LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class SOI L. S AND FERTILIZERS BY HARRY SNYDER, B.S. PROFESSOR OF AGRICULTURAL CHEMISTRY, UNIVERSITY OF MINNESOTA, AND CHEMIST OF THE MINNESOTA EXPERIMENT STATION SECOOND EC DJ T I O N ^v.TTXHv^ ^ O- THE X UNIVERSITY 1 OF EASTON, PA.: THE CHEMICAL PUBLISHING CO. 1905. (ALL RIGHTS RESERVED) COPYRIGHT, 1899, BY EDWARD HART. 1905, " PREFACE TO SECOND EDITION The first edition of -this work was published under the title " The Chemistry of Soils and Fertilizers." In the revision of the text the subject matter has been entirely rewritten, new material has been added, and the laboratory practice has been made a more promi- nent feature. These additions have changed the scope of the book to such an extent as to necessitate a change of name. The work as now presented includes all of the topics and laboratory practice relating to soils as outlined by the Committee on methods of teaching Agriculture, appointed by the Association of Agricul- tural Colleges and Experiment Stations. The aim of the book as presented in the preface ro the first edition has been kept in view in the preparation of the second edition. HARRY SNYDER. UNIVERSITY OF MINNESOTA, COLLEGE OF AGRICULTURE, ST. ANTHONY PARK, MINN. June i , 1905. PREFACE TO FIRST EDITION. 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 necessitate 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 bear- ing 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 75, 1899. CONTENTS INTRODUCTION Early uses of manures and explanation of their action by alche- mists; Investigations prior to 1800 : Work of De Saussure, Davy, Thaer, and Boussingault ; Liebig's writings and their influence ; Investigations of Lawes and Gilbert ; Contributions of other in- vestigators ; Agronomy ; Value of soil studies. Pages i-S. 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 ; Crop growth and phys- ical properties. Soil types — Potato and truck soils ; Fruit soils ; Corn soils ; Medium grass and grain soils ; Wheat soils ; Sandy, clay and loam 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 trans- piration ; Drainage influence of forest regions ; Influence of culti- vation upon the water supply of crops ; Capillary water and culti- vation ; Shallow surface cultivation ; Cultivation after rains ; Roll- ing ; Sub-soiling ; Fall plowing; Spring plowing ; Mulching; Depth of plowing ; Permeability of soils ; Fertilizers and their Influence upon moisture content of soils ; Farm manures and soil moisture ; Relation of soils to heat ; Heat from chemical reactions within the soil ; Heat and crop growth ; Organic matter and iron compounds ; Color of soils ; Odor and taste of soils ; Power to absorb gases ; Relation of soils to electricity ; Importance of physical properties of the soil. Pages 9-44. CHAPTER II Geological Formation and Classification of Soils. — Agricultural geology ; Formation of soils ; Action of heat and cold ; Action of water ; Glacial action ; Chemical action of water ; Action of air and gases ; Action of micro-organism ; Action of vegetation ; Combined action of the various agents ; Distribution of soils ; Sedentary and VI CONTENTS transported soils ; Rocks and minerals from which soils are derived as quartz, feldspar, mica, hornblende, zeolites, granite, apatite, kaolin ; Disintegration of rocks and minerals ; Value of geological study of soils. Pages 45-56. CHAPTER III Chemical Composition of Soils. — Elements present in soils ; Clas- sification of elements ; Combination of elements ; Forms in which elements are present in soils ; Acid-forming elements, silicon, double silicates, carbon, sulphur, chlorine, phosphorus, nitrogen, oxygen, hydrogen; Base-forming elements, aluminum, potassium, calcium, magnesium, sodium, iron ; Forms of plant food ; 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 anal- ysis ; Distribution of plant food in the soil ; Composition of typical soils ; "Alkali " soils and their improvement ; Acid soils ; Organic compounds of soil ; Sources; Classification; Humus; Hutuates ; Humification ; Humates produced by different kinds of organic matter; Value of humates as plant food, amount of plant food in humic forms ; Physical properties of soils influenced by humus ; 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 differ- ent methods of farming upon humus. Pages 57-96. CHAPTER IV Nitrogen of the Soil and Air, Nitrification and Nitrogenous Manures. — 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 legumi- nous 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 com- pounds ; 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 cul- CONTENTS Vll tivation upon these conditions ; Nitrous acid organisms, ammonia- producing organisms, denitrification, number and kind of organ- isms in soils ; Inoculation of soils with organisms ; Chemical pro- ducts produced by organisms ; Losses of nitrogen by fallowing rich prairie lands; Influence of plowing upon 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 ; Leguminous crops as nitrogenous fertilizers ; Sod- ium nitrate, ammonium salts ; Cost and value of nitrogenous fer- tilizers. Pages 97-130. CHAPTER V Farm Manures. — Variable composition of farm manures ; Average composition of manures ; Factors which influence composition of manures ; Absorbents ; Use of peat and muck as absorbents ; Rela- tion of food consumed to manures produced ; Bulky and concen- trated foods ; Course of the nitrogen of the food during digestion ; Composition 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 ma- nure ; Horse manure ; Sheep manure ; Hog manure ; Hen manure; Mixing manures ; Volatile products from manure ; Human excre- ments ; Preservation of manures ; Leaching ; Losses by fermenta- tion ; Different kinds of fermentation ; Water necessary for fermen- tation ; Heat produced during fermentation ; Composting manures; Uses of preservatives ; Manure produced in sheds; Value of pro- tected manure ; Use of manures ; Direct hauling to field ; Coarse manures may be injurious ; Manuring pasture land ; Small piles of manure in fields objectionable ; Rate of application ; Most suitable crops to apply to ; Comparative value of manure and food ; Lasting effects of manure ; Comparative value of good and poor manure ; Summary of ways in which manures may be beneficial. Pages I3I-I59. CHAPTER VI Fixation. — Fixation a chemical change, examples of ; Due to zeolites ; Humus and fixation ; Soils possess different powers of fix- ation ; Nitrates do not undergo fixation ; Fixation of ammonia ; Fixation may make plant food less available ; Fixation a desirable property of soils ; Fixation and the action of manures. Pages 160-163. Vlll CONTENTS CHAPTER VII Phosphate Fertilizers. — Importance of phosphorus as plant food ; Amount removed in crops ; Amount and source of phosphoric acid in soils ; Commercial forms of phosphoric acid ; Phosphate rock ; Calcium phosphates ; Reverted phosphoric acid ; Available phos- phoric acid; Manufacture of phosphate fertilizers, 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 164-176. 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 ; Muriate of potash ; Sulphate of potash ; Other Stassfurt salts ; Wood ashes, composition of; Amount of ash in different kinds of wood ; Action of ashes on soils; Leached ashes ; The alka- linity of ashes; Coal ashes; Miscellaneous ashes; Commercial value of potash ; Use of potash fertilizers ; Joint use of potash and lime. Pages 177-186. 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 ; Pul- verized lime rock ; Marl ; Physical action of lime ; Judicious use of lime ; Miscellaneous fertilizers ; Salt and its action on the soil ; Magnesium salts ; Soot ; Sea-weed ; Strand plant ash ; Wool wash- ings ; Street sweepings. Pages 187-195. 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 condi- CONTENTS IX tion 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 ; Judicious use of ; Field tests ; Preliminary experiments ; Verifying results ; Deficiency of nitrogen, phosphoric acid, potash and of two elements ; Import- ance of field trials ; Will it pay to use fertilizers? Amount to use per acre ; Influence of excessive applications ; Fertilizing special crops; Commercial fertilizers and farm manures. Pages 196-214. 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 ; Potatoes ; Sugar-beets ; Roots ; Turnips ; Rape ; Buckwheat ; Cotton ; Hops ; Hay and grass crops ; Leguminous crops ; Garden crops ; Fruit trees ; Lawns. Pages 217-229. CHAPTER XII Rotation of Crops.— Object of rotating crops; Principles involved in crop rotation ; Deep and shallow rooted crops ; Humus-consum- ing and humus-producing crops ; Crop residues ; Nitrogen-consum- ing and nitrogen-producing crops ; Rotation and mechanical con- dition 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; Use of crops ; Two systems of farming compared ; Losses of fertility with different methods of farming ; Problems on income and outgo of fertility from farm. Pages 230-246. CHAPTER XIII Preparation of Soils for Crops, — Importance of good physical condition of seed bed ; Influence of Methods of Plowing upon the condition of the seed bed ; Influence of moisture content of the soil at the time of plowing ; Influence upon the seed bed of pulverizing and fining the soil ; Aeration of seed bed necessary ; Preparation of seed bed without plowing ; Mixing of sub soil with seed bed ; Cultivation to destroy weeds ; X CONTENTS Influence of cultivation upon bacterial action ; Inoculation of soils ; Cultivation for special crops ; Cultivation to prevent washing and gullying of lands ; Bacterial diseases of soils ; Influence of crowding of plants in the seed bed ; Selection of crops ; Inherent and cumulative fertility of soils ; Balanced soil conditions. Pages 247-260. CHAPTER XIV Laboratory Practice.— General directions ; Notebook ; Apparatus used in work ; Determination of Hydroscopic moisture of soils ; Determination of the capacity of loose soils to absorb water ; Deter- mination of Capillary water of soils ; Capillary action of water upon soils ; Influence of manure and shallow surface cultivation upon moisture content and temperature of soils ; Weight of soils ; Influ- ence of color upon the temperature of soils ; Rate of movement of air through soils ; Separation of sand, silt and clay ; Sedimentation of clay ; Properties of rocks from which man}' soils are derived ; Form and size of soil particles ; Pulverized rock particles ; Reaction of soils ; Absorption of gases by soils ; Acid insoluble matter of soils ; Acid soluble matter of soils ; Extraction of humus from soils ; Nit- rogen in soils ; Testing for nitrates ; Volatilization of ammonium salts ; Testing for phosphoric acid ; Preparation of acid phosphate ; Solubility of organic nitrogenous compounds in pepsin solution; Preparation of fertilizers ; Testing ashes ; Extracting water soluble materials from a commercial fertilizer ; Influences of continuous cultivation and crop rotation upon the properties of soil ; Sum- mary of results with tests of home soil. Pages 261-274. References ; Review Questions. Index, pages 275-283, 284-287. OF THE UNIVERSITY OF SOILS AND FERTILIZERS 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, although the fundamental principles under- lying their use were not understood. It was believed that they acted in some mysterious way. The alche- mists had advanced various views regarding their ac- tion ; one was that the so-called " spirits " left the de- caying manure and entered the plant, producing more vigorous growth. As evidence, the worthless charac- ter of leached manure was cited. It was thought 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 com- position of matter. The alchemists held that one substance, like copper, could be changed to another substance, as gold. Plants were supposed to be water transmuted in some mys- terious 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 5 pounds, which he duly watered with rain (i) 2 SOILS AND FERTILIZERS and distilled water. After five years he pulled up the willow and it now weighed 169 pounds and 3 ounces." * He concluded that 164 pounds of roots, bark, leaves, and branches had been produced by the direct trans- mutation 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 was established. The discovery of oxygen by Priestly, in 1774, of the composition of water by Cavendish in 1781, and of the role which carbon dioxide plays in plant and animal life by DeSaussure and others in 1800, form the nucleus of our present knowledge regarding the sources of matter stored up in plants. It was between 1760 and 1800 that alchemy lost its grip, because of advances in knowledge, and the way was opened for the development of modern chemistry. The work of DeSaussure, entitled " Recherches sur la Vegetation," published in 1804, was the first sys- tematic work showing the sources of the compounds stored up in plant bodies. He demonstrated, quanti- tatively, that the increase in the amount of carbon, hydrogen, and oxygen, when plants were exposed to sunlight, was at the expense of the carbon dioxide of the air, and of the water of the soil. He also main- tained 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 INTRODUCTION 3 been verified by many investigators, and are substan- tially those held at the present time regarding the fundamental principles of plant growth. They were not, however, accepted as conclusive at the time, and it was not until nearly half a century later, when Boussingault, Liebig, and others repeated the investi- gations 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 Sir Humphry Davy. In 1813 he published his " Es- sentials of Agricultural Chemistry," which treated of the composition of air, soil, manures, and plants, and of the influence of light and heat upon plant growth. About this same period, Thaer published an important 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 inadequate idea re- garding the source of plant food, and for a time it prevented the actual value of humus as a factor of soil fertility from being recognized. The writings of Thaer were of a most practical nature, and they did much to stimulate later investigations. 4 SOILS AND FERTILIZERS About 1830 there was renewed interest in scientific investigations relating to agriculture. At this time Boussingault, a French investigator, became actively engaged in agricultural research. He was the first to establish a chemical laboratory upon a farm, and to make practical investigations in connection with agri- culture. This marks the establishment of the first agricultural experiment station. Boussingault's work upon the assimilation 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 con- tent. His study of the production of saltpeter did much to prepare the way for later work on nitrifica- tion. The investigations of Boussingault covered a variety of subjects relating to plant growth. He re- peated and verified much of the earlier work of DeSaussure, and also secured many additional facts relating to the chemistry of crop growth. As to the source of nitrogen in crops, he 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 be- coming fertilizing by the effect of time." As to the INTRODUCTION 5 absorption of the gaseous nitrogen of the air by vege- table earth, he says : " I am not acquainted with a single irreproachable observation that establishes it ; not only does the earth not absorb gaseous nitrogen, but it gives it off." 2 The investigations of DeSaussure and Boussingault, and the writings of Davy, Thaer, Sprengel, and Schub- 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 agricultural problems. He assailed the humus theory of Thaer, and held 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-ash 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 im- portance as plant food. Liebig's writings on the com- 6 SOILS AND FERTILIZERS position of plant-ash, and his emphasizing the import- ance of supplying crops with mineral food, led to the commercial preparation of manures, which in later years has developed into the commercial fertilizer in- dustry. The work of L,iebig was not conducted in connection with field experiments. It had, however, a most stimulating influence upon investigations in agri- cultural chemistry, and to him we owe, in a great de- gree, the summarizing of previous disconnected work and the mapping out of valuable lines for future in- vestigations. Iviebig'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 of science to subjects which so well merit to engage their talents and energies. Perfect agriculture is the true foundation of trade and industry ; it is the founda- tion 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 ever conducted have been carried on by Lawes and Gilbert INTRODUCTION 7 at Rothamsted, Eng. Dr. Gilbert had previously been a pupil at L,iebig, and his becoming associated with Sir J. B. La wes marks the establishment of the second experiment station. Many of the Rothamsted experi- ments have been continued since 1844, and results of the greatest value io agriculture have been obtained. The investigations on the non-assimilation of the at- mospheric nitrogen by crops, published in 1861, were accepted as conclusive evidence upon this much-vexed question. The work on manures, nitrification, the nitrogen supply of crops, and on the increase and de- crease of the nitrogen of the soil when different crops are produced, has had a most important bearing upon maintaining the fertility of soils. u 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 properties of soils. The work of Pasteur, while it did not directly relate to soils, indirectly had great influence upon soil investigations. His researches upon fermentation made it possible for Schlosing to 8 SOILS AND FERTILIZERS prove that nitrification was the result of the workings of living organisms. These have since been isolated and studied by Warington and Winogradsky. During recent years the agricultural experiment stations of this and other countries have made soils a prominent feature of their work ; some of the results obtained are noted in the following chapters. Our knowledge regarding the chemistry, physics, geology and bacteriology of soils is still far from complete, bat many facts have been discovered which are of the greatest value to the practical farmer. The literature relating to soils and fertilizers has become very exten- sive, and in the classification of agricultural subjects for study, soil forms one of the main divisions of agronomy. In soil investigations it has frequently happened, owing to imperfect interpretation of results and to the presence of many modifying influences, that the 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 free atmospheric nitrogen, where seemingly opposite conclusions now form a complete theory. A scientific study of soils is valuable from an edu- cational point of view, as well as because the practical knowledge obtained can be utilized in the production of crops. In the cultivation of the soil it should be the aim to conserve the fertility and to produce as large yields as possible of the most valuable crops. This can be accomplished only as the result of a thorough knowledge of soils and fertilizers. CHAPTER I 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 merely a 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, when jointly considered, determine largely the agri- cultural value of a soil. 2. Physical Properties Defined. — The physical properties of a soil are : 1. Weight. 2. Color. 3. Size, form, and arrangement of the soil particles. 4. The relation of the soil to water, heat, and cold. 5. Odor and taste. 6. The relation of the soil to electricity. 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 10 SOILS AND FERTILIZERS 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 example, 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. A peaty soil containing i per cent, of nitrogen and weighing 30 pounds per cubic foot has less total nitro- gen than a soil containing 0.40 per cent, of nitrogen and weighing 80 pounds per cubic foot. The weight of soils per cubic foot is approximately as follows : 5 Pounds. Clay soil 70 to 75 Fine sandy soil 95 to 1 10 Loam soil 75 to 90 Peaty soil 25 to 60 Average prairie soil 75 Uncultivated prairie soil 65 Figures for the weight per cubic foot and 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. The volume of a soil varies with the conditions to which it has been subjected. Usually about 50 per cent, of the volume 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 com- pacted. Hence it is that soils have both a real and an apparent specific gravity. The apparent specific SIZE OF SOIL PARTICLES II gravity of a soil is sometimes less than half of the real specific gravity. The specific gravity of different soils as given by Shoen is as follows : 6 Specific gravity. Clay soil • • 2.65 Sandy soil 2.67 Fine soil 2.71 Humus soil 2.53 4, Size of Soil Particles.— The size of 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, or loam. The term ' fine earth ' is used to designate that part of a 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 amounts of fine earth and skeleton are variable. Ara- ble 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 : Millimeters. Inches. Medium sand 0.5 to 0.25 0.02 to o.oi Fine sand 0.25 to o.i o.oi to 0.004 Very fine sand- ... o.i to 0.05 0.004 to 0.002 Silt 0.05 to o.oi 0.002 to 0.0004 Fine silt o.oi to 0.005 0.0004 to 0.0002 Clay 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 12 SOILS AND FERTILIZERS 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- ^n 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 large amount of water, and will remain suspended in water for a long time. The roiled appearance of many streams and lakes is 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 accumu- lated surface water must be removed by the slow process of evaporation. 6. Silt. — 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 per- meable, but is not as open and porous as a sandy soil. SAND 13 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 deposit in ditches and drains, where the water moves slowly, is mainly silt. 7. Sand. — There are three grades of sand. The characteristics, as permeability and non-cohesion of Fig. i. Medium sand X 150. Fig. 2. Fine sand X 150- Fig- 3- Very fine sand X 150- Fig. 4. Silt X 325. Fig. 5. Fine silt X 325. Fig. 6. Clay X 325. 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. 14 SOILS AND FERTILIZERS 8. Form of Soil Particles, — Soil particles are ex- tremely varied in form. When examined with the microscope they show the same diversity as is observed in larger stones. In some soils the particles are spher- ical, while in others they are angular. The shape 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 im- portant factors to consider in dealing with the water content of soils. In the wheat lands of the Red River Valley of the North, the particles are small and spher- ical, 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 a minimum of inter soil spaces. The silt particles being angular and embedded in the clay, the soil has more the char- acter of clay than of silt. While these two soils are unlike in physical composition, the form and arrange- ment of the particles give each nearly the same water- holding power. Two soils may have the same mechan- ical composition and yet possess materially different physical properties because of a difference in the form and arrangement of the soil particles. In some soils 10 per cent, of clay is of more agricultural value than in other soils. Ten per cent, of clay associated with 60 or 70 per cent, of silt makes a good grain soil, while 10 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, SEPARATING SOII, PARTICLES 15 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 Hopkins7, in which the square root of ten is taken as the constant ratio between the grades of soil particles. 9. 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 1,700,000,000 are unproduc- tive. The number of particles in a given volume of soil varies with their size and form. According to Whitney8 the number of particles per gram of differ- ent soil types is as follows : Early truck 1,955,000,000* Truck and small fruit 3,955,000,000 Tobacco 6,786,000,000 Wheat 10,228,000,000 Grass and wheat 14,735,000,000 Limestone 19,638,000,000 Assuming that the particles are all spheres, it is 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. i o . Methods Employed in Separating Soil Particles . — Sieves with circular holes 0.5, 0.25 and o.i mm. are employed for the purpose of separating the three coarser grades of sand. The sieve a, 0.5 mm. size, is con- * Figures below sixth place omitted and cyphers substituted. i6 SOILS AND FERTILIZERS nected with the filtering flask c by means of the tube l>, and the flask is connected at point d with a suction- pump. Ten grams of soil, after soft pestling with 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 c, containing the particles less than 0.5 mm. are then passed through a sieve having holes 0.25 mm. in diameter. Finally a o.io 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 with more water and allowed to settle ; this operation is repeated until the micro- scope shows the soil particles to be nearly all of one grade. The separation of silt and clay is facilitated by the use of a centrifu- gal.9 The clay is obtained Figs. 8 and 9. by evaporating an aliquot portion of the washings or by determining the total per cent, of the other grades of particles and the volatile matter and subtracting the sum from 100. This is the modified Osborne sed- imentation method.10 Hilgard's elutriator" is a valuable apparatus for separating the soil particles. SOIL TYPES 11. Crop Growth and Physical Properties. — The 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 grain crops 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 per cent, of silt, and (2) 1 8 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 about 8 per cent, of water. In a sandy soil, vegetation may reduce the water to a much lower point than in a clay 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 unbalanced chemical composition or lack of plant food. 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 50 per cent, of sand are best suited for growing small fruits. Such soils will retain from 10 to 1 8 per cent, of water. There is a noticeable differ- MEDIUM GRASS AND GRAIN SOILS 1 9 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. As a rule, however, a silt soil is most capable of being adapted to the various conditions 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 require more cultivation and 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 a soil contains a high per cent, of neutral organic matter, good corn crops may be pro- duced where there is less than 12 per cent, of clay. Soils containing a high per cent, of sand are usually too deficient in available water to produce a good corn crop. On the other hand, heavy clay soils are slow in warming up and are not suited to corn culture. The best types of corn soils have the necessary mechanical composition for the production of good crops of sorghum, cotton, flax, and sugar-beets. How- 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- 20 SOILS AND FERTILIZERS duction of grass and grain a larger amount of water is required than for corn. The yield is determined largely by the amount of water which the soil con- tains. For an average rainfall of about 30 inches, good grass and grain soils should contain about 15 per cent, of clay and 60 per cent, of silt. 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, me- chanically, 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 closer texture are required than for other small grains. There are three classes of wheat soils. The first (i in Fig. 10) contains from 30 to 50 per cent, of clay particles, these being mostly disintegrated limestone. The soil of the Red River Valley of the North belongs to the first class. The surface soil contains from 8 to 12 per cent, of vegetable 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 con- tain 20 per cent, of water. A crop can, however, be produced with less water, but a smaller yield is ob- tained. 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 WHEAT SOILS 21 per cent, of sand, 50 per cent, of silt, and from 20 to 30 per cent, of clay. Soils of this class when well stocked with moisture in the spring are capable of producing good crops of wheat, but are not able to withstand drought so well as soils of the first class ; during wet seasons, however, they produce larger yields than heavier clay soils. 1834 Fig. 10. Soil types. i. Heavy wheat soil. 2. Average wheat soil. 3. Medium wheat and grain soil. 4. Corn soil. To the third class of wheat soils (3 in Fig. 10) be- long those which are composed mainly of silt, contain- ing usually 75 per cent., and from 10 to 15 per cent, 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 22 SOILS AND FERTILIZERS on silt soils, it is essential that a good supply of organic matter be kept in the soil so as to bind the soil particles. The special peculiarities of the different grain crops as to soil requirements are con- sidered in connection with the food requirements of crops. 17. Sandy, Clay, and Loam Soils. — In ordinary agricultural literature, the term l sandy,' * clay,' or ' 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. The term 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. They are sub- soils in the western states which have clay -like char- acteristics but contain only about 15 percent, of clay, the larger part of the soil being silt. A loam soil is a 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 : I2 BOTTOM WATER 23 Average amount. Minimum amount. Tons water. Tons water. Clover •• 400 310 Potatoes 400 325 Wheat 350 300 Oats 375 3oo Peas -. 375 3°° Corn 300 Grapes 375 Sunflowers6 6000 The rainfall during the time of growth is frequently less than the amount of water required for the pro- duction of a crop. One inch of rainfall is equal to about 90 tons per acre. An average rainfall of 2 inches per month during the three months of crop growth is equivalent to only 540 tons of water per acre, a large 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 to produce crops, and hence the water stored up in the subsoil 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 the capacity of the subsoil for storing and supplying water as needed is a matter of much importance, 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 : (i) bottom water, (2) capillary water, and (3) hydroscopic water. 19. Bottom Water is water which stands in the soil 24 SOILS AND FERTILIZERS 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 at such a depth that it can be brought to the plant roots by capillarity, but when too 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. Fig. ii. Water films surrounding soil particles. 20. Capillary Water. — The water held in the minute 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. If a series of glass tubes of dif- ferent diameters be placed in water it will be observed that in the smaller tubes water rises much higher than in the larger. The water rises in all of 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 CAPILLARY WATER gravity, and the water is drawn np 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 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 capil- lary action of water is confined to a few feet. The Fig. 12. Comparative height to which water rises in glass tubes. 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 are decreased ; by stirring, the air spaces are increased. In soils of a close texture, as heavy clays, 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 pro- duction exist when the soil contains water to the extent of about 40 per cent, of its total capacity of saturation. 26 SOILS AND FERTILIZERS 21. Hydroscopic Water, — By hydroscopic water is meant the water content of the soil absorbed from the atmosphere. The air which occupies the non-capillary spaces of the soil is charged with moisture in propor- tion to the water in the soil. Under normal condi- tions the soil atmosphere 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 unless the soil is supplied with hydroscopic water from heavy fogs. 22. Loss of Water by Percolation. — Whenever a soil becomes saturated, percolation or a downward 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 limited 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 number 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, LOSS OF WATER BY EVAPORATION 27 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 management must be varied to suit the re- quirements of different soils. In regions of heavy rainfall and mild winters the losses of both water and plant food by percolation are often large. 23. Loss of Water by Evaporation. — The factors which influence evaporation are temperature, humid- ity, and rate of movement of the air. When the air contains 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, which has been taken from the soil, and, unless checked by cultivation, the subsoil water is brought to the surface by capil- larity and lost. In porous soils, a greater free- dom of movement of the air is possible, which increases the rate of evaporation. When the sur- face 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 28 SOILS AND FERTILIZERS of different texture is 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 influenced. Hot, dry winds may cause crops to wilt because the water lost by transpiration exceeds the amount which the plant takes from the soil. 25. Drainage. — Good drainage is essential in order to properly regulate the water supply. An excessive amount of water in the soil is equally as injurious as a scant amount. 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 as much water as possible in the subsoil and to pre- vent surface accumulation and loss. Good drainage is accomplished by thorough cultivation, and in re- gions 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. The drainage of wet and low lands forms an important feature of rural engineering. Many swampy lands are highly productive when properly drained. CAPILLARITY INFLUENCED BY CULTIVATION 29 The reclamation of such lands is briefly considered in Chapter III. 26. Influence of Forest Regions. — The deforesting of large areas near the sources 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 forests. Good drainage is necessary not only for individual farms, but also for an entire community. Good stor- age capacity in the form of forest lands, for the surplus water which accumulates near the sources of large rivers is also a necessity to agriculture. The three ways in which crops are deprived of water are by (i) 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 27. Capillarity Influenced by Cultivation. — The capillarity of the soil can be influenced by 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 30 SOILS AND FERTILIZERS secure the best water supply for crops must vary with the rainfall, the nature of the soil, and the crop to be produced. It frequently happens that the annual rainfall is sufficient to produce good crops, but is too unevenly distributed, and hence is not all utilized to the best advantage. It is possible, to a great extent, to vary the cultivation so as to conserve the moisture of the soil and meet the requirements of crops. 28. Shallow Surface Cultivation. — When shallow surface cultivation is practiced, the capillary spaces Fig. 13. Soil with surface cultivation. near the surface are destroyed and the direct connec- tion of the subsoil water with the surface is broken, a layer of finely pulverized earth covers the surface, and the soil particles have been disturbed so 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 surface, but if the surface is covered with a layer of fine earth of different texture, the subsoil water can- not readily pass through such a medium, and evapora- tion is checked. Hence shallow surface cultivation conserves the soil moisture. The means by which surface cultivation is accom- SHALLOW SURFACE CULTIVATION 31 published must, of necessity, vary with the nature of the soil. If a harrow is used, the pulverization should be complete. If a disk is used, the teeth should be set at an angle, and not perpendicularly, so as to prevent, as suggested by King,13 the formation of hard ridges which hasten evaporation. When the disk is set at an 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 Fig. 14. Soil without surface cultivation. deep, and the finer the condition in which the surface soil is left the better. Shallow surface cultivation is an effectual means of conserving soil moisture. It can be practiced in con- nection with deep plowing, shallow plowing, subsoil- ing, or rolling ; in fact, it can be combined with any method of treating the land. Shallow surface cultiva- tion does not mean that the soil should not be pre- viously well prepared by thorough cultivation. The following example shows the extent to which shallow surface cultivation may conserve the soil water.14 Per cent, of water in cornfield. With shallow sur- face cultivation. Soil, depth 3 to 9 inches 14.12 Soil, depth 9 to 15 inches 17.21 Without shallow surface cultivation. 8.02 12.38 32 SOILS AND FERTILIZERS 29. 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.13 The following example shows the extent to which, the subsoil water may be brought to the surface.14 Per cent, of water. Surface soil. Subsoil. I to 3 inches. 6 to 12 inches. Before the shower 9.77 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 per cent. The subsoil showed a loss of 1.52 per cent, while the sur- 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 a shower a movement of the subsoil water to the sur- face. 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 hard thin crust should never be allowed to form SUBSOILING 33 after a rain, because it hastens losses by evaporation, while a soil mulch formed by surface cultivation has the opposite effect. 30. 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 condition, 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, at the expense of the subsoil water.13 Unless rolled land receives surface cultivation, excessive losses by evaporation, due to improved capillarity, may result. The use of the roller on heavy clay land during a wet season results unfavorably. In some localities rolling and subsequent surface cultivation are not admissible on account of the drifting of the soil, caused by heavy winds. 31. Subsoiling. — By subsoiling is meant pulveri- zing of the soil below 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 improved 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 (3) 34 SOILS AND FERTILIZERS 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 all cf the conditions most favorable for this practice. 32. Fall Plowing followed by surface cultivation conserves the soil water, by checking evaporation and leaving the land in better condition to retain moisture. If conditions allow, fall plowing should be followed by surface cultivation. In some localities heavy winds prevent this from being practiced. Evaporation may take place from unplowed land during the fall, and in the spring the soil contain 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. 33. Spring Plowing. — When land is plowed late in the spring there has been a loss of water by evapora- tion, and the soil has not been able to store up as much of the rain and snow as if fall plowing had been practiced.15 Dry soil is plowed under and moist soil brought to the surface. If surface cultivation does not follow, this moisture is readily lost by evapo- ration, good capillary connection of the surface soil and subsoil is not obtained, and the furrow slice soon becomes dry. Per cent, of water in14 April 25th. Fall plowed Spring plowed land. land. From 2 to 6 inches 24.7 22.4 " 6 to 12 " 26.6 2\.i " 12 to 18 " 28.8 26.5 Average difference 2.37 per cent. DEPTH OF PLOWING 35 Surface cultivation should immediately follow both spring and fall plowing. 34. 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 be compacted, — a loose pile of straw is not a mulch. In reclaiming lands gullied by water, mulching is very beneficial. A light 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 advantageously combined.14 Per cent, of water in Mulched straw- berry patch. Unmulched. Soil 2 to 5 inches 18.12 11.17 " 6 to 12 " 22.18 18.14 " 12 to 18 " 24.31 21.11 35. 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 rule. 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. Also, the depth of plowing should be regulated by the season. In the prairie regions, and in the northwestern part of 36 SOILS AND FERTILIZERS , the United States, shallow plowing is more generally practiced 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:16 "If plowing is continued at one 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 is 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. 36. 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. A soil is permeable when it is of such a texture that it does not allow the water to accumulate and clog the non-capillary spaces. Cultivation may change the tilth of even a clay soil to such an extent as to render it permeable. Deep plowing increases per- FARM MANURES 37 meability. In regions of heavy rains increased per- meability is very desirable for good 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. 37, Fertilizers. — When water contains dissolved salts, it is more susceptible to the influence of surface- tension, and is more readily brought to the surface of Fig. 15. Sandy soil without manure. the soil. In commercial fertilizers soluble salts are present. The beneficial effects of commercial fertili- zers upon the moisture content of soils are liable to be over-estimated, 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. 38. 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, SOILS AND FERTILIZERS and the non-capillary spaces are made capillary. 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 : I4 Fine sandy soil. Per cent. Capacity for holding water 25 95 per cent, fine sandy soil and 5 per cent, manure. Per cent. 42 The manure enables the soil to retain more water near the surface and prevents losses by percolation. The difference in moisture content between manured and unmanured land is particularly noticeable in a dry season.14 Sandy soil well manured. Water. Per cent. Sandy soil unmanured. Water. Per cent. Soil one to six inches 10.50 Coarse leached manure may have just the opposite effect by producing an open and porous condition of the soil. RELATION OF THE SOIL TO HEAT 39. The Sources of Heat in soils are (i) solar heat, and (2) heat resulting from chemical action. Solar heat is the main source for crop production. The action of heat upon soils has been studied exten- sively by Schiibler. 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 Schiibler'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 :6 White coating. Black coating. Sand 43 50 Gypsum 43 51 Humus 42 49 Clay 41 48 L,oam 42 50 The presence of water in the soil modifies the power for absorbing heat. A sandy soil retains about 12 per cent, of water, while a humus soil retains 35 per cent. The additional amount of water in the humus soil causes 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 up in warm- ing the water. A sandy soil readily warms up in the spring on account of the relatively small amount of water which it contains. 40 SOILS AND FERTILIZERS The specific heat of a soil is the amount of heat re- quired to raise a given weight i° C., as compared with the heat required to raise the same weight of water i°. 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. At a depth of 2 or 3 feet there is not such a marked difference in the temperature of wet and dry soils. It is to 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 nganure, when it rots in the soil, gives off the same amount of heat as if it were burned. Manured land is usually i° or 2° warmer in the spring than unmanured land ; this is due to the oxidation of the manure. In an acre of rich prairie soil it has been estimated that the amount of or- ganic matter which undergoes oxidation produces as much heat annually as would be produced from a ton ORGANIC MATTER AND IRON COMPOUNDS 4! of coal.17 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 utilized 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 case of early frosts, crops on well-manured land will often escape. 4. 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 the formation of the plant's tissues. 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 with the mineral matter of the soil produces compounds brown or black in color. When moist, many soils are darker than when dry, and soils in which the organic matter 42 SOILS AND FERTILIZERS has been kept up by the use of manures are darker than unmanured soils.18 When rich, black, prairie soils lose their organic matter through improper 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. A greenish tinge is supposed to be due to the pres- ence of ferrous compounds, such soils being so close in texture as to prevent the oxidizing action of the air. Color may serve, to a slight extent, as an index of fer- tility. Black and yellow soils are, as a rule, the most productive. 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. 43. Odor and Taste of Soils.— Soils containing liberal amounts of organic matter have characteristic odors. The odoriferous properties of a soil are due to the presence of aromatic bodies produced by the de- composition 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 RELATION OF SOILS TO ELECTRICITY 43 acids. Alkaline soils have variable tastes according to the prevailing alkaline compound. The taste of a soil frequently reveals a fault, as acfdity or alkalinity. 44. Power of Soils to Absorb Gases. — All soils pos- sess, to a variable extent, the power of absorbing gases. When decomposing animal or vegetable matter is mixed with soil, the gaseous products given off are absorbed. Absorption is the result of both chemical and physical action. The chemical changes which occur, as the fixation 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 has the power of absorbing large amounts. This action is similar to that of a charcoal filter in removing noxious gases from water. 45. Relation of Soils to Electricity. — There is al- ways 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, but in order to change the composition of the soil so as to render the unavailable plant food available, would require a current destruc- tive to vegetation. When plants are subjected to too strong a current of electricity, they wilt and have all of the after-effects of frost. A feeble current has either an indifferent or a slightly beneficial effect upon crop growth. The slightly beneficial action is not sufficient, however, to warrant its use as yet in general crop pro- duction on account of cost. The action of a weak 44 SOILS AND FERTILIZERS current of electricity is undoubtedly physiological rather than chemical, unless it be in the slighty favor- able influence which it exerts upon nitrification. The electrical conductivity of soils has been taken by Whit- ney as the basis for the determination of moisture ; I9 the conductivity of a soil, however, is dependent largely upon the nature and amount of dissolved salts. 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 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 differences in chemical composition and amounts of available plant food. Attempts have been made to over-estimate 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 or other properties. In fact the four sciences, chemistry, physics, geology, and bacteriology, are all closely connected and each contributes its part to our knowledge of soils. CHAPTER II GEOLOGICAL FORMATION AND CLASSIFICATION OF SOILS 47. Agricultural Geology. — The geological study of a soil concerns itself with the past history of that soil; the materials out of which it has been produced, 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 agencies which have distributed them. The principles of soil formation and soil distribution should be understood, because they have such an important bearing upon soil fertility. Agricultural geology is of itself a separate branch of agricultural science. In this work, only a few of the topics which are of most importance in agriculture are treated and only in a general way. 48. Formation of Soils. — Geologists state that the surface of the earth was at one time solid rock. It is now held that soils have been formed from rock by the joint action of the various agents : ( i) heat and cold, (2) water, (3) gases, (4) micro-organisms and vegetable life. One of the best evidences 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 46 SOILS AND FERTILIZERS was embedded. The process of soil formation is a slow one and the various agents have been at work for an almost unlimited period. 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 other agents. The un- equal cooling of the rocks caused a partial separation of the different minerals of which the rocks were com- posed, resulting in the formation of smaller rock par- ticles from the larger rock masses. This is well illustrated by the familiar splitting and crumbling of stones when heated. Shaler estimates that a variation of 150° F. will make a difference of i inch in the length of a granite ledge 100 feet long. As a result of changes in temperature there is a lessening of the cohesion of the rock particles. The action of frost also is favorable to soil formation. The freezing of water in rock crevices results in breaking up the lock masses, forming smaller bodies. The force exerted by water when it freezes is sufficient to rend large rocks. 50. Physical Action of Water. — Water acts upon soils both chemically and physically. It is the most important agent that has taken a part in soil forma- tion. The surface of rocks has been worn away by moving water and in many cases deep ravines and canons have been formed. This is called erosion. The pulverized rock, being carried along by the water and deposited under favorable conditions, forms alluvial soil. This physical action of water is illus- GLACIAL ACTION 47 trated in the workings of large rivers where the pulverized rock is deposited along the river and at its mouth. Large areas of the soil in valleys and river bottoms have been formed in this way, and in most cases these soils are of high fertility. The action of water is not alone confined to forming soils along water courses, but is equally prominent in the forma- tion 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 larger areas than at present.20 Changes 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 farther up, moving down the side of the mountain and carrying along crushed stones and soil. 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 48 SOILS AND FERTILIZERS 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 the pulverization and mixing of a great variety of rock. 52. Chemical Action of Water. — The chemical action of water has been an important factor in soil formation. While nearly all rocks are practically in- soluble in water there is always some material dis- solved, 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 fer- rous oxide, into hydroxides. The chemical action of water may produce new compounds more soluble or readily disintegrated, as deposits of clay, which have been formed from feldspar rock by the chemical and physical action of water. When rocks disintegrate, chemical changes often occur; the addition of water or hydration of the molecule, particularly of the sili- cates, is one of the most important chemical changes. Water takes as prominent a part in the decay of rocks as in the decay of vegetable matter. Limestone is quite readily disintegrated by water. Dissolved min- erals produce 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 of the ACTION OF VEGETATION 49 chemical reactions in the soil which result in render- ing plant food available. 53. Action of Air and Gases. — In the disintegra- tion of materials to form soil, air takes a prominent but less important part than water. By the aid 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. The carbon dioxide of the air under some conditions favors the formation of carbonates. The disintegrating action of air, moisture, and frost is illustrated in the case of building stones which in time crumble and form a powder. This is called weathering. Many of the benefits of cultivation are due to aeration of the soil. 54. Action of Micro-organisms. — Micro-organisms, found on the surface and in the crevices of rocks, and in decaying vegetable matter, are active agents in bringing about rock decay. The nitrifying organisms have taken an important part in rendering soils fer- tile, and these with others have 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 the air.21 This action results in adding vegetable matter to the soil. 55. 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 (4) 50 SOILS AND FERTILIZERS of rocks, obtaining food from the air, and leaving a certain amount of vegetable matter which undergoes decay and is incorporated with the rock particles, pre- paring the way for higher orders of plants which take their food from the soil. When this vegetable matter decays, it enters into chemical combination with the pulverized rock, forming humates.18 The disinte- grating action of plant roots and vegetable matter upon rocks has been an important factor in soil forma- tion. The action of vegetable remains in soil produc- tion is discussed in Chapter III. 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, micro-organisms, and vegetation — have been act- ing jointly, and have produced more rapid disinte- gration than if each agent were acting separately. Wind also has been an important factor in the pro- duction and modification of soils. The denuding effects of heavy wind storms are well known. Large areas of wind-formed soils are found in some coun- tries. . Sand dunes are transported by winds and often their subjugation by soil-binding plants is necessary in order to prevent their encroaching upon valuable farm lands and inundating villages. Soils formed by the action of winds are called aeolian soils. DISTRIBUTION OF SOILS 57. Sedentary and Transported Soils, — The place which a soil occupies is not necessarily the place where it was produced ; that is. a soil may be pro- COMPOSITION OF ROCK 51 duced 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 before rock surface is reached. The stones in such soils, except where modified by weathering, have sharp angles because they have not been ground by transportation. In the southern part of the United States, east of the Mississippi River, there are large areas of sedentary soils as ferrogenous clays in an ad- vanced state of decay. Transported soils are those which have been formed in one locality and carried by various agents as glaciers, rivers and winds to other localities, the angles of stones in these soils having been ground off during transpor- tation. Transported soils are divided into classes ac- cording to the ways in which they have been formed; as, drift soils produced by glaciers, alluvial soils formed by rivers and deposited by lakes, aeolian soils formed by winds, and colluvial soils formed of rocks and debris from mountain sides. In some localities volcanic soils are found. They are extremely varied in texture and composition ; some are very fertile and contain liberal amounts of alkaline 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 Rocks. — Rocks are composed of either a single mineral or of a combination of minerals. Most of the common minerals are definite chemical 52 SOILS AND FERTILIZERS compounds and have a variable range of composition, due to the fact that one element or compound may be partially or entirely replaced by another. Most rocks from which soils have been produced contain minerals as feldspar, mica, hornblende, and quartz. 59. Quartz and Feldspar. — Quartz is the principal constituent of many rock formations. Pure quartz is silicic anhydride (SiO2). White sand is nearly pure quartz or silica. Silica enters into combination with many elements, forming a large number of minerals. 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 replace 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 feldspar or orthoclase. The members of the feldspar group are insoluble in acids and before disintegration takes place are not capable of supplying plant food. Potash feldspar contains from 12 to 15 per cent, of potash, none of which is of value as plant food. When feldspar undergoes disintegration it produces kaolin or clay. A soil formed from feldspar is usually well-stocked with potash. Orthoclase, AlKSi3O8 Potash feldspar. Albite, AlNaSi3O8 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 ZEOLITES 53 members of the alkali family in hornblende. The augites are double silicates of iron, manganese, cal- cium, 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 unavailable as plant food, and when disintegrated do not as a rule form very fertile soils. 61, Mica, — Mica is quite complex in composition, is an abundant mineral, and is composed of silica, iron, alumina, manganese, calcium, magnesium, and potassium. Mica is a polysilicate. The color may be white, brown, black, or bluish green owing either to the absence of iron, or to its presence in 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 disintegrated mica are usually fertile, owing to the variety of essential elements present. Frequently small pieces of undecomposed mica are found in soils. 62. Zeolites. — The zeolites are a large group of secondary or derivative minerals formed from disin- tegrated rock. They are polysilicates containing alumina and members of the alkali and lime families, and all contain water held in chemical combination. They are partially soluble in dilute hydrochloric acid 54 SOILS AND FERTILIZERS and belong to the group of compounds which are capable, to a certain extent, of becoming available as plant food. In color, they are white, gray, or red. Zeolites are quite abundant in clay and are an import- ant factor in soil fertility. It is this group of hydrated silicates which takes such an important part in the process of fixation. The zeolites, when disintegrated, particularly by glacial action, form very fertile soils. 63. Granite is composed of quartz, feldspar, and mica. It is a very hard rock and slow to disintegrate. The different shades of granite depend upon the pro- portion in which the various minerals are present. Inasmuch as granite contains so many minerals it usually follows that thoroughly disintegrated granite soil is very fertile. Pure powdered granite before undergoing disintegration furnishes no plant food. After weathering, the plant food gradually becomes available. Gneiss belongs to the granite series but differs from true granite in 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_(PO4)2, 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 is 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- DISINTEGRATION OF ROCKS AND MINERALS 55 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, Al4(SiO4)3.H2O. Impure varieties of clay are colored red and yellow on account of the presence of iron and other impurities. Pure kaolin is white, is insoluble in acids, and is incapable of supplying any nourisment to plants. Clay soils are fertile on account of the other minerals and organic matter mixed with the clay and are usually well-stocked with potash be- cause of the incomplete removal of the potash from the disintegrated feldspar. It is to be observed that the term clay used- chemically means aluminum sili- cate, while physically it is any substance, the particles of which are less than 0.005 mm- in diameter. 66. Disintegration of Rocks and Minerals. — In ad- dition to the rocks and minerals which have been mentioned, there are many others that contribute to soil formation as limestone which is calcium carbon- ate, dolomite a double carbonate of calcium and mag- nesium, serpentine a silicate of magnesium, and gyp- sum or calcium sulphate. All rocks and minerals are subject to disintegration and change in chemical com- position and physical properties. The process of soil formation has resulted in numerous chemical and physical changes. These changes are still taking place, and as a result plant food is constantly being made available. 56 SOILS AND FERTILIZERS CHEMICAL COMPOSITION OF ROCKS" 8 . es c g Id1 |4 h 1* Is Scd rt be •-^ E? ?9, '&'& << < ^W 5^ ^0 SS fcto ^ K Quartz.... Feldspar 2O— 2Q O— 12 I— IO I— II Kaolin.. d6 -7Q 14 Apatite C7 ^P2O5\ s V 42 ; Mica AO—A ? 12—77 5-12 I— S Hornblende O— IS Granite... 60-80 IO-IS '"' 2-^ 67. Value of Geological Study of Soils. — Agri- cultural geology is a valuable aid in studying soil problems, but like other sciences it is incapable alone of solving all of the problems of soil fertility. Means have not as yet been devised for accurately de- termining the extent of rock disintegration and the rapidity with which it has taken place or the extent to which disintegrated minerals have been removed from rocks by leaching and other agencies. It is known that the rate of weathering of soils is influenced by various factors, as origin, texture, composition, humidity and other climatic conditions, presence of de- caying organic matter, micro-organisms, mechanical treatment and manipulation of the soil, fertilizers, sun light and vegetation. Some of these agencies for soil disintegration are under the control of the farmer and are utilized by him in rendering plant food avail- able. CHAPTER III THE CHEMICAL COMPOSITION OF SOILS 68. Elements Present in Soils. — Physically consid- ered, a soil is composed of disintegrated rock mixed with animal and vegetable matter; chemically con- sidered, the rock particles are composed of a large number of simple and complex compounds, each com- pound in turn being composed of elements chemically united. Elements unite to form compounds, com- pounds to form minerals, minerals to form rocks, and disintegrated rocks form soil. When rocks decom- pose, the disintegration, except in a 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. 69. Classification of the Elements. — The elements found most abundantly in soils are divided into two classes : 58 SOILS AND FERTILIZERS Acid-forming elements Base-forming elements Oxygen O Aluminum Al Silicon Si Potassium K Phosphorus : P Sodium Na Sulphur S Calcium Ca Chlorine Cl Magnesium Mg «* Nitrogen N Iron Fe * Hydrogen H Carbon C* j Boron, fluorine, manganese, and barium are usually present in small amounts, besides others which may be present in traces, as the rare elements lithium and titanium. For crop purposes the elements of the soil may be divided into three classes. 1. Essential elements most liable to be deficient:' nitrogen, potassium, phosphorus, and calcium. 2. Essential elements usually abundant : iron, mag- nesium, and sulphur. f 3. Unnecessary and accidental elements, usually abundant, as chlorine, silicon, aluminum, and man- ganese. 70. Combination of Elements. — In dealing with the composition of soils, the percentage amounts of the individual elements are not given, except in the case of nitrogen, but instead, the percentage amounts of the various oxides. This is because the elements do not exist as free elements in the soil, but are com. bined with oxygen and other elements to form com. pounds. When considered as oxides, the acid- and base- o rming elements may form various compounds as : SILICON 59 Calcium Silicate Phosphate Chloride w Potassium..../,/// Sodium Y/ Sulphate Carbonate Magnesium.y Iron .. The following reactions will explain some of the more elementary forms of combinations : CaO + SiO2 = CaSiO3 CaO + N2O5 = Ca(NO3)2 3CaO + P205=Ca3(P04)2 K2O + SO3 = K2SO, CaO + S03 = CaSO, Na2O + SO3 = Na.SO, CaO + CO2 = CaCO3 MgO + SO3 = MgSO4 When considered as the oxide, calcium may com- bine with any of the oxides of the acid-forming ele- ments, as indicated by the reactions, to form salts. Each of the compounds formed from the more com- mon elements may have a separate value as plant food, hence it is important to consider the combina- tions of each element separately. ACID-FORMING ELEMENTS 71. Silicon. — The element silicon makes up from a quarter to a third of the solid crust of the earth and next to oxygen is the most abundant element found in the soil. Silicon never occurs in the soil in the free state. It either combines with oxygen to form silica (SiOa), or with oxygen and some base-forming element or elements to form silicates. Silica and the various silicates are by far the most abundant com- pounds present in the soil. Silicon is not one of the elements absolutely necessary for plant growth, and 60 SOILS AND FERTILIZERS even if it were, all soils are so abundantly supplied that it would not be necessary to use it in fertilizers. 72. Double Silicates. — When two or more base- forming elements are united with the silicate radical, a double silicate is formed. In fact the double sili- cates are the most common forms present in soils. There are also a number of forms of silicic acid which greatly increase the number of silicates, and a study of the composition of soils is largely a study of these various silicates. 73. Carbon is an acid-forming element and belongs to the same family as silicon. It is found in the soil as one of the main constituents of the volatile or organic compounds. Carbon also unites with oxygen and the base-forming elements, producing carbonates, as calcium carbonate or limestone. The carbon of the soil takes no direct part in forming the carbon com- pounds of the plant. It is not necessary to apply carbon fertilizers to produce the carbon compounds of plants because the carbon dioxide of the air is the source for crop production. It is estimated that there are 30 tons of carbon dioxide in the air over every acre of the earth's surface.22 The carbon in the soil is an indirect element of fertility, because it is usually combined with elements, as nitrogen and phosphorus, which are absolutely necessary for crop growth. 74. Sulphur occurs in all soils mainly in the form of sulphates, as calcium sulphate, magnesium sul- phate and sodium sulphate. It is an important ele- ment of plant food. There is generally less than NITROGEN 6l o.io per cent, of sulphuric anhydride in ordinary soils, but the amount required by crops is small and there is usually an abundance in all soils. 75. Chlorine is present in all soils, generally in combination with sodium, as sodium chloride. It may be in combination with other bases. Soils which con- tain more than o.io per cent, are, as a rule, sterile. Chlorine is present in the soil in soluble forms. It occurs in all plants, although it is not absolutely necessary for plant growth, and its combination in fertilizers is unnecessary. Chlorine with sodium, as common salt, is sometimes used as an indirect fertilizer. 76. Phosphorus, one of the essential elements for plant growth, is combined with both the volatile and non-volatile elements of the soil. Plants cannot make use of it in other forms than those of phosphates. Phosphorus is usually present in the soil as calcium phosphate, magnesium phosphate, or aluminum phos- phate, and may also be combined with the humus, forming humic phosphates. The form in which the phosphates are present, as available or unavailable, is an important factor in soil fertility. Soils are quite liable to be deficient in phosphates, inasmuch as they are so largely drawn upon by many crops, particularly grain crops where the phosphates accumulate in the seed, and are sold from the farm. 77. Nitrogen. — This element is present in soils in various forms. As a mineral constituent it is com- bined with oxygen and the base-forming elements as 62 SOILS AND FERTILIZERS potassium, sodium, or calcium, forming nitrates and nitrites, which, on account of their solubility, are never found in average soils in large amounts. Nitro- gen is present mainly in organic combinations, being associated with carbon, hydrogen, and oxygen as one of the elements forming the organic matter of soils. Nitrogen may also be present in small amounts in the form of ammonia, or of ammonium salts, derived from rain water and from the decay of vegetable- and ani- mal matter. While nitrogen is present in the air in a free state in large amounts, it can be appropriated indirectly as food in this form by only a limited num- ber of plants. For ordinary agricultural crops, par- ticularly the cereals, nitrogen must be supplied through the soil as combined nitrogen. This element is the most expensive and is liable to be the most de- ficient of any of the elements of plant food. No other element takes such an important part in agriculture or in life processes. 78, Oxygen. — Oxygen is combined with both the acid- and base-forming elements and is present in nearly all of the compounds of the soil. It has been estimated that about one-half of the crust of the earth is composed of oxygen, which is found in large amounts combined with silicon, forming silica. That which is held in chemical combination in the soil takes no part in the formation of plant tissue. In ad- dition to being present in the soil, oxygen constitutes eight-ninths of the weight of water and about one-fifth of the weight of air. It also forms about 50 per cent. ALUMINUM 63 of the compounds found in plants and animals. Oxy- gen in the interstices- of the soil is an active agent in bringing about many chemical changes, as oxidation of the organic matter, and disintegration of the soil particles. 79. Hydrogen. — This element is never found in a free state in the soil, but is combined with carbon and oxygen as in animal and vegetable matter, with oxy- gen to form water, and in a few cases with some of the base elements to form hydroxides. It is not found in large amounts in the soil, and that which forms a part of the tissues of plants and animals conies from the hydrogen in water. Hydrogen in the organic matter of soils takes no part directly in producing the hydrogen compounds of plants. On account of its lightness, hydrogen never makes up a very large pro- portion, by weight, of the composition of bodies. BASE-FORMING ELEMENTS 80. Aluminum is present in the soil in the largest quantity of any of the base elements. It is calculated that it forms from 6 to 10 per cent, of the solid crust of the earth. As previously stated aluminum is one of the constituents of clay, and is not necessary for plant growth. Physically, however, the aluminum compounds take an important part in soil fertility. Aluminum is usually in combination with silica or with silica and some base-forming element, as iron, potassium, or sodium. The various forms of alumi- num silicates are the most numerous compounds pres- ent in soils. 64 SOILS AND FERTILIZERS 81. Potassium is present in the soil mainly in the form of silicates, and is one of the elements absolutely necessary for plant growth. The term potash (potas- sium oxide, K2O) is usually employed when the potas- sium compounds are referred to. The amount and form of the soil potash have an important bearing upon fertility. Potassium is one of the three elements of plant food usually supplied in fertilizers. The form in which it is present in the soil and its economic supply as plant food, are important factors of crop growth, and are considered in detail in Chap- ter VIII. The amount of potash in soils ranges from 0.02 to 0.8 per cent. In a fertile soil it rarely falls below 0.2 per cent. 82. Calcium is present in the soil in a variety of forms, as calcium carbonate, calcium silicate, and calcium phosphate. The calcium oxide (CaO) of the soil is generally spoken of as the lime content. Calcium carbonate and sulphate are important factors in imparting fertility. A subsoil with a good supply of lime will stand heavy cropping and remain in ex. cellent chemical and physical condition for crop growth. In a good soil there is usually 0.2 per cent, or more of lime mainly as calcium carbonate. 83. Magnesium is present in all soils and is usually associated with calcium, forming the mineral dolo- mite, which is a double carbonate of calcium and magnesium. Magnesium may also be present in the soil in the form of magnesium sulphate or magnesium chloride. All crops require a certain amount of mag- ACID-SOLUBLE MATTER OP SOILS 65 nesia in some form, in order to reach maturity and produce fertile seeds. There is generally in all soils an amount sufficient for crop purposes, hence it is not necessary to consider this element in connection with fertilizers. 84. Sodium is found in the soil mainly as sodium silicate, and is present to about the same extent as potassium which it resembles chemically in many ways. It cannot, however, replace in plant growth the element potassium. Inasmuch as sodium takes an indifferent part in plant nutrition it is never used as a fertilizer except in an indirect way. 85. Iron is an element necessary for plant food and is found in all soils to the extent of from i to 4 per cent. Crops require only a small amount of iron, hence there is always sufficient for crop purposes. Iron is present in soils in the form of oxides, hydrox- ides, and silicates. FORMS OF PLANT FOOD 86. Three Classes of Compounds. — For agricul- tural purposes, the compounds present in soils may be divided into three classes :17 (i) Compounds soluble in water and dilute organic and mineral acids ; (3) compounds soluble in more concentrated acids ; (3) in- soluble compounds decomposed by strongest acids and fluxes. 87. Water- and Dilute Acid-soluble Matter of Soils. — This class includes silicates and other compounds of potash, soda, lime, magnesia, phosphorus, etc., which are soluble in the soil water and in very dilute organic (5) 66 SOILS ANE> FERTILIZERS and mineral acids, and represents the most soluble and the most active and valuable forms of plant food. There is only a very small amount in these forms. In 100 pounds of soil, rarely more than 0.005 pound of any one of the important elements is soluble in the soil-water or more than 0.05 pound in dilute or- ganic acids. Experiments have shown that the soluble plant food from a fertile soil is not sufficient for plant growth.85 When oats, wheat and barley were seeded in prepared sand and watered with the leach- ings from a pot of fertile soil, they made only a lim- ited growth. For comparisons with plants grown in fertile soil, see Plate I. The oats grown in the pre- pared sand and watered with soil leachings assimilated only 25 per cent, as much phosphoric acid as the plants grown in fertile soil. 88. Acid Soluble Matter of Soils,— The plant food of the second class is in a somewhat more insoluble form, and consists of all those compounds and zeolitic silicates which are soluble in hydrochloric acid of 23 per cent, strength, sp. gr. 1.115. This represents the limit of the solvent action of the roots of plants.17 In this second class are also included all of the mineral elements combined with the humus and soluble in dilute alkalies. As a rule, not over 15 or 20 per cent, of the total soil is in forms soluble in hydrochloric acid, and of the more important elements only i to 6 per cent, form a part of this 15. In 200 samples of soil, the potash, nitrogen, lime, magnesia, and phosphoric and sulphuric acids, amounted to 3.5 per cent. In PI.ATK I, ACID-INSOLUBLE MATTER OF SOILS / 2.3. Total /nsolub/e Matter- Fig. 17. Graphic composition of 200 soils, i. Nitrogen. 2. Potash. 3. Phosphoric acid. many fertile soils the sum of the nitrogen, phosphoric acid, potash, lime, magnesia, and sulphuric and car- bonic anhydrides is less than 1.50 per cent. This means that in every 100 pounds of soil there are only from 1.5 to 3.5 pounds of matter which can take any active part in the support of a crop, and 96 to 98.5 pounds are present simply as so much inert material. Not all of the plant food soluble in hydrochloric acid is equally valuable. In fact, the acid represents more than the limit of the crop's feeding power, when there is not enough of more soluble forms to aid in the first stages of growth. 89. Acid-Insoluble Matter of Soils. — This class in- cludes all of those compounds of the soil which re- quire the joint action of the highest heat and the strongest chemicals in order to decompose them. The 68 SOILS AND FERTILIZERS insoluble residue obtained after digesting a soil with strong hydrochloric acid, contains potash, soda, and limited amounts of magnesia, and phosphoric acid, with other elements which are of no value as plant food. When seed was planted in soil extracted with strong hydrochloric acid, it made no growth after the reserve food in the seed had been exhausted. A plant grown in such a soil is shown in the illustration,1? Fig. 18. The acid-insoluble matter of soils is capable of under- going disintegration and in time may be changed to the second or zeolitic class of silicates. This process, how- ever, is too slow to be relied upon as an immediate source of plant food. In the following table the percentage amounts of com- FiS- l8- Oat Plant Srown in soil extracted with hydro- pounds soluble and insoluble chloric acid. in hydrochloric acid are given :17 SOLUBLE AND INSOLUBLE POTASH, ETC. 69 Wheat Heavy clay Grass and soil. soil. grain soil. Solu- Insolu- Solu- Insolu- Solu- Insolu- ble in ble ble in ble ble in ble HC1 residue HC1 residue HC1 residue Insoluble matter... 63.07 84.77 84.08 Potash 0.54 2.18 0.21 3.46 0.30 1.45 Soda 0.45 3.55 0.22 2.95 0.25 0.25 Lime 2.44 0.36 0.48 0.16 0.51 0.35 Magnesia 1.85 0.25 0.34 0.47 0.26 0.46 Iron 4.18 0.78 3.76 0.72 2.56 1.07 Alumina 7.89 5.54 6.26 5.44 2.99 9.72 Phosphoric acid.... 0.38 0.12 0.08 0.23 0.05 Sulphuric acid o.n 0.24 0.09 0.25 0.08 0.02 The insoluble matter, after digestion with hydro- chloric acid, was submitted to fusion analysis, and the figures given under insoluble residue represent the amounts of potash, soda, etc., insoluble in acids. In the clay soil, 94 per cent, of the total potash is in forms insoluble in hydrochloric acid. 90. Soluble and Insoluble Potash and Phosphoric Acid. — From the preceding table it is to be observed that the larger portion of the potash in the soil is in- soluble in hydrochloric acid. A soil may contain from 2 to 3 per cent, of total potash, and 90 per cent, or more may be in such firm chemical combination with aluminum, silicon, and other elements, as to re- sist the solvent action of plant roots. The larger por- tion of the phosphoric acid of the soil is soluble in hydrochloric acid. In some soils, however, from 20 to 40 per cent, is present as the third class of com- pounds. When a soil is digested with hydrochloric acid, the insoluble residue is usually a fine, gray powder. Some clay soils retain their red color even after treatment with acids showing that the iron is in 70 SOIIvS AND FERTILIZERS part in chemical combination with the more complex silicates. In order to decompose the insoluble residue obtained from the treatment with hydrochloric acid, fluxes, as sodium carbonate and calcium carbonate, are employed which act upon the complex silicates at a high tem- perature, and produce silicates soluble in acids. Plants, however, are unable to obtain food in such complex forms of chemical combination. 91. Action of Organic Acids upon Soils. — Dilute organic acids, as a i per cent, solution of citric acid, have been proposed as solvents for the determination of easily available plant food. It has been shown in the case of the Rothamsted soils which have produced 50 crops of grain without manures, and which are markedly deficient in available phosphoric acid, that a i per cent, solution of citric acid dissolved only 0.003 per cent, of phosphoric acid while the soil contained a total of o.i 2 per cent. In the case of an adjoining plot which had received phosphate manures until the soil contained a sufficient amount of available phos- phoric acid to produce good crops, there was present 0.03 per cent, of phosphoric acid soluble in a i per cent, citric acid solution.23 Dilute organic acids are, to a certain extent, capable of showing deficiency of plant food. A soil which shows 0.03 per cent, of potash or phosphoric acid sol- uble in i per cent, citric acid is, as a rule, well stocked with available phosphoric acid. Prairie soils of high fertility yield from 0.03 to 0.05 per cent, of both pot- ACTION OF ORGANIC ACIDS UPON SOILS 7 1 ash and phosphoric acid soluble in dilute organic acids ; soils which are deficient in these elements usu- ally contain less than o.oi per cent. The action of a single organic acid of specific strength cannot be taken as the measure of fertility for all soils and crops alike, because different plants do not have the same amount or kind of organic acid in the sap. Of the various organic acids, citric pos- sesses the greatest solvent action upon lime, magnesia, and phosphoric acid, while oxalic has the strong- est solvent action upon the silicates. Tartaric acid appears to be less active as a solvent than either citric or oxalic acid. The combined use of dilute organic acids, as citric, with hydrochloric acid (sp. gr. 1.115), will generally give an accurate idea of the character of a soil. . A fifth-normal solution of hydrochloric acid has also been proposed as a measure of the soil's active phosphoric acid, and has given satisfactory results.24 The use of dilute organic acids renders it possible to detect small amounts of readily soluble phosphoric acid and potash. It has been stated that when a soil has been manured a few years with a phosphate fer- tilizer and brought into good condition as to avail- able phosphoric acid, a chemical analysis will fail to detect any difference in the soil before or after the treatment with fertilizer. In the case of hydrochloric acid as a solvent, this is true because an acre of soil to the depth of one foot weighs about 3,500,000 Ibs. and 500 pounds of phosphoric acid would increase the total amount of phosphoric acid about 0.015 per cent. When a dilute organic acid is used, only the more SOILS AND FERTILIZERS easily soluble phosphoric acid is dissolved, and this readily allows fertilized and unfertilized soils to be distinguished. By the use of dilute organic acids and salts decided differences have been shown between soils fertilized and unfertilized with potash.26 92. Sampling of Soils. — A composite sample of soil is obtained from a field by taking several small samples to a depth of 6 to 9 inches, from different places, and uniting them to form one sample. Samples of subsoil also are taken from the same places. There is usually a sharp line of demarkation between the surface and subsoils. It is the aim to secure in both cases as representative samples as possible. All coarse stones and roots are removed and a record is made of the amount of these materials. The soil is air-dried, the hard lumps are crushed, and the mate- rials mixed and passed through a sieve with holes 0.5 mm. in diameter. Only the fine earth is used for the chemical analysis. 93. Analysis of Acid- soluble Ex- tract of Soils. — Ten grams of soil are weighed into a soil digestion flask, and 10 cc. hydrochloric acid (sp. gr. 1.115), are added for every gram of soil used. The soil digestion flask is then placed in a hot water-bath and the digestion carried on for twelve hours Fig. 19. Diges- at the temperature of boiling water.27 tion flask. After digestion is completed the con- tents of the flask are transferred to a filter and separated ACID-SOLUBLE EXTRACT OF SOILS 73 ^3 P 8«S§:| I' " WT2.& ?• 1 _ - >~* *~" C P. l^'f o Crq' ft> c a L B C/3 £. o ^-' w T fb Q H rt K-. A* &• ^ 3 pa ^ ^ ^. £• a £>d £.>d &r a >d 3 g P. 3 rtplirfilit *?»?": Wl R.|g*£g| *s° fi'tlffr-il sl|i!lHHi liifltfW •"•MB-fttt »« N»»P o> P rt tt P ** rfHllMli TI ai a* [trate is used as noted below. iltrate, after removing soluble precipitate obtained. ^drochloric acid and fitered, ai ANALYSIS o l|| !l 2. 1 P c* i r 1 c » |"| 3 ?T O (T ^ S PB ^ >-»• CJ gi w |-4 U3 i-! 1 EL' i-J 3 *2.8 3 g" 2.^3^51° r? ».=• P P B.JJ- §. §*§•' «" - ^ | g E S3 E o* • C3 C ^^ rT1 ^^ *"* o ^0 P •& |r0j*fel o ' S. 5" rs a 1 ? flrriiij g. n g hd rt w' p i. a g- p.a P S- a' p S ^ o 3. p JJ ^ 0 Pkl 2 o' ft i - O fD *^ M* 0 2 cu » g: &i ^ so « 51 a pj ^ pj — a o P' P •-t >-t & •Ti a P a a <"'' n o P CU 1 0 Y ^ *t l B W> p * P T 74 SOILS AND FERTILIZERS into an insoluble part, and the acid solution which contains the soluble compounds of the various elements. The table on page 73 gives a general idea of the process of soil analysis. One-half of the acid solu- tion is used for obtaining the metals as noted on page 73. The second half is divided into two portions. The first portion is used for the deter- mination of phosphoric acid, which is precipitated with ammonium molybdate. The second portion is used for the determination of sulphuric acid, which is precipitated as barium sulphate. Carbon dioxide is determined in a fresh portion of the original soil j the acid is liberated with hydrochloric acid and the carbon dioxide retained by absorbents and weighed. The nitrogen and humus are determined in separate portions of the original soil. The analysis of soils involves the use of accurate and well-known methods of analytical chemistry, a discussion of which would not be germane to this work. 94. Value of Soil Analysis. — Opinions differ as to the value of soil analysis. It is claimed by some that a chemical analysis of a soil is of no practical value because it fails to give the amount of available plant food. A soil may have, for example, 0.4 per cent, of potash soluble in hydrochloric acid and still not con- tain sufficient available potash to produce a good crop, while another soil may contain 0.2 per cent, of potash soluble in hydrochloric acid and produce good crops. While these facts are frequently true, it does not necessarily follow that the chemical analysis of a soil VALUE OF SILT ANALYSIS 75 is of no value. Other solvents than hydrochloric acid are used in soil analysis with excellent results. Hydro- chloric acid is generally used because it represents the limit of fhe solvent power of plants.17. The figures obtained by the use of hydrochloric acid are valuable inasmuch as they indicate whenever an element is present in amounts which are too limited to admit of crop production. Suppose a soil contain 0.02 per cent, of acid-soluble potash; this would be too small an amount to produce good crops. On the other hand, the soil might contain 0.5 per cent, and yet not have sufficient available potash for crop growth. Hence it is, that in interpreting results, the hydrochloric acid solvent may show when a soil is wholly deficient in any one element, as is sometimes the case, but it does not necessarily show a deficiency in the case of a soil rich in acid-soluble potash ; this can, however, be ap- proximately indicated, by the use of other solvents, as explained in Section 91. Hydrochloric acid is mainly valuable in determining the general character of the soil, rather than its amount of available plant food. In the analysis of soils their reaction as acid, alka- line, or neutral, should be determined, because plant food exists in a different form in each class of soils. If a soil contain from 0.3 to 0.5 per cent, or more of lime and from o.i to 0.4 per cent, of combined carbon dioxide, and is not strongly alkaline, there is a reason- able content of lime carbonate. If, however, the soil contain only a trace of carbon dioxide, the lime is not present as carbonate, but is probably present as a 76 SOILS AND FERTILIZERS silicate, in which case the soil may be deficient in ac- tive lime compounds. In the case of phosphoric acid, a soil which gives an alkaline or neutral reaction, contains 0.15 per cent, of phosphorus pentoxide and is well supplied with organic matter and lime, is amply provided with phos- phoric acid, and under such conditions the extensive use of phosphate fertilizers is not required, except pos- sibly for special crops. Hilgard states that should the per cent, of phosphoric acid be as low as 0.05, there is, in all probability, a poverty of this element. It frequently happens that in acid soils the phosphoric acid is unavailable until a lime fertilizer is used to neutralize the acid. Soils containing less than 0.07 per cent, of total nitrogen are usually deficient. A soil containing as high as 0.15 or 0.2 per cent, of nitrogen may fail to re- spond to crop production. Such cases are generally due to some abnormal condition of the soil, as a lack of alkaline compounds which are necessary for nitri- fication. The appearance of the crop is the best indi- cation as to a deficiency of nitrogen. A soil which contains less than o.io percent, of pot- ash soluble in hydrochloric acid is quite apt to be de- ficient in this element. Soils which contain 0.5 per cent, or more of lime carbonate will produce good crops on a smaller working supply of potash than soils which are proverty-stricken in lime. As a rule the best agricultural soils contain from 0.3 to 0.6 per cent, of potash. Sandy soils of good depth may contain VALUE OF SILT ANALYSIS 77 less plant food than the figures given, and not be in need of fertilizers. The term volatile matter is sometimes confused with the term organic matter. The volatile matter includes the organic matter and the water which is held in chemical combination as in the hydrated silicates. A soil may have a high per cent, of volatile matter and contain very little organic matter. Indeed all clays contain from 5 to 9 per cent, of water of hydration. The per cent, of humus, as will be explained in the next chapter, does not represent all of the organic matter. The best results are obtained from soil analyses when an extended study is made of the soils of a lo- cality. Then an unknown soil of that locality can be compared with a productive soil of known composition. An isolated soil analysis, like an isolated analysis of well water, frequently fails in its object because of a lack of proper normal standards for comparison. When extended series of soil analyses have been made, much valuable information has been obtained. Suppose a soil contain 0.40 per cent, of acid-soluble potash and field experiments indicate that there is a deficiency of available potash. This may be due to some abnormal condition of the soil, as an insufficient amount of other alkaline compounds as calcium car- bonate to take the place of the potash which has been withdrawn by the crop, in which case the deficiency of potash can be remedied without purchasing solu- ble potash fertilizer, to become insoluble by fixation processes. If a soil contain only 0.04 per cent, of y8 SOILS AND FERTILIZERS acid-soluble potash, the purchasing of potash fer- tilizers is more necessary, but with 0.40 per cent. of acid-soluble potash the way is open to render this potash available for crops. The various ways of ren- dering acid-insoluble potash and other compounds available for crop production, as by rotation of crops, use of farm manures, use of lime and green manures, or by different methods of cultivation have not been sufficiently studied as yet to offer a solution to all of the problems of how to render inert plant food avail- able. 95. Distribution of Plant Food. — In studying the chemical composition of a soil, the surface soil and the subsoil both require consideration. It frequently happens that the surface soil and subsoil have entirely different chemical, as well as physical, properties, and that a soil fault, as lack of potash in the surface soil, is corrected by a high per cent, of that element in the subsoil. This is particularly true of the western prairie soils, where the surface soils generally contain less potash and lime, but more nitrogen and phosphoric acid than the subsoils. When jointly considered the surface and subsoil have strong crop-producing powers, but if considered separately each would have weak points. Since crops take their food mainly from the silt and clay, the amount of plant food present in these grades of particles determines largely the reserve fertility of the soil. A soil in which 70 per cent, of the total potash is present in the silt and clay, is in better con- dition for crop production than a similar soil with a COMPOSITION OF TYPICAL SOILS 79 like amount of potash which is present mainly in the sand. Because a soil has a given composition, it does not follow that all of the different grades of particles have the same composition. In fact the different grades of soil particles in one soil may have as varied a composition as is met with among different soils.26 The figures under i in the table give the composi- tion of the particles, while under 2 are given the re- sults calculated on the basis of the total amount of each element. For example, the clay contains 1.47 per cent, of potash, while 50.8 per cent, of the total potash of the soil is in the clay particles. A soil may contain a comparatively low per cent, of potash or phosphoric acid, mainly in the finer particles and evenly distributed so that the crop is better sup- plied with food than if more were present in the larger particles, unevenly distributed. The distribu- tion of the plant food in the soil has not been so ex- tensively studied as the question of total plant food. The distribution of plant food in both surface soil and subsoil, as well as in the various grades of soil parti- cles, is an important factor of fertility. 96. Composition of Typical Soils.— A few exam- ples are given, in tabular form, of the chemical com- position of soils from different regions in the United States. On account of variations in the same locality, the figures represent the composition of only limited areas of soils. There have been made in the United States a large number of soil analyses, which as yet have not been compiled nor studied in a systematic way. 8o SOILS AND FERTILIZERS r i—Q«'-|TtlO'-H>-iQ u crt 00 • « rt- ^ q q 5 . / i*o3 J5 "" d\ M ' o •-< 06 oo" o o" d> v£> 10 • M TJ- 04 10 04 O O I *» . ** 0" • M ^f ^ °° "? 9 "? §NCOON* M^'-'Oj^dlO N;X ...^csw lo^a- V SVD P4cOTtcOvOVOO4>-i04 — Cto.— IOCS i-< Tj-t>>.cOi-i OvO c?c?M co o" 6 d o* -4 -4 d o 10 o °° , v o g !} *• «o « 'odvd>o4' 'i>. _l.5° * I O O S "*• foONCOOOvO^T'^'cOcOtN g 10 . 04 04 04 M N CO VO O O t>« >o2'HoJdc56dp<^*od'-i 6 O w ioO.Oo4<^-O--cO O -M.M t^vO-«>«04*^'-^*«<' rt g N xo ^ * CO M' N 04' .aS I°-S1 ^£?" vd d 6 o o M M* o* d o* a j4*gfi o U ••••••_-•• flj • . • > • *v • IN I : : .-S : « '§ | ^CL,^^^fe<^C«> COMPOSITION OF TYPICAL SOILS 8l £.' •5 1 5 3 /5 Volatile T Carboni 03 "d £ ^ •t Q Aluniim § GK? 3 £• 3 (D *^ 8 S * • X en . . i|| 1 g & a L I f? >-i o 2. o p 3 S* " &• rt . ' ' : ^. 3 ; ?? R I oJ . o • p Oi I O ^J ON K> I-H 1 o o Surface. Per cent. Subsoil. Percent. Surface. Per cent. Subsoil. Per cent. Per cent. - X " O O « to k> Surface. Percent. IP Fft (6) 82 SOILS AND FERTILIZERS Cotton soil.32 Brazos River soil.33 Wash- Kentucky soil.35 California36 Surface. Subsoil. Surface. Subsoil. soil. Virgin. vated. Surface. Subsoil. LO ^ LO cO cs r-« t^ co LO CO ON 8s Humic phos- Humic phoric acid. potash. Cow manure humus : Grams. Grams. In original manure and soil 1.17 1.06 In final humus product (after hu- mification) 1.62 1.27 Gain in humic forms 0.45 0.21 Green clover humus : In original soil and clover 3.21 5.26 In final humus product 3.74 4.93 Gain in humic forms 0.53 (Loss) 0.33 VALUE AND COMPOSITION OF HUMATES 89 Humic phos- Humic phoric acid. potash. Meat scrap humUS : Grams. Grams. In original meat scraps and soil- • • 1.07 0.25 In final humus product 1.18 0.36 Gain o.n o.n Sawdust humus : In original sawdust and soil 0.85 0.67 In final humus product 0.78 0.70 Oat straw humus : In original straw and soil • 1.02 2.42 In final humus product 1.03 2.41 105. Comparative Value and Composition of Hu- mates. — The humus produced from nitrogenous bodies as meat scraps, is more valuable than that pro- duced from cellulose bodies, as sawdust, because the former has greater power of combining with the phosphoric acid and potash of the soil. The non- nitrogenous compounds, as cellulose, starch, and sugar, undergo fermentation but seem to possess little, if any, power to form tuimates. There is also a great differ- ence in soils as to their humus-producing powers. Soils deficient in lime or alkaline compounds possess only a feeble power to produce humates. There is also a marked variation in the composition of the humus produced from different kinds of organic matter. Straw, sawdust, and sugar, materials rich in cellulose and other carbo-hydrates, yield a humus characteris- tically rich in carbon and poor in nitrogen. Materials rich in nitrogen, like meat scraps, green clover, and manure, produce a more valuable humus, rich in nitro- gen and possessing the power to combine with the 90 SOILS AND FERTILIZERS potash and phosphoric acid of the soil to form hu- mates. COMPOSITION OF HUMUS PRODUCED BYSO Cow Green Meat Wheat Oat Saw- manure, clover, scraps, flour. straw. dust. Sugar Carbon 41.95 54.22 48.77 51.02 54.30 49.28 57.84 Hydrogen 6.26 3.40 4.30 3.82 2.48 3.33 3.04 Nitrogen 6.16 8.24 10.96 5.02 2.50 0.32 0.08 45-63 34-14 35-97 40.14 40.72 47-°7 39-°4 Total 100.00 100.00 100.00 100.00 100.00 IOD.OO 100.00 Highest. Lowest. Difference. Carbon 57.84 41.95 15.89 Hydrogen 6.26 2.48 3.78 Nitrogen 10.96 0.08 10.88 Oxygen 47.07 34.14 12.93 Variations in composition are noticeable. The humus produced from each material as green clover, oat straw, or sawdust, is different from that produced from any other material. The humus from green clover is very complex in nature. It contains both nitrogenous and non-nitrogenous compounds, and each class has a different action in humification 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 nitroge- nous humus. 106. Value of Humates as Plant Food. — Various opinions have been held regarding the actual value, as plant food, of this product from partially decayed animal and vegetable matter. Humus was formerly regarded as composed only of carbon, hydrogen, and VALUE OF HUMATES AS PLANT FOOD 9 1 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,17 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.84. Cul- ture experiments have shown that under normal con- ditions plants like oats and rye may obtain their min- eral food entirely from humate sources. Seeds when planted in a mixture of pure sand and neutral 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 organisms found in fertile fields must also be introduced. The following example is given of oats which were grown when the only supply of mineral food was in humate forms. NITROGEN AND ASH ELEMENTS.17 In. six oat In six mature seeds. plants. Gram. Gram. Nitrogen 0.0040 0.0556 Potash 0.0013 0.0640 Soda o.ooor 0.0079 Lime 0.0002 0.0249 Magnesia 0.0005 o.oi 10 Iron 0.0064 Phosphoric anhydride 0.0016 0.0960 Sulphuric anhydride o.ooor 0.0090 Silicon 0.0026 0.7300 92 SOILS AND FERTILIZERS 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 indicates a way by which inert plant food may be converted into more active and available forms. It also explains that stable manure is valuable because it makes the inert plant food of the soil more available. 107. Amount of Plant Food in Humate Forms. — In a prairie soil containing 3 y2 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. Similar soils which have been under long cultivation without the restoration of any humus contain from 300 to 500 pounds each of humic potash and phos- phoric acid.18 A decline in crop-producing power has in many cases been brought about by the loss of humus. 108. Loss of Humus. — Loss of humus from soils 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 or 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 PHYSICAL PROPERTIES OF SOILS, ETC. 93 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, nitro- gen.18 After the fire there were present 0.41 per cent, humus and 0.03 per cent, nitrogen. The forest fire caused a loss of 2,500 pounds of nitrogen per acre. In clearing new land1, particularly forest land, there is frequently an unnecessary destruction of humus mate- rials. Instead of burning all the vegetable 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 and humus. When the vegetable matter has been only partially removed, the crops at first may be smaller, but in a few years returns will be greater than if all of the vegetable matter had been burned. 109. 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, heat, and water-retaining power of soils is discussed in the chapter on the physical properties of soils. Soils re- duced in humus content have less power of storing up water and resisting drought. This fact is illustrated in the following table : 31 PER CENT. WATER. After 10 hours exposure in In soil. tray, to sun. Soil rich in humus (3.75 per cent.) 16.48 6.12 Adjoining soil poorer in humus (2. 50 percent.) 12.14 3-94 94 SOILS AND FERTILIZERS no. Humic Acid. — In the absence of calcium car- bonate or other alkaline compounds, the vegetable matter may produce acid products destructive to the growth of some crops. The acidity in such cases can be readily corrected by the use of lime or wood ashes. Acid soils can be distinguished by their action upon blue litmus paper. A soil may, however, give an acid reaction and contain a fair amount of lime as a silicate. The subject of acid soils and liming is considered in Chapter IX. Studies conducted by the Rhode Island Experiment Station indicate that the areas of acid soils are quite extensive. in. Soils in Need of Humus. — Sandy and sandy Fig. 20. Hunris from old scil. Fig. 21. Humis from new soil. loam soils that have been cultivated for a number of years to corn, potatoes, and small grains without rota- tion of crops or the use of stable manures, are deficient in humus. Clay soils, as a rule, do not stand in need of humus so much as loam and sandy soils. The me- DIFFERENT METHODS OF FARMING, ETC. 95 chanical condition of heavy clays is, however, im- proved by the addition of humus-forming material. The addition of humus to loam or sandy soils is bene- ficial in preventing the soil from drifting, because it binds together the soil particles. There are but few arable soils, under ordinary cultivation, to which it is not safe to add humus-forming materials, either alone or jointly with lime. Ordinary prairie soils, for the first ten years after breaking, are usually well supplied. Swampy, peaty, and muck soils contain large amounts, in fact, they are often overstocked. "Alkali" soils are usually deficient in humus. 112, Active and Inactive Humus. — When soil has been long under 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.18 Humus from new soil. Per cent. Humus from old soil. Percent. 50.10 4.80 33-70 6.50 A.QO Oxv^en • • . ^ 1 6 8 12 Ash.. 6.60 Total humus material.. 5.30 3.38 113. Influence of Different Methods of Farming upon Humus. — The system of farming has a direct effect upon the humus content and the composition of the 96 SOILS AND FERTILIZERS soil. Where live stock is kept, the manure judiciously 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 differ- ent systems of farming upon the humus content and other properties of the soil may be observed in the following table : 3I S-8 bee Character of soil. ^p^ Sp, £01 PL,O,C&. Cultivated thirty-five years ; rotation of crops and ma- nure ; high state of pro- ductiveness 70 3.32 0.30 0.04 48 Originally same as i ; con- tinuous grain cropping for thirty-five years ; low state of productiveness 72 1.80 0.16 o.oi 39 Cultivated forty-two years ; systematic rotation and manure ; good state of pro- ductiveness 70 3.46 0.26 0.03 59 Originally same as 3 ; culti- vated thirty-five years ; no systematic rotation or ma- nure ; medium state of productiveness 67 2.45 0.21 0.03 57 CHAPTER IV NITROGEN OF THE SOIL AND AIR, NITRIFICATION, AND NITROGENOUS MANURES 114. Importance of Nitrogen as Plant Food. — The illustration (Fig. 22) shows an oat plant which re- ceived no nitrogen, while potash, phosphates, lime, and all other essential elements of plant food were liberally supplied. Observe the pe- culiar and restricted growth, with but limited root development. The leaves were yellowish. In the absence of nitrogen a plant makes 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 is centered in one or two leaves. 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.16 Just at the critical point when the plant was dying of nitrogen starvation, a few milligrams of calcium nitrate were given. In 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. (7) Fig. 22. Oat plant grown with- out nitrogen. 9§ SOILS AND FERTILIZERS During the time of seed formation more nitrogen was added, but with no beneficial result. All of the es- sential elements for plant growth were liberally pro- vided, except nitrogen, which was very sparingly sup- plied 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 want of nitro- gen, 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 necessary 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 85 per cent, of the total nitrogen required has been taken from the soil.36 Corn also takes up all of its nitrogen from four to five weeks before the crop matures. Flax takes up 75 per cent, of its nitrogen during the first fifty days of growth.38 Nitrogen is demanded by all crops. It forms the chief building material for the proteids of 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 of chlorophyl, *the green coloring-matter of plants, hence when there is a lack of nitrogen only a limited amount of chlorophyl can be produced. Plants with ATMOSPHERIC NITROGEN 99 large, well-developed leaves of a rich green color are not suffering for nitrogen. Nitrogenous fertilizers have a tendency to produce a luxurous growth of foliage, deep green in color. ATMOSPHERIC NITROGEN AS A SOURCE OF PLANT FOOD 115. Early Views. — In addition to carbon, hydro- gen, and oxygen, which form the organic compounds of plants, it was known as early as the beginning of the present century that plants also contained nitrogen. The sources of the carbon, hydrogen, and oxygen for crop purposes were much easier to determine and understand than the sources of nitrogen. Priestley, the discoverer of oxygen, believed that the free nitro- gen of the air was a factor in supplying plant food. De Saussure arrived at just the opposite conclusion. Neither of these assumptions were convincing because methods of chemical analysis had not yet been suffi- ciently perfected to solve the question.39 116. Boussingault's Experiments. — Boussingault was the first to make a careful study of the subject. In a prepared soil, free from nitrogen, and containing 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 protected 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 : 4° IOO SOILS AND FERTILIZERS NITROGEN. In seed sown. In plant. Gain. Gram. Gram. Gram. Clover, 2 nios o. n 0.12 o.oi " 3 " 0.114 0.156 0.042 Wheat, 2 " 0.043 °-°4 — 0.003 " 3 " 0.057 0.06 0.003 Peas, 2 " 0.047 o.io 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 sources was not suffi- cient to feed the plant and allow it to reach full maturity. By many these results were not accepted as conclusive. Fifteen years later (1853) Bous- singault repeated his experiments, but in a different way. The plants were now grown in a large carboy with a limited volume of air so as to cut off all sources of combined nitro- gen, as ammonia. By means of a second glass vessel (b, Fig. 23) the carboy was kept liberally supplied with 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 :4° Fig. 23. Plants grown in carboy. ATMOSPHERIC NITROGEN IOI NITROGEN. In seeds. In plant. Loss. Gram. Gram. Gram. Dwarf beans o. 1001 0.0977 — 0.0024 Oats 0.0109 0.0097 — 0.0012 White lupines 0.2710 0.2669 — 0.0041 Garden cress 0.0013 0.0013 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. In 1854 Boussingault again repeated his experi- ments on nitrogen assimilation. This time he grew the plants in a glass case so constructed that there was a free circulation of air from which all combined nitro- gen had been removed. These experiments were similar to his second series; the plants, however, were not grown in a limited volume of air. The results obtained showed that the free nitrogen of the air, under the conditions of the experiment, took no part in the food supply of the plants. If anything, there was less nitrogen recovered in the dwarfed plants than there was in the seed sown. 117. 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 are 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 com- 102 SOILS AND FERTILIZERS mission to review the work of Ville. The commis- sion consisted of six prominent scientists. They reported that UM. Ville's conclusions are consistent with his labor and results."39 118. Work of Lawes and Gilbert. — A little later L,awes and Gilbert carried on such extensive ex- periments 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 disturbing factors. The results in the aggregate clearly indicate that plants, when acting in a sterile medium, are unable to make use of the free nitrogen of the air for the pro- duction of organic matter.39. 119. Atwater's Experiments. — Atwater carried on similar experiments in this country.41 His results indicate that when seeds germinate they lose a small part of their nitrogen, and that when legumes are grown in a sterile soil, but are subsequently ex- posed to the air, a fixation of nitrogen may occur. 120. Field and Laboratory Tests. — By a five years' rotation of clover and other leguminous plants, Lawes and Gilbert found tha4: a soil gained from two to four hundred pounds of nitrogen per acre, in addition to that removed in the crop, while land which produced wheat continuously had gradually lost nitrogen. The ATMOSPHERIC NITROGEN 103 amount in the subsoil remained nearly the same. All of these facts plainly indicated that crops like clover had the power of gaining nitrogen from unknown sources. The results of prominent German agricul- turists led to the same conclusion. It was known that wheat grown after clover gave as good results as the use of nitrogenous manures for the wheat, but for many years this fact was unexplained. Laboratory 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 the work of the different investigators prior to 1888, plants were grown mainly in sterilized soils, and under such conditions they were unable to make use of the free nitrogen of the air, except when subse- quently innoculated from the air. 121. Hellriegel's Experiments. — Hellriegel grew leguminous 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 matur- ity 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 104 SOILS AND FERTILIZERS plants had well-formed swellings or nodules, while those that were watered with distilled water alone had none. The loam leachings contained only a trace of nitrogen.42 122. Experiments of Wilfarth. — Experiments by Wilfarth give more exact data regarding the amount of nitrogen taken from the air. Two plots of lupines were grown, one was watered with distilled water, while the other received in addition leachings from an old lupine field. Watered with distilled water. Watered with soil leachings. Dry matter. Nitrogen. Dry matter. Nitrogen. Grams. Grams. Grams. Grams. 0.919 0.015 44-72 1-099 0.800 0.014 45-6i i .153 0.921 0.013 4448 I-I95 i. 021 0.013 42.45 T-337 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. 123. 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., while the dark-colored and older ones contained 3.21 per cent. The entire nodules of the root, both active and inactive, con- ATMOSPHERIC NITROGEN 105 tained 4.60 per cent, nitrogen. The root itself con- tained 2.21 per cent.43 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. Experiments have shown that these organisms are capable of being propogated in nutritive media, separate from clover roots.87 124. Nitrogen in the Root Nodules Returned to the Soil. — Ward has shown that when clover roots decay, the organisms and nitrogen present in the nodules are distributed within the soil.38 Hence, whenever 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 legumes, 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 106 SOILS AND FERTILIZERS from those associated with another, as lucern. The amount of nitrogen which the various legumes return to the soil is variable. Hellriegel's results are of the greatest importance to agriculture, because they show how the free nitrogen of the air can be utilized in- directly as food by crops unable to appropriate it for themselves. THE NITROGEN COMPOUNDS OF THE SOIL 125. 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 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 culti- vation, because the tendency of ordinary cropping is to reduce the supply of soil nitrogen. 126. 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 elements, form- ing nitrates. The organic forms of nitrogen, it is generally considered, are incapable of supplying plants NITROGEN COMPOUNDS OF THE SOU, 1 07 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, and are present mainly as insoluable pro- teids.85 When decomposition occurs, arnides, organic salts, and other allied bodies are without doubt pro- duced as intermediate products before nitrification 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. In other soils the nitrogen is present in less complex forms. The organic nitrogen of the soil may vary in complexity from forms like the nitrogen of urea to forms like that of peat. 127. 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. There is usually two or three times more nitrogen in the surface soil than in the subsoil. In sandy soils which have been allowed to decline in fertility, there 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 108 SOILS AND FERTILIZERS available as plant food.44 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, it is that a soil may contain a large amount of total nitrogen, and yet be deficient in available nitrogen. 128. 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 the crop which removes the largest amount of nitrogen leaves the land in the most impoverished condition. Wheat and other grains, while they do not remove such a large amount of nitrogen in the crop, leave the soil more exhausted 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 crop.38 Pounds of nitrogen per acre. Wheat, 20 bushels 25 Straw, 2,000 pounds 10 Total 35 Barley, 40 bushels 28 Straw, 3,000 pounds 12 Total 40 Oats, 50 bushels 35 Straw, 3,000 pounds 15 Total 50 Flax, 15 bushels 39 Straw, i ,800 pounds 15 Total 54 Potatoes, 150 bushels 40 Corn, 65 bushels 40 Stalks, 3,000 pounds 35 Total 75 NITROGEN COMPOUNDS OF THE SOIL 1 09 129. 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 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 cal- cium, combined with nitrogen and oxygen. A nitrite contains less oxygen than a nitrate. Potassium nitrate, KNO3> sodium nitrate, NaNO3, and calcium nitrate, Ca(NO3)2, are the nitrates which are of most importance in agriculture. The nitrites, as potassium nitrite, KNO2, are present to a less extent than the nitrates. Nitrates and nitrites are found 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. 130. 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 organic matter of the soil. The ammonium compounds are all soluble and readily undergo fixa- tion. See Section 207. They cannot accumulate in arable soils, because of nitrification. They are usually 110 SOILS AND FERTILIZERS found in surface well waters. In the soil, the ammonium compounds may be oxidized and form nitrates. Compounds, as ammonium chloride or am- monium carbonate, if present in a soil in excessive amounts, will destroy vegetation in a way similar to the alkaline compounds in alkaline soils. 131. 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.44 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. 132. 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.45 In some soils the ratio of nitrogen to carbon may be i to 6, while in others it may be i to 18, or more. That is, in the organic matter of some soils there is i part of nitrogen to 6 parts of carbon, while in others the organic matter contains i part of nitrogen to 18 parts of carbon. In NITROGEN COMPOUNDS OF THE SOIL III a 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 un- favorable. 133. 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, for every 25 pounds of nitrogen removed in the crop there is a loss of 146 -pounds from the soil due to the de- struction of the organic matter.18 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. When a soil rich in nitrogen is given arable culture the oxidation of the organic matter and the losses of nitrogen take place rapidly. The longer a soil is cultivated, the slower the oxidation of the humus and the relative loss of nitrogen. 134. 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 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.44 112 SOILS AND FERTILIZERS Age of Pasture Nitrogen Years. Per Cent. Arable land o. 14 Barn-field pasture 8 0.151 Apple-tree pasture 18 0.174 Meadow 21 0.204 Meadow 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 manured 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 : l8 CONTINUOUS WHEAT CULTURE — Nitrogen in soil at beginning of experiment 0.221 per cent. Nitrogen at end of 5 years continuous wheat culti- vation 0.193 " " 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 0.231 ' Gain to soil per annum per acre 61 pounds. Nitrogen removed in crops per annum 44 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 followed are such as to de- crease the nitrogen content and crop producing power of the soil when this could be prevented. NITRIFICATION 135. 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 de- composition of organic matter caused a union be- tween the oxygen of the air and the nitrogen of the organic matter. Fermentation studies 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 Miintz, established the fact that nitrifi- cation is produced by a living organism. 136. Nitrification Caused by Micro-organisms. — Nitrification is the process by which nitrates or nitrites are produced in soils, by the workings of or- ganisms. 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 nitrification have been isolated and studied by War- ington, and by Winogradsky. 137. Conditions Necessary for Nitrification are : 1. Food for the nitrifying organisms. 2. A supply of oxygen. 3. Moisture. 4. A favorable temperature. 5. Absence of strong sunlight. 6. The presence of some basic compound. (8) 114 SOILS AND FERTILIZERS 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. 138. Food for the Nitrifying Organisms. — All liv- ing organisms require food, and one of the food re- quirements 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 food91. The principal organic food of the nitrifying 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 presence 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 conditions nitrify- ing organisms may take all of their food in inorganic forms ; that is, nitrification may take place in the ab- sence of organic matter provided the proper mineral food be supplied. When growth under such condi- tions takes place the organisms assimilate carbon from the combined carbon of the air, and produce organic carbon compounds. An organism, working in the absence of sunlight and unprovided with chlorophyl, may construct organic carbon com- pounds.44 The nitrification which takes place in the absence of nitrogeneous organic matter is of too NITRIFICATION 115 limited a character to supply growing crops with all of their available nitrogen. For general crop pro- duction 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. 139. 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 elements in the final product of nitrification as in cal- cium nitrate, Ca(NO )a. In the absence of oxygen the nitrification process is checked. When soils are saturated with water, the process cannot go on for want of oxygen. Cultivation, particularly of clay soils, favors nitrification increasing the supply of oxygen in the soil. 140. Moisture Necessary for Nitrification. — Nitri- fication cannot take place in a soil deficient in mois- ture. As in all fermentation processes, so with nitri- fication, moisture is necessary for the chemical changes to take place. In a very dry time nitrification is ar- rested for want of water. Water is as necessary to 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. 141. Temperatures Favorable for Nitrification. — The most favorable temperatures for nitrification are between 12° C. (54° F.) and 37° C. (99° F.). It may Il6 SOILS AND FERTILIZERS take place at as low a temperature as 3° or 4° C. (37° and 39° F.); at 50° C. (122° F.) it is feeble, while at 55° C. (130° F.) there is no action.44. In northern latitudes nitrification is checked during the winter, while in southern latitudes this change takes place during the entire year. As a result many soils in southern latitudes contain less nitrogen than soils in northern latitudes where fermentation and leaching of nitrates is checked by climatic conditions. Crops which require their nitrogen early in the growing season are frequently placed at a disadvantage be- cause there is less available nitrogen in the soil at that time than later. 142. 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 sunlight is excluded by the surface soil, it is most active. In a cornfield it is more active than in a compacted fallow field. 143. Base-forming Elements Essential for Nitrifi- cation.— The presence of some base-forming element to combine with the nitric acid produced is a neces- sary condition for nitrification, and for this purpose calcium carbonate is particularly valuable. The ab- sence 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 strong acid or alkaline solution, consequently in such soils nitrification cannot take place.17 NITRIFICATION 1 17 144. 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 being completed by the nitric organ, ism. Warington says that " both organisms are present in the soil in enormous numbers, — and the action of the two organisms proceeds together, as the conditions are favorable to both." 145. 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 nitri- fication.46 146. Denitrification is just the reverse of the nitri- 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 organisms belong 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.47 147. 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 Il8 SOILS AND FERTILIZERS 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.48 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 chemical products which are destructive to a succeeding 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, and cholera, may propagate and develop in a moist soil under certain conditions, and then find their way through drain water into surface wells, and cause these diseases to spread. 148. 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: (i) the action of the organism itself, and (2) the chemical action of the pro- duct 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 n9 take place during humification result in the produc- tion 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 pro- duction of some chemical compound, and then the action of this compound upon other bodies. In ren- dering 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. 149. Inocculating Soils with Organisms. — In grow- ing leguminous crops on soils where they have never before been produced, it has been proposed to supply the essential organisms which assist the crops to ob- tain their nitrogen. For example, if clover is 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 condi- tions for growth exist. Some soils are benefitted by inocculation, while others are not. The extent to which it is necessary to inocculate different soils with organisms for the assimilation of nitrogen, has not yet been determined by actual field experiments. 150. 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. If a soil is rich in nitrogen and lime, summer fallowing causes the production of more nitrates than 120 SOILS AND FERTILIZERS can be retained in the soil. The crop utilizes only a part of the nitrogen rendered available, the rest being lost by drainage, ammonincation, and denitrification. Hence the available nitrogen is increased while the total nitrogen is greatly decreased.17 Soil before Soil after fallowing. fallowing. Total nitrogen 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 0.012 per cent, of total nitrogen. For every pound of available nitrogen there was a loss of six pounds. Bare fallowing of land should not be practiced, except occasionally to destroy weeds or insects, as it results in permanent injury to the soil. 151. Influence of Plowing upon 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 growth, due to an excess of available nitrogen. Deep plowing and thorough cultivation aid nitrification. The longer a soil has been cultivated, the deeper and more thorough must be the cultivation. Early 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 nitro- NITROGENOUS MANURES 121 gen 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 cultiva- tion as deep and shallow plowing, spring and fall plowing, and surface cultivation have as much influ- ence upon the available nitrogen supply of crops as upon the water supply. The saying that cultivation 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 152. Sources of Nitrogenous Manures. — The mate- rials used for enriching soils with nitrogen, to promote crop growth, may be divided into two classes : (i) organic nitrogenous manures, (2) mineral nitrogenous manures. Each of these classes has a different value as plant food, and in fact there are marked differences in fertilizer value between materials 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 nitro- gen in these substances is principally in the form of protein. When peat and muck are properly used they also may be classed among the nitrogenous manures. The mineral nitrogenous manures are nitrates, as sodium nitrate, and ammonium salts, as ammonium sulphate. 123. Dried Blood. — This is obtained by drying 122 SOILS AND FERTILIZERS the blood and debris from slaughter-houses. Fre- quently 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 contain 14 per cent, of nitrogen. As usually sold, it contains from 10 to 20 per cent, of water, and has a nitrogen content of from 9 to 13. Dried blood 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 nitri- fication. On account of its fermentable nature, it is a quick-acting fertilizer, and is one of the most valu- able of the organic materials used as manure. 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. Dried blood may be applied as a top dressing on grass land, and it is also an excellent form of fertilizer to use on many garden crops, but it 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 ap- plied at one time. When too much is used losses of nitrogen may occur by leaching and by denitrification. 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 fer- tilizers as blood should be applied before seeding or soon after. An application of dried blood to partially NITROGENOUS MANURES 123 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.22 " 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 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 $28 per ton is equiva- lent to 15.55 cents Per pound for the nitrogen (2000 X 0.09 — 180. $28.00 -*r 180 = 15.55 cents). 154. Tankage is composed.of 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.14 First year. Second year. Third year. Moisture 10.5 9.8 10.9 Nitrogen 5.7 7.6 6.4 Phosphoric acid 12.2 10.6 11.7 124 SOILS AND FERTILIZERS 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 ferlizer 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 $32 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 $22.40. The 140 pounds of nitrogen in the ton of fertilizer would be worth $22.40, or 16 cents per pound. In eastern markets the price of tankage is usually much higher than near the large packing houses of the west. 155, Flesh Meal. — The flesh refuse from slaugh- NITROGENOUS MANURES 125 ter-houses is sometimes kept separate from the tank- age and sold as flesh meal, the fat and gelatin being 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. 156. Fish Scrap. — The flesh of fish is very rich in nitrogen.49 The offal parts, as heads, fins, tails and in- testines, are dried and prepared as a fertilizer. Some 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. 157. Seed Residues. — Many seeds, as cottonseed and flaxseed, are exceeding 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 is 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 and meal are not so quick-acting as dried blood, but when used in south- 126 SOILS AND FERTILIZERS ern latitudes a little time before seeding, the nitrogen becomes available for crop purposes. Oil meals, as cottonseed and linseed, containing a high per cent, of oil are much slower in decomposing than those which contain but little oil. It is better economy to feed the cake to stock and use the manure than to apply the cake directly to the land. Occasionally however cottonseed meal has been so low in price that its use as a fertilizer has been admissible. A ton of cottonseed meal costing $20 and containing 2 per cent, of phosphoric acid and 7 per. cent of nitrogen would be equivalent to 13.1 cents per pound for the nitrogen, which is frequently cheaper than purchasing some other nitrogenous fertilizer. 158. 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. One of the methods employed to detect, in fertili- zers, the presence of inert forms of nitrogen as leather, is to digest the material in prepared pepsin solution.50 Substances like dried blood are nearly all soluble in the pepsin, while leather and other inert forms are only partially so. The solubility of the organic nitro- gen in pepsin solution determines, to a great extent, the value of the material as a fertilizer.51 Soluble in prepared pepsin solution Per cent, of nitrogen. Dried blood 94. 2 Ground dried fish 75.7 Tankage 73.6 Cottons eed meal 86.4 Hoofand horn meal 30.0 Leather 16.7 NITROGENOUS MANURES 1 27 159. Peat and Muck.— Many samples of peat and muck are quite rich in nitrogen. The nitrogen is, however, in an insoluble form, and is with difficulty nitrified. When mixed with stable manure, particu- larly liquid manure, with the addition of a little lime fermentation may be induced, and a valuable manure produced. Muck and peat should be dried and sun- cured, and then used as absorbents in stables. Peat differs from muck in being fibrous. If the muck gives an acid reaction, lime (not quicklime) should be used with it in the stable, as directed under farm manures. When easily obtained muck is one of the cheapest forms of nitrogen. COMPOSITION OF DRY MUCK SAMPLES.17 Nitrogen. Per cent. Marshy place, producing hay 2.21 Marshy place, dry in late summer 2.01 Old lake bottom 1.81 160. Leguminous Crops as Nitrogenous Manures. — The frequent use of leguminous crops for manurial purposes is the cheapest way of obtaining nitrogen. When the crop is not removed from the land but is plowed under while green, the practice is called green manuring. This does not enrich the land with any mineral material but results in changing to humate forms inert plant food. Green manuring, with le- guminous crops, should take the place of bare fallow, as its effects upon the soil are more beneficial. With green manuring, nitrogen is added to the soil while with bare fallow there is a loss of nitrogen. Legu- minous crops, as clover, peas, crimson clover, and cow peas, should be made to serve as the main source of the nitrogen for crop production. 128 SOILS AND FERTILIZERS 161. Sodium Nitrate. — The nitric nitrogen most frequently met with in commercial forms is sodium nitrate, commonly known as Chili saltpeter. It is a natural deposit found extensively in Chili, Peru, and the United States of Colombia. Various theories have been proposed to account for these deposits, but it is difficult to determine just how they have been formed.10 Their value to agriculture may be estimated from the fact that there are annually used in the United States about 100,000 tons, and in Europe about 700,000 tons. The commercial value of nitrogen in fertilizers is reg- ulated by the price of sodium nitrate which, when pure, contains 16.49 Per cent- of nitrogen. Commer- cial sodium nitrate is from 95 to 97 per cent. pure. An ordinary sample contains about 16 per cent, of nitrogen and costs from $50 to $60 per ton, making the nitrogen worth from 15 to 18 cents per pound. Sodium nitrate is the most active of all the nitrogenous manures. It is soluble and does not have to undergo the nitrification process before being utilized by crops. On account of its extreme solubility it should be ap- plied sparingly, for it cannot be retained in the soil. As a top dressing on grass, it will respond by impart- ing a rich green color. It may be used at the rate of 250 pounds per acre, but a much lighter application will generally be found more economical. Sodium nitrate may contain traces of sodium perch lorate, which is destructive to vegetation if the fertilizer is used in excess.52 Sodium nitrate, in small amounts, is the fertilizer most frequently resorted to when the forcing of crops is desired as in early market garden- NITROGENOUS MANURES 129 ing. Its use for fertilizing horticultural crops has be- come equally as extensive as for general farm crops. Excessive amounts may produce injurious results. Sodium nitrate stimulates a rank growth of dark green foliage, and retards the maturity of plants, "but when properly used is one of the most valuable of the nitrogenous "fertilizers. 162. Ammonium Salts. — Ammonium sulphate is obtained as a by-product in the manufacture of illumi- nating gas and is extensively sold as a fertilizer. It usually contains about 20 per cent, of nitrogen, equiv- alent to 95 per cent, of ammonium sulphate, the re- maining 5 per cent, being moisture and impurities. Ammonium sulphate is not generally considered the equivalent of sodium nitrate. It is, however, a valua- ble form of nitrogen. The statements made regarding the use of sodium nitrate apply equally well to the use of ammonium sulphate. Ammonium chloride and ammonium carbonate are not suitable for fertilizers on account of their destructive action upon vegetation. 163. Nitrogen and Ammonia Equivalent of Fer- tilizers. — Nitrogenous fertilizers are sometimes represented as containing a certain amount of ammo- nia instead of nitrogen. Fourteen-seventeenths of ammonia is nitrogen, and if a fertilizer contains 2.25 per cent, ammonia, it is equivalent to 1.85 per cent, of nitrogen. To convert NH results to an N basis multiply by 0.823. 164. Purchasing Nitrogenous Manures. — In pur- chasing nitrogenous manure, the special purpose for which it is to be used should always be considered. (9) 130 SOILS AND FERTILIZERS Under some conditions, as forcing a crop on an im- poverished soil, sodium nitrate is desirable. Under other conditions tankage, cottonseed cake, or some other form of nitrogen may be made to answer the purpose. There is annually expended in purchasing nitrogenous fertilizers a large amount of money which could be expended more ecomically, if the science of fertilizing were given a more careful study. The uses of nitrogenous fertilizers for special crops and the testing of soils to determine any deficiency in nitrogen are discussed in Chapters X and XI which treat of commercial fertilizers and the food require ments of farm crops. CHAPTER V FARM MANURE 165. Variable Composition of Farm Manures. — The term farm manure does not designate a prod- uct of definite composition. Manure is the most variable in chemical composition of any of the mate- rials produced on the farm. It may contain a large amount of straw, in which case it is called coarse ma- nure ; or it may contain only the solid excrements and a little straw, the liquid excrements being lost by leaching ; then again it may consist of the droppings of poorly fed animals, or of the mixed excrements of different classes of well-fed animals. The term stable manure has been proposed for that product which contains all of the solid and liquid excrements with the necessary absorbent, before any losses have been sustained.16 The term barnyard manure is restricted to that material which accumu- lates around some barns and farm yards, and is ex- posed to leaching rains and the drying action of the sun. 1 66. Average Composition of Manures. — The solid excrements of animals contain from 60 to 85 per cent, of water ; when mixed with straw, and the liquid ex- crements are retained, the mixed manure contains about 75 per cent, of water. The nitrogen varies from 0.4 to 0.9 per cent., according to the nature of the food and the extent to which other factors have 132 SOILS AND FERTILIZERS affected the composition. In general, animals consu- ming liberal amounts of coarse fodders produce manure Fig. 24. Average composition of Fig. 25. Manure after six fresh manure? months' exposure, i. Nitrogen. 2. Phosphoric acid. 3. Potash. 4. Mineral matter. with a higher per cent, of potash than of phosphoric acid. This is because the potash in the food exceeds the phosphoric acid. The average composition of mixed stable manure is as follows : Average Per cent. Nitrogen 0.50 Phosphoric acid 0.35 Potash 0.50 Range Per cent. 0.4 to 0.8 0.2 tO 0.5 0.3 to 0.9 In calculating the amount of fertility in manures, it is more satisfactory to compute the value from the food consumed and the care which the manure has received, than to use figures expressing average com- position. 167. Factors which Influence the Composition and Value of Farm Manure. — I. Kind and amount of absorbents used. II. Kind and amount of food consumed. FARM MANURE 133 III. Age and kind of animals. IV. Methods employed in collecting, preserving and utilizing the manure. Any one of the above, as well as many minor factors, may influence the composition and value of farm manure. 168. Absorbents. — The most universal absorbent is straw. Wheat straw and barley straw have about the same manurial value. Oat straw is more valu- able. The average composition of straw and other absorbents is as follows : Straw. I^eaves. Peat. Sawdust. Per cent. Per cent. Per cent. Per cent. Nitrogen 0.40 0.6 i.o o.i Phosphoric acid 0.36 0.3 .. 0.2 Potash 080 0.3 .. 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 : I4 Per cent, of water absorbed. Fine cut straw 30.0 Coarse uncut straw 18.0 Peat 60.0 Sawdust 45.0 The proportion of absorbents in manure ranges from a fifth to a third of the total weight of the manure. 169. Use of Peat and Muck as Absorbents. — On account of the high per cent, of nitrogen in peat and 134 SOILS AND FERTILIZERS the power which it possesses when dry of absorbing water, it is a valuable material to use as an absorbent in stables. As previously explained, peat is slow of decomposition, but when mixed with the liquid ma- nure it readily yields to fermentation, particularly if a little land plaster or marl be used in the stable along with the peat. Peat has high absorptive power for gases as well as liquids, and when used stables are rendered particularly free from foul odors. RELATION OF FOOD CONSUMED TO MANURE PRODUCED 170. Bulky and Concentrated Foods. — The more concentrated and digestible the food consumed, the more valuable is the manure. Coarse bulky fodders always give a large amount of a poor quality of ma- nure. For example, the manure from animals fed on timothy hay and that from animals fed on clover hay and grain, show a wide difference in composition. The dry matter of timothy hay is about 55 per cent, digestible. From a ton of timothy hay there will be about 790 pounds of dry matter in the manure. The nitrogen, phosphoric acid, and potash in the food con- sumed are nearly all returned in the manure, except under those conditions which will be noted. The manure from a ton of mixed feed, as clover and bran, is smaller in amount but more concentrated than that produced from timothy. In a ton of timothy and in a ton of mixed feed (1500 Ibs. clover, 500 Ibs. bran) there are present : Timothy. Mixed feed. Lbs. Lbs. Nitrogen 25.0 40.0 Phosphoric acid 9.0 24.0 Potash 40.0 30.0 FARM MANURE 135 The nitrogen, phosphoric acid, and potash in these two rations are retained in the animal body in dis- similar amounts ; 10 per cent, more of these elements being retained from the more liberal ration, due to more favorable conditions for growth. Making al- lowance for this fact there will be present in the ma- nure from the mixed feed one-half more nitrogen, and two and one-half times as much phosphoric acid, as in the manure from the timothy hay, which, _ free from bedding, contains about 790 pounds of indigesti- ble matter while the manure from the mixed feed con- tains 760 pounds, the mixed ration being more digesti- ble. If both manures contain the same amount of ab- sorbents, the manure from the ton of mixed clover and bran will weigh slightly less, but contain more fertility than that from the timothy hay. The value of manure can be accurately determined from the composition of the food consumed and the care which the manure has received. Only a small amount of the nitrogen in the food is retained in the body. The larger portion is used for repair purposes. The nitrogen of the tissues which have been renewed is voided as urea in the liquid excre- ments. Some of the nitrogenous compounds of the food are utilized for the production of fat, in which case the nitrogen is voided in the excrements. The fact that but little of the nitrogen and mineral matter of the food, under most conditions, is retained in the body may be observed from the figures of Lawes and Gilbert relating to the composition of the flesh added to animals while undergoing the fattening process.55 136 SOILS AND FERTILIZERS INCREASE DURING FATTENING. Dry Nitrogenous Water. matter. Fat. matter. Ash. Ox . 24.6 75.4 66.2 7.69 1.47 Sheep 20.1 79.9 70.4 7.13 2.36 Pig 22.0 78.0 71.5 6.44 0.06 The results of numerous digestion experiments show that when the food undergoes digestion from 5 to 15 per cent, of the nitrogen is, as a rule, retained in the body. The nitrogen of the food is utilized largely to replace that which has been required for vital functions. The nitrogen of the food enters the body, undergoes digestion changes, is utilized for some vital function, and is then voided in the excre- ments. The digestion of food has been compared to the combustion of fuel : the undigested products of the solid excrements represent the ashes, and the urine represents the volatile products. When wood is burn- ed the nitrogen is converted into volatile products. When food is digested and utilized by the body the digestible nitrogen is mainly converted into urea, while the indigestible nitrogen is voided in the dung. In the solid and liquid excrements of animals, from 80 to 95 per cent, of the nitrogen, phosphoric acid and potash of the food are present. 171. Composition of Solid and Liquid Excrements Compared. — In composition the liquid excrements .differ from the solids in having a much larger amount (.of nitrogen and less phosphoric acid.56 FARM MANURE 137 Water. Solids. Liquids. Nitrogen. Solids. Liquids. Phosphoric acid. Solids. Liquids. Potash. Solids. Percent. Percent. Percent. Percent. Percent. Per cent. Per cent Cows . . 76 89 0.50 1. 2O 0-35 ... 0.30 Horses 84 92 0.30 0.86 0.25 O. IO Pigs... 80 97.0 0.6o 0.80 0-45 0. 12 0.50 Sheep . 53 86.5 0-75 1.40 0.6 > 0.05 0.30 The nitrogen in the food consumed influences the amount of water in the manure. As a rule, a highly concentrated nitrogenous ration, produces a higher per cent, of water in the manure than a well-balanced ration. There is but little phosphoric acid in the liquid excrements of horses and cows, while the urine of sheep and swine contains appreciable amounts of this element. The liquid manure is more constant both in compo- sition and amount than the solid excrements. This fact may be observed from the following table, which gives the composition of the solid and liquid excre- ments from hogs when fed on different amounts of grain.57 Solid excrements. Liquid excrements. g U a £3 1 i S~s * "2 3 o • o o ^TJ 0 lu S'-o y S.3 i ^ I'gt *'«« Lbs. Kind of food daily. 1 9f Barley and shorts 8 0-57 0.72 2.05 0.06 6 Barley 4 0.43 0.70 2.06 0.16 si Corn and shorts. 2\ 0.80 .... 2.65 O.2O 6t Corn I* 0.82 0.80 2.OS. 0.20 (In each experiment the amount of liquid excrements was four pounds.) 138 SOILS AND FERTILIZERS The amount of nitrogenous waste matter in the urine is nearly the same whether an animal be gaining or losing in flesh, consequently the urine is more con- stant in both composition and quantity than the solid excrements. The amount and composition of the solid excre- ments vary with the amount and kind of food con- sumed. If the food is indigestible the solid excrements contain a larger part of the nitrogen as indigestible protein. When an animal is properly supplied with food for all purposes, normal conditions exist, and the amount of nitrogen voided in the liquid and solid ex- crements is equal to that supplied in the food con- sumed, except in the case of growing and milk pro- ducing animals. Experiments at the Rothamsted station have shown that from 57 to 79 per cent, of the total nitrogen in the food of farm animals is voided in the liquid ex- crements, and from 16 to 22 per cent, is voided in the solid excrements. Nearly all of the mineral elements in the food is voided in the excrements, less than four per cent, being retained in the body ; in the case of milk cows about 10 per cent, of the ash in the food is recovered in the milk. 172. Manural Value of Foods. — The manurial value of a fodder is determined by the amount of nitro- gen, phosphoric acid, and potash present in the material. Timothy hay, for example, has a manurial value of $5.30 per ton, which means that if the nitro- FARM MANURE 139 gen, phosphoric acid, and potash in 'the timothy hay were purchased in commercial forms they would cost $5.30. Lawes and Gilbert estimate that 80 per cent, of the fertility in fodders is, as a rule, returned in the manure. In the following table are given the pounds of nitrogen, phosphoric acid, and potash per ton of some food materials :57 Nitrogen. Phosphoric acid. Potash. Lbs. lybs. lybs. Timothy hay 25 9 40 Clover hay 35 14 30 Wheat straw n 4 12 Oat straw 12 4 18 Wheat : 45 20 12 Oats 33 1 6 ii Barley 40 18 II Rye 42 20 13 Flax '... 87 32 14 Corn 32 14 8 Wheat shorts 48 31 20 Wheat bran 54 52 30 Linseed meal 100 35 25 Cottonseed meal 130 35 56 Milk 10 33 Cheese 90 23 5 Live cattle 53 37 3 Potatoes 7 3 u Butter i i i Live pigs.. 40 17 3 173. Commercial Value of Manures. — When the value of farm manure is calculated on the same basis with commercial fertilizers it will be found that stable manure is worth from $2 to #3.50 per ton. The value of the increased crops resulting from its use 140 SOILS AND FERTILIZERS varies with conditions. Farm manures favorably in- fluence the yield of crops for a number of years. After a dressing of 8 tons of farm manure, average prairie land will yield 20 bushels per acre more corn the first year, 5 bushels more wheat the second year, and 8 bushels more of other grains the third year, with slightly increased yields in subsequent years. It takes about three years for the manure to entirely repay the cost of its application. Its influence is felt however for a much longer time. It is sometimes stated that the phosphoric acid and potash in stable manure is not as soluble as that in commercial fertilizers, and consequently is worth less. While not so soluble in the form of manure, it frequently happens that the phosphoric acid and potash in the commercial fertilizers become, through fixation processes, less soluble when mixed with the soil than the same elements in stable manure. Stable manure is valuable not only for the fertility contained but also because it makes the inert plant food of the soil more available and exercises such a favorable influence on the water supply of crops ; hence it is justifiable to assign the same value to the elements in well-prepared farm manures as to those in commercial fertilizers. If well-prepared stable manure is not worth $2.50 per ton, then too much, accordingly, is paid for com- mercial forms of plant food. INFLUENCE OF AGE AND KIND OF ANIMAL 174. Manure from Young and Mature Animals. — AGE AND KIND OF STOCK 141 The manure from older animals is somewhat more valuable than that from young animals, even when fed the same kind of food. This is because more of the phosphoric acid and nitrogenous matters are re- tained in the body of a young animal. It is not so much a difference in digestive power as a difference in retentive power. In older animals the proportion of new nitrogenous tissue produced is much less than in young animals, and more of the nitrogen of the food is used for repair purposes and subsequently voided in the manure, while with younger animals more of the nitrogen of the food is retained for the construction of new muscular tissue. When an animal is neither gaining nor losing in flesh, and is not producing milk, an equilibrium is es- tablished between the nitrogen in the food supply and the nitrogen in the manure. Under such conditions practically all of the nitrogen of the food is returned in the manure.57 175. Cow Manure. — A milch cow when fed a bal- anced ration, will make from 60 to 70 pounds of solid and liquid manure a day, of which 20 to 30 pounds are liquid excrements. The solid excrements contain about 6 pounds of dry matter. When a cow is fed clover hay, corn fodder, and grain, about half of the nitrogen of the food is in the urine, about one-fourth in the milk, and the remainder in the solid excre- ments. Hence, if the solid excrements only are col- lected but a quarter of the nitrogen of the food is ob- tained, while if both solids and liquids are utilized 142 SOILS AND FERTILIZERS three-quarters of the nitrogen is secured. Cow manure is extremely variable in composition, and is the most bulky of any manure produced by domestic animals. A well-fed cow will produce about 80 Ibs. of manure per day, including absorbents. 176. Horse Manure. — Horse manure contains less water than cow manure, and is of a more fibrous nature, doubtless due to the horse possessing less power for digesting cellulose materials. Horse ma- nure readily ferments and gives off ammonia products. When the manure becomes dry, fire-fanging results, due to rapid fermentation followed by the growth of fungus bodies. Horse manure is sometimes consider- ed of but little value. This is because it so readily deteriorates in value and when used it has lost much of its nitrogen by fermentation. When mixed with cow manure, both manures are improved, the rapid fermentaion of the horse manure is checked, and at the same time the cow manure is improved in texture. It is estimated that horses void about three- fifths of their manure in the stable. A well-fed horse at ordinarily hard work will produce about 50 pounds of manure per day, of which about one-fourth is urine. A horse will produce about 6 tons of manure per year in the stable. If properly preserved and used it is a valuable, quick-acting manure, but if allowed to fer- ment and leach it gives poor results. 177. Sheep Manure. — Sheep produce a small amount of concentrated manure, containing less water than that produced by any other domestic animal. It AGE AND KIND OF STOCK 143 readily ferments and is a quick-acting fertilizer. When mixed with horse and cow manure the mixture ferments more evenly. Because of the small amount of water, sheep manure is very concentrated in composi- tion. It is valuable for general gardening purposes, or whenever a concentrated quick acting manure is desired. 178. Hog Manure. — Hog manure is not constant in composition on account of the varied character of the food consumed. The manure from fattening hogs which are well fed compares favorably in composition and value with the manure produced by other ani- mals. It contains a high per cent, of water, and, like cow manure, may be slow in decomposing. On ac- count of containing so much water, losses by leach- ing readily occur. From a given weight of grain, pigs produce less dry matter in the manure than sheep or cows. The liquid excrements of well-fed hogs are rich in nitrogen, containing, on an average, about 2 per cent. The solid excrements when leached, fermented and deprived of the liquid excrements have but little value as fertilizer. 179, Hen Manure. — Like all other farm manures hen manure is variable in composition. The nitrogen is present mainly in the form of ammonium com- pounds. This makes it a quick-acting fertilizer. When fowls are well-fed the manure contains about the same amount of nitrogen as sheep manure. Hen manure readily ferments, and if not properly cared for losses of nitrogen, as ammonia, occur. It is not advisable to mix hard wood ashes or ordinary lime 144 SOILS AND FERTILIZERS with hen manure because the ammonia is so readily liberated by alkaline compounds. The value of hen manure is due to its being a quick-acting fertilizer rather than to its containing such a large amount of fertility. A hen produces about a bushel of manure per year.56 COMPOSITION OF HEN MANURE. Per cent. Water 57.50 Nitrogen. 1.27 Phosphoric acid 0.82 Potash. 0.28 1 80. Mixing of Solid and Liquid Excrements. — The solid and 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 with the urine, when mixed with soil, readily undergo nitrification. The nitrogen in the solid excrements is in the form of indigestible protein, and is rendered available as plant food more slowly. Land heavily dressed with leached manure has received an unbal- anced fertilizer deficient in nitrogen but fairly well supplied with mineral matter. A soil thus manured may fail to respond because of the unbalanced char- acter of the manure. 181. Volatile Products from Manure. — Fermen- tation of manure in stables results in the production of a large number of volatile compounds and in loss of manurial value. Urea, when it ferments, produces ammonia, which combines with the carbon dioxide always present in stables in liberal amounts as a pro- AGE AND KIND OF STOCK 145 duct of respiration, and forms ammonium carbonate, a volatile compound. When the stable atmosphere becomes charged with ammonium carbonate some of it is deposited on the walls of the stable, forming a white coating. The white coating found on harnesses and carriages stored in poorly ventilated stables, is ammonium carbonate. Accumulations of manure in the stable and poor ventilation are the conditions fav- orable to the production of this compound. 182. Human Excrements. — The use of human ex- crements as manure is sometimes advised, and in some countries they are extensively used. When fresh, they may contain a high per cent, of nitrogen and phosphoric acid ; when fermented, a loss of nitrogen has occurred. Heiden estimates that in a year 1,000 pounds of excrements per person are made, which contain #2.25 worth of fertility.59 For sanitary rea- sons, 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, Leibig expressed the fear that the essential 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.60 Many political economists shared the same fear. Since that time the fixation of atmos- pheric nitrogen through the agency of leguminous crops has been discovered, extensive beds of sodium nitrate, phosphate rock and Stasfurt salts, have been utilized and larger areas of more fertile soils have been (10) 146 SOILS AND FERTILIZERS brought under cultivation, so that it is not now so essential to devise means for utilizing human excre- ments as manure. THE PRESERVATION OF MANURE 183. Leaching. — Leaching of manure is the greatest 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 weather- ing it may lose in six months nearly 60 per cent, of its most valuable fertilizing constituents. The tab- ular results are as follows : l6 April 25. Sept. 28. Loss. Lbs. Lbs. Per cent. Gross weight 4,000 1,73° 57 Nitrogen 19.60 7.79 60 Phosphoric acid ... 14.80 7.79 47 Potash 36.0 8.65 76 Value per ton $2.80 $i .06 Cow manure, on account of its more compact nature, does not leach so readily as horse manure. A similar experiment with cow manure, conducted at the same time, showed the following losses : April 25. Sept 28. LOSS. Lbs. L,bs. Per cent. Gross weight 10,000 5,125 49 Nitrogen 47 28 41 Phosphoric acid 32 26 19 Potash 48 44 8 Value per ton .... $2.29 $1.60 When mixed cow and horse manure was compacted and " placed in a galvanized iron pan with a perfo- rated bottom " for six months, the losses were as fol- lows : THE PRESERVATION OF MANURE 147 March 29. Sept. 30. Loss. Lbs. L>bs. Per cent. Gross weight 226 222 Nitrogen 1.04 i.oi 3.2 Phosphoric acid •• 0.61 0.58 4.7 Potash 1.20 0.43 35.0 Value per ton $2.38 $2.16 1 84. Losses by Fermentation. — When rapid fer- mentation takes place in manure, appreciable losses of nitrogen may occur. When the manure is well com- pacted and the pile is so constructed as to prevent the rapid circulation of air through it, losses are reduced to the minimum. Experiments have shown that when leaching is prevented, the loss of nitrogen by fermentation of the mixed manure is very small. Under poor conditions losses by fermentation may exceed 15 per cent. Hen manure, sheep man- ure and horse manure suffer the greatest losses by rapid fermentation. When extreme conditions, as ex- cessive moisture, drought and high temperature, fol- low each other, then the greatest losses occur. 185. Different Kinds of Fermentation. — The large number of organisms present in manure all belong to one of two classes : (i) aerobic, or (2) anaerobic. The aerobic ferments require an abundant supply of air in order to carry on their work. When deprived of oxygen they become inactive. The anaerobic fer- ments require the opposite condition. They become inactive in the presence of oxygen and can thrive only when air is excluded.- In the center of a well-con- structed manure pile anaerobic fermentation takes place while on the surface aerobic fermentation is act- 148 SOILS AND FERTILIZERS ive. The anaerobic ferments prepare the way for the action of the aerobic bodies. When aerobic fermenta- tion is completed the organic matter is converted into water, carbon dioxide, ammonia and • allied gases. From what has been said regarding the action of these two classes of ferments it is evident that anaerobic fermentation is the most desirable. Fig. 26. Fermentation of Manure. 186. Water Necessary for Fermentation. — In order to produce the best results in fermenting manure, water is necessary. If the manure becomes too dry abnormal fermentation takes place. Water is always beneficial on manure so long as leaching is prevented; for it encourages anaerobic fermentation by excluding the air. An excessive amount of water, such as falls on piles from the eaves of buildings, is more than is required for good fermentation. During a dry time it is beneficial, if conditions admit, to water the com- post pile. 187. Heat Produced During Fermentation. — Dur- ing active fermentation of horse and sheep manure, a temperature of 175° F. may be reached by the fer- menting mass. Ordinarily, however, the temperature THE PRESERVATION OF MANURE 149 of the manure pile ranges from 110° to 130° F. The highest temperature is near the surface where fermen- tation is most rapid. The temperature of fermenta- tion may be sufficiently high, if the manure is mixed with litter, to cause spontaneous combustion. 1 88. Composting Manure May Improve Its Quality; — Composting manure so that leaching and rapid fer- mentation do not take place may improve its quality, making it more concentrated. Pound for pound, composted manure is more concentrated than fresh manure, because, if properly cared for, nearly all of the nitrogen, phosphoric acid, and potash of the orig- inal manure are obtained in a smaller bulk. A ton of composted manure is obtained from about 2,800 pounds of stable manure. Composting is sometimes resorted to in order to destroy obnoxious weed seeds. Fresh Composted manure. manure. Per cent. Per cent. Nitrogen 0.50 0.60 Phosphoric acid o. 28 0.39 Potash 0.60 0.80 In composting manure it should be the aim to in- duce anaerobic fermentation by excluding the air and retaining the water. This can be accomplished best by using mixed manure and making a compact pile, capable of shedding water. The compost pile should be shaded to secure better conditions for fermentation. If the pile becomes offensive a little earth on the sur- face will absorb the odors. 189. Use of Preservatives. — The use of preserva- tives, as gypsum and kainit, has been recommended 150 SOILS AND FERTILIZERS to prevent fermentation losses. Opinions differ as to their value. Moist gypsum, when it comes in contact with ammonium carbonate, produces ammonium sul- phate, a non- volatile compound, (NH4)2C03 + CaS04= (NH4)2SO4 + CaCCX Gypsum is used at the rate of about one-half pound per day for each animal.59 Experiments have shown that it may prevent a loss of 5 per cent, of the nitro- gen of horse manure. It may be safely Iprinkled in the stalls as it has no action on the feet of animals. When it is necessary to use gypsum as a fertilizer it is advantageous to use it in stables. It is not advisable to use lime in any other form than the sulphate. Un- slaked lime will decompose manure and liberate am- monia. Neither kainit nor gypsum should be used when manure is exposed to the leaching action of rains. Preservatives cannot be made to take the place of care in handling manure ; they should be used only when the manure receives the best of care. 190. Manure Produced in Sheds and BoxStalls. — Manure produced under cover as in sheds and box stalls is of superior quality to that prepared in any other way. Losses by leaching are avoided, the manure is compacted by the tramping of the animals, the solid and liquid excrements are more evenly mixed with the absorbents, and the conditions are favorable for anearobic fermentation. By no other system is there such a large percentage of the fertility recovered. Manure from well-fed cattle, when col- THK USE OF MANURE 15! lected and prepared in a shed, will have about the following composition : Per cent. Water 70.00 Nitrogen 0.90 Phosphoric acid 0.60 Potash 0.70 191. Value of Protected Manure. —Manure that is produced under cover has greater crop-producing power than when cared for in any other way. Ex- periments by Kinnard show that such manure pro- duced 4 tons more potatoes per acre than pile manure, while 1 1 bushels more wheat per acre were obtained from land which had the previous year received the covered manure than from land which received the uncovered manure.62 THE USE OF MANURE 192. Direct Hauling to Fields.— It is always desir- able, whenever conditions allow, to draw the manure directly to the field and spread it, rather than to allow it to accumulate about barns or in the barnyard. When taken directly to the field from the stable no losses by leaching occur, and the slight loss from fer- mentation and volatilization of the ammonia are more than offset by the benefits derived from the action of the fresh manure upon the soil. When manure un- dergoes fermentation in the soil, as previously stated, it combines with the mineral matter of the soil and produces humates. The practice of hauling the ma- nure directly to the field and spreading it with a ma- nure spreader is the most economical way of caring for it. 152 SOILS AND FERTILIZERS With scant rainfall, composting the manure before spreading is necessary, but with liberal rainfall it is not essential. On a loam soil a direct application of stable manure is more advisable than on heavy clay or light sandy soils. In the case of sandy soils there is frequently an insufficient supply of water to prop- erly ferment the manure. Manure sometimes fails to show any beneficial effects the first year on heavy clay land, because of the slow rate of decomposition, but the beneficial effects are noticeable the second and third years. 193. Coarse Manure May Be Injurious.— The ap- plication of coarse leached manure may cause the soil to be so open and porous as to affect the water supply of the crop, by introducing, below the surface soil, a layer of straw, which breaks the capillary connection with the subsoil. Coarse manure and shallow spring plowing are sometimes injurious, where fine or well- composted manure and fall plowing are beneficial. The trouble resulting from the use of coarse manure may be due to its being allowed to leach before it is used, so that it does not readily ferment in the soil. 194. Manuring Pasture Land. — In regions where manure decomposes slowly, it is sometimes advisable to spread it upon pasture land as a top dressing. The manure encourages the growth of grass, so that it ap- propriates plant food otherwise lost ; it also acts as a mulch preventing excessive evaporation. Then when the pasture land is plowed and prepared for a grain crop it contains a better store of both water and avail- THE USE OF MANURE 153 able plant food. The manuring of pasture lands is one of the best ways of utilizing the manure when trouble arises from slow decomposition. Fig. 27. Manured land. Fig. 28. Unmanured land. 195. Small Manure Piles Undesirable. — It is sometimes the custom to make a large number of small manure piles in fields. This is a poor practice, for it entails additional expense in spreading the ma- nure, and the small piles are usually so constructed that heavy losses occur, and the manure, when finally spread, is not uniform in composition. Oats grown on land manured in this way present an uneven ap- pearance. There are small patches of thrifty, overfed oats, corresponding to the places occupied by the former manure piles, while large areas of half-starved oats may be observed. 154 SOILS AND FERTILIZERS 196. Rate of Application. — The amount of manure that should be applied depends upon the nature of the soil and the crop. On loam soils intended for general truck purposes heavier applications may be made than when grain is raised. For general farm purposes, 6 to 8 tons per acre are usually sufficient. It is better economy to make frequent light applications than heavier ones at long intervals. When manure is used frequently the soil is kept in a more even state of fertility, and losses by percolation, denitrification, and ammonification are prevented. Too often the manure is not evenly distributed about the farm, fields adjacent to stables are heavily manured, while those at a distance receive none. For growing garden crops 20 tons and more per acre are sometimes used. It is better, however, not to use stable manure in excess for trucking, but to supplement it with special fertilizers as the crops may require. Soils which contain a large amount of cal- cium carbonate will not become acid when farm ma- nure is used, and hence admit of more frequent and heavier applications than soils which are deficient in this compound. The lime aids fermentation and ni- trification. 197. Crops Most Suitable for Manuring. — Soils which contain a low stock of fertility admit of manur- ing for the production of almost any crop. Soils well stocked with plant food, like some of the western prairie soils, which are in need of manure mainly for its physical action, will not admit of its direct use on THE USE OF MANURE 155 all crops. On a prairie soil of average fertility an application of well-rotted manure may cause wheat to lodge. When manure cannot be applied directly to a crop, it may be used indirectly. It never injures corn by causing too rank a growth, and when wheat follows corn which has been manured there is but little danger of loss from lodging. On some soils stable manure cannot be used for growing sugar-beets ; on other soils it does not seem to exercise an injurious effect. Tobacco is injured as to quality by manure. Crops, as flax, tobacco, sugar- beets and wheat, which do not admit of direct appli- cations of stable manure all require the manuring of preceding crops. When in doubt as to what crop to apply the manure to, it is always safe to apply it to corn, and then to follow with the crop which would have been injured by its direct application. The facts that coarse, leached manure may cause trouble in a dry season, and that well-rotted manure may cause grain to lodge, are no substantial reasons why manure should be wasted as it frequently is in western farming by being burned, used for making roads, thrown away in streams, or used for filling up low places. 198. Comparative Value of Forage and Manure. — The manure from a given amount of grain or fodder always gives better results than the food itself used directly as manure. The manure from a ton of bran will give better returns than if the bran itself were used. This is because so little of the fertility 156 SOILS AND FERTILIZERS is lost during the process of digestion, and the action of the digestive fluids upon the food makes the manure more readily available as a fertilizer than the food- which has not passed through any fermentation stages. It is better ecomony to use products as lin- seed meal and cottonseed meal for feeding stock, and to take good care of the manure, than to use the mate- rials directly as fertilizer. 199. Lasting Effects of Manure. — No other ma- nures make themselves felt for so long a time as farm manures. In ordinary farm practice an application of stable manure will visably affect the crops for a num- ber of years. At the Rothamsted Experiment Station, records have been kept for over fifty years as to the effects of manures upon soils. In one experiment farm manure was used for twenty years and then dis- continued for the same period. It was observed that when its use was discontinued there was a gradual de- cline in crop-producing power, but not so rapid as on plots where no manure had been used. The manure which had been applied for the twenty-year period made itself felt for an ensuing period of twenty years. 200. Comparative Value of Manure Produced on Two Farms. — The fact that there is a great differ- ence in the composition and value of manures pro- duced on different farms may be observed from the following examples : On one farm 10 tons of timothy are fed. The liquid manure is not preserved and 25 per cent, of the fertility is leached out of the solid excre- THE USE OF MANURE 157 merits, while 5 per cent, of the nitrogen is lost by volatilization. It is estimated that half of the nitro- gen and potash of the food is voided in the urine. On account of the scant amount and poor quality of the food no milk or flesh is produced. On another farm 7.5 tons of clover hay and 2.5 tons of bran are fed. The liquid excrements are collected 3r|ariic: Matter Bj:§§§|' 4. Sja- Fig. 29. Good manure. Fig. 30. Poor manure. i. Nitrogen. 2. Phosphoric acid. 3. Potash. 4. Mineral matter. and the manure is taken directly to the field and spread. It is estimated that 20 per cent, of the nitro- gen and 4 per cent of the phosphoric acid and potasli are utilized for the production of flesh and milk. The comparative value of the manures from the two farms is as follows : FARM No. i. In 10 tons timothy, Lbs. Nitrogen .......................... 250 Phosphoric acid .................... 90 Potash ............................ 400 in urine. 250-=- 2 — 125 Ibs. nitrogen 400 -r- 2 = 200 Ibs. potash 158 SOILS AND FERTILIZERS FARM No. i. — (Continued}. Loss by Reaching. 125 X 0.30 = 37.50 Ibs. nitrogen 90 X 0.25 =• 22.50 Ibs. phosphoric acid 200 X 0-25 = 50 Ibs. potash Total loss. Lbs. Per cent. Nitrogen 162.5 65 Phosphoric acid 22.5 25 Potash 250.0 62 Present in final product, manure from i ton timothy. Lbs. Nitrogen 8.75 Phosphoric acid 6.75 Potash 15.00 Relative money value $1.00 FARM No. 2. In 10 tons mixed feed. Lbs. Nitrogen 400 Phosphoric acid 240 Potash 300 LOSS, sold in milk and retained in body. Lbs. Per cent. Nitrogen 400 X °-2° 80 20 Phosphoric acid, estimated... 10 4 Potash 12 4 Present in final product, manure from i ton feed. Lbs. Nitrogen 32.0 Phosphoric acid 23.0 Potash 26.0 Relative money value $3-8o 201. Summary of Ways in which Stable Manure May Be Beneficial. — Farm manures act upon soils both chemically and physically : (a) Chemically : i. By adding new stores of plant food to the soil. THE VALUE OF MANURE 159 2. By acting upon the soil, forming humates and rendering the inert mineral plant food of the soil more available. 3. By raising the temperature of the soil, as the re- sult of chemical action. (b) Physically: 4. By making the soil darker colored. 5. By enabling soils to retain more water and to give it up gradually to growing crops. 6. By improving the physical condition of sandy and clay soils. 7. By preventing the denuding effects of heavy wind storms. CHAPTER VI. FIXATION. 202. Fixation, a Chemical Change. — When a fer- tilizer is applied to a soil, chemical reaction takes place between the soil and the fertilizer. There is a general tendency for the soluble matter of fertilizers to undergo chemical change and become insoluble. This process is known as fixation. If a solution of potassium chloride be percolated through a column of clay, the filtrate will contain scarcely a trace of potas- sium chloride, but instead calcium and other chlo- rides. . The element potassium of the potassium chlo- ride has been replaced by the element calcium present in the soil. As a result of this change between the two bases, an insoluble compound of potash is formed in the soil. 203. Fixation Due to Zeolites. — It has been shown by experiments, particularly by those of Way and Voechler,53 that fixation is due mainly to zeolitic sili- cates (See section 62). Sandy soils containing but little clay have only feeble power of fixation. Clay soils when digested with hydrochloric acid to remove the zeolitic silicates, lose their power of fixation. The fixation of potassium chloride and the liberation of calcium chloride may be illustrated by the follow- ing reaction : Zeolite. Zeolite. H,O + CaCl2 etc FIXATION l6l 204. Humus May Cause Fixation. — Other com- pounds of the soil as humus and calcium carbonate also take an important part in fixation. In the case of humus, a union takes place betweenthe minerals in the fertilizers and the organic acids formed from the decay of the humus in the soil, resulting in the production of humates. (See Section 104.) 205. Soils Possess Different Powers of Fixation. — All soils do not possess the power of fixation to the same extent. Heavy clays have the greatest fixative power while sandy soils have the least. Experi- ments have shown that in the first nine inches of soil, from 2,000 to 8,000 pounds per acre of potash and phosphoric acid may undergo fixation.54 Hence it is that a fertilizer, after being applied to a soil, may be entirely changed in composition, so that the plant feeds on the chemical products formed, rather than en the original fertilizer. 206. Nitrates Cannot Undergo Fixation. — Nitro- gen in the form of nitrates or nitrites cannot undergo fixation. This is because all of the ordinary forms of nitrates are soluble. If potassium nitrate be added to a soil, calcium or sodium nitrate will be obtained as the soluble compound. The potassium undergoes fix- ation, but the nitrate radical does not. Chlorides also are incapable of undergoing fixation because all of the chlorides found in soils are soluble. 207. Fixation of Ammonia. — Ammonium com- pounds readily undergo fixation, particularly in the presence of clay., (See experiment No. 15.) Theam- 1 62 SOILS AND FERTILIZERS moniuin radical, NH4, like potassium is capable of re- placing soil bases. After undergoing fixation, the am- monium compounds readily yield to nitrification (See Section 145), hence they serve as a temporary but important form of insoluble nitrogen. The gen- eral tendency of the nitrogen compounds of the soil is to pass from insoluble to soluble forms through pro- cesses of decay, and to resist fixation changes. 1 08. Fixation May Make Plant Food Less Avail- able. — If a liberal dressing of phosphate fertilizer be applied to a heavy clay soil, the phosphoric acid which is not utilized the first year or two may undergo fix- ation to such an extent that part becomes unavailable as plant food. It is not desirable to apply heavy dressings of fertilizers at long intervals because of fix- ation. It is always best to make lighter applications and more frequently. 109. Fixation, a Desirable Property of Soils. — If it were not for the process of fixation, soils in regions of heavy rains would soon become sterile. On ac- count of the plant food being rendered insoluble, it is retained in the soil. The plant food which undergoes fixation is, as a rule, in an available condition or may readily become so by cultivation unless the soil be one of unusual composition. The process of fixation in the soil regulates the supply of plant food. Many fertilizers, if they did not undergo this process, would be injurious to crops for there would be an abnormal amount of soluble alkaline or acid compounds which would be destructive. The process of fixation first taking place removes, to a great extent, the injurious FIXATION 163 water-soluble salts, particularly when the reaction is one of union rather than replacement. Then the plant is free to render soluble its own food in quantities and at times desired. Farm manures and commercial fertilizers alike un- dergo the process of fixation and, in studying ferti- lizers, their Action upon the soil and the products of fixation are matters of prime importance. Soil water obtained by leaching soils is an exceed- ingly dilute solution of various mineral salts and organ- ic compounds. Through rock disintegration, mineral matter is rendered soluble, but the process of fix- ation prevents accumulation in the soil solution of compounds of such elements as potassium and phos- phorus. As a result of disintegration and fixation, numerous chemical changes take place iri the soil, and the soil solution is an important factor in bringing about these reactions. Many of the phenomena which have been studied in connection with solutions in physical chemistry, take place in the soil. Diffusion, absorption, osmotic pressure and ionization,88 — disassociation of the molecule in solution, — all occur in soils and are due largely to the physical and chemical action of the soil solution. The soil solution from different soils varies with the composition and disintegration of the soil ; in the same soil at different times variations in the composition of the soil solution are noticeable. The soil solution is more important as an agent in bringing about chemical and physical changes in the soil than as a storehouse of plant food. CHAPTER VII PHOSPHATE FERTILIZERS 210. Importance of Phosphorus as Plant Food. — Phosphorus in the form of phosphates is one of the essential elements of plant food. None of the higher orders of plants can complete their growth unless supplied with this element in some form. The illus- tration (Fig. 31) shows an oat plant which received no phosphates, but was supplied with all of the other elements of plant food. As soon as the phosphates stored up in the seed had been utilized, the plant ceased to grow, and after a few weeks, died of phosphate starvation, having made the total growth shown in the illustration. All crops demand their phosphates at an early stage in their development. Wheat Fig. 31. takes up eighty per cent, of its Oat plant grown phosphoric acid in the first half of without phosphorus . . - , ., , the growing period,37 while clover has assimilated all of its phosphoric acid by the time the plant reaches full bloom.43 Phosphates ac- cumulate, to a great extent, in the seeds of grains and hence are sold from the farm when grain farming is extensively followed. All crops are very sensitive to PHOSPHATE FERTILIZERS 165 the absence of phosphates ; an imperfect supply re- sults in the production of light weight grains. The nitrogen and phosphates are to a great extent stored up in the same parts of the plant, particularly in the seed, which is richer in both nitrogen and phosphorus than is any other part. Nitrogen is the chief element of protein, while phosphorus is necessary to aid in transporting the protein compounds through the cell walls of plants. In speaking of the phosphorus in plants and in fertilizers, as well as in soils, the term phosphoric acid or phosphoric anhydride is used. This is because phosphorus is an acid-forming ele- ment and, as already explained, the anhydride of the element is always considered instead of the element itself. 211. Amount of Phosphoric Acid Removed in Crops. — The amount of phosphoric acid removed in an acre of different farm crops ranges from 18 to 30 pounds : Phosphoric acid per acre. Lbs. Wheat, 20 bu 12.5 Straw, 2,000 Ibs 7.5 Total . 20.0 Barley, 40 bu 15 Straw, 3,000 Ibs 5 Total 20 Oats, 50 bu 12 Straw, 3,000 Ibs 6 Total 18 166 SOILS AND FERTILIZERS Phosphoric acid per acre. Lbs. Corn, 65 bu 18 Stalks, 4,000 Ibs 4 Total 22 Peas, 3,500 Ibs 25 Red Clover, 4,000 Ibs 28 Potatoes, 150 bu . . . 20 Flax, 15 bu 15 Straw, i, 800 Ibs 3 Total... 18 212. Amount and Source of Phosphoric Acid in Soils. — To meet the demand of growing crops for 25 pounds of phosphoric acid per acre, there are present in soils from 1,000, and less, to 8,000 pounds of phos- phoric acid per acre, of which, however, only a frac- tion is available as plant food at any one time. The availability of phosphoric acid is a factor which has a great deal to do in determining crop-producing power. Many soils contain a large amount of total phosphoric acid which has become unavailable, because of poor cultivation and the absence of stable manure and lime to combine with the phosphates and render them available. The phosphates in soils are derived mainly from the disintegration of phosphate rock and from the remains of animal life. The phosphate deposits found in various localities are supposed to have been derived either from the remains of marine animals or from sea-water highly charged with soluble phos- PHOSPHATE FERTILIZERS 167 phates. These deposits have been subjected to various geological and climatic changes which have resulted in the formation of soft phosphate, pebble phosphate and rock phosphate.63 213. Commercial Forms of Phosphoric Acid. — The commercial sources of phosphate fertilizers are : (i) phosphate rock, (2) bones and bone preparations, (3) phosphate slag and (4) guano. With the exception of phosphate slag and guano, the prevailing form of phosphorus is tricalcium phosphate. Before being used for commercial purposes, the tricalcium phos- phate, which is insoluble and unavailable, is treated with sulphuric acid which produces monocalcium phosphate, a soluble and available form of plant food. Cas (P04)2 + 2H2S04 + 5H20 = CaH4(PO4)2 + H2O + 2CaS04,2H20. In making phosphate fertilizers from bones or phos- phate rock an excess of the rock is used so that there will be no free acid in the fertilizer to be injurious to vegetation. The usual form in which calcium phosphate is found in nature is tricalcium phosphate, Cas(PO4)2. Unless associated with organic matter or salts which render it soluble it is of but little value as plant food. When tricalcium phosphate is treated with sulphuric acid, monocalcium phosphate, CaH (PO )2, is formed. This compound is soluble in water and directly avail- able as plant food. When tricalcium and monocal- cium phosphate are brought together in a moist con- dition, dicalcium phosphate is produced. 168 SOILS AND FERTILIZERS Cas(P04). + CaH4(P04)2 = Another form of phosphate of lime, met with in basic phosphate slag, is tetracalcium phosphate, (CaO)4P2O5. 214. Reverted Phosphoric Acid. — When mono- and tricalcium phosphate react, the product is known as reverted phosphoric acid, which is insoluble in water, but is not in such form as to be unavailable as plant food. It is generally considered that the reverted phosphoric acid is available as plant food. It is soluble in a dilute solution of ammonium citrate, and is sometimes spoken of as citrate-soluble phosphoric acid. Citrate-soluble phosphoric acid may also be formed by the action, upon the monocalcium phos- phate, of iron and aluminum compounds present as impurities- in the phosphate rock. This process is a fixation change, as described in Chapter VI. In an old fertilizer there may be present citrate-soluble phos- phoric acid in two forms, as dicalcium phosphate and as hydrated phosphates of iron and aluminum. The citrate-soluble phosphoric acid in fertilizers is not all equally valuable as plant food because of the different phosphate compounds that may be dissolved by this solvent. 215. Available Phosphoric Acid. — As applied to fertilizers, the term available phosphoric acid includes the water-soluble and citrate-soluble phosphoric acid. These solvents do not, under all conditions, make a sharp distinction as to the available and unavailable phosphoric acid when it comes to plant growth. Some forms of bones which are insoluble in an am- PHOSPHATE FERTILIZERS 169 inonium citrate solution are available as plant food, an'd then again some forms of aluminum phosphate which are soluble are of but little value as plant food. The terms available and unavailable phosphoric acid, as applied to commercial fertilizers, refer to the solubility of the phosphates, and as a general rule the value of the phosphates as plant food is in accord with their solubility. The more insoluble the less valu- able the material. 216. Phosphate Rock. — Phosphate rock is found in many parts of the United States, particularly in South Carolina, North Carolina, Florida, Virginia and Tennessee. The deposits occur in stratified veins, as well as in beds and pockets. There are different types of phosphates as hard rock, soft rock, land pebble and river pebble. The pebble phosphates are found either on land or collected, in cavities in the water courses, and are generally spherical masses of variable size. The soft rock phosphate is easily crushed, while the hard rock requires pulverizing with rock crushers. Phosphate rock usually contains from 40 to 70 per cent, of calcium phosphate, the equiva- lent of from 17 to 30 per cent, phosphoric acid. The remaining 30 to 60 per cent, is composed of fine sand, limestone, alumina and iron compounds, with other impurities, which often render a phosphate unsuitable for manufacture into high-grade fertilizer. Raw phos- phate rock is sold at the mines for from $1.75 to $4.50 per ton. 217. Superphosphate. — Pulverized rock phosphate 1 70 SOILS AND FERTILIZERS known as phosphate flour, is treated with commercial sulphuric acid to obtain soluble monocalcium phos- phate. The amount of sulphuric acid used is deter- mined by the composition of the rock. Impurities as calcium carbonate and calcium fluoride react with sul- phuric acid and cause a loss of acid. Ordinarily, a ton of high-grade phosphate rock requires a ton of sulphuric acid. The mixing is done in lead-lined tanks. A weighed amount of phosphate flour is placed in the tank, and the sulphuric acid added, through lead pipes, from the acid tower. The mixing of the acid and phosphate is done with a mechanical mixer, driven by machinery. From the mixing tank the material is passed into other large tanks, where two or three days are allowed for the completion of the reaction. When the mass solidifies, it is ground and sold as superphosphate. In the manufacture of superphosphate, gypsum (CaSO4.2H2O) is always pro- duced. A ton of superphosphate prepared from high- grade rock in the way outlined will contain about 40 per cent, of lime phosphate, equivalent to 18 per cent. phosphoric acid. If a poorer quality of rock is used a proportionally smaller amount of phosphoric acid is obtained. A more concentrated superphosphate is ob- tained by producing phosphoric acid from the phos- phate rock, and then allowing the phosphoric acid to act upon fresh portions of the rock, the reactions be- ing as follows : 64 Ca (P04X + 3H3S04 = 3CaSO + 2H3(PO4). Ca(PO ), + 4H PO 3H,0 = 3[CaH (PO4).,H.O]. Ca (PO ;>.+ 2H3P04+ i2H,0=3[Ca,H,(P04).,4H.O]. PHOSPHATE FERTILIZERS 17 1 The phosphoric acid is separated from the gypsum be- fore acting upon the phosphate flour. In this way, superphosphate containing' from 35 to 45 per cent, of phosphoric acid is produced. When fertilizers are to be transported long distances this concentrated product is preferable. The terms ( acid ' and ( super- phosphate ' have been generally used to designate both the first product produced by the action of sul- phuric acid and that produced by phosphoric acid, but of late there is a tendency to restrict the term ( acid phosphate ' to the product formed by the action of sulphuric acid, and the term ' super-phosphate ' to the concentrated product formed by the action of phos- phoric acid. 218. Commercial Value of Phosphoric Acid. — The commercial value of phosphoric acid in fertilizers is determined by the value of the crude phosphate rock, cost of grinding and treating with sulphuric acid, and cost of transportation. The price of phosphoric acid in superphosphates usually ranges from 5 to 6 cents per pound. The field value, that is the increased yields obtained from the use of superphosphates, may not be in accord with the commercial value because so many conditions govern their use. The phosphoric acid obtained from feed-stuffs is usually considered worth about a cent a pound less than that from super- phosphates. Water-soluble phosphoric acid is general- ly rated a half cent per pound higher than citrate-sol- uble phosphoric acid. 219. Phosphate Slag. — In the refining of iron ores 172 SOILS AND FERTILIZERS by the Bessemer process, the phosphorus in the iron is removed as a basic slag. The lime, which is used as a flux, melts and combines with the phosphorus of the ore, forming phosphate of lime. The slag has a varia- ble composition. The process by which the phos- phorus of pig iron is removed-and converted into basic phosphate slag is known as the Thomas process, and the product is sometimes called Thomas' slag. At the present time but little basic slag is produced for fer- tilizer purposes in this country. In Germany and some other European countries large amounts are used. Phosphate slag is ground to a fine powder and is applied directly to the land, without undergoing the sulphuric acid treatment. The phosphoric acid is present mainly in the form of tetracalcium phosphate, (CaO)4P,05. 220. Guano is the Spanish for dung, and is a concen- trated form of nitrogenous and phosphate manure of interest -mainly on account of its historic significance. It is a mixture of sea-fowl droppings, accumulating along the seacoast in sheltered regions, with dead animals and debris, which has undergone fermen- tation. Guano and is concentrated in both nitro- gen and phosphoric acid. The introduction of guano into Europe marked an important period in agri- culture, inasmuch as its use demonstrated the action and importance of concentrated fertilizers. All of the best beds of guano have been exhausted and only a little of the poorer grades are now found on the mar- ket. The best qualities of guano contained from 12 PHOSPHATE FERTILIZERS 173 to 15 per cent, of phosphoric acid, 10 to 12 per cent, of nitrogen, and from 5 to 7 per cent, of alkaline salts. BONE FERTILIZERS 221. Raw Bones contain, in addition to phosphate of lime, Ca (PO )2, organic matter which makes them slow in decomposing and slow in their action as a fer- tilizer. Before being used as a fertilizer they should be fermented in a compost heap with wood ashes in the following way, a protected place being selected so that no losses from drainage will occur. A layer of well- compacted manure is covered with wood ashes, the bones are then added and well covered with manure and wood ashes. From three to six months should be allowed for the bones to ferment. The large, coarse pieces may then be crushed and are ready for use. The presence of fatty material in a fertilizer retards its action because fat is so slow in decomposing. Bones from which the organic matter has been removed are more active as a fertilizer than raw bones. Bones contain from 18 to 25 per cent, of phosphoric acid and from 2 to 4 per cent, of nitrogen. The amount and value of the citrate-soluble phosphoric acid are extre- mely variable. 222. Bone Ash is the product obtained when bones are burned. It is not extensively used as a fertilizer because of the greater commercial value of bone-black. It contains about 36 per cent, of phosphoric acid, and is more concentrated than raw bones. 223. Steamed Bone. — Raw bones are subjected to superheated steam to remove the fat and ossein to be 174 SOILS AND FERTILIZERS used for making soap and glue ; they are then pul- verized and sold as fertilizer under the name of bone meal, which contains from 1.5 to 2.5 per cent, of nitro- gen and from 22 to 29 per cent, of phosphoric acid. Steamed bone makes a more active fertilizer than raw bone. Occasionally, well prepared bone meal is used for feeding pigs and fattening stock in the same way that flesh meal is used. 224. Dissolved Bone. — When bones are treated with sulphuric acid as in the manufacture of super- phosphates the product is called dissolved bone. The tricalcium phosphate undergoes a change to more available forms, as described, and the nitrogen is ren- dered more available. Dissolved bone contains from 2 to 3 per cent, of nitrogen and from 15 to 17 percent, of phosphoric acid. 225. Bone-black. — When bones are distilled bone- black is obtained. It is extensively employed for re- fining sugar, and after it has been used and lost its power of decolorizing solutions, it is sold as fertilizer. It contains about 30 per cent, phosphoric acid and is a concentrated phosphate fertilizer. 226. Use of Phosphate Fertilizers. — The amount of phosphoric acid advisable to apply to crops, varies with the nature of the soil and the kind of crop to be produced. On a poor soil 400 pounds of acid-phos- phate per acre is an average application. It is usually applied as a top dressing just before seeding, and may be placed near the hills of corn or potatoes,, but not in contact with the seed. It is not advisable to make PHOSPHATE FERTILIZERS 175 heavy applications of superphosphates at long inter- vals, because the process of fixation may take place to such an extent that crops are unable to utilize the fer- tilizer. Lighter and more frequent applications, as 100 to 200 pounds per acre, are preferable. Phos- phates should not be mixed with lime carbonate before spreading ; 22 it is best to apply the fertilizer directly to the land. Phosphates may be used in con- nection with farm manures. Many soils which con- tain liberal amounts of phosphoric acid are im- proved by phosphate dressing of 75 pounds per acre. Such soils, however, should be more thoroughly cultivated, and manured with farm manures, to make the phosphates available. There is frequently an apparent lack of phosphoric acid in a soil when in reality the trouble is due to other causes, as lack of organic matter to combine with the phos- phates or to a deficiency of lime. Before using phos- phate fertilizers, careful field tests should be made to determine if the soil is in actual need of available phosphoric acid. Directions for making these tests are given in Chapter X. 227. How to Keep the Phosphoric Acid Available. — Phosphoric acid associated with organic matter in a moderately alkaline soil, is more available than that in acid soils. Soft phosphate rock may be mixed with manure or materials like cottonseed meal and made slowly available for crops. Soils which contain a good stock of phosphoric acid, when kept well ma- nured, and occasionally limed if necessary, have a lib- eral supply of available phosphoric acid. As an illus- 176 SOILS AND FERTILIZERS tration, the following example of two soils from ad- joining farms, which have been cropped and manured differently, may be cited :31 Soil well manured No manure and and crops continuous wheat rotated. raising. Per cent. Per cent. Total phosphoric acid 0.20 0.20 Humus 4.25 1.62 Humic phosphoric acid-- 0.06 0.02 It is more economical to keep the insoluble phos- phoric acid of the soil in available forms by the use of farm manures, lime, rotation of crops and thorough cultivation, than it is to purchase superphosphates in commercial forms. CHAPTER VIII POTASH FERTILIZERS 228. Potassium an Essential Element of Plant Food. — Potassium is one of the three elements most essential as plant food. In its ab- sence plants are unable to develop. Oats seeded in a sterile soil from which potash only was withheld made the total growth shown in the illustration (Fig. 32). When potash is present in the soil in' liberal amounts and associated with other essential elements vig- orous plants are produced. Potash like phosphoric acid and nitrogen is utilized by crops in the early stages of growth. Potassium does not accumulate in seeds to the same extent as phosphoric acid and nitrogen, but is present Fig. 32. Oat plant mainly in stems and leaves, con- grown without potash. Sequently when straw crops are utilized in producing manure the potash is not lost or, as in the case of nitrogen, sold from the farm. But with ordinary grain farming excessive losses of potash do occur, particularly when the straw is burned and the ashes are wasted. 229. Amount of Potash Removed in Crops. — In (12) 178 SOILS AND FERTILIZERS grain crops from 35 to 60 pounds of potash per acre are removed from the soil. For grass crops more pot- ash is required than for grains, while roots and tubers require more than grass. The approximate amount of potash removed in various crops is given in the following table :38 Potash per acre tt>s. Wheat, 20 bu 7 Straw, 2,000 Ibs 28 Total 35 Barley, 40 bu 8 Straw, 3,000 Ibs 30 Total 38 Oats, 50 bu 10 Straw, 3,000 Ibs 35 Total 45 Corn, 65 bu 15 Stalks, 3,000 Ibs 45 Total 60 Peas, 30 bu 22 Straw, 3,500 Ibs 38 Total 60 Flax, 15 bu 8 Straw, i, 800 Ibs 19 Total 27 Mangels, 10 tons 15° Meadow hay, i ton 45 Clover hay, 2 tons 66 Potatoes, 150 bushels 75 POTASH FERTILIZERS 179 230. Amount of Potash in Soils. — In ordinary soils there are from 3,500 to 12,000 pounds of potash per acre to the depth of one foot. Many soils with apparently a good stock of total potash give excellent results when a light -dressing of potash salts is applied. The amount of available potash in the soil is more difficult to estimate than the available phosphoric acid. There is a great difference in crops as to their power of obtaining potash. Some require greater help in procuring this element than others. A lack of available potash is sometimes indirectly due to a deficiency of lime or other alkaline matter in the soil, which prevents the necessary chemical changes taking place in order that the potash may be liberated as plant food. 231. Sources of Potash in Soils. — The main source of the soil's potash is feldspar, which, after dis- integration, is broken up into kaolin and potash com- pounds. Mica and granite also, in some localities, contribute liberal amounts. A valuable source of potash are the zeolitic silicates. The amount of water-soluble potash in soils, except in alkaline soil, is extremely small. By the action of many fertilizers the potash compounds undergo changes in composition. For example, the gypsum which is always present in acid phosphates, liberates some potash. The potash compounds of the soil are in various degrees of com- plexity from forms soluble in dilute acids to insoluble minerals as feldspar. 232. Commercial Forms of Potash. — Prior to the ISO SOILS AND FERTILIZERS introduction of the Stassfurt salts, wood ashes were the main source of potash. Since the discovery and development of the Stassfurt mines, the natural prod- ucts as kainit, and muriate and sulphate of potash have been extensively used for fertilizing purposes. A small amount of potash is obtained also from waste products as tobacco stems, cottonseed hulls, and the refuse from beet-sugar factories. STASSFURT SALTS 233. Occurrence.6* — The Stassfurt mines were first worked with the view of procuring rock salt. The various compounds of potash, soda and magnesia, associated with the layers of rock salt, were regarded as troublesome impurities, and attempts were made by sinking new shafts to avoid them, but with the result of finding them in greater abundance. About 1864 their value as potash fertilizer was established. It is supposed that at one time the region about the mines was submerged and filled with sea-water. The tropi- cal climate of that geological period caused rapid evaporation, which resulted in forming mineral depos- its, the less soluble material as lime sulphate being first deposited, then a layer of rock salt, and finally layers of potash and magnesium salts in the order of their solubility. 234. Kainit is a mineral composed of potassium sulphate, magnesium sulphate, magnesium chloride and water of crystallization. As it comes from the mine it is mixed with gypsum, salt, potassium chlo- ride, and other bodies. Kainit contains from 12 to STASSFURT SALTS - iSl 12.50 per cent, potash, and is one of the most import- ant of the Stassfurt salts. It is extensively used as a potash fertilizer, and is also mixed with other mater- ials and sold as a commercial fertilizer. The mag- nesium chloride causes it to absorb water, and the presence of other compounds results in the formation of hard lumps, whenever kainit is kept for a long time. Kainit is soluble in water, and can be used as a top dressing at the rate of 75 to 200 pounds or more per acre. 235. Muriate of Potash. — This material is exten- sively used as a fertilizer and is valuable for general garden and farm crops. It is a manufactured product and ranges in purity from 60 to 95 per cent, of potas- sium chloride, equivalent to from 35 to 60 per cent, of potash, the chief impurity being sodium chloride. Potassium chloride is readily soluble and is a quick acting fertilizer. When used in large amounts, mu- riate of potash and other chlorides may unfavorably affect the quality of some crops as potatoes, sugar beets and tobacco. Ordinarily, muriate of potash is one of the cheapest and most active forms of potash and can be used as a top dressing at the rate of 200 pounds or more per acre when preparing soils for crops. It is valuable for grass and grain crops, and has given good results on pasty lands.93 236. Sulphate of Potash. — High-grade sulphate of potash is prepared from some of the crude Stassfurt salts, and may contain as high as 97 per cent. K2SO . Low-grade sulphate of potash is about 90 per cent, pure. High-grade sulphate of potash contains about 182 SOILS AND FERTILIZERS 50 per cent, of potassium oxide (K2O), and is one of the most concentrated forms of potash fertilizer. It is particularly valuable because it can be safely used on crops as tobocco and potatoes which would be in- jured in quality if muriate of potash were applied, or if much chlorine were present. 237. Miscellaneous Potash Salts. — Carnallit, 9 per cent. K2O,— composed of KCl,MgCl2,6H2O. Poly- halit, 15 per cent. K2O,— composed of K3SO4,MgSO4- (CaSO )2,H2O. Krugit, 10 per cent. K2O, — composed of K2SO4,MgSO4,(CaSO4)4,H2O. Sylvinit, 16 to 20 per cent. K2O, — composed of KCl,NaCl and impur- ities. Kieserit, 7 per cent. K2O, — composed of MgSO4 and carnallit. 238. Wood Ashes. — For ordinary agricultural pur- . poses, wood ashes are an important source of potash. Ashes are exceedingly variable in composition. When leached the soluble salts are extracted and there is left only about i per cent, of potash. In un- leached 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 :6s Average composition. Range. Per cent. Per cent. Potash 5.5 2.5 to 10.2 Phosphoric acid 1.9 0.3 to 4.0 Lime 34.3 18.0 to 50.9 IN 10,000 POUNDS OF WOOD. Potash. Phosphoric acid. Lbs. Lbs. White oak 10.6 2.5 Red oak 14.0 6.0 Ash 15.0 i.i Pine 0.8 0.7 Georgia pine 5 .o 1.2 Dogwood .* 9.0 5.7 WOOL ASHES 183 239. Action of Ashes on Soils. — Ashes act upon soils both chemically and physically. They are usu- ally regarded as a potash fertilizer only, but they also contain lime and phosphoric acid, and may be very beneficial in supplying these elements. The potash is present mainly as potassium carbonate. Ashes are valuable, too, because they add alkaline matter to the soil, which corrects acidity and aids nitrification. A dressing of ashes improves the mechanical condition of many soils by binding the soil particles. This property is well illustrated in the so-called "Gumbo" soils, which contain so much alkaline matter that the soil has a soapy taste and appearance, and when plowed the particles fail to separate. 240. Leached Ashes. — When ashes are leached the soluble salts are extracted ; the insoluble matter which is left is composed mainly of calcium carbonate and silica.66 Unleached ashes. Leached ashes. Per cent. Per cent. Water 12.0 30.0 Silica, etc 13.0 13.0 Potassium carbonate 5.5 i.i Calcium 61.0 51.0 Phosphoric acid 1.9 1.4 241. 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, cool and filter. To 50 cc. of the filtrate add about 3 drops of cochineal indicator, and then a standard solu- 184 SOILS AND FERTILIZERS tion of hydrochloric acid from a burette until the solu- tion is neutral. If a standard solution of acid cannot be procured, one containing i5cc. 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 i gram while unleached ashes require from 10 to 18 cc. In pur- chasing wood ashes, if a chemical analysis cannot be secured, the alkalinity of the ash should be determined. 242. 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 contain more potash than those from hard coal, but it is held in such firm 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. Per cent. Per cent. Hard coal ashes o.io o. 10 Soft coal ashes 0.40 • 0.40 Sawmill ashesu 1.20 i.oo Peat-bog ashes1* 1.15 0.54 Peat-bog ashes (timbered)14 3.68 2.56 Tobacco stem ash 4.00 7.00 Cottonseed hulls, ash 20.00 7.00 243. Commercial Value of Potash. — The market value of potash is governed by the selling price of USE OF POTASH FERTILIZERS 185 high-grade sulphate of potash and kainit. Ordinarily, the price per pound of potash varies from 4 to 5 cents. As in the case of nitrogen and phosphoric acid, the market and field values as determined by crop yields may be entirely at variance. Before potash salts are .used, careful field tests should be made to determine the actual condition of the soil as to its need of potash. (See chapter X, Commercial Fertilizers.) 244. 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 deficient in potash, and previous tests indicate that larger amounts are safe and advisable. Potash fertilizers should be evenly spread and not allowed to come in direct con- tact with plant roots. 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 de- sired to encourage 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. 245. Joint Use of Lime and Potash. — When a pot- ash 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 observed that land manured for several years with potassium chloride finally produced sickly crops, but that an application l86 SOILS AND FERTILIZERS of slaked lime restored a healthy appearance to suc- ceeding crops.67 If the soil is well stocked with lime its joint use with potash fertilizers is not necessary ; if it is acid, lime should be used to correct the acidity before the potash is applied. The use of potash fer- tilizers for special crops is discussed in Chapter 10. CHAPTER IX. LIME AND MISCELLANEOUS FERTILIZERS 246. 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 potassium. It takes an essential part in plant growth, and when- ever withheld growth is checked. The effect of withholding cal- cium is shown in the illustration (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- iness. They are not so able to withstand drought or unfavorable climatic conditions, as plants grown on soils well supplied with this element. Calcium does not accumulate in the seeds of plants, but is present mainly in the leaves and stems where it takes an im- Oat pla,!tSgrown with- POrtallt Part in the Production out calcium. of new tissue. The term lime, used in connection with crops and soils refers to their content of calcium oxid. 188 SOILS AND FERTILIZERS 247. Amount of Lime Removed in Crops.38 — Pounds per acre. Wheat, 20 bushels i Straw, 2000 pounds 7 Total 8 Corn, 65 bushels i Stalks, 3000 pounds i [ Total 12 Peas, 30 bushels 4 Straw, 3500 pounds • • • 71 Total 75 Flax, 15 bushels 3 Straw, 1800 pounds . 13 Total 16 Clover, 4000 pounds 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 by a clover or pea crop. 248. Amount of Lime in Soils. — There is no other element in the soil in such variable amounts as cal- cium. It may be present from a few hundredths of a per cent, to twrenty per cent, or more. Soils which contain from 0.4 to 0.5 per cent, of lime as carbonate are usually well supplied. The lime 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. 249. Different Kinds of Lime Fertilizers. — By the term 'lime fertilizer' is usually meant land plaster (CaSO4,2H2O). Occasionally quicklime (CaO) and LIME FERTILIZERS 189 slaked lime (Ca [OH] 2) are used on very sour land. In general a lime fertilizer is one which supplies the element calcium ; common usage, however, has re- stricted the term to sulphate of lime. 250. 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 thus prevents 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 pre- vents losses, as the washing away of fine earth. 251 . 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. Nitrogen, phosphoric acid, and potash may all be present in liberal amounts, but in the absence of lime poor results will be obtained. Experiments by Wheeler at the Rhode Island Experiment Station in- dicate that there are large areas of acid soils in the Eastern States which are much improved when treat- ed with air-slaked lime.68 There is great difference in the power of plants to live in acid soils. Some agricultural crops as legumes are particularly sensi- tive, while many weeds have such strong power of endurance that they are able to thrive in the presence of acids. Weeds frequently reflect the character of a soil as to acidity, in the same way that an "alkali" soil is indicated by the plants produced. SOILS AND FERTILIZERS 252. 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 as explained in the chapter on fixation. The extent to which potash may be liber- ated by lime depends upon the firmness of chemical combination 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 re- sults are as follows :69 Kilos per hectare. In crop not litned. In limed crop. First Second First Second year. year. year. year. Lime 32.2 32.2 79.4 102.8 Potash 26.7 28.6 95.6 97.2 Phosphoric acid • n.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.5 Occasionally applications of superphosphate fertilizers give large yields due to the gypsum which they contain, and not to the phosphorus. 253. Quicklime and Slaked Lime. — When it is de- sired to correct acidity slaked lime is used. Air- slacked lime is not as valuable as water-slaked lime. Quicklime cannot be used on land after a crop has LIME FERTILIZERS IQI been seeded. Both slaked lime and quicklime should be applied some little time before seeding and not to the crop. Tne action of quicklime upon organic matter is so rapid that it destroys vegetation. Slaked lime is less injurious to vegetation. 254. 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. It is also beneficial on acid sods. 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, and it is frequently very beneficial. 255. 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 169. Many sandy lands in the vicinity of peat and marl deposits would be greatly improved, both physically and chemically, by the use of these materials. 256. 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 IQ2 SOILS AND FERTILIZERS condition of the soil. The physical action of lime in 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, is frequently sufficient to warrant their use. 257. 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 ferti- lizer but simply an amendment and an indirect ferti- lizer.10 If used to excess it may get the soil in such condition that plant food is not easily rendered avail- able. A common saying is " Lime makes the father rich but the son poor."21 This is true, however, only when lime is used in excess. When used occasion- ally in connection with other manures, it has no injur- ious effect upon the soil and is a valuable fertilizer, especially where clover is grown with difficulty. MISCELLANEOUS FERTILIZERS 258. 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 lib- erated. An early experiment of Wolff illustrates this MISCELLANEOUS FERTILIZERS 193 point : a buckwheat plot fertilized with salt produced a crop with more potash and less sodium than a sim- ilar 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. It should not be used on a tobacco or potato crop, because it injures the quality of the product. Salt is beneficial in preventing some forms of fungus diseases from becoming established in soils. 259. 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 is not necessary to apply it in fer- tilizers. Some of the magnesium salts, as the chloride, are injurious to vegetation, but when associated with lime as carbonate, magnesia imparts fertility. In many of the Stassfurt salts magnesium is present. 260. Salt. — The deposits formed in boiler flues and chimneys when wood and soft coal are burned contain small amounts of potash and phosphoric acid. Soot is valuable mainly as a mechanical fertilizer and is slow in decomposing. There is but little plant food in soot, as shown by the following analysis: Soft coal soot. Hard wood soot. Percent.14 Per cent. 70 Potash 0.84 1.78 Phosphoric acid 0.75 0.96 ('3) 194 SOILS AND FERTILIZERS 261. Seaweeds. — Seaweeds are rich in potash and near the sea coast are extensively used for fertilizer. Composition of mixed seaweeds. Per cent.™ Water 81.50 Nitrogen o. 73 Potash i .50 Phosphoric acid o. 18 262. 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 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 stand of grain had been obtained. The ashes of strand plants and weeds are extremely variable in composi- tion. 263. Wool Washings and Waste — The washings from wool contain sufficient potash to make them valuable as fertilizer. In wool there is a high per cent, of potash, which is soluble, and readily re- moved 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. 264. Street Sweepings. — The horse manure and debris collected from paved streets in cities and known MISCELLANEOUS FERTILIZERS 195 as street sweepings have some value as fertilizer, and are occasionally used for market gardening purposes. Street sweepings, because of the loss of the liquid ex- crements, have a lower value than average stable manure. They cannot be used economically when labor and the cost of hauling are high-priced, or when a quick-acting manure is desired. For sanitary rea- sons, the use of street sweepings is not always desir- able, as mixed with the horse droppings frequently there are associated accumulations of filth from dwell- ings contaminated with disease producing germs. Crude garbage has a low manurial value, but when sorted and cremated, the burned residue can be used to better advantage as a fertilizer than the raw gar- bage, and is without the objectionable and unsanitary features. CHAPTER X COMMERCIAL FERTILIZERS AND THEIR USE 265. Development of the Commercial Fertilizer Industry. — The commercial fertilizer industry owes its origin to L,eibig's work on plant ash. The first superphosphate was made 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."44 Since 1860 the commercial fertilizer industry in this country has developed rapidly, until now the amount of money expended in purchasing commercial ferti- lizers 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. 266. Complete Fertilizers and Amendments. — The term commercial fertilizer is applied to those materials made by mixing different substances which contain plant food in concentrated forms. When a commer- cial fertilizer contains nitrogen, phosphoric acid, and potash, it is called a complete fertilizer, because it supplies the three elements which are most liable to be deficient. Materials as sodium nitrate which supply only one element are called amendments. It frequently happens that a soil requires only one element in order to produce good crops. In such COMMERCIAL FERTILIZERS 1 97 cases only the one element needed should be supplied. Complete fertilizers are sometimes used when the soil is only in need of an amendment. 267. Variable Composition of Commercial Ferti- lizers. — Since commercial fertilizers are made by mix- ing various materials which contain different amounts of nitrogen, phosphoric acid, and potash, it follows that they are extremely variable in composition and value. No two samples are the same, hence the im- portance of knowing the composition of every separate brand purchased. The composition of fertilizers is varied to meet the requirements of different soils and crops. Some fertilizers are made rich in phosphoric acid, while others are rich in nitrogen and potash. 268. How a Fertilizer is Made. — The most com- mon materials 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 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 : Pounds. Nitrate of soda 225 Kainit 425 Phosphate 1350 198 SOILS AND FERTILIZERS The ton of fertilizer would then contain about 35 pounds of nitrogen, 189 pounds of phosphoric acid and 53 pounds potash. These amounts are deter- mined by multiplying the percentage composition by the weight of material taken : Pounds. Nitrogen 225X0.155= 34.9 Potash 425* X o. 125 = 53. i Phosphoric acid 135° X °- 14 = 189.0 The fertilizer would then contain approximately 1.75 per cent, nitrogen, 2.65 per cent, potash, and 9.45 per cent, phosphoric acid. The percentage amounts are obtained by dividing the total pounds by 20. This fertilizer, if made at home from materials purchased in the market, would cost, exclusive of transportation and mixing, $18.79. Pounds. Cost. Nitrogen 34.9 @ 14^ cents = $5.06 Phosphoric acid 189.0 @ 6 cents =11.34 Potash 53.1 @ 4l/2 cents = 2.39 Total $18.79 A more concentrated fertilizer could be prepared by using high-grade sulphate of potash, superphosphate, and ammonium sulphate. A fertilizer composed of these ingredients would contain : 111 Total % 6'S Pounds. Percent. pounds. Value. PL, 8«£ 300 Sulphate of ammonia 20 N 60 @ 14^ cents = $8.70 3.00 500 Sulphate of potash. . 50 K2O 250 @ 4^ cents =11.25 12.50 1200 Superphosphate 35 P2O5 420© 6 cents = 25.20 21.00 Total $45.15 COMMERCIAL FERTILIZERS 199 So concentrated a fertilizer as the preceeding is rarely, if ever, found on the market, although the price, $45.15 per ton, is frequently charged. This example is given to show the composition and cost of one of the most concentrated fertilizers that can be produced. Any one of the different materials mentioned in the chapters on special fertilizers could be used in making commercial fertilizers, as dried blood, tankage, nitrate of soda, sulphate of ammonia, raw bone, dissolved bone, raw phosphate rock, dissolved phosphate rock, basic slag, kainit, muriate or sulphate of potash, and many others. Inasmuch as each of these materials has a different value, it follows that fertilizers, even of the same general composition, may have widely different crop-producing powers. 269. Inert Forms of Plant Food in Fertilizers. — A fertilizer of the same general composition as the first 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. Inert forms of plant food are akin to indigestible forms of animal food ; in each it is the part which is assimi- lated that is of value. 200 SOILS AND FERTILIZERS 270. 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 available nitrogen, phosphoric acid and potash. Inspection has been found necessary in order to protect the farmer and the honest manufacturer. As the result of inspection and analysis occasionally a fraud is revealed like the fol- lowing : 7I Natural plant food, $25 to $28 per ton. Composition. Per cent. Total phosphoric acid 22.21 Insoluble " " 20.81 Available " " 1.40 Potash soluble in water. 0.13 Actual value per ton, $1.52. . 271. Mechanical Condition of Fertilizers. — When a fertilizer is purchased, its mechanical condition should be considered. The finer the fertilizer, as a rule, the better it is for promoting crop growth. Some combinations of plant food produce fertili- zers which become so hard and lumpy that it is diffi- cult to crush the lumps before spreading. The mass must be pulverized so that it may be evenly dis- tributed, otherwise the plant food will not be econom- ically used. A fertilizer that passes through a sieve with holes 0.25 mm. in diameter is more valuable and can be used to better advantage than one of the same composition with particles 0.5 mm. in size. 272. Forms of Nitrogen in Commercial Fertilizers, COMMERCIAL FERTILIZERS 2OI —Nitrogen is present in commercial fertilizers in three forms : (i) Ammonium salts, (2) nitrates, and (3) organic nitrogen. The organic nitrogen is divided into two classes : (a) available, and (£) unavailable. Pepsin and also potassiu mpermanganate are used as solvents for determining the availability of the organic nitrogen. The relative values of the different forms of nitrogen are discussed in Chapter IV. Three fer- tilizers may have the same amount of total nitrogen and still have entirely different crop-producing powers. No. i. No. 2. No. 3. Nitrogen as : Percent. Percent. Percent. Ammonium compounds-... 1.75 0.25 o.io Nitrates. 0.15 0.15 o.io Organic nitrogen : Soluble in pepsin o.io 1.25 0.55 Insoluble in pepsin 0.35 1.25 Total 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 which it is present. In No. 3 the nitrogen is in an inert form like leather, while in No. 2 it is largely in the form of dried blood, and No. i has mainly am- monium compounds. Each of these fertilizers, as ex- plained in the chapter on nitrogenous manures, has a different plant food value. 273. Phosphoric Acid. — There are three forms of phosphoric acid in commercial fertilizers : (i) 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 202 SOILS AND FERTILIZERS is derived from dissolved phosphate rock, and is in the form of monocalcium phosphate. The citrate-soluble is mainly dicalcium 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. No. 2. No. 3. Per cent. Per cent. Per cent. Water-soluble phosphoric acid. 8.00 0.25 0.25 Citrate-soluble " " 1.50 8.00 0.75 Insoluble 0.50 1.75 9.00 Total 10.00 10.00 10.00 No. 3 is of but little value ; the fertilizer contains insoluble phosphate rock or some matarial of the same nature. No i is the most valuable, because it con- tains dissolved phosphate rock or dissolved bone and but little insoluble phosphoric acid. No. 2 is com- posed of such materials as the best grade of basic slag or roasted aluminum phosphate or fine steamed bone. 274. Potash. — The three forms of potash in fer- tilizers are: (i) water-soluble, (2) acid-soluble, and (3) insoluble. Sulphate of potash, kainit, and muriate of potash, are soluble in water and belong 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 other COMMERCIAL FERTILIZERS 203 organic forms of potash. Substances like feldspar, which contain insoluble potash, are of no value in fer- tilizers. As a rule, the potash in commercial ferti- lizers is soluble in water ; in only a few cases are acid- soluble forms met with. Insoluble potash would be considered an adulterant. 275. 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 ammonia con- tains 14 parts nitrogen and three parts by weight of hydrogen, it follows that the ammonia content is pro- portionally greater than the nitrogen content, be- cause of the additional hydrogen carried by the ammo- nia. And so with sulphate of potash which contains about 50 per cent, potash and 50 per cent, of sulphuric anhydrid. This method of stating the composition can be considered in no other way than as a fraud, especially when the fertilizer contains no sulphate of potash, but cheaper materials, and the phosphoric acid is not derived from bone. 276. 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 at $25 and $30, respectively, each having a different composition, the estimated values of each would be obtained in the following way : 204 SOILS AND FERTILIZERS COMPOSITION OF FERTILIZERS. No. i. Selling price $25. Per cent. Nitrogen as nitrates 1.50 Phosphoric acid, available 8.00 " " insoluble 2.00 Potash (water-soluble) 2.00 POUNDS PER TON. No. i. Nitrogen i .50 X 20 = 30 Phosphoric acid • • 8.0 X 20 — !6o Potash 2.0 X2o= 40 ESTIMATED VALUE. No. i. Nitrogen 30 X 0.145 = $4-35 Phosphoric acid 160 X °-o6 = 9.60 Potash 40X0.045— i. 80 NO. 2. Selling price $30. Per cent. 2.IO IO.OO 0.50 3-50 No. 2. 2.IOX 20 — 42 IO.O X 2O = 2OO 3.5 X 20= 70 No. 2. 42 Xo.i45 = $6-°9 200 X 0.06 =12.00 70X0.045= 3.15 $15-75 Difference between estimated value and price, No. i, $9.25; No. 2, $8.76. $21.24 selling Fig. 34. Composition of Fertilizers. 277. Home Mixing of Fertilizers. — At the New Jersey Experiment 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 fertilizer contains about 300 pounds of COMMERCIAL FERTILIZERS 205 actual fertilizing constituents per ton. These figures are practically true of other states where large quan- tities of commercial fertilizers are used."72 In states where smaller amounts are used the difference between the estimated cost and selling price is greater than P-50. These facts emphasize the economy of home mix- ing. The difference in price between the raw mate- rials and the product sold is frequently so great that it is an advantage for the farmer to purchase the raw materials, as sulphate of potash, nitrate of soda, and •8 gj fS if a'5 N FORMULA No. i. g &3 Pounds. Pounds. £ g£ Nitrate of soda 500 containing nitrogen 77.5 3.87 Acid phosphate 1200 containing phos. acid... 168.0 8.40 Sulphate of potash .. 300 containing potash 150.0 7.50 Total 395.5 FORMULA No. 2. Nitrate of soda 250 containing nitrogen 38.7 1.99 Acid phosphate 900 containing phos. acid... 126.0 6.3 Sulphate of potash . . 450 containing potash 225.0 11.5 Plaster, etc 400 Total 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 . . 150 containing potash 75.0 5.75 Plaster, etc 150 Total 316.0 206 SOILS AND FERTILIZERS acid phosphate, and mix them as desired. By so doing a fertilizers of any composition may be pre- pared and there is 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 ingredients as with machinery. 278. Fertilizers and Tillage. — Commercial fer- tilizers cannot be made to take the place of good till- age, which is equally as important when 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- ougly 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 question but what better tillage, better care and use of farm manures, the culture of clover and the sys- tematic rotation of crops would result in greatly re- ducing the amount annually spent for commercial fertilizers, and also increasing the yield of crops. The better the cultivation, the less the amount of commer- cial fertilizer required. Cultivation cannot, however, entirely take the place of fertilizers. 279. 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 COMMERCIAL FERTILIZERS 207 usually due to deficiency of humus and available nitrogen. If the nitrogen were supplied, improved cultivation together with the chemical action of the humus on the soil would generally furnish the avail- able potash and phosphoric acid, but instead of pro- viding the one element needed, others which may already be present in the soil in liberal amounts, are often supplied at an unnecessary expense. Another abuse of fertilizers is their application to the wrong crop. A heavy application of potash fertilizer 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 waste of money. 280. Judicious 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 assimilat- ing food ; turnips, for example, have very restricted powers of phosphate assimilation, hence they require phosphate manures. Wheat requires help in obtain- ing its nitrogen. In some soils a wheat crop may starve for want of nitrogen, while an adjoining corn crop will scarcely feel its need. Wheat has strong power of assimilating potash, while clover has less. Hence in the use of fertilizers the power of the plant to obtain its food must be considered. A light appli- cation of either a special purpose or a complete fertili- zer at the time of seeding is often advantageous, as it encourages plant growth by supplying food at the 208 SOILS AND FERTILIZERS time when it is most needed. There should be some plant food in the soil in a highly available condition for the use of young plants, after that stored up in the seed has been exhausted. Before commercial fertilizers are used, careful field trials should be made. 281. Experimental Plots.— A piece of land well 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 lofeet 8 inches, area 2176 square feet. Between each plot a strip 3 feet wide is left. The plan is to apply one element or a combination of elements to a plot and compare the results with other plots treated differently.70 282. 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 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. COMMERCIAL FERTILIZERS 209 The sixth plot receives phosphoric acid and potash. The seventh plot receives potash. The eighth plot receives phosphoric acid. No fertilizer' N N N P205 P205 K2O K2O i. 2. 3- 4- N P205 K20 P205 K2O 5- 6. 7- 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 is in want of nitrogen. From the eight plots it will be possible to tell which of the various elements it is advisable to use. The fertilizers should be applied after the land has been thoroughly prepared and before seeding. Corn is a good crop for the first trials. The number of plots may be increased by using well-prepared stable manure and gypsum on plots 9 and 10 respectively. The second year the results should be verified. 283. 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 less difficulty in obtaining this element. The cultivation of each (14) 210 SOILS AND FERTILIZERS crop should be that which experience has shown to be the 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 nitrogen, the soil is in need of available nitrogen. If, however, the wheat responds and the corn does not, the soil is not in great need of nitrogen but does not contain an abundance in available forms. 284. 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 1 6 pounds of acid phosphate are applied. If both crops show marked additional yields the soil is in need of available phorphoric acid. If only the turnips respond 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 phosphoric acid. 285. 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 sulphate 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 from either crop the soil is not in need of potash. COMMERCIAL FERTILIZERS 211 286. Deficiency of Two Elements. — If the prelim- inary trials indicate a deficiency of two elements as nitrogen and phosphoric acid, in verifying these results, both elements are used together, in the same way as described for deficiency of nitrogen, with addi- tional plots for the separate application of nitrogen and phosphoric acid. 287. Importance of Field Trials. — While it is a difficult 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 might take 8 years to indicate what the soil really as deficient in if a different fertilizer is used each year, and during all this period, either the soil fails to receive its proper fertilizer, or expensive and unnecessary plant food is provided. Field tests to be of value must be continued for a number of years and the results verified. 288. Will it Pay to Use Commercial Fertilizers? — This question can be answered only by trial. If a soil is in need of available plant food, the additional yield of crops 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 necessary. In the production of large areas of staple 212 SOILS AND FERTILIZERS crops as wheat and corn, in the western prairie states, they have tfot as yet been used. If there is a good stock of natural fertility, the soil is well tilled, farm manures are used, and crops systematically rotated, the use of commercial fertilizers can be avoided. With poor cultivation and a soil that has been impover- ished by injudicious cultivation their use is more necessary. Commercial fertilizers sometimes fail to give beneficial results, because of either an excessively acid or alkaline condition of the soil. 289. Amount of Fertilizer to Use per Acre. — When commercial fertilizers are used, it should be the aim in general farming to apply just enough to produce normal yields. Heavy applications at long intervals are not as productive of good results as light applica- tions 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 deter- mined by the crop to be grown. The fertilizer should not come in direct contact with seeds, neither should it be plowed under or worked into the soil to such a depth that it may be lost by leaching before it can be appropriated by the crop. 290. Excessive Applications of Fertilizers Injuri- 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 solu- tion is concentrated abnormal growth results. Pota- COMMERCIAL FERTILIZERS 213 toes heavily manured with nitrate of soda make a luxuriant growth of vines but produce only a few small tubers. When a medium dressing is used along with potash and phosphoric acid, a more balanced 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 aro too heavy, plants take up unnecessary amounts of food and fail to make good use of it. In fact crops may be overfed or fed, an unbalanced ration, the same as animals. Hence in the use of fertilizers excessive or unbalanced appli- cations are to be avoided. 291. 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 diffi- culty in obtaining food. When the soil does not show a marked deficiency in any one element, light dress- ings of special purpose manures may be made to the following crops : Wheat. — Nitrogen first, then phosphoric acid. Barley, oats, and rye require manuring like wheat, but to a less extent. Each crop has a different power of obtaining nitrogen. Wheat requires the most help and barley and rye the least. 214 SOILS AND FERTILIZERS Corn. — Phosphoric acid first, then nitrogen and potash. Potatoes. — General manuring, re-enforced with pot- ash. Ma ngels. — N i tr ogen . Turnips.— Phosphoric acid. Clover. — Lime and potash. Timothy. — General manuring. 292. — Commercial Fertilizers and Farm Manures. — Commercial fertilizers should not replace farm manures, but simply re-enforce them. Although commercial fertilizers are called complete manures, they fail to supply organic matter. It is more im- portant 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. 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 have received only applications of com- mercial fertilizers. This is due to the action of the humus in the soil. At the Canadian Dominion Ex- perimental farms where comparative trials have been made for fourteen years with farm manures and com- mercial fertilizers, it has been found that farm manures even on new lands give better results than commercial fertilizers for production of wheat and corn. » CHAPTER XI FOOD REQUIREMENTS OF CROPS 293. 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 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 is not a measure of the power of crops to obtain food. 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 impover- ished condition than corn, because corn has greater power for procuring nitrogen and for utilizing that formed by nitrification after the wheat crop has com- pleted its growth. The available nitrogen if not utilized by a crop may be lost in various ways. Man- gels require about twice as much phosphoric acid as flax, but are a strong feeding crop and require less help in obtaining this element. It was formerly believed that the plant 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 2l6 SOILS AND FERTILIZERS to the soil of all elements removed in the crop. Ex- periments have shown that this view is incorrect. The composition of plants cannot be taken as the PI^ANT FOOD REMOVED BY CROPS37 Pounds per acre. Phos- Gross Nitro- phoric Pot- Sil- Total Crops. weight. gen. acid. ash. lyime. ica. ash Wheat, 20 bus I2OO 25 12.5 7 I I 25 Straw 2000 IO 7-5 28 7 115 185 Total 35 20 35 ^8 116 2IO Barley, 40 bus I92O 28 15 8 i 12 40 Straw 3000 12 5 3° 8 60 I76 Total 40 20 38 9 72 216 Oats, 50 bus I6OO 35 12 IO 1-5 15 55 Straw 3000 15 6 35 9-5 60 150 Total 50 18 45 II. 0 75 205 Corn, 65 bus 2200 40 18 15 i i 40 Stalks 3OOO 35 2 45 ii 89 1 60 Total 75 2O 60 12 90 200 Peas, 30 bus 1800 .. 18 22 4 i 64 Straw 3500 .. 7 38 71 9 176 Total 25 60 75 10 240 Mangels, lotons.. 2OOOO 75 35 150 3° 10 350 Meadow hay, i ton 2OOO 3° 20 45 12 50 175 Red Clover Hay, 2 tons 4OOO .. 28 66 75 15 250 Potatoes, 150 bus.. 9000 40 20 75 25 4 125 Flax, 15 bus 9OO 39 15 8 3 05 34 Straw 1800 15 3 J9 13 3 53 Total 54 18 27 16 3-5 87 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 nitro- gen were applied to an acre of clover and 35 pounds to an acre of wheat, poor results would follow, be- cause clover can obtain its own nitrogen while wheat FOOD REQUIREMENTS OF CROPS 217 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 ob- tained from a study of the different elements of fer- tility removed in crops. In making use of the pre- ceding table, other factors, as the influence of the crop upon the soil and the power of the crop to ob- tain its food, must also be considered. 294. Plants Exert a Solvent Power in Obtaining Food. — It was supposed at one time that plants ob- tained all of their mineral food from the mineral matter dissolved in the soil water. See Section 87. Experiments by L,iebig demonstrated that plants have the power of rendering a large portion of their own food soluble, provided it does not exist in forms too inert to under- go chemical change. Liebig 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 crops. His results showed that 92 per cent, of the potash in the crop was obtained from forms insoluble in water.73 Other experiments have shown that the leachings from a fertile soil do not contain sufficient plant food to grow a normal crop.87 2l8 SOILS AND FERTILIZERS In the roots of all plants there are present various organic acids and salts. 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 serves as a membrane. All of the conditions are favorable for osmosis. The sap from the roots finds its way into the soil in exchange for some of the soil water. The acid and compounds, excreted by the roots, act upon the mineral matter, rendering portions of it soluble, when it is taken up by the plant. Different plants con- tain different kinds and amounts of solvents, 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 assimilating food. This action of living plant roots upon soils is a digestion process which is somewhat akin to the digestion of food by animals. Plants not only possess the power of rendering their food soluble but they are also able to select their food and to reject that which is unnecessary. For ex- 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.37 CEREAL CROPS 295. 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 soil74 liberating the base elements and using them as food, while the silica is deposited in the outer surface of the straw. As previously stated, FERTILIZERS FOR CEREAL CROPS 2 19 cereal 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 assimilating nitrogen. Next to nitrogen these crops stand most in need of phosphoric acid. The humic phosphates are utilized by nearly all of the cereals. 296. 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 L,awes and Gilbert have given valuable information regarding the effects of manures on wheat. Their results are given in the following table : 74 AVERAGE YIELD OF WHEAT PER ACRE. Bushels. No manure for 40 years ........................ 14 Minerals alone for 32 years ..................... 15^ Nitrogen " " " " ..................... 23.1 Farmyard manure for 32 years .................. 32f Minerals and nitrogen for 32 years1 ............. 36^ 1 86 pounds of nitrogen as sodium nitrate. 2 86 " " " " ammonium salts. The food requirements of wheat are such that it should be given a favored position in the rotation. It may follow clover provided the clover sod is light and is fall plowed. On some soils, however, wheat does not thrive following a sod crop, as it takes nearly a year for a heavy sod residue to get into suitable food 220 SOILS AND FERTILIZERS forms for a wheat crop. Under such a condition, 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 by surface cul- tivation, leaves the land in good condition for spring wheat. It is not advisable to have wheat follow bar- ley, 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. When a corn crop is well manured, wheat may follow. The food requirements of wheat are best satisfied following a light, well cultivated clover sod, or following oats, which have been grown on heavy sod, or following corn that has been well manured. When wheat is judiciously grown in a rotation and farm manures are used it is not an exhausting crop. 297. 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 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 nitrogen assimilative powers than wheat. Barley, however, responds liberally to manuring, particularly FERTILIZERS FOR CEREAL CROPS 221 to nitrogenous manures. The experiments of Lawes and Gilbert on the growth of barley are briefly sum- marized in the following table.75 AVERAGE YIELD OF BARLEY PER ACRE FOR 34 YEARS. Bushels. No manure 17! Superphosphate alone 23^ Mixed minerals 24^ Nitrogen alone 3o| Nitrogen and superphosphate 45 Farmyard manures .... 49*- 298. Oats. — Oats are capable of obtaining food un- der more adverse conditions than either barley or wheat. They are also less exacting as to the physical condition of the soil. The oat plant will adapt itself to either sandy 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. Oats are, however, greatly benefited by fertilizers particularly by those of a nitrogenous nature. 299. Corn. — Experiments with corn indicate that under ordinary conditions it requires most help in ob- taining phosphoric acid. Corn removes a 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 222 SOILS AND FERTILIZERS after one or two corn crops have been removed. The food requirements of corn are satisfied by applications of stable manure, occasionally re-enforced with a little nitrogen and 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 rotation. MISCELLANEOUS CROPS 300. 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 weak feeding crop. There are but few roots near the surface and consequently it has restricted powers of nitrogen assimilation.38 Flax should be indirectly manured. Direct applications of stable manure produce poor results, but when the manure is applied to the preceding crop excellent re- sults are obtained. 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. The best conditions for flax cul- ture require that it should be grown on the same land only once in five years. Flax straw does not form suitable manure for flax lands. Dr. Lugger has demonstrated that there are produced, when the roots and straw of flax decay, products which are destruc- tive to succeeding flax crops.77 Flax diseases are also introduced into land by the use of diseased flax seed. 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. FERTILIZERS FOR ROOT CROPS 223 Flax and spring wheat are much alike in food require- ments. 301. Potatoes.* — Potatoes are surface feeders and when grown continually upon the same soil without manure, the yield per acre decreases more rapidly than that of any other farm crop. Experiments with pota- toes by Lawes and Gilbert, using different manures, gave the following result : ?8 AVERAGE YIELD PER ACRE FOR 12 YEARS. Tons. Cwt. No manure i 19! Superphosphate 3 5 Minerals alone 3 yf Nitrate of soda alone 2 4f Mixed manures and nitrogen 5 17! Farm manures, alternate years 4 3! Potatoes require liberal general manuring re-enforced^ with wood ashes or other potash fertilizer. In the rotation they should follow grain or pasture land, pro- vided the fertility of the soil is kept up. 302. Sugar-Beets. — This crop is more exacting in its food requirements than any other root crop. Ex- cessive fertility is not conducive to a high content of sugar. Soils in a medium state of fertility usually give the best results.79 Sugar-beets should not receive heavy dressings of stable manure, because an abnor- mal growth results. Nitrogenous fertilizers can be applied 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. 224 SOILS AND FERTILIZERS 303. Roots. — Mangels are gross feeders and re- move a larger amount of fertility from the soil than any other farm crop.74 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 phos- phate assimilation. Manures for turnips should be phosphatic in nature. 304. Rape is a type of strong feeding plant capa- ble of obtaining its food under conditions adverse to grain crops. When grown too frequently upon the same soil it does not thrive. On account of its great capacity for obtaining food, it is a valuble crop to use for green manuring purposes.80 305. Buckwheat is a 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 used as a manurial crop, being plowed under while green to serve as food for weaker feeding crops. 306. Cotton. — On average soils cotton stands in need first of phosphoric acid, second of nitrogen.81 It is most able to obtain potash. Organic nitrogen as cottonseed meal and stable manure appear equally as effective as nitric nitrogen. Phosphoric acid must FERTILIZERS FOR GRASS CROPS 225 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, which is composed mainly of calcium carbonate, combines with the acids formed from the decay of this vegetable matter and as a result the plant food of the soil is more available, a result which is beneficial to both soil and crop. There are but few crops which respond so readily to fertilizers as cotton. 307. Hops, — The hop plant is exacting in regard 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 untnanured. Very light applications of com- mercial fertilizers may be used in connection with stable manure, but such use should be made only after a preliminary trial on a small scale. 308. 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 discourag- ing 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.82 On some soils ('5) 226 SOILS AND FERTILIZERS 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 introduced as an important crop in the rota- tion. Permanent meadows should receive an annual dressing of farm manure or of a commercial fertilizer containing phosphoric acid, potash and a fair amount of nitrogen. 309. Leguminous Crops. — For leguminous crops potash and lime fertilizers have been found of most value. Analyses of clover and peas, show large amounts of both potash and lime. Some crops as clover fail when grown too frequently upon the same soil, not because the soil is exhausted but be- cause of the development in the soil of organic pro- ducts which are destructive to growth. As the result of growing leguminous crops and after their inex- pensive food requirements are met, the soil is en- riched with nitrogen and the phosphoric acid is changed to available forms. 310. Garden Crops. — For general garden purposes, there should be a liberal supply of plant food. Well composted farm manure can advantageously be rein- forced with commercial fertilizers. A liberal use of manures insures not only the maximum yield, but crops of the best quality. Maturity of crops also is influenced by fertilizers. Voorhees89 recommends as a fertilizer for general gar- den purposes one containing : FERTILIZERS FOR GARDEN CROPS 227 Per cent. Nitrogen 4.00 Phosphoric acid 8.00 Potash . 10.00 This and similar fertilizers can be applied at the rate of looo pounds per acre. To meet the requirements of special crops, as spinach and cabbage, an additional dressing of nitrate of soda may be used. Asparagus should preferably be fertilized after harvesting the crop so as to encourage new growth and the storing up of reserved builing material in the roots for next year's growth. For early maturing garden crops, a fair but not excessive amount of nitrogen should be applied, also a more liberal supply of phosphates will be found advantageous. Some garden crops, as cu- cumbers, pumpkins and squash thrive best when their food is supplied in organic forms, as the humate compounds derived from farm manures. A continu- ous supply of available plant food is thus furnished to the growing crop. Onions are benefited by a gener- ous dressing of soluble nitrogen. Celery also should be well supplied with soluble nitrogen combined with soluble forms of mineral food. Tomatoes require general fertilizing ; for early maturity, nitrogen, as nitrate of soda, is beneficial, but an excess should be avoided ; for late maturity, farm manures and com- mercial fertilizers containing less nitrogen can be used. For general garden purposes, a complete fertili- zer is preferable to an amendment, as a better bal- anced growth is secured which favorably affects both yield and the quality of the crop. 228 SOILS AND FERTILIZERS 311. Fruit Trees. — In the manuring of fruit trees, it should be the object first to produce thrifty trees as sub- sequent fertilizing to produce fruit will not give satis- factory results with poorly grown and partially de- veloped trees. In order to promote growth, a liberal supply of a complete fertilizer should be used. When an orchard is in full bearing, there is as heavy a draft upon the soil as when a wheat crop is grown.?0 To meet this, farm manures and commercial fertilizers should be used liberally. The quality of the fruit is often adversely affected by a scant supply of plant food. A quick acting fertilizer containing kainit, nitrate of soda, and dissolved phosphate rock should be used in the spring, followed if necessary by a light dressing of some manure which yields up its fertility more slowly. Stone fruits are benefited by the addi- tion of lime to the fertilizer. 312. Lawns. — In the preparation of a lawn, a mixture of six parts of bone ash, two parts of muriate of potash and one part of nitrate of soda can be ap- plied at the rate of 5 to 7 pounds per square rod prior to seeding. A good lawn should have a subsoil that is fairly retentive of moisture, one containing 10 to 15 per cent, of clay or a large amount of fine silt. Too much potash and lime encourage exclusive growth of clover and crowding out of grasses. During the season, two or three applications can be made of a commercial fertilizer containing about 3 per cent, of nitrogen, 10 per cent, of phosphoric acid, and 3 per cent, of potash, at the rate of about one pound per MISCELLANEOUS CROPS 229 square rod. When part of the nitrogen is in the form of nitrates and part as ammonium salts, better results are secured than when the nitrogen is all in one form. It is also advisable to supply the phosphoric acid in more than one form. An even application of fertili- zer to a lawn is quite necessary, otherwise the growth is " patchy." Hard wood ashes evenly spread at the rate of i to 2 pounds per square rod can also be used advantageously as a lawn fertilizer, and when used, they should be reinforced with nitrate of soda. CHAPTER XII ROTATION OF CROPS AND CONSERVATION OF SOIL FERTILITY 313. Object of Crop Rotation. — The object of 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 culti- vation and judicious 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 rotation is required 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 can 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 there are other losses as described in the chapter on nitrogen. When wheat is system- atically grown in alternation with other crops, losses of nitrogen are reduced to a minimum. When remunerative crops can no longer be produced the soil is said to be exhausted. Soil exhaustion may be due either to a lack of fertility or to the soil being temporarily out of condition because of a one-crop system and poor methods of cultivation. ROTATION OF CROPS 231 314. Principles Involved in Crop Rotation, — In the systematic rotation of crops there are a few funda- mental principles with which all rotations should con- form. 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 will do the most good. 9. Rotations should be planned so as to produce fodder for stock, and so that every year there will be some important crop to be sold. 315. Deep and Shallow Rooted Crops. — When deep and shallow rooted crops alternate, the draft upon the surface soil and subsoil is more evenly distributed. 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- 232 SOILS AND FERTILIZERS lieved of continuous heavy drafts upon the elements present in scant amounts. 316, Humus-consuming and Humus-producing Crops. — When grain or hoed crops are grown con- tinually, 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. 317. Crop Residues. — 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, on an average soil, to follow clover and timothy with mangels, 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 ROTATION OF CROPS 233 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 lime 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. 318. 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 134 an example 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 grain can be sold from the farm without purchasing nitrogenous manures. The con- servation of the nitrogen and the humus of the soil is one of the most important points to consider in the rotation of crops. 319. Influence of Rotation upon the Mechanical Condition of Soils. — With different kinds of crops, the mechanical condition of soils is 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 rotation the 234 SOILS AND FERTILIZERS action of the crop upon the mechanical condition of the soil should be considered, otherwise the soil may get into poor condition 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 treatment. The rotation should be made to conform to the requirements of the soil. 320. 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. During years of heavy rainfall catch crops can be grown as green manure to increase the humus con- tent of the soil. Crops removing excessive amounts of water should not be grown too frequently. Sun- flowers, for example, remove twenty times more water than grain crops. Cabbage removes from the soil more water than many other crops. With a good rotation and systematic cultivation it is possible to carry a water balance in the soil from one year to the next, so that crops will be supplied in times of drought. 321. 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 is so plain that its discussion is unnecessary. It is one of the most important points to consider in ROTATION OF CROPS 235 economic farming, and should not be lost sight of in planning rotations. 322, 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 or some other manure. If com- mercial 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 re- quire commercial fertilizers for general crop produc- tion. It is more economical to reenforce the farm manures with fertilizers especially adapted to the soil and crop, than to purchase complete fertilizers for all crops. 323. Salable Crops. — In all farming, something must be sold from the farm. It should be the aim to 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 is 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 at seeding time the indica- tions are that wheat will be a poor paying crop and flax command a high price, flax should be sown. The rotation should be such that one of two or three crops may be grown as circumstances require. 236 SOILS AND FERTILIZERS 324. Rotation Advantageous in Other Ways. — A good rotation will be found advantageous in other ways. With one line of cropping, land becomes foul with weeds and insects which are unable to thrive when crops are rotated. Frequently the rota- tion must be planned so as to reclaim the land from weeds, and ravages caused by insect pests. Many in- sects are capable of living only on a special crop ; w.hen this crop is grown continually on the same land the best conditions for insect ravages exist, and relief is only secured by rotation of crops. Fungus diseases also are most liable to occur on soils which produce annually the same crop, as the conditions are favorable for the propagation and hybernating of disease pro- ducing spores. 325. Long- and Short- Course Rotations. — Rota- tions vary in length from 2 to 17 years. Long-course rotations are more generally followed in European and other of the older countries. The length of the rotation can only be determined by the conditions ex- cisting in different localities. As a general rule long- course rotations should be attempted only after a careful study of all of 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 unsuitable for other localities or conditions. Because of variations in soil, climate, ROTATION OF CROPS 237 and rainfall, no definite standard rotation can be pro- posed that will be applicable to all conditions. 326. 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 of the conditions. For example, a farm of 160 acres is to be rotated with the main ob- ject of producing fodder for live stock, and a small amount of grain for sale. To meet these require- ments the rotation outlined on pages 238 and 240 is given.83 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, 10 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 de- rived from the sale of live stock and dairy products. 6 i t/r i «j u 0) 53 r; 4) •S 0 -2 °- °S 1 f 1 fS 2~ o a^= <^> U 3 •3^ i-t b^ > d cd ^<5 ,d Ti cj ,2 £ •j i^« "1 0,3 .d ^^^^^ O v— * _c *i i >. O i j^ j^ 05 £** HD cd 3 ^i d § ^5 ^ i^33 ''d ^ D 1 S d — cd n o «S «2 6 ^ £ 3 O « O 0 en r< -; ' 4) ^J D rQ O »-c »*^ O •4-> 53 SH C+H | . -2 ° ^ d •M 1 1 &||i 3 cd n 3 ^ • ^3 _2 i tj l» X d u O "o ^ a s 1 3 O 1 d cd & o 'd O o*" 5 z «"5 ^frQ o Q d o 0 "§ ^l2 N . 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O O l-t 3 c" g 1 O O •->> •-h O B 0 0 3 ? 3 p. ft >-+> *^ *"*"* M^ X s. *^ o ^ ^^^ ^_^ S3> ^* 3 p 3 * g- ^ "^ o1 c 3 P^ P 2 3 |"f * 3 3 n O 3^ *^ Q* W d 3* n> B P 3 O J* 3s--« PI s* ^r- C^ o5-"5 «rt §• * o 3 n | ^§ § ro -t fB fP en &3 & n n 2 3 o ^ C/3 ^ CD il 240 SOILS AND FERTILIZERS Problems on Rotations 1. Plan a rotation for general farming ( 160 acres) using the following 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 ob- ject being potato culture. 3. Plan a seven-year rotation for grain farming, using manure and a commercial fertilizer once during the rotation. The soil is a 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 from a 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, in rotation and con- tinually ? 7. Plan a rotation for a northern latitude, where corn cannot be grown, except for fodder, and where clover and timothy fail to do well ; wh^at and all small grains thrive, also millet, bromus inermis, rape, and some of the root crops. The soil is a clay loam, resting on a marl subsoil. Manure is very slow in decomposing. The rotation should be suited to general farming, wheat or flax being the important market crop. 8. Plan for a southern farm a rotation in which cotton forms an important part. CONSERVATION OF FERTILITY 327. 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 crops are sold from the farm and no restoration is maed, 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. 328, 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 rio restoration of fertility is made, while in the case of stock farming, the manure produced contains fertility in proportion to the food 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 and often a gain of fertility. Between these two extremes, exclusive grain farming and stock farming, many different systems of farming are practiced which remove from the soil various amounts of fertility. (16) 242 SOILS AND FERTILIZERS . 329. 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 is occuring. In studying the income and outgo of fertility, it is necessary to calculate the amounts of the three principal elements, nitrogen, phosphoric acid, and potash in the crops and products sold. For making these calculations tables are given in Sections 172 and 293. In the handling of manure it is impossible to prevent losses, but it is possible to reduce them to very small amounts. Hence in the calculations, a loss of 3 per cent, is al- lowed for mechanical waste, and for uneven distribu- tion of the manure ; that is, in addition to the fertility sold from the farm a mechanical 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 40 acres, wheat 50 acres, oats 20 acres, barley 50 acres ; no stock is kept, the straw is burned, and the ashes are wasted. 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. See CONSERVATION OF FERTILITY 243 section 133. This would make the total loss of nit- rogen 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 is sold. Ex- periments at the Minnesota Experiment Station showed that after a soil had been cultivated 40 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.18 EXCLUSIVE GRAIN FARMING. Sold from the Farm. Phosphoric Nitrogen. acid. Potash. ^ Pounds. Pounds. Pounds. Flax, 40 acres 1600 600 800 Flax straw 600 120 320 Wheat, 50 acres 1250 625 350 Wheat straw 500 375 1400 Oats, 20 acres 700 240 200 Oat straw 300 1 20 700 Barley, 50 acres 1400 750 400 Barley straw 600 250 1500 Total 6950 3080 5670 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. On a similar farm of 160 acres the crops are rotated as described in Section 326. 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. 244 SOILS AND FERTILIZERS STOCK FARMING. Sold from the Farm. Phosphoric Nitrogen. acid. Potash. Pounds. Pounds. Pounds. Butter, 5000 pounds - •• 555 Young cattle, 10 head 200 190 16 Hogs, 20 of 250 pounds each. . 100 40 10 Steers, 2 48 38 4 Wheat, 10 acres 250 125 70 Flax, 10 acres 390 150 190 Rye, 10 acres 285 128 85 Total 1278 676 380 Raised and Consumed on the Farm. Clover, 20 tons oo 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 40 20 75 Straw, 40 tons 400 200 1000 Peas, 5 acres 85 200 Oats, 20 acres 700 240 200 Barley, 20 acres with straw • • 800 400 760 4265 1780 4795 Mechanical loss of food con- sumed, 3 per cent 128 53 144 Food and Fuel Purchased. Phosphoric Nitrogen. acid. Potash Pounds. Pounds. Pounds. Bran, 5 tons 275 260 150 Shorts, 5 tons 250 150 100 Oil meal, ton 100 35 25 Hard-wood ashes 25 100 625 470 375 CONSERVATION OF FERTILITY 245 Mechanical loss in material purchased $% T9 J4 Io Sold from farm 1278 676 380 Loss in food consumed, etc.. 128 53 144 Total 1425 743 534 Food and fuel purchased 625 470 375 Balance lost from farm 800 273 159 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 nitrogen gained by the clover and peas more than balances the loss of nitrogen in other crops. Experiments have shown that a rotation similar to this caused an in- crease in soil nitrogen.18 Manure, meadow and past- ure all tend to increase the soil's humus and nitrogen. The losses of phosphoric acid and potash are exceed- ingly small, averaging about a pound per acre for each. The action of the manure on this farm is con- tinually bringing into activity the inert plant food of the soil so that every year there is a larger amount of more active plant food, which results in producing larger yields per acre. The method of farming has a marked effect upon crop yields. The average yield of wheat in those counties in Minnesota where live stock is kept and crops are rotated, is over 10 bushels per acre greater than in similar counties where exclusive grain farm- ing is followed. 246 SOILS AND FERTILIZERS Problems. Calculate the income and outgo of fertility from the following farms. T. Sold from the farm : Wheat 40 acres, oats 40 acres, barley 40 acres, rye 20 acres, flax 10 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 10 steers. Purchased : Bran 3 tons, shorts 2 tons, oil meal i ton. Crops produced and fed on farm : Clover and timothy hay 40 tons, corn fodder 3 acres, corn 10 acres, oats and peas 10 acres, roots i acre, millet I acre, and barley 5 acres. 3. Sold from the farm : Wheat 10 acres, sugar beets 5 acres, milk 100,000 pounds, butter 500 pounds, 20 pigs, 6 head of young tock, 2 acres of potatoes. Purchased : 5 tons of bran, 2 tons of oil meal, i ton of cottonseed meal, 15 cords of wood, i ton of acid phosphate, 1000 pounds of potassium sulphate, and 500 pounds of sodium nitrate. 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 10 acres, corn 20 acres. 4. Calculate the income and outgo of fertility from your own farm. CHAPTER XIII PREPARATION OF SOILS FOR CROPS 330. Importance of Good Physical Condition of Seed Bed. — But few soils are in suitable condition for seeding without farther preparation than simply plowing the land. If the plowing is poorly done, a good seed bed cannot be prepared. The depth of plowing is of prime importance and is determined largely by the character of the soil, as sand, clay or loam. (See Section 35). The character of the seed bed is influenced not only by the depth of plowing but by the nature of the plowing as the way in which the furrow slice is left. Treatment of the soil after plow- ing, as disking, harrowing, cultivating and light roll- ing must be determined largely from the character of the soil. Too frequently the preparation of the soil is not given sufficient attention and crops suffer be- cause of poorly prepared seed beds. 331. Influence of Methods of Plowing Upon the Condition of the Seed Bed. — A poor seed bed is some- times formed by complete inversion of the furrow slice and the soil not being sufficiently pulverized. If a heavy sod has simply been inverted, subsequent harrow- ing and cultivation will fail to pulverize and loosen the tough sod in the lower part of the furrow slice. 248 SOILS AND FERTILIZERS A good seed bed cannot be made upon such a foun- dation. When the land is plowed so that the furrow slice is left at an angle of 30 to 45 degrees, the surface is corrugated and all vegetation is buried in loose soil. When land which has been plowed in this way is culti- vated and harrowed, a better seed bed is formed than is possible on a completely inverted furrow slice. Fig. 35. A poor way of plowing sod land (after Roberts). Fig. 36. Plowed land left in good condition for formation of seed bed (after Roberts). In plowing, it should be the aim to thoroughly pul- verize the soil, completely bury all surface vegetation, and leave the land in a corrugated condition with the furrow slice at an angle but firmly connected with the subsoil. The plowing should cause as thorough dis- integration of the soil as possible and this can best be accomplished by the use of a plow with a bold rather than too flat a moldboard. Roberts16 states that only about 10 per cent, of the energy required for plowing is used by the friction of the moldboard: " About 35 per cent, of the power necessary to plow is used by the friction due to the weight of the plow, and 55 per cent, by severing the furrow slice and the friction of PREPARATION OF SOILS FOR CROPS 249 the land slide." In the preparation of the seed bed, it is economy to secure as much pulverization of the soil by the action of the plow as possible rather than to leave too much for subsequent treatment. 332. Influence of Moisture Content of the Soil at the Time of Plowing. — The condition of the soil, particularly as to moisture content at the time of plow- ing, has much to do with the production of a good seed bed. If soils are too dry when plowed they fail to pulverize, and disking, harrowing, and in some cases light rolling, making additional expense, must be re- sorted to in order to produce a fine, mediumly compact and well pulverized seed bed. If clay soils are plowed when too wet, the pores of the subsoil become clogged, a condition known as puddling takes place, and the furrow slice dries and forms hard lumps and clods. The condition in which the soil is left after plowing, particularly in the case of clay soils, has much to do with the character of the seed bed and the subsequent yield of crops. 333. Influence Upon the Seed Bed of Pulverizing and Fining the Soil. — If a soil is lumpy, and the lower strata of the seed bed is not pulverized and firmed, the soil readily loses water by percolation, evaporation takes place rapidly and the crops are poorly fed because the roots are unable to penetrate the hard lumps and secure plant food. If a soil is in- clined to be lumpy, the cultivation including the plow- ing should be carried on largely with the view of thoroughly pulverizing the soil. When a seed bed is 250 SOILS AND FERTILIZERS well prepared, the soil warms up more readily. The loosening and pulverizing of the land enables the heat from the sun's rays to more readily penetrate the soil and bring the land into good condition for promoting growth. 334. Aeration of Seed Bed Necessary. — Air is required for functional purposes by the roots of crops. In sand and loam the air spaces make up a half or more of the total volume. With such soils it is not neces- sary to cultivate with the view of increasing the air spaces, but in compact soils, as heavy clays, plowing should result in aeration of the soil and an increase in the number of air spaces, as the air of the soil takes an important part in rendering plant food available. (See Section 53). If soils are plowed when too wet they are not sufficiently aerated. The amount and kind of cultivation to secure the ventilation and aeration neces- sary for crop production must be regulated according to the character of the soil as sand, clay or loam, and the climatic conditions. The cultivation which is given soils for purposes of conservation of the moisture also secures the proper aeration. 335. Preparation of Seed Bed Without Plowing. - Loam soils which have been subjected to a sys- tematic rotation of crops and upon which corn has been grown, need not be plowed but the seed bed for the succeeding grain crop can be prepared simply by disk- ing. Surface tillage of the corn crop has sufficiently loosened and aerated the soil and has caused an accu- mulation of available plant food near the surface which PREPARATION OF SOILS FOR CROPS 251 would be buried and be less available to the crop if the land were plowed too deeply. On heavy clay lands this method of preparing the seed bed without plowing is not advisable but on the silt soils of the northwest it is a practice which has given excellent results and is beneficial as a means of conserving the soil moisture. 336. Mixing of Sub-Soil With Seed Bed. — Some soils are improved by deep plowing and by mixing the surface soil and sub-soil to form the seed bed. Such soils are usually acid in character and contain a large amount of organic matter, in which case the mixing of the surface soil and subsoil improves both the physi- cal and chemical properties of the seed bed. In the case of sandy soils, the mixing of the surface soil with the sub-soil is not advantageous as it dilutes the stores of plant food which are greater in the surface soil ; then too the physical properties of the soil are not im- proved. The combining of the surface soil and sub- soil in the case of heavy clay should be done gradu- ally and at each period in the rotation after an appli- cation of farm manure. In the cultivation of clay soils, it should be the aim to secure a deep layer of thoroughly pulverized, aerated and fertilized soil. In the preparation of the seed bed the character and con- dition of the subsoil is equally as important as of the surface soil. 337. Cultivation to Destroy Weeds. — One of the chief objects of cultivation is to destroy weeds. Cul- tivation for this purpose should be given early in the 252 SOILS AND FERTILIZERS year before the weeds become firmly established. Weeds are most easily destroyed at the time of germ- ination and before the leaves appear above ground. The plow should be relied upon largely for the de- struction of deep rooted perennial weeds, while the cultivator is effectual for the destruction of annuals. When weeds are plowed under or destroyed by culti- .vation they add vegetable matter and humus to the soil and thus are made to improve the condition of the soil instead of reducing the yield of crops by appropriating fertility as they do if allowed to grow and mature. Cultivation which secures aeration of the soil and conservation of the soil moisture is also effectual for the destruction of weeds. 338. Influence of Cultivation Upon Bacterial Action. — The cultivation of the soil has a marked influence upon bacterial action. Some of the soil organisms as the nitrifying organisms, (See Section 139) require oxygen for their existence, hence culti- vation which increases the supply of oxygen in the soil increases the activity of such organisms. In acid peaty soils, aeration induces bacterial action which re- sults in more rapid decay and a lowering of the. per cent, of total organic matter including the deleterious organic acids. The neutralizing of the organic acids of soils by applications of lime and wood ashes hastens bacterial action. During the process of nitrifica- tion, the bacterial action is not alone confined to the nitrogenous compounds of the soil, the nitrifying organisms require phosphates as food which are left PREPARATION OF SOILS FOR CROPS 253 after nitrification in a more available condition as plant food91. The mineral as well as the organic matter of the soil is subject to the action of micro- organisms, and the cultivation which the soil receives can be made either to accelerate or to retard this action. Many of the chemical changes which take place in the soil resulting in the liberation of plant food are induced by micro-organisms, hence the rela- tion between cultivation of the soil and bacterial action. Each type of soil has its own characteristic microscopic flora. 339. Inoculation of Soils. — In old soils where the process of nitrification is feeble, it has been pro- posed to inoculate the soils with more active forms of bacteria so as to make the inert humus nitrogen more available as plant food. In order to secure the best results from inoculation, suitable food must be sup- plied for the organisms and any adverse condition, as excess of acids or alkalies, must be corrected. Most soils contain the requisite soil organisms but frequently they are unable to do their work because of unfavor- able soil conditions, as the presence of injurious matter or the lack of cultivation or food. For the production of legumes, inoculation of the soil is often beneficial. The commercial production and distribution of the organisms forming the nodules on the roots of clover and other leguminous crops and which cause fixation of atmospheric nitrogen, was first proposed and inau- gurated by Nobbe94 ; later a modified form of soil in- oculation was proposed by Moore87. The method 254 SOILS AND FERTILIZERS of inoculation consists in first multiplying the organ- isms in water containing nutritive substances, and then sprinkling the seeds with this solution diluted. Inoculation with soil from a field where clover or lupines have previously been grown has also been suc- cessful, particularly in reclaiming sandy waste lands where mineral fertilizers containing potash and phos- phates are used to furnish these elements of plant food, while the more expensive nitrogen is acquired indi- rectly from the air through the clover. Soils in a high state of productiveness are not usually in need of inoculation as they already contain all of the essen- tial soil organisms. 340. Cultivation for Special Crops. — While the general principles of cultivation apply to all crops, the extent to which loosening or compacting of a soil should be carried, must be determined by the charac- ter of the soil and the crop that is to be produced. The methods of cultivation must be varied to meet the requirements of different soils and different crops. The physical requirements of the soil for general farm crops are discussed in Chapters I. and XL For the production of a special crop, the cultivation must be adapted to the specific requirements of that crop. A knowledge of the requirements can best be obtained by a study of the subject as based upon experimental evidence. The cultivation of an untried crop should not be attempted on a large scale without a knowledge of the food requirements and the most suitable soil conditions. The production of sugar beets for PREPARATION OF SOILS FOR CROPS 255 the manufacture of sugar, flax for fine fiber, or tobacco under shade, requires a high degree of both knowledge and skill. For the production of special crops the preparation of the seed bed and the subsequent cultivation of the crop are matters of prime importance, and should receive careful consideration on the part of the cultivator. Many times agricultural industries undertaken in new countries have failed because the cultivation of the special crop used in the industry has not been successfully accomplished on account of lack of knowledge of the cultural methods necessary for successful crop production. 341. Cultivation to Prevent Washing and Gully- ing of Land. — In regions of heavy rain fall, rolling lands of clay texture often become gullied by the water flowing in large amounts over the surface. Under such conditions the preparation of a seed bed, and cultivation of the soil so as to prevent washing are often difficult problems. To prevent gullying, the water currents should be divided as much as possible by plowing narrower 'lands' and by increasing the num- ber of shallow dead furrows. The larger drains should be constructed with the view of preventing the forma- tion of deep gullies, this can in part be accomplished by encouraging the growth of special grasses with fibrous roots which serve as soil binders. Soils which gully are improved by the addition of farm manures and other humus forming materials which bind the soil particles ; also by seeding and cultivating at right angles to the slope of the land so as to break the force 256 SOILS AND FERTILIZERS of the water. The water should be encouraged to per- colate through the soil rather than to flow over the surface. (See Section 25). 342. Bacterial Diseases of Soils. — Many of the bacterial diseases to which crops are subject are caused primarily by a diseased condition of the soil. These diseases can often be held in check by the right kind of cultivation, by securing good drainage and by proper soil ventilation supplemented with the application of alkaline matter as wood ashes and land plaster. Both bacterial and fungus diseases of soils are capable of being controlled by cultivation particularly when the cultivation improves the general sanitary condition of the soil. With the improvement of the sanitary con- dition, there is less liability of bacterial diseases becom- ing established and causing destruction of the crop. The use of soil disinfectants is possible only when a small area is involved ; they are not applicable to large tracts as they destroy the beneficial as well as the injurious soil organisms. A good sanitary condi- tion of the soil is as essential for the production of crops as are suitable hygienic surroundings for the rearing of live stock. Sunlight and air are important factors in bringing about an improved sanitary condi- tion of diseased soils. By the rotation of crops many bacterial diseases as flax wilt and clover sickness are held in check. Some bacterial diseases are dissemin- ated by the use of infected seed. By sprinkling the seed grain with a disinfectant as a dilute solution of formalin (i pound of formalin in 50 gallons of water) PREPARATION OF SOILS FOR CROPS 257 bacterial diseases, as grain smuts are held in check. Low forms of plants, as fungi, also develop in soils when conditions are favorable, and they take an im- portant part in changing the character of the soil ; their action may be either beneficial or injurious de- pending upon the condition of the soil. Some of the organisms which are propagated in the soil cause bac- terial diseases of dairy and other farm products. There is a very close relationship between soil sanitation, crop diseases, and the quality of agricultural products. 343. Influence of Crowding Plants in the Seed Bed. — The number of plants which a seed bed should produce is dependent mainly upon the supply of water and plant food. By means of thick or thin seeding the general character of crops may be influenced within definite limits. Either an excessive or a scant amount of seed gives poor results. If over crowded plants fail to develop normally it is either for want of plant food or water or because of lack of room for de- velopment. Experiments have shown that excessive amounts of seed wheat, as more than 100 pounds per acre of spring wheat, do not give good results. Each crop has its limits beyond which it is not desirable to crowd the plants in the seed bed. When there is ex- cessive crowding, unhygienic conditions prevail and the lack of air, sunlight and good ventilation encourage bacterial diseases, while on the other hand too few plants in the seed bed favor the growth of weeds and an abnormal development of the crop. In the seeding of grains and other farm crops, the amount of seed to 258 SOILS AND FERTILIZERS be used per acre should be determined by the quality of the seed and the local conditions, as climate and soil, together with any special objects desired as in- fluencing the composition and character of the crop. 344. Selection of Crops. — The selection of the most suitable crops to be grown is largely a local problem and must be determined by climatic and soil conditions. The preferences of farm crops for certain types of soil are discussed in Sections n to 17, and it is not advisable to attempt to grow crops upon soils to which they are not naturally adapted or under un- favorable climatic conditions. Practical experience is the best guide to follow in regard to the selection of crops or the most suitable line of farming to follow, and it will be found that this experience is usually in harmony with the laws governing the conservation of the fertility of the soil. Temporary methods of farming, as exclusive grain raising, can be followed for a short time on new soils but it is desirable that each type of soil should be subjected to a judicious system of cultivation, fertilizing and cropping rather than to the production of one or only a few market crops at random. The selection of the farm crops and their utilization for market or feeding purposes should be determined mainly by the system of farming that is best adapted to the soil of the farm, and the farm should be managed largely with the view of maintaining the fertility of the soil. 345. The Inherent and Cumulative Fertility of Soils95. — There is present in nearly every soil a vari- PREPARATION OF SOILS FOR CROPS 259 able amount of inherent fertility produced by disin- tegration and other changes to which soils are subject. In some long-cultivated soils the amount of fertility produced annually by weathering and natural agencies is sufficient to yield from 10 to 15 bushels of wheat. This does not represent the maximum crop producing power of the soil but simply the inherent or natural fertility. When the natural fertility is reinforced with farm manures and other fertilizers, cumulative fertility has been added and maximum yields of crops are secured. In many soils there are large amounts of cumulative fertility or residues from former appli- cations of manures. The condition of a soil as to crop producing power is dependent both upon the inherent and the cumulative fertility, as well as upon the mechanical condition of the soil. In the production of crops, it should be the aim to utilize all of the in- herent fertility to the best advantage, and to add to the cumulative fertility so that the stock of total fer- tility may be increased. Soils of the highest fertility are those which are composed of a large amount of silt or particles of equivalent value, are well drained, but sufficiently retentive of moisture for crop production, and are of good capillarity. Such soils have usually been deposited by water ; they are uniform in texture, of great depth and contain large amounts of organic matter rich in nitrogen and mineral matter contain- ing all of the essential elements of plant food. When such soils are cultivated, the organic matter readily undergoes decay with liberation of plant food. 346. Balanced Soil Conditions. — A high state of 260 SOILS AND FERTILIZERS fertility necessitates a balanced condition of the physi- cal and chemical properties of a soil. Some soils are of good texture and have all of the necessary physical requisites for crop production but fail to produce good crops because of a scant supply of the essential ele- ments of plant food. Other soils contain the neces- sary plant food but are unproductive because of poor physical conditions. Soils may be unproductive on account of either chemical or physical defects causing an unbalanced condition of the various factors of soil fertility. In the cultivation of a soil it should be the aim to discover any defect and then to apply the necessary corrective measures. Soil problems are ex- tremely varied in character and the cultivator of the soil should seek aid jointly from the sciences of chem- istry, physics, biology and geology, and also from prac tical experience founded upon observations in the cultivation of soils and the production of crops. The utilization and maintenance of the fertility of the soil necessarily form the basis of any rational agricultural system. CHAPTER XIV LABORATORY PRACTICE The laboratory practice is an essential part of the work in Soils and Fertilizers as the experiments illustrate many of the funda- mental principles of the subject. The student should endeavor to cultivate his powers of observation so as to grasp the principles in- volved in the work rather than to do it in a mere mechanical or perfunctory way. Neatness is one of the essentials for success in laboratory practice ; an experiment performed in a slovenly way is of but little value. A careful and systematic record of the laboratory work should be kept by the student in a suitable note-book. In recording the re- sults of an experiment the student should give in a clear and con- cise form the following : 1 i ) Title of the experiment. (2) How the experiment is performed. (3) What was observed. (4) What the experiment proves. The note-book should be a complete record of the student's in- dividual work, and should be written up at the time the experi- ments are performed. The student is advised to review at the time the experiments are performed those topics presented in the text which have a bearing upon the experiments, so that a clearer conception can be gained of the relationship between the laboratory work and that of the class room. Students who have had but little laboratory practice are advised to study the chapters on Laboratory Manipulation, and Water and Dry Matter, given in " The Chemistry of Plant and Animal Life." Some of the pieces of apparatus are loaned to the student when needed to perform the experiment ; for this apparatus a receipt is taken, and the student is credited with the apparatus when it is returned. The following are supplied to each student : 262 SOILS AND FERTILIZERS Crucible Tongs. Pkg. Filter Paper. Test Tube Clamp. Evaporator. Stirring Rod. 3 Beakers. 6 Test Tubes, i Test Tube Stand, i Funnel, i Mortar and Pestle. 2 Bottles. Large Cylinder. Sand Bath. Hessian Crucible. Wooden Stand. Tripod. Ring Stand and 3 Rings. Single Clamp. Burner and 2Ft. RubberTubing Brush. The student should plan to make judicious use of his time while in the laboratory. Experiment No. i. Determination of the Hydroscopic Moisture of Soils. Weigh in grams to the second decimal place an aluminum dish Fig. 37. Apparatus for Determining Moisture Content of Soils. or tray. Place about ten grams of air dry soil in the dish and weigh again. Then place the dish containing the soil in the water EXPERIMENTS 263 oven and leave it four hours for the soil to dry. Cool and weigh at once so there may be as little absorption of water from the air as possible. From the loss of weight, calculate the per cent, of hydroscopic moisture in the soil. (Soils from the students' home farms are to be used in experiments Nos. i, 2, 4, 6, 9, 12, 14, 16, 17, and 19, each student working with his own soil). Experiment No. 2. Determination of the Capacity of Loose Soils to Absorb Water. To 100 grams of air dry soil in a beaker, add 100 cc. of water. Mix the soil and water, then pour the mixture on a filter paper fitted into a funnel and previously saturated, but not dripping. For transferring the soil, 50 cc. more water may be used. Measure the drain water in a graduate. To prevent evaporation, keep the moist soil in the funnel covered with a glass plate. Deduct the leachings from the total water used. Calculate the per cent, of waiter retained by the air dry soil. Repeat the experiment, using sand, and note the difference in absorptive power. Repeat, using 95 per cent, of sand and 5 per cent, of dry and finely pulverized manure. Experiment No. 3. Determination of the Capillary Water of Soils. For this experiment, a sample of soil directly from the field is to be used. The sample is to be taken at a depth of from 3 to 9 inches or at any depth desired. One hundred grams of soil are weighed into a tarred drying pan, exposed in a thin layer to the room temperature for twenty-four hours and then reweighed. After an interval of from two to four hours the soil is weighed again, and if the weight is fairly constant the per cent, of water lost by air drying, representing the capillary water of the soil at the time of sampling, is calculated. If desired this experiment can be repeated, using different types of soil, as sand, clay and loam. Experiment No. 4. Capillary Action of Water Upon Soils. Firmly tie a piece of linen cloth over the end of along glass tube 4 inches in diameter, then fasten a piece of wire gauze over the 264 SOILS AND FERTILIZERS cloth. Fill the tube with sandy soil (No. i). Compact the soil after the addition of each measured quantity of soil by allowing the weight from the compaction machine to drop twice from the 12 inch mark. Fig. 38. Capillary Action of Water on Soils. In a similar way, fill a second and a third tube respectively with clay and loam ; then immerse the lower ends of the tubes in a cylinder of water and support the tubes, as shown in the illustra- tion. Measure each day for one week the height to which the water rises in the soils. If desired, three additional tubes filled loosely with the soils can be used, and the influence of compaction upon the capillary rise of water in the soils noted. Experiment No. 5. Influence of Manure and Shallow Surface Cultivation Upon the Moisture Content and Temperature of Soils. Weigh and fill four boxes, each a foot square and a foot deep, as EXPERIMENTS 265 follows : One with air dry sand, one with clay, one with loam, and one with sand containing 5 per cent, of fine dry manure. Deter- mine the hydroscopic moisture of each sample. Weigh the boxes after adding the soils which should be moderately compacted. To each add the same amount of water slowly from a sprinkling pot, carefully measuring the water used. The soil should be well moistened, but not supersaturated. Each box is to receive shal- low surface cultivation, using for the purpose a gardener's small tool. Leave the boxes exposed to the sun or in a moderately warm room. At the end of two or three days take a sample of soil from the center of each box at a depth of four inches and determine the moisture content as directed in Experiment No. i. Note the differ- ences in moisture content. Weigh the boxes. Take the tempera- ture of the soil in each box. Experiment No. 6. Weight of Soils. Determine the cubic contents of a box about 4 inches square. Weigh the box. Determine its weight when filled, not compacted, wTith air dry sand, with clay, with loam and with peaty soil. Com- pute the weight per cubic foot of each soil. Fig. 39. Determining the Weight of Soils. Experiment No. 7. Influence of Color Upon the Temperature of Soils. Expose to the sun's rays, dry clay, dry sand, and moist and dry peat. After two hours exposure take the temperature of each. The bulb of the thermometer should just be covered with the soil. All of the observations should be made under uniform conditions. 266 SOILS AND FERTILIZERS Experiment No. 8. Movement of Air Through Soils. Fill a tube 12 inches high and 3 inches in diameter with sifted loam soil without compacting. Attach the soil tube to the aspira- tor by means of a rubber tube. Note the time required to draw 5 liters of air through the soil. In like manner fill tubes with sand, Fig. 40. Apparatus to Determine Rate of Air Movement Through Soils. (Adapted from Bui. 107, U. S. Dept. Agr., Office of Expt. Stations). gravel, peat, and clay, and determine the time required for 5 liters of air to be aspirated through each. In filling the tubes, care should be taken that all are treated alike. Repeat the experiment using soil from your own farm loosely filling one tube, and mod- erately compacting another tube with the compacting machine. Note the difference in the time required for the air to pass through the loose and the compact soil. Experiment No. 9. Separation of Sand, Silt and Clay. For this experiment, the student should use some of the soil from his home farm. Ten grams of soil which have been passsd through a sieve with holes .5 mm. in diameter are placed in a mor- EXPERIMENTS 267 tar, and about 20 cc. of water added. The soil is pestled with a rubber tipped pestle with the object of separating adhering parti- cles without pulverizing the individual soil grains. After two or three minutes rubbing, more water is added and the soil and water are allowed to sediment for about one minute ; the turbid liquid is then decanted into a beaker. This process of soft pestling and decantation is repeated two or three times until the remaining soil grains appear free from adhering smaller particles. With some soils this is a tedious process. The contents of the mortar are then transferred to the beaker and enough water is added to nearly fill the beaker. The contents of the beaker are thoroughly stirred, and after three to five minutes sedimentation, the turbid liquid is decanted into a second beaker leaving the sediment in the first beaker. More water is added to the first beaker and the process of stirring, sedimentation and decantation are repeated until the sediment consists mainly of clean and fine sand. The turbid liquid in the second beaker is decanted into a large cylinder ; the sedi- ment in the second being washed with more water and the wash- ing added to the cylinder. It is to be noted that the sediment in the second beaker is composed of finer particles than the sediment in the first beaker. The sediment in the first beaker consists mainly of medium and fine sand, and in the second beaker, of fine sand and coarse silt. Some sand particles are carried along in the washings into the large cylinder. It is difficult to make even an approximate separation of a soil into sand, silt and clay particles. In the mechanical analysis of soil, the chemist uses the microscope to determine when the separations are reasonably complete. The sediment in the cylinder consists mainly of silt. The fine parti- cles which remain suspended in the water of the cylinder and cause the roiled appearance are mainly the clay particles. In this experiment note approximately what grades of soil particles pre- dominate in your soil. Save the liquid in the cylinder for the next experiment. Experiment No. 10. Sedimentation of Clay. In each of three separate cylinders or beakers place 200 cc. of the turbid liquid saved from Experiment No. 9. To beaker No. I, add .5 gm. calcium hydroxid and stir. To beaker No. 2, add i gm. of calcium hydroxid and stir. The third beaker is used for pur- 268 SOILS AND FERTILIZERS poses of comparison and no calcium hydroxide is added. After 24 hours examine the three beakers and note the influence of the cal- cium hydroxid in precipitating the clay and clarifying the liquid. Experiment No. n. Properties of Rocks from which many Soils are Derived. Study the laboratory samples of rocks and fill out the following table : Comparative General vSoluble Rocks. Hardness. Color. Form. in HC1 Feldspar .... Mica Quartz Granite Hornblende. . . limestone . . . Experiment No. 12. Form and Size of Soil Particles. (Note. Special directions for manipulating the microscope, placing the material on the microscopical slide, and focusing will be given by the instructor). Place on a microscopical object slide a small amount of soil, dis- tribute it in a thin layer, as directed by the instructor, and examine with a low power microscope. Observe the form and size of the soil particles, distinguish the various grades of sand, silt and clay, and make drawings of some of the particles. Experiment No. 13. Pulverized Rock Particles. Examine with a low power microscope samples of pulverized mica, feldspar, granite, and limestone. Note any similarity to the soil particles examined in Experiment No. 12. Experiment No. 14. Reaction of Soils. For this experiment use peaty, mildly alkaline and clay soils. Bring in contact with each soil, moistened with distilled water, pieces of sensitive red and blue litmus paper. Note any changes in color of the litmus paper and state what the results show. In a similar way test the soil from your own farm . EXPERIMENTS 269 Experiment No. 15. Absorption of Gases by Soils. Weigh 50 grams of soil into a wide mouthed bottle, add 50 cc. of wgter and i cc. of strong ammonia. Note the odor. Cork the bottle, shake, and after 24 hours again note the odor. To what is the absorption of the ammonia due? Is this a physical or a chem- ical change. Define fixation. Experiment No. 16. Acid Insoluble Matter of Soils. Weigh 10 grams of soil into a beaker, add 100 cc. hydrochloric acid (50 cc. strong acid and 50 cc. H2O); cover the beaker with a watch glass ; heat on the sand bath in the hood for two hours, re- placing the acid solution, if necessary, in case excessive evapora- tion takes place. Filter, transfer and wash the residue, using 50 cc. distilled water. Note the appearance and quantity of insoluble residue. Of what does it consist ? What is its value as plant food ? How does it resemble the original soil and in what ways does it differ? Save the filtrate for the next experiment. Experiment No. 17. Acid Soluble Matter of Soils. Divide the filtrate from the preceding experiment into three equal portions, (i) To one portion add ammonia until alkaline. The precipitate formed consists of iron and aluminum hydroxid and phosphoric acid. Note the color and gelatinous appearance of this precipitate. When dried it occupies only a small volume. Filter and remove this precipitate. This filtrate contains lime, magnesia, potash and soda. To the filtrate add 20 cc. of ammonium oxalate, warm on the sand bath and note any precipitate of calcium oxalate that is formed. (2) Evaporate the second portion nearly to dry- ness. Add 20 cc. distilled H2O and 3 cc. HNO3 ; warm to dissolve any residue. Add 5 to 7 cc. of ammonium molybdate, heat gently and shake. The precipitate is ammonium phosphomolybdate, which contains the element P in chemical combination. (3) Evaporate third portion in the evaporating dish on the sand bath. What does the residue consist of and what elements does it con- tain? 270 SOILS AND FERTILIZERS Experiment No. 18. Extraction of Humus from Soils. Ten grams of soil are placed in a bottle (preferably a glass stop- pered one) and 200 cc. H2O and 5 cc. HC1 added. Shake aad allow 10 to 24 hours for the acid to dissolve the lime so that the humus can be dissolved by the alkali. Filter the acid and wash the soil on the filter with distilled water until the washings are no longer acid to litmus paper. Transfer the soil to the bottle again, add loo cc. H2O and 5 cc. KOH solution. Shake, and after two to four hours filter off some of the solution, which is dark-colored and contains dissolved humus compounds. To 10 cc. of the filtered humus solution, add HC1 until neutral. The precipitate that is formed is mainly humic acid and soil humates. Evaporate a second portion of 10 to 20 cc. to dryness ; the black residue obtained is humus material extracted from the soil. Experiment No. 19. Nitrogen in Soils. Mix 5 grams of soil and an equal bulk of soda lime in a mortar ; transfer to a strong test tube. Connect the test tube with a deliv- ery tube which leads into another test tube containing distilled water. Heat cautiously the test tube containing the soil and soda lime with the Bunsen burner, for from 5 to 10 minutes. Test the liquid with litmus paper and note the reaction. Soda lime aided by heat decomposes the organic matter of the soil and forms CO2> H2O and NH3. The nitrogen in the form of ammonia is distilled and absorbed by the water in the second test tube ; the reaction is due to the presence of the ammonia. Experiment No. 20. Testing for Nitrates. Dissolve about 50 milligrams of sodium or potassium nitrate in loo cc. H2O. To 15 cc. of this solution, add 2 cc. of a dilute and clear solution of FeSO4, and place the test tube in a cylinder. Through a long stemmed funnel add 2 or 3 cc. H2SO4. Observe the dark brown ring that is formed ; H2SO4 liberates HNO3 as a free acid, which in turn changes the iron from the ferrous to the ferric state ; the dark brown color is due to the nitric acid forming intermediate iron compounds during this operation. EXPERIMENTS 271 Experiment No. 21. Volatilization of Ammonium Salts. In separate test tubes, place about .1 gtn. each of ammonium car- bonate and ammonium sulphate. Apply heat gently to each and observe the result. Observe that the ammonium carbonate readily volatilizes and some is deposited on the walls of the test tube while the ammonium sulphate is much less volatile. In poorly venti- lated barns, deposits of ammonium carbonate are frequently found. Experiment No. 22. Testing for Phosphoric Acid. Dissolve .5 gm. bone ash in 15 cc. H2O and 3 to 5 cc. HNO3 and filter. To the warm filtrate, add 5 to 7 cc. ammonium molybdate and shake. The yellow precipitate formed is ammonium phospho- molybdate. See Experiment No. 17. Experiment No. 23. In a test tube, heat .5 gm. of bone ash with 20 cc. distilled H2O ; filter. To the warm filtrate, add 5 cc. ammonium molyb- date and shake. Note the result as compared with that when HNO3 was used with the distilled water. What does the result show ? Experiment No. 24. Preparation of Acid Phosphate. Place 100 gms. bone ash in a large lead dish. Add slowly and with constant stirring 100 gms. 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 pulverize and examine. The mixing of the acid and phosphate should be done in a place where there is a good draft. Test yz gram for water soluble phosphates as directed in Experiment No. 23. Experiment No. 25 Solubility of Organic Nitrogenous Compounds in Pepsin Solution. Prepare a pepsin solution by dissolving 5 gms. of commercial pepsin in a litre of water, adding i cc. of strong HC1. Place in separate beakers .5 gm. each of dried blood, tankage and bone ash. Add 200 cc. of pepsin solution to each and place the beakers in a water bath kept at a temperature of about 40 deg. C. Stir occasion- 272 SOILS AND FERTILIZERS ally, and at the end of five hours observe the comparative amounts of insoluble matter remaining in the beakers, also the color and appearance of the solution in each beaker. See Section 158. Experiment No. 26. Preparation of Fertilizers. Mix in a box 200 gms. acid phosphate, (saved from Experiment 24) 50 grams kainit, and 50 gms. sodium nitrate. Calculate the percentage composition of this fertilizer and its trade value. Experiment No. 27. Testing Ashes. Test samples of leached and unleached ashes in the way de- scribed in Section 240. Experiment No. 28. Extracting Water Soluble Materials from a Commercial Fertilizer. Dry and weigh a 7 cm. filter paper. Fit it in a funnel, and place in it 2 gms. of commercial fertilizer. Pass through the filter, a little at a time, a half litre of pure water at about 40 deg. C. (dis- tilled water preferred). Transfer the filter paper and contents to a watch glass, dry in a water oven, weigh and calculate the per cent, of material extracted by the water. If the fertilizer is made of such materials as acid phosphate, kainit, muriate or sulphate of potash, nitrate of soda and sulphate of ammonia, from 60 to 90 per cent, will dissolve. Inspect the insoluble residue and note if it is composed of dried blood, bones or animal refuse materials. In a high grade complete commercial fertilizer, from 40 to 80 per cent, or more should dissolve in water. Experiment No. 29. Influences of Continuous Cultivation and Crop Rotation upon the Properties of Soils. For this experiment, a soil that has been under continuous culti- vation, and also one of a similar character from an adjoining field where the crops have been rotated and farm manures have been applied, should be used. Make the following determinations with each soil : Weight per cubic foot. Capacity to hold water. EXPERIMENTS 273 Note the color of each, and the percentages of nitrogen and humus obtained by chemical analysis. Experiment No. 30. Summary of Results of Tests with Home Soil. Hydroscopic moisture as determined in Experiment No. i. Capacity of the loose soil to absorb water in Experiment No. 2. Height of rise of capillary water in tube in Experiment No. 4. Weight per cubic foot in Experiment No. 6. Prevailing kind of soil particles in Experiment No. 9. Reaction of soil in Experiment No. 14. Amount of acid soluble matter in Experiment No. 17. Amount of humus extractive material in Experiment No. 18. Amount of lime. Crops most suitable for production upon this soil as indicated by physical and chemical tests. How does this agree with your experience with the crops raised on the soil ? Probable deficiencies or weak points as indicated by tests or past experience. What is the most suitable line of farming to follow with this soil in order to conserve its fertility ? Scheme of Soil Classification. (Adapted from Bureau of Soils Report, U. S. Dept. Agr). Coarse sand contains more than 20 per cent, of coarse sand and more than 50 per cent, of fine gravel, coarse sand, and medium sand, less than 10 per cent, of very fine sand, less than 15 per cent, of silt, less than 10 per cent of clay, and less than 20 per cent, of silt and clay. Medium sand contains less than 10 per cent, of fine gravel, more than 50 per cent, of coarse, medium, and fine sand, less than 10 per cent, of very fine sand, less than 15 per cent, of silt, less than 10 per cent, of clay, and less than 20 per cent, of silt and clay. Fine sand contains less than 10 per cent, of fine gravel and coarse sand, more than 50 per cent, of fine and very fine sand, less than 15 per cent, of silt, less than 10 per cent, of clay, and less than 20 per cent, of silt and clay. Sandy loam contains more than 20 per cent, of fine gravel, coarse sand and medium sand, more thanr2o per cent, and less than 35 (18) 274 SOILS AND FERTILIZERS per cent, of silt, less than 15 per cent, of clay, and less than 50 per cent, of silt and clay. Fine sandy loam contains more than 40 per cent, of fine and very fine sand and more than 20 per cent, and less than 50 per cent, of silt and clay, usually containing 10 to 35 per cent, of silt and from 5 to 15 per cent, of clay. Silt loam contains more than 55 per cent, of silt and less than 25 per cent, of clay. Loam contains less than 55 per cent, of silt, and more than 50 percent, of silt and clay, usually containing from 15 to 25 per cent, of clay. Clay loam contains from 25 to 55 per cent, of silt, 25 to 35 per cent, of clay, and more than 60 per cent, of silt and clay. Clay contains more than 35 per cent, of clay. Sandy clay contains more than 30 per cent, of coarse, medium, and fine sand, less than 25 per cent, of silt, more than 20 per cent, of clay, and less than 60 per cent, of silt and clay. Silt clay contains more than 55 per cent, of silt and from 25 to 35 per cent, of clay. ^^ OF THE UNIVERSITY OF OF THE UNlVERStT REVIEW QUESTIONS CHAPTER I. i. 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 be the order? 5. What is the absolute and what the apparent specific gravity of soils? 6. Define the terms : Skeleton, fine earth, fine sand, silt and clay. 7. What are 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? ir. 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 struc- ture 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 required to produce an average grain crop, and how do the rainfall and the water removed in crops dtfring the growing season com- pare? 17. In what forms may water be present in soils? 18. What is bottom water and when may it be utilized by crops ? 19. What is capillary water? 20. Explain the capillary movement of water. 21. Explain how the capillary and non-capillary spaces in the soil may be influenced by cultivation. 22. What is hydro- scopic water and of what value is it to crops ? 23. What is perco- lation ? 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 evapora- tion ? 29. Why is it necessary to cultivate the soil after a rain ? 30. Explain the movement 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 per- meability of a soil? 37. How may cultivation influence permea- bility of a soil ? 38. How may commercial fertilizers influence 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 agricultural value of a country ? 42. What are the sources of heat in soils? 43. 276 SOILS AND FERTILIZERS To what extent does the color of soils influence the temperature ? 44. What is the specific heat of soils ? 45. To what extent does drainage influence soil temperature? 46. How do manured and unmanured land compare as to temperature ? 47. VVhat 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. WThat effect does a weak current of electricity have upon crop growth ? 52. Do all soils possess the same power to absorb gases ? Why? CHAPTER II. 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. Explain 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 following rocks and minerals and state the quality of soil which each produces : Granite, mica, hornblende, zeolites, kaolin, apatite, and limestone. CHAPTER III. 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. WThat influence would o. 10 per 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 REVIEW QUESTIONS 277 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 acids be employed in soil analysis? 87. Why are dilute organic acids used ? 88. Is the plant food equally distributed in both sur- face and subsoil ? 89. Do different grades of soil particles, from the same soil, have the same composition? 90. What are "alkali soils " ? 91. 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. 101. 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. To what 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 many different methods of farming influence the humus content of soils? CHAPTER IV. no. What may be said regarding the importance of nitrogen as plant food? in. What are the functions of nitrogen in plant nu- trition ? 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 experi- ments. 117. How did field results compare with laboratory exper- iments? 1 1 8. In what ways were the conditions of field experi- ments 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 Hell- riegel ? 122. What is the source of the soil's nitrogen ? 123. How may the organic nitrogen compounds of the soil vary as to com- plexity ? 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 ammonium compounds found in 278 SOILS AND FERTILIZERS 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 content ? 130. What methods of cultivation cause the most rapid decline in the nitro- gen 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 temperature, 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 pro- duce nitrates, nitrites, and ammonia? 139. What chemical products do these various organisms produce ? 140. Why are soils sometimes inoculated with organisms? 141. Why does summer fallowing of rich lands cause a loss of humus and 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 composition, 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 employed to detect the presence of leather, hair, and wool waste in fertilizers ? Why are these ma- terials 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 sul- phate, as a fertilizer, compare in value with nitrate of soda? 153. What is the difference between the nitrogen content and the am- monia content of fertilizers ? CHAPTERS V AND VI. 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 manure? 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. W7hat 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 REVIEW QUESTIONS 279 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 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 ? 191. 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 in a field? Why? 198. At what rate per acre may manure be used? 199. 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 ? CHAPTER VII. 204. What may be said regarding the importance of phosphorus 280 SOILS AND FERTILIZERS 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 commercial sources of phosphate fertilizers ? 209. Give the four calcium phosphates and their relative fertilizer values. 210. Define reverted phosphoric acid. 211. Define available phos- phoric acid. 212. In what forms do phosphate deposits occur? 213. State the general composition of phosphate rock. 214. Ex- plain the process by which acid phosphates are made. Give re- actions. 215. How is the commercial value of phosphoric acid de- termined? 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 dissolved bone? 220. How is bone-black obtained, and what is its value as a fertilizer? 221. How are phosphate fer- tilizers applied to soils? In what amounts? 222. How may the phosphoric acid of the soil be kept in available condition ? CHAPTER VIII. 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 an ash ? 234. Of what value, as fertilizer, are hard- and soft- coal ashes? 235. What is the fertilizer 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 determined? 241. How are potash fertilizers used? 242. Why is it sometimes necessary to use a lime fertilizer in connection with a potash fertilizer? CHAPTER IX. 243. What can be said regarding the importance of lime as a plant food? 244. To what extent is lime removed in crops? 245. To what extent do soils contain lime ? 246. What are the lime fer- tilizers? 247. Explain the physical action of lime fertilizers. 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 REVIEW QUESTIONS 281 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? Explain its action. 258. Are sea- weeds of any value as fertilizer? CHAPTER X. 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. Explain how a commercial fertilizer is made. 263. Why are the analysis and inspection of fertilizers necessary ? 264. What are the usual forms of nitrogen in commercial fertilizers? 265. Of phosphoric acid and potash ? 266. How is the value of a commer- cial fertilizer determined? 267. What is gained by home mixing of fertilizers? 268. What can be said about the importance of tillage when fertilizers are used ? 269. How are commercial fer- tilizers sometimes injudiciously used? 270. How may field tests be conducted to determine a deficiency in available nitrogen, phos- phoric acid, or potash? 271. To determine a deficiency of two elements? 272. How are the prelinilbary results verified ? 273. Why is it essential that field tests with fertilizers be made? 274. Under what conditions does it pay to use commercial fertilizers ? 275. What is the result when commercial fertliizers are used in excessive amounts? 276. Under ordinary conditions, what special help do the following crops require : Wheat, barley, corn, potatoes, mangels, turnips, clover and timothy? 277. In what ways do commercial fertilizers and farm manures differ? CHAPTER XI. 278. Does the amount of fertility removed by crops indicate the nature of the fertilizer required ? In what ways are plant ash analyses valuable ? 279. Explain the action of plants in render- ing 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 require- ments 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 a rotation ? On what soils does flax thrive best ? 289. What is the essential point to observe in the manuring of potatoes ? 290. What kind of manuring do sugar-beets require? 291. Why should the 282 SOILS AND FERTILIZERS manuring of mangels be different from that of turnips? 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 ? For garden crops, for orchards, or lawns ? CHAPTER XII. 295. What is the object of rotating crops? 296. Should the whole farm undergo the same rotation system? 297. What is meant by soil exhaustion ? 298. What are the nine important principals to be observed in a 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 ? 30 r. What is the object of growing crops of dissimilar feed- ing 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 con- dition of the soil ? 305. How may the best use be made of the soil water ? 306. How 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 regarding long and short-course rotations? 310. How is the conservation of fertility 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 com- pared in Section 323? 313. Is it essential that all elements re- moved in crops should be returned 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 fertility ? 317. Why in continued grain culture does the loss of nitrogen from a soil exceed the amount removed in the crop? CHAPTER XIII. 318. Why do soils need further treatment for the preparation of the seed bed? 319. Why should different soils receive different methods of treatment in the preparation of the seed bed ? 320. How would you determine the best treatment to give a soil for the preparation of the seed bed ? 321. How do different methods of plowing influence the condition of the seed bed ? 322. Why does complete inversion of sod frequently form a poor seed bed ? 323. How should the plowing be done to form a good seed bed? 324. Why is it economy to pulverize the soil as much as possible when it is plowed? 325. What effect does the moisture content of the REVIEW QUESTIONS 283 soil at the time of plowing have upon the condition of the seed bed ? 326. What effect does an excess of moisture have upon the plowing and working of clay soils? 327. In what condition should the seed bed be left as to fineness ? 328. What is gained by fining and moderately firming the seed bed ? 329. Why is aeration of the soil necessary? 330. Why do different soils re- quire different amounts of aeration? 331. Under what conditions can the seed bed be prepared without plowing? 332. On what kinds of soil is such a practice not advisable? 333. When is it advisable to mix the sub soil with the surface soil? 334. When is it not advisable to mix the surface soil and sub soil? 335. How can the plowing and the cultivation of the soil best be carried on to destroy weeds? 336. In what way does cultivation influ- ence bacterial action in the soil? 337. What classes of com- pounds in the soil are subject to bacterial action? 338. How does the action of bacteria affect the supply of available plant food ? 339. What is meant by the inoculation of soils? 340. In what two ways can this be accomplished? 341. What soils are most improved by inoculation ? 342. What soils are least in need of inoculation ? 343. What other treatment must often be combined with inoculation? 344. Why do different crops require different cultivation ? 345. How can the best kind of cultivation for a crop be determined? 346. How can soils best be cultivated to prevent washing and gullying? 347. What treatment should such soils receive to be permanently improved? 348. What relationship exists between bacterial diseases of soils and crops? 349. What treatment should soils receive to prevent bacterial diseases? 350. How can the spreading of bacterial diseases through infected seed be prevented? 351. Why must the sanitary condition of a soil for crop production be considered? 352. What effects do some forms of fungi have upon soils? 353. In what way does thick or thin seeding affect plant growth? 354. What effect does abnormal crowding of plants have upon growth? 355. How would you determine the most advantageous quantity of seed for crop production ? 356. How would you determine the most suit- able crop for production upon any soil? 357. What should be the aim in the selection of crops for soils? 358. Why should the crop selected vary with different types of soil ? 359. What is the inherent fertility of soils? 360. What is the cumulative fertility of soils? 361. How can the total fertility of soils be best in- creased? 362. Describe soils of the highest fertility. 363. Why must the amount of plant food as well as the physical condition of the soil be considered in the improvement of soils ? 364. What relation does the fertility of the soil bear to any agricultural system ? REFERENCES 1. 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. 8. Maryland Agricultural Experiment Station, Bulletin No. 21. 9. Minnesota Agricultural Experiment Station, Bulletin No. 41. 10. Osborne : Journal of Analytical Chemistry, Vol. II, Part 3. 11. Wiley : Agricultural Analysis, Vol. I. 12. Hellriegel : Calculated from Beitrage zu den Naturwissen- schaft Grandlagen des Ackerbaus. 13. King : Wisconsin Agricultural Experiment Station, Report 1889. 14. Unpublished results of author. 15. King : Soils. 1 6. Roberts : Fertility of the Land. 17. Minnesota Agricultural Experiment Station, Bulletin No. 41. 18. Minnesota Agricultural Experiment Station, Bulletin No. 53. 19. Whitney : Division of Soils, U. S. Department of Agriculture, Bulletin No. 6. 20. Merrill : Rocks, Rock-weathering and Soils. 21. Miintz : Comptes Rendus de 1' Academic des Sciences, CX (1890). 22. Storer : Agriculture, Vol. I. 23. Dyer: Journal of the Chemical Society, March, 1894. 24. Goss : Association of Official Agricultural Chemists, Report 1896. 25. Peter : Association of Official Agricultural Chemists, Report 1895. 26. Loughridge : American Journal of Science, Vol. VII (1874). 27. Hilgard : Year-book U. S. Department of Agriculture, 1895. 28. Houston : Indiana Agricultural Experiment Station, Bulle- tin No. 46. REFERENCES 285 29. Mulder : From Mayer : Lehrbuch der Agrikulturchemie, 2. 30. Journal of the American Chemical Society, Vol. XIX, No. 9. 31. Year-book U. S. Department Agriculture, 1895. 32. Loughridge : South Carolina Agricultural Experiment Sta- tion, Second Annual Report. 33. Association of Official Agricultural Chemists, Report 1893. 34. Washington Agricultural Experiment Station, Bulletin No. 13. 35. Association of Official Agricultural Chemists, Report 1894. 36. California Agricultural Experiment Station, Report 1890. 37. Minnesota Agricultural Experiment Station, Bulletin No. 29. 38. Minnesota Agricultural Experiment Station, Bulletin No. 47. 39. Lawes and Gilbert : Experiments on Vegetation, Vol. I. 40. Boussingault : Agronomic, Tome I. 41. Atwater : American Chemical Journal, Vol. VI, No. 8 and Vol. VIII, No. 5. 42. Hellriegel : Welche Stickstoff Quellen stehen der Pflanze zu Gebote ? 43. Minnesota Agricultural Experiment Station, Bulletin No. 34. 44. Warington : U. S. Department of Agriculture, Office of Ex- periment Stations, Bulletin No. 8. , 45. Hilgard : Association of Official Agricultural Chemists, Re- port 1895. 46. Marchal: Journal of the Chemical Society (abstract), June, 1894. 47. Kiinnemann : Die Landwirthschaftlichen Versuchs-Sta- tionen, 50 (1898). 48. Adametz : Abstract, Biedermann's Centralblatt fur Agrikul- turchemie, 1887. 49. Atwater: American Chemical Journal, Vol. IX (1887). 50. Stutzer: Biedermann's Centralblatt fur Agrikulturchemie, 1883. 51. Jenkins: Connecticut State Agricultural Experiment Sta- tion, Report 1893. 52. Wagner : Biedermann's Centralblatt fur Agrikulturchemie, 1897. 53. Journal of the Royal Agricultural Society, 1850. 54. From Sachsse : Lehrbuch der Agrikulturchemie. 55. Lawes and Gilbert : Experiments with Animals. 286 SOILS AND FERTILIZERS 56. Beal : U. S. Department of Agriculture, Farmers' Bulletin No. 21. 57. Minnesota Agricultural Experiment Station, Bulletin No. 26. 58. Mainly from Armsby : Pennsylvania Agricultural Experi- ment Station, Report 1890. Figures for grains calculated from original data. 59. Heiden : Dungelehre. 60. Liebig : Natural Laws of Husbandry. 61. Cornell University Agricultural Experiment Station, Bulle- tins Nos. 13, 27 and 56. 62. Kinnard : From Manures and Manuring by Aikman. 63. Wyatt : Phosphates of America. 64. Wiley : Agricultural Analysis, Vol. III. 65. Goessmann : Massachusetts Agricultural Experiment Station, Report i8Q4. 66. Connecticut (State) Agricultural Experiment Station, Bulle- tin No. 103. 67. Goessmann: Massachusetts Agricultural Experiment Station, Report 1896. 68. Wheeler : Rhode Island Agricultural Experiment Station, Reports 1892, 1893, etc. 69. Boussingault : From Storer : Agriculture. 70. Handbook of Experiment Station Work. 71. New York (State) Agricultural Experiment Station, Bulle- tin No. 1 08. 72. Voorhees : U. S. Department of Agriculture, Farmers' Bul- letin No. 44. 73. Liebig : Die Chemie in ihrer Anwendung auf Agrikultur und Physiologic. 74. Warington : Chemistry of the Farm. 75. Lawes and Gilbert : Growth of Wheat. 76. Lawes and Gilbert : Growth of Barley. 77. Lugger : Minnesota Agricultural Experiment Station, Bulle- tin No. 13. 78. Lawes and Gilbert : Growth of Potatoes. 79. Minnesota Agricultural Experiment Station, Bulletin No. 56. 80. Shaw : U. S. Department or Agriculture, Farmers' Bulletin No. ii. 81. White : U. S. Department of Agriculture, Farmers' Bulletin No. 48. REFERENCES 287 82. Lawes and Gilbert : Permanent Meadows. 83. Thompson : Graduating Essay, Minnesota School of Agri- culture. 84. Nefedor : Abstract, Experiment Station Record, Vol. X, No. 4. 85. Minnesota Agricultural Experiment Station, Bulletin No. 89. 86. Journal Analytical and Applied Chemistry, Vol. VII, No. 6. 87. Moore : U. S. Department of Agriculture, Bureau of Plant Industry, Bulletin No. 71. 88. Meyer : Outlines of Theoretical Chemistry. 89. Voorhees : Fertilizers. 90. Cornell University Experiment Station, Bulletin No. 103. 91. Fraps : Annual Report 1904, Association Official Agricultural Chemists. 92. Illinois Experiment Station, Bulletin No. 93. 93. Canadian Experiment Farms, Report 1903. 94. D. Land. Vers. Stat., 1899, 52- 95. A. D. Hall : The Soil. INDEIX Absorbents 133 Absorption of heat by soils . . 39 of gases by soils . 269 Absorptive power of soils . . . 43 Acid soils 85 Acid soluble matter, of soils. 65, 269 Acids in plant roots 218 Aeration of soils 250 Aerobic ferments 147 Agricultural geology 45 Agronomy 8 Air movement through soils -266 Albite 52 Alchemy i Alkaline soils 83 Aluminum of soils 63 Amendments, soils 196 Amonium compounds 109 salts 129 Anaerobic ferments 148 Analysis of soil, how made • . 72 value of 74, 78 Apatite rock 54 Apparatus, list of 262 Application of fertilizer 212 cf manures 151, 154 Arrangement of soil parti- cles 14 Ashes 182 action of, on soils .... 183 testing of 272 Assimilation of nitrogen .... 97 of phosphates 165 Atmospheric nitrogen 99 Atwater 102, 125 Availability of plant food. . . 77 Avail able phosphates... 1 68, 175 nitrogen 108, 126 Bacterial action and cultiva- tion 115, 252 Barley, fertilizers for 213 food requirements of. .220 Blood, dried . . . .' 121 Bone, dissolved 174 fertilizers 173 Boneash 1 73 Bone-black 174 Boussingault's experiments. ioo, 101, 399 Calcium as essential element. 187 carbonate and nitrifi- cation 116 compounds of soils. . . 64 phosphate 55 Capillary water, determina- tion of 263 Capillarity 24 and cultivation 29 Carbon of soil 60 sources for plant growth 60 Chlorine of soil 61, 83 Citric acid, use of in soil analysis 70 Classification of soils, scheme for 273 INDEX 289 Clay, formation of 54 particles 12 sedimentation of 267 Clover as manure 127 nitrogen returned by. 102, 112, 245 root nodules 104 manuring of 226 Coaf ashes 184 Color of plants, influenced by nitrogen 98 of soils 41 and soil temperature . . 265 Combination of elements in soils 58 Commercial fertilizers ..196-214 abuse of 206 and tillage 206 and farm manures. ... 214 composition of 197 extent of use 196 field tests with 208 for special crops 213 home mixing of 204 inspection of 200 judicious use of 207 mechanical condition of 200 misleading statements. 203 nitrogen of 200 phosphoric acid of 201 plant food in 199 potash of 202 preparation of 197 valuation of 203 variable composition • 197 Composition of soils 80, 82 Composting manures 149 Corn, fertilizers for 213 food requirements of. .221 and manure 155 Cotton, fertilizers for 224 Cottonseed meal 125 Cow manure 141 Crop residue 232 Cultivation after rains 32 and bacterial action.. 252 shallow surface 30 and soil moisture .... 265 Cumulative fertility 259 Davy, work of 3 Deficiency of nitrogen 209 of phosphoric acid . . • • 210 of potash 210 of two elements 211 Denitrification 117 De Saussure, work of 3, 99 Diseases of soils 256 Dissolved bone 1 74 Distribution of soils 50 Drainage . 28, 40 Dried blood 121 Early truck soils 17 Electricity of soil 43 Evaporation 27 Excessive use of fertilizers.. 21 2 Experiments 261, 274 Experimental plots 208 Fallow fields 119 Fall plowing 34 Farm manures 131, 159 and commercial fertil- izers 214 Feldspar 52, 199 Fermentation of manures. . 147 Fertility, conservation of 241 importance of p • . 260 removed in crops 216 2 go INDEX Fertilizers, amount to use- . -212 influence upon soil water 37 on barley 213 on wheat 213 Field tests with fertilizers . . . 208 Fine earth 1 1 Fish fertilizer 125 Fixation 160 of ammonia 161 due to zeolites 160 nitrates not fixed 161 and available plant food 162 Flax, food requirements of. .222 soils 19 Flesh meal 124 Forest fires 92 Formation of soils 45, 50 Form of soil particles 14 Fruit soils 18 Fruit trees, fertilizers for. . -228 Gains of humus 95 of nitrogen in Garden crops, fertilizers for- 226 Geological study of soil, value of 56 Glaciers, action of 47 Grain soils 19 Granite 54 Grass lands, fertilizers for- . .225 Grass soils 19 Guano 172 Gullying of soils 255 Gypsum and manure 149 Hay land, fertilizing 225 Heat and crop growth 41 produced by manures. 148 of soil 39-40 Heiden 145, 150 Hellriegel 22, 28, 105 Hen manure 143 Hog manure 143 Hops, fertilizers for 225 Hornblende 52 Horse manure 142 Human excrements 145 Humates s 87 as plant food 90 Humification 87 Humic acid 94 Hutnic phosphates 88, 176 Humus 87 active and inactive • • • 95 causes fixation 161 composition of 90 extraction of, from soils 270 loss of, from soils 92 soils in need of 94 Hydroscopic moisture 26 determination of 262 Importance of field trials 211 Income and outgo of fertil- ity 242-245 Infected seed and soil dis- eases 256 Inherent fertility 259 Injury of coarse manures. 38, 152 Inoculation of soils 119, 253 Insoluble matters of soils-67-68 Iron compounds of soil 65 Kainit 180, 204 Kaolin 54 King 31. 33, 34 Laboratory note book 261 practice 262-274 INDEX 291 Lawes and Gilbert. . .6, 102, 219 Lawn fertilizers 228 Leached ashes 183 Leaching of manure 146 Leather 126 Leguminous crops, fertilizers for 226 as manure 1 27 nitrogen assimilations of 102-105 Liebig 5, 6, 145, 216 Liquid manure 136 Lime, action on soils 189 amount of,' in soils • • • 188 amount removed in crops 188 excessive use of 192 fertilizers , 188 indirect action of 190 physical action of 189 use of 192 and acid soil 189 and clover 190 Loam soils 22 Loss of fertility in grain farm- ing 243 Loss of humus 292 nitrogen in, 119 Losses from manures 146-7 Magnesium compounds of soils 64 salts as fertilizers • • • . 193 Mangels, fertilizers for 214 Manure from cow 141 hen 143 hog 143 horse 142 sheep 142 Manures, farm 131 composition of 132 Manures, composting of 149 crop producing value. 139 direct application of. • 151 fermentation of 147 influence of, on soil temperature 264 on moisture 264 influenced by foods.- 134 leaching of 146 liquid 136 mixing of 144 and soil water 37, 93 use of 151, 154 use of in rotation 235 value of 158 Manurial value of foods.... 138 Manuring of crops. . • 154 pasture land 152 Marl 191 Mechanical analysis of soils. 15 condition of fertilizers. 200 Methods of farming, influ- ence of, upon fertil- ity 95 Mica 53 Micro-organisms and soil for- mation 45, 49, Mixing manures 144 Movement of water after rains 32 Mulching 35 Nitrate of soda '128 Nitric nitrogen 128 Nitrification 113 conditions necessary for 113 and plowing 120 Nitrogen, assimilation ..99, 102 of clover plant • • • 102, 105 as plant food 97 292 INDEX Nitrogen, compounds of soil. 61 compounds, solubility of 271 deficiency of, in soil . . 209 loss of, by fallowing.. 1 19 losses of, from soil 1 1 1 ratio of, to carbon no removed in crops.... 108 in commercial fertil- izers 200 amount of, in soils... 107 in organic forms 106 as nitrates 109 availability of 107 forms of 106 origin of 106 Nitrogenous manures 121 Number of soil particles 15 Odor of soils 42 Organic acids, action of, upon soils 70-1 Organic compounds of soil, classification of 86 source of 86 Organic nitrogen 121, 126 Organisms, ammonia produc- ing 117 of soil 117 nitrifying 114 products of 118 Osborne 16 Orthoclose 52 Oxidation of soil 40 Peat 127, 133 Percolation 26 Permanent meadows, manur- ing of 226 Permeability of soils 36 Phosphate fertilizers .164 commercial forms 167 manufacture of 170 as plant food 164 removed by crops 165 reverted 168 rock 169 slag 171 use of 171 Phosphoric acid of commer- mercial fertilizers ..167 available 164, 176 acid in soils 166 acid, deficiency of 210 removal in crops 165 testing for 271 value of 171 Phosphorus compounds of soils 61 Physical analysis of soils . . . 267 property of soils 9 modified by farming. . 96 Plant food, classes of . 65-6 ash and fertilizers 216 distribution of 78 in soil solution • . . .66, 163 Plants, crowding of, in seed bed 257 Plowing, depth of 35 energy required for . . 248 fall 34 spring 34 influence of, on soil --249 influence of moisture on 247 influences nitrifica- tion 247 Potash fertilizers 177 use of 185 of commercial fertil- izers 202 INDEX 293 Potash in soils, sources of- . . 1 79 and lime, joint use of • 185 muriate of • • • . 181 sulphate 181 removed in crops 177 Potassium compounds of soil. 64 Potato, fertilizers for 223 food requirements of. 223 soils 17 Preliminary trials, with fer- tilizers 208 Pulverizing soils 249 Questions 275 Rainfall and crop produc- tion 23 Rape, food requirements of .224 Reaction of soils, determina- tion of 268 References 284-7 Relation of crop and soil type 258 Reverted phosphoric acid • • . 168 Review questions 275-283 Roberts 36, 146, 248 Rock disintegration 45, 55 Rocks, composition of 51, 56 properties of 268 Rolling of soils 33, 249 Roots, action on soil... 214, 233 Root crops, fertilizers for . . .224 Rotation of crops 230-7 principals involved ... 231 length of 236 problems 237 and farm labor 234 and humus 232 and insects 236 and soil nitrogen 233 Rotation and soil water . • . 234 and weeds 236 Salt as a fertilizer 193 Sand, grades of 1 1, 13 Seaweeds as fertilizers 194 Sedentary soils 50 Seed, amount of per acre • • 257 Seed bed, preparation of 247 Seed residues 125 Sheep manure 142 Silicon and silicates 59-60 Silt particles 12 Size of soil particles 1 1 Skeleton of soils I r Small manure piles • • • 153 Sodium compounds of soils. 65 Soil, composition of 80- 1 conservation of fertil- ity 241 exhaustion 230, 259 management 258 particles, study of. • • . 268 solution of 65, 163 types 17 Soils and agriculture, rela- tion of 260 crops suitable for 258 Soot 193 Specific gravity of soil 1 1 Spring plowing 34 Stassfurt salts- 180 Stockbridge . . « 1 1 , 23 Stock farming and fertility . . 243 Storer 60, 123 Strand's plant ash 194 Street sweepings 194 Stutzer 126 Sub-soiling 33 Sugar beets, fertilizers for- • -223 beet soils 19 294 INDEX Sugar beets and farm man- ures 155 Sulphate of potash 181 Sulphur compounds of soil . . 60 Superphosphates 169 Surface sub-soil, mixing of.. 251 Tankage 123 Taste of soils 42 Temperature of soils 39 Tests with fertilizers 208 Thaer, work of 3 Tobacco, manuring of 155 Tobacco stems 184 Transported soils 50 Truck farming and fertiliz- ers 226 Turnips, fertilizers for.. 214, 224 Ville ioi Volcanic soils 51 Volume of soils 10 Voorhees 204, 226 Washing of land 255 Water, action of, upon rocks and soils 46 in rock decay 48 bottom 23 capillary 24 capillary conservation of 29-30-1 Water holding capacity of soils 263 hydroscopic 26 losses by evaporation . 27 losses by transpiration 28 of soil 23, 28 of soil influenced by drainage .... 28 forest regions 29 manures .... 37 mulching ... 35 plowing .... 34 rolling 33 sub-soiling . . 33 required by crops .... 22 soluble matter of soils. 163 Warington -US, 115. 116 Weeds, cultivation to de- stroy 251 fertility in 194 Weight of soils 9 how determined 265 Wheat, fertilizers for 213 food requirements of. .219 soils 20-1 Whitney 15, 44 Wilfarth 104 Wind as agent in soil forma- tion 51 Wood ashes 182 Wool waste 1 26, 1 94 Zeolites 53, 160 O' THE UNIVERSITY OF CORRECTIONS Page 7, line 2, "of Uebig's" not "at Page 22, line 16, "there are" not "they are." 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