition to the carbon, hy- drogen, and oxygen, which form the organic com- pounds of plants, nitrogen also, at the beginning of the present century, was known to be present. ‘The sources of carbon, hydrogen, and oxygen, for crop purposes, were much easier to determine and under- stand than the sources of nitrogen. Priestley, the dis- coverer of oxygen, believed that the free nitrogen of the air was a factor in supplying plant food. De Saus- sure arrived at just the opposite conclusion. The facts which led to these beliefs were not convincing because the methods of chemical analysis had not yet been sufficiently perfected to solve the question.%° 111, Boussingault’s First Experiments.—Boussin- gault was the first to make a careful study of the sub- ject. In a prepared soil, free from nitrogen, and con- taining all of the other elements necessary for plant growth, he grew clover, wheat, and peas, carefully determining the nitrogen in the seed. The plants _ were allowed free access to the air, being simply pro- ATMOSPHERIC NITROGEN 105 tected from dust, and were watered with distilled water. But little growth was made. At the end of two months the plants were submitted to chemical analysis, and the amount of nitrogen present was determined. His first results are given in the following table :% NITROGEN. In seedsown. In plant. Gain. Gram. Gram. Gran. @lOWER) 2 M1OSs we chats orcve O.1I O.12 0.01 Bs FSS Sas ithe tetera O.114 0.156 0.042 Wiest oo sciatica cic aeve 0.043 0.04 —O.003 ee Beet PN eRe fot ayatolavaterara' 0.057 0.06 0.003 CAS eT ra 1 Wie ete St eneneiat loys 0.047 0.10 0.053 Boussingault concluded that when plants, in a sterile soil, were exposed to the air, there was with some a slight gain of nitrogen but the amount gained from atmospheric b sources was not sufficient to feed the plant and allow it to reach full ma- turity. By many these results were not accepted as conclusive. 112. Boussingault’s Second Ex- periments.— Fifteen years later (1853) Boussingault repeated his ex- periments ina different way. The plants were grown in a large carboy with a limited volume of air so as to Fig. 23. Plants grown cut off all sources of combined nitro- ree gen, as ammonia. By means of a second glass vessel 106 SOILS AND FERTILIZERS (6, Fig. 23) the carboy was kept supplied with a liberal amount of carbon dioxide, so that plant growth would not be checked for lack of this material. When experiments were carried on in this way using a fertile soil, the plants reached full maturity, but when a soil free from nitrogen was used, plant growth was soon checked. A general summary of this work is given in the following table :39 NITROGEN. In seeds. In plant. Loss. Gram. Gram. Gram. Dwarf beans......... O.IOOI 0.0977 —0,0024 @CyaE Shes cae cushoie ote ronclers! ore 0.0109 0.0097 —O.O0OI2 White lupines ....... 0.2710 0.2669 —0O.0041 Garden cress......... 0.0013 oH @ 6 Ne em AOE These experiments show that with a sterilized soil, and all sources of combined atmospheric nitrogen cut off, the free nitrogen of the air takes no part in the food supply of the plant. 113. Boussingault’s Third Experiments. — In 1854 Boussingault again repeated his experiments; this time he grew the plants in a glass case so constructed that there was a free circulation of air from which all combined nitrogen had been removed. These exper- iments were similar to his second series; the plants, however, were not grown in a limited volume of air. The results, without going into detail, showed that the free nitrogen of the air, under the conditions of the experiment, took no part in the food supply of plants. ATMOSPHERIC NITROGEN IO7 If anything, there was less nitrogen recovered in the dwarfed plants than there was in the seed sown. 114. Ville’s Results. — About the same time Ville carried on a series of experiments of like nature, but in a different way, and arrived at just the opposite conclusions. In short, his experiments indicated that plants were capable of making liberal use of the free nitrogen of the air for food purposes. The directly opposite conclusions of Boussingault and Ville, led to a great deal of controversy. The French Academy of Science took up the question, and appointed a commis- sion to review the work of Ville. The commission consisted of six prominent scientists. They reported that ‘‘M. Ville’s conclusions are consistent with his labor and results.” 3° 115. Work of Lawes and Gilbert.— Lawes and Gilbert, however, carried on such extensive exper- iments under a variety of conditions as to remove all doubt regarding the question. Plants were grown in sterilized soils, in prepared pumice stone, and in soils with a limited and known quantity of nitrogen beyond that contained in the seed. Different kinds of plants were experimented with. The work was carried on with the utmost care and with apparatus so constructed as to eliminate all controllable factors. The results in the aggregate clearly indicate that plants, when acting in asterile medium, are unable to make use of the free nitro- gen of the air for the production of organic matter. * 108 SOILS AND FERTILIZERS 116. Atwater’s Experiments. — Atwater carried on similar experiments in this country.*? Some of his results indicate that when seeds germinate they lose a small part of their nitrogen, and when grown in a sterile soil, they fail to fix any of the free nitrogen of the*air In all of the work of the different investigators prior to 1888, plants were grown in a sterilized medium, and under these conditions they are unable to make use of the free nitrogen of the air. 117. Field and Laboratory Tests. — Experiments with sterilized soils do not represent the normal conditions of growing crops, where all of the bacteriological agencies of the soil, the air, and the plant, are free to act. Experiments have shown that these agencies have an important bearing upon plant growth. In a five years’ rotation of clover and other legu- minous plants, Lawes and Gilbert found that a soil gained from two to four hundred pounds of nitrogen in addition to that removed in the crop, while land which produced wheat continuously had gradually lost nitrogen. The amount in the subsoil remained nearly the same. All of these facts plainly indicated that crops like clover have the power of gaining nitrogen from unknown sources. The results of prominent German agriculturists led to the same con- clusion. It was known that wheat grown after clover ATMOSPHERIC. NITROGEN 109 gave as good results as the use of nitrogenous manure for the wheat, but for many years this fact was unex- plained. 118. Hellriegel’s Experiments.— He grew legu- minous plants in nitrogen-free soils. One set of plants was watered with distilled water, while another had in addition small amounts of leachings from an old loam field. The plants watered with distilled water alone made but little growth, while those watered with the loam leachings reached full maturity and contained something like a hundred times more nitrogen than was in the seed sown. The dark green color was also developed, showing the presence of a normal amount of chlorophyl. The roots of the plants had well- developed swellings or nodules, while those that were watered with distilled water alone had none. ‘The loam leachings contained only a trace of nitrogen.” 119. Experiments of Wilfarth.— Experiments by Wilfarth give more exact data regarding the amount of nitrogen taken from the air. Lupines were grown in the same way, and one lot watered with distilled water, while another lot received in addition leachings from an old lupine field. Watered with distilled water. Watered with soil leachings. Dry matter. Nitrogen. Dry matter. Nitrogen. Grams. Gram. Grams. Grams. 0.919 0.015 44.72 1.099 0.800 0.014 45.61 L538 0.921 0.013 44.48 1.195 1.021 0.013 42.45 12337 FTO SOILS AND FERTILIZERS These experiments have been verified by many other investigators until the fact has been established that leguminous plants may, through the agency of micro-organisms, make use of the free nitrogen of the air. ‘The work of Hellriegel was not accidental but the result of careful and systematic investigation. As early as 1863 he observed that clover would develop along the roadway in sand in which there was scarcely a trace of combined nitrogen. 120. Composition of Root Nodules.— The root nodules referred to, are particularly rich in nitrogen. In one experiment, the light-colored and active ones contained 5.55 per cent. of nitrogen while the dark- colored and older ones contained 3.21 per cent. The entire nodules of the root both active and inactive contained 4.60 per cent. nitrogen. The root itself contained 2.21 per cent. nitrogen.‘ The root nodules also contain definite and charac- teristic micro-organisms, and it was the spores of these organisms that were present in the soil extract in both Hellriegel’s and Wilfarth’s experiments. In the ster- ilized soils they were not present. These organisms found in root nodules, are the essential agents which aid in the fixation of the free nitrogen of the air, and in its ultimate use as plant food. 121. Nitrogen in the Root Nodules Returned to the Soil.— Ward has shown that when clover roots decay, the organisms and nitrogen present in the nod- NITROGEN COMPOUNDS OF THE SOII, Lit ules are distributed within the soil.s° Hence when- ever a leguminous crop is raised, nitrogen is added to the soil, instead of being taken away, as in the case of a grain crop. The amount of nitrogen per acre returned to the soil by a leguminous crop as clover, varies with the growth of the crop. In the roots of a clover crop a year old there are present from 20 to 30 pounds of nitrogen per acre, while in the roots and culms of a dense clover sod, two or three years old, there may be present 75 pounds or more of nitrogen. Peas, beans, lucern, cow peas, and all members of the leguminous family possess the power of fixing the free nitrogen of the air by means of micro-organisms. The micro-organisms associated with one species as clover differ from these associated with another as lucern. The amount of nitrogen which the various legumes return to the soil is variable. Hellriegel’s re- sults are of the greatest importance to agriculture because they show how the free nitrogen of the air can be utilized indirectly as food, by crops unable to appro- priate it for themselves. THE NITROGEN COMPOUNDS OF THE SOIL 122. Origin of the Soil Nitrogen.—The nitrogen of the soil is derived chiefly from the accumulated re- mains of animal and vegetable matter. The original source of the soil nitrogen, that is the nitrogen which furnished food to support the vegetation from which our present stock of soil nitrogen is obtained, was | SOILS AND FERTILIZERS probably the free nitrogen of the air. All of the ways in which the free nitrogen of the air has been made available to plants of higher orders which require combined nitrogen, are not known. It is supposed, however, that this has been brought about by the workings of lower forms of plant life, and by micro- organisms. Whatever these agencies have been they do not appear to be active in a soil under high cultiva- tion, because the tendency of ordinary cropping is to reduce the supply of soil nitrogen. 123. Organic Nitrogen of the Soil. —In ordinary soils the nitrogen is present mainly in organic forms combined with the carbon, hydrogen, and oxygen; and to a less extent with the mineral ele- ments forming nitrates. The organic forms cof nitrogen, it is generally considered, are incapable of supplying plants with nitrogen for food purposes until the process known as nitrification takes place. The nitrogenous organic compounds in cultivated soils are derived mainly from the undigested protein compounds of manure and from the nitrogenous compounds in crop residues. When decomposition occurs, amides, organic salts, and other allied bodies are without doubt produced as intermediate products before nitrifi- cation takes place. The organic nitrogen of the soil may be present in exceedingly inert forms similar to leather. In fact in many peaty soils there are large amounts of inactive organic compounds rich in NITROGEN COMPOUNDS OF THE SOIL II3 nitrogen. In other soils the nitrogen is present in less complex forms. The organic nitrogen of the soil may vaty in complexity from forms like the nitrogen of urea to forms like that of peat. 124. Amount of Nitrogen in Soils. — The fertility of any soil is dependent, to a great extent, upon the amount and form of its nitrogen. In soils of the highest degree of fertility there is usually present from 0.2 to 0.3 per cent. of total nitrogen, equivalent to from 7,000 to 10,000 pounds per acre to the depth of one foot. Many soils of good crop-producing power contain as low as 0.12 per cent. of nitrogen. There is usually two or three times more nitrogen in the surface soil than in the subsoil. In many sandy soils which have been allowed to decline in fertility the nitrogen may be less than 0.04 per cent. Of the total nitrogen in soils there is rarely more than 2 per cent. at any one time, in forms available as plant food.8 A soil with 5,000 pounds of total nitrogen per acre would contain about 100 pounds of available nitrogen of which only a part comes in contact with the roots of crops. Hence itis that a soil may con- tain a large amount of total nitrogen and yet be defi- cient 1n available nitrogen. 125. Amount of Nitrogen Removed in Crops. — The amount of nitrogen removed in crops ranges from 25 to 100 pounds per acre depending upon the nature of the crop. It does not necessarily follow that Lia SOILS AND FERTILIZERS the crop which removes the largest amount of nitrogen leaves the land in the most impoverished condition. Wheat and many grains, while they do not remove such a large amount of nitrogen in the crop, leave the soil more exhaused than if other crops were grown. This, as will be explained, is caused by the loss of nitrogen from the soil in other ways than through the erop.?/ Pounds of nitrogen per acre. Wheat, 20 bushels ..--..- 22000 cece ccccee cecnee 25 Straw, 2000 pOUNndS..+.+--eeeee ce eeee cece cece cees 10 Ota n\ ed susites oara iols oka gece 35 Barley, 4o PITS THE Gree acrelleystctelsevole)ereien sleelebienttatterohMerematte 28 Straw, 3000 poundS..++eeeeee ceeeeeceee cece ecence 12 TOTAL aicts sian vate orale islele wale whale sate seterer 4O Oats, 50 bushels. .--- .+ee cece ee cece cece cece ceeeee 35 Straw, 3000 pounds.-++++++veeeee cece cece eeeeees 15 AS @ tecllisce te tedetere ter enalouerere tel hakeveuensictcherMeloRelte 50 Flax, 15 bushels. ....-2.seessccceve ceccce cece sees 39 Straw, 1800 pounds. ...eeeeeeereeeeeeee ress ceeees 15 SGA seks, «fo lea) « is sale wYeln oe otaiereuehoenleiats 54 Potatoes, 150 bushels....-- sees eee ee cece cece eees 40 Corn, 65 bushels ...-.0 eee cece ee eee cece ee ee eees 4o Stalks, 3000 pounds..-..---- se teen cence teen cons 35 AL Gta ese a etinieel' Mvetisy utah Oo aie ae a che egeey siete 75 126. Nitrates and Nitrites. —’The amount of nitro- - gen in the form of nitrates and nitrites, varies from mere traces to 150 pounds per acre. Calcium nitrate NITROGEN. COMPOUNDS: OF THE SOIL PIS is the usual form met with, especially in soils which are sufficiently supplied with calcium carbonate to allow nitrification to progress rapidly. Nitrates and nitrites are the most valuable forms of nitrogen for plant food. Both are produced from the organic nitrogen of the soil. A nitrate is a compound com- posed of a base element as sodium, potassium, or calcium, combined with nitrogen and oxygen. A nitrite contains less oxygen than a nitrate. Potassium nitrate, KNO,, sodium nitrate, NaNO,, and calcium nitrate, Ca(NO,),, are the nitrates which are of most importance in agriculture. ‘The nitrites, as potassium nitrite, KNO,, are met with to a less extent than the nitrates. Nitrates and nitrites are present in surface well waters contaminated with animal and vegetable matter. Many well waters possess some material value as a fertilizer on account of the nitrates, nitrites, and decaying animal and vegetable matters which they contain. 127. Ammonium Compounds of the Soil.— The amount of ammonium compounds in a soil is usually less than the amount of nitrates and nitrites. The sources of the ammonium compounds are: rain-water and the ammonia formed from the decay of the organic matter. Like the nitrates and nitrites, the ammonium compounds are all soluble and hence can- not accumulate in soils which receive an average amount of rainfall. They are usually found in all Tro SOILS AND FERTILIZERS surface well waters. In the soil, the ammonium com- pounds may be oxidized and form nitrates. Com- pounds asammonium chloride or ammonium carbonate, if present in a soil in excessive amounts, will destroy vegetation in a way similar to the alkaline compounds in alkaline souls. 128. Nitrogen in Rain-water and Snow.— The amount of nitrogen which is annually returned to the soil in the form of ammonium compounds dissolved in rain-water and snow, is equivalent to from 2 to 3 pounds per acre. At the Rothamsted experiment station the average amount for eight years was 3.37 pounds.*? When a soil is rich in nitrogen the gain from rain and snow is only a partial restoration of that which has been given off from the soil to the air or lost in the drain waters. The principal form of the nitrogen in rain water is ammonium carbonate which is present in the air to the extent of about 22 parts per million parts of air. 129. Ratio of Nitrogen to Carbon in the Organic Matter of Soils.—In some soils the organic matter is more nitrogenous than in others. In those of the arid regions the humus contains from 15 to 20 per cent. of nitrogen, while soils from the humid regions contain 4 to 6 per cent.## In some soils the ratio of nitrogen to carbon may be 1 to 6, while in others it may be 1 to 18 or more. ‘That is, in some soils there is I part of nitrogen to 6 parts of carbon, while in NITROGEN COMPOUNDS OF THE SOIL rY7 others the organic matter contains 1 part of nitrogen to 18 parts of carbon. Ina soil where there exists a wide ratio between the nitrogen and carbon, it is believed that the conditions for supplying crops with available nitrogen are unfavorable. 130. Losses of Nitrogen from Soils. — When a soil rich in nitrogen is cultivated for a number of years exclusively to grain crops there is a loss of nitrogen exceeding the amount removed in the crop, caused by the rapid oxidation of the organic matter of the soil. Experiments have shown that when a soil of average fertility is cultivated continually to grain that for every 25 pounds of nitrogen removed in the crop there is a loss of 146 pounds from the soil due to the destruction of the organic matter.*? In general, any system of cropping which keeps the soil continually under the plow, results in decreasing the nitrogen. When a soil is rich in nitrogen the greatest losses occur; when poor in nitrogen there is relatively less loss. There is a tendency toward the establishment of an equilibrium as to the nitrogen content of soils. When a soil rich in nitrogen is given arable culture the oxidation of the organic matter and the losses of nitrogen take place rapidly. 131. Gain of Nitrogen in Soils. — When arable land is permanently covered with vegetation, there is a gain of nitrogen. Pasture land contains more nitro- gen than cultivated land of a similar character; also 118 SOILS AND FERTILIZERS in meadow land there is a tendency for the nitrogen to increase. These facts are well illustrated in the investigations of Lawes and Gilbert, at Rothamsted. Age of pasture. Nitrogen. Years. Per cent: JANG all Oy (eee leh ala Perko Goro Gro ic DOUGH A 0.14 Barn-field pasture ..-...+-+.-.-- 8 0.151 Apple-tree pasture..-......++--- 18 0.174 Wea Gay sie oe austere cine gnet aaa erate 21 0.204 Whe cloy asserts sche bite Meet ette eo cten sles 30 0.241 After deducting the amount of nitrogen in the manure added to the meadow land, the annual gain of nitrogen was more than 44 pounds per acre. Another source of gain of nitrogen is the fixation of the free nitrogen of the air by the growth of clover and other leguminous crops. If a soil is properly imanured and cropped the amount of nitrogen may be increased. A rotation of wheat, clover, wheat, oats, and corn with manure will leave the soil at the end of the period of rotation in better condition as regards nitro- gen than at the beginning. These facts are illustrated in the following table :%7 Continuous wheat culture— Nitrogen in soil at beginning of experiment....... 0.221 per Cent, Nitrogen at end of 5 years continuous wheat cultiva- PUGH eves ees I nO ee a ao Ao cae 0.193" ae Loss per annum per acre (in crop 24.5, soil 146.5)-- 171 pounds. Rotation of crops— Nitrogen in soil at beginning of rotation.......... 0,221 per cent: Nitrogen at Close‘of rotation seem oe eye2- ~~ a seiels ers Oar ae Gain to soil per annum per a@re ..0: 22.65 ose ote 61 pounds. Nitrogen removed in crops per annum...........- 4A NITRIFICATION 11g It is to be regretted that in the cultivation of large areas of land to staple crops as wheat, corn, and cotton, the methods of cultivation are such as to decrease the nitrogen content and crop-producing power of the soil when this can be prevented. NITRIFICATION 132. Former Views Regarding Nitrification. — The presence of nitrates and nitrites in soils was formerly accounted for by oxidation. The theory was held that the production of nascent nitrogen by the decomposition of organic matter caused a union between the oxygen of the air and the nitrogen of the organic matter. The studies of fermentation by Pasteur led him to believe that possibly the formation of nitric acid in the soil might be due to fermentation. It was, however, 15 years later before the French chemists, Schlosing and Muntz, established the fact that nitrification is produced by a living organism. 133. Nitrification Caused by Mlicro-organisms. —Nitrification is the process by which nitrates or nitrites are produced in soils, by the workings of organisms. Nitrification results in changing the com- plex organic nitrogen of the soil to the form of nitrates or nitrites. It is the process by which the inert nitrogen of the soil is rendered available as crop food. The organisms which carry on the work of nitrifica- tion have been isolated and studied by Warington, and by Winogradsky. 120 SOILS AND FERTILIZERS 134. Conditions Necessary for Nitrification are: . Food for the nitrifying organisms. . A supply of oxygen. Moisture. . A favorable temperature. . Absence of strong sunlight. . The presence of some basic compound. Nn Pw Nd HH In order to allow nitrification to proceed, all of these conditions must be satisfied. The process is fre- quently checked because some of the conditions, as presence of a basic compound, are unfulfilled. 135. Food for the Nitrifying Organisms. — All living organisms require a supply of food and one of the food requirements of the nitrifying organism is a supply of phosphates. In the absence of phosphoric acid, nitrification cannot take place. The change which the phosphoric acid undergoes in serving as food for the nitrifying organism is unknown, but it doubtless makes the phosphoric acid more available as plant food. ‘The principal organic food of the nitrify- ing organism is the organic matter of the soil. Organic matter, only when incorporated with soil, can serve as food for the nitrifying organism. In the pres- ence of a large amount of organic matter, as in a manure pile, nitrification does not take place. The process can take place only when the organic matter is largely diluted with soil. Under favorable condi-_ Fia. |. Nitric ORGANISM IN POTASSIUM NITRITE SOLUTION. Fic. 2. BACILLUS REDUCING NITRATES TO FREE NITROGEN GAS. PLATE |. i te ald 9g ; che aden ee NITRIFICATION jf | tions nitrifying organisms may take all of their food as inorganic forms; that is, nitrification may take place in the absence of organic matter provided the proper mineral food be supplied. When growth under such conditions takes place the organisms assim- ilate carbon from the combined carbon of the air, and produce organic carbon compounds. ‘That is, an organism, working in the absence of sunlight and un- provided with chlorophyl, may construct organic car- bon compounds.*#? The nitrification which takes place in the absence of nitrogenous organic matter is of too limited a character to supply growing crops with all of their available nitrogen. For general crop produc- tion the organic matter of the soil is the source of the nitrogen which undergoes the nitrification process, and which furnishes food for the nitrifying organisms. 136. Oxygen Necessary for Nitrification.— The second requirement for nitrification is an adequate supply of oxygen. The nitrification organism belongs to that class of ferments (aerobic) which requires oxy- gen for existence. Oxygen is present as one of the ele- ments in the final product of nitrification as in calcium nitrate, Ca(NO,),. In the absence of oxygen the nitri- fication process is checked. When soils are saturated with water, the process cannot go on for want of oxygen. In well-cultivated soils, particularly clay soils, the con- ditions for nitrification are improved by aeration be- cause the supply of oxygen in the soil spaces is increased. 122 SOILS AND FERTILIZERS 137. Moisture Necessary for Nitrification. — Nitri- fication cannot take place in a soil deprived of mois- ture. Asin all fermentation processes, so with nitri- fication, moisture is necessary for the chemical changes to take place; -In a veryadry time mitrificationgie arrested for the want of water. Water is as necessary for the growth and development of the living organism which carries on the work of nitrification, as it is to the life of a plant of higher order. 138. Temperatures Favorable for Nitrification. — The most favorable temperatures for nitrification are between’ 12° 'C:(54> F.) and 37° "C..4{69> F.). 4 sities take place at as low a temperature as 3° or 4° C. (37° atid’ 39°F); .absgo® Ce (1222 BS yeni is seems while: at 55°C. (230° °F), there 1s no action, ia northern latitudes nitrification is checked during the winter, while in southern latitudes this change takes place during the. entire: year. Crops whichgece. quire their nitrogen early in the growing season are frequently placed at a disadvantage because there is less available nitrogen in the soil at that time than later. 139. Strong Sunlight Checks Nitrification.—Nitri- fication cannot take place in strong sunlight; it pre- vents the action of all organisms of this class. In fallow land there is no nitrification at the surface but immediately below where the surface soil excludes the sunlight, it is most active. In a cornfield it is more active than in a compacted fallow field. NITRIFICATION E23 140. Base-forming Elements Essential for Nitrifi- cation. — The presence of some base-forming element to combine with the nitric acid produced is a necessary condition for nitrification, and for this purpose calcium carbonate is particularly valuable. The absence of basic materials is one of the frequent causes of non- nitrification. In acid soils, the process is checked for the want of proper basic material. The organisms which carry on the work cannot exist in a strong acid or alkaline solution, consequently in strong acid or alkaline soils the ordinary process cannot take place.” 141. Nitrous Acid Organisms. — There are at least two nitrifying organisms in the soil: one produces nitrates and the other nitrites or nitrous acid. It is believed that the process takes place in two stages, the first being performed by the nitrous organism, and the process completed by the nitricorganism. Warington says that “both organisms are present in the soil in enormous numbers,—and the action of the two organ- isms proceeds together, as the conditions are favorable to both.” 142. Ammonia-producing Organisms. — ‘There are also present in the soil organisms which have the power of producing ammonia from proteid bodies. The ammonium compounds produced are acted upon by the nitrifying organisms and readily undergo nitrification. 45 143. Denitrification is just the reverse of the nitri- E24 SOILS AND FERTILIZERS fication process, and is the result of the workings of a class of organisms which feed upon the nitrates form- ing free nitrogen which is liberated as a gas. One of the conditions for denitrification is absence of air, as the organism belongs to the anaerobic class. Denitri- fication readily takes place in soils saturated with water, and where the soil is compacted so that air is practically excluded. * 144. Number and Kinds of Organisms in Soils. — In addition to the micro-organisms which carry on the work of nitrification, denitrification, and ammonifica- tion, there are a great many others, some of which are beneficial while others are injurious to crop growth. It has been estimated that in a gram of an average sample of soil there are from 60,000 to 500,000 bene- ficial and injurious micro-organisms. ‘7 There are pro- duced from many crop residues, by injurious ferments, chemical products which may be destructive to crop growth. Flax straw for example when it decays in the soil forms products which are destructive to a suc- ceeding flax crop. A moist soil, rich in organic matter, and containing various salts, may form the medium for the propaga- tion of all classes of organisms. Sewage-sick soils, clover-sick soils, and flax-diseased lands are all the re- sults of bacterial diseases. Many of the organisms. which are the cause of such diseases as typhoid fever, cholera, and diphtheria, may propagate and develop NITRIFICATION E25 in a moist soil under certain conditions, and then find their way through drain waters into surface wells, and cause the spreading of these diseases. 145. Products Formed by Soil Organisms. —In considering the part which micro-organisms take in plant growth, as well as in all similar processes, there are two phases to be considered: (1) the action of the or- ganism itself, and (2) the chemical action of the product of the organism. In the case of nitrification, the action of the organism brings about a change in the composition of the organic matter, producing nitric acid which is merely a product formed as a result of the action of the organism. The nitric acid then acts upon the soil producing nitrates. In the case of soils rich in organic matter, the fermentation changes which take place during humification result in the production of acid products. This is simply the result of the action of the ferments. The acids then act upon the soil bases and produce humates or organic salts. In many fermentation changes there is first the production of some chemical compound, and then the action of this compound upon other bodies. In rendering plant food available, as in nitrification and humification, it is the final product, and not the first product of the organism, which is of value. 146. Inocculating Soils with Organisms. — In grow- ing leguminous crops on soils where they have never before been produced, it has been proposed to supply 126 SOILS AND FERTILIZERS the essential organisms which assist the crops to obtain--their nitrogen. © For example, ai. cloversas grown on new land, the soil is liable to be deficient in the organisms which assist in the assimilation. of nitrogen and which are present in the root nodules of the plant. If these organisms are supplied, better conditions for growth exist. The extent to which it is necessary to inoculate soils with organisms for the assimilation of nitrogen, has not yet been determined by actual field experiments. 147. Loss of Nitrogen by Fallowing Rich Lands. —Summer fallowing creates conditions favorable to nitrification. A fallow is beneficial to a succeeding crop because of the nitrogen which is rendered avail- able. Ifa soil is rich in nitrogen and lime, summer fallowing causes the production of more nitrates than can be retained in the soil. The crop utilizes only a part of the nitrogen rendered available, the rest being lost by drainage, ammonification, and denitrification. Hence the available nitrogen is increased while the total nitrogen is greatly decreased. *7 Soil before Soil after fallowing. fallowing. Total nitrogen.......--seeeee eee 0.154 0.142 Soluble nitrogen..............--- 0.002 0.004 The gain of 0.002 per cent. of soluble nitrogen was accompanied by a loss of o.o12 per cent. of total nitrogen. For every pound of available nitrogen there was a loss of 6 pounds. NITRIFICATION 127 148. Deep and Shallow Plowing and Nitrification. —In a rich prairie soil nitrification goes on very rapidly. This is one reason why shallow plowing on new breaking gives better results than deep plowing. Deep plowing at first causes nitrification to take place to such an extent that the crop is overstimulated in erowth. Deep plowing and thorough cultivation aid nitrification. The longerasoil has been cultivated, the deeper and more thorough must be the cultivation. 149. Spring and Fall Plowing, and Nitrification. —FE arly fall plowing leaves more available nitrogen at the disposal of the crop than late fall plowing. Nitrification takes place only near the surface. Hence when late spring plowing is practiced there is brought to the surface raw nitrogen, while the available nitrogen has been plowed under, and is beyond the reach of the young plants when they require the most help in obtaining food. The various methods of cultivation as deep and shallow plowing, spring and fall plowing, and surface cultivation have as much influence upon the available nitrogen supply of crops as upon the water supply. The saying that cultiva- _ tion makes plant food available is particularly true of the element nitrogen, the supply of which is capable of being increased or decreased to a greater extent than that of any other element. NITROGENOUS MANURES 150. Sources of Nitrogenous Manures. — The materials used for enriching soils with nitrogen, to promote crop growth, may be divided into three classes: (1) organic nitrogenous manures, (2) nitrates, and (3) ammonium salts. Each of these classes has a different value as plant food. In fact there are marked differences in fertilizer value between mate- rials belonging to the same class. ‘The nitrogenous organic materials used for fertilizing purposes are: dried blood, tankage, meat scraps and flesh meal, fish offal, cottonseed meal, and leguminous crops as clover and peas. The nitrogen in these substances is princi- pally in the form of protein. When peat and muck are properly used they may also be classed among the nitrogenous manures. 151. Dried Blood. — This is obtained by drying the blood and débris from slaughter-houses. Frequently small amounts of salt and slaked lime are mixed with the blood. It is richest in nitrogen of any of the organic manures. When thoroughly dry it may con- tain 14 per cent. of nitrogen. As usually sold, it con- tains from 16 to 20 sper cent. sof water and iaed nitrogen content -of from 9 to. 13. Died bileaa contains only small amounts of other fertilizer ele- ments. It is strictly a nitrogenous fertilizer, readily yielding to the action of micro-organisms and to NITROGENOUS MANURES 129 nitrification ; on account of its fermentable nature, it is a quick-acting fertilizer, and is one of the most valuable of the organic materials used as manure. Dried blood may be applied as a top dressing on grass land. It gives the best returns when used on an impoverished soil to aid crops in the early stages of growth, before the inert nitrogen of the soil becomes available. It is also an excellent form of fertil- izer to use on many garden crops, butit should not be placed in direct contact with seeds, as it will cause rotting, nor should it be used in too large amounts. Three hundred pounds per acre is as much as should be applied at one time. Wheu too much is used losses of nitrogen may occur by leaching and by denitrifica- tion. It is best applied directly to the soil, as a top dressing in the case of grass, or near the seeds of garden crops, and not mixed with unslaked lime or wood ashes, but each should be used separately. As all plants take up their nitrogen early in their growth, nitrogenous fertilizers as blood should be applied be- fore seeding or soon after. An application of dried blood to partially matured garden crops will cause a prolonged growth and very late maturity. Storer gives the following directions for preserving any dried blood produced upon farms.7* ‘The blood is thoroughly mixed in a shallow box with 4 or 5 times its weight of slaked lime. The mixture is cov- ered with a thin layer of lime and left to dry out. It 130 SOILS AND FERTILIZERS will keep if stored in a cool place, and may be applied directly to the land or added to a compost heap.” The price per pound of nitrogen in the form of dried blood can be determined from the cost and the analysis of the material. A sample containing 9 per cent. of nitrogen and selling for $20 per ton is equiva- lent to 11.11 cents per pound for the nitrogen (2000 G00 1808! $70.00 - 180:—— Ii. (cis): 152. Tankage is composed of miscellaneous refuse matter as bones, trimmings of hides, hair, horns, hoofs, and some blood. The fat and gelatin are, as a rule, first removed by subjecting the material to superheated steam. This miscellaneous refuse, after drying, is ground and sometimes mixed with a little slaked lime to prevent rapid fermentation. Tankage contains less nitrogen but more phosphoric acid than dried blood. Owing to its miscellaneous nature, it is quite variable in composition, as the fol- lowing analyses of tankage from the same abattoir at different times show. First year. Second year. Third year. WIGISEMEE ferelc scat ree e oe 10.5 9.8 10.9 Nero ees. cerca. aici 537 7.6 6.4 Phosphoric acid........ 12.2 10.6 il ay As a general rule, tankage contains from 5 to 8 per cent. of nitrogen and from 6 to 14 per cent. of phos- phoric acid. It is much slower in its action than dried blood, and supplies the crop with both nitrogen and phosphoric acid. Tankage is a valuable form of NITROGENOUS MANURES T31 fertilizer to use for garden purposes. It may also be used as a top dressing on grass lands, and may be spread broadcast on grain lands. It is best to apply the tankage, when possible, a few days prior to seed- ing, and it should not come in contact with seeds. Two hundred and fifty pounds per acre is a safe dress- ing, and when there is sufficient rain to ferment the tankage, 400 pounds per acre may be used. A dressing of 800 pounds in a dry season would be destructive to vegetation. On impoverished soil more may be used than on soils which are for various reasons out of condition. The cost of the nitrogen, as tankage, may be determined from the composition and selling price. If tankage containing 7 per cent. of nitrogen and 12 per cent. of phosphoric acid is selling for $22 per ton, what is the cost of the nitrogen per pound? The market value of phosphoric acid, in the form of bones, should first be ascertained. Suppose that bone phos- phoric acid is selling for 4 cents per pound. The phosphoric acid in the ton of tankage would then be worth $9.60, making the nitrogen cost $12.40. The 140 pounds of nitrogen in the ton of fertilizer would then be worth $12.40, or 8.8 cents per pound. In eastern markets the price of tankage is usually much higher than near the large packing houses of the west. 153. Flesh Meal. — The flesh refuse from slaugh- ter-houses is sometimes kept separate from the tank- age and sold as flesh meal, the fat and gelatin being 132 SOILS AND FERTILIZERS first removed and used for the manufacture of glue and soap. Flesh meal is variable in composition and may be very slow in decomposing. — It contains from 4 to 8 per cent. or more of nitrogen with an appreciable amount of phosphoric acid. Occasionally it is used for feeding poultry and hogs, and cattle to a limited extent. When thus used the fertilizer value of the dung is nearly equivalent to the original value of the meal. 154. Fish Scrap. — The flesh of fish is very rich in nitrogen.*® The offal parts, as heads, fins, tails, and in- testines, are dried and prepared as a fertilizer. Many species of fish which are not edible are caught in large numbers to be used for this purpose. In sea-coast regions fish fertilizer is one of the cheapest and best of the nitrogenous manures. It is richer in nitrogen than tankage or flesh meal, and in many cases equal to dried blood. It readily undergoes nitrification and is a quick-acting fertilizer. 155. Seed Residues. — Many seeds, as cottonseed and flaxseed, are exceedingly rich in nitrogen. When the oil has been removed, the flaxseed and cottonseed cake are proportionally richer in nitrogen than the original seed. This cake is usually sold as cattle food, but occasionally used as fertilizer. Cotton- seed cake contains from 6 to 7 per cent. of nitro- gen, and compares fairly well in nitrogen content with animal bodies. Cottonseed cake or meal is not so NITROGENOUS MANURES 133 quick-acting a fertilizer as dried blood, but when used in southern latitudes a little time before seeding, the nitrogen becomes available for crop purposes. Cot- tonseed or linseed meal containing a high per cent. of oil is much slower in decomposing than that which contains but little oil. It is generally considered bet- ter economy to feed the cake to stock and use the manure than to apply the cake directly to the land. Of late years cottonseed-meal has been so reduced in price that its use as a fertilizer has been admissible. A ton of cottonseed-meal costing $20 and contain- ing 2 per cent. of phosphoric acid and 7 per cent. of nitrogen would be equivalent to buying the nitrogen at 13.1 cents per pound, which is frequently cheaper than purchasing some other nitrogen fertilizer. 156. Leather, Wool Waste and Hair are rich in nitrogen, but on account of their slow rate of decom- posing are unsuitable for fertilizer purposes. When present in fertilizers they give poor field results. 157. Solubility of Organic Nitrogenous Mate- rials. — The method employed to detect, in fertilizers, the presence of inert forms of nitrogen as leather, is to digest the material in prepared pepsin solution.” Substances like dried blood are nearly all soluble in the pepsin, while leather and inert forms are only par- tially so. The solubility of organic nitrogen in pep- sin solution determines, to a great extent, the value of the material as a fertilizer.* 134 SOILS AND FERTILIZERS Soluble in prepared pepsin solution. Per cent. of nitrogen. TOPIC WLOOE! arora wise sors wie) s ehots we alate raters 94.2 Ground ried iSly: to. trates wie earner 75.7 Tankagwe «< we)s ee on Seles sieisiete ticles oe 73.6 Cottonseed. aneal: ve c ws = 0.80 0.3 sia 0.4 When a large amount of straw is used the per cent. of nitrogen and phosphoric acid is decreased, while the per cent. of potash is slightly increased. Sawdust and leaves both make the manure more dilute. Dry peat makes the manure richer in nitrogen. The ab- sorbent powers of these different materials are about as follows :73 144 SOILS AND FERTILIZERS Per cent. of water absorbed. ENneCuteStrawin en cea oe eee 30.0 @Woarse UWMICUE SERAW 120 0.35 oe 0.30 Horses. 84 92 0.30 0.86 0.25 ote 0.10 Pigs... 80 97.0 0.60 0.80 O15) > s COMPOSITION OF HEN MANURE. Per cent. OE SS alg al eae Ap a Sa a a 57-50 Nitrogen Pets en seGa a Gard Eran SoS OF ST Re ae I a RO £27 PAGS AOTC VAC I 5 «sock eek ae Pee ow oho nase eee 0.82 POM Mine ee ence & ats woe ee aie eis Jo eats Tenstha levers ene 0.28 186. Mixing of Solid and Liquid Excrements. — The solidand liquid excrements, when properly mixed, make a well-balanced manure. ‘The urine alone is not a complete manure, as it is deficient in phosphoric acid and other mineral matter. ‘The solid excrements and the urine, when mixed with soil, readily undergo nitri- fication. The nitrogen in the solid excrements is in the form of indigestible protein, and is rendered avail- able as plant food more slowly. Land which has been heavily dressed with leached manure has re- ceived an unbalanced manure, and is deficient in nitrogen but fairly well supplied with mineral matter. Such a soil may fail to respond because of the unbal- anced character of the manure. 187. Volatile Products from Manure. — The fer- mentation of manure in stables may cause the pro- duction of alarge number of volatile compounds. ‘The ammonia and nitrogen compounds are products which cause losses of value to the manure. Urea, when it ferments, produces ammonia or ammonium carbonate. If ammonia is produced it combines with the carbon 156 SOILS AND FERTILIZERS dioxide, which is always present in stables in liberal amounts as a product of respiration, and forms ammo- nium carbonate, a volatile compound. When the stable atmosphere becomes charged with ammonium carbonate, some of it 1s deposited on the walls of the stable, forming a white coating. The white coating found on harnesses and carriages stored in poorly ven- tilated stables, is ammonium carbonate. Accumula- tions of manure in the stable and poor ventilation are the conditions favorable to the production of this com- pound. 188. Human Excrements. — The use of human ex- crements as manure is sometimes advised, and in some countries they are extensively used. When fresh, human excrements may contain a high per cent. of nitrogen and phosphoric acid ; when fermented, a loss of nitro- gen occurs. Heiden estimates that in a year 1,000 pounds of excrements per person are made, which con- tain $2.25 worth of fertility.5® For sanitary reasons, human excrements should be used with great care. It is doubtful with the abundance and cheapness of plant food whether their extensive use as manure is advisable. About 1840, Liebig feared that the essen- tial elements of plant food would accumulate in the vicinity of large cities and be wasted, and that in time there would be a decline in fertility due to this cause. Many political economists shared the same fear. Since that time the fixation of atmospheric nitrogen PRESERVATION OF MANURE 157 through the agency of leguminous crops, the exten- sive beds of sodium nitrate, phosphate rock, and Stas- furt salts, have been discovered, and larger areas of more fertile soil have been brought under cultivation, so that it is not now considered so essential to devise means for utilizing human excrements as manure. THE PRESERVATION OF MANURE 189. Leaching. — Leaching of manure is the gteat- est source of loss. Experiments by Roberts have shown that when horse manure is thrown in a loose pile and subjected to the joint action of leaching and weathering it may lose nearly 60 per cent. of its most valuable fertilizing constituents in six months. ‘The tabular results are as follows :"5 April 25. Sept. 28. Loss. Lbs. Lbs. Per cent: Gross Weight... . 4,000 1,730 57 NEI OP Clas 2,6 7s 5 3 19.60 7.79 60 Phosphoric acid .. 14.80 GES 47 ROS 2 eas as derate' 36.0 8.65 76 Wale per tont.a@:O;——composed ‘of .KCIl.MeCl 6H O: Polyhalit, 15 per cent. K,O,—composed of KSO..Mg SO,.(CaSO_),-H,O. Krugit, 10 per cent. K,O,—com- posed of K,SO..MgSO,.(CaSO,).H,O. Sylvinit, 16 to 20 per cent. K,O,—composed of KCl.NaCl and impurities. Kuieserit, 7 per cent. K,O, —composed of MgSO, and carnallit. 237. Wood Ashes. — For ordinary agricultural pur- poses, wood ashes are the most important source of potash. Ashes are exceedingly variable in composi- tion. When leached the soluble salts are extracted and there is left only about 1 per cent. of potash. In unleached ashes the amount of potash ranges from 2 to 10 per cent. Soft wood ashes contain much less potash than hard wood ashes. Goessmann gives the following as the average of 97 samples of ashes :* Average composition. Range. Per cenk Per cent. PGtaShiys cocoa a ee oie’ 6, Sates « 5-5 2.5 to 10.2 Phosphoric acid........- 1.9 0.3 to 4.0 TRAE) So ssn Ste ates VR awe ale ne eo ie 18.0 to 50.9 In 10,000 pounds of wood. Potash. Phosphoric acid. Lbs. Lbs. Rabe, rte eraiee et, cha cies sfeiee aie 10.6 25 Be phe Gee ina ae stata wears we peel 6.0 i Glatat aides sherensuktatis tava aic ah ube case 15.0 I.i Pie ah as ce een ers oo s aie 0.8 0.7 Georgia pine --............. 5.0 1.2 POO WIG we co ois ales gin ore t ewe 9.0 5:7 192 SOILS AND FERTILIZERS 238. Action of Ashes on Soils. — In ashes, the pot- ash is present mainly as potassium carbonate. Ashes are usually regarded as a potash fertilizer only, but they also contain lime and phosphoric acid, and may be very beneficial in supplying these elements. They are valuable too because they add alkaline matter to the soil, which corrects acidity and aids nitrification. A dressing of ashes improves the mechanical condi- tion of many soils by binding together the soil parti- cles. This property is well illustrated in the so-called “Gumbo” soils, which contain so much alkaline mat- ter that the soil has a soapy taste and feel, and when plowed the particles fail to separate. 239. Leached Ashes. — When ashes are leached the soluble salts are extracted, and the insoluble matter which is left 1s composed mainly of calcium carbonate and silica.°> Unleached ashes. Leached ashes. Bemcent: Per cent. NNSA Tees takceleice fel cohen ists. Socibaus i enetebe 12.0 30.0 Silica, QWGcnoncgoSodcuuoges 3.0 13.0 Potassium carbonate....... 5-5 ia Calcium ag eee 61.0 51.0 Phosphoric acid .--....+.-. 1.9 ae 240. Alkalinity of Leached and Unleached Ashes. — A good way to detect leached ashes is to deter- mine the alkalinity in the following way: Weigh out 2 grams of ashes into a beaker, add 100 cc. dis- tilled water, and heat on a sand-bath nearly to boiling, STASSFURT SALTS 193 cool, and filter. To so cc. of the filtrate add about 3 drops of cochineal indicator, and then a standard solu- tion of hydrochloric acid from a burette until the solu- tion is neutral. Ifa standard solution of acid cannot be procured, one containing 15 cc. concentrated hydro- -chloric acid per liter of distilled water may be used for comparative purposes. Leached ashes require less than 2 cc. of acid to neutralize the alkaline matter in 1 gram while unleached ashes require from 10 to 18cc. In pur- chasing wood ashes, if a chemical analysis cannot be secured, the alkalinity of the ash should be determined. 241. Coal and Other Ashes. — Since the amount of phosphoric acid and potash in coal ashes is very small, they have but little fertilizer value. Soft-coal ashes con- tain more potash than those from hard coal, but itis held insuch forms of combination as to be of but little value. The ashes from sawmills where soft wood is burned and the ashes are unprotected, are nearly worthless. When peat-bogs are burned over, large amounts of ashes are produced. If the bogs are covered with timber, the ashes are sometimes of sufficient value to warrant their transportation and use. Phosphoric Potash. acid. Percent: Percent: PatCOAN se eint he voles iee 22 oe 0.10 0.10 WORMCOAL aps eek. ois Sas 0.40 0.40 Sanyaililt sasises!? oka e754 1:20 T.00 Peat-bog ashes! oo... sc... 1.15 0.54 Peat-bog ashes (timbered j!? 3.68 2.56 Fobaceo Stems. «2 2). + s% 4.00 7.00 Cottonseed hulls.......... 20.00 7.00 194 SOILS AND FERTILIZERS 242. Commercial Value of Potash.— The market value of potash is determined from the selling price of high-grade sulphate of potashand kainit. Ordinarily, the price per pound of potash varies from 4 to 5 cents. As in the case of both nitrogen and phosphoric acid, the market and the field values may be entirely at variance. Before potash salts are used, careful field tests should be made to determine the actual condi- tion of the soil as to its needs in potash. 243. Use of Potash Fertilizers. — Wood ashes, or Stassfurt salts, should not be used in excessive amounts. Not more than 300 pounds per acre should be applied unless the soil is known to be markedly de- ficient, and previous tests indicate that larger amounts are safe and advisable. Potash fertilizers should be evenly spread and not allowed to come in contact with plant tissue. They should be used early in the spring before seeding or before the crop has made much growth. Wood ashes make an excellent top dressing for grass lands, particularly where it is desired to en- courage the growth of clover. There are but few crops or soils that are not greatly benefited by a light application of wood ashes, and none should ever be allowed to leach or waste about a farm. When a potash fertilizer is used, a dressing of lime will frequently be beneficial. The potash undergoes fixation, and when it is liberated there should be some basic material as lime to take its place. Goessmann STASSFURT SALTS 195 observed that land manured for several years with potassium chloride finally produced sickly crops, but that an application of slaked lime restored a healthy appearance to succeeding crops.© If the soil is well stocked with lime its joint use with potash fertilizers is not necessary. CHAPTER: IX LIME AND MISCELLANEOUS FERTILIZERS 244. Calcium an Essential Element of Plant Food. — Calcium is present in the ash of all-plants, and is usually more abundant in soils than phosphorus or Fig. 33. Oat plant grown with- out lime. Se oe potassium. It takes an essential part in plant growth, and when- ever withheld growth is checked. The effect of removing calcium from the soil is shown 1n theillus- tration (Fig. 33), which gives the total growth made by an oat plant under such a condition. Plants grown on soils deficient in calcium compounds, lack hard- mess. They are not so -ableie withstand drought, or climatic changes, as plants grown on soils well supplied with this element. Calcium does not accumulate in the seeds of plants, but 1s pres- ent mainly in the leaves and stems where it takes an impor- tant part in the production of new tissue. The term lime is used in speaking of the calcium oxide content of soils and crops. LIME AND MISCELLANEOUS FERTILIZERS 197 245. Amount of Lime Removed in Crops.37— Pounds per acre. DV eAt ee naS MENS, 2 saie ts ine ais wees nui © Si axel wrote de I SEAN, DOO MOU IN Sy ae. > wie steel ox ont eaten awa ee =, 21 ee 7 ARC Ea ekg reo RO OE SCORE Henn ee 8 Germ NG5t Site lS ate stats ous ot tain yatn he's etal ose wrernle 0 I Stalks, 2000 Pounds «Gris since mnie ess oh css seed II Siot alin Aattewnm street he ac ote ato es tie a teaolee 12 IRGAS, aio WoaSels oye << eh ave'em a ai wei wie ein eo ee el 4 Straw, 3500 pounds..-- -+++ sseees cece vcccccvecees *B! GWe) SnAg we NN aa DIE eS cis 75 Bl. 5 DUS He Gat ctew aie a's ro sate a ee she oe « Sierate a eevee z Straw, 1900 pounds. <2.) =) 2s eennmise te ates e's ile! 4 80) 22 5 Abs ee RR SIT SO i tse. ot 16 Clover, 4000 pounds. .... -.200-seee seccee cece cece 75 Clover and peas remove so much lime from the soil that they are often called lime plants. The amount required by grain and hay is small compared with that required for a clover or pea crop. 246. Amount of Lime in Soils. — There is no ele- ment in the soil in such variable amounts as calcium. It may be present from a few hundredths of a per cent. to twenty per cent.; soils which contain from 0.4 to 0.5 per cent. are usually well supplied. The hme in a soil takes an important part in soil fertility; when deficient, humic acid may be formed, nitrification checked,and the soil particles will lack binding material. 198 SOILS AND FERTILIZERS 247. Different Kinds of Lime Fertilizers. — By the term ‘lime fertilizer’ is usually meant land plaster (CaSO..2H,O). Occasionally quicklime (CaO) and slaked lime (Ca(OH),) are used on exceedingly sour land. In general a lime fertilizer 1s one which sup- ples the element calcium; common usage, however, has restricted the term to sulphate of lime. 248. Action of Lime Fertilizers upon Soils. — Lime fertilizers act both chemically and physically. Chem- ically, lime unites with the organic matter to form humate of lime and prevent the formation of humic acid. It aids in nitrification and acts upon the soil, liberating potassium and other elements of plant food. Physically, lime improves capillarity, precipitates clay when suspended in water, and prevents losses, as the washing away of fine earth. 249. Action of Lime upon Organic Matter. — When soils are deficient in lime, an acid condition may de- velop to such an extent as to be injurious to vegeta- tion. In fact nitrogen, phosphoric acid, and potash may all be present in liberal amounts, but in the absence of lime poor results will be obtained. Ex- periments at the Rhode Island Experiment Station indicate that there are large areas of acid soils in the Eastern States which are much improved when treated with air-slaked lime.” There is a great difference in the power of plants to live inacidsoils. Agricultural plants are particularly sensitive, while many weeds LIME AND MISCELLANEOUS FERTILIZERS 199 have such strong power of endurance that they are _ able to thrive in the presence of acids. The charac- ter of the weeds frequently reflects the character of the soil as to acidity, in the same way that an “alkali” soil is indicated by the plants produced. 250. Lime Liberates Potash. — The action of lime upon soils well stocked with potash results in the fixa- tion of the lime and the liberation of the potash; the reaction takes place in accord with the well-known exchange of bases. The extent to which potash may be liberated by lime depends upon the firmness with which the potash is held in the soil. Boussingault found that when clover was limed there was present in the crop three times as much potash as in a similar crop not limed. His results are as follows: Kilos per hectare. In crop not limed. In limed crop. First Second First Second year. year. year. year. Time’.....-.+--: a2 32,2 79.4 102.8 POtshy <2 as e~ «2s 2657, 28.6 95.6 97.2 Phosphoric acid. I1.o 7.0 24.2 22.9 The indirect action of land plaster upon Western prairie soils in liberating plant food, particularly potash and phosphoric acid, is unusually marked. Laboratory experiments show that small amounts of gypsum are quite active in rendering potash, phos- phoric acid, and even nitrogen soluble in the soil water.>° 200 SOILS AND FERTILIZERS 251. Quicklime and Slaked Lime. — When it is de- sired to correct acidity slaked lime is used. Air- slaked lime is not as valuable as water-slaked lime. Quicklime cannot be used on land after a crop has been seeded... Both ‘slaked lime and quickiime should be applied some little time before seed- ing and not to the crops. The action of quicklime upon organic matter is so rapid that it destroys vege- tation. Slaked lime is less injurious to vegetation. 252. Pulverized Lime Rock. — In some localities pulverized lime rock is used. It may be applied as a top-dressing in almost unlimited amounts. It is most beneficial on light, sandy soils, where it performs the function of fine clay as well as being beneficial in its chemical action. Not all soils are alike responsive to applications of limestone, and before using, it is best to determine to what extent it will be beneficial. There are no conditions where limestone is injurious to soil or crop. 253. Marl. — Underlying beds of peat, deposits of marl are occasionally found. Marl is a mixture of disintegrated limestone and clay, and contains varia- ble amounts of calcium carbonate, phosphoric acid, and potash. When peat and marl are found together they may be used jointly with manure as described in Section 1'75. Many sandy landsin the vicinity of peat and marl deposits would be greatly improved, both physically and chemically, by the use of these materials. LIME AND MISCELLANEOUS FERTILIZERS 201 254. Physical Action of Lime.— The addition of _ lime fertilizers to sandy soils improves their general physical condition. Heavy clays lose their plasticity when limed; the fine clay particles are cemented and act as sand, which improves the mechanical condition of the soil. The physical action of lime upon soils is well illustrated in the case of ‘loess soils,’ which are composed of clay and limestone. The lime cements the clay particles and forms compound grains, making the soil more permeable, and more easily tilled. The improved physical condition alone which follows the application of lime fertilizers, 1s fre- quently sufficient to warrant their use. 255. Application of Lime Fertilizers.— Lime is generally used as a top-dressing on grass lands at the rate of 200 to 500 pounds per acre. Excessive appli- cations are undesirable. Lime as gypsum is particu- larly valuable when applied to land where crops are grown which assimilate large amounts of lime. It should be remembered that it is not a complete, but mainly an indirect, fertilizer. If used to excess it may get the soil in such a con- dition that no more plant food can be rendered avail- able. A common saying is ‘‘ Lime makes the father rich but the son poor.”** ‘This is true, however, only when lime is used in excess. When used occasion- ally in connection with other manures, it has no inju- rious effects upon the soil and is a valuable fertil- 202 SOILS AND FERTILIZERS izer, especially where clover is grown with difficulty. MISCELLANEOUS FERTILIZERS 256. Salt is frequently used as an indirect fertilizer. Sodium and chlorine, the two elements of which it is composed, are not absolutely necessary for normal plant growth. When salt is applied to the soil and the sodium undergoes fixation, potassium may be liberated. An early experiment of Wolff illustrates this point: a buckwheat plot fertilized with salt pro- duced a crop with more potash and less sodium than a similar unfertilized plot. Salt may be used to check the rank growth of straw during a rainy season, and thus prevent loss of the crop by lodging. It should not be used in excessive amounts, as it is destructive to vegetation; 200 pounds per acre is a fair application. Salt also improves the physical condition of the soil by increasing the surface- tension of the soil water. Salt should not be used on a tobacco or potato crop, because it injures the quality of the product. 257. Magnesium Salts.— Magnesium is present in the ash of all plants, and is an essential element of plant growth. Usually soils are so well stocked with this element that it 1s not necessary to apply it in fertilizers. Some of the magnesium salts, as the chloride, are injurious to vegetation, but when associa- ted with lime as carbonate, magnesia imparts fertility. In many of the Stassfurt salts magnesium is present. MISCELLANEOUS FERTILIZERS 203 258. Soot.— The deposits formed in boilers and chimneys when wood and soft coal are burned contain small amounts of potash and phosphoric acid. They are valuable mainly as mechanical fertilizers impart- ing the properties of organic matter. ‘There is but little plant food in soot, as shown by the following analysis: Soft-coal soot. Hard-wood soot. Per cent.13 Per cent.69 PGEASM, 2% 6 Seicinaisied, stan 0.84 1.78 Phosphoric acid ........... 0.75 0.96 259. Seaweeds. — Seaweeds are rich in potash and near the sea coast are extensively used for fer- tilizers. Composition of mixed seaweed. Per cent.69 NN PR ahiomin ciate oars wists 5 eee Duo Rw b cat ehowes 81.50 CUSED CCE RS SS-ereer ga er GT eee RR O73 ei aGh nets spt ste els a tiv be Seca) Gomme 1.50 EOS PROC AG ecto s Soi se ats cel nies cw ae eas 0.18 260. Strand Plant Ash. — Weeds and plants pro- duced on waste land along the sea are in many Euro- pean countries burned, and the ashes used as fertilizer on other lands. By this means waste land is made to produce fertilizer for fields which are tillable. The amount of fertility removed in weeds is usually greater than that in agricultural plants, because weeds have a greater power of obtaining food from the soil. When wheat or other grain is raised, and a small crop of grain and a large crop of weeds are the result, there is more fertility removed from the soil than if a heavy 204 SOILS AND FERTILIZERS stand of grain were obtained. The ashes of strand plants and weeds are extremely variable in composition. 261. Wool Washings and Waste. —The washings from wool contain sufficient potash to make this material valuable as a fertilizer. In wool there is a high per cent. of potash, which is soluble, and readily removed in the washings. Wool waste may contain from I to 5 per cent. of potash and from 4 to 7 per cent. of nitrogen in somewhat inert forms. CHAPTER. X COMMERCIAL FERTILIZERS AND THEIR USE 262. Development of the Commercial Fertilizer Industry. — The commercial fertilizer industry owes its origin to Liebig’s work on plant ash. The first superphosphate was inade by Sir J. B. Lawes, about 1840, from spent bone-black and sulphuric acid. His interest had previously been attracted to the use of bones by a gentleman who farmed near him, ‘ who pointed out that on one farm bone was invaluable for the turnip crop, and on another farm it was useless.’’4 Since 1860 the commercial fertilizer industry in this country has developed rapidly, until now the amount of money expended in purchasing commercial fer- tilizers and amendments is estimated at $60,000,000 annually. Nearly all of this sum is expended in less than a quarter of the area of the United States. 263. Complete Fertilizers and Amendments. — The term commercial fertilizer is applied to those materials which are made by the mixing of different substances which contain plant food in concentrated forms. When a commercial fertilizer contains nitrogen, phos- phoric acid, and potash, it is called a complete fer- tilizer, because it supplies the three elements which are liable to be most deficient. Materials as sodium nitrate 206 SOILS AND FERTILIZERS which supply only one element are called amend- ments. It frequently happens that a soil requires only one element in order to produce good crops. In such cases only the one element needed should be sup- plied. Complete fertilizers are sometimes used when the soil is only in need of an amendment. 264. Variable Composition of Commercial Fer- tilizers.— Since commercial fertilizers are made by mixing various materials which contain different amounts of nitrogen, phosphoric acid, and potash, it follows that they are extremely variable in composi- tion and value. No two samples are the same, hence the importance of knowing the com- position of every separate brand purchased. The composition of fertilizers is varied to meet the require- ments of different soils and crops. Some fertilizers are made rich in phosphoric acid, while others are rich in nitrogen and potash. 265. How a Fertilizer is Made. — The most com- mon imaterials used in making complete fertilizers are: Nitrate of soda, kainit, and dissolved phosphate rock. ‘These materials have about the following com- position : Nitrate of soda........ 15.5 per cent. nitrogen. Kainit....-...---..--. 12.5 per cent. potash. Dissolved phosphate-.. 14.0 per cent. phosphoric acid. The fertilizer may be made rich or poor in any one element. Many fertilizers contain about twice as COMMERCIAL FERTILIZERS 207 much potash as nitrogen and five times as much phos- phoric acid as potash. In order to make a ton of such a fertilizer it would be necessary to take about Pounds. MEET OL SGAAt ered wash. bis Sok wilak Sos. 225 CATAAIL: eta aera ea ode OE oe he oes Se ee 425 MOS HALCs 12 cis (haan eae mek an cack Sete ol xc 1350 The ton of fertilizer would then contain about 35 pounds of nitrogen, 189 pounds of phosphoric acid and 53 pounds of potash. These amounts are deter- mined by multiplying the percentage composition by the weight of material taken : Pounds. WIRE O BETAS rpin su Shen rs aks Goisrars sae. 225 0.4155 — wg PORAS IA «6s to os 6's, oa = oY siatm alae bie 425K O25 — 58-4 PNBSPMOME ATIC: «sos wea oe Se 1350 X 0.14 = 189.0 The fertilizer would then contain about I:75 per cent. nitrogen, 2.65 percent. potash, and 9.45 per cent. phosphoric acid. The percentage amounts are ob- tained by dividing the total pounds by 20. This fer- tilizer, if made at home from materials purchased in the market, would cost, exclusive of transportation and mixing, $18.79. Pounds. Cost. PUREST acl Se aS sos g 5 x 34-9 @ 14% cents = $5.06 Phosphoric acid ........ 189.0 @ 6 cents — 11.34 SUAS iets 2 =i hisie' < gees a 53-1 @ 4% cents— 2.39 Total $18.79 A more concentrated fertilizer could be prepared by using high-grade sulphate of potash, superphos- 208 SGILS AND FERTILIZERS phate, and ammonium sulphate. A fertilizer com- posed of these ingredients would contain : ba al ° cee £3 § pes Containing Total Es eS Pounds. percent. pounds. Value. 4 Sw 300 Sulphate of ammonia 20 N 60 @ 14% cents = $8.70 3.00 500 Sulphate of potash.. 50 K,O 250@ 4% cents = 11.25 12.50 1200 Superphosphate .--- 35 P,O; 420@ 6 cents = 25.20 21.0 Total $45.15 So concentrated a fertilizer as the preceding is tarely, if ever, found on. the market; althouehwoe price, $45.15 per ton, is frequently charged. This example is given to show the composition and trade value of one of the most concentrated fertilizers that could be produced. Any one of the different materials mentioned in the chapters on special fertilizers could be used, as dried blood, tankage, nitrate of soda, sulphate of ammonia, raw bone, dissolved bone, raw phosphate rock, dis- solved phosphate rock, basic slag, kainit, muriate or sulphate of potash, and many others. Inasmuch as each of these materials has a different value, it fol- lows that fertilizers, even of the same general com- position, nay have widely different crop-producing powers. 266. Inert Forms of Plant Food in Fertilizers. — A fertilizer of the same general composition as the first COMMERCIAL FERTILIZERS 209 example could be made from feldspar rock, apatite rock, and leather. The leather contains nitrogen, the apatite contains phosphoric acid, and the feldspar, potash. Such a fertilizer would have no value when used on a crop, because all of the plant food elements are present in unavailable forms. Hence, in purchas- ing fertilizers, it is necessary to know not only the percentage composition, but also the nature of the materials from which the fertilizer was made. 267. Inspection of Fertilizers.—In many states laws have been enacted regulating the manufacture and sale of commercial fertilizers, and provision is made for inspection and analysis of all brands offered for sale. The label on the fertilizer package must specify the percentage amounts of nitrogen, available phos- phoric acid and potash. Inspection has been found necessary in order to protect the farmer and the honest manufacturer. Occasionally a fraud is revealed like the following : 7” Natural plant food $25 to $28 per ton. Con position. Pericene. Total phosphoric actd« 5 <). 564 sce 2a eeee snes 22.21 Insoluble ‘‘ Gye hs te eesie acne nian, SiGe a arte 20.81 Available ‘‘ GR cater Yeah Inia Spee oe Ne 1.40 GES) Gis Ie CIA WALEED nc. < 2.0 nies «ores cs. dais eae woe 0.13 Actual value per ton, $1.52. 268. Mechanical Condition of Fertilizers.— When a fertilizer is purchased, the mechanical condition should also be considered. The finer the fer- 210 SOILS AND FERTILIZERS tilizer, as a rule, the better it is for promoting crop growth. Some combinations of plant food produce fertilizers which become so hard and lumpy that it is difficult to crush the lumps before spreading. The mass must be pulverized so as to be evenly distributed, otherwise the plant food will not be economically used. A fertilizer that passes through a sieve with holes 0.25 mm. in diameter 1s more valuable and can be used to better advantage than one of the same com- position that requires a 0.5 mm. sieve. 269. Forms of Nitrogen in Commercial Fertilizers. — Nitrogen is present in commercial fertilizersin three forms : (1) Ammonium salts,(2) nitrates, and (3) organic nitrogen. ‘The organic nitrogen is divided into two classes: (a) soluble in pepsin solution, and (4) insolu- ble in pepsin solution. The relative values of these different forms of nitrogen are discussed in Chapter IV. Three fertilizers may have the same amount of total nitrogen and still have entirely different crop- producing powers. No. I. INOm2: No. 3 . = he Nitrogen as: Percent. Percent. Percent. Ammonium compounds .«-- 1.75 0.25 0.10 INA ERAGE ate late motets hora cio 0.15 0.15 0.10 Organic nitrogen : Soluble in pepsin........... 0.10 1.25 0.55 Insoluble in pepsin ......-. ee 0.35 moe OR OEAe ne aie tate Mie istetafals 2.00 2.00 2.00 In purchasing fertilizers it is important to know not only the amount of nitrogen, but also the form in COMMERCIAL FERTILIZERS FN which it is present. In No. 3 the nitrogen is in inert forms like leather, while in No. 2 it is largely in the form of dried blood, and No. 1 has mainly ammonium compounds. Each of these fertilizers, as explained in the chapter on nitrogenous manures, has a different plant food value. 270. Phosphoric Acid. — There are three forms of phosphoric acid in commercial fertilizers: (1) Water- soluble, (2) citrate-soluble, and (3) insoluble. The water- and citrate-soluble are called the available phos- phoric acid. In most fertilizers the phosphoric acid is derived from dissolved phosphate rock, and is in the form of monocalcium phosphate. The citrate-soluble is mainly dicalciuin phosphate with variable amounts of iron and aluminum phosphates in easily soluble forms. The insoluble phosphoric acid is tricalcium and other phosphates which are soluble only in strong mineral acids. The insoluble phosphoric acid in fer- tilizers is considered as having but little value. As in the case of nitrogen three fertilizers may have the same total amount of phosphoric acid and yet have entirely different values. No. I. INO: 2: No. 3. Percent. ) Bencent. Per cent. Water-soluble phosphoric acid. 8.00 0.25 0.25 Citrate-soluble a Se 1.50 8.00 0.75 Insoluble ‘ are O50 E75 9.00 AGGAL s sive sina Sede Sie eee 10.00 10.00 10.00 No. 3 is of but little value; the fertilizer contains in- ZL2 SOILS AND FERTILIZERS soluble phosphate rock or some material of the same nature. No. 11s the most valuable, because it con- tains the least insoluble phosphoric acid. This fer- tilizer contains dissolved phosphate rock or dissolved bone. No. 2 is composed of such materials as the best grade of basic slag or roasted aluminum phosphate or fine steamed bone. 271. Potash.— The three forms of potash in fer- tilizers are: (1) water-soluble, (2) acid-soluble, and (3) insoluble. Materials as sulphate of potash, kainit, and muriate of potash, which are soluble in water, be- long to the first class. In some states the fertilizer laws recognize only the water-soluble potash. In the second class are found materials like tobacco stems and the organic forms of potash. Substances like feldspar, which contain insoluble potash, are of no value in fertilizers. Asa rule, the potash in commer- cial fertilizers is soluble in water; in only a few cases are acid-soluble forms met with. Insoluble potash would be considered an adulterant. 272. Misleading Statements on Fertilizer Pack- ages. — Occasionally the percentage amounts of nitro- gen, phosphoric acid, and potash are’ stated in mis- leading ways as ammonia, sulphate of potash, and bone phosphate of lime. Inasmuch as 14/17 of am- monia is nitrogen, the percentage figure for ammonia is proportionally greater than the nitrogen. And so with sulphate of potash which contains about 50 per COMMERCIAL, FERTILIZERS 21 cent. potash. This method of stating the composition can be considered in no other way than a fraud, especially when the fertilizer contains no sulphate of potash, but cheaper materials, and the phosphoric acid is not derived from bone. 273. Estimated Commercial Value of Fertilizers. — The estimated value of a commercial fertilizer is obtained from the percentage composition and the trade value of the materials used. Suppose that two fertilizers are selling for $25 and $30, respectively, each having a different composition, the estimated values would be obtained in the following way : COMPOSITION OF FERTILIZERS. Nop tr: NO. 2. Selling ptice $25. Seiling price $30. Per cent. Per cent. Nitrogen as nitrates...........++- 1.50 2.10 Phosphoric acid, available.......-. 8.00 10.00 * <) rasoltiole. «<0 2.00 0.50 Potash ( water-soluble)........-- » 2.00 3.50 POUNDS PER TON. No. I. No. 2. Nitrogen ........ 1350 ><. 20 == 30 1G X 2oOr=" 42 Phosphoric acid . 8.0 & 20= 160 . 10.0 XX 20 == 200 Potash. oes coe 3 os 2 120. “AS 3.5. X20: ==" 70 ESTIMATED VALUE. No. I. No. 2. Nitrogen nOOo GoKO eG 30 X 0.145 = $4.35 42 X 0.145 = $6.09 Phosphoric acid---- 160 * 0.06 = 9.60 206: X 0106 = 12.00 bes Sp pe eee gee e A C1085 == 11580 70 X 0.045 = 3.15 $15.75 $21.24 214 SOILS AND FERTILIZERS Difference between estimated value and _ selling price, No: 1,°$6.25%, N@..27 $8: 76: 274. Home Mixing. — At the New Jersey Experi- ment Station it has been shown that ‘“ the charges of the manufacturers and dealers for mixing, bagging, shipping, and other expenses are on the average $8.50 per ton, and also that the average manufactured fer- tilizer contains about 300 pounds of actual fertilizing constituents per ton. These figures are practically Fig. 34. Composition of Fertilizers. true of other states where large quantities of commer- cial fertilizers are used.”7* In states where smaller amounts are used the difference between the estimated cost and selling price is greater than $8.50. These facts emphasize the economy of home mixing. The difference in price between the raw materials and the product sold is frequently so great that it is an advantage for the farmer to purchase the raw mate- rials, as sulphate of potash, nitrate of soda, and acid COMMERCIAL FERTILIZERS ars phosphate, and mix them as desired. By so doing a fertilizer of any composition may be prepared and there 1s less danger of securing an inferior article. Of course it is not possible by means of shovels and sieves to accomplish as thorough mixing of the ingre- dients as with machinery. S S30 RON FORMULA NO. I. yen Pounds. Pounds. Z oo Nitrate of soda...... 500 containing nitrogen..... TI 387 Acid phosphate ..--. 1200 containing phos. acid... 168.0 8.40 Sulphate of potash-. 300 containing potash....... 150.0 7.50 SUR (ell Wrecenar ca eetetors tetas Yole! oe rauet ere aie saeneee tenolinto 395.5 FORMULA NO. 2. Nitrate of soda...... 250 containing nitrogen..... 29.7. 1:09 Acid phosphate ----. 900 containing phos. acid... 126.0 6.3 Sulphate of potash-- 450 containing potash....... 225.0 I1.5 Plaster, etc..-..... - 400 A eophezallee ot foresee ee tok So tat og ns arep-k ate, age 389.7 FORMULA NO. 3. Nitrate of soda...... 200 containing nitrogen.-.-. 31.0 1.55 Acid phosphate..... 1500 containing phos. acid... 210.0 10.50 Sulphate of potash-. I50 containing potash..-..--- 75.0 5.75 Plaster, etc ----..-. - 150 BURG ical (eons tacecan sevete ia tai SOs ois Adtas DVRi swore ke Se a es 316.0 275. Fertilizers and Tillage.— Commercial fer- tilizers cannot be made to take the place of good tillage, which is equally as important when fertilizers 216 SOILS AND FERTILIZERS are used as when they are omitted. Scant crops are as frequently due to the want of proper tillage as to the absence of plant food. Poor cultivation results in getting the soil out of condition; then instead of thor- oughly preparing the land, commercial fertilizers are resorted to, and the conclusion is reached that the soil is exhausted, when in reality it is suffering for the want of cultivation, for a dressing of land plaster, for farm manures, or for a change of crops. There is no ques- tion but what better tillage, better care and use of farm manures, the culture of clover and the systematic rotation of crops would result in greatly reducing the $60,000,000 annually spent for commercial fertilizers, without reducing the yield of crops. The better the cultivation, the less the amount of commercial fer- tilizer required. 276. Abuse of Commercial Fertilizers.— When a soil produces poor crops, a complete fertilizer is fre- quently used when an amendment only is needed. Restricted crop production in long cultivated soils is due to deficiency of available nitrogen. If the nitro- gen were supplied, improved cultivation would gen- erally furnish the available potash and phosphoric acid, but instead of providing the one element needed, others which may already be present in the soil in liberal amounts, are often supplied at a great expense. Another abuse of fertilizers is their application to the wrong crop. A heavy application of potash fertilizer FIELD TESTS WITH FERTILIZERS 2i7 to a wheat crop grown on a clay soil, or an application of nitrate of soda on land seeded to clover, or of land plaster to flax grown on a limestone soil, would be a useless waste of money. 277. Proper Use of Fertilizers. —In order to make the best use of commercial fertilizers, both the soil and the crop must be carefully considered. All crops do not possess the same power of obtaining food from the soil; turnips, for example, have very restricted powers of phosphate assimilation, hence they require special manuring with »hosphates. Wheat requires help in obtaining its nitrogen. A wheat crop will starve for the want of nitrogen, while an adjoining corn crop will scarcely feel its need. Wheat has strong power of assimilating potash compounds, while clover has less. Hence in the proper use of fertilizers the power of the plant to obtain its food must be considered. An application of potash to clover, nitrogen to wheat, and phosphoric acid to turnips, would be a judicious use of these fertilizers, while if-a mixture of the three ele- ments were applied to each crop alike, the clover would not be particularly benefited by the nitrogen or the wheat by the potash. Before commercial fertili- zers are used, careful field trials should be made with different crops. FIELD TESTS WITH FERTILIZERS 278. Experimental Plots.—A piece of land well 218 SOILS AND FERTILIZERS tilled and of uniform texture, should be used for field trials with fertilizers. After preparation for the crop, small plots, 1/20 of an acre, are staked off. A con- venient size is, length 204 feet, width ro feet 8 inches, area 2176 square feet. Between each “plot .a“stemmma feet wide should be left. In these experiments the plan is to apply one element or a combination of elements to a plot and compare the results with other plots treated differently.” 279. Preliminary Trials. — It is best to make pre- liminary trials one year and verify the conclusions the next. In making the tests the first year eight plots are necessary and fertilizers are applied in the follow- ing way: , The first plot receives no fertilizer and is used as the basis for comparison. The second plot receives a dressing of 8 pounds of nitrate of soda, 16 pounds acid phosphate, and 8 pounds sulphate or muriate of potash. The third plot receives nitrogen and phosphoric acid. The fourth plot receives nitrogen and potash. The fifth plot receives nitrogen. The sixth plot receives phosphoric acid and potash. The seventh plot receives potash. The eighth plot receives phosphoric acid. FIELD TESTS WITH FERTILIZERS ZiI9 Naotlese 2 Nae hb ene P5O2 PO: 2.30 K,O I a 4 N PO: K,O EO: K,O 5 6. ae 8. Should good results be obtained on plot No. 3, the indications are that there is a deficiency of the two elements nitrogen and phosphoric acid. An increased yield from No. 4 indicates deficiency of nitrogen and potash. Under such conditions the use of a complete fertilizer would be unnecessary. If No. 5 gives an additional yield the soil isin want of nitrogen. From the eight plots it will be possible to tell which of the various elements it will be advisable to use. The fer- tilizers should be applied after the land has been thor- oughly prepared and before seeding. Corn is a good crop for the first trials. "The number of plots may be increased by usiug well-prepared stable manure and gypsum on plots g and 10 respectively. The second year the results should be verified. 280. Deficiency of Nitrogen.—If the results indi- cate a deficiency of nitrogen, select two crops, one as wheat which is particularly benefited by dressings of nitrogen, and another as corn which has no difficulty in obtaining this element. The cultivation of each crop should be that which experience has shown to be the 220 SOILS AND FERTILIZERS best. On one wheat, and one corn plot, 8 pounds of nitrate of soda should be used, a plot each of wheat and corn being left unfertilized. If both the corn and the wheat are benefited by the application of nitro- gen, the soil is in need of available nitrogen. If, how- ever, the wheat responds and the corn does not, the soil is not in great need of nitrogen but does not con- tain an abundance in available forms. 281. Deficiency of Phosphoric Acid. — In experi- menting with phosphoric acid, turnips are grown on two plots and barley on two plots. To one plot of each 16 pounds of acid phosphate are applied. If both crops show marked additional yields the soil is in need of available phosphoric acid. If only the turnips re- spond while the barley is indifferent the soil contains a fair amount of available phosphoric acid. Barley and turnips are used because there is such a marked difference in the power of each to assimilate phos- phoric acid. 282. Deficiency of Potash. — In order to determine the condition of the soil as to potash, potatoes and oats may be used as the trial crops, and 8 pounds of sul- phate of potash should be applied to one plot of each. Marked additional yields indicate a poverty of availa- ble potash ; an increased potato crop and an indiffer- ent oat crop indicate potash not in the most available forms. If no additional yields are obtained the soil is not in need of potash. FIELD TESTS WITH FERTILIZERS 224 283. Deficiency of Two Elements. — If the prelim- inary trials indicate a deficiency of two elements as nitrogen and phosphoric acid, both elements are used together, in the same way as described for deficiency of nitrogen, with additional plots for the separate ap- plication of nitrogen and phosphoric acid. 284. Importance of Field Trials. — While it seems a troublesome matter to determine the actual needs of a soil, it will be found that both time and money are saved by a systematic study of the question. Suppose fertilizers are used in a “hit or miss” way year after year on a soil, deficient only in phosphoric acid. It would take 8 years to find out what the soil was deficient in, if a different fertilizer were used each year, and during all this period, either the soil has failed to receive its proper fertilizer, or expensive and unneces- sary plant food has been provided. 285. Will it Pay to Use Commercial Fertilizers? — This question can be answered only by trial. Ifa soil is in need of available plant food, the additional amount of crop produced should pay for the fertilizer and the expense of using it. Some fertilizers have an influence on two or three succeeding crops, and only partial returns are received the first year. When large crops must be produced on small areas, as in truck farming, commercial fertilizers are generally neces- sary. In the production of large areas of staple crops as wheat and corn, in the western prairie states, 222 SOILS AND FERTILIZERS they have never been used. If the soil is properly tilled and there 1s a good stock of natural fertility, the use of cominercial fertilizers can be avoided. With poor cultivation anda soil that has been impoverished by injudicious cultivation their use is more necessary. 286. Amount of Fertilizer to Use per Acre. — When commercial fertilizers are used, it should be the aim to apply just enough to produce normal yields. Heavy applications at long intervals are not as productive of good results as light applications more frequently. From 400 to 600 pounds per acre is as much as should be used at one time unless previous trials have shown that heavier applications are necessary. The way in which the fertilizer is to be applied, as broadcast or otherwise, must be determined by the crop to be grown. ‘The fertilizer should not come in direct con- tact with seeds, neither should it be worked into the soil to such a depth that it may be lost by leaching before it can be appropriated by the crop. 287. Excessive Applications of Fertilizers Taek ous. — An overabundance of plant food has an inju- rious effect upon crop growth. Plants take their food from the soil in dilute solutions, and when the solution is concentrated abnormal growth results. Potatoes heavily manured with nitrate of soda makea luxuriant growth of vines but produce only a few small tubers. Whena medium dressing is used along with potash and phosphoric acid, a more balanced FIELD TESTS WITH FERTILIZERS ps5 growth is obtained, and a better yield is the result. Heavy applications of nitrate of soda produce a rank growth of straw, with a low yield of grain. The ex- cessive amount of nitrogen causes the mineral matter to be utilized for straw production and leaves only a small amount for grain production. When applica- tions of commercial fertilizers are too heavy, plants take up unnecessary amounts of food and fail to make good use of it. In fact crops may be overted the same as animals. Hence in the use of fertilizers ex- cessive applications are to be avoided. 288. Fertilizing Special Crops. — There are crops which need special help in obtaining some one ele- ment, and in the use of fertilizers it should be the rule to help those crops which have the greatest difficulty in obtaining food. When the soil does not show a marked deficiency in any one element, light dressings of special purpose manures may be made to the follow- ing crops : Wheat. — Nitrogen first ; phosphoric acid to a less extent Barley, oats, and rye require manuring like wheat, but toa less extent. Each crop has a different power of obtaining nitrogen. Wheat requires the most help and barley and rye the least. Corn. — Phosphoric acid first ; then nitrogen and potash. 224 SOILS AND FERTILIZERS Potatoes. —General manuring ; reenforced with pot- ash. Mangels. — Nitrogen. Turnips. — Phosphoric acid. Clover. — Lime and potash. Timothy. — General manuring. 289. Commercial Fertilizers and Farm Manures. — Commercial fertilizers should not replace farm ma- nures, but simply reenforce them. Although com- mercial fertilizers are called complete manures, they fail tosupply organic matter. It is more important in some soils than in others, that the organic matter be maintained because in some soils the organic matter takes a more important part in crop production than does the food applied in commercial forms. For example, when a rich prairie soil is reduced by grain cropping and is allowed to return to pasture, heavier yields of grain are afterwards obtained than from sim- ilar soils which received applications of commercial fertilizers. CHAPTER XI FOOD REQUIREMENTS OF CROPS 290. Amount of Fertility Removed by Crops. — From an acre of soil, producing average crops, the amount of fertility removed varies between. wide lim- its. For example, an acre of mangels removes 150 pounds of potash, while an acre of flax removes 27 pounds; an acre of corn removes about 75 pounds of nitrogen, while an acre of wheat removes about 35 pounds. Crops which remove the most fertility do not always require the most help in obtaining their food. This is because the amount of plant food assimilated, and the power of crops to obtain this food, are not the same. An acre of corn, for example, takes over twice as much nitrogen as an acre of wheat, but wheat will often leave the soil in a more impoverished con- dition than corn, because corn has greater power for procuring nitrogen and for utilizing that formed by nitrification after the wheat crop has completed its growth. The available nitrogen if not utilized by a crop may be lost in various ways. Mangels require about twice as much phosphoric acid as flax, but are a strong feeding crop and require less help in obtain- ing this element. It was formerly believed that the amount of plant 226 SOILS AND FERTILIZERS food present in the matured crop indicated the kind and amount of fertilizing ingredients to apply, and that a correct system of manuring required a return to the soil of all elements removed in the crop. Ex- periments have shown that both of these views are in- correct. The composition of plants cannot be taken as the basis for their manuring. For example an acre of wheat contains 35 pounds of nitrogen while an acre of clover contains 70 pounds. If 70 pounds of nitrogen were applied to an acre of clover and 35 pounds to an . acre of wheat, poor results would follow, because clo- ver can obtain its own nitrogen while wheat is nearly helpless in obtaining it,and the 35 pounds would not necessarily come in contact with the roots so that it could all be assimilated. While the amount of plant food removed in crops cannot serve as the basis for their manuring, valuable results are obtained from the study of the different elements of fertility removed in crops, and in making use of the following figures, other fac- tors, as the influence of the crop upon the soil and the power of the crop to obtain its food, must also be con- sidered. FOOD REQUIREMENTS OF CROPS ZP55| PLANT FOOD REMOVED BY CROPS?’ Pounds per acre. hos- Gross’ Nitro- alone Pot- Sil- Total Crops. weight: gen. acid. ash. Lime, aca.) Vash Wheat, 20 bus...--- 1200 25 12.5 7 I I 25 Sk Peers 2000 10 gists Meee, 6 ik = eagiona War to) 27 Rariceeicreies sees 35 20 35 S/he, 2S Barley, 40 bus----- 1920 28 15 8 Eat 4O Straw .---+-+..--- 3000 12 5 30 oa t60. 4476 Total...-...-. 40 20 38 Gy 72> 7, 200 Oats, 50 bus...-.--- 1600 35 12 fe) Oe a 55 STE 2 Teer oreo 3000 15 6 35 9.5 60 150 Total 50 18 Ao ae Og 5 205 Corn, 65 bus...... 2200 4o 18 15 I I 4O Stalks......++---. 3000 35 2. = 6s hee OO: POO GEA Se etetnrace © Seer vhs 20 60." 12-90. -200 Peas, 30 bus..----- 1800 18 22 4 I 64 Straw .---.220..s- 3500 7 38 71 9 176 Total ........ 25 GO.) 75) 10" 7240 Mangels, Io tons-- 20000 75 35 150° «+30! ALO!) B50 Meadow hay, 1 ton 2000 30 20 Ay 12) 50. - 175 Red Clover Hay, 2 tons....-... 4000 .- 28 GOs 2750-2 15 S250 Potatoes, 150 bus-- 9000 40 20 Te tet 2S AS 125 Flax, 15 bus...---- goo 39 15 8 2 O:5,. 34 Straw ee 1800 1S 3 19 13 a 53 AR GiEAll bias ware: ecatic = Soke 54 18 7 es 18) 225 87 291. Plants Render Their Own Food Soluble. — It was supposed at one time that plants obtained all of their mineral food from the mineral matter dissolved in the soil water. Experiments by Liebig demonstra- ted that plants have the power of rendering their own food soluble, provided it does not exist in forms 228 SOILS AND FERTILIZERS too inert to undergo chemical change. Ljiebig grew barley in boxes so constructed that all of the water- soluble plant food could be secured. Two of the boxes were manured and two left unmanured. In one box which received manure and one which received none, barley was grown. One each of the manured and unmanured boxes was left barren. He collected all of the drain waters and determined the soluble mineral matter present, also weighed and analyzed the crop. His results showed that 92 per cent. of the potash in the crop was obtained from forms insoluble in water.7 In the roots of all plants there are present various organic acids. Between the rootlet and the soil there is a layer of water. The plant sap and the soil water are separated by plant tissue which acts asa membrane. All of the conditions are favorable for osmosis. The acid sap from the roots finds its way into the soil in exchange for some of the soil water. This acid, excre- ted by the roots, acts upon the mineral matter, render- ing it soluble, when it is taken up by the plant. Different plants contain different kinds and amounts of organic acids as well as present different areas of root surface to act upon the soil, and the result is that agricultural crops have different powers of assimila- ting food. Plants not only possess the power of rendering their food soluble but they are also able to select their own food and to reject that which is unnecessary. For ex- CEREAL CROPS 229 ample, wheat grown on prairie soil containing soda in equally abundant and soluble forms as the potash, will contain relatively little soda compared with the potash in the crop.%° CEREAL CROPS 292. General Food Requirements. — Cereal crops con- _tain a high per cent. of silica and evidently possess the power of feeding upon some of the simpler silicates of the soil, liberating the base elements which are utilized as food, while the silica is deposited in the outer surface of the straw. As previously stated, cer- eal crops although they do not remove large amounts of total nitrogen from the soil require special help in obtaining this element. There is, however, a great difference among the cereals as to power of assimila- ting nitrogen. Next to nitrogen these crops stand most in need of phosphoric acid. The humic phos- phates are utilized by nearly all of the cereals. 293. Wheat.— This crop is more exacting in its food requirements than barley, oats, or rye. Wheat is comparatively a weak feeding crop, and the soil should be in a higher state of fertility than for other grains. The extensive experiments of Lawes and Gilbert have given valuable information regard- ing the effects of manures on wheat. The results are given in the following table :” 230 SOILS AND FERTILIZERS AVERAGE YIELD OF WHEAT PER ACRE. Bushels. No manure for GO VEATS+ 61+ cece cece cece ce ee ccees 14 Minerals alone for 32 years «-.. +222. eevee eee 15+ 14 as ce oe is ail Nitrogen ss Zeidaalyouece QV of Sy'e te a ot etoneranene te 234 Farmyard manure for 32 years .-+- sees cere ee ee ee 323 Minerals and nitrogen for 32 years'........-+ee6- 364 oe as es Ce Tene (icy 9. 3 se niente sy oteretaate 323 The food requirements of wheat are such that it should be given a favored position intherotation. Wheat may follow clover provided the clover sod is light and is fall plowed. On some soils, however, wheat does not thrive following asod crop. It takes nearly a year for a heavy sod residue to get into suitable food forms fora wheat crop. Under such conditions, oats should first be sown, then wheat may follow. On average soil a medium clover sod, plowed late in summer or in early fall, and followed with surface cultivation, leaves the land in good condition for spring wheat. It is not advisable to have wheat follow barley, because the soil will be too porous, and barley being a stronger feeding crop leaves the land in poor condition as to available plant food. Whena corn crop is well ma- nured, wheat may follow. The food requirements of wheat are best satisfied following a light, well cultiva- ted clover sod, or following oats which have been grown on heavy sod, or following corn that has been well manured. 186 pounds of nitrogen as sodium nitrate. 2 86 s ae x ‘* ammonium salts. CEREAL CROPS 221 294. Barley. — While wheat and barley belong to the same general class of cereals, they differ greatly in their habits and food requirements. Barley is a stronger feeding crop, has a greater root development near the surface, and can utilize food in cruder forms. In many of the western states, soils which produce poor wheat crops, from too long cultivation, give ex- cellent yields of barley. This is due to changed con- ditions, of both the chemical and mechanical composi- tion of the soil. Long cultivation has made the soil porous and reduced the nitrogen content. Barley thrives best on a rather open soil and has greater ni- trogen assimilative powers than wheat. Barley, how- ever, responds liberally to manuring, particularly to m1- trogenous manures. The experiments of Lawes and Gilbert on the growth of barley are briefly summa- rized in the following table.” AVERAGE YIELD OF BARLEY PER ACRE FOR 34 YEARS. Bushels. Tice atad OTHERS Nevereie cic Bhererarcia hac Saciadete Tee die aanicroset ovelane's 174 Superphosphate alone ---. +++ see eee eee cree eee 231 WiteeCa ater ails acme a cies cies erase 6 eye aie a on kim ws 241 Nitrogen alone..+. sees cee ee cece ee cece eee en's) 302 Nitrogen and superphosphate...--.-++++++.++--- A5 Farmyard manureS.------+++eeee ee cece cece ce eee 4g} 295. Oats. — Oats are capable of obtaining food un- der more adverse conditions than either barley or wheat. They are also less exacting as to soil require- iments. The oat plant will adapt itself to either sandy 232 SOILS AND FERTILIZERS or clay soil, and will thrive in the presence of alkaline matter or humic acid where wheat would be destroyed. In a rotation, oats usually occupy a position less favored by manures. They are, however, greatly benefited by fertilizers particularly by those of a nitrogenous na- ture. 296. Corn. — Experiments with corn indicate that under ordinary conditions it requires most help in ob- taining phosphoric acid. Corn removesa large amount of gross fertility but its habits of growth are such that it generally leaves an average soil in better condition for succeeding crops. Corn is not injured as are many grain crops by heavy applications of stable manure. It does not, like flax, produce waste products which are destructive to itself. Rich prairie soils when newly broken give better results for wheat culture after one or two corn crops have been removed. The food requirements of corn are satisfied by applications of stable manure, occasionally reenforced with a little phosphoric acid. After clover, corn gives excellent returns, and when corn is the chief market crop it should be favored by having the best position in a ro- tation. MISCELLANEOUS CROPS 297. Flax is very exacting in food requirements and for its culture the soil must be in a high state of fertility. It is a type of a weak feeding crop. ‘There are but few roots near the surface and consequently it MISCELLANEOUS CROPS 233 has restricted powers of nitrogen assimilation.37 Flax does not remove a large amount of fertility but if grown too frequently the tendency is to get the land out of condition rather than to exhaust it. Flax should be indirectly manured. Direct applications of stable manure produce poor results, but when the ma- nure is applied to the preceding crop excellent results are obtained. ‘The best conditions for flax culture re- quire that it should be grown on the same land only once in five years. Dr. Lugger has demonstrated that there are produced, when the roots and straw ‘of flax decay, products which are destructive to succeed- ing flax crops.” The food requirements of flax are met when it follows corn which has been well manured, or a sod which has been given the cultivation described for wheat. Flax and spring wheat are much alike in food requirements. 298. Potatoes. — Potatoes are surface feeders and when grown continually upon the same soil without manure, the yield per acre decreases more rapidly than any other farm crop. Experiments with potatoes by Lawes and Gilbert using different manures gave the following result :77 AVERAGE YIELD PER ACRE FOR I2 YEARS. Tons. Cwt. i Mie Oe ote helo nesses I 19? Superphosphate.........----+.+--- 5 IGMEEAIG ANON > bites ois 2 ans on se se = 3 3 Nitrate of soda alone.-.-.--....--- 2 2 Mixed manures and nitrogen ...... 5 173 Farm manures, alternate years.....- 4 3 234 SOILS AND FERTILIZERS Potatoes require liberal general manuring reenforced with wood ashes or other potash fertilizers. In the rotation they should follow grain or pasture land, pro- vided the fertility of the soil is kept up. 299. Sugar-beets. — This crop is more exacting in its food demands than other root crop. Excessive fertility is not conducive to a high content of sugar. Soils in a medium state of fertility usually give the best results.” Sugar-beets should not receive heavy dressings of stable manure, because an abnormal growth results. Nitrogenous fertilizers can be ap- plied only in limited amounts, heavier dressings of potash and phosphoric acid are more admissible. When sugar-beets follow corn which has been manured, or grain which has left the soil in an average state of fertility, the food requirements are well met. 300. Roots. — Mangels are gross feeders and re- move a larger amount of fertility from the soil than any other farm crop.77 When fed to stock and the manure is returned to the soil they materially aid in making the plant food more available for delicate feeding crops. Mangels are better able to obtain their phosphoric acid than are turnips and need the most help in the way of nitrogen. Turnips are surface feeders with stronger power of nitrogen assimilation than the grains but with restricted power of phosphate assimilation. Manures for turnips should be phos- phatic in nature... MISCELLANEOUS CROPS 235 301. Rape is a type of a strong feeding plant capa- ble of obtaining its food under conditions adverse to grain culture. When grown too frequently upon the saine soil it does not thrive. On account of its great capacity for obtaining food, it is a valuable crop to use for green manuring purposes.” 302. Buckwheat isa strong feeding crop and its demands for food are easily met. On rich soil, a rank growth of straw results, with poor seed formation. Buckwheat is usually sown upon the poorest soil of the farm. Being a strong feeder it is frequently used as a manurial crop, being plowed under while green to serve as food for weaker feeding crops. 303. Cotton. — On average soils cotton stands in need first of phosphoric acid, second of Hitmen? At is most able to obtain potash, but soils deficient in pot- ash require its use. Organic nitrogen as cottonseed meal and stable manure appear equally as effective as nitric nitrogen. Phosphoric acid must be applied in the most available forms. In fertilizing cotton, the use of green manuring crops as cow peas with an application of marl gives beneficial results. Marl, how- ever, should not be applied alone because of the forma- tion of insoluble phosphate of lime. Lime combines with the decaying organic matter in preference to phosphates, a result which is beneficial to both soil and crop. 304. Hops. — The hop plant is peculiar in regard 236 SOILS AND FERTILIZERS to its food requirements. An excess of easily soluble plant food is injurious while a lack is equally so. An abundance of food in organic forms is most essential. Heavy dressings of farm manures may be applied. Where hops are grown there is a tendency to use all of the manure on the hops while the rest of the farm is left unmanured. Very light applications of com- mercial fertilizers may be used in connection with sta- ble manure, but such use should be made only after a preliminary trial on a smaller scale. 305. Hay and Grass Crops. — Most grass crops have shorter roots than grain crops; they are surface feed- ers and not so able to secure mineral food. When a number of crops have been removed the soil may stand in need of available mineral matter. Farm manures are particularly well adapted for fertilizing grass. - Ap- plications of nitrogenous manures result in discoura- ging the growth of clover. Heavy manuring of grass land has a tendency to reduce the number of species and one kind is apt to predominate.** On some soils ashes, and on others lime fertilizers, have been found very beneficial. The manuring of grass lands must be varied to meet the requirements of different soils. Permanent meadows require different manuring from meadow simply introduced as an important crop in the rotation. 306. Leguminous Crops. — For leguminous crops pot- ash and lime fertilizers have been found of most value. MISCELLANEOUS CROPS 2a Analyses of leguminous crops, as clover and peas, show large amounts of both potash and lime. Many crops as clover fail when grown too frequently upon the same soil, not because the soil is exhausted but because of the development in the soil of organic products which are destructive togrowth. When the inexpen- sive food requirements of leguminous crops are sup- plied, the soil is enriched with nitrogen and phos- phoric acid which have been changed to more availa- ble forms. CHAPTER XII ROTATION OF CROPS AND CONSERVATION OF SOIL FERTILITY 307. Object of Crop Rotation. — The object of the systematic rotation of crops is to conserve the fertility of the soil, and at the same time to produce larger yields. In order to accomplish this, the food require- ments of different crops must be met by good cultiva- tion and proper manuring. Rotations must be planned according to the nature of the soil and the system of farming that is to be followed. For general grain farming a different system must be practiced than for exclusive dairying. Whatever the nature of farming the whole farm should gradually undergo a systematic rotation. If the farm is uneven in soil texture, differ- ent rotations must be practiced on the various parts. There is no way in which soils are more rapidly de- pleted of fertility than by the continued culture of one crop. In exclusive wheat raising for example the losses which occur are not confined to the fertility re- moved in the crop but may take place in other ways as described in the chapter on nitrogen. When wheat is properly grown in alternation with other crops, losses of nitrogen are reduced to the minimum. When remunerative crops can no longer be produced the soil is said to be exhausted. Soil exhaustion may ROTATION OF CROPS 239 be due either to a lack of fertility or to getting the soil out of condition because of the “ one-crop system” and poor methods of cultivation. 308. Principles Involved in Crop Rotation. — In the systematic rotation of crops there are a few funda- mental principles with which all rotations should be made to conform. Briefly stated these principles are : 1. Deep and shallow rooted crops should alternate. 2. Humus-consuming and humus-producing crops should alternate. 3. Crops should be rotated so as to make the best use of the preceding crop residue. 4. Crops should be rotated so as to secure nitrogen indirectly from atmospheric sources. 5. Crops should be rotated so as to keep the soil in the best mechanical condition. 6. In arid regions crops should be rotated so as to make the best use of the soil water. 7. An even distribution of farm labor should be se- cured by a rotation. 8. Farm manures and fertilizers should be used in the rotation where they wilJl do the most good. g. Rotations should be planned so as to produce fod- der for stock, and so that every year there will be some important crop to be sold. 309. Deep and Shallow Rooted Crops. — When deep and shallow rooted crops alternate, the draft upon the surface soil and subsoil is more evenly distributed. 240 SOILS AND FERTILIZERS In many soils nitrogen and phosphoric acid are more abundant in the surface soil while potash and lime predominate in the subsoil. When such a condition exists, the alternating of deep and shallow rooted crops is very beneficial, because the surface soil is re- lieved of continuous heavy drafts upon the elements — present in scant amounts. 310. Humus-consuming and Humus-producing Crops. — When grain or hoed crops are grown con- tinuously, oxidation of the humus occurs, and the chemical and physical properties of the soil may be entirely changed by the loss of the humus. The ro- tating of grass and grain crops and the use of stable manure serve to maintain the humus equilibrium. On some soils lime may be required along with the humus to prevent the formation of humic acid, and in such cases the best conditions exist when both lime and hu- mus materials are supplied. The alternation of hu- mus-producing and humus-consuming crops is one of the essential matters to consider in a rotation. 311. Crop-Residue. — Crop residues should always » be placed at the disposal of weak feeding crops. For example, after a light clover and timothy sod, wheat or flax should be grown in preference to barley or mangels. The weak feeding crop should then be fol- lowed by a strong feeding crop, and each is properly supplied with food. It would be poor economy, onan average soil, to follow clover and timothy with mangels, ROTATION OF CROPS 241 then with barley, and finally with flax, because the flax would be placed at a serious disadvantage follow- ing two strong feeding crops. If reversed, the crops would be placed in order of assimilative power, and the best use would be made of the sod crop residue. When crops of dissimilar feeding habits follow each other in rotation not only are the crop residues used to the best advantage, but the soil is relieved of excessive demands on special elements. For example, wheat and clover take different amounts of potash and hme from the soil. Wheat has the power of feeding upon silicates of potash which clover cannot assimilate, hence wheat and clover in rotation relieve the soil of excessive demands on the potash. 312. Nitrogen-consuming and Nitrogen-producing Crops. — It is possible in a five-course rotation to main- tain or even increase the nitrogen of the soil without the use of nitrogenous manures. In Section 131 an ex- ample is given of a rotation which has left the soil with a better supply of nitrogen than at the begin- ning. When a soil produces a good clover crop once in five years, and stable manure is used once during the rotation, the soil nitrogen is not decreased. By means of rotating nitrogen-producing and nitrogen- consuming crops it is possible to sell nitrogenous grain products from the farm without purchasing nitroge- nous manures. The conservation of the nitrogen of the soil is the most important point to consider in the 242 SOILS AND FERTILIZERS rotation of crops, because it is the most expensive ele- ment and is the most liable to be deficient. 313. Influence of Rotation upon the Mechanical Condition of Soils. — With different kinds of crops, the mechanical conditions of soils are constantly under- going change. Grain crops and hoed crops tend to make the soil open in texture. Grass crops have the opposite effect. All soils should undergo periodic compacting and loosening. Some require more of one treatment than of the other. In a good rotation the mechanical action of the crop upon the soil should be considered, otherwise the soil may get into poor condi- tion to retain water or become so loose that heavy losses occur through wind storms. Sandy soils are improved by those methods of cropping which compact the soil, while heavy clays require the opposite treat- ment. The rotation should be made to conform to the requirements of the soil. 314. Economic Use of Soil Water. — The rotation should not be of such a nature as to make excessive demands upon the soil water. For example, after a grain crop has been produced, it is best in regions of scant rainfall to plow the land and get it into condi- tion to conserve the water for the next year’s crop, rather than to attempt to raise a catch crop the same year. Crops removing excessive amounts of water should not be grown too frequently. Sunflowers, for example, remove twenty times more water than grain ROTATION OF CROPS 243 crops. Cabbage removes from the soil more water than many other crops. With a good rotation it is possible to carry the water balance in the soil from year to year, so that crops will be supplied in times of drought. 315. Rotation and Farm Labor. — The rotation of crops should be planned so that an even distribution of farm labor is secured. The importance of this principle is so plain that its discussion is unnecessary. It is a topic outside of the domain of chemistry, but is nevertheless one of the most important to con- sider in economic farming, and should not be lost sight of in planning rotations. 316. Economic Use of Manures. — Farm manure should be applied to those crops which experience has shown to be the most benefited by its use. At least once during a five years’ rotation the land should receive a dressing of stable manure. If commercial fertilizers are used, they should be applied to the crops which require the most help in obtaining food. With the growing of clover and the use of farm manures, only the poorer kinds of soil will require commercial fertil- izers for general crop production. It is more econom- ical to reenforce the farm manures with fertilizers especially adapted to the soil and crop than to purchase complete fertilizers. 317. Salable Crops.—In all farming, something must be sold from the farm. It should be the aim to 244 SOILS AND FERTILIZERS sell products which remove the least fertility, or if those are sold which remove large amounts, to return in cheaper forms the fertility sold. In a good rotation - it ‘1s the plan to have at least one salable crop each year. The whole farm need not undergo the same rotation at the same time and the rotation may be subject to minor changes as circumstances require. To illustrate, wheat and flax occupy about the same position in a rotation. If when the crop is to be seeded the indications are that wheat will be a poor paying crop and flax sell well, flax should be sown. The rotation should be such that one of two or three crops may be grown as circumstances require. 318. Rotations Advantageous in Other Ways. — A good rotation will be found advantageous in many ways. With one line of cropping, land becomes foul with special kinds of weeds which are unable to thrive when crops are rotated. Frequently the rota- tion must be planned so as to reclaim the land from weeds. . Relief from insect pests is often secured by a proper rotation. Many insects are capable of living only on a special crop and when this crop is grown continually on the same land the best conditions for insect ravages exist. 319. Long- and Short-course Rotations. — Rota- tions vary in length from 2 to 17 years. Long-course ROTATION OF CROPS 245 rotations are more generally followed in European countries. The length of the rotation can only be de- termined by the conditions existing in different local- ities. Asa general rule long-course rotations should be attempted only after a careful study of all the conditions relating to the system of farming that it is desired to follow. For northern latitudes a rotation of four or five years gives excellent results. In some localities three-course rotations are the most desirable. A rotation that is suitable for one locality or kind of farming may be unsuited for other localities or con- ditions. Because of variations in soil, climate, and rainfall, no‘definite standard rotation can be pro- posed that will be suitable for all conditions. 320. Example of Rotation. — In dealing with the subject of rotations it is best to take actual problems as they present themselves and plan rotations that will best meet all conditions. For example, a farm of 160 acres is to be rotated with the main object of pro- ducing fodder for live stock, and a small amount of grain for sale. The following rotation has been pro- posed:to meet such conditions.” ‘1IPPoO} u10d Yyinoj-ouo ‘adr YANO; -9u0 ‘sevod yjInoj-au0 ‘soojzejod Yjinoj-9ug ‘Aopleg ‘xey jrey -9u0 «=‘JeoyM Jyey-9ug ‘(peinuem) u10d ‘oinjseg ‘MOpRd| ‘(Any -OWT}] PUB IIAOID) s}VO y ‘(Aq -OWIT} pue IIAO]D) s}VO “MOPROT "2IN}8Cd| ead yyAZ ‘lop -poJ UIOD YINOJ-9u00 ‘9A1 YJANOJ-9u0 ‘svad ; YVANo} auO ‘sjoo1 pue (Ay s90jejod = yymoj-aug|-OMH =~ pue 19A0jo) syeO ‘MOpRayy| seat yI9 ‘lop “poy UO YyInofF-ouo0 | ‘QAI YJINOJ-au0 ‘sead YVANOJ-9u0 ‘sjoor pue | ‘(AYA ‘Aapreg s90zej0d YWNojJ-9uQ)| -OWll puUue IIAOCTD) syeO| sedk yy ‘IIPpojJ us099 YyAnoj-9u0 ‘9AI YANO; ‘Xey jrey -9u0 ‘seod yyINOJ-3u0 -900 ‘yeosyM jley-3ug ‘Aopieg|‘soojejod = yymoj-aug| redh yb “xep Jey ‘(peinuem) u1oD|-auo0 ‘yeaym jyey-auGQ ‘(poinueu) Aspieg} iPad pal ‘xep jrey ‘oInj\sedg ‘(poeimuewt) u10D|-90u0 ‘yeaymM Jyey-auQ) 3ze3dA puz “MOPRII ‘JIn\seg ‘(peinuem) ulod} 3e9h 4sI oC: YF OF ‘WUVyY AYIVG AOA NOLLV LOY ‘sdo10 snoou -B[[QOSTI 1OJ P9ATISIY ‘(pomurur) Aopreg “Xe jyeu -9uo0 «=‘yeoyM $jJyey-9uO ‘(poimuerit) U10D) ‘o1njsed ‘MOpRdTN ‘(Aq -OUuTT pue IdAO]O) $}eQ ‘Jappof UIO YRANOFJ -su0 ‘seod wYINO;J -auo ‘aAI Y}INOJ-9u0 ‘saoyejod yVnoj-9ug “xey jvey -au0 ‘yeoyM = jJley-9uQ ‘(pommuentl) U10D ‘J1n\seg ‘MOpPRdTN “(Au -OUNT}] PUB IDAOTD) SEO ‘lOppOJ} UO YJANOFJ -au0 ‘seod wYINOFJ -9u0 ‘dA YZINOJ-9u0 ‘soozejod YVANojJ-9uQ ‘(poinuemt) Aopreg ‘(poinueml) U1OD ‘QIn\sed “MOPRIIN ‘(Auy -OUWT} PUR IDAOTD) S}VO ‘IOppoj UsoS yWnoj-ouo ‘svad yyAINOo;J -9uo0 ‘asfI YINOJ-9u0 ‘saozejod YqAnoj-9uO, ‘(painueur) Aopieg “xep jTey -su0 ‘yeayM jley-9uO qeak W434 ies 439 ieah 43S ieok yy qeak pit reak puz eo jsI LZ 9 “"WUVy AYIVG AOA NOWVLOY S 248 SOILS AND FERTILIZERS The farm is divided into eight fields of 20 acres each; seven fields are brought under the rotation, while one field is left free for miscellaneous purposes. Each year there are produced 20 acres of corn, 20 acres of timothy and clover hay, ro acres each of wheat and flax, 20 acres of barley, and five acres each of corn fodder, rye, peas, and potatoes, while 20 acres are reserved for pasture. The main income is derived from the sale of live stock and dairy products. Problems on Rotations 1. Plan a rotation for general farming (160 acres), using the fol- lowing crops: clover, timothy, barley, oats, potatoes, and corn. The soil is in an average state of fertility. Twenty-five head of stock are kept. 2. Plan a three-course rotation for a sandy soil, the main object being potato culture. 3. Plan a seven-year rotation for grain farming, using manure and sodium nitrate once during the rotation. The soil isa clay loam in a good state of fertility. 4. Plan a rotation for general farming on a sandy loam. 5. How would you proceed to bring an old grain farm froma low to a high state of productiveness? Begin with the feeding of the stock. 6. Using commercial and special-purpose manures, how would you proceed to raise wheat, potatoes, and hay, each continuously ? 7. Plan a rotation for a northern latitude, where corn cannot be grown, and where clover and timothy fail to do well; wheat and all small grains thrive; also millet, peas, rape, and some of the root crops. The soil is aclay loam, resting on a marl subsoil. Manure is very slow in decomposing. The rotation should be suited to general farming, wheat being the important market crop. CONSERVATION OF FERTILITY 321. Manures Necessary for Conservation of Fer- tility. — In order to conserve the fertility of the soil, not only must a systematic rotation be practiced, but a proper use must be made of the crops produced. When they are sold from the farm and no restoration is made soils are gradually depleted of their fertility. No soil has ever been found that will continue to pro- duce crops without the use of manures. Many prairie soils give large yields for long periods without manur- ing, but they are never able to compete in productive- ness with similar soils that have been systematically cropped and manured. With a fertile soil the decline of fertility is so gradual that it is not observed unless careful records are kept of the yields from year to year. 322. Use of Crops.— The use made of crops whether as food for stock or sold directly from the farm, deter- mines the future crop-producing power of the soil. With different systems of farming different uses are made of crops. When exclusive grain farming is fol- lowed no restoration of fertility is made, while in the case of stock farming, the manure produced contains fertility in proportion to the crops consumed. If good care is taken of the manure, and in place of the grains sold, mill products are purchased and fed, there is no loss of fertility. Between these two extremes, exclusive grain farming and stock farming, there are found in actual practice, different systems of farming, 250 SOILS AND FERTILIZERS which remove various amounts of fertility from the soil. 323. Two Systems of Farming Compared.— The losses of fertility from farms are determined by the crops and products sold, the care of the manure, and the fertility in the products purchased and used on the farm. If an account were kept of the income and outgo of the fertility of farms it would be found that with some systems, the soil is gaining in fertility, while with others a rapid decline occurs. In studying the income and outgo of fertility, it is necessary to calcu- late the amount of the three principal elements, nitro- gen, phosphoric acid, and potash in the crops and products sold. For making these calculations tables are given in Sections 1'78 and 290. Inthe handling of ma- nure it is impossible to prevent losses, but it 1s possible to reduce them to very small amounts. Hence in the calculations, a loss of 3 per cent. is allowed for mechan- ical waste, and for uneven distribution of the manure; that is, in addition to the fertility sold from the farm a loss of 3 per cent. is allowed for all crops raised and consumed as food by stock. On one farm the crops raised and sold are: Flax 4o acres, wheat 50 acres, oats 20 acres, barley 50 acres; no stock is kept, the straw is burned, and the ashes are wasted. CONSERVATION OF FERTILITY 2 EXCLUSIVE GRAIN FARMING. Sold from the Farm Phosphoric Nitrogen. acid. Potash. Pounds. Pounds. Pounds. Flax, 40 acres.......... 1600 600 Soo ape straws lie wie oe 600 120 320 Wheat, 50 acres.-..-...-. 1250 625 350 Wheat straw ...--..---- 500 375 1400 Oats, 20 acreS.......... 700 240 200 Oat straw..-+-+-eeeeeee 300 120 700 Barley, 50 acres.....---- 1400 750 400 Barley straw .....-..---- 600 250 1500 AG GAG scores ss hereon oretae 69 50 3080 5670 In addition to the nitrogen removed in the crops other losses must be considered. Experiments have shown that when exclusive grain farming is practiced, for every pound of nitrogen removed in the crop, four pounds are lost from the soil in other ways. This would make the total loss of nitrogen over 28,500 pounds or 177 pounds per acre, which large as it may seem is the actual loss from the soil when grain only is raised and sold. Experiments at the Minnesota Experiment Station have shown that after a soil had been cultivated 4e years, the annual loss per acre of nitrogen in exclusive wheat raising was 25 pounds through the crop and 146 pounds due to the oxidation of the nitrogenous humus of the soil.’ When exclusive grain farming is followed, the annual losses of fertility from a farm of 160 acres are 28,500 pounds of nitrogen, 3000 pounds of phosphoric acid, and 5500 pounds of potash. 252 SOILS AND FERTILIZERS On a similar farm of 160 acres the crops are rotated as described in Section 320. The amounts of fertility in the products sold, the crops raised and consumed as fodder, and the food and fuel purchased, are given in the following table: STocK FARMING. Sold from the Farm Phosphoric Nitrogen. acid. Potash. Pounds. Pounds. Pounds. Butter, 5000 pounds.......-. 5 5 5 Young cattle, 1o head ....-.. 200 190 16 Hogs, 20 of 250 pounds each. 100 4o 10 SieeuSS Bile onieletec winte > ait = erelaiei 48 38 4 Wheat, IO acreS---+++-++- eee. 250 125 70 Flax, IO acres. .....--.++ eee 390 150 190 Rye, 10 ACres «sees e cere eens 285 128 85 POEs aw ca eae ace eo Bre ret ens 1278 676 380 Raised and Consumed on the Farm Clover, 20 toms....--eee+ee-s 66 270 600 Timothy, 20 tons....--+.-+-- 600 180 800 Corn, 20 acres -.--+---- --+- 1500 300 800 Corn fodder, I acre ---.-.--.- 75 15 60 Mangels, 2 acreS----+-+---++-- 150 70 300 Potatoes, I ACre -+++ eeeeee ees 4o 20 75 Straw, 40 tons -.-...+.- ses» 400 200 1000 Peas, 5 ACES sees cree cece eens 56 85 200 Oats, 20 ACTeES....-. --- +--+. 700 240 200 Barley, 20 acres with straw-- 800 400 760 é 4265 1780 4795 Mechanical loss of food con- sumed, 3 per cent..--..- 128 53 144 CONSERVATION OF FERTILITY 253 Food and Fuel Purchased Phosphoric Nitrogen. acid. Potash. Pounds. Pounds. Pounds. Bran, 5 tons ---- eee ee ee eee 275 260 I50 Shorts, 5 tonsS.........2. 506. 250 150 100 Oil meal, 2 tons ...«...6.200 100 35 25 Hard-wood ashes ........... oe 25 100 625 470 375 Sold from farm ............- 1278 676 380 Lossin food consumed, etc.... 128 53 144 MRO TAI Seto see witete ore are eiaiene 1406 729 524 Food and fuel purchased ..... 625 470 375 Balance lost from farm ...... 781 259 149 The manure produced and used on this farm results in the production of larger crop yields than is the case with exclusive grain culture. The clover and peas more than balance the loss of nitrogen. Ex- periments have shown that a rotation similar to this caused an increase in soil nitrogen. Manure, meadow and pasture all tend to increase the soil humus and nitrogen. The losses of phosphoric acid and potash are exceedingly small, averaging less than a pound per acre of each. The action of manure on this farm is continually bringing into activity the inert plant food of the soil so that every year there is a larger amount of active plant food, which results in producing larger yields per acre. The increase or decrease of fertility on farms has a marked effect upon crop yields. For example the 254- SOILS AND FERTILIZERS average yield of wheat in those counties in Minnesota where live stock is kept, is 7 bushels per acre greater than in similar counties where all grain farming 1s followed. . Problems Calculate the income and outgo of fertility from the following farms : 1. Sold from the farm : wheat 4o acres, oats 4o acres, barley 40 acres, rye 20 acres, flax Io acres. The straw is burned and no use is made of any manures. 2. Sold from the farm: wheat 20 acres, barley 20 acres, flax 5 acres, 1000 pounds of butter, 10 hogs, and Io steers. Purchased : Bran 3 tons, shorts 2 tons, oil meal 1 ton. Crops produced and fed on farm : Clover and timothy hay 4otons, corn fodder 3 acres, corn Io acres, oats and peas Io acres, rootsI acre, millet 1 acre, and bar- ley 5, acres. 3. Sold from the farm : Wheat Io acres, sugar beets 5 acres, milk 100,000 pounds, butter 500 pounds, 20 pigs, 6 head of young stock, 2 acres of potatoes. Purchased : 5 tons of bran, 2 tons of oil meal, t ton of cottonseed meal, 15 cords of wood, 1 ton of acid phosphate, 1000 pounds of potassium sulphate, and 500 pounds of sodium ni- trate. Raised and consumed on the farm : Corn fodder 15 acres, mangels I acre, peas and oats 5 acres, clover 20 tons, timothy 10 tons, straw from grain sold, oats, Io acres, corn 20 acres. REFERENCES I. Venable: History of Chemistry. 2. Gilbert : Inaugural Lecture, University of Oxford. 3. Liebig: Chemistry in Its Applications to Agriculture and Physiology. 4. Gilbert: The Scientific Principles of Agriculture (Lecture). 5. Minnesota Agricultural Experiment Station, Bulletin No. 30. 6. Stockbridge: Rocks and Soils. 7. Association of Official Agricultural Chemists, Report 1898. NOTE :— This sentence should read: A division has recently been suggested by Hopkins in which the sguare root of ten ts taken as the constant ratio between the grade of soil particles. 8. Maryland Agricultural Experiment Station, Bulletin No. 21. g. Osborne : Journal of Analytical Chemistry, Vol. II, Part 3. Io. Wiley: Agricultural Analysis, Vol. I. 11. Hellriegel : Calculated from Beitrage zu den Naturwissen- schaft Grandlagen des Ackerbaus. 12. King: Wisconsin Agricultural Experiment Station, Report 1889. 13. Unpublished results of author. 14. King: Soils. 15. Roberts: Fertility of the Land. 16. Minnesota Agricultural Experiment Station, Bulletin No. 41. 17. Minnesota Agricultural Experiment Station, Bulletin No. 53. 18. Whitney : Division of Soils, U. S. Department of Agriculture, Bulletin No. 6. Ig. Merrill: Rocks, Rock-weathering and Soils. 20. Muntz: Comptes Rendus de 1l’Acadeiie des Sciences, CX (1890). 21. Storer: Agriculture, Vol. I. 22. Dyer: Journal of the Chemical Society, March, 1894. 23. Goss: Association of Official Agricultural Chemists, Report 1896. 256 SOILS AND FERTILIZERS 24. Peter: Association of Official Agricultural Chemists, Report 1895. 25. Loughridge: American Journal of Science, Vol. VII (1874). 26. Hilgard : Year-book U. S. Department of Agriculture, 1895. 27. Houston: Indiana Agricultural Experiment Station, Bulle- tin No. 46. 28. Mulder: From Mayer: Lehrbuch der Agrikulturchemie, 2. 29. Journal of the American Chemical Society, Vol. XIX, No. 9. 30. Year-book U. S. Department Agriculture, 1895. 31. Loughridge : South Carolina Sa Experiment Sta- tion, Second Annual Report. 32. Association of Official Agricultural Chemists, Report 1893. 33. Washington Agricultural Experiment Station, Bulletin No. 34. Association of Official Agricultural Chemists, Report 1894. 35. California Agricultural Experiment Station, Report 1890. 36. Minnesota Agricultural Experiment Station, Bulletin No. 29. 37. Minnesota Agricultural Experiment Station, Bulletin No. 47. 38. Lawes and Gilbert : Experiments on WG GN) Vol, i. 39. Boussingault : Agronomie, Tome I. 4o. Atwater: American Chemical Journal, Vol. VI, No. 8 and Vol. VILL. No. 5. 41. Hellriegel : Welche Stickstoff Quellen stehen der Pflanze zu Gebote? 42. Minnesota Agricultural Experiment Station, Bulletin No. 34. 43. Warington : U. S. Department a Agriculture, Office of Ex- periment Stations, Bulletin No, 8. 44. Hilgard : Association of Official Agricuitural Chemists, Re- port 1895. 45. Marchal: Journal of the Chemical Society (abstract), June, 1894. 46. Kunnemann: Die Landwirthschaftlichen Versuchs- Stationen, 50 (1898). 47. Adametz: Abstract, Biedermann’s Centralblatt fur Agrikul- turchemie, 1887. 48. Atwater: American Chemical Journal, Vol. IX (1887). REFERENCES 257 49. Stutzer: Biedermann’s Centralblatt fur Agriculturchemie, 1883. 50. Jenkins: Connecticut State Agricultural Experiment Sta- tion, Report 1893. 51. Wagner: Biedermann’s Centralblatt fur Agrikulturchemie, 1897. 52. Journal of the Royal Agricultural Society, 1850. 53. From Sachsse: Lehrbuch der Agrikulturchemie. 54. Lawes and Gilbert : Experiments with Animals. 55. Beal: U. S. Department of Agriculture, Farmers’ Bulletin Nea,27: 56. Minnesota Agricultural Experiment Station, Bulletin No. 26. 57. Mainly from Armsby: Pennsylvania Agricultural Experi- ment Station, Report 1890. Figures for grains calculated from original data. 58. Heiden : Dungelehre. 59. Liebig: Natural Laws of Husbandry. 60. Cornell University Agricultural Experiment Station, Bulle- tins Nos. 13, 27, and 56. 61. Kinnard: From Manures and Manuring by Aikman. 62. Wyatt: Phosphates of America. 63. Wiley : Agricultural Analysis, Vol. III. 64. Goessmann : Massachusetts Agricultural Experiment Station, Report 1894. 65. Connecticut (State) Agricultural Experiment Station, Bulle- tin No. 103. 66. Goessmann: Massachusetts Agricultural Experiment Station, Report 1896. 67. Wheeler: Rhode Island Agricultural Experiment Station, Reports 1892, 1893, etc. 68. Boussingault : From Storer: Agriculture. 69. Handbook of Experiment Station Work. 70. New York (State) Agricultural Experiment Station, Bulle- tin No. 108. 71. Voorhees: U.S. Department of Agriculture, Farmers’ Bulletin No. 44. 258 SOILS AND ‘FERTILIZERS 72. Liebig: Die. Chemie in ihrer Anwendung auf Agrikultur und Physiologie. 73. Warington : Chemistry of the Farm. 74. Lawes and Gilbert : Growth of Wheat. 75. Lawes and Gilbert : Growth of Barley. 76. Lugger: Minnesota Agricultural Experiment Station, Bulle- tin No. 13. 77. Lawes and Gilbert : Growth of Potatoes. 78. Minnesota Agricultural Experiment Station, Bulletin No. 56. 79. Shaw: U.S. Department of Agriculture, Farmers’ Bulletin. No. II. 80. White: U.S. Department of Agriculture, Farmers’ Bulletin No. 48. 81. Lawes and Gilbert : Permanent Meadows. 82. Thompson : Graduating Essay, Minnesota School of Agricul- ture: 83. Nefedor : Abstract, Experiment Station Record, Vol. X, No. 4. EXPERIMENTS 1. Pulverized Rock and Soil.— Pulverize in an iron mortar, pieces of feldspar, mica, granite, and limestone. Examine each with a lens. Finally mix all of the pulverized material, and com- pare the mixture with samples of soil. 2. Weight of Soils.— Weigh a cubic foot of air-dried sand, clay, and peat. For this purpose use a box holding ¥/ of a cubic foot of soil. Do not compact the soil. 3- Form of Soil Particles. — Examine under a microscope soil particles and distinguish the various grades of sand and silt. Ob- serve the form of the soil particles and make drawings of them. 4. Separation of Soil Particles. — By means of sieves, with holes, I, %, and & mm. in diameter, separate these three grades of parti- cles as described in Section 10. To what type does the soil examined belong? 5. Capillarity.— Place small glass tubes of various sizes in a vessel of water and note the height to which water rises by capil- larity. 6. Capillarity of Soils.— Fill glass tubes 2 inches in diameter with clay and fine sand, respectively. Support the tubes so that one end will touch the water in a cylinder. Observe the rate and height to which the capillary water rises, making daily measure- ments for a week. 7- Hydroscopic Moisture. — Place 5 grams of air-dried soil on a watch-glass, in a water-oven, and after two hours reweigh and de- termine the loss of weight. Calculate the per cent. of hydroscopic moisture. 8. Influence of Cultivation on Soil Water. — Fill four boxes, each a foot square and a foot deep, with air-dried loam soil. Weigh the boxes and soil used. Each box is to be treated separately as fol- lows : Measure one-half gallon of water intoa watering-pot. Allow the water from the watering-pot to flow on the soil, regulating the flow so that it is all absorbed. The soil should be saturated, but 260 SOILS AND FERTILIZERS there should be no dripping. Measure or weigh any water left in the watering-pot. One box 1s to receive shallow surface cultivation, using for the purpose a small gardener’s tool. Another box is to be left without receiving any treatment. The third is to receive treatment imitating that of the disk harrow, having the disks set per- pendicularly. A sharp knife may be used for this purpose. In the fourth box the disk cuttings are to be made at an angle. Leave each box exposed to the sun or in a heated room, and determine the loss of weight every day for a week. From the loss of weight, determine the per cent. of water lost and the per cent. left in the soil. 9. Capacity of Soil to Absorb Water.— Weigh 100 grams of dry soil. Fit a medium-sized filter-paper in a funnel. Moisten the paper so that it will not absorb any more water. Then place the soil in the filter and add slowly from a beaker, containing exactly 100 cc. of water, enough to thoroughly saturate the soil. Collect all of the drippings from the funnel. Measure the drippings and the unused water in the beaker. Calculate the per cent. of water absorbed by the soil. 10. Capacity of Sand for Holding Water. — Repeat Experimentog, using sand. 11. The Influence of Manure upon the Water-holding Power of Soil. — Repeat Experiment 9, using 95 grams of sand and 5 grams of dry and finely pulverized manure. The sand and manure should be thoroughly mixed before performing the experiment. 12. Action of Heat upon Soils. — Expose to the sun’s rays samples of dry clay, peat, and sand; after two hours’ exposure, obtain the temperature of each. The bulb of the thermometer is simply cov- ered with soil. All of the observations should be made under sim- ilar conditions. 13. Influence of Manure upon Soil Temperature. — Expose to the sun’s rays, moist clay soil, and mixed clay and fresh horse manure. After two hours observe the temperature of each, 14. Odor and Taste of Soils.— Observe the odor of dry, peaty soil that has been kept in a corked bottle. Note the taste of EXPERIMENTS 261 peaty and of alkaline soils; test each with moistened litmus paper. 15. Absorption of Gases.— Put 50 grams of soil into a wide- mouthed bottle, add 50 cc. of water and 1 cc. strong ammonia. Note the odor. Cork the bottle, shake, and after twenty-four hours again observe the odor. 16. Insoluble and Soluble Products of Soil. — Digest in a covered beaker 10 grams of soil with roo cc. hydrochloric acid (50..ce. strong hydrochloric acid and 50 cc. water). After two hours’ diges- tion, cool and filter, using 25 cc. water to wash the acid from the insoluble residue. Note the quantity and appearance of the insol- uble matter. To one-half the filtrate add ammonia until alkaline. What is the precipitate? Remove it by filtering, and to this second filtrate add ammonium oxalate. What is the precipitate ? Evaporate the remainder of the original filtrate nearly to dryness. Add 20 cc. water, 3 cc. nitric acid, and 5 Ces. OF ammonium molybdate. After shaking the test-tube con- taining the mixture, it is placed in a beaker of water and heated to about 65°C. What is the yellow precipitate ? 17. Testing Soils for Combined Carbon Dioxide.—One gram of soil is placed in a test-tube (Fig. 35) and 5 cc. of water and 3 cc.of hydrochloric acid added. A small looped tube a, containing a drop of lime-water, is then inserted into the test-tube. The test-tube is warmed. Observe the precipitate formed in the loop. What is it ? 18. Humus from Soils. — Five grams of soil are placed in a glass-stoppered bottle, 100 cc. water and 3 cc. hydro- chloric acid added. After shaking, the contents of the bottle are left twenty-four hours to subside. The acid is then poured off and 100 cc. of water added. ‘The soil is left until the next day, when the water is poured off and 100 cc. of water and 5 cc. of ammonia are added. After Fig. 35. shaking and allowing a little time for the soil to settle, the ammo- nia solution is filtered off. To a portion of the filtrate add hydrochloric acid until the solu- tion is just acid, Observe the precipitate. Evaporate another por- tion of the solution to dryness. What is the black residue? 262 SOILS AND FERTILIZERS 19. The nitrogen of soils. — Place in a strong test-tube a mixture of 5 grams of soil and an equal bulk of soda-lime. Connect the test-tube with a delivery-tube which leads into another test-tube containing distilled water. Heat the test-tube containing the soil for five or ten minutes. Then test with litmus paper the liquid in the second test-tube, neutralize with standard acid asin Experiment 30. 20. Nitrates.— Examine laboratory samples of the following nitrates: Potassium, calcium, and sodium. Place in separate test- tubes % gram of each, add Io cc. of water, and heat gently. To each when cool add a few drops of sulphuric acid, then a few drops of an indigo solution. 21. The Nitrogen of Blood.— Repeat Experiment 19, using I00 milligrams of dried blood in place of the soil. 22. Organic Nitrogen Soluble in Pepsin. — Prepare a pepsin solu- tion by dissolving 5 grams of commercial pepsin in a liter of water, adding 1 cc. of strong hydrochloric acid. Place in separate test- tubes 5 grams each of dried blood, tankage, and horn meal. Add 25 cc. of pepsin solution and place the test-tubes in a cylinder con- taining water at a temperature of 40°C. Shake the test-tubes occa- sionally, and at the end of one-, two-, and five-hour periods observe the amounts of insoluble matter remaining in the test-tubes. 23. Testing for Nitrates.— Dissolve some sodium nitrate, not exceeding 100 milligrams, in 10 cc. water. Add 2 cc. of a dilute solution of ferrous sulphate, and place the test-tube in a cylinder of water. Sulphuric acid is then added by means of a long stemmed funnel. Observe the dark ring formed. 24. Water in Manure.— Dry i100 grams of fresh manure in a water-oven for four hours. Determine the loss of weight and the per cent. of water. 25. Leaching Manure.— Place 5 kilos of manure, the same as used in Experiment 24, in a box provided with small holes in the bottom, so that the manure can be leached. Place the box over a sink or a receptacle for receiving the leachings. Percolate 3 gallons of water through the manure, daily, for five days. Finally weigh the manure, determine the per cent. of water, and the total loss of dry matter.. EXPERIMENTS 263 26. Volatilizing Ammonium Salts. —In separate test-tubes place about Ioo milligrams each of ammonium carbonate and ammonium sulphate. Apply heat gently and observe the results. Place a cold glass rod in the test-tube when the white fumes are being given off. 27. Testing for Phosphoric Acid. — Dissolve a small piece of bone (5 grams) in 20 cc. nitric acid (10 cc. strong nitric acid and Io ce. water). Filter. To the filtrate add 3 cc. of ammonium molybdate, warm, and shake. In a second test-tube dissolve 100 milligrams of sodium phosphate in Io cc. water and add 3 cc. ammonium mo- lybdate. Compare the result with that obtained with the bone. 28. Testing for Water-soluble and Acid-soluble Phosphates. — Place 1 gram of tricalcium phosphate in a test-tuhe with 10 cc. water. Boil. Filter througha close filter. To the filtrate add 3 cc. of ammonium molybdate. Repeat the experiment, using dilute nitric acid in place of water. Repeat the experiment, using mono- calcium phosphate and water. 29. Preparation of Acid Phosphate.—Place 100 grams of pow- dered tricalcium phosphate in a large lead dish. Add slowly and with constant stirring 100 grams of commercial sulphuric acid, using an iron spatula for the purpose. Transfer the mixture to a wooden box and allow it to act for about three days. Then pul- verize and examine. The material is saved for Experiment 34. The mixing of the acid and phosphate should be done in a place where there is a good draft. 30. Testing Ashes. — Test samples of leached and of unleached ashes in the way described in Section 240. 31. Flocculation of Clay.— Ten grams of clay soil are placed in a tall beaker or cylinder, 1000 cc. of water added, and the material triturated. The water containing the suspended clay is divided into two portions. To one portion 1 gram of calcium carbonate is added and the mixture stirred. After twoor three hours compare the two portions. 32. Action of Lime on Acid Soil.—In a flask place 100 grams of acid peaty soil, add 5 grams of recently slaked lime and 200 cc. water ; connect the flask by means of a delivery-tube with a wash- bottle containing lime-water and observe the results. 264 SOILS AND FERTILIZERS 33. Marl. — Test a sample of marl for lime and carbon dioxide, as directed in Experiments 16 and 17. Observe the nature of the insoluble residue. Test the marl with litmus paper. 34. Testing Land Plaster.— Test for carbon dioxide as directed in Experiment 17. There should be but little carbon dioxide in the best grades of land plaster. Digest 1 gram of gypsum in a test- tube with 10 cc. dilute hydrochloric acid. Observe the nature and the amount of insoluble matter. 35. Mixing Fertilizers. — Mix in a large box 200 grams acid phosphate (saved from 28), 50 grams kainit, 50 grams sodium nitrate. Calculate the approximate composition of this fertilizer and its trade value. 36. Testing Fertilizers.— Test the above fertilizer for water- soluble phosphoric acid, as directed in Experiment 27. Test for nitrogen pentoxide, as directed in Experiment 1g. 37. Calculating Results. — A fertilizer is said to contain 3.1 per cent. ammonia, 12 per cent. bone phosphate of lime and 6 per cent. potassium sulphate ; calculate the equivalent amounts of nitrogen, phosphoric acid, and potash. REVIEW QUESTIONS 1. From what are soils derived? 2. What are the physical prop- erties of soils? 3. Why do soils differ in weight? Arrange clay, sand, loam, and peat in order of weight per cubic foot. 4. When wet, what would bethe order? 5. What isthe absolute and what the apparent specific gravity of soils? 6. Define the terms : Skeleton, fine earth, fine sand, silt, andclay. 7. Whatare the physical properties of clay? 8. What are the forms of the soil particles? 9. How do different types of soil vary as to the number of soil particles per gram of soil? 10. How is a mechanical analysis of a soil made ? 11. Why do certain crops thrive best on definite types of soil? 12. What factors must be taken into consideration in determining the type to which a soil belongs? 13. Explain the mechanical structure of a good potato soil. 14. How does a wheat soil differ in mechanical structure from a truck soil? 15. A good corn soil is also a good type for what other crops? 16. How much water is re- quired to produce an average grain crop, and how do the rainfall and the water removed in crops during the growing season compare ? 17. In what forms may water be present in soils? 18. What is bot- tom water and when may it be utilized by crops? 19. What is capil- lary water? 20. Explain the capillary movement of water, 21. Ex- plain how the capillary and non-capillary spaces in the soil may be influenced by cultivation. 22. What is hydroscopic water and of what value is it to crops? 23. What is percolation? 24. To what extent may losses occur by percolation? 25. What are the factors which influence evaporation? 26. What is transpiration? 27. In what three ways may water be lost from the soil? 28. Why does shallow surface cultivation prevent evaporation? 29. Why is it necessary to cultivate the soil after a rain? 30. Explain the move- ment of the soil water after a light shower. 31. What influence has rolling the land upon the moisture content of the soil ? 32. What is subsoiling and how does it influence the moisture content of soils? 33. What influence does early spring plowing exert upon the soil moisture? 34. What is the action of a mulch upon the soil? 35. Why should different soils be plowed to different depths? 36. What is meant by the permeability of a soil ? 37. How may cultivation influence permeability? 38. How may commercial fertilizers influ- ence the water content of soils? 39. Explain the physical action of well-prepared farm: manures upon the soil and their influence upon the soil water. 40. What is the object of good drainage? 41. Why does deforesting a region unfavorably influence the agri- cultural value of a country? 42. What are the sources of heat in soils? 43. To what extent does the color of soils influence the tem- 266 SOILS AND FERTILIZERS perature? 44. What is the specific heat of soils? 45. To what ex- tent does drainage influence soil temperature? 46. How do manured and unmanured land compare as to temperature? 47. What relation does heat bear to crop growth? 48. What materials impart color to soils? 49. What is the effect of loss of organic matter upon the color of soils? 50. What materials impart taste to soils? Odor? 51. What effect does a weak current of electricity have upon crop growth? 52. Do ail soils possess the same power to absorb gases? Why? 53. What is agricultural geology? 54. What agencies have taken part in soil formation? 55. How does the action of heat and cold aid in soil formation? 56. Explain the action of water in soil formation. 57. What is glacial action, and how has it been an important factor in soil formation? 58. Ex- plain the action of vegetation upon soils. 59. How has the action of micro-organisms aided in soil formation? 60. Explain the terms: Sedentary, transported, alluvial, colluvial, volcanic, and windformed soils. 61. What is feldspar and what kind of soil does it produce? 62. Give the general composition of the follow- ing rocks and minerals and state the quality of soil which each produces: Granite, mica, hornblende, zeolites, kaolin, apatite, and limestone. 63. What elements are liable to be the most deficient in soils? 64. Name the acid- and base-forming elements present in soils. 65. What are the elements most essential for crop growth ? 66. State some of the different ways in which the elements present in soils combine. 67. Why is it customary to speak of the oxides of the elements and to deal with them rather than with the elements? 68. Do the elements exist in the soil in the form of oxides? 69. What are double silicates? 70. In what forms does carbon occur in soils? 71. Is the soil carbon the source of the plant carbon? 72. What can you say regarding the occurrence and importance of the sulphur compounds? 73. What influence wouldo.!loper cent. chlorine have upon the soil? 74. In what forms does phosphorus occur in soils? 75. What is the principal form in which the nitro- gen occurs in soils? 76. What can be said regarding the hydrogen and oxygen of the soil? 77. State the principal forms and the value as plant food of the following elements: Aluminum, potas- sium, calcium, sodium, and iron. 78. For plant food purposes, what three divisions are made of the soil compounds? 79. Why are the complex silicates of no value as plant food? 80. Give the relative amounts of plant food in the three classes. 81. How is a soil analysis made? 82. What can be said regarding the economic value of a soil analysis? 83. What are some of the important facts to observe in interpreting results of soil analysis? 84. Under what | conditions are the results most valuable? 85. Do the terms volatile matter and organic matter mean the same? 86. How may organic OT es REVIEW QUESTIONS 267 acids be employed in soil analysis? 87. Why are dilute organic acidsused? 88. Isthe plant food equally distributed in both surface and subsoil? 8g. Do different grades of soil particles, from the same soil, have the same composition? go. What are “alkali soils’’? g1. Why is the alkali sometimes in the form of a crust? 92. Are all soils with white coating strongly alkaline? 93. Give the treatment for improving an alkali soil. 94. How may a small ‘‘alkali spot’’ be treated? 95. What are the sources of the organic compounds of soils? 96. How may the organic compounds of the soil be classified? 97. Explain the term humus. 98. How is the humus of the soil obtained? 99. What is humification? What is a humate? How are humates produced in the soil? 100. Explain how different materials produce humates of different value. tor. Arrange in order of agricultural value the humates produced from the following materials : Oat straw, sawdust, meat scraps, sugar, clover. 102. Of what value are the humates as plant food? 103. How much plant food is present in soils in humate forms? 104. What agencies cause a decrease of the humus content of soils? 105. Towhat extent does humus influence the physical properties of soils? 106. What is humic acid? 107. What soils are most liable to be in need of humus? When are soils not in need of humus? 108. In what ways does the humus of long-cultivated soils differ from that of new soils? 109. How may different methods of farming influence the humus content of soils? tI10. What may be said regarding the importance of nitrogen as plant food? 111. What are the functions of nitrogen in plant nutrition? 112. How may the foliage indicate a lack or an excess of this element? 113. In what three ways did Boussingault conduct experiments relating to the assimilation of the free nitrogen of the air? 114. What were his results? 115. What conclusions did Ville reach? 116. Give the results of Lawes and Gilbert’s experiments. 117. How did field results compare with laboratory experiments? 118, In what ways were the conditions of field experiments different from those conducted in the laboratory? 119. Give the results of Hellriegel’s and Wilfarth’s experiments. 120. What is noticeable regarding the composition of clover root nodules? 121. Of what agricultural value are the results of Hellriegel? 122. What is the source of the soil’s nitrogen? 123. How may the organic nitrogen compounds of the soil vary as to complexity? 124. To what extent may the nitrogen in soils vary? 125. To what extent is nitrogen removed in crops? 126. To what extent are nitrates, nitrites, and ammo- nium compounds found in soils? 127. To what extent is nitrogen returned to the soil in rain-water. 128. How may the ratio of nitrogen to carbon vary in soils? Of what agricultural value is this ratio? 129. Under what conditions do soils gain in nitrogen con- tent? 130. What methods of cultivation cause the most rapid de- 268 SOILS AND FERTILIZERS cline in the nitrogen content of soils? 131. What is nitrification? 132. What are the conditions necessary for nitrification? and what are the food requirements of the nitrifying organism?’ 133. Why is oxygen necessary for nitrification? 134. How does tem- perature, moisture, and sunlight influence this process? 135. What part does calcium carbonate and other basic compounds take in nitrification? 136. How is nitrous acid produced? 137. What is denitrification? 138. What other organisms are present in soils besides those which produce nitrogen pentoxide, nitrogen trioxide, and ammonia? 139. What chemical products do these various or- ganisms produce? 140. Why are soils sometimes inoculated with organisms? 141. Why does summer fallowing of rich lands cause a loss of nitrogen? 142. What influence have deep and shallow plowing, and spring and fall plowing upon the available soil nitrogen? 143. Into what three classes are nitrogenous fertilizers divided? 144. How is dried blood obtained? What is its compo- sition, and how is it used? 145. What is tankage? How is it used, and how does it differ in composition from dried blood? 146. What is flesh meal? 147. What is fish scrap fertilizer, and what is its comparative value? 148. What seed residues are used as fertilizer? What is their value? 149. What method is em- ployed to detect the presence of leather, hair, and wool waste in fertilizers? Why are these materials objectionable? 150. How may peat and muck be used as fertilizers? 151. What is sodium nitrate ? How is it used, and what is its value as a fertilizer? 152. How does ammonium sulphate, as a fertilizer, compare in value with nitrate of soda? 153. What is the difference between the nitrogen content and the ammonia content of fertilizers? 154. What is fixation? Give an illustration. 155. To what is fixation due? 156. What part does humus take in fixation? 157. Why do soils differ in fixative power? Why are nitrates not fixed? 158. Why is fixation a desirable property of soils? 159. Why is it necessary to study the subject of fixation in the use of manures? 160. Why are farm manures variable in composition? 161. What is the distinction between the terms stable manure and farm-yard manure? 162. About what per cent. of nitrogen, phosphoric acid, and potash is present in ordinary manure? 163. Coarse fodders cause an increase of what element in the manure? 164. What four factors influence the composition and value of manure? 165. What influence do absorbents have upon the composition of manures? 166. What advantages result from the use of peat and muck as absorbents? 167. Compare the value of manure produced from clover with that from timothy hay. 168. How may the value of manure be determined from the nature of the food consumed ? 169. To what extent is the fertility of the food returned in the manure? 170. Is much nitrogen added to the body during the REVIEW QUESTIONS 269 process of fattening? 171. Explain the course of the nitrogen of the food during digestion and the forms in which it is voided in the manure. 172. Compare the solid and liquid excrements as to constancy of composition and amounts produced. 173. What is meant by the manurial value of food? 174. Name five foods with high manurial values; also five with low manurial values. 175. What is the usual commercial value of manures compared with commercial fertilizers? 176. How does the manure from young and from old animals compare as to value? 177. How much manure does a well-fed cow produce per day? 178. What are the characteristics of cow manure? How do horse manure and cow manure differ as to composition, character, and fermentability ? 179. What are the characteristics of sheep manure? 180. How does hen manure differ from any other manure? 181. Why should the solid and liquid excrements be mixed to produce balanced manure? 182. What volatile nitrogen compound may be given off from manure? 183. What may be said regarding the use of human excrements as manure? 184. Is there any danger of an immediate scarcity of plant food to necessitate the use of human excrements as manure? 185. To what extent may losses occur when manures are exposed in loose piles and allowed to leach for six months? 186. What two classes of ferments are present in manure? 187. Explain the workings of the two classes of ferments found in manures. 188. How much heat may be produced in manure dur- ing fermentation? 189. Is water injurious to manure? 190. How should manure be composted? What is gained? I91. How does properly composted manure compare in composition with fresh manure? 192. Explain the action of calcium sulphate in the pre- servation of manure. 193. How does manure, produced in open barnyards, compare in composition with that produced in covered sheds? 194. When may manure be taken directly to the field and spread? 195. How may coarse manures be injurious to crops? 196. What is gained by manuring pasture land? 197. Is it econom- ical to make a number of small manure piles ina field? Why? 198. At what rate per acre may manure be used? Igg. To what crops is it not advisable to add stable manure? 200. How do a crop and a manure produced from that crop compare in manurial value? 201. Why do manures have such a lasting effect upon soils? 202. Why does manure from different farms have such variable values and composition? 203. In what seven ways may stable manures be beneficial? 204. What may be said regard- ing the importance of phosphorus as plant food? What function does it take in plant economy? 205. How much phosphoric acid is removed in ordinary farm crops ? 206. To what extent is phosphoric acid present in soils? 207. What are the sources of the soil’s phosphoric acid ? 208. What are the commer- 270 SOILS AND FERTILIZERS cial sources of phosphate fertilizers ? 209. Give the four cal- cium phosphates and their relative fertilizer values. 210. Define reverted phosphoric acid. 211. Define available phosphoric acid. 212. In what forms do phosphate deposits occur? 213. State the general composition of phosphate rock. 214. Explain the process by which acid phosphates are made. Give reactions. 215. How is the commercial value of phosphoric acid determined? 216. What is basic phosphate slag and what is its value as a fertilizer? 217. What is guano? 218. How do raw bone and steamed bone compare as to field value? As to composition? 219. What is dis- solved bone? 220. How is bone-black obtained, and what is its value as a fertilizer? 221. How are phosphate fertilizers applied to soils? In what amounts? 222. How may the phosphoric acid of the soil be kept in available condition? 223. What is the function in plant nutrition of potassium? 224. To what extent is potash removed in farm crops? 225. To what extent is potash present in soils? 226. What are the sources of the soil’s potash? 227. What are the various sources of the potash used for fertilizers? 228. What are the Stassfurt salts, and how are they supposed to have been formed? 229. What is kainit? 230. How much potash is there in hard-wood ashes? 231. In what ways do ashes act on soils ? 232. How do unleached ashes differ from leached ashes? 233. What is meant by the alkalimetry of anash? 234. Of what value, as fertilizer, are hard- and soft-coal ashes? 235. Whatis the fer- tilizer value of the ashes from tobacco stems? 236. Cottonseed hulls? 237. Peat-bog ashes? 238. Saw-mill ashes? 239. Lime- kiln ashes? 240. How is the commercial value of potash deter- mined? 241. How are potash fertilizers used? 242. Why is it sometimes necessary to use a lime fertilizer in connection with a potash fertilizer? 243. Whatcan be said regarding the importance of lime asa plant food? 244. To what extent is lime removed in crops? 245. To what extent do soils contain lime? 246. Whatare the lime fertilizers? 247. Explain the physical action of lime fer- tilizers. 248. Explain the action of lime on heavy clays. 249. On sandy soils. 250. In what ways, chemically, do lime fertilizers act? 251. How may lime aid in liberating potash? 252. What is marl? 253. How are lime fertilizers applied? 254. What is the result when land plaster is used in excess? 255. Explain the action of salt on soils? 256. When would it be desirable to use salt as a fertilizer? 257. Is soot of any value as a fertilizer? Ex- plain its action. 258. Are sea-weeds of any value as fertilizer? 259. What is a commercial fertilizer? An amendment? 260. To what does the commercial fertilizer industry owe its origin? 261. Why are commercial fertilizers so variable in composition? 262. Ex- plain how a commercial fertilizer is made. 263. Why are the analysis and inspection of fertilizers necessary? 264. What are the REVIEW QUESTIONS 271 usual forms of nitrogen in commercial fertilizers? 265. Of phos- phoric acid and potash? 266. Howis the value of a commercial fer- tilizer determined? 267. What is gained by home mixing of fer- tilizers? 268. What can be said about the importance of tillage when fertilizers are used? 269. How are commercial fertilizers sometimes injudiciously used? 270. How may field tests be con- ducted to determine a deficiency in available nitrogen, phosphoric acid, or potash? 271. Todeterminea deficiency of two elements? 272. How are the preliminary results verified? 273. Why is it essential that field tests with fertilizers be made? 274. Under what conditions does it pay tu use commercial fertilizers? 275. What is the result when commercial fertilizers are used in excessive amounts? 276. Under ordinary conditions, what special help do the following crops require : Wheat, barley, corn, potatoes, man- gels, turnips, clover, and timothy? 277. In what ways do commer- cial fertilizers and farm manures differ? 278. Does the amount of fertility removed by crops indicate the nature of the fertilizer re- quired? In what ways are plant ash analyses valuable? 279. Ex- plain the action of plants in rendering their own food soluble. 280. Why do crops differ as to their power of procuring food? 281. Why is wheat less liable to need potash than nitrogen? 282. What position should wheat occupy in a rotation? 283. In what ways do wheat and barley differ in feeding habits? 284. What can be said regarding the food requirements of oats? 285. Corn removes from the soil twice as much nitrogen as a wheat crop, yet a wheat crop usually thrives after a corn crop. Why? 286. What help is corn most liable to need in the way of food? 287. What position should flax occupy in arotation? 288. On what soils does flax thrive best? 289. What is the essential point to observe in the manuring of po- tatoes? 290. What kind ot manuring do sugar-beets require? 291. Why should the manuring of mangels be different from that of tur- nips? 292. What may be said regarding the food requirements of buckwheat and rape? 293. What kind of manuring do hops and cotton require? 294. What kind of manuring is most suitable for leguminous crops? 295. Whatis the objectof rotating crops? 296. Should the whole farm undergo the same rotation system? 297. What is meant by soil exhaustion? 298. What are the nine impor- tant principles to be observed ina rotation? 299. Explain why it is essential that deep and shallow rooted crops should alternate. 300. Why is it necessary that the humus be considered in a rota- tion? 301. What is the object of growing crops of dissimilar feeding habits? 302. How may crop residues be used to the best advantage? 303. In what ways may a decline of soil nitrogen be prevented by a good rotation of crops? 304. In what ways do different crops and their cultivation influence the mechanical condition of the soil? 305. How may the best use be made of the soil water? 306. How 273 SOILS AND FERTILIZERS may a rotation make an even distribution of farm labor? 307. How are manures used to the best advantage in a rotation? 308. In what other ways are rotations advantageous? 309. What may be said re- garding long- and short-course rotations? 310. How is the conser- vation of fertilitv best secured? 311. Why does the use made of crops influence fertility? 312. What are the essential points to be observed in the two systems of farming compared in Section 323? 313. Is it essential that all elements removed in crops should be re- turned to the soil in exactly the amounts contained in the crops? Why? 314. How does manure influence the inert matter of the soil? 315. What general systems of farming best conserve fertility? 316. Under what conditions may farms be gaining in reserve fer- tility? 317. Why in continued grain culture does the loss of nitro- gen from a soil exceed the amount removed in the crop? CORRECTIONS Page 25, line 19, for ‘‘three months,’’ read ‘‘two months.”’ Page 28, line 18, after soil, add : ‘‘absorbed from the air.’’ Page 28, line 26, add: ‘‘when reduced below 4 per cent.”’ Page 64, line 5, for ‘‘one-half,’’ read ‘‘one-tenth.”’ Page 72; line 18, read“94,”’ mot “‘96.” Page 150, line 2, read ‘‘clover hay nitrogen, 35,’’ not ‘‘45.”’ Page 187, under Flax, transpose ‘‘I9’’ and ‘‘8.”’ INDEX PMRISOTMETIES eo ee tieix Chi sta woke. 143 Absorption of heat by soils...... 42 Absorptive power of soils....... 46 Acids in plant roets.--...... .228 Aerobic ferments---...-... 121, 158 Apiciitiral geology = .22- <.. J. AQ PRSSTADIAOUA Y x o05 = 40> wim we oe aie ns Sa) aeys 9 PEE SS eet ea ot hes 6s te ee ee 56 PAE. SOUS. cae ss. cose! oes hee 87 PRIMATOL SOUS) -.< 252% 2. 2a. 66 PAMCHOMETIES 6 cia >. nex sox nen es 205 Ammonium compounds ....... 115 SAG Wee rneks oie crete eicee Olean T 36 Pureromic ferments ----....... 159 Analysis of soil, how made..73, 74 at-soil, yalue of...-... 76, 80 PALA TORIC 30s 1s sa). cies 2s =~) 2 Asia ore 58 Application of fertilizer........ 222 Gb, TIANVITES «0's. s<.:s. 02 163, 165 Arrangement of soil particles...-16 AMES ee Ae ignb aha kie a Ridhos oe IQI acon of, OM .soils:..< 25. 192 POSEITON OL sie arenes baces ots 193 Assimilation of nitrogen....... 102 of phosphates........... 173 Atmospheric nitrogen ......... 104 PAE VALE Ts oictaic lela crete ee cl ccs S's LO hs 2 Availability of plant food....... 79 Available phosphates ..... 177, YO4 nitrogen etait sauabave terials £12, 423 Baticy, fertilizers for. s. 20.015 she's 212 PUSPECMISE OF =. +). << <%,.140 27 NAMGATONMOT 2+ 2 oats Hae se. 213 Composition of soils ........ 83, 85 Composting manures....-..... 160 Corne Terilizers fOr ..<: 2 0%! satencie 223 food requirements of ...-232 Sister bt eri gomoreeeeseer pee 167 Cotton, fertilizers: for«..-.i 2s: 235 274 Cottonseed meals. i. . sil is oe ~132 (Giop mnie (ohg sk a kee ee pe eee 152 Croperesid dG s. 2 eiie hne ee beta ohe 239 Cultivation-aites rains. = as. .t.e Bo shallow surface ..... a eiahe 3 DAWN WORK GOE Maarten myonaate xa as oes a Missolved hone. sscse waoee coe 183 Distribution Of Sousa sas ach oie 16-54 DeMtrincCatiOin ces 5 senses Se 123 De Saussure, work of ....... 2,-104 Draiwtaeen se ae: 3 vee cas Al, 43 ADE: LOO: 5 ac soners eres eee was 128 NDS oles wis nice ato iawn wate ae vi eel atiao 80 Early truck soils...............19 Electricity of soil ....--........ 47 Evaporation etn Lice sete ete ternlattole = 30 Excessive use of fertilizers..... yea) Experiments SAO ee 259 Bahlow: GielGls os a:eieie eaters Seeccnelenenats 126 Fall plowing See ae ions, ater Sinaia. rate oto 35 Farm manures......+...-. LAN. ya Farm manures and commercial FOLtilizerSeas oc ocr are 224 Meldspars: oleae ang soil-waterm...- ..s". 39, 98 Manurial value of foods ....---- Manuring of crops ----++++--- . 166 pasture land .....-.. --. ie oa ee oer - 200 Mechanical analysis of soils-.---17 condition of fertilizers...210 Methods of farming, influence of, upon fertility.....-.-- 100 eoevreer essere eee es ace cee moe a. 2s one eee ag Micro-organisms and soil for- MiatION «. >. - voce eeees4Q, 53 Mixing manures .........5.---155 Movement of water after rains. .33 Mulching Swleit = .n os oles tee se ep € 30 275 Nitrate Or SOtaee vcels eae beset 135 Nitric nitrogen..-.-.+.+......- 136 Ra aa neNIal Goce eo oe tee sa. 119 conditions necessary for 120 and sunlight......... eo? and plowing..-....--..-. 127 Nitrogen assimilation......-.--104 as plant food.....--...-. 102 compounds of soil..-..--. 65 deficiency of, in soil..... 219 losses of, from soil ..---.117 Lato Of» 1O-CAafDOll-. 222.116 removed in crops-------- 114 of commercial fertilizers. 210 amount of, in soils...-.-113 as organic forms ....---- Li2 AE aig eientt oleate 2,5 © 114 availability of........-.-.113 FOTHIS: Oli wae ome wie Ste I12 origin of..... Shara Serna gies Tey Nitrogenous manures.--...-...128 Number of soil particles -.-.-.-. Odor Gf {S0101Ss s65 52s se s Foie Organic acids, action of, upon SOUS: 225+. -ee02ce ss. 7Q, 80 Organic compounds of soil, classification of ...-..----90 SOUECE Of - 6:25 -2 20+ «62-2390 Organic nitrogen ----.----128, 133 Organisms,ammonia-producing, I 23 OF O6ill a nt an Pere Dstwe eae nitrifying ......+---.---120 products of ..-.---. +++. 125 Mehoersew eee. <6. ety iene se i8 (hat bGeMAGE ec sie oe pers oor we ee ae 56 Oxidation) 11 Soil... 05....- .. 3 JESS e Gn Foo aces oeeeee 134, 144 [DE ein Ds eae ee Permeability of soils ------+++++3 Phosphate fertilizers .--.-.---- 172 MSOUOE Sxies bes. cleie wer since cies EOS RRA a ia ate. oe Reb ian aa eters 177 9 Ee 276 INDEX Phosphoric acid of commercial Rotation and soil water........ 242 POTEMA ZOE Sic. chats: ni eghar shave cmte 211 AnlGdeweed Succ aaciie eee 244 ACU Pi SOLIS ac eral ed ote wares 174 acid, deficiency of....... 220 Saltas a fertilizer . ..\s.ckeeeeee 202 acid removed in crops:.-.173 Sand, grades of. ........... 13 A Phosphorus compounds of soils. .64 Seaweeds as fertilizers ........ 203 Physical property of soils...~10, 47 ‘Sedentary soils...) /.. see rene 54 modified by farming..... Tol ‘Seed tesidués:-<-/=.. . sen eee 132 Plant tood (classes 'Of «/.is sume eee 12 SS PUNT insoles od iarer wie wierene, = oats 26).Skeleton of Soils '.< 2. 52% sane eee 12 influences nitrification...127 Small manure piles............ 165 Potash. fertilizers.- ==. .3--<%- > 186 Sodium compounds of soil....-. 68 fertilizers, use of........ 194 Soil, composition of......... 83, 85 of commercial fertilizers. 212 exhaustion ..«. 2.00 se 238 AIESOUIS cere sich tia ceen acre casas 188 ty PES 40/52 50's 6. ne a cee 19 in soils, sources of....... 188 "Soot. cos fc Pe oo. ee eee 203 removed in crops---. ++. 187 Specific gravity of soil.......... 12 and lime; joint use of....-194° Spring plowing <.10s-4.seheeeee 36 Potassium compounds of soil... 67 Stockbridge ............200. 12, 25 Potato, fertilizers for.......... 224 Stock farming and fertility....254 food requirements of; «---'233.(Starer == =i 2 es at emele teleees 63, 129 SOWS Virak ok oe cece cia mons TQ) OEMEZER Jo airs eke arte oie ee alenel ee 133 Sulb-soi linge co cone seein ee 35 VU CSEVCHTS 72, ahalsvn ene etree ee een a 265 Sugar beets, fertilizers for..... 234 beet solsa sa. eee -21 Rainfall and crop production. ..25 beets and farm manures. -167 Rape, food requirements of....235 Sulphate of potash............ 190 ReFEKemGOS -s:a)sa1< 0) sertasae ae 255, 257 Sulphur compounds of soil’ ..... 64 Reverted phosphoric acid...... 176 Superphosphates ...........-- 178 ERO CEES vasctece elsveretcvareee ts Bet erotay cee a7. 7 Rocks, composition of...... 559 59 LaWwka@e x.sies ee cinco renee 130 Rock disintegration......-..... 49 Taste of soils ........eses eeeees 46 BRO Uae ew 2 =) pen ne eine arenes 34 Temperature of soils.........-22 42 Roots. action: On) Soil. <<: si0.0. 50% 228 ‘Tests with fertilizers <<< ««..59m5 Rotation of crops......... 228, 254 “Thaer, worl ‘Of > sn<<. en eee a of crops, principles in- Tobacco, manuring of ......... 167 VOLVER: ivcioce leas. ialerecta 8 236. TODACCO StEMIS =< +2 seen oes 193 length OES este a alecarohe ates 244 Transported SOUS. ss «eee 54 problems ssciok oo come. 248 Truck farming and fertilizers ..221 and farm labor.......... 243 Turnips, fertilizers for......... 224 ANG WAMIUS cen eee 241 and insects ...... stein BAAS Villewces 25 6c siete ere eee 107 and soil nitrogen........ 241 Volcanic soils.--..+++ +++ seeeee 55 .INDEX elite OF -SOLIS «sc 6 oS walatasaionet. 12 Wiovard (Vane Gi mero a ame GG OLOOC 214 Water, action of, upon rocks and Bh Sea eee cee be Rots 50 |BTE A DEY Ch ne We eee en NOE aie A 26 capillary -..-----+.--+--- 27 capillary, conservation of sEekolavereeevekake cteeecees Ale Bere hydroscopic ..--.-+-+++-+- 28 losses by evaporation---- -30 losses by transpiration. -.-30 GiSOM Ee eas ee eee 26, 4I of soil influenced— by drainage-.... AI plowing --35, 36 forest regions, 4I manures. -39, 98 277 Water of soil influenced— by mulching... .36 rolling ...... 34 subsoiling « -.35 required by crops -.-.-.--- 25 Warington..... FIOVI2E,. 123, 220 Weeds, fertility in ...-........ 203 Weight of soils ...--.......---- II Wheat, fertilizers for.......... 223 food requirements of ---- 229 ROLLS rts ue eine wert valle tor cca mets 2222) Whitney -..-... .+..-- see. 17, 47 A Laie hiers Wie ore cate cf oe si sssiaeoe oe TOg WOOG ASIAES 0 erreeie et -I9I WOO eWASt elisa scutes se i0s sc © one 204 IBA hE Ser CE OG SOCIO OIEe 57,230 Partial List of __—_!- Our Publications. SIE HART. Third Edition. Chemistry for Beginners.—By EDwarp HArkt, Professor of Chemistry in Lafayette College. Third Edition, Revised and Greatly Enlarged - - - - - - - $1.50 12mo. Flexible cloth, with 62 illustrations and 2 plates. Beautifully printed, in large clear type, with carefully drawn illus- trations, most of which are original. 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