arte et wy IO ws ibe “2 en Ae onsale ie { i crt ape We Sage —e sheath a or oe ey or eyecen es “a — COPYRIGHT DEPOSIT. Che fRiural Cext-Book Aeries Epitep BY L. H. BAILEY t THE PRINCIPLES OF SOIL MANAGEMENT THE MACMILLAN COMPANY NEW YORK + BOSTON CHICAGO ATLANTA + SAN FRANCISCO MACMILLAN & CO., Limitep LONDON + BOMBAY - CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, Lt. TORONTO Plowing—the most fundamental and far-reaching operation in soil management. THE PRINCIPLES SOIL MANAGEMENT hae BY T.. LYTTLETON LYON, Py: 1; AND ELMER O. FIPPIN, B.S.A. PROFESSORS OF SoIL TECHNOLOGY, IN THE NEW YORK STATE COLLEGE OF AGRICULTURE AT CORNELL UNIVERSITY dew Bork THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., Lp. 1909 All rights reserved CopyRIGHT, 1909 By THE MACMILLAN COMPANY Set up and electrotyped. Published, December, 1909 Mount Pleasant Press J. Horace McFarland Company Harrisburg, Pennsylvania ©O©blLA252805 PREFACE TO THE RURAL TEXT-BOOK SERIES In 1895 the preface was written for the Rural Science Series. It set forth the purpose of the Series to be the desire to place in readable form the best results of scientific thought and discovery relating to agriculture and country life, in order that the general public might be made aware of the progress, and that farmers might be led more effectively to apply the information in their daily work. It was the hope that the Series, under the present writer’s direction or another’s, might gradually extend itself to the whole range of agricultural scientific literature. The books now included in The Rural Science Series are about two dozen, making nearly two volumes, on the average, for each year. The number of writers on agricultural topics is increasing, the knowledge on all subjects is rapidly accumulating, and the reading-public is gradually enlarging; there is every reason to expect, therefore, that the Series will extend itself still more rapidly in the years to come. It was considered to be an auspicious circumstance that the Rural Science Series began with a book on the soil, for this grounded the enterprise. The scientific and (v) vi PREFACE TO THE RURAL TEXT-BOOK SERIES literary character of this first volume also won a good hearing for the undertaking. The time has come when special texts on agri- cultural and rural subjects are needed in educational institutions; and I now, therefore, project another line of rural books, to be known as The Rural Text-Book Series. This Series is to be codrdinate with the other Series, the former designed primarily for popular read- ing and for general use, this one for class-room work and for special use in consultation and reference. It is planned that the Rural Text-Book Series shall cover the entire range of public-school and college texts. I consider it to be significant that I am able to begin this new Series, also, with a book on the soil. These two soil books well illustrate the two methods of treat- ment of a subject; and this later one impels us anew not to forget, in all our new discussions, and especially amid the social and economic speculations on which we are now entering, that a well-maintained soil is the first essential, not only to agricultural progress but to human prosperity. The soil is the greatest natural resource. We must never, in our philosophy, get away from the land. Attention is called to the analysis of the subject- matter of this volume as outlined in the table of contents and expanded in the text. The educational value of any subject or volume lies not so much in the information PREFACE TO THE RURAL TEXT-BOOK SERIES vii that is presented as in the organization of the information into a systematic treatment, whereby a philosophy of the subject is developed. A college text should be a unity, rounding up the subject so completely as to give the student a grasp of the material as one problem, and at the same time expounding the reasons on which the treatment rests. When the student has completed any text, he should have a clear mental topography of the subject that it treats. So may the agricultural subjects be made the agencies in developing clear think- ing, sound argument, constructive imagination, and effective application to the needs of life. Li? Tis BALL Y. Ithaca, N. Y. October 1, 1909 AUTHORS’ PREFACE In teaching introductory courses in soil technology to agricultural students, the authors feel that the use of a text book enables the student to get a more thorough mental discipline and a better grasp of the details of the subject than can result from a course of lectures. The present book is the outgrowth of their experience in teaching soil technology through a period of several years. It has been their endeavor to present the appli- cation of science to soil problems from the standpoint of crop-production rather than that of any one of the underlying sciences of geology, chemistry, physics or bacteriology. This has necessitated drawing from a wide range of literature, and arranging the material in a form which it is thought adequately represents all phases of the subject. The sources of such data have been freely _ drawn upon, and the authors take this opportunity to express their obligations for the aid they have received from a very large number of papers and books dealing with soils, and which it has not been found practicable to credit specifically in the text, as has been done in many instances. It may happen that some teachers will not wish to (ix) x AUTHORS’ PREFACE follow the entire text, in which event we think it will be found possible to omit certain sections and yet have a connected treatment of the subject. On the other hand, very little attempt has been made to supply illustrations of the principles which are explained. Such illustrations and amplifications are left to be added by the teacher as local conditions and interests may dictate. The book, as its title implies, deals largely with the Principles of Soil Technology, and applications of these to local practice should constitute a part of the instruc- tion. 3 Attention is called to the outline of contents, which shows the method of treatment and the relation of the several parts of the subject. As an elementary treatise, it has been the aim to properly balance the discussion of all phases of the subject, which may be followed in greater detail in advanced courses. In the illustrations, endeavor has been made to include cuts of all of the more common types of soil- working implements. We are indebted to the United States Bureau of Soils for several illustrations, and to Pfeffer’s ‘Pflangenphysiology’ for three cuts which, by mistake, were not credited in the text. THE AUTHORS CORNELL UNIVERSITY, Ithaca, N. Y. October 18, 1909. OUTLINE AND TABLE OF CONTENTS A. THe Sor As A MepiumM ror Root-DEVELOPMENT Pee ie Pete ATI Nhs DLOGUCHT Shor. sos hess ae ad a os 2 Phe elements mr mlant-fond..§ on os oo es ee ee a. Elements essential to plant-growth (1).* b. General abundance of plant-food elements (2). II. Important soil-forming minerals .................. a. Soil-forming minerals, their composition and properties (3). b. Relative abundance of common minerals (4). EY. troportant soil-forming rocks -... 2. $250. .05.2.... a. Igneous, Aqueous, Afolian and Metamorphic rocks (5). JV. Chemical and physical agencies of rock decay.... a. Atmosphere (6). b. Heat and cold (7). c. Water (8). d. Ice—Glaciers (9). e. Plants and animals (10). V. Geological classification and chemical composition She BU a aie eras Re es bre dang Sd Fahd oie, eee ols 2 a. Sedentary soils (11). (1) Residual (12). (2) Cumulose (13). b. Transported soils (14). (1) Gravity or Colluvial (15) (2) Water (16). (a) Marine soils (17). (b) Lacustrine soils (18). (c) Alluvial soils (19). (3) Ice—Glacial soils (20). (4) Wind—Abolian soils (21). *Number in parenthesis refers to section (xi) Se ek 14 xl OUTLINE AND TABLE OF CONTENTS WT. Pivisnid wir eee ee oo ee A ies 2 ee ees VII. Résumé of scheme of classification and general char- acteristics OF fhe groups:. .. oi... ek tee 2. The soil mass. Physical properties of the soil and their Us, ows boo tas 4 fs 5 td oe a. Soil and subsoil (22). J. Inorganic. canabibuanitate od kee whe a. Texture (23). (a) Textural classification (24). (1) Textural groups (25). (2) Agricultural classes based on texture (26). (b) Some physical properties of arid and humid soils (27). (c) Some properties of soil separates and classes (28). (1) Number of particles (29). (2) Surface area of particles (30). (3) Chemical composition of soil separates (31). (d) Modification of soil texture (32). 5. Structure (33). (a) Some aspects of soil structure (34). (1) Ideal arrangement (35). (2) Porosity (36). (3). Weight (37). (4) Plasticity (38). (5) Cementing materials (39). (6) Color (40). (7) Physical absorption (41). (b) Conditions affecting structure (42). (c) Means of modifying structure (43). (1) Variation in moisture content (44). (2) Formation of ice crystals (45). (3) Tillage (46). (4) Growth of plant roots (47). (5) Organic matter (48). (6) Soluble salts (49). (7) Animal life (50). (8) Rainfall (51). OUTLINE AND TABLE OF CONTENTS II. Organic constituents of the soil a. Sources, derivation and forms (52). b. Chemical composition (53). c. Amounts present (54). d. Some physical properties (55). (1) Solubility (56). (2) Weight (57). (3) Absorptive properties (58). (4) Volume changes (59). (5) Plasticity (60). e. Effects of organic matter (61). (1) Physical effects (62). (2) Chemical effects (63). j. Maintenance of organic matter (64). & (8 (Ole ee. eo ae eS). eee» B. Tue Sort as A RESERVOIR FOR WATER Pe ViGnis Wl WEAN G- POWERS... ay ose os Litho ne chante fie semount Gt Water tiv THE BUM... 5... 6 ele eee aces Determined by a. The supply (65). b. Retentive capacity (66). 1. Statement of water-content (67). 2. Forms and availability (68). 3. Amounts of each form (69). (a) Hygroscopic water (70). (b) Capillary water (71). Determined by (1) Texture (72). (2) Structure (73). (3) Content of organic matter (74). (a’) Volume of water held by different soils —maximum, minimum and opti- mum water-content (75). (b’) Available water in some field soils (76). (c’) Relation of surface tension to capil- larity (77). (c) Gravitational water (78). c. Amount and rate of loss (79). X1V OUTLINE AND TABLE OF CONTENTS PAGE IT]. Moveimnent of soi-water,: isc) cn cg ures. 0 aes © ee eee ee 308 Bromus inermis or alkali son Vig. W045 5e4 ee ee ee 317 W ates of manure, “Pigs t0G,)) 0.366 eee none hee 364 Manure piled m the field. ~ Pig. 107... 5.5.4: so. S723 Be ee Oe 382 Alfalfa root-tabercles.\ “Mig. P14. . ...5.0 328 ets ee eee 424 Heavy. sod freshly. brokemr ig BaQie<).00) so eae: baie oe 445 Erosion on gravelly hillside. Pie: P50)... 5.4 9a. hse srs 491 Terraces used in southern farming. Fig. 151..........0....... 492 Side-hill ditches to prevent erosion. Fig. 152................. 493 Pisnt roets ariderosion. . Wigs Last ws) 03 ash te ae, alee eee 495 Celery and lettuce on muck soil. Fig. 154................... 498 Farm scene on light:sand soil: Wie loa. 2) on ta oy oe 500 Farm scene on limestone loam soil. Fig. 156................. 502 Influence of crop rotation on growth of corn. Fig. 157........ 507 Diagram. Relative size of textural groups. Fig. 19........... 72 Diagram. Ideal arrangement of soil particles. Fig. 26........ 89 Diagram. Forms and proportion of soil water. Fig. 43........ 141 Diagram. Distribution of soil water. Fig. 45................. 147 Diagram. Adjustment of capillary soil water. Fig. 52........ «ae Diagram. Relation of root-hairs to soil water. Fig. 53........ 174 Diagram. Structure of mulched and unmulched soil. Fig. 62.. 199 Diagram. Water table in tile-drained land. Fig. 78 .......... 245 aa . 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110, pid. 12. 113. 114. 115. 116. CLASSIFIED LIST OF ILLUSTRATIONS XXVli PAGE Diagram. Gridiron system of arranging drains. Fig. 84...... 254 Diagram. System of arranging drains. Fig. 85.............. 255 Diagram. System of arranging drains. Fig. 86.............. 255 Diagram. Natural system of arranging drains. Fig. 87....... 256 Diagram. Sectional view of ditching machine. Fig. 90....... 259 Diagram. Relation of root-hairs to soil particles. Fig. 99. ... 287 Diagram. Effect of deep and shallow tillage on roots. Fig. 100. 294 Diagram. Effect of alkali salts on plant cells. Fig. 103....... 312 Diagram. Nematodes entering a root. Fig. 108............. 392 Diagram. Types of soil bacteria. Fig. 109.................. 395 Diagram. Influence of surface slope on sunshine received. Need toe hon ko SpE a eon TENN cles bi eed palate alo AGG 2 458 Curves. Relative size of textural groups. Fig. 20............ 74 Curves. Average analysis of common classes of soil. Fig. 24. 78 Curves. Relation of texture to crop adapation. Fig. 25...... 79 Curves. Relation of texture to water capacity. Fig. 44...... 145 Curves. Distribution of water in columns of soil. Fig. 46. ... 148 Curves. Relation of texture to capillary water capacity. Fig.47. 150 Curves. Relation of structure to water capacity. Fig. 48 .... 152 Curves. Water capacity of sandy soil in field. Fig. 49........ 156 Curves. Water capacity of clay soil in field. Fig. 50......... 157 Curves. Water capacity of silt soil in field. Fig. 51.......... 157 Curves. Relation of capillary rise to texture. Fig. 54........ 175 Curves. Relation of capillary rise to texture. Fig. 55........ 177 Curves. Relation of capillary rise to texture. Fig. 56........ 179 Curves. Relation of capillary rise to texture. Fig. 57........ 179 Curves. Lateral capillary movement. Fig. 58.............-- 184 Curves. Annual precipitation and percolation,England. Fig. 61. 193 Curves. Relation of evaporation to mulch formation. Fig. 64. 204 Curves. Relation of soil moisture to yield of dry matter. Effect RNS Rie EUR Fe vsute i ec be 3h 2 os Spayndh aalaw vedi boaim #38 hye, 9: 209 Curves. Influence of cloth tent on soil moisture. Fig. 68.... 215 Curves. Relation of soil condition to the formation of nitrates. On RES OO A Oa eee ee ee 414 Curves. Daily range of soil temperature. Fig. 122........... 454 Curves. Mean annual range of air and soil temperature. Ne- aR Nea re Aas ide, Sec ges xi wa Gil! o> 0,5 5054 S Shale SR 455 Curves, Effect of color on soil temperature. Fig. 124........ 457 Moldboard plow with shares. Fig. 34.............0.e-e-0-- 111 RIP PCRCE PLOW. BA To eiu i ni nie © 90350, 0 ajed Ce eels ae 236 Merle plow, Big. LEB o 2. oo cine wate ew oe een e a ee ale a bo 441 Plow with parts named. Fig: 127..........000.cccneneecnss 466 Peeeieminte of Plow. Mig. 128 2... ec etiam ee dene ee ee ass 467 Bulky moldboard plow. Fig. 129... .........ccecceeeeeaces 468 XXViil CLASSIFIED LIST OF ILLUSTRATIONS 117. 118. 119. 120. 121. 122. 123. 124, 125. 126. 127. 128. 129. 130. 131. 132. 133. 134. 135. 136. 137. 138. 139. 140. 141. 142. 143. 144. 145. 146. 147. 148. 149. 150. 151. 152. 153. 154. 155. 156. 157. 158. PAGE Balk ies Peewee ASS: bi Le ee eat rin beees ve 476 Bik: pane Peasy UE Ase fee cNie oe eens ccseeeve beeen 473 Bubeoid Hise Oi Soa yy vee os oe e's duke bia ve Oe eee 218 Babs pla Weyer sicie Sis. cc wed bce u's ve De a ee 219 One-horse toothed cultivator. Fig. 60 ..............ec0000- 191 W eGcleri Piet ct let ele acct bkle unladen tod 4 5.0 alee ne 187 Large-shovel ‘Gultivator. Wig DiBen. . .on)e oe on cin wate be oso be 407 Small-shovel oultivncor., Wig. LIST. jo. a cen cn bn maemne ce nd 419 Spring-toothed cultivator. Fig. 114...........cccencaceeces 402 Blade wiltnvetar, vem ME A oa ely ok ie alge ww wd Sceed 433 isd Climate Oa Bee ss oo 5 ake Se Pe ee eee 436 ET earicd: UDG yee, ee ee as oa vis sae wine nw al OR ae ee 438 " GWOCls 7 GULORAE MOET gua ors solace cele caine vale eek eee 479 Hand: tillage implemente. Pie. 08.05 so cba ace Voce cee 281 Spring-toothed harrow, Wig. SG... ... 0.6 sce eee cee dec ewe es 114 Spike-togtwerd“barhow,. Fets AB... . occ ek oie vis coke caw cae 140 ice Sl elicit Manian, | UP amet OR fees sno cau een we ke Skew ehek wae 130 Mecker harrow. -Fs Uae os asa le wn cee cae en mae dae 487 Meeker harrow. Near view. Fig. 37.........++. eietavete se hoe 118 Cut-out-dise harrG wes Pim Gs oo. ook cece vse Uv boye se ee a 276 Spading-dise harrow. Pigs BAe ow Saban aot en tae © ee 463 Extension disc harrow. Fig. 136......... Leh Sica se teanlinmin ee aaa 477 Acme harrow. Pig Tio s,s co 5', Wig, “147.0 05)-. Jwds ss Sa Stee a te ae ae ee 487 “Float” or plank smoother. Fig. 149...........0.eeeee000 489 Campbell sub-surface ‘packer. Fig. 67.........5. 0005000 ¥en 212 Broadcast seetler. (Wig. 138... 2. score ae wets es op oe 480 Gyrsars ‘eeu Fee Ta ce o's Boe ae be teen ec ica oe 485 Sulley later.’ "Wigs 2300.5. og-5 Ss spond a eters tole 470 One-horse grain drill, Fig: 190. 2.22.) ccigs ans «ane ¥ sae eee 481 miubble dipper “Figg: 143. 20.0 Sines Se eee ae ee ee 484 irarden seeder. “Fig 133...) cs so oe oes a eee Sees 474 merry hoe, Tig. 134) oo 6a ees ee ee eae ite Sane see 475 Bect'louseher. Fig. 141; ov Sep Ss CR ete cece eee 482 Cotton-and-corn planter. Fig. 1423.00. so 55¢teg. os eo oes 483 Corn planter? Wigs T4557) 2s. 2 steered es sue Oe ie ee ee 486 Potato dinger.. Pig ia) i255 262 ewes ee oe ek ee eee 488 Hand drainage toola. “Fig, $9.5 3557) wae «see ara «Sree ae 258 Types of coulters:- Wig. 131 370207, sees wen se ae ae ss 471 INTRODUCTION By L. H. BAILEY The exposed surface of the crust of the earth tends always to pass into a loose and disintegrated layer. In this layer many organisms live, and out of it many of them derive an essential part of their nourishment. The organisms die and their remains return to the place whence they came. In every successive epoch of the earth’s history, this layer has tended to become more differentiated and complex in each epoch supporting a higher type of plant, and in each succeeding age main- taining a more advanced kind of activity. Thus the soil has been formed, and the evolution of it and of the plant tribes that grow out of it have been reciprocal, one con- tributing to the other. If the soil is essential to the growing of plants, so have the plants been essential to the formation of soil. This marvelously thin layer of a few inches or a very few feet that the farmer knows as ‘the soil,’’ supports _all plants and all men, and makes it possible for the globe to sustain a highly developed life. Beyond all calculation and all comprehension are the powers and the mysteries of this soft outer covering of the earth. We do not know (xxix) XXX INTRODUCTION that any vital forces pulsate from the great interior bulk of the earth. For all we know, the stupendous mass of materials of which the planet is composed is wholly dead; and only on the veriest surface does any nerve of life quicken it into a living sphere. And yet, from this attenuated layer have come numberless generations of giants of forests and of beasts, perhaps greater in their combined bulk than all the soil from which they have come; and back into this soil they go, until the great life principle catches up their disorganized units and builds them again into beings as complex as themselves. The general evolution of this soil is toward greater powers; and yet, so nicely balanced are these powers that within his lifetime a man may ruin any part of it that society allows him to hold; and in despair he throws it back to nature to reinvigorate and to heal. We are ac- customed to think of the power of man in gaining domin- ion over the forces of nature,—he bends to his use the expansive powers of steam, the energy of electric cur- rents, and he ranges through space in the light that he concentrates in his telescope; but while he is doing all this he sets at naught the powers in the soil beneath his feet, wastes them, and deprives himself of vast sources . of energy. Man will never gain dominion until he learns from nature how to maintain the augmenting powers of the disintegrating crust of the earth. There are three great kinds of natural resources,— INTRODUCTION Xxx the earth itself, the atmosphere that envelopes it and which may be considered an outer layer of it, and the sunshine. From these three, and all the materials and forces that are in them contained, we derive the conditions of our existence and express our outlook to destiny. We can do little to control or modify the atmosphere or the sunlight; but the surface of the earth is ours to do with it much as we will. It is the one great resource over which we have dominion. Within this crust are great stores of minerals and of metals and of other materials that we can use for our comfort; these materials we can save and we may use them with economy, but we cannot cause them to increase. But the soil may be made better as well as worse, more as well as less; and to save the producing powers of it is far and away the most import- ant consideration in the conservation of natural resources. The man who owns and tills the soil, therefore, owes an obligation to his fellowmen for the use that he makes of his land; and his fellowmen owe an equal obligation to him to see that his lot in society is such that he will not be obliged to rob the earth in order to maintain his life. The natural resources of the earth are the heritage and the property of every one and all of us. We shall reach the time when we shall not allow a man to till the earth unless he is able to leave it at least as fertile as he found it. A man has no moral right to skin the earth, unless he is forced to do it in sheer self-defence and to XXxli INTRODUCTION enable him to live in some epoch of an unequally devel- oped society; and if there are or have been such social epochs, then is society itself directly responsible for the waste of the common heritage. On every side, therefore, it is important that we study the soil. Beyond all mere technical agricultural practice, the principles of soil management must be compre- hended and taught. There is no good sociology that does not recognize this fact. We tend always to discuss great subjects from one point of view. So has the soil usually been treated from the chemical point of view, from the geological, from the agricultural. In this book, the authors have attempted to discuss the soil in all its relations to plant production, developing the inter-dependence of geological, chemical, bacteriological, physical and industrial relationships in such a way as to give the student a grasp, albeit a brief one, of the entire subject in its many bearings. In its treatment, the book considers, first, the soil as a medium for root development ; second, as a reservoir for water ; third, as a source of nutrients; fourth, as a realm of organisms; fifth, in its relation to air; sixth, its relation to heat; and the relation of man to the soil follows as a consequence and conclusion. The past few years constitute a period of great activity in the study of the soil, so much so that many of our most established opinions have been challenged. Perhaps it INTRODUCTION XXXill is yet too early to rationalize all the new discussions into a clear course of practice, but we are surely getting nearer to the fundamental problems, and we shall evolve a better system of agricultural procedure. The stimula- tion of inquiry and imagination cannot fail to produce great results. So am I glad of every new effort that puts men ration- ally on their feet on the soil. It will bea great thing when the soil is known in schools. I wait for good politics and good institutions to grow out of the soil. I wait for the time, also, when we shall have good poetry and good artistic literature developing from subjects associated with the soil; for we want good literature to appeal to all men. . THE PRINCIPLES OF SOIL MANAGEMENT A. THE SOIL AS A MEDIUM FOR ROOT DEVELOPMENT The soil is a medium for the development of plants. {n the main, the plants which are of agricultural impor- tance are differentiated into root and top, and the former penetrates the soil in order to obtain food and moisture, and to afford a firm support for the aérial portion. Every plant has definite requirements for its best development. The character of the mature plant is the result of two sets of forces. The first of these is the inherent capacity of the seed to develop and produce a normal individual of its kind. The second set of forces constitute the environment in which the plant grows, and of which the soil is one part, the other component being climate. Every plant is an expression of the combination and interaction of these three groups of forces—the seed, the climate, and the soil. The external factors in plant growth may be further differentiated into the following: (1) Food, (2) moisture, (3) heat, (4) light, (5) air, (6) mechanical support, and (7) freedom from biological enemies, such as fungous disease and animal attack. With the exception of light, every one of these factors is partially or wholly deter- A (1) 2 THE PRINCIPLES OF SOIL MANAGEMENT mined by the character and condition of the soil. It is the source of the majority of the nutritive elements, it contains the water necessary for the plant and in which is carried its food, it holds air in its pores, and it absorbs and transmits the necessary heat. Enemies of one plant’may or may not be present; but, if present, they may exercise a controlling influence. All the parts of the soil mechanism—for such it must be considered— are closely related to each of these essential factors, and it is from this point of view of the growing plant that the following treatment is developed. The characteristics of the soil may be viewed from both the origin of the material and its properties. The first of these may be termed ‘‘The Rock and Its Prod- uct,” and, second,—in so far as they pertain to physical properties, —‘The Soil Mass.’” 1. Tut Rock anp Its PrRopucts Since all soil material forms a part of the structure of the earth, its origin and derivation constitute a part of the field of geology. The following discussion of the rock and its products deals primarily with these facts and processes. But the discussion is not taken up because of its geological interest, great as that is, but because of the fundamental connection these ‘have to the physical, chemical and biological proper- ties of the soil which determine its ability to grow plants. The kinds of minerals and rocks in which the essential elements of plant-food originally occur, and the changes ELEMENTS OF PLANT-FOOD g which they may have undergone in their transition to the present combinations in the soil, as well as the fact that the physical properties of the soil are primarily determined by its derivation, render their study of . fundamental concern in order to understand the soil as a medium for plant-growth. The classification and detailed study of the soil is inseparably linked with its derivation, because determined by it. On one side, it supplies certain elements of food whose relative abun- dance is determined by their distribution in the original rocks and their concentration or dissipation through geological changes, and, on the other side, it affords the physical medium for the development of the plant. I. THE ELEMENTS OF PLANT-FOOD The plant must have certain food elements for its growth and development. These elements are affected by the changes to which the rock is subjected, and in the end will reflect the character of these changes. 1. Elements essential to plant-growth.—The essen- tial elements of plant-food are ten in number, to which may be added three others which seem to be useful under certain conditions. The essential elements may be divided into two groups, on the basis of their origin: (1) The elements derived entirely and only from the solid portion of the soil. These are calcium, magnesium, potassium, phosphorus, iron and sulfur. (2) The ele- ments derived either directly or indirectly from air and water. These are carbon, hydrogen, oxygen and nitrogen. . 4 THE PRINCIPLES OF SOIL MANAGEMENT 2. General abundance of the plant-food elements.— Having now in mind the essential food elements it is of interest to know their general abundance in the earth’s crust. The following table is given by Clark: Oxypet os pete ss Serle Phosphorus... -. 4° 0.09 SHON. 53° sg atae vs 28.06 Manganese ........ O07 Atamimim 25.3. ; 8.16 PRUE ae My Foe O07 AFORE ee see ete 4.64 PATTI | «cat ktm ecco ss ey) Calelian (2350! 4 she 3.50 Stromiiuimms:.|..22.0 >.) +28 Magnesium ......... 2.62 Chromium. oc252 34s O01 RSCTA 4705 oe 2.63 Lal Sa eee Ses O1 Potaseiinn 5 cen. Diag Litnuin;, a fe Ol Trtaniaiuy. 2. < 42s Al (Clalorat. 22 Sores otek: Ol fiydrogen. 0.) eet 17 iuprigg, 200:ee. O1 Giriban sors ee 12 —_—— 100.00 The first eight elements form 98.8 per cent of the earth’s crust. In this list are found all of the food ele- ments except nitrogen, which forms four-fifths of the atmosphere. All of the food elements except nitrogen appear among the first thirteen, and in amounts of not less than .07 per cent. This gives assurance that none of the food elements are rare. It will appear later that they are all very generally distributed. The ultimate source of the elements of the first or so-called incom- bustible groups is the minerals of the earth’s crust. II. IMPORTANT SOIL-FORMING MINERALS Minerals are the units of which soils and rocks are primarily composed. A mineral is a compound occurring in nature having approximately a definite chemical SOIL-FORMING MINERALS 5 composition, usually a distinct crystalline form and definite physical properties. A very large number of species of minerals which differ greatly from each other in composition and physical properties have been recog- nized. It is these differences which renders necessary a study of those important species which are found in the soil, in order to gain a thorough knowledge of the relations which they bear to plant nutrition and the phys- ical and chemical characteristics of the soil mass. By their chemical and physical weakness or resistance, they modify the supply of food elements and determine the physical make-up of the soil, with all the attendant physical conditions of heat, moisture, air, etc., which this limits. While the number of minerals known is very great, only a comparatively small number occur in the soil in important amounts; but these are thoroughly repre- sentative. All minerals may be divided into two groups: (1) The original or primary constituents which were formed at the first consolidation. (2) The secondary constituents which result from changes in the minerals subsequent to their first consolidation, and which are due in large part to the chemical action of percolating water. 3. Soil-forming minerals; their composition and properties.—The soil is composed of a great variety of minerals and probably almost every recognized species could be found in some soil. But the number of minerals which make up the bulk of soil is rela- tively small. The following table includes the most important soil-forming minerals and their leading properties: Or € SCE | GS O86 FE ST ¢ cP 0G € T Ia}BM IayeM aplae, eind on uy er. -cL:d- Ur APTIGNIOS S10]OO [TV oy M OFT M. poi-ued14y MOT[OA-U9014) yortq pues Avr yovyq-uses1sy WBLA-ALVC per-97TG M ABiy Ov MM. Yso py axe TC -MOT[OA-SS9]1O[OD RCo) (el) SaILLuadoug fe |, os Li ‘10 ‘0 ‘d 80 6% OF O ‘0 ‘SIN ‘80 Le og Ro Bo: rE c’9 19 ‘TV ‘H ‘O “80 rE Oz O ‘Ig SIN O's cz (OS ‘TV ‘SIN Sd “EN ‘MH re eg | O'S TV Oa 0 SN ce Le (O'S ‘TW ‘UW ‘on SIM “VO 9% 09 O ‘tS ‘TV ‘EN “M VS 09 O ‘iS ‘TV ‘M LZ 0'9 O ‘IS ‘TV ‘80 ‘EN 9% 09 oO ‘tS ‘TV ‘M pd OL O ‘IS AY ssou Reser S -preyy yueseid s}uSTUe[ A 10 ‘Td*(FOd) 89 *(°OO) (2 “eD) e018) IO Ig [y*eOH 1OIS *(@ ASN) So}BOI[IS-ATOg So} BOTTIS-ATOG So}BVorIs-AJOg *O*S*TV2(@N “M) 1(OIS) VM ZOIg9 “OAV ‘O (VO ‘BN)|* * “AVdspya,T 2OISO “OAV ‘O*M 70 18 punod -W00 Jo IayOBIEYD oe og a ayyedy "ST PE 2 Mie "++ aqruTofod “ZT ‘ -opUuosery pue spoey “TT —___— “*** agopidy ‘OT sek oe aUIATO °6 J++ +s s-peorpT “g “**sourxoidg *y ‘sojoqrydury *g "seqyeyden *¢ Same aqionery “F ¢ esepoIsV[g * ‘+ sredspya.T aSBPOYWO °S [BroulUL JO eWIBN HIGHT, GNVY STVYYUANIFY DONINUYOY-TIOG NOWWO)—'‘] @IAV], ‘14 o) ie aeOnes-o AN |g’ | OF vows eeee u9018-941Y AA LZ OE a as el Ses eee eevee iat te Mat MOTIOA ssvig 6'F 0'9 ae ale u9018-MOTIO X 10 hi ONG 00009E, —- Paa-o3 TT AA Zz | eZ ee a0 2 os MO][OA-UMOIG, O'F-9'E Gc yor re | o9 CT Z YOR |q-pory zg | gg 2 ae Gate peel ies anyq ynq S10]09 ][@ pur pay |E'F-Z'E| OL 009% | O6ez | Ustppar-oyymM | ez | O doqiv| 220d a al ee: sso Bo) (01) “ACIS | Dig joyloedg Leta = ‘urd -d ut AYTIGn]OS - oO ‘Is ‘TW ‘od “ON SW 8D “M) OF +eq oyVorIS-AJog|* oyrUOONeTD *2z Ig ‘Tv ‘OH ZOISS OV ‘OFHZ = |° °° opTUTIOVY, 97 H ‘O's ‘TV ‘80 ‘eN ‘SM | O*H+soq"oris-AJog [+++ ': Soqy]OIZ “Cs H ‘O ‘ts ‘SW O*H°OISP ‘OSE of IL t—~ H ‘tS ‘O ‘TV ‘IN O*HZ “O!S “O*TV ‘OBINZ|***** 891914 “Ez 9g ‘aq wQoJ ** QPISBOIBI, pue ost ‘7% H ‘O ‘9 ‘SW O*7HZ “OSs ‘OFWE |° euUedseg “1z 10 “®@N le ihe ser ESS WTVH “0% O ‘H 4 (O27 T+ O7HEO29T |° °° eytuowUrT ‘ET O ®O%0,.J + O84 “aqrtqgouseyy “ST O a O70, * OU4BUOH ZT O ‘ts ‘10 ‘TV “@N AOMUG*TVIOVWN “"** aypepog “gT O TS ‘TV ‘UW “SW “8D | 7OtIgeTye(UOTSWRO) [°° °° qouler “CT Ho's ‘30 O7HZ + 'OSBO "* ummsdAn “FT, punod quesaid s}usWIe[y Je19urU Jo ouIeN -Wi09 jo 1aj0RIBYD ponurjuoo ‘saILuddoug WIGHT, GNV SIVUANIJ DNIWUOI-1IOG NOWWOD—] @TaVy, 8 THE PRINCIPLES OF SOIL MANAGEMENT 4. Relative abundance of the common minerals.— Hall quotes D’Orbigny as saying that in the earth’s crust the chief minerals are present in the following proportions: Peldinars:. irr. ae svheg ee estas Soe 6 bk s «kn owe 48 EE Sos as tae en ee errs bee leh REN SIs a ace ote 35 Unit eae emerge ree Tana e (hare 2 yt ee eh ey CaS 8 Me Pree tele Aimee ce CNL es Cat TEM © Us ary Riper Sea) 5 Carbonate of lime and ma enestigna oes... feck ee ke ws ii Horubleng, ‘aupite) ete 27% igo: 2,200 ere ave vipa teoera/ ae 1 All other minerals and weathered products............ 2 100 These general relations agree with the statements of Chamberlin and Salisbury, who give the following summary of the salient facts relating to the composition Fic. 1. Section of granite, magnified. The ‘ z : crystals are orthoclase, microline, plagioclase, their combination quartz, black mica or biotite, white mica or mus- covite. (Merrill.) they form a series of minerals: ‘“ (1) Out of the sev- enty-odd chemical elements in the earth, eight form the chief part of it. @)> One See these elements uniting with the rest forms nine leading oxides. (3) One of these ox- ides acts as an acid, and the rest as bases. (4) By SOIL-FORMING ROCKS 9 of silicates, of which a few are easily chief. (5) These silicates crystallize into a multitude of minerals, of which again a few are chief. (6) These minerals are aggregated in various ways to form rocks.”’ Hundreds of analyses of rocks have been made in this country and abroad and from these Clark finds the mineralogical composition of igneous rocks of the earth’s crust to be as follows: SRR NE otc ONY a" sae Take bade ere tor a nor ia al EN 59.5 PIGEMMOCIC ANG. VTORING 5.0 5c co.¥x whose cis, yw «ica, 16.8 PEUMEAE Maer cos (ha Ryne a ier seater Se nL, 8 WL Ue re 12.0 Reeaetee ICAL. oO. cen ee oes Sine atk cia ee 3.8 Dpeaiieen Taine rale 5 sme oe oS ee ed Sate pee es < 88s 1.5 co 1 MIR Pag amen 2 US ai na ea 0.6 94.2 This leaves 5.8 per cent to be distributed among the more rare minerals. III. IMPORTANT SOIL-FORMING ROCKS, THEIR PROPER- TIES AND OCCURRENCE A rock is an aggregate of minerals. Moreover, it usually exhibits a considerable degree of consolidation, and forms an essential portion of the earth’s structure. Very few minerals occur in nature in large pure masses. They are usually grouped together in different combi- nations, and, while it is essential to trace the changes of each mineral, it is also necessary to give attention to the groups of minerals—rocks—since the association of minerals determines very largely the processes by which rocks are transformed into soil and the character- istics of the resulting soil. 10 THE PRINCIPLES OF SOIL MANAGEMENT These aggregates of minerals, or rocks, are essentially without order or arrangement. The minerals are in irregular crystals or fragments of greatly differing sizes closely packed to- gether. The great variety of miner- als, as well as the different physical forms of the same mineral, is pro- ductive of an infi- nite variety of rocks. While in- dividuals may dif- fer greatly, there is an easy and gradual transition from one form to Fig. 2. Photomicrograph of diorite rock. Com- : pare with Figs. 3, 5, and 6, which have a different another which mineral composition, crystalline form and struc- A ture. These differences determine the type and renders it 1Mmpos- rate of their weathering. (Lord.) sible to draw har d and well-defined lines separating each species of rock from every other species. They blend one into the other, not only in structure and crystalline form but also in chemical composition. The classification of rocks is based upon these facts, and they are grouped broadly under four main heads, the distinctions being their origin and structure. Each of the main divisions is again divided into groups and families, the distinctions being those of mineral and chemical composition, structure and mode of occurrence. STRUCTURE OF IGNEOUS ROCKS ty The main divisions are: Igneous rocks—sometimes called eruptive—which have been brought up from below in a molten condition from which they have cooled and solidified. They usually have two or more essential minerals, and are massive, crystalline, glassy, or, in certain altered forms, colloidal in structure. Aqueous rocks have been formed mainly through the agency of water, as (a) chemical precipitates, or as (b) sedimentary deposits. They are usually fragmental, but may be crystalline or colloidal, but never glassy. They have a laminated or bedded structure, and usually have many constituent minerals. Molian rocks are formed from wind-drifted material. They are fragmental in character and ir- regularly bedded in structure. Met- amorphic rocks embrace those of any of the fore- going divisions which have been changed from their original con- dition through the agencies of dyna- d § Fic. 3. Photomicrograph of basalt (trap) rock. mic and chemical (Lord.) forces so that they exhibit new properties. They may have one or many constituent minerals, and in structure they are usually crystalline and bedded or foliated. 12 THE PRINCIPLES OF SOIL MANAGEMENT 5. Igneous, aqueous, aeolean and metamorphic rocks.—The igneous rocks are parent to all the other forms. They may be arranged according to the amount of silica they contain, those that are rich in that com- pound being termed acid, and those that are lean, basic. In this order, some of the most abundant rock types are granite, quartz, syenites, diorites, gabbro, diabase and _ ba- salts. Of the aqueous rocks the chemical precipitates are relatively of small importance. They seldom form ex- tensive rock masses and are usually intimately Fic. 4. Photomicrograph of fossiliferous lime- M1Ng§ led with stone. (Lord.) other types of rock, especially those of the sedimentary group. The most important ones agriculturally are the sulfates, represented by gypsum beds. Certain phosphatic deposits and some chlorides also belong in this group. The aqueous sedimentary rocks are the most import- ant agriculturally of any of the groups of rock. and especially of the aqueous rocks, because of their ‘arge surface distribution and their physiography. ‘They are composed of the fragments derived from the degenera- STRUCTURE OF SEDIMENTARY ROCKS 13 tion of all the older rocks and from the inorganic remains of plant and animal life. These comprise clay and shale (ar- gillaceous), sand- stone, conglom- erate and breccia (arenaceous); limestone and dol- omite (calcare- ous) together with minorrocks of vol- canic, phosphatic and carbonaceous character. The sand- stones, shales, limestone and dol- omite are easily the most promi- nent of this group, and, in fact, of all the types of rock, in their present agricultural im- portance. They compose immense strata of rock, and Fic. 6. Photomicrograph of sandstone. (Lord.) 14 THE PRINCIPLES OF SOIL MANAGEMENT are usually arranged in alternating layers of variable thickness and extent, and have given rise to important areas of soil. AXolian rocks are relatively insignificant, and are generally of a sandy or clayey character. Metamorphic rocks are correlated with all the other types of rock, and have resulted from pronounced alterations in other rocks. Their individual properties ¢ are therefore similar to the rock from which they were formed. Often their resistance to decay is increased by the process, as in quartzite and slate. IV. CHEMICAL AND PHYSICAL AGENCIES OF ROCK-DECAY There are five chief agencies of rock-decay. They are, (a) the atmosphere, (b) heat and cold, (c) water, (d) ice, and (e) plants and animals. The operations of each of these agencies are of two sorts: (1) chemical; (2) mechanical. The products of these two types of force are distinctly different in their relaiton to the plant. The chemical action of the various agencies results in a changed composition of the minerals. It results in the breaking down of the mineral com- pounds, with the possible removal of the elements, as when feldspar is changed to kaolinite. Here the base— potash, soda or lime—is replaced by the elements of water, and may be carried entirely away. The hydrated residue loses some of its silica, and kaolinite is the result. In other cases the change may be effected by the addi- tion of material, as when pyrite is oxidized by the .19Y}OUB 0} WIOJ GUO WIOIJ UOT}ISUBI} UI YOOI,, SV pouyosp useq sey [log ‘uorEIedo Ur A]]eNUTUOD SI UledE oVq PUB YOO 0} [SLIG}VUI [IOS JO UOIJIPUOD ay} WOIJ oBURYY Jo sseD01d 9Y} SNYT, “OUI JolIve suOs 4B sjuBld Jo YIMOIS oY} JO} [IOS SE PoAIOS BABY ABUT SYD 9soy} Furjnjz1su0d [BUJU CYT, “[IOS SB aAIOS AJoVBUI[N ABUT 71 a1aYM UOT}IsOd JaYy}O ouIOS ul pazIsodap si Sessvur YOOI VSey} Jo Avoop oy} Ul PEAOUIAL [VLIO}VUI OYJ, “eUOJSpuS JO ULIOJ UOISOLe [BOIdAT, *y “OI 16 THE PRINCIPLES OF SOIL MANAGEMENT atmosphere to the sulfate by the direct union of oxygen with the compound. Whether the process be an addition or subtraction of material, it usually changes the stabil- ity of the mineral, and perhaps the stability of the mass of which the mineral is a part. The chemical action of one agency often opens the way for the chemical and mechanical action of other agencies, so that the decay processes are hastened. This chemical breaking down of minerals, and thereby of rock masses, is termed decomposition. The mechanical breaking up of rocks whereby only the state of division of the material is changed is termed disintegration. The breaking up of rocks due to expanison of heat, the freezing of water, flowing of water, the grinding of glacial ice, and the expansion of plant roots, are types of disintegration by which the rock is simply reduced to a finer state of division. The general tendency is for finer material to result from decomposition than from simple disin- tegration. 6. Atmosphere.—The atmosphere is composed of a mixture of the gases nitrogen and oxygen, in the propor- tion of four parts of the former to one part of the latter, together with very minute quantities of carbon dioxide, nitric oxide, ammonia, and, in even less amounts, other volatile compounds, and a variable, but usually very considerable amount of water-vapor, evidenced by clouds, rain, snow, dew, etc. These gases, dissolved in the atmospheric moisture, come in contact with rock masses and change certain of its minerals into com- pounds more or less soluble than they were originally. The iron compounds are perhaps the most affected, SOIL-FORMATION, ATMOSPHERE ¥é and the change of the mineral pyrite is typical of the process. 2Fe S,+70,+2H,0 =2Fe SO,+2H,SO, Fe SO, +2H,0 =Fe(OH), + H,S0, ‘All of these changes of iron compounds under the action of moist atmosphere are imperfectly understood, but it is agreed that the above products may result from the process. Since the sulfate is much more soluble than the sulfid, the mineral is in this way easily removed. The purely chemical action of the atmosphere is less pronounced in its effects than its mechanical action. As wind, it exerts some pressure upon projecting masses tending to push them over, but its great work is accom- blished when the wind carries solid particles of dust and sand and when it acts on vegetation as a lever. In arid and semi-arid regions, particularly, the amount of solid material carried in the atmosphere is very large at some seasons. There frequently occur dust storms, when the atmosphere is so filled with wind-driven par- ticles as to obscure the sun and all objects, at even a short distance away. In the region of western Nebraska and Kansas these dust storms are well known, and on certain soils it is unwise to plow in the fall, because by spring the soil will have been blown away to the depth of the furrow, and indeed this sometimes results from plowing at any other season of the year. Further west in the mountain region this wind-blown material is most effective, where the particles may be driven against the bare rock faces. It then becomes a titanic sand blast to drill away the rock. It eats into the rock surface with remarkable rapidity, carving fantastic B 18 THE PRINCIPLES OF SOIL MANAGEMENT forms, as a result of the varying hardness of the rock and the uneven distribution of the particles. The abraded particles are born along by the wind and be- come new tools of destruction. In humid regions this form of disintegration is less prominent, but in sandy regions it performs some ef- fective work. As an example of this effectiveness, Merrill describes a large sheet of plate-glass, once a window, in a lighthouse on Cape Cod,—well known for its sand-dunes. During a severe storm, of not above forty-eight hours’ duration, this became on its exposed surface so ground by the impact of grains of sand blown against it as to be no longer transparent, and to necessitate its removal. He reports that window-panes in dwelling-houses in the vicinity are frequently drilled quite through by the same means. Material blown about by wind is very much rounded and smoothed by the impacts to which it has heen sub- ject, a characteristic very much less in evidence in water-moved material of the same fineness. Winds also act in conjunction with plants where the roots have penetrated into a crevice or joint, using the tops as a lever to push off or further fracture masses of rock. This process is most effective in rough mountainous regions where the larger vegetation is just getting a foot- hold. In passing, attention may be called to this process of overturning plants as one of nature’s cultural methods, whereby the soil is subjected to very thorough, if long- drawn-out, tillage. 7. Heat and cold.—In general, heat accelerates all chemical processes. It greatly increases the solvent SOIL-FORMATION, HEAT AND COLD 19 power of water for many substances, and renders it a more destructive agent generally. This action can not be discussed separately, but must be kept in mind in the consideration of those other agencies of decompo- Fic. 8. Two types of rock disintegration. The forms reflect the different hardness and composition of the rocks sition. Especially important are alterations of tempera- ture, by which compounds whose rates of solution are differently affected by temperature may be successively acted upon. Heat acts mechanically in two ways to break up rocks: (1) Through expanison and contraction due to 20 THE PRINCIPLES OF SOIL MANAGEMENT changes in temperature. All substances change volume with changes in temperature. Different minerals expand at different rates, and the same mineral may have different rates of expansion along different axes. So that, when a rock made up of several minerals has its temperature changed, it expands unequally, and a strain is set up all through the mass, which, if severe enough, and repeated often enough, will break it into small fragments. Further, even if a rock did expand uniformly in all its parts with changes of temperature, these changes of temperature are far from uniform. Heat is conducted slowly into a rock. Since the rock may have very different temperatures at points a short distance apart, as a result of this slight conductivity a great strain may result from expansion due to tem- perature differences. Merrill quotes Bartlett to the effect that granite expands .000004852 inch per foot for each degree of Fahr., marble .000005668 inch, and sandstone .000009532 inch. While these movements appear exceedingly small, they are multiplied through many feet of rock and through many degrees of temperature. The differences in temperature between day and night on rock surfaces exposed to the sun is extreme, although it varies with the color of the rock. (2) When water is carried below its freezing-point, it may be exceedingly destructive. In freezing, water expands about one- eleventh of its volume. It has been determined that water at a temperature of—1°C. exerts an expansive force of 150 tons per square foot, and that to keep it from becoming ice would require the weight of a column of granite 1,800 feet high. All rocks are somewhat SOIL-FORMATION, WATER 21 porous. Soils have a porosity anywhere from 30 to 75 per cent of their volume. Sandstone may have as much as 25, limestone from .1 to .01. marble .008, and granite .O1 per cent. If this spore space is filled with water, as is generally the case in nature, and the rock is cooled below the freezing-point, it is evident that it will be shattered. As the process is repeated, the fractures become larger and more numerous. 8. Water.—The chemical and mechanical action of water in rock-decay may be discussed separately. (1) The chemical action may be divided into: (a) The changes due to pure water. (b) Changes due to material in solution in the water. Owing to the porosity of rocks, water is distributed through all the earth’s crust to a depth of many thousand feet. The first direct result of the presence of water is the assumption of its elements by many of the minerals. This is hydration. It may be the direct imbition of water, as when calcium sulfate in crystallizing takes into its constitution several molecules of water; or it may be the substitution of the elements of water for some elements already in the mineral. The alterations in the mineral orthoclase feldspar may be taken as the type of this kind of changes as follows: K,0, Al,0,, 6Si0, +6 H,O=2KOH + H,0, Al,0,, 6Si0,, 4H,0 Since water is so widely diffused, this process of hydration is an especially important one. The signifi- cant chemical effect of hydration is that it alters the solubility of the mineral, and particularly of the elements composing the mineral. : 22 THE PRINCIPLES OF SOIL MANAGEMENT The second direct chemical action of water, and perhaps the most important of all the chemical changes involved in soil formation, is that of solution. It is worth while to remember that no mineral is completely Fie. 9. Traces of residual soil in a limestone quarry. Note the joints and partings. Soil of a dark red, silty character insoluble. They differ greatly in solubility, ranging from the readily soluble common salt to the exceedingly insoluble silica or quartz. But all are amenable to the action of pure water. In the above instance of hydration of feldspar, we have a type of a large number of changes in minerals which alter their solubility. And by altering the solubility of one mineral the other minerals present SOIL-FORMATION, WATER 2a are opened to attack by any one of many agencies, both mechanical and chemical. In feldspar, which is very slightly soluble, hydration and hydrolysis develops potassium hydrate, a very soluble compound and there- fore readily removed. Its removal may develop a cavity, and thus weaken the rock. Agriculturally, the removal of the base is also significant. It is the basic element, and therefore largely plant-food elements, or those which condition soil-productiveness, such as potash, lime and soda, which are removed by this process. It is because of the unequal solubility of minerals that soil results from the process of solution. If all the minerals of a rock were equally soluble, the rock might be removed bodily from the exposed surface inward. Solubility, operating differently for different minerals in a rock mass, removes one, and leaves the others in a less coherent mass, which we term soil. It therefore happens that residual soils comprise the less soluble portions of the rock from which they were formed. Materials in solution in water greatly affect its capacity to dissolve minerals. Carbon dioxid is present in the air in the pores of rocks and soils in much larger proportion than in the air above the earth’s surface. It is particularly abundant in the surface layers, where it is derived from organic decay. It is taken up by the ‘water as it passes along and becomes a means of solution. The most striking example of this is in the case of lime carbonate or limestone. In pure water this mineral is soluble only to the extent of about one part in twenty-five thousand, but in carbonated water its solubility is about one part in one thousand, or twenty-five times as 24 THE PRINCIPLES OF SOIL MANAGEMENT soluble. It is this solvent action of carbonated water which has formed the extensive caverns and passages in every fairly pure limestone formation, and thereby has given rise to such features as the Mammoth Cave and the great sinks of Southern Missouri, Kentucky, Tennessee, Georgia, Florida and many other regions underlain by limestone. In the superficial layers of soil, organic acids also add to the solvent power of the water. Since water is dn universal solvent, in the earth it contains a large variety of mineral compounds, all of which affect its solvent power, usually increasing it. The destructive action of solution is indicated by the ‘ considerable amount of dissolved substances in all | natural waters. The Mississippi river carries in solution annually sufficient material to cover a square mile of land ninety feet deep; the Danube, sufficient material | for a depth of eighteen feet; and the Nile, sufficient \. material for a depth of thirteen feet. (2) The mechanical action of water.—The destructive action of running water transcends all other agencies of rock degradation in its extent. It has been the most potent force in carving the earth’s surface into its present form. It is continually at work reducing elevations and filling depressions. This destructive action is due largely to the power of running water to carry material. This transported material becomes the tool of the water in wearing away its channel. The transporting power of water varies as the sixth power of its velocity of flow. That is to say, if the SOIL-FORMATION, WATER 20 Fic. 10. “Pot holes’’ formed in shale rock. The boulders and pebbles in the “ pot”’ are set in motion by flowing water and thereby the rock is broken down with the formation of soil material. velocity of a stream is doubled, its carrying power will be increased sixty-four times. But the volume, and therefore the weight, of a body varies as the cube of its diameter. Therefore the diameter of the material carried does not vary directly as the velocity of the current. but at a less rate. This power of flowing water to carry rock material 26 THE PRINCIPLES OF SOIL MANAGEMENT is exemplified in every stream of whatever size. Where the flow is checked and thereby the carrying power reduced, some of the coarsest material is deposited. Where the flow is increased, instead of deposition, coarser material is picked up. Changing an obstruction causes extensive regrading of the channel by the current. Bends in the stream which require a greater velocity on one side of the channel than on the other cause the same sort of rearrangement, and this is nicely illustrated in the meandering of streams. They wind over their course always cutting away the material on the outer side of the curves, and depositing it on the inner side of the curves lower down. Thus the stream is continually changing its course. It meanders from one side of its flood-plane to the other. It cuts off large curves and proceeds to form new ones. All these processes may be observed in any rivulet, yet they are the exact counterpart of the things which are taking place in every large river valley. Careful determinations re- | ported by Bobb, show that the large rivers of the world remove annually in suspension the following amounts of material: Height in feet of Thickness of sedi- column of sedi- ment, in inches ment with base if spread over 1 mile square. drainage area. Messi pl LLVer > 1.5 ees dines by 5 241.4 1g Py tt ae eh MR Zee SO a on 4.0 .00433 ie VANE, oe: ss iol ts OF ARR a 2.8 .00116 PR UOUI WC oo gt acts ua ceed dee ee 10.6 00085 PIG oe SG. eae Te ste eae eee = Ue .1075 Bhat hd & beste as e's od eaneene We ae 59.0 .01139 BeIT OO: 50% kos le a le eR Ree 93.2 .00354 Piles. oo hi el Lek eee 38.8 .00042 MWGaE 0 i .c6cc kone x oR oe ee 00614 SOIL-FORMATION, ICE 27 In addition to the material carried in suspension, a large amount is rolled along the bottom of the channel. Because of the unequal carrying power of streams of different velocity, the load of debris is sorted into groups of somewhat uniform size. In this way have been formed great areas of clay, silt, sand and gravel found in all farming sections, and which owe their peculiar crop-producing properties most largely to this sorting action of water. 9. Ice—glaciers.—Masses of ice have exerted a tremendous influence in the reduction of rocks to soil material. Their action is chiefly mechanical, but is inti- mately associated, as a rule, with the action of water. The chief agency of ice is in the form of glaciers, which issue from regions of high latitude, or of great elevation, and in times past have pushed down over much larger areas of country than they now occupy. A large part of allof the continents have been overrun by such masses, which, through their great weight and almost resistless movement, ground even the hardest rocks to fine powder and mixed the materials from many sources. Fragments of rock imbedded in the bottom of the ice became its tools to scratch and crush the floor upon which it rested. In this way has come about the scouring and pulverization of rocks, analogous to the action of water. The ice appears to have attained a depth of thousands of feet in some places, and consequently was able to override even mountainous areas, sweeping away and grinding to fragments the smaller eminences and irregularities. Since the access of water was limited, there was little opportunity for pronounced chemical 28 THE PRINCIPLES OF SOIL MANAGEMENT change, or the removal of constituents, which fact is shown in the tables of soil-composition on pages 32-57. Their influence on surface topography is profound, and of great importance to the pursuit of agriculture because of the leveling which results. Fie. 11. Lichen growing on a granite boulder. These low forms of plants disintegrate the rock and assist in the decomposition of its constituent minerals. 10. Plants and animals.—Plants and animals unite with the other agencies mentioned to effect the breaking down of minerals and rocks. Like the other processes, they have both their mechanical and their chemical side. The development of plant roots in crevices of rock SOIL-FORMATION, PLANTS AND ANIMALS 29 created by other agencies, exertssufficient pressure to force them further apart and extend the fractures. Occasional striking examples of the forcing apart of rock-masses by plant-growth may be observed. The process is well Fie. 12. Growing roots of the tree have broken apart and otherwise disinte- grated the granite boulder, thereby assisting in the formation of soil illustrated by the lifting of sidewalks and the tipping over of stone fences, due to the development of trees near by, and even such soft tissues as those of mush- rooms have been observed pushing up through cement 30 THE PRINCIPLES OF SOIL MANAGEMENT and brick sidewalks. In mountainous regions wnere vegetation has gained a foothold in the crevices, the tops serve the wind as a lever to pry rocks apart. The overturning of trees is a familiar example of the process. Animal life also has a part in the mechanical breaking down of rocks. Burrowing animals are most active. The gopher, the prairie dog, the badger, the rabbit, moles, etc., all burrow in the ground and, in the aggre- gate, move large masses of material. Cray-fish and earth-worms are even more widespread, and the latter by their large numbers have a capacity which is likely to be underrated because it is largely out of sight. Ants are another very active form of animal life in effecting soil formation. They burrow into crevices of rocks and into soil formations, and deposit the material from the passages at the surface mixed with their acid saliva. Like the earth-worms, they handle immense amounts of material. Vv. GEOLOGICAL CLASSIFICATION AND CHEMICAL COMPOSITION OF SOILS All soil material may be divided into two groups, depending upon the extent to which it has been moved in the process of formation. Those materials which have not been subject to any appreciable transportation are termed (a) Sedentary. Those which have been carried to their present position—that is, have been appreciably moved—are termed (b) Transported. There are several agencies of transportation, such as gravity, water, ice and wind. These give rise to subdivisions. SEDENTARY SOILS ‘31 11. Sedentary soils.—Sedentary soils are of two kinds: (1) Residual, or soils consisting of the residue left behind in rock decomposition. (2) Cumulose, or soils resulting from the slow pnleaubersie ery and decay of plant remains. 12. Residual soils—There may be as many kinds of residual soil as there are rocks. Because of similarity between the species in a group of rocks, a few of these groups may be considered as types. The most promi- nent groups are the igneous rocks, the calcareous rocks, shale or slate and sandstone. Attention will be directed as far as possible to the relation of the soil composition to the composition of the original rock and to the char- acter of the material lost in the transition. In calculating the relative loss of the different ele- ments in the transition process, some one element— usually iron or aluminum, and, in the case of limestone, silicon—is assumed to have suffered no loss. This method, adopted from Merrill, is, of course, not strictly accurate, since every element is subject to losses; but it serves as a fair comparative basis for the study of the loss of plant-food elements. The important areas of residual soil in North America occur south of the limit of glaciation, which extends roughly from New York to Cincinnati, thence to St. Louis and up the Missouri river to the Dakotas, and west to the Sound region of Washington, where it again loops well to the south. The residual soils are further hemmed in by coastal deposits, which have their greatest extent in the South Atlantic and Gulf Coast region, where they reach a width of more than a hundred miles. 32 THE PRINCIPLES OF SOIL MANAGEMENT TABLE II. — COMPLETE CHEMICAL COMPOSITION OF Rocks AND RESIDUAL SOILS. . Silica (SiO,). . . Alumina (Al,O,) ot el Ferric iron (Fe,O,) .... Ferrous iron (FeO) Sulfur trioxid (SO) oP a a te . Phosphoric acid (P,O,). . Lime (CaQ).. . Carbon Dioxid . Soda (Na,O). . Potash (K,O). 2. Ignition [wa- ter (H,O)]... ; 2 ‘ Basalt. G te. G ‘ Diabase. District of Atpartinsls Boreal H Mabie Columbia Co., Va. Guiana View Fag e I II III IV V VI VII VIII Re- Re- e- Re- Fresh | sidual | Fresh | sidual | Fresh | sidual | Fresh | sidual Rock | Sand | Rock | Clay | Rock | Clay | Rock Soil 69.33 | 65.69 | 60.69 | 45.31 | 49.35 | 43.38 | 48.29 | 37.09 14.33 | 15.23] 16.89'| 26.55 | 15.30 | 18:36.) 16:25) are 4.00; 4.39] 9.06 | 12.18 | 14.25 | 20.39] 17.12) 4.31 0.10 | (O06: 0.25'| OPP See 1 ee 3.21} 2.63) 4.44 t 9.60| 2.37 | 7.387) 8.97 . 244) 2.64] 1.06) 0.40] 7.38| 3.45) 70315 2.70) “2A24 252) O22 1:98: |. O44) -2efa LOL 2.67 | 2.00} 4.25)|. 1.10). 0.851 0.59) 1.88 eee 1.22| 4.70| 0.62}13.75] 3.25 | 11.34] 4.92) 16.55 99.60 | 99.77 In addition to these large areas, many small areas occur scattered through areas of other kinds of soil. The most nearly original soil is that formed from igneous rocks.. That is to say, the composition of such a soil might be expected to approach most nearly to that of the original rock. The relative composition of several igneous rocks and the soils derived from them, ON On FF wW Ne . Soda (Na,O) . . Potash (K,O). . Ignition [wa- CHEMICAL COMPOSITION OF RESIDUAL SOILS Shs) TasBLe II].—CoMPLETE CHEMICAL COMPOSITION OF ROCK AND RESIDUAL SoOILs, continued. . Alumina PGs)... . Ferrie iron (Fe,0,).... . Ferrous iron ey... _ Sulfur trioxid acid (P,O,). . Lime (CaO).. . Carbon dioxid as6) cue ter (H,O)]. Igneous} Sand- Shales MnO Soapstone Rscle. bxtonas Limestone Aver- | Com- | Com- | Com- age of | posite | posite | posite Albemarle about. | analy- | analy- | analy- | Carboniferous, County, Va. 700 ses 253] ses 78 |ses 345 Arkansas sam- | sam- | sam- | sam- ples ples ples ples 1.€ x x XII SEED SCT, XV rie hath | sida Brash | tdi Rock Soil Rock | Clay ‘ Silica (SiO,). . 38.85 | 38.82 | 59.87 | 78.66 | 58.38] 5.19| 4.13 | 33.69 12.77 | 22.61 | 15.02] 4.78] 15.47] 0.81 | 4.19 | 30.30 12.86 | 13.33.| 2.58} 1.08] 4.03] 0.54| 2.35) 1.99 3.40] 0.30} 2.46 0.28 0.07 0.65} 0.05 RAS Se 0.26} 0.08] 0.17} 0.04) 3.04] 2.54 G12) Gio | C4797). 5.52 | 312 | 42.61 | 44.79 |. 3.91 0.52] 5.04] 2.64 | 41.58 | 34.10 eee) Sat) 200) Ee) 2.451. 7.90) 0.30) 0:26 Ott 0:20: 3:39). 045) L3sh) 0.05). 0.16) O61 O19) O48) 2.93) 1.32). 3.25] 0.33) 0.35) 0.96 6.52| 9.21] 1.86] 1.64] 5.02] 0.77| 2.26 | 10.76 0.05| 4.33 | 14.98 as given by Merrill, is shown in Table II, numbers I to ViITL Numbers I and II represent a gray foliated granite from the District of Columbia, the soil of which is very sandy. By reference to Column II of Table III, C TOTSD) x 9F'SS cT'09 TS’6€ LOOP * * £06 | GOLF Ist | Fees] ee'O | seer] so" | zo'es "1" Ort | irs 2st | 28°96 | 892 | 0°96 Qe AE OLOL| 240 | 88°96 | GT'2 | 4619) O80 | OL'F2 99% |SVPP| OPE | F2LF/ 90'S | €2E8! FFF |00'O0T wey eeee a) aha: 6 a ae Oe ans) tee Se alke ules ules LV EI : OT Sx ee | acid CHD | 86S | 2 ZL || oo Bele S a a to |e se — Pe dee lees YoO1 911}ua 10} SSO] JU90 19g yuenyysuo0s yore JO sso] 3U@0 Jag BIquIn[od jo 704sIq “OUIUBIS wo1j pues foe 1 OF LY PT PeOL | PS ee) TORT ree rt ioe sees ah ie" ote | pee Nm a Bit oe an G6'9T | 8S°EF | FEOE | 99°S9 | 26°02 | OF ZF | OB TE | SF ZS ® ® ees ee ot a eae et nee * ee es eh sae ‘eee ae ee orn = Or aoa orn aos orm aA a o 8 = 3 9 a 8 ic) 5 e Q 55 8g 5s 8§ nS 88 53 88 O 5 as Oo 5 = © ct 5 co © ct B > = ox as oa ~ ~ Led — Se sttaee | Se | ge) 2h) 8a] Ss Com ew mr Ea a =a) Pe =e) es | Bo eo. 1 eater eh fe CO Q) prxoy anging ‘G Fh eg cg 19 EST Eg'es a) ee is me ee © wiele Pe RX Mn Sie” | (Oey hae We Sot Wr a tea sair (02,4) uOodl SNOL19 J st 9L'T 02°89 ow. ee le wise eure ont 82°83 ig A 99°68 Mec ce eevee (*9°2,7) uOdl OIL19 J "e SOLE. (Os ees) eee aoe” | 2 Wie CEOs | TemeeL ails COTY) vurumnyy °Z Citard see 6F'2Z 9c"2¢ FE'CZ L¢°2G cee Wiletie) fe ie ees emt 6) )) BOTTI *T oO oO oO oO io eee Per ge lee b ge loge 5.8 ae =.8 28 =.8 28 2.8 28 oo ces 3 & ge 3 che 3 cet ab | ee | oe | 28 | 27 | ey | 3F | ge ai Pie a a Fi ga ma gt 5 5 o s Ba s BS, g Be, TAX | sae ENON AX AIX INN Dé TIX Ix SasA[Bue 9}ISOdUIOD| SesAleuB 93ISsOduI0D uo peseq ‘auojspues uo poseq ‘soyeys pusAreyy SBVSUByIV 0} SYOOI SnOsUSI 0} SYOOI snousst ‘a7 BIS *9U0}SOUIT] uloly UOT} ISUBI} WO1j} UOTJISUBIY ulO1f [LOS [BN pIseyY | UlOIF [los [BNpIsoy UI SSO] BSBIOAY UI SSO] OBBIBAY (35) SUSATVNY GLATANOD “IVINALV]Y IIOG OL GNV HAHLONY OL WuO ANO WOUd SHOOY AO NOIWISNVU], NI SsSOT JO ADVINGOUAG—'ponutyuoo ‘[{] ATAVY, 36 THE PRINCIPLES OF SOIL MANAGEMENT it will be seen that the total loss from the rock is 13.47 per cent. Column III of Table III represents a gneiss from Albemarle county, Virginia, under almost the same climatic conditions as the granite. But the soil is a red clay of the Cecil series, and represents a loss in transition from the rock of 44.67 per cent, or three and one-half times as much as from the granite. The composition of the two rocks is not greatly different. The differences in the two soils illustrate the two types of rock-decay. The granite soil, which is very sandy, probably does not represent the same advanced stage of decay as the eneiss soil, and apparently has been subjected most largely to disintegration, or physical breakdown. On the other hand, the gneiss soil represents both the disin- tegration and an advanced stage of chemical change or decomposition. In general, the productiveness of a soil depends even more on its physical characteristics than on its chemical composition. The physical characteristics of a residual soil depend quite as much on the stage and type of decay to which it has been subject as to its chemical composition. Mechanical processes, such as abrasion and fracture due to impact, temperature changes and frost, never produce the same fine texture which may result from chemical processes, and therefore such material is usually very sandy. A sand composed of aluminum silicate minerals in large proportion is increas- ingly subject to chemical decay, which will reduce it to a gritty clay of progressive coarseness from the surface downward. These principles may be summed up in the statement that the characteristics of a soil are determined COMPOSITION OF RESIDUAL SOILS 37 by two factors: (1) The original chemical and physical composition of the rock. (2) The relative prominence of physical and chemical processes in its formation. These facts make possible the existence of a full series of soil from any group of rocks. The composition of other rocks and soils than those mentioned above are shown in Columns V to X of Table II. For comparative purposes, Column XI is also of great interest, as showing the average composition of over 700 bulk analyses of igneous rocks as given by Clark. This gives some idea of the relative abundance of the several plant-food constituents in the rocks. It will be noted that the least abundant elements, sulfur and phosphorus, are present in amounts of several thousand pounds per acre foot. Columns XII, XIII and XIV give the analysis of a composite of many samples of sandstone, shales and limestones. The first two may be considered as ancient soils, and their average composition of the mineral elements should be much the same as modern soils of the same origin. Columns XIV to XVI give the composition of lime- stones, and of a residual soil from such a rock in Ar- kansas. From a comparison of the first two columns, it will be found that the rock from which ‘the soil is derived is far from the average, especially in the amounts of manganese and phosphorus it carries. A study of the soil analysis also shows that, while it is derived from a lime rock, it is not rich in lime, a condition not uncommon. Turning now to Table III, there is given the propor- 38 THE PRINCIPLES OF SOIL MANAGEMENT tion of loss of the different elements calculated to the amount of the element originally present, and to the proportion the loss bears to the original rock. This exhibits some of the reasons for the difference between Fic. 13. Residual soil from limestone. Showing relation to underlying rock many soils and the rocks from which they were derived. Assuming that there is any element which is constant in amount, these figures show that the total loss suffered by different rocks ranges from 97.64 per cent for the limestone to 13.47 for the granite. In other words, a limestone soil represents the supplementary materials in the original rock, the main constituent having been LOSSES IN RESIDUAL SOIL FORMATION 39 removed. In this particular sample, 100 feet of rock would produce only 2.34 feet of soil. It is not uncommon in limestone soil regions, as Kentucky, Tennessee and the Ozark region, to find soils forty and more feet in depth, and, since the average limestone contains nearly 90 per cent of carbonate, these deep layers of soil must represent some hundreds of feet of rock. This is the re- sult almost entirely of solution by carbonated waters, which gradually develop crevices and caverns in the rock. Other types of rock, however, do not suffer such a large amount of loss. The loss, of course, varies with the character of the processes which are at work, as has been pointed out in the case of granite and gneiss. In Columns V and VI, a clay from diabase rock suffered a loss of 39.51 per cent, and a basalt soil in France rep- resented a loss of over 60 per cent. The latter are much more basic than the granite or gneiss, and would there- fore be more amenable to chemical decay. The soap- stone, which results from the alteration of pyroxinite rock, undergoes a loss of 52 per cent in the transition to soil. In Columns XV to XVIII are given the calcu- lated loss in changing from the average analysis of igneous rocks to shale and sandstone respectively. As was stated above, these latter are ancient soil material, or potential soil material, and the figures given represent an attempt to determine the average change which takes place in the derivation of a shale or sandstone (corre- sponding to clay or sand soil) from igneous rocks. These calculations are, of course, less accurate than the pre- vious figures on such loss, because these rocks have been 40 THE PRINCIPLES OF SOIL MANAGEMENT subject to mechanical sorting by wind and water, in addition to the fact that no single element has come through without loss. The figures in the first column of each pair show the proportionate loss of each constituent. The second column shows what would be expected, viz., that the elements present in largest amount would be subject to the largest total loss. But the first column shows that certain elements are more weak chemically than others. These elements are lime, magnesium and the alkalies. While the figures are limited, still phosphoric acid appears to be subject to a large loss. There is almost invariably the assumption of water, and frequently of carbon dioxid, indicating alterations in chemical com- binations which, while freeing some elements, may render others more resistant. The striking change in the physical properties of a residual soil from the parent rock depends in part upon this unequal loss of elements. As a rule, unweathered residual soils are highly colored, usually red or yellow. This results from the accumulation and alteration of the iron. Hence, a gray limestone will produce a dark red clay. Other properties, as the texture, result in the same way. Any very refractory material, as chert in limestone or quartz in igneous or secondary rocks, is likely to persist and remain scattered through the soil. The cherty hills of Tennessee and the Ozarks are examples of the former, and the topography of the coun- try is largely determined by the accumulation of this material. Some of the stony soils of the Piedmont regions are examples of the second type of soils. The CUMULOSE SOILS 41 occurrences of these refractory materials in layers may exercise a very unfavorable effect on the agricultural value of such land. Further, residual soils are seldom uniform in texture. The clays are usually gritty, especially when derived from igneous rocks. It has been suggested that this is due to the accumulation of silica set free from the silicic minerals in their loss of alkaline materials. In this state much of it passes into solution and is removed, which probably explains some of the large losses of this ele- ment. But, where the decay is rapid, not all of the silica can be so removed, and it combines with oxygen, to form quartz particles. All of these considerations should be kept in mind in the study of residual soils, as they assist in under- standing their characteristics. 13. Cumulose_ soils. —Cumulose_ soils consist of years and even centuries of accumulations of plant remains. They occur in every section of the coun- try in areas of from a fraction of an acre: to thou- sands of acres, known as peat bogs and muck swamps. The one condition which always accompanies these deposits, and is most largely responsible for their existence, is poor drainage. Such a condition may result from a variety of circumstances. In the North Central states of the glacial section, scattered over the undulating country, are numerous small depressions where water accumulates during much of the year, together with a small amount of sediment from the surrounding hills. These conditions favor the large growth of vegetation which, upon its death, is slowly = = ra = ~ = EOI A eS a a A TE NE Tt — ayBUOgIeS eT] JO e10UI JO yUVO Jad Qf Sulurezuod ssoy, “Ajund puw ssouxoryy Ut Ayjyvois AIvA sjisodep esey,y, sl Pp Wi Joo} XIs SI Y}BoUEd FIVUI BY, “[lOS YONUI Jo S}sisuood JOAB] soVjiNs Yep ey, “YoNu Jopun (®OO BO) IWeul jo 4yIsodeq “FT "DLT " PQ —_~ IR I ES , - ~ CUMULOSE SOILS 43 accumulated on the bottom of the depression. The dead remains are kept saturated with water, which excludes the air and keeps down the temperature, and otherwise hinders decay, so that the annual additions exceed the annual loss by decay. Hence, an accumu- lation of vegetable remains is inevitable. This is the genesis of hundreds of the mucky marshes throughout the country. Old abandoned stream channels are a common beginning of such accumulations. Very similar in origin are muck and peat beds, which were formerly deep lakes. A peculiarity of fresh water deposits of this sort are beds of marl, or impure lime carbonate, beneath the vegetable matter. A slightly different type of these deposits are the seacoast swamps from Massachusetts to Texas, many of which are of large extent. These have formed in brackish water The chemical composition typical of many of the cumulose deposits is shown in the accompanying table. The physical and chemical properties of such soil will be more fully discussed under the head of physical properties of organic soils. Cumulose deposits are characterized chemically by their large percentage of carbonaceous matter. If the vegetation suffered no decay and received no mineral matter, it would be simply a mass of plant tissue; but, as has been stated, there is every degree of ‘‘ wash’’ mixed with the dead plants. These also have accumu- lated to all depths from almost nothing to many feet in thickness. Many areas of soil, such as Miami black clay and the Clyde soils of the northern states, and the 44 THE PRINCIPLES OF SOIL MANAGEMENT TaBLeE IV CHEMICAL COMPOSITION OF CUMULOSE DEPOSITS DONBARWHe II Ill | IV | Vv VI | VII Merrill, p. 315. tH 7 Swamp Illinois Bulletin 123 = “3 North River 2 ag Carteret Co., Seq 23 N. Carolina aS B00 = es by faa ie og ck: a% | g@ | 8, | Aa | ea *S B | 25 | #2 | 82 | er | aR | BF e< | dy | 56 | a" | me ° MoIshare. oa wos So i eo» | 49.001 2.50.) 3.601. .... | Volatile matter =) ...| 71.80) .... ).....:] 222 | 84.72 | SG:70 Pee . Organic matter ....| .... | 30.00] 7.70 | 87.25 | 42.36 | 43.35 | 39.62 Insoluble matter <..| 18:47 | 17.00:] 3...) 225 4 sexe] eon . Soluble sihea (S10) yo... | A eee Insoluble silica (SiO,.| .... | .... | 80.84] 1.52 PBA Ce een heen sia aja; 1) NOt tec eich mete . tron axide (Fe,0,)...| 2.60% .)..0) TiS Gale . Alumnia (ALO,) ...) 1.38) ..<. | 260) -039 Aarne (Gai. Sete 0.51) .... | 0.44] 0.36 4 Catpon tox (COL) 3.987 13. ol ee eel ee . Magnesia (MgO) ...| 0.10|] .... | 0.22] 0.14 ‘ . Boda (Na,O). 2.0205) 0:20)... 2) 0.02:). (O.48.) . Potash (K,O).......| 0.82] 0.14] 0.07| 0.06/0.318| 0.36 | 0.366 . Phosphoric acid P,O,| 0.32/ 0.10} 0.08] 0.06|0.196| 0.15} 0.12 . Nitrogen (N)....... 0.62) 141) 2... la.) €48 ) ae . Sulphuric acid (SO,).| 1.06] .... | 0.06 Portsmouth and other soils of the southern states, represent the very first stages in the formulation of such cumulose deposits. That is, they are simply mineral soils with a high content of organic matter. . 14. Transported soils.—The four great agencies of soil-transportation are (1) water, (2) ice, (3) wind, and a De ——— =e eer ee eee TRANSPORTED SOILS 45 (4) gravity. It will be remembered that each of these agencies was mentioned as active in soil-formation through the physical and chemical forces brought to bear on rocks. The material is moved from its original position and laid down under new conditions which develop properties entirely different from those pos- sessed by sedentary soils. Of the four groups, those soils transported by water are easily the most extensive, and next to these in area stand those moved by glacial action. Wind-moved soils are of much importance in some sections, but gravity-moved soils are of small extent. 15. Gravity or colluvial soils—In mountainous or hilly regions, soil material of all dimensions is moved down the slope under the pull of gravity. In those sections of the country where stone fences are common, the accumulation of soil on the uphill side of the fence, due to gravity movement, not infrequently reach the top of the wall. Because of its associations with a hill . (Collis meaning hill), such material is termed colluvial. The first footings of soil in the niches and at the base of a rocky ledge are usually of this sort, and in mountain regions the accumulation of such material is sometimes large. ; 16. Water.—It has been shown how water is able to transport sand and even boulders several times heavier than itself, if it be flowing with a sufficient velocity. (See page 24.) This large transporting power may be observed in any creek or rivulet, and in every hilly region it is brought forcibly to the farmer’s notice in the gullies formed by heavy rains. The bed of every 46 THE PRINCIPLES OF SOIL MANAGEMENT stream is strewn with material which has been dropped by the water. If the bed of the stream is steep, it is paved almost entirely with large stones and boulders. If the bed is very flat and the flow slow, the bottom is formed by sand or silt. These variations are well illus- trated by the ripples and quiet pools of almost any stream, the former being stony, the latter more fine- textured. This principle of the varying carrying power of flowing water is of great agricultural importance. It results in sorting the material which comes into the water, and the particles of one size are deposited to- gether. In this way is accumulated a fine pure clay in one place, a sand at another place, and gravel at still another. These formations are strikingly different in their relations to plant-growth because of their dif- ferent physical and chemical properties, as will be shown in the further discussion of these matters. The character of such soil depends upon two factors: (1) The character of the rocks from which it is derived. (2) The conditions under which it is deposited. The soils of this group are by far the most important, agriculturally, of any which will be discussed, on account of both their relative area and crop relations. In a general way, they may be divided into three sub-groups; but it is impossible to draw any sharp line of distinction between these groups. These are: (1) Marine soils. (2) Lake and pond deposits, or lacustrine soils. (3) Stream-laid, or alluvial soils. 17. Marine soils—The marine soils occupy large areas in the United States and many other countries. They consist of stratified gravels, sands, silts and clays SOILS DEPOSITED BY WATER 47 deposited in shallow off-shore water, and subsequently raised above sea-level, where they have been subject to erosion by the present drainage channels, so that they are furrowed by a ramifying system of shallow, steep-sided gorges. These channels reveal the different sorts of material from coarse to fine, and have exposed each of them over considerable areas. The material has not been deposited long enough or buried deep enough to be much consolidated, although there are very soft shales and limestones in the Gulf states which are only partially consolidated. 18. Lacustrine soils.—Closely related to the marine soils are soils deposited in lakes, such as those fringing the Great Lakes. These lacustrine soils differ from the former in the different source of their material and somewhat different conditions of deposition. Most of them are fresh-water bodies, but in some instances, as Great Salt Lake, they are brackish. It is impossible to draw any definite line of distinction between these two sub-groups of soils further than in the extent and character of the waters in which they were deposited, and for a specific understanding of their characteristics the respective types must be studied in detail. 19. Alluvial soils—Along every stream course is a ribbon of material formed by the deposition from the water of that stream at either normal or flood time. Along the steep-bedded streams it is very narrow and usually coarse, often with a base of stone covered by a veneer of fine material. As the course becomes less steep, it widens and is more meandering. The stream swings from side to side of its valley in large sweeping 48 THE PRINCIPLES OF SOIL MANAGEMENT curves, which become actually tortuous in very flat bottoms. Such a crooked channel is much reduced in capacity over a straight channel, and therefore in flood season the water is piled up over the bank and ° Fie. 15. Shows the stratified arrangement of a gravelly soil overflows the adjacent land. When the water passes from the deep channel, its velocity is checked, and -ome of the material—the coarsest—is deposited on the bank. The finer material is carried further out. If there is a general movement over the whole bottom the very finest material may not be deposited, and con- CHEMICAL COMPOSITION OF MARINE SOILS 49 TABLE V CHEMICAL COMPOSITION OF SoILS DEPOSITED BY WATER. CoMPLETE ANALYSES CoASTAL PLAIN Sorts oF MARYLAND OONOOPWNH J II III IV V ane cage au Gn = 8a |Gez,| gee |Bs> | 38 Has = 2, Ss aay O8o LS 4fo Ey: AS 12 a. oO aq doe |gasd | Shee|ess | a2 Zao | es | eee | 284. | of got aa S| a oae tee & = OR ag Sane eee ee wa fe Gig | -8@60 | Se=5/F Sg | ° 3 Boot | see at eo.) eas gs Soa) $388 | BeS3 | Peso | Fe "gea| "esa | s28!°SS5 | “Se US rs agape igh the ae: be ea ee OL ke 92.30 | 83.86 | 80.55 | 64.26 | 94.32 Pema (ALO)... 0... 5. 3.20 6.10 8.82 | 19.92 2.66 ere iron (Fe,O,) ...... 0.91 2.63 2.67 5.74 1.25 . Ferrous iron (FeO) ...... are Aeris A bate ane ) pulur trioxid (SO,) ..... 0.08 0.12 0.07 V0 ee . Phosphoric acid (P,O,) ...}| 0.05 0.23 0.42 0.16 0.02 ON 6) 0.41 0.50 0.47 0.44 0.04 ; Carbon dioxid (CO,)..... 0.08 0.06 0.05 13s Ee eins . Magnesia (MgO)......... 0.35 0.45 0.29 0.59 0.07 OE EA 6 0.50 0.56 0.49 0.58 (te ere CID) 2 ee la 0.70 0.92 1.22 1.50 0.12 ee 0.23 1.30 1.28 ORV: fh) aia ee } Organic matter.......... Ge rey, ee sit wt eons . Volatile matter.......... Bld 3.00 3.26 6.58 L.2Y sequently the accumulated soil is a fine, friable loam rather than a clay. Heavy alluvial clay is seldom found outside the larger river bottoms and generally in depressions remote from the channel. Another source of heavy soil is ponds formed by the cutting off of bends in the channel. These ‘‘ox-bow D 50 THE PRINCIPLES OF SOIL MANAGEMENT TABLE V, continued CHEMICAL COMPOSITION OF Soits DEPOSITED BY WATER. CoMPLETE ANALYSES Brick CLAYS OF SOUTHERN PLAIN oO SOP WN VI Brick clay. Columbia for- mation. North Carolina < — Le Brick clay. Pleistocene for- mation. North Carolina Taylor Si —_ Sandy brick clay. Pleis- tocene formation Co., Texas. IX Co., Brick clay. Pleistocene i Harris formation. OME cry ea katte ce CA (BIOS) 3s 55.f0 . Alumina (AL0O,) ..| . 24.91 . Ferrie iron (Fe,O,)| 7.99 . Ferrous iron (FeO) .... . Sulfur trioxid (SO, . Phosphoric acid EOE sii iera ee ee oeulite ACR ON S< 2 0.70 . Carbon dioxid CO,.| .... . Magnesia (MgO)..| 1.12 eds (ea. Oc ae 2.94 =P ouasir (ROW oo ale po Le eee “Ye the Be 1.03 . Organic matter... . Volatile matter... bends,”’ ‘‘cut-offs,’’ or ‘‘ bayous,’ ) 44.40 “A Sandy loam, pine woods, Mississippi 2.33 First-class | 4 pine. Florida = Sandy loam. 1.88 as they are variously termed, become in succession lakes, ponds and marshes, where the clay-laden water is gradually evaporated or filtered away, leaving behind only the very fine material that may be carried in suspension almost indefinitely. As a result of these processes much of the ~ eS a ee ee ees , a ae CHEMICAL COMPOSITION OF GLACIAL LAKE SOILS 51 TaBLE V, continued CHEMICAL COMPOSITION OF Soits DEPOSITED BY WATER. CoMPLETE ANALYSES GLACIAL AND WESTERN SOILS XII XIII XIV XV XVI ss 2 7 > =e & é 5 s2 | ge ae il gels BS | Bod 5 a7 3 © qa = | & 4 Sete ee 0 Baio ae iz se $s SoM | add 3 eS 5 3 4 2s & < 3 Og 4 = ne OS 0) a a re ae: mate Se soe. as ae oe tS? 0 Sia aca ne 55.60 | 66.69 | 19.24 | 56.17 | 40.22 wrumina (ALO.). 2... 20... 14.80 | 14.16 3.26 | 24.25 8.47 Ferric iron (Fe,O,)....... 5.80 4.38 Ut eae 2.83 Ferrous iron (FeO) ...... Osea 3 ap ee 3.54 0.48 psuuur trioxid (SO,y) ..... - dine 0.41 oS Ss eee 0.13 Pe hesnnoric acid (P.0.)...| 0:15 0.29 ZG We ps. ea 0.05 Le 00) 5.70 2.49 | 38.94 2:09 | 15:65 . Carbon dioxid (CO,)...... 4.94 A ele oe ae 18.76 . Magnesia (MgO)......... 2.48 1.28 2.75 2.57 7.80 Oo St CE re 1.07 0.67 t 2.25 0.84 eS a 6) ao 121 t 4.06 2.36 RR sia a ves side ss 5.18 4.84 1.67 4.69 1.95 PMreamG Matter. . vr... ... ae 2.00 cB) i ene 0.32 p volawie matter.......... re wath ae ene ieee soil formed in stream bottoms is friable and easily tilled, but they also give rise to some of the heaviest and most intractable clay soil known. Soils of this sub-group may be either very uniform or exceedingly variable in fine- ness. It is evident from what has been said that, the smaller the stream, the more variable the soil is likely to OONAAEWHH a2 THE PRINCIPLES OF SOIL MANAGEMENT TaBLe V, continued CHEMICAL COMPOSITION OF SOILS DEPOSITED BY WATER. StronG Hyprocuioric Acip ANALYSES. Virgin. First bottom. Oklahoma XVII | XVIII] XIX xx © a E 3 Kae g a 3 r= Bat ca eer ag | 38 | g8 | “8 = we Sa gH g = Fe s P| Eo ee m ~ § = Sa Sees oD) = NM . Anpoluble 5% <4 0% 70.92 | 44.23 | 77.05 | 83.22 . Silica (SiO,).. wie, Sha. PA Ee fe . Alumina (Al, a a 5.58 1.58 4.91) 204: . Ferric iron (Fe, same eee { ; bo! 66 | 5.82 . Ferrous iron (FeO) .| .... PR ae . Sulfur trioxid (SO,).| 0.29} 0.15 0.02 | . Saks . Phosphoricacid(P,O,| 0.34] 0.12] 0.18 | 0.243 “pre (CaO ya i. 5.66 | 23.98 | 1.03] 0.56 . Carbon dioxid ee: 4.00 | 18.00} 0.81] 0.44 . Magnesia (MgO). . 1.85} 0.94] 0.93] 1.13 , pOdaA MeO) os 6: 0.23} 0.25} 0.96] 0.40 . Potash (K, . 0.88; 0.22} 1.45] 0.48 g) Seas) Scosche tere S.20| 242) Bet, Ase Organic matter..... eal Ree Tee aa Volatile matter... .. 2.69| 7.34] 6.52] 4.60 * Soluble. 4 a XXI. Oklahoma First bottom. Subsoil of XXIII Second bottom. Station farm. Oklahoma be. It embraces large areas of the most productive soils. Properly drained, bottom lands are generally regarded Corn is prob- ably the most grown. Wheat is important on the heaviest soils. They are generally rich in organic matter to an unusual depth because they represent largely the wash with favor for several of the staple crops. CHEMICAL COMPOSITION OF ALLUVIAL SOILS NoHo ) N OOP wne Pimsouiple ss. sa. moieni(oiW,).. -.-. . Alumina (AI,O,) .. . Ferric iron (Fe,O,) . Ferrous iron (FeO) . Sulfur trioxid ie . Phosphoric acid J ae amine: (CaO) i... . Carbon dioxid(CO,) . Magnesia (MgO). . aod (Na) ..:.. e Porash (KO): ..... hi a . Organic matter... . Volatile matter... TaBLe V, continued CHEMICAL COMPOSITION OF So1ts DEPOSITED BY WATER. STRONG Hyprocutitoric Actin ANALYSES XXIV xXXV ROVE | eke Xe PEE re Alle mH - = 8+ ae ba gs S.4 =% uo = = eg Pa, >] oq om o “A si Ae o¢ n a ie aS ae ig >a a6 | 32 | oe | a | ee a. mS =e os a Se) ae ea, a ee peu) eee Poke) See. hee Oba |. “aey | ae sa 3° a> a >a 4 Q AD.2 ¥. 39.17 | 60:22 | 45.06 |' 51.06 8.37 | 15.09 9.00 | 16.43 | 20.70 10:72 1). Tab 9.15 | 10:20 | 10.54 3.48 3.98 3.94 4.22 5.82 0.10 0.06 i 0.09 0.02 0.19 0.28 0.16 0.27.) (0.30 7.45 8.10 1.07 8.84 1.35 14.26) 13.27 0.13 7.22 he 4.48 2.04 0.84 3.02 1.67 0.48 0.40 0.61 0:27 0.33 0.25 0.60 0.90 0.81 1:10 Tea et e-) ek a 6.22 3.20 14.29 2.61 t.04 53 XXIX Silt loam, Colorado river, San Diego Co., California 3.34 from the surface layer of the upland soils, and they are not old enough to have lost this supply of organic matter by decay. Frequently, the supply is replenished by annual additions. Table V illustrates the variations in the propor- tion of the different elements in water deposits of 54 THE PRINCIPLES OF SOIL MANAGEMENT different physical properties, from different parts of the United States. Many of these analyses are less complete with reference to some of the plant-food con- stituents than is desirable for the purpose here intended. So far as possible, analyses of the entire soil have been used, but, where these could not be obtained, analyses of the strong hydrochloric acid extract are given. 20. Ice—glacial soils—In many parts of the world there exist soils which have been formed under the influence of large bodies of ice. In earlier times, masses of ice extended far to the southward over the country now devoted to agricul- tural purposes. Around the world this mass of ice appears to have extended down from the north and south poles to a zig-zag limit. It reached into Asia, Central Europe and the American Continent as far south as New York City, Cincinnati, St. Louis, Kansas City and Omaha, and farther west in the Puget Sound region it extended south across the Columbia river. All the country north of this line with the exception of one or two small areas was covered by an immense sheet of ice which moved slowly down from the north- ward. In the southern hemispheres are similar—though more limited—traces of the same condition. The depth of the ice was so great that it flowed over such elevations as Mount Washington in New ‘’ Hampshire and over the Adirondacks in New York. Its general movement in the northern hemisphere was southward. Its flow was modified by the original topog- raphy of the country, but its depth was so great it was able to disregard and override many of the land GLACIAL SOILS 55 forms. It advanced first through the valleys, and at the bottom of the mass appears to have been guided in its flow by these channels. The advance probably consumed a long period of years, or even centuries, and the retreat was similarly slow. Along the margin, as in modern glaciers, there were annual fluctuations in the position of the ice front which are indicated by the greater or less accumulation of rock debris, as undulating piles of earth or terminal moraines. This ice picked up immense amounts of material along its way. Most of the original soil overlying the rocks was swept away. Prominences were torn away or planed down, and depressions were filled up. Masses of rock were ground to powder, and boulders were transported to entirely new surroundings. The advance of the ice over the country largely disregarded the rock forma- tions, as it did topographic forms, so that the rocks and soil materials from many sources were mixed and ground together. In this way, the granite boulders strewn over the surface near the southern margin of the ice extension in the United States were derived from points hundreds of miles to the northward, even into northern Canada. The movement was not straight south, but deflected by broad obstructions in the land, so that the source of the soil in any region is determined by the direction of movement in that section. This movement may often be traced by the kind of rocks which have been left, and may lead back to the ledges from which they were derived. The relation of glacial soils to the underlying rock depends entirely on the conditions which prevailed 56 THE PRINCIPLES OF SOIL MANAGEMENT in that region when it was formed. In central Michigan, the soil bears scarcely any relation to the underlying rock of the region; but, in Southern New York and Northern Pennsylvania, the very shaley character of the soil may be traced to the broad area of shale rock which underlies all that section of country, and which was the main source of the glacial debris. As one passes northward through the finger-lake region of New York, the proportion of limestone and other foreign material resting on the gray shale increases until the exposures of ledge limestone are met at Syracuse and Rochester, portions of which rock had been raked far southward by the ice-movement. This shifting and mingling of material must always be kept in mind in examining glacial soils. Purely glacial deposits differ in chemical and physical properties from soils derived from the same formations by other means. There is a large element of mechanical grinding without any large amount of chemical change or solution.. The particles have not been subjected to long-continued leaching, which characterizes residual or marine soils. Such material is chiefly rock-flour, that is, pulverized rock. The readily soluble minerals and ele- ments are therefore present in proportionately larger amounts than in soil formed by other means. While a residual soil from limestone may be very poor in lime carbonate, a glacial soil formed from lime-rock is often rich in lime, sometimes containing 50 per cent of that constituent, as has been found in some Dakota soils. As appears from the tables of analyses, such soils are gen- erally rich in all of the basic elements. OONROTNP WHE CHEMICAL COMPOSITION OF GLACIAL SOILS 5d TABLE VI CHEMICAL COMPOSITION OF GLACIAL SOILS HyprocuHioric AciIp ANALYSES gi II III IV V ‘Val x) ° ye ee a] | 6] © |3.6/35 co] €s5 | gy | Ge | 388 | See 8g | 82 | 32 | 28 | #ae| #38 oo = pe @ = 3 ae | a2 | "5 | de | 3 | ie inca clan) a eure es Gs >) 7) SAMBO NTIE. 2 2..).ct 87.85 | 83.80 | 83.87 | 89.20 | 73.95 | 74.05 Lo SUN (STO) ee DCSE IRPIRS ed Ly nn eat eal | ONCE: Th Se . Alumnia (AI,O,) ....| 3.46] 4.11] 4.26] 3.69] 4.63) 3.27 . Ferric iron (Fe,O,)...} 3.30] 4.72] 3.638] 2.26] 3.05] 5.44 Meer rte CE CLI] aac fi dsace ls ee sae Die poe ate Op ate ens Sulfur trioxide (SO,).| 0.04| 0.03} 0.10} 0.03} 0.04] 0.12 Phosphoricacid(P,O,)} 0.11] 0.09] 0.15] 0.12} 0.26] 0.16 remme (OA)... a. 0.25| 0.18} 0.69} 0.13] 0.70] 0.51 Wenn cioxia (CO) 1.02. | ccs fie | ees | O86) 0.09 . Magnesia (MgO) ....| 0.39] 0.45] 0.62) 0.387] 0.36] 0.22 30 6) 0.34] 0.29] 0.78} 0.23] 0.42) 0.16 peonada (oO)... 2. ; 0.25} 0.22| 0.56) 0.21) 0.40] 0.22 OSS a a See Ce are ea O Ts Gechar a trea a ita ees . Organic matter ..... Rear ORM Co rere oa Kaede fees won . Volatile matter ..... 4.09| 5.92] 5.64] 3.86] 9.12] 7.29 The physical properties of glacial soils are also dis- tinctive. Excepting subsequent modifications due to water, such deposits show little or no stratification or sorting. They are heterogeneous in material and arrange- ment. Much of such material is termed boulder clay, from the mixture of coarse and fine particles. It is also to be noted that such soils contain, relatively, a larger proportion of silt particles, and a smaller amount 58 THE PRINCIPLES OF SOIL MANAGEMENT Fic 16. Section of glacial soil, showing its uneven texture and dense structure. When unmodified by water action, it usually shows no stratification of clay, than soil formed by purely chemical process from the same rock. Associated with the results of pure ice-action is much modified glacial till, due to the influence of great volumes of water. Naturally, the melting of the ice results in immense volumes of water, which drain away over, under, or along the ice margin. Temporary streams of large size and great violence existed GLACIAL SOILS 59 and there were also ponds and lakes, some of the latter of very large extent. This water further assisted in moving the ice debris. Such deposits are called modi- fied drift, or aqueo-glacial deposits. For this reason, they have in part been included with glacial soils. The streams, ponds and lakes associated with the ice have given rise to much stratified material, and these de- posits are intimately related in many ways to the purely ice deposits. Beds of gravel, sand and clay are frequently found, and so intimate is their relation to the purely ice deposits that they are sometimes, though incor- rectly, classed with them. These deposits of modified till generally rest upon the distinctly ice deposits, and are of large extent. Around the Great Lakes and in the large valleys of New York and New England, in the valley of the Red River of the North, and in many other places in the Central States, are large areas of such stratified glacial material, ranging in fineness from heavy clay to coarse gravel. These materials constitute some of the most valuable agricultural lands of the country. The Great Lakes region is notably productive, and the Red River Valley of the North is celebrated for its production of small grains. The thickness of glacial deposits varies greatly. Pre-glacial valleys may be filled in, and the evidence of their presence completely obliterated. In general, the topographic effect of glacial action is to level the surface. However, in the New England states, where the country is very mountainous, the rocks very hard and the pre- glacial soil blanket meager, the present soil covering is generally thin and very stony. 60 THE PRINCIPLES OF SOIL MANAGEMENT Further west, where the country is less rugged and the rocks less refractory, the soil covering is of greater depth and generally less stony. In the states of the Mississippi valley, the broad, level areas of excellent agricultural soil are very largely the result of these glacial influences. 21. Wind or eolian soils.—Attention has been di- rected to the transporting power ‘of wind. It is continu- ally picking up particles, which are deposited in accord with the same general laws which govern water deposits. The material thus carried, often to great heights, is again brought to the surface by gravity. These particles are frequently accelerated in their fall by rain and snow. Every particle of fog, of rain and of snow has for its nucleus a particle of dust around which con- densation began, and for this reason the atmosphere is always most clear after precipitation. Large amounts of material are, in the course of time, brought to earth in this way. This continual deposition from the atmosphere is illustrated by the layer of dust that quickly accumu- lates in any unoccupied building, however tightly it may be closed. Besides this general filtering of dust particles from the atmosphere, there is the definite drifting of soil by wind, of which sand-dunes are the most common illustration. These occur in many parts of the world. They are likely to be developed wherever dry sand is exposed to the wind. Related to these modern wind deposits are immense areas of soil of great agricultural value, the origin of AEOLIAN SOILS, LOESS 61 _ which is not clearly understood, but which appears to owe its existence, at least in part, to wind deposition. This is the so-called loess, a fine, silty soil of remarkable uniformity in physical and mineralogical composition. It covers thousands of square miles of country through- out the Mississippi valley and its tributaries, from Cin- cinnati to western Nebraska, and from west-central Wisconsin to southern Mississippi. It lies uncomformably over formations of many ages, as a mantle of soft earth of varying thickness. It does not extend over the whole of the region mentioned, but alternates with other formations, especially drift. It imparts to the regions on which it rests a soil character greatly different from what would exist were it absent. Neither is it limited to the United States, for it occurs extensively in central Europe, where it extends from northern France across Belgium, and up the Rhine, Oder and Vistula valleys in Germany; and into central and southern Russia, where it is the basis of the famous “black earth,”’ or tschernosem. In northern China, von Richtofen has described it as covering a large part of the region drained by the Hoang-Ho, where it reaches a thickness of 1,000 feet. In thickness it varies greatly. Over much of the United States it is only a few feet in thickness, generally thinning toward the outer margin. In the central areas it may be 150 to 200 feet in thickness, and, simi- larly, in other countries it is of variable thickness, reaching the great depth mentioned above for China. A striking physical character of the loess is its ability to stand for a long time in vertical cliffs, although 62 THE PRINCIPLES OF SOIL MANAGEMENT so soft it may be easily carved with a shovel. Another character common to much of the formation is the presence of nodules and tubes formed by cementation by lime carbonate. The loess is associated in occurrence with the margin of the glacial deposits, especially in America and Europe, and possibly in China.: Just what this relation is is not known, but much of the loess seems to be a fine rock- flour of glacial origin, which has been drifted by the wind and deposited on both purely glacial deposits and on residual and water deposits, for it extends from Illinois southward over the limestone region on to the coastal plain in Mississippi. The adobe soils of the arid regions are thought by some to be related to the loess in mode of formation. Adobe also has peculiar physical properties, later to be mentioned, but it exhibits a closer relation to water deposits with which it has been classed. In parts of Kansas, Nebraska and other western states, are soils formed of dust from volcanic vents and deposited from the atmosphere. Such dust may be so fine as to be carried long distances and remain in sus- pension for a long period. Dust from the eruption of Krokatoa, in the island of Java, was wafted around the world, and gave a red glow to the sunset for a year after its discharge. Table VII shows the chemical composition of the wind deposits, chiefly loess. Columns I and X are analyses of the hydrochloric acid solution. All others are complete analyses. Agriculturally, sand-dunes are of small value, largely because of their unfavorable 160: 1 aes 122 Ee bse eames Satie 60°¢ 90. | OST 89'S 670 | est aa { roan S10 Po ee GOL | PZT eee i 1° ee'6 | 19° sco | IST ss6 | 88g 600 | TIO a ES i aon | ae TO. ae ee Soi Io’ cer | Zo'Z 96° L bes ot { 166 | 92°0T 1629| 60°TL | 26°89 | OT'2Z9 coy ances 4055 | OF At al zh ot = a Zo | a ee | a9 OD oH) Ss 1 a a <5 Bo ais BZ =r ca 5 cas g tap ° ro) =) e| 8 E x XI IIIA IIA "S820T IIIS opBi0joy ‘raAueq IA OLS VIL 80'T (StS oo P €9°6 96°8 éT'0 G10 L£9°0 19'S c6'2 69°09 Iddississtyq ‘BINGSYOIA *S820T IIS ree ye 194} BUI OII}BIOA, 19}} BU DIUBSIO Cleves ae eh ae ee Pe ace (OS) Used (O*8N) Bpog (O®]X) Bisouseyy a6). egret ny et "* COO) Prxorp woqrey ° sVetistes on hie rate (O89) oull'T Co*d) prov oroydsoyg OS) Rison antis ake (O24) UOIL SNOIL9 Sie “°C'aq) WOM O10 Woes: # ints wale. COIS) BoTTIS ee Srqnyost] “spIos ‘soTdules ¢ asvIOAY *SoUBJS UleJSaMYIION puy ‘SUOISO1 ysnp ‘pueseuy AZIIS GO'% | 09'Z ESL (S02) €Fz SPI |S | 89'T Crit 6o%. | 10T 6F'0 | 189 | 6E'0 69T | Tre | 6¢°T 60°0 | 900 | €2'°0 90°0 | ITO | TS'0 clO | 190 | 96'0 SoG |LOG 1 ee 97'S | F9'OT | GOST OF TL | T9'F9 | 89°92 ob : aw Ge 4 geriia a ey Evie seo a 5. ey fo} mn ce | | 2 ws a Q A AI III I NOILNTOS dlIoy OIHOTHOOUGAFL “IIOG ssdoT AO NOILISOdNOY) TVOINGAH,) IIA YTavy, ° Co TY) vrawnyy ° IIJVM * ANMHISDOSOKROD (63) 64 THE PRINCIPLES OF SOIL MANAGEMENT physical properties. They are also likely to be highly silicious. But the loess formations are of great agricul- tural importance, and in this country they constitute some of the most important soil types. In some sections its value has been greatly reduced by erosion. Some of the bluff areas along the Mississippi river are thus modified, and some of the loess of China is also deeply eroded. , But the physical properties, as well as the chemical properties of loess, combine to give it in general a high agricultural value. VI. HUMID AND ARID SOILS In discussing the process by which soil is derived from rock, attention was directed to the fact that phys- ical disintegration results in material having different properties from those derived through chemical decom- position, and that the relative prominence of these — two processes is dependent largely on climate. Aridity is one of those phases of climate which markedly alters the balance between these two processes, giving the larger ascendancy to the physical. Soils formed under arid conditions are less fine in texture than those formed from the same rock in humid regions. A study of soils in the two regions reveals a much greater prevalence of the coarser soils—the sandy and loamy soils—in the arid region. But chemical processes are not absent, for in every arid region there is some precipitation which is able to bring about changes in the minerals, although the CHEMICALCOMPOSITION OF ARID AND HUMID SOILS 65 products of these chemical changes are likely to accu- mulate in the soil because of the absence of sufficient moisture to leach them away. (See page 307.) Their presence is evidenced by incrustations on the particles either at the surface or in the mass of the soil. For this reason, the unfavorable conditions which would tend to result from the coarser grade of the material is more than offset by the large amounts of readily soluble elements present. These differences are well illustrated by the following table, compiled by Hilgard from the results of many acid analyses in the two regions. All soils derived from limestone are excluded. TaBLE VIII CHEMICAL COMPOSITION oF ARID AND Humip SoIts StrRoNG HyprocHitoric Actin ANALYSES I Ti Ill Semi-arid re- gions. Average Arid regions. Humid regions. Ave of a fo) aie sanwples pee EO ac ekn 1. Insoluble residue..... 84.17 75.04 69.16 2. Soluble silica (SiO,)... 4.04 8.46 6.71 3. Alumnia (AlI,O,)...... 3.66 4.57 ak 4. Ferric iron (Fe,O,).... 3.88 2.08 5.48 5. Sulfur trioxid (SO,)... 0.05 0.02 0.06 6. Manganese (MnO,) ... 0.13 Le 0.11 7. Phosphoric acid (P,O.). 0.12 0.21 0.16 me rame (CaQ).:......... 0.13 0.70 1.43 9. Magnesia (MgQO)...... 0.29 0.47 1.27 moods (NaO) ........ 0.14 0.32 0.35 meer otaeh (1KO)... 2... . 0.21 0.33 0.67 MeCRP IIIS os ce es 1.22 3.24 113 13. Water and organic PMEREUOE NS 6 che ys sta e5 4.40 8.55 5.15 66 THE PRINCIPLES OF SOIL MANAGEMENT From this table it appears that, in spite of the finer texture, the humid soils contain 15 per cent less soluble material and, as compared with the semi-arid region, 9 per cent less soluble material. VII. RESUME OF SCHEME OF CLASSIFICATION AND GEN- ERAL CHARACTERISTICS OF THE GROUPS From the foregoing discussion it appears that each group of materials may have properties which are fairly characteristic. Physically, the sedentary materials differ from the transported material chiefly in arrange- ment. In the transported soils those laid down by wind and water are distinctly stratified—that is, ar- ranged in layers. This is the result of settling or sedi- mentation from a fluid, and such soils are frequently spoken of as sedimentary. Wind and water are the only two media in which sedimentation occurs in nature, and therefore this arrangement indicates their influence. Thereby the extent and variation of such epee may be largely interpreted. Upon the basis of these formative differences, it is ._pessible not only to identify the different soil materials but to represent their extent upon maps. The broadest separations represented by sedentary and transported soils may be termed divisions. Within these divisions are sub-divisions, according to the agency or material involved. These are termed provinces, that is, meaning the region or province where a certain set of conditions prevailed. For example, in the sedentary division are residual soils from igneous rocks and from limestone SOIL CLASSIFICATION 67 rocks. These latter constitute soil groups, and, simi- larly, in the transported division there is the sub-division or province of soils deposited in water, and these are further sub-divided into those formed in the ocean, marine; in lakes, lacustrine, and by streams alluvial, each constituting a soil group. Within the soil group the first division is the soil series, based upon the fine- ness of the material, color, drainage and other properties, and each series is made up of soil types, the material in each one being practically identical in all respects. The series and type distinctions will be better under- stood after a consideration of the physical properties of soil. Maps of soils based upon such a classification are constructed by several countries and institutions, the most extensive being the United States department of Agriculture. These maps are constructed upon dif- ferent scales, but one inch to one mile is the most com- mon. The maps are accompanied by legends and reports, for the proper explanation of the conditions in the area reported upon. Chemically, there is also a wide variation among soil materials in the total amount of the elements present. It might be expected that the repeated and long-con- tinued mixing of materials from many kinds of rock would result in a very great uniformity in all soils. This is true of the number of elements present, for no important element is absent from any soil. But the amount may differ greatly. Aside from organic soils (cumulose), the most striking differences occur in sand soils. While the average analyses of many sandstones and sand soils reveals a fair amount of all elements, 68 THE PRINCIPLES OF SOIL MANAGEMENT there are materials composed almost entirely of the refractory mineral quartz. Such, for example, is the barren LaFayette sand of Maryland, which contains 94.4 per cent of silica, and a sandstone occurring in Utah contains 96.6 per cent of silica. Doubtless, dune sands as rich in quartz might be found. Not all silica is in the form of quartz, but it is an indication of the latter. Fine-textured soils also exhibit much variation, but do not go nearly to the extreme in silica content shown by sand soils. It is the very exceptional soil of any grade of fineness which does not contain, in its ultimate analysis, a fair amount of all of the essential mineral plant-food ele- ments. Other conditions must also be taken into account in determining the crop value of such soil—its physical. properties, the climate, the crop, the introduction of new materials by wind, the movements of water and the action of plants and animals. 2. Tue Sort Mass. PuysicAL PROPERTIES OF THE SoIL AND THEIR MODIFICATION The term soil is used to designate that superficial portion of the earth’s surface in which plant roots distribute themselves. This includes sand, gravel and boulders, containing practically no available plant-food material, as well as rich garden soil. 22. Soil and subsoil—A common and natural dis- tinction is made of (a) the top soil, which is called “‘soil,”’ and which usually extends to the depth of the - ee I = —— ee THE SOIL AND SUBSOIL 69 furrow slice or a little deeper. It is characterized by being darker in color, and more friable and porous than (b) the subsoil, which constitutes the material beneath the soil in which plant roots are found. (See Fig. 13.) A distinction is sometimes.made between the upper and the lower subsoil, the former being the layer of subsoil lying between the top soil and a depth of twenty- four inches from the surface, the remainder of the sec- tion being the lower subsoil. In humid regions the subsoil is usually less productive than in arid regions, owing to the greater amount of leaching, and to deficient aération consequent on the movement of large quantities of water through the subsoil. Plowing up the subsoil in the humid region frequently results in a decreased productiveness, while in an arid region the soil and subsoil may be freely mixed without injury, and good crops may be grown even where the top soil has been entirely removed, as is sometimes done in preparing land for irrigation. The soil substance may be conveniently divided into two groups of constituents which exhibit quite different properties. These are the inorganic and the organic. I. INORGANIC CONSTITUENTS The inorganic constituents of the soil are more or less modified particles of rock, varying in size from boulders and coarse sand to the finest dust. Each particle may consist of several minerals, but in those smaller than coarse sand it is unusual to find them com- posed of more than one mineral. 70 THE PRINCIPLES OF SOIL MANAGEMENT 23. Texture.—The size of the individual -particles in a soil is a large determining factor in all of its prop- erties. The term texture is used to refer to the size of the individual par- ticles of which a soil is composed. In shape the particles are very irregular. Being minerals or mineral ageregates, they tend to have the characteristic lines and faces of their species. Ordinarily, however, the nu- 4 pe be Bie ene photoes Magi merous forces that ed about 11 iameters. ifferences in color indicate differences in mineral composition. Each have been at work particle composed of one mineral. in the formation of the soil have rounded or broken the mineral into angu- lar, jagged or partially smoothed fragments. The relative number of particles of corresponding sizes varies greatly in different soils, some being composed largely of coarse particles while others are made up largely of fine ones. The relative proportion of these various -sized particles influences greatly the physical properties of the soil. 24. Textural classification.—When a soil is divided into groups of particles of approximately one size, the process constitutes a mechanical analysis and each group is a soil separate. The limit in size of each of these groups is arbitrarily arranged, and is determined SOIL TEXTURE ; at by the relative value of the different sizes in determin- ing the properties of the soil and its crop-producing power. It is found that the fine groups exert relatively much more in- fluence, weight for weight, than the coarse ones. There- fore there are more divisions made among the finethan among the coarse particles. 25. Textural groups.— A num- ber of systems of erouping have been devised. The limits of these groups Pacts Pe soil, pig paerorraph. aaeenined S about iameters. Stained so that differences have been deter in mee some reee ee oe so age age a } as in Fig. : e particles have the same char- mined b y. t h € acteristics as those of fine sand. Some of the method of analysis smallest particles are of the size of clay. used by the investigator and by his judgment of the relativé agricultural importance of each group. A further element which limits the number of groups is the practicability of recognizing distinctions in the field based upon them. The following table, from Bulletin 24 of the United States Bureau of Soils, exhibits the most generally known of these systems of grouping employed in mechanical analysis. Some of these multiply groups in the small particles, while others give prominence to the sand particles, ‘Ul'Ul GOO’ uvy} sso] ‘ABIO *S “Uru TC -CO0 “I]IS eUlY “2 “Uru GO-TO’ “HIS ‘9 ‘wreul [’—¢O ‘pues ouy Ale A *G ‘Ulu CZ'-T° ‘pueB “ur Ul O'T-G ‘pues eslBvO0yD pus [Is ‘pues ‘JeAvIS JO SUIBIS JO 9OZIS BATLBIAY ‘GL “OIA S$ OUI ‘fF ‘WU G’'—cz ‘puBs UINIpey “E “- Z UrWO'Z-O'T ‘JeAvIS OUT *T :ABlO c (4eqerenpine uo) ‘AVT) UNV LUG “UWS “TID IO SNVUD AO TLIG AMINTTY TEXTURAL GROUPS te TABLE VIII a U.S. Bureau BP i agree | OSRORRE | oP tne oo) a Boers oeienstaie eee 3.000 3.00 2.000 1.0000 ES or ans 1.000 1.00 1.000 0.3200 eA 0.500 0.50 0.500 0.1000 aE ees 0.300 0.25 0.250 0.0320 Bee A (eee aes 0.160 0.05 0.100 0.0100 BES Soe 0.120 0.01 0.050 0.0032 es hares AS. 0.720 Be 0.005 0.0010 Whe ha PRAT tas « 0.047 ees, ah ae eget LRG eee 0.036 (i) AS sm 0.025 SP lpg a 0.016 Pee ete 5 0.010 ae ae ne toes Of these systems, that of the Bureau of Soils has been applied to the largest number of samples and is most widely known. The names which it applies to its dif- ferent groups or separates are as follows: ae got nl x as ee ee 2.000—1.000 m.m. Ps a ANE Cs OS ae a 1.000—0.500 m.m. Sooke tlihigcc(( 2 ak, ee 2 0.500—0.250 m.m. a aE SS ee 0.250-0.100 m.m. PEM GINA ef ds hc be ee 0.100—0.050 m.m. 2 ls Aine Ses aaa 0.050-0.005 m.m. (1 BE Shy anes nea re 0.005—0.000 m.m. All that material above two millimeters in diameter is classed as gravel and stone, and in any complete examination must also be taken into account. The material resulting from the above analysis is sometimes termed the fine earth, in distinction from the gravel, etc. That there are distinctions which should be made between the grades of gravel is obvious, for small 74 THE PRINCIPLES OF SOIL MANAGEMENT pebbles constitute a very different condition from large boulders in all phases of tillage. The relative dimensions of the particles in the groups may be illustrated graphically by the following diagram. Fic.20. Diagram illustrating the relative size of the groups of particles, made in mechanical analysis by the Bureau of Soils Classification 26. Agricultural classes based on texture.— Ob- viously, no natural soil iscomposed entirely of material like any one of these groups, but a soil may contain a large proportion of material of any one size. Thus, a sandy soil is one containing a large proportion of sand par- ticles, and the coarser the sand or the larger its propor- tion the more sandy the soil appears. A clay soil is one containing a large proportion, but not necessarily a larger quantity of clay than of material of any other size. A given amount of fine particles has a larger effect on the properties of the soil than the same amount of coarse particles. The presence of silt particles in addition to clay serves to make a soil more heavy than if the same quantity of sand were substituted for the silt. MECHANICAL COMPOSITION OF SOILS 75 i Spee ene _. Fie. 21. Fine sand soil, showing the mechanical composition. Each vial contains the proportion of particles of given size found in the samples. Clay on the right; fine gravel on the left. Hor key to sizes, see Fig. 19 and page 73. Fia. 22. Silt loam, showing the mechanical composition. For explanation, see Fig. 21 76 THE PRINCIPLES OF SOIL MANAGEMENT A mixture of all the groups without the preponderance of the properties of any one group constitutes a loam soil. For purposes of a soil survey, a classification is made that permits of finer distinctions. The textures which have been recognized are given in the table opposite, together with the limits in mechanical composition Fic. 23. Heavy clay, showing the mechanical composition. For explanation, see Fig. 21. Compare with Figs. 21, 22. which they represent. It is of course, impossible to fix all of the limits in such a classification, and therefore only certain groups are specified. This scheme has been devised by the United States Bureau of Soils in its soil-survey work. All those soils having the same general texture, although they may have been derived in a very different way, constitute a soil class. Thus there is the sandy loam class, the silt class, the clay class, etc. The fol- lowing curves exhibit the average composition of several Silt loam Clay loam AGRICULTURAL CLASSES OF SOIL re TaBLE IX 1 2 3 + 5 6 a Me- Very Fine | Coarse} dium Fine Fine Gravel| Sand | Sand | Sand | Sand Silt Clay 2-1. | 1-.5 |.5-.25 |.25 -.10].10 -.05} .05-.005 005-0 m.m. m.m. m.m. m.m. m.m. m.m. m.m. More than 25 Gate Coarse Go (ise 2) |. ; ee ics sand More than 50% Less than 20% (1+2+4+3) (6+7) Less than 20% 0-15 —] Medium (1+2) : : sand More than 20% Less than 20% (1+2+3) (6+7) Fine Less than 20% Ls a ese sand (1+2+3) Less than 20% (6+7) 10-35 _ . | 5-15 sees ae bee: ee 7 More than 20% and less than 50% (6+7) Firie 10-35 | Doe sandy at ee < ae More than 20% and less loam than 50% (6+7) | 15-25 Less than Loam 55% (6) More than 50% (6+7) More than | Less than eb | 55% (6) 25% (7) 25-55 | 25-35 More than 60% (6+7) Sandy clay Silt clay Clay Less than | More than 25% (6) 20% (7) Less than 60% (6+7) More than | 25%-35% 55% (6) (7) More than 35% (7) More than 60% (6+7) 78 THE PRINCIPLES OF SOIL MANAGEMENT classes, as they are found in the field. The field classi- fication may not be strictly in aecord with the mechani- cal analysis, for the reason that the same essential conditions may result from more than one mixture of groups. By experience much facility in judgment may be attained. “3 SANDY ee amen 2 1 FINE 2 COARSE 3 MEDIUM 4 FINE 5 VERY 6 SILT 7 CLAY GRAVEL SAND SAND SAND FINE SAND * SOIL SEPARATES Fig. 24. Curves representing the average analysis of seven common field classes of soil Taking the soils formed in the same general way, alluvial for example, they are found, to exhibit all gradations of fineness from clay up to the coarsest gravel and stony loams. All these classes constitute a soil series. In the same way, there may be a glacial series or even several of them, lacustrum series, residual series, etc. The river-bottom soils of the Central states are chiefly classified by the Bureau of Soils into the Wabash and Waverly series. Some of the glacial soils into Miami, Volusia, etc.; coastal plain soils into Norfolk (yellow), Orangeburg (red), etc., through all the divis- ions, provinces and groups. TEXTURE AND CROP RELATIONS 79 This means that, while sandy loams or silt loams as a class are similar in texture, they may differ in many other properties of importance in plant production. A complete series is one in which all the possible classes are represented. Some idea of the relation of these classes of soil to crops is given by the following curves. These soils are especially suited to the production of the crops with which they are associated. 1 _ NORFOLK, COARSE SAND 8. COLORADO FINE SANDY|LOAM | 4__ WABASH LOAM x _5 _ MIAMI CLAY LOAM 8 _ DUNKIRK CLAY ~ — 1 2 3 + 5 6 7 FINE GRAVEL COARSE SAND MEDIUM SAND FINE SAND VERY FINE SAND SILT CLAY SOIL SEPARATES Fia. 25. Curves showing the relation of soil texture to crop adaptation 27. Some physical properties of arid and humid soils.—In discussing the formation of soils, attention was directed to the effect of climate upon the process, and it was noted that under arid conditions physical disintegration is likely to predominate over chemical decomposition, which results in an average coarser text- ure of the soil. This appears especially in the greater proportion of soils of the sandy and loam classes to those of the silt and clay classes. Climate also exercises a modifying effect as between SO THE PRINCIPLES OF SOIL MANAGEMENT the soil and the subsoil. In humid regions, the large rainfall and consequent seepage through the soil is associated with a greater degree of fineness in the sub- soil than in the soil. On the other hand, in arid regions where there is not this large rainfall, and consequent leaching, the subsoil is not finer than the soil, and, in fact, is inclined to be more coarse. 28. Some properties of soil separates and classes.— As has been indicated, the justification for a study of _ individual soil particles from an agricultural standpoint is in their fundamental relation to the management of the soil. Every farmer is well acquainted with the striking difference in crop relations and tillage properties of sand and clay. He well knows that they must be managed differently and are suited to different crops. He knows sand to be better suited to early maturing crops, like truck, than to late crops and the grasses. He knows that one does not withstand dry weather, while the other will carry a crop through a long period of drought. The cause traces back to the size and consequent properties of the soil units. This will appear more clearly in the discussion of soil moisture. 29. Number of particles.—Since soil particles run to very small diameters, the number in any given mass or volume is very great. This is shown in the following table, which gives the number of particles in 1 gram (1 lb. equals 453.6 gr.) of each of the fine earth separates, considering the particles to be spheres of mean diameter and of specific gravity 2.65. If the particles of a soil are assumed to be spheres NUMBER OF SOIL PARTICLES 81 of uniform diameter and weight, the number in a given mass of soil may be calculated from the following formula: Hennes ciiage Si NN Hg aR? X2.65 1D? X2.65 6 Where N = Number of particles. W = Weight of soil used. R= Mean radius in centimeters. D= Mean diameter in centimeters. $7R? = Volume of sphere. For example, the mean diameter of the medium sand class is .0375 centimeters, and in 3.5 grams of this material there would be 3.5 3.5 . N 0875" X2.65 0000737 70 Parhieles 6 From the mechanical analysis which gives the weight of each class of particles in a given amount of soil, the number of particles of each size may be calculated by use of the above formula, and the sum of the particles in each class gives the total number in the sample. TABLE X.—NUMBER OF PARTICLES IN ONE GRAM OF PURE SOIL SEPARATE, SUPPOSING THAT ALL PARTICLES ARE SPHERICAL Diameter in Number of particles m.m. In one gram Te PAVE ee ee 2.000—1.000 De Woerde sand.) 0 30s. 1.000—0.500 L723 Mediim Band... 4.546 8.0%: 0.500—0.250 13,500 LOS a a 0.250—0.100 132,600 N Ory AMG SAMO: soy. boss. ees. 0.100—0.050 1,687,000 RES EE Se Ee a tg a 0.050—0.005 65,100,000 S17 7 ay aL Se an eed GER 0.005-0.000 45,500,000,000 F 82 THE PRINCIPLES OF SOIL MANAGEMENT Since normal field soils are mixtures in different proportions of these groups, the number of particles in unit weight of any class will be different from those shown above, and will not reach the extreme upper limits. The number of particles in one gram of the classes of soil whose analyses are shown by the curves on page 78 is approximately as follows: TABLE XI.—APPROXIMATE NUMBER OF PARTICLES IN ONE GRAM OF SOIL RO Gri eattER ooh. Sas sd wR ac os os eee 3,276,000,000 Meera win aU) See eae, Bele 3,956,000,000 PME MONI oF. 10. ca Yu 2 wares ve Au yheti Woh e RAE 6,485,000,000 OMS HANEY FORT: wk. inc a ke 4,902,000,000 Sep ation ti oL, Bas Leeper ees ARGUE 9,639,000,000 Re OnE sas a tet 2 asia, br agaens ole Naan me 16,371,000,000 RI Rd Grav oe 4s waghtetn 5. die Puts a 19,525,000,000 30. Surface area of soil particles.—The significance of these large numbers of soil particles in any mass of soil lies in their relation to the surface area of the particles. These surfaces of the particles hold on to the moisture the more, the greater their area. This large surface also increases the rate of chemical solution, by which the food constitutes contained in the mineral particles become available for the plant’s use. Another important property of this immense surface area of soils is to retain food materials in a semi-available form, as will be ex- plained in discussing the absorptive power of soils. (See page 299.) The surface area of a fine-textured soil is greater than the first thought might indicate. This immense area exposed by soils is shown by the following table, which SURFACE AREA OF SOIL PARTICLES 83 gives: (1) The area in square feet of one gram of the soils represented by the curves on page 78. (2) The surface area per pound of the same soil. (3) The ap- proximate weight per cubic foot of the material in the field. (4) The approximate area of surface in one cubic foot of these soils as they occur in the field. The surface area of the particles in a given weight of soil may be calculated from the formula. S=7rD2N. Where S=Surface area in square centimeters. D=Mean diameter in centimeters. N=Number of particles in the class or separate. Thus in the calculation on page 81 there were found to be approximately 47,500 particles in 3.5 grams of medium sand. Their surface area, provided the particles were spherical, would be: S = 7.0375? X 47,500 =212 sq. em. =32.8 sq. in. TaBLE XII.—INTERNAL SURFACE AREA OF FIELD SOILS IN SQUARE Fret (Analysis of first seven represented by curves on page 78) I II Beats | IV pproximate Area pergram| “Totud. | weight per” |per' "cubic foot aL Sq. ft. Padada’ Sq. ft. . Coarse sand..... 0.8900 405.0 100 40,500 . Medium sand... 1.0440 473.0 96 44,500 . Sandy loam..... 1.8000 816.0 83 66,600 . Fine sandy loam. 1.6600 756.0 82 62,000 seeatb loam... >.) 2.9600 1,340.0 77 104,000 Cray loam... ... 4.0250 1,825.0 75 136,500 PUNE Shc hs week 4.4130 2,000.0 71 142,000 Sree AMEN io sees os 0.0708 32.2 110 3,540 OWNS RWNHe . Hobart clay .... 7.2820 3,316.0 60 200,000 84 THE PRINCIPLES OF SOIL MANAGEMENT From this table it appears that one pound of the average agricultural soil may have from about 400 square feet, in the case of coarse sand, to 2,000 square feet internal surface area, in the case of the average clay. A more reasonable basis of comparison, because of differences in volume weight, is that of one cubic foot of the material, as shown by the fourth column, from which it appears that these soils have from one to three acres of surface area. These are striking dif- ferences, particularly those between soils 8 and 9, which represent extremes in light and heavy soils, respectively. Number eight is the sand-hill soil of the Carolinas, and is of exceedingly low agricultural value. Number nine, Hobart clay, occurs in eastern North Dakota, and is derived from shale rock. The range in surface area per cubic foot of these soils is from one- twelfth of an acre, for the sand, to almost five acres for the clay. The latter contains 76 per cent of clay in the subsoil, the former 2 per cent. 31. Chemical composition of the soil separates.— There is some relation between the soil classes or senarates and their chemical composition. Quartz, for example, in the original rock resists decay and comes through largely as sand particles, while the silicate min- erals undergo much more decay which results in a larger proportion of clay particles, and this partial difference in derivation is reflected in the composition of the sepa- rates. The distribution of plant-food constituents and the general chemical composition of the classes of a soil is shown by the following table of results of acid anal- ysis, obtained by Loughridge as reported by Merrill. COMPOSITION AND SOLUBILITY OF SOIL CLASSES 85 TaBLE XIII Conventional name....... Clay Finest silt Fine silt |Medium silt re niet Per cent present in soil.... 21.64 23.56 12.54 13.67 13.11 Diameter of particles .... ees ae 11 oes cae 033-038 Constituents Per cent Per cent Per cent Per cent Per cent 1. Insoluble residue...| 15.96 tole 87.96 94.13 96.52 2. Soluble silica (SiO,)| 33.10 9.95 4.27 2.35 abit 4 3. Aluminum (Al,O,).| 18.19 4.32 2.64 2h 4. Ferric iron (Fe,O,;).| 18.76 4.76 2.34 1.03 5. Phosphoric anhy- arid. (P.0,) ... 0.18 O24 0.03 0.02 6. Sulfur trioxid (ic aes Ones 0.06 0.02 0.03 0.03 yonlgume: (CaQ)...... 0.09 0.13 0.18 0.09 8. Magnesia (MgO) .. 1.33 0.46 0.26 0.10 Beoda (Na.O) ..... Be, 2 0.24 0.28 0.21 19. Potash (K,Q) .. 1.47 0.53 0.29 0.12 11. Volatile matter .. 9.00 5.61 1.72 0.92 eae a oS. 99.84 99.30 100.00 100.21 Total soluble constitu- Sir SS ea le i or nr 75.18 20.52 10.32 5.16 This table illustrates, coarse-textured class. (1) The much greater solu- bility of the fine particles in strong hydrochloric acid. (2) That the absolute amount of food elements dis- solved is greater in the fine-textured class than in the (3) That the ratio of food ele- ments dissolved to the aluminum and other refractory constituents dissolved is narrower in the coarse than in the fine-textured class. Failyer’s results are summarized in the following table. 90°¢ 10° zo Z9°2 98'S % ACI Cie 08% eel es'T LEG % HIS (OM) YseI0g Al Ill TI I STIOQ NVOINANY FO YHAEWAN ADUVT V JO AVARTAY h ‘SALVUVdEAG TIOG JO NOILISOdWO) TVOINUH(Y) TVILUVG— AIX aTav GT SOE + Seo). 26-6 -|-6F 1 } 80'S, 260-607 cY BiG) Se aoe te aes [10s | | jeune ‘Apues ‘puy °z CLL OB T 88-4. Fg 69:6 UG Bell 98° G6 SIN ae ae as ar "* S[fos | [BIssoo] pue ]RDe[y ‘OL £6. Ly a 60° go jai LO" ve’ OL sO) | Ure [e880 ‘s[10s OULIBU WUNIpey, “2 gael OR a Wm ef 666 | 96°01 | 9CCI | LE eres BG Tle eat eae 80} 84S / | [e1jU9,) “eu SOUUT] | ‘sjlos yenptso1 AAvoPT “¢ OOF) Ce 96. ser v6 | G8 os OL GG L0° " * $0784S U194SBiT | ‘syoo i orydiowe | -jouw pur ouryyeysAso | ‘ros Jenpisor AABOPT “E % % oe i 9 % % % % % % pusg | Avg | ats = pueg | AtIQ | IS | pueg | APIO | AIS | pues sojdures jo puly pue Joaquin (OSX) Plsouse]Y (OB8D) sry (S{Q%q) plow ouoYydsoyd (86) MODIFICATION OF SOIL TEXTURE 87 These figures, and those published by a number of other experimenters, clearly show the larger portion of the phosphorus, calcium, magnesium and potassium in the fine-textured classes in all kinds of soil. The absolute amount of the food elements is also greatest in the fine separates. It is shown that those soils which have undergone the greatest weathering—the coastal plain soils—are much the lowest in the food elements through- out the different classes. On the other hand, glacial soils are relatively rich in these food elements. There is also much less difference in composition between the clay and the sand particles in glacial soils, presumably because these soils have been formed largely by mechani- cal processes, without much weathering or leaching. The arid soils presented are not fully representative, but they illustrate the high percentages of the food elements in all the classes of particles, although the same concentration in the fine particles is apparent. It is, therefore, concluded that clay particles are relatively richer in food elements than. sand particles. But in glacial and arid soils, and to a degree in residual soils, the sand particles are much richer in food elements than they are in soils of water-deposition, such as the coastal plain. 32. Modification of soil texture.-—The only feasible method of changing the texture of a soil is by adding to it material of a different texture. Thus, the green- house man considers the requirements of his crops, and by mixture of fine and coarse material obtains the texture which is necessary for their best development. This is entirely practicable where only a small volume 88 THE PRINCIPLES OF SOIL MANAGEMENT of soil is involved, but under field conditions modifica- tions of texture artificially are not practicable, because of the expense involved. The farmer must generally accept the texture of the soil as he finds it, and make the best of his conditions by suitable selection of crops adapted to his soil, and by such modifications of the structure of the soil as its texture will permit. 33. Structure.—Soil structure deals with the arrange- ment of the soil particles independently of their size. 34. Some aspects of soil structure.—The arrangement of the soil particles may be viewed in many different ways. Upon this arrangement depend several very important physical properties, which in turn have a fundamental bearing on chemical and biological prop- erties. 35. Ideal arrangements.—Taking the simplest case first, that of spherical particles of one size, these may be arranged in general forms: (1) In columnar order, with each particle touching its neighbors at only four points. (2) In oblique order, with each particle touch- ing its neighbors at six points. (3) These spheres may be gathered into larger spheres which rest together in the second order. In the first the unoccupied or pore space is 47.64 per cent of the total volume occupied by the spheres. In the second it is 25.95 per cent. In the third case, however, where there are spheres within spheres, the pore space is greatly increased—to 74.05 per cent. (4) On the other hand, if there are spheres of several sizes so that the small ones may rest in the spaces between the large ones, the total pore space will be reduced below 25.95 per cent, and the spaces may ARRANGEMENT OF SOIL PARTICLES 89 continue to be filled in by smaller spheres until the mass is practically solid, without pores. (See Fig. 26.) It is of course recognized that under field conditions these ideal arrangements do not pertain, but these figures illustrate the underlying factors which determine differences in pore space, and, also, differences in other physical properties. Soil particles are irregular in shape and uneven in size. When brought very close together, Fic. 26. Ideal arrangements of spherical soil particles: (1) Columnar order, 47.64 per cent of pore space. (2) Oblique order, 25.95 per cent of pore space. (3) Compound spheres in oblique order, 74.05 per cent of pore space. (4) Three sizes of spheres with closest packing, about 5 per cert of pore space. as occurs in mixing in a wet condition, their molecular attraction is brought into operation and, especially when dry, they are held together very securely. In this way the normal molecular attraction of the soil particles is increased by the deposition around them of the material in solution. Applying these principles to the soil, it is observed that there may be two general arrangements of the particles. (1) Each particle may be separate and free from its neighbors. This is a separate-grain structure. That is, each particle of soil functions separately. When by proper manipulation the particles are so packed together that the small particles quite completely fill in the spaces between the large ones, so that a very dense 90 THE PRINCIPLES OF SOIL MANAGEMENT mass is formed (Fig. 26, No. 4), the structure is termed puddled. The term puddled, in this connection, is re- lated to the fact that such an arrangement can be Fic, 27. An example of undesirable structure. A clay soil which had been uddled by tramping when wet. “Bad tilth.””’Compare with Fig. 28, showing ‘ideal tilth.” Note also a type of auger used in examining soils. A common one and one-half inch wood auger welded to a one-half-inch shank, giving a total length of about three feet. obtained only in fine-textured soils when they are mixed (puddled) in a very wet condition, so that the fine particles will move into the large spaces. GOOD AND BAD TILTH 91 On the other hand, the small particles may adhere to the large ones, or a number of small particles may adhere together as a group or granule. When a number of united particles function together as a single larger particle or granule, the structure is termed granular. Fic. 28. Ideal tilth of a soil This arrangement is also termed the crumb structure. According as these groups are prominent or incon- spicuous, the soil is said to be well or poorly granulated. But when the granules reach large size, so that they interfere with the best functioning of the soil, they are termed clods. That is, a clod is an unsizable granule. 92 THE PRINCIPLES OF SOIL MANAGEMENT It is well known that a box of baseballs, or a pile of boulders, or even a box of sand, does not adhere together to any appreciable extent. That is, in all the coarser-textured classes, certainly down to the size of very fine sand, there is very little tendency to granu- late. But in the silt, to a small extent, and in the clay, to a very great extent, granulation is strong. 36. Porosity.—In a mass of particles there is some unoccupied or pore space. If the particles are fine, then the intervening spaces are correspondingly small; if large, the spaces are large. In the discussion of ideal particles above, it was shown that the pore space is theoretically independent of the size of the particles, with any given arrangement. There would be as much pore space in a cubic foot of buckshot as in one of marbles. But in the soil this is not true. For, the finer the particles, the larger the proportion of pore space is found to be. A clay has much more total pore space than a sand, although the individual spaces or openings between the particles are much smaller in the clay. The approxi- mate per cent of pore space ‘in a soil may be calculated by use of the following formula. Vw veo as Vp r= Vs 100 sae Where P= Per cent of pore space. Vs=Volume in c.c. occupied by the soil. Vw = Weight of water equal to weight of soil in grams. Vp= Volume in c.c. of pore space in soil. 2.65=Specific gravity of soil particles. POROSITY OF SOIL 93 Another and more simple formula which may be used in the calculation of the pore space is as follows: . gaa ADOBE SE P=100 ae 100 Where P= Per cent of pore space. Ap. Sp.=Apparent specific gravity or volume weight. Ab. Sp.=Absolute specific gravity of soil material. 100% =Total space occupied by soil mass. This relation between texture and pore space is exhibited by the following table of figures for soils in field condition. Per cent by volume BR rer AMA 8 nti 2 oes: Sie an PES RGSS wR © ade 8S 33.50 “EC SS CoE 1 Milan ym Rees Se Bem gs aa a 40.00 See memimna saints (a7. oo ete th Ga. ea. Raed '.41.80 ME MIC TSRING AI ic Got oa ta ti neh wi Spe cage o didphie Wee 44.10 Oe CT '5 dk FE ee ee 51.00 yeu ANON Y WORNTEBE S . a'8 oo = se Cah ves ole Sg le ae 50.00 Po SECT ap lA OS el SHAE 4 ear ak ea ae ae 53.00 BO ROME LE Surtees es Pes a ia os 3 54.00 SRE Cymer ee E RONG ers es tN AE Sea, abe wtlac a! ake Het 56.00 10; “Gumbo velay OWedtetield) 0c... o ses seta’ es 58.46 it Heavy clay (Potomac puddled).. 0c... 5.00555. 47.19 12. Very heavy clay CaT) oe ls Wy Danae nee ane Pa 65.12 The reason for the greater porosity of the finer soils appears to be, that the smallest particles are so light that they do not settle so closely together in proportion to their size as do the sand particles, because of the greater friction between their surfaces. When this is overcome by mixing in water, such material becomes dense. Treatment greatly affects the structure and therefore the porosity of the soil. This is well shown 94 THE PRINCIPLES OF SOIL MANAGEMENT by figures from the Rothamsted fields. The porosity of the surface nine inches of soil in an old pasture was 56.8 per cent, while in the same depth of a cultivated field it was 45.5 per cent. Extensive areas of loam soils in the North Central states have a porosity of from 45 per cent to 49.6 per cent. In many of the heavier soils it much exceeds 50 per cent, and in well-granu- lated clays it may reach 70 per cent, or in light sand it may be less than 40 per cent. In general, it may be said that about one-half of the volume of ordinary cultivated soils of intermediate texture is pore space. The diameter of the individual pore spaces is of importance, as well as the total volume of pore space, since these determine the capacity of the soil to retain and move water and to permit the circulation of gases in the soil mass, as well as to facilitate the extension of the plant-roots. 37. Weight.—The weight of soil is the result of two factors. These are, first, the absolute weight of the indi- vidual particles, or absolute specific gravity, and second, the volume of pore space in the mass. By reference to the table of minerals on page 6, it will be seen that the minerals entering into the soil vary greatly in specific gravity—that is, their weight as compared with an equal volume of water. They range from about 2.5 to 6 or 8, but the minerals which make up the great bulk of the soil—quartz, feldspars, micas, calcite, etc.,—all have a specific gravity of from 2.6 to 2.8. (See Table I, pages 6 and 7.) Many deter- minations of this property have been made. Fineness does not appear to have any material effect upon it. WEIGHT OF SOIL 95 Whitney has obtained the following specific gravities of composite soil separates. TABLE XV Conventional name Diameter (m.m.) | Specific gravity WRG ANC oe oo ccid se hae e poms 2.647 ares Ba tt oe Gee es 5b 1-.5 2.655 Whethive Satie. ees’ 6-.25 2.648 eS a a ane een eee .25-.10 2.659 Nermme Band. 2b ee .1-.05 2.680 eee Bates add Nay) EAB Dts .050-—.005 2.698 eRe eis cceans co G/s ao. HAIN S pe a 8 .005—.000 2.837 There is a very small increase in the specific gravity of the clay group, probably due to the greater concentra- tion of the iron compounds here as a result of chemical processes; but it is not sufficient to materially change the result. The average specific gravity of soil material is, therefore, usually taken as 2.65, and this figure is used in all calculations here given. Since the pore space enters into the calculation of the weight of any volume of field soil, this figure is much more variable for different soils than the one just given. It is directly related to pore space, and the larger the volume of pore space, the smaller the unit weight. ) Combining the figures for pore space given above with that for average specific gravity, the figures in the following table are obtained. The weight of a given volume of soil may be deter- mined from the pore space and specific gravity of the material, by use of the following formula. 96 THE PRINCIPLES OF SOIL MANAGEMENT Ws = Ww x (2.65 X (100 — P). Where Ws= Weight of given volume of soil. Ww = Weight of volume of water equal to volume of soil. P=Per cent of pore space. (100 — P) = Per cent of volume occupied by soil. Or the following formula may be used, and is often more convenient. Ws = Ap. Sp. X Ww. Where Ws = Weight of soil. Ap. Sp.=Apparent specifie gravity. Ww = Weight of volume of water equal to that occupied by the soil. Taste XVI | Weight per Weight per Volume weight ecubie foot acre foot or apparent | 3 - specific gravity, ah ee: Lbs. } . Clean Bae to Sis oe be 1.76 50.0 | 110.0) 4,800,000 ROBO REG as sb nen 1.60 45.5 | 100.0) 4,856,000 3... Medium Reme 3 665 | Oats ...... 557 Buckwheat.| 371 | Buckwheat.) 664 Lupine ....| 373 | Mustard ...| 843 23 ee 377 | Sunflower ..| 490 The variation exhibited by the figures for the crop, as well as for different crops, illustrates the influence of climate and soil upon transpiration. Other things ‘equal, more water will be required in an arid region than in one of humid climate; more in a warm region than in a cold region; more on a clay soil than on a sandy soil; more in a windy section than in a region of still atmosphere; more with a high soil moisture content; more on a poor soil; and, finally, more water is used per pound of dry matter produced in a small crop than is required in a large crop. All of these figures agree in indicating the large amount of water used in the production of crops. Not only is the total seasonal requirement to be considered, but the maximum de- mands of the crop at any period of its growth must be met. King observed that a single corn plant during the first week of August, when it was coming into tassel and the ear was forming, used water at the rate of 1,320 WATER REQUIRED BY CROPS 135 grams (one and one-half quarts) per day. Hunt observed in Illinois that in one week in July the growth of corn amounted to 1,300 pounds of dry matter per acre. As- suming the requirement observed in Wisconsin,—272 pounds per pound of dry matter,—this is equivalent to 1.55 inches of water. Assuming the average production of dry matter to be two tons per acre, the amount of water required ey ty, cS to produce such a yield of the staple crops, under the best conditions of management, would amount, accord- ing to the above figures, to from 427 tons to 1,820 tons of water per acre, which is equivalent to a rainfall of 3.7 and 15 inches, respectively. II. AMOUNT OF WATER IN THE SOIL Soils exhibit great differences in moisture content and in their ability to meet the needs of the plants for water. In some of the southeastern states, where the 136 THE PRINCIPLES OF SOIL MANAGEMENT rainfall is from fifty to sixty inches, crops suffer more from a lack of moisture than they do in some of the states of the northern Mississippi valley, with only a third of the rainfall. The hght truck soils of the At- lantic coast suffer much more from a lack of water than do the interior soils of heavy texture which are under the same rainfall and general temperature con- ditions. Plants in a dry greenhouse use more water than in the more moist outside air. These illustrations serve to emphasize the three factors which determine the amount of moisture a soil contains. These are (a) the available supply of water; (b) the retentive capacity of the soil for water; (c) the rate and amount of loss of water from the soil. Each of these factors depends on many conditions. 65. The supply.—The supply of water is obviously controlled by conditions external to the soil. These are the precipitation in the forms of rain and snow, under- eround seepage, and irrigation. 66. Retentive capacity of the soil.—The retentive capacity of the soil varies greatly according to its physical properties, As soils ordinarily occur in the field, they show the presence of moisture. This moisture is held quite intimately. Two soils may appear equally moist, yet have very different capacities to maintain crops. Plants suffer much more quickly from dry weather on sand soil than on clay soil, even when the soils appear equally wet at the outset. 67. Statement of water content.—Five different methods are commonly used in stating the moisture content of soils. These are: (1) In terms of per cent s9}8}Q pou 9y} Ul uUONEIIdIOoId TenUUe TRULION ‘TH ‘OTT 138 THE PRINCIPLES OF SOIL MANAGEMENT based on the dry weight of the soil. (2) In terms of per cent based on the wet weight of the soil. (3) In terms of the per cent of volume based on the total volume occupied by the soil. (4) In cubic inches per cubic foot, or in cubic centimeters per liter or per cubic meter. (5) In inches in depth of water over the surface of the soil. Of these methods the first is most largely used, because it gives the most definite and constant basis from which to derive any other quantities. The dry weight of a soil remains constant, and percentages referred to that base are always comparable. But it has several disadvantages which lead to inconsistent results in practical work. For example, 10 per cent of water in a cubic foot of clay soil represents a very different quantity of water from the same percentage in a sand or a muck soil, because of the very different volume weights of these materials. In the clay it would mean about 7 pounds, or 3.5 liters; in the sand soil 10 pounds or 4.5 liters; and in the muck soil 3.5 pounds, or 1.6 liters,—manifestly very different quantities of water. Or, to state the matter in a different way, 30 per cent of water in a clay, 12 per cent in sand, and 150 per cent in muck, do not represent as different volumes of water as is indicated by the figures, because of the relative weights of the soils. But, because almost any other figure can be readily derived from the moisture percentage expressed in terms of dry weight of soil, it has been very generally used, especially in laboratory studies. In field practice, a volume method is more convenient. STATEMENT OF SOIL MOISTURE CONTENT 139 The second method—that based on the wet weight of the soil—is unsatisfactory, because it is not only open to the objections made to the first method, but also because figures on moisture content of the same sample of soil are not comparable. They do not repre- sent the same degree of wetness indicated by the per- centages. For example, 100 grams of wet clay contain- ing 10 per cent of water would consist of 10 grams of water in 90 grams of soil, and 100 grams of wet clay containing 20 per cent would consist of 20 grams of water in 80 grams of soil. In the first case, the ratio of water to soil is as 1 to 9; while, in the second, case the ratio is 1 to 4, instead of 1 to 4.5, as the percentage comparison would indicate. The difficulty in deriving other figures from percentages based on wet weight makes its use undesirable. The third method, statement of percentage of water by volume, is the most rational of the first three. It gives a direct practical basis of comparison for all soils. It shows the volume of water held by the soil, which is really the important consideration from the point of view of the plant. For purposes of comparing the moisture content of different soils in the field, it is probably the most satisfactory method. Derivation of these quantities involves considerable calculation, and often the determination of some quantities not readily obtainable. The fourth method of statement is really a variation in detail from the third method by which specific quan- titive statements are made. One hundred seventy-two and eight-tenths cubic inches of water in one cubic 140 THE PRINCIPLES OF SOIL MANAGEMENT foot of soil, is a cumbersome method of saying the soil contains 10 per cent of water by volume. The fifth method is most generally used in field prac- tice in stating quantities of water. In irrigation practice, water is often measured in inches in depth per acre of area. In stating the quantity of water held within root range by different soils, this method is also direct and convenient. For example, a sand soil of a certain tex- Fic. 42. A common’ type of spike-tooth, iron-framed harrow. It operates as a shallow cultivator, and may often be very effective in mulching the soil and conserving moisture. ture will hold in the four feet surface 9 acre-inches of water; clay soil, 16; and a muck soil, 40 inches; which figures are directly comparable for purposes of crop- production. The method used in stating the moisture content of a soil will therefore depend upon the line of investiga- tion and the application of the results to be made. Both the percentage of dry weight and the percentage of volume will be used in this book, according to the point of view of the discussion. FORMS OF SOIL MOISTURE 141 68. Forms and availability.—There are three forms in which water may exist in soils: (1) Gravitational water, or that which is free to move through the soil under the influence of gravity. (2) Capillary or film water, or that which is held against gravity by the surface tension of the films of water surrounding the soil particles. (3) Hygroscopic moisture, or that which condenses from the atmosphere on the surface of the FORMS OF SOIL WATER HYGROSCOPIC CAPILLARY GRAVITATIONAL a TN | DRY_SOIL : RATED SO! UNAVAILABLE AVAILABLE INJURIOUS AVAILABILITY OF SOIL WATER TO PLANTS Fic. 43. Diagram illustrating the forms, proportions and availibility of soil water. soil particles, when the soil is allowed to become air dry. There is no sharp change.in the moisture condition of the soil in passing from one form to the other. Still, it is true that there are certain marked changes in some of the physical properties of the soil, such as volume, weight and resistance to penetration, which are in a general way associated with these transition points. Not all of the water in the soil is available to use of plants. It is a matter of general experience that for most farm crops the saturated condition of the soil is unfavorable to the best development. There are, of course, many plants which are adapted to such con- 142 THE PRINCIPLES OF SOIL MANAGEMENT ditions, as for example the swamp type of vegetation. About the only cultivated crops of this sort are rice and cranberries. Practically all of the common culti- vated crops, from vegetables to fruit trees, are adapted to growing in soil from which the gravitational moisture has been removed. The gravitational water is directly injurious to the growth of these plants, and its practical removal from the soil constitutes the practice of agri- cultural drainage, later to be considered as a phase of soil management. It may therefore be stated that gravitational water in the root zone is injurious to most | farm crops, and consequently it is in a sense unavailable. - It is the film or capillary moisture which supports plants. The roots of ordinary crops are adapted to take the moisture needed by threading their way between the soil particles, where they may come in intimate contact with these moisture films and absorb the needed supply of water, without being excluded from the air supply which promotes their growth. For, in the capillarily moist soil, the water is retained chiefly in the very small spaces, and the large spaces are occupied by air. While capillary moisture is practically the only form upon which plants depend, it is not possible for them to use all of this form of moisture in the soil. They take their supply most readily when the films are relatively thick, and when the globules between the particles are large. But, as the thickness of the films is reduced by the use of the plant and by evaporation, it becomes increasingly difficult for the plant roots to take their needed supply. Before all of the capillary moisture has been removed, this difficulty becomes so great that it HYGROSCOPIC MOISTURE IN SOIL 143 practically amounts to the prohibition of further extrac- tion by the plant. At this stage, if evaporation from the leaves continues, the plants wilt, because they are not supplied with moisture by the roots as rapidly as it is being lost. Since plants cannot utilize all of the capillary moisture it is manifestly impossible for them to derive any benefit from the hygroscopic moisture, which is held much more intimately by the soil particles than is the capil- lary moisture. In other words, the hygroscopic moisture capacity of a soil represents that much water unavail- able to plants, to which must be added the proportion of the capillary moisture which is also unavailable. 69. Amounts of each form.—The relative amount of each form of water varies with the soil, and.is deter- mined by its physical properties. The forms of water merge one into the other. 70. Hygroscopic water.—The amount of each of the three forms of soil water depends on the physical properties of the soil. These are best explained by first considering the hygroscopic capacity. This depends on the texture of the particles and the content of organic matter. Since hygroscopic moisture is a function of the surface exposed, it results that the larger the surface area exposed by the soil particles, the greater the hygro- scopic capacity of the soil. Reference to the table on page 83 shows fine-textured or clay soils to have the greatest surface area, and these hold the most hygro- scopic moisture. Sand soils, with a relatively small surface area, hold a small amount of this form of water. This fact is illustrated by the following table. 144 THE PRINCIPLES OF SOIL MANAGEMENT Per cent of hygroscopic water at 21° C. Very: Bie amie, 7st yids 2a hos ite Ye 1.8 ott Ra a, CAE Pe care ee Oe LY goatee 7.3 eS ei ite ht 2 oe RO Ae ee AMES NaS et 16.5 NEEL Sie iL ts eae es oe 3 te oy ee eine 48.0 The above soils were pure separates derived by mechanical analysis. These figures serve to show the direct relation between the (1) surface area exhibited by soil particles and the hygroscopic moisture retained. The hygroscopic moisture content of a soil depends also on the (2) temperature, and the (3) humidity of the atmosphere. The hygroscopic moisture decreases with increase in temperature. It varies directly as the relative humidity of the atmosphere with which the soil is in contact. Consequently, in the air-dried condition, while a soil always retains some moisture, it seldom exhibits its maximum hygroscopic capacity. Under average conditions of humidity, a light sand may retain from .5 to 1 per cent, a silt loam from 2 to 4 per cent and a clay from 8 to 12 per cent. This is, of course, unavailable for the use of plants. 71. Capillary water.—The capillary water capacity is much larger than the hygroscopic capacity. Its amount is determined by three things: (1) Texture, (2) structure; (8) content of organic matter. 72. Texture.—Texture is well known to be the great- est determining factor in the water-holding capacity of soils, due to its control of the internal surface, and this is particularly true with reference to the capillary form. The following table illustrates this effect of texture. Se ee ah CAPILLARY MOISTURE IN SOIL 145 TABLE XIX Per. cent of moisture retained Class Per cent of clay against force 2,940 times that of gravity Camree, Sad si. )2. fake aee date 4.8 4.6 Medium sandy loam.......... 7.3 7.0 Fine sandy team. oi). 2... e 12.6 11.8 pain ees BR rene 15> ea, Dts 2 10.6 12.9 LES CEST LT ae aa a 17.7 26.9 Be MRE ATM Iner isch ates 8 ovU SESS o§ Ce s o ors ees toa = = a = Per cent | Per cent | Per cent ~ Dine sand. <<: .63. 80 10.7 40.5 29.8 23.8 1:3.8 .. Pearse sand. 227+ 81 10.6 39.5 28.9 23.4 ba . Fine sandy loam ..|_ 83 18.0 38.0 | 20.0 16.6 ° | ie > Sete Goeth Sh). ees 83 20.9 38.0 18.9 15.7 > | Ses Ue eee ya 68 30.4 54.5 13.9 9.5: +A eatce . Witek aol so 7204 15 250.0 | 333.0 83.0 12.5)" |: 8 eee GRAVITATIONAL WATER AND DRAINAGE 163 recorded in the last table. If this per cent be subtracted from the per cent given in Column IV of the last table. the per cent of actual gravitational water in those soils may be determined. This is shown by the preceding table. The amount in Column V represents the pounds of water per cubic foot which would be lost by drainage from each of the soils if their pores were all completely filled with water. Such a soil is said to be saturated. That plane in the soil to which level all of the pores are filled with water—saturated—is known as the water-table. This region of saturation is sometimes known as the ‘‘ ground water.” It is possible to have such a structure in a fine clay soil that all of its spaces are practically filled with water held capillarily. It will be noted from the table that the proportion of the total water capacity which is permanently retained increases with the fineness of the soil, and consequently with the decrease in the size of the individual pores, as is shown in Column VI. The clay in the above tables appears to be very thoroughly granulated, which is responsible for the similarity in the ratios for the silt and clay. Gravitational water is directly injurious to upland crops, but when it exists at a depth of from four to six feet below the surface, it may serve as a reservoir from which moisture is withdrawn by capillarity, to offset losses by evaporation. Water may be removed by capillarity from the saturated zone to the point where the loss is taking place, and under these conditions the ground water—which then becomes capillary water— 164 THE PRINCIPLES OF SOIL MANAGEMENT is directly beneficial, and the process constitutes a form of natural sub-irrigation. The figures presented above illustrate the effect of texture on the total water capacity of a soil, and upon the proportion of gravitational water. Anything which increases the pore space increases the total water capac- ity. When there is not a corresponding increase in the capillary capacity, as happens in a sandy soil, the total amount of gravitational water is thereby increased. That is, in such a soil, there is a larger amount of water which may be lost by percolation. In so far as organic matter alters the structure of the soil, it modifies the gravitational water content of a soil in the manner — just outlined. 79. Amount and rate of loss.—Near the outset of the discussion of soil moisture, it was stated that the amount of water in a soil depends upon the extent and rate of loss of water, as well as upon the factors which have just been explained. For example, fifteen inches of water is far more efficient in crop production when applied to a loam soil in a humid region, like the New England states, than when applied to the sand of the Imperial Desert, California. In the latter case, the loss by percolation and evaporation is so great and so rapid that the amount of moisture available to crops is very small. The two forms of loss which affect the moisture in the soil are: (1) Percolation. (2) Evaporation. Percolation is the gravitational flow of water through the pores of a soil. Percolation concerns the gravitational water. The total loss in any given soil will depend upon the distribution of the rainfall or the irrigation supply. MOVEMENT OF SOIL WATER 165 Evaporation takes place at the surface, and from the plants growing in the soil. The rate of such loss depends on the climatic conditions. In those regions where the rainfall comes in frequent small showers, which wet the soil to a depth of only a few inches, a very large proportion of this water is immediately returned to the surface by capillarity, and lost by evapo- ration. On the other hand, if the rainfall occurs at long intervals and in large amounts, so that it percolates deeply into the subsoil. it may be held there by appro- priate surface tillage. III. MOVEMENT OF SOIL WATER Soil moisture is subject to movement in three ways. This movement may be injurious if it facilitates the loss of moisture, which should be retained for the crop; it may be beneficial when it serves to replenish the moisture supply upon which the plant is dependent. In the discussion of the moisture content and capacity of soils, it was pointed out that no soil retains within the surface four feet enough water to meet the needs of a full-crop yield under average field conditions. This indicates the necessity for the movement into the root zone of moisture, to take the place of that removed by the plant and lost in other ways. The movement of moisture from adjacent supply in the soil,—as the deep subsoil—is just as useful as the direct addition of water to the soil by rainfall. The three types of movement of soil moisture are (a) gravitational, (6) capillary and (c) thermal. 166 THE PRINCIPLES OF SOIL MANAGEMENT 80. Gravitational movement.— Gravitational move- ment is the result of the gravity pull upon the soil water. The slower the downward movement of water, the longer the water will be in the root zone of the crop, and therefore the greater use will the plant be able to make of that particular supply of moisture. This gravitational movement concerns primarily the gravi- tational water, and is not effective to move either the hygroscopic or the capillary forms of water, although these are subject to the same gravity pull. The reason is, so far as these forms of moisture are concerned, that the gravity pull upon them is overbalanced by other forces. It will be noticed, in fact, that gravita- tional water is defined as that part of the soil water which is free to move under the influence of gravity, Such movement constitutes percolation. The rate of percolation depends upon two primary conditions. These are: (1) The texture of the soil. (2) The structure of the soil. The rate of movement depends directly upon the diameter of the individual soil spaces. The larger the size of spaces, the more freely will the water descend. King has observed the following movement of water through sands of different texture in twenty-four hours: TaBLE XXVIII Sands Clay loam Black marsh Mean diameter in m.m. Inches | Inches | Inches | Inches Inches Inches 301 | 160 | 73.2 | 39.7 1.6 0.7 GRAVITATIONAL MOVEMENT 167 The columns were one-tenth of a foot in cross-section and fourteen inches high, and a head of two inches of water was maintained above the top of the soil. These figures show very clearly the reduction in the flow of water as the texture becomes finer. Under field conditions, the percolation of water through the soil is much facilitated by the presence of numerous cracks, root passages, and worm and insect burrows, because of their relatively large diameter. Several other factors affect the percolation of water. The entrance of rain or irrigation water into the dry soil where it is applied in a sheet over the surface is hindered by the presence of the air in the pores in the soil. If the subsoil is dense, or is filled with water, this inter- mediate band of air-filled soil serves to hold back the surface water, except as the air may escape in bubbles through the upper layer. For this reason, in part, a heavy shower of rain sinks into the soil to a very small depth, and is relatively ineffective. Entrance of the water may be greatly facilitated by a loose condition of the soil, which affords quite large as well as small spaces. The large spaces are less likely to be entirely filled with water, and hence afford means for the escape of air, while the water passes in through the smaller pores. There is another hint here in the conservation of rainfall. If the soil is in a very loose condition to a depth of eight or ten inches, the water will percolate into this layer, and its movement will be so much re- tarded that a larger part will find its way into the deep subsoil and be permanently retained than if the surface soil is uniformly fine. 168 THE PRINCIPLES OF SOIL MANAGEMENT Changes of temperature affect the flow of water through soils in several ways. It affects the gravita- tional water directly by changing its viscosity. Warm water is more limpid and flows more freely than cold water, just as oil is thinned by heating. Consequently soils drain more readily in summer than in winter. (See also page 183.) Changes in temperature also affect percolation indirectly through their effect on the free air in the soil, and the air in the water in the soil. Air, in common with all gases, expands very greatly with a small in- crease in temperature, and it thus exerts a pressure which may force water out of the soil into the larger drainage channels. Conversely, a lowering of the temper- ature contracts the air, and causes water to be sucked into the soil. In the same way, barometric changes affect the drain- age of soils. Alternate periods of low and high pressure sweep over the country at intervals of a few days apart, and the changes in volume of the outer air are trans- mitted to the air in the soil, which expands or contracts and tends to draw water into the soil, or forces it out as the pressure is decreased or increased. The suctional effect of winds may have a similar effect. Strong winds considerably modify the air pressure, and where this is brought to bear on the soil through a tile drain or other underground channel it increases the flow of water. Water does not necessarily percolate vertically into the soil. It may flow off nearly horizontally, depending on the character of the soil and its conditions. A hard CAPILLARY MOVEMENT 169 subsoil will deflect its movement. Entrapped air will do the same thing, and this has been found to be a potent source of contamination of open wells with shal- low curbing. This is particularly true in heavy soils, where the escape of entrapped air is especially difficult. One of the beneficial effects of under drains is that they facilitate the entrance and movement of rain-water in the soil by affording a channel for the escape of entrapped air. (See page 241.) 81. Capillary, or film movement.—Capillary water has been described (see page 141) as occurring in the soil in a thin film overspreading the particles, and thick- ened into a waist-like form at their points of contact. Toward the bottom of any soil column the film is always thicker than at the top, owing to the less weight which the surface tension must bear. This form of distribution has given rise to the term film water, from which is derived the idea of film movement, to describe this type of capillary movement. Film movement expresses very accurately the actual condition of affairs, for if there is any translocation of water at this stage it must be through this film. 82. Principles governing capillary movement.—It will be remembered (page 147) that, when equilibrium is established in any mass of wet soil short of saturation, the water surfaces are comparable to a stretched elastic membrane. The more closely this film is drawn about the particles, the more surface there is exposed, and the greater pull the surface tension exerts. Consequently the greater the amount of water whigh will be retained. In a soil capillarily saturated with water there is 170 THE PRINCIPLES OF SOIL MANAGEMENT no movement. For the pull at any one point is balanced by the pulls from every other point, due to the surface curvature of the film and to the weight of the liquid. In the bottom of the column, where the weight of the water acts in conjunction with the curvature of the film, the curvature is less than at the top of the column, where the only effective pull is due to the curvature of the water surfaces. This may be illustrated by the fol- lowing diagram. (Fig. 52.) P represents soil particles carrying their maximum film of water, and therefore in equilibrium at every point, so that no movement may take place. The force or pull exerted by the film at the different points is represented by the arrows at A, B, C, D, E, etc., the © length of the arrow being proportional to the pull exerted by the film, and in the same direction, or toward the center of curvature of the surface. The difference in the pull, and therefore the length of the arrows at the top and bottom, is compensated by the weight of the water at the bottom. If water is now taken from the film into the rootlet at R, the curvature of the film at that point will be increased. Therefore it will exert a greater pull than the curvatures in the other spaces, and water will be moved to R along the lines U, to replace that taken in by the root. So that the new adjustment would be represented by the dotted lines which show the new curvature assumed at each point, when equilibrium is reéstablished, and the water comes to rest. If water continues to be lost to the root, or by evaporation from the soil at R, the movement of water to that point will be continuous as long as movement is CAPILLARY ADJUSTMENT wa fis tie sy bis a "4 = : a ~ s > Ky : eis ca ae <2) in ns fs Le ies wer> oy? <7 Coy ~ ha: Sp eens aot =Sy oS oS Kons Nis Sh globes ys a le D 2 pas < Neh aoe Le pet eletg ao Saat Fo STI g Me: tet A Taye Fic. 52. Showing the distribution of water around a group of soil particles, and the distribution of forces and direction of movement in the re-establish- ment of equilibrium after thé removal of water by a rootlet. For further explanation see text. possible; the curvatures meanwhile increasing, and the films become thinner and thinner. It will be noted that the curvature at every point in the plane 1 is the same, and that a similar uniformity prevails for planes 2 and 3. Likewise, in the columns I, II and III the relative curvatures are the same. 172 THE PRINCIPLES OF SOIL MANAGEMENT Theoretically, therefore, there is no limit to which this adjustment might take place in the horizontal plane. Water might be moved in from a distance of one inch or one rod. Vertically, however, there would be a limit to the height to which water could be lifted, because of the limit to the pull of the surfaces in plane 1. The larger the number of curves, the greater the total pull per unit area, and consequently the higher could water be lifted—yjust as there is a definite limit to which water will rise in glass tubes of different sizes. It is therefore possible to keep trimming off the upper end of a column of soil, whose lower end dips in water, until the maximum height through which water may be lifted and lost by evaporation, or otherwise, is determined. This is the maximum capillary efficiency of the soil, or the maximum height to which it could deliver water. According to the above propositions, the movement of water would go on freely and uniformly until the mini- mum thinness of film was reached. This free movement is modified, however, by another condition. Water, in moving from any point, as C to R, must pass through the thin part of the film between the points of contact, and where it comes in close contact with the soil sub- stance. In this, friction is developed, and the thinner the film, and the closer it is drawn about the particle, the greater does this friction become until it all but stops movement. For a period, when the film is thick, the movement is relatively free; but, after the water comes within the range of great attraction of the particle, the friction increases rapidly, and therefore the movement of water IMPORTANCE OF CAPILLARY MOVEMENT 173 is correspondingly cut down. This factor of friction greatly limits the effective capillary capacity of a soil both vertically and horizontally. If the coefficient of friction is great, it will soon overcome the pull due to curvature, and water will be quickly moved in from only a short distance. In proportion as the friction coefficient is reduced, the range of movement is ex- tended. It should be noted that friction retards move- ment rather than stops it. The greater the surface over which a given volume of water is spread, the slower therefore will be its movement. (See page 183.) In the above discussion it was assumed that the water is uniform in all its properties, and therefore that corresponding curvatures were the same. H, how- ever, anything modifies the surface tension of the liquid at one point—as change of temperature, solution, etc.,— this would be expected to disturb the balance, and result in film movement. Such is the case, as later examples will show. (See page 183.) It is probable that, in the soil, equilibrium is never established, because of these disturbing variations all through the soil mass. Further, the last end of the process of adjustment is exceedingly slow, and probably never actually takes place; because the force producing the motion is successively reduced as equilibrium is attained, and because the difference in curvature of the films is so slight. 83. Extent, rate and importance of ee move- ment.—Capillary movement of water is of great conse- quence to growing plants. Since it concerns the capillary water, it affects that form of soil water upon which ordinary crops are directly dependent. The withdrawal 174 THE PRINCIPLES OF SOIL MANAGEMENT of water at any point by a rootlet is made up by move- ment of water from the adjacent soil zones. But the plant is not dependent entirely on the movement of water to its roots. The roots are themselves constantly pushing into fresh soil zones, where the moisture, and perhaps also the food, have not been so thoroughly qu Will Mg i} \\ \J 4 Y USS / { < p} \\ \ \\ \ a l \\ f \\ ( ~ i i 5 eee Hy rs) : ji} hi) Y | OF ON Wi Ne | 1 AY Fic. 53. Penetration of root-hairs through the soil. (h, h’) root-hairs; (7') soil particles; (s, 7) air-spaces. Water is indicated by concentric lines. withdrawn. The roots go to meet the capillary advance of the soil water. This advance of the fine rootlets is rapid, and of great consequence in the nourishment of the plant. It also enables the roots to come into more intimate contact with the soil; for, as the water is extracted, it is lost first and most readily from the large pores. The latter amount of water is found in the smaller spaces, and consequently the roots are CAPILLARY MOVEMENT AND TEXTURE 175 led toward these small pores by their attraction for water. Three primary soil factors govern the capillary movement of water. These are: (a) Texture, (b) struc- ture, (c) dampness of the soil. In addition to these, the movement is affected by (d) the surface tension of the soil water, and (e) by the condition of the surfaces of the soil particles. 75 a Sanne Fo ae ee Jeeseeoa aces Bee ee ae eee Se ee ne ae ae z w 30 ye > J SVee SS Se oo a 25 Seep ee A Pe CE eerie raped TTT 8 a bal 12 14 16 18 20 TIME IN HOURS Fig. 54. Curves showing the height and rate of rise of water in dry soils of different texture as given in Table XXIX. 84. Texture.—The influence of texture was explained in the principles outlined above. The finer the soil, the more surface it will expose, the more points of con- tact there will be between the particles, and therefore the greater total curvature the water surfaces will have. For this reason, a clay containing 20 per cent may draw water from a sand containing 10 per cent of water. The capillary capacity of a soil may be measured in two ways: (1) By the height to which water will — On Hm Ww bo 176 THE PRINCIPLES OF SOIL MANAGEMENT be raised in soils of different texture. (2) By the total amount of water raised through a given height in a definite time. The time element enters into both sorts of measurements, and is an especially important con- sideration in clay soil where the movement is generally very slow. TaBLE XXIX SHOWING HeiGcHT oF RISE OF WATER IN Dry SoILs oF DIFFERENT TEXTURE, AS SHOWN IN THE ABOVE CURVES Time Min. Hours Days 15 if 2 if 3 8 13 19 Inches | Inches | Inches | Inches | Inches | Inches | Inches | Inches . Silt and very fine sand ...| 2.7 4.7 | 7.0 | 20.0 | 30 | 45.0 | 52.0 | 56.0 . Very fine sand | “7.6.1: 100.)-12.4 |.210 | 23. | 260) 275 [2a . Fine sand.....| 9.0 951100 | 11.6 13 14.3. 152°) 166 . Coarse and me- diumsand..| 5.8 6.0 6.3 12D 9 10.0 | 11.5 | 12.5 . Fine gravel ...| 4.0 5.0 5.3 6.4 8 9.0 | 10.0 | 10.8 These materials were sifted to fairly uniform sizes, according to the scale given above (page 73). The silt was a natural material, containing a large amount of very fine sand, together with some clay. It might be termed a light silt loam. It will be particularly noted that the smaller classes of particles—silt and clay— have a relatively large influence on capillary movement. Above the class of fine sand, there is not much variation in the height of rise for different textures, the total height attained being slight. CAPILLARY MOVEMENT AND TEXTURE | Loughridge has made very careful determinations of the capillary power of four dry soils of known physical composition over a period ranging from 6 to 195 days. These soils range in texture from light sandy loam to heavy clay adobe of the following mechanical com- position. TaBLE XXX Per cent of each separate present Clay less than Coarse Fine silt alt Sand Limits used in diameter of particles 01 01-.025 | .025-.047 | .047-.5 mm. mm. mm. mm. fos IE | a re 2.82 3.03 3.49 89.25 . Light sandy loam ..... 3.21 5.53 15.42 72.05 NN MOATIE So 5. wis ee eos « 15.02 15.24 25.84 45.41 BMA Ms ou. oa ate) 8 made a 44.27 25.35 13.47 13.37 me OOD) The composition of these soils is also shown in the following curves: PERCENT. OF SEPARATE PRESENT SAND G00000000000000 pea eee. dododddctbdssaut SANDS COARSE SILT FINE SILT CLAY (047. —.5 MM.) (.025 -.047 MM.) (.01 — .025 mm.) (>.01) Fic. 55. Curves showing the mechanical composition of the soils whose analysis is given in Table XXX, and whose capillary water capacity is given in Table XX XI and Figs. 56 and 57. L 178 THE PRINCIPLES OF SOIL MANAGEMENT The capillary rise of water in these soils was as fol- lows: TABLE XX XI.—TIME In Hours Min Hours 30 1 | Pe 6 | 12 Height of rise in inches A MG 5 7s MMe nt a eA came a as Sei Mt 8.0 | 10.0 | 12.0 13 2. Light sandy loam... 0S 6.3 | 90°} E27: | TOO eee ps Ne O82 5 eee or Regt lees or oy 2.7 4.8 8.8. | at Bp MOL Car end a tate ate eats vee 0.8 1.4 edhe 5.0 8 TABLE XXXI, continued.—TIME In Days Days 1 fa] oe |. 26 48,| 90 | 160 | 195 Height of rise in inches Le Band 6 Seder 14.0/15.5| 17.0 2. Light sandy loam 2.2.5.5} 2e2 150.5 |35.0) 38°) 417 44 463 Oo. pulty-loam..- 55% 13:0} 17.0) 20.5. 25.31.5135: |40.0). 43) fon Shs RAI te aston Mee 16:0:|.24.0|20.0| 23°) 2655)\'>. ie a As is always the case, the rise is most rapid immedi- ately after the soil is placed in contact with the water and the rate of rise decreases progressively as the limit _ 1s reached. The more coarse the texture of the material, “the more quickly is the limit of rise attained. These figures are shown in the following curves: (1) For the first twelve hours; (2) for the full period. CAPILLARY MOVEMENT AND TEXTURE 179 bo 00° HEIGHT OF RISE IN INCHES 5 6 7 TIME IN HOURS Fic. 56. Curves showing the capillary rise of water in twelve hours in dry soils of different texture as given in Table XX XI. id i \2 G |< see a ee tee th peer onlay a oF a iat ae tas 7k a eee Ber ert! “=| eae iar a Pe a ae ae al eS ee ee a poesia a S > = o> a. us Ws 3 Hs SS a2) ae] me) 1. Fine quartz sand so. 3 1 2.0¢ | 166 | 2.07 | 146 | 1:23 2. Clay loam. ....| (2.05); 144 )| 1.62 .| 113. |:4.00% 7 .90 63 As remarked by Professor King, these figures prob- ably do not represent the maximum capacity of these soils to the heights stated: The shorter the column, the less accurate are the figures. For in the short col- umns the evaporation was correspondingly less than the movement. From the results, it appears that the AMOUNT OF WATER MOVED 187 clay soil was in a very well-granulated condition, which brings its rate very near that of the sand. It also appears from this data, as was shown in the data on height and time of capillary rise, that, up to three or four feet, the fine sand is as efficient as the soil of much finer texture. In studies on the capillary rise of water in moist Sea Island cotton soil—a fine sandy loam,—Briggs found Fic. 59. The weeder, with riding attachment. For very shallow cultivation in mellow soil free from stone and rubbish. the movement to be at the rate of 1.3 pounds per square foot per day, or 91 inches per year, through a height of 85 centimeters (34 inches). But when the column of the sand soil was 165 centimeters long, water was raised at the rate of .32 of a pound per square foot per day, or 21.4 inches per year,—a decreased efficiency from doubling the height of the column of 75.4 per cent, When the column was 185 centimeters in height, no appreciable loss took place,—indicating that this sand 188 THE PRINCIPLES OF SOIL MANAGEMENT was not able to raise water to the height, even when moist. - Buckingham obtained the following results, which show a very considerable vertical movement in fine sandy loam soils to a height of nearly four feet. TABLE XXXIV I Il IIl IV Height of Dry Pounds of Inches of column. porosity water per day water per Inches per sq. ft. year 1. Takoma lawn...... 46 48 3 51.6 2. Podunk fine sandy loam, . 5. 46 395 .06 39.4 It must be kept in mind, in examining these figures, that the evaporation conditions in the different experi- ments were not uniform, and therefore, that the results are not strictly comparable. They do, however, show the movement of a very large amount of water in this way through distances of several feet. The amount so moved in these sandy soils per year is several times the total amount required to produce normal crops. (See page 134.) There is also indication that in the short period of a day the amount of water moved is sufficient to meet the needs of a considerable mass of growing plants. It is regrettable that no figures are available for silt and clay soils, and to greater heights and hori- zontal distances, in order that a more complete idea of the availibility of water supplies at a distance of six, THERMAL MOVEMENT OF WATER 189 eight and ten feet, or even more, may be had. This is an important body of information yet to be gained. 90. Thermal movement.—Water moves through the soil in the form of vapor. If a glass vessel or tube filled with moist soil be set on a hot surface, the bottom of the column will be seen to become lighter in color, indicating a loss of moisture. If the whole column is not heated and the moisture is determined in successive sections, beginning at the top, or coldest portion, the moisture content will be found greatest a short distance above the heated layer at the bottom. When the moist soil is heated, steam is formed, which develops a pressure that forces the vapor rapidly through the soil. But, at ordinary temperatures, this vapor movement is the result of simple diffusion, and it obeys the same laws. Buckingham has shown that the diffu- sion of air through the pores of the soil is exceedingly slow, and therefore that this phase of soil aération is of small effect. (See page 439.) He has also shown that the diffusion of water vapor through the fine pores of the soil is very slow. (See table below.) It is well known that water does not necessarily ’ evaporate at the surface of the soil. It may evaporate in the deep pores in the soil if the air at that point is sufficiently dry. Atmosphere in a moist soil is very near saturation. In a mulched soil (see page 199) evapo- ration may take place at the top of the moist layer. The loss of water will therefore depend very largely upon the loss of moisture by diffusion through the mulch. Buckingham obtained the interesting results given in Table XX XV bearing on this point: 190 THE PRINCIPLES OF SOIL MANAGEMENT TaBLE XXXV.—Loss or WaTER BY EVAPORATION FROM BELOW CoLUMNS OF DIFFERENT AIR-DRIED SOILS : Death of nitial Rate of loss Soil aise teed ees 2 Inches Per cent Inches Coarse sand ioe 2 Ce 2 45 4.30 Fine sandy loam......... 1 48 2.52 Fine sandy loam ......... 2 46 1.59 Fine sandy loam......... + 4] 0.93 Fine sandy loam ......... 6 46 0.67 SST b AINE. cates. atin woe 1 54 2.F4 Silt tonne ce Pl eee 2 LL 1.60 PVEEE OREINN «hci 5. op eon te ta 4 49 0.95 Pits 10a -o.5,° =. ok Se ae 6 oa! 0.69 2 46 0.60 Rise ro chan te hae It appears from these figures that the thermal move- ment of water by simple diffusion is determined: (1) By the size of the individual pores. (2) By the total amount of pore space in the soil. (3) Upon the thickness of the soil layer. When equally dry the fine-textured soil retains moisture as vapor more effectively than does coarse-textured soil. In so far as the structure of the soil modifies either the size of the pores or their total volume, it may modify the loss of water. A coarsely cloddy mulch would therefore be ineffective. Particu- larly striking is the small depth of soil which is effective to prevent the loss of water. Even the one-inch mulch has a wonderfully high efficiency. IV. CONTROL OF SOIL WATER In the control of soil moisture it is desired to accom- plish one of two things: (a) The average water content CONTROL OF SOIL MOISTURE 191 of the soil is increased or, (b) the average water content of the soil is decreased. If the crop is likely to suffer from a deficiency of water, or from conditions associated with a deficiency of water—as food,—we aim to in- crease the moisture supply by conserving the rainfall, or by direct additions of water. On the other hand, in soils saturated with water, or which are too cold, or too poorly aérated because of an excess of water, it is desired to remove this excess either by drainage or appropriate tillage methods. 91. Means of in- creasing the water content of the soil.— The average water content of the soil ey be increased in Fic. 60. One-row toothed cultivator. three ways: (1) By Adapted to shallow tillage and the mainte- decreasing the losses nce of a mulch. from (a) percolation and (b) evaporation. (2) By increasing the capacity of the soil for water (a) by modifications of texture and structure, and (b) by in- creasing the humus content. (3) By the direct addition of water to the soil, which is irrigation. 92. Decreasing loss.—The water which comes on the soil is subject to two forms of loss. (a) It may percolate through the soil and beyond the reach of plant roots. (b) It may evaporate. 93. Percolation.—The amount of loss in this way is very great. (See page 192.) Water percolates most rapidly in large spaces, and whether these large spaces 192 . THE PRINCIPLES OF SOIL MANAGEMENT are the result of coarse texture or of a loose, cloddy structure, the final result is the loss of water. The fol- lowing table shows the average results of the Rothamsted drain gages for thirty-four years, by months from 1871 to 1904, on a rather heavy loam or clay loam soil, and twenty, forty and sixty inches in depth. These gages have an area of one thousandth of an acre each, and are kept free from vegetation. TABLE XXXVI Drainage. parourn Proportion of rainfall Raiic soi drained through soil ile? See 20 | 40 | 60 20 40 60 Depth in inches Per cent SATIS HY.5 5 of oe 2.32} 1.82} 2.05| 1.96] 78.5 | 88.4 | 84.5 Bebruary: (jc... 25. 1:97}. 1.42) 1.87) TAS) 72.2.) SOO Nita TL een erty ila * 183] 0.87] 1.02| 0.95 | 47.6°) 55.6 | 520 PETS ee Phrases 1.89 | 0.50] 0.57) 0.53) 265 | 300 | {288 May... 2:11} 0.49) 0.55 0:50) 23:2.) 26.1 ) 2aa IE oe A es: 2.36 | 0.63). 0.65| 0.62) 24.0 | 2736 |.263 PUL 2 ee eee ve 2.43 | 0.69.) 0.70 | 0.65.) 25:3 4) 25:65). 2a8 Amorests aie oe 2.67 | 0:62 |. 0.62 }..0:58:| 23.2.1 23.2 ekg September ...... 2.52} 0.88} 0.83} 0.76} 35.0 | 32.8 | 30.0 Oetober 3.201 2:385-) 1:84) B68 Shs 1a 7a i ae November ....... 2.86)\: 2AL. |: ‘2.18 | 2.04) 7659 ch iG hee December... ..'....}- 2.024-2.02| 2:15 2.04 °80:3-) 654) Sig Mean total Bat year........,..| 28.98 | 13.90 | 14.73 | 13.79 | 48.2 | 51.0 | 48.0 Results for maximum and minimum rainfall Maximum........| 38.70 | 23.50 | 23.60 | 24.30 | 60.7 | 61.0 | 63.0 Minimum. 2 53..4<: 20.501 7:382.{° 7.90) 7.701 35.7. | 28:5: LOSS BY PERCOLATION 193 The rainfall and relative loss through gages of differ- ent depths is shown in the following curves, based upon the above figures. Bea : ea Fea Z ae cles Fic. in: Gites Eicon ie ihe aa Sa a ceccelniicn eacoukk 20, 40 and 60 inches of soil by months. Rothamsted, England. Average of 34 years. It appears from these figures and curves that about 50 per cent of the rainfall is lost by percolation, under the climate of England. It also appears that the loss is slightly less from the sixty-inch than from the twenty- inch gage. Under a climate less humid, this difference is greater. This is illustrated in two ways: (1) In the above table it is clear that the proportion of water lost by drainiage is much less in summer than in. winter. (See page 195.) The saving is somewhat larger in the deep than in the shallow gage, as the proportionate M 194 THE PRINCIPLES OF SOIL MANAGEMENT capacity of the soil for water is somewhat greater in this case. (2) It has been estimated that the annual run-off of the streams in the eastern half of the United States amounts to about 50 per cent of the rainfall; but in the basin of the Missouri river the run-off is not over 20 per cent of the rainfall, and in the Great Basin it is practically nil. These figures give some idea of the total amount of water lost by percolation through the soil, and repre- sent a supply which it is the aim of good soil manage- ment to lessen or eliminate, according to the needs of the crop. Loss from percolation may be reduced in two ways, which depend upon the fact that the rapidity of such loss is directly proportional to the size and volume of the pore spaces in the soil. These are (a) by modifi- cations of texture, (b) by modifications of the structure of the soil. The primary method is, or course, that modification of structure which breaks down the granular arrangement and permits a greater compactness. When rain falls on the soil, its fall is not stopped. It continues to fall through the soil at a reduced rate as gravitational water. And, as the movement of this gravitational water is directly determined by the fineness of the soil spaces, it is possible to very greatly reduce this type of move- ment by compacting the soil structures. The greater compactness of the soil lengthens out the period during which the soil contains hydrostatic water, and, if the roots of growing plants are distributed through the soil, they are able to make a larger use of this free water than would be possible if the wave of saturation, as a result of rainfall or irrigation, quickly passed beyond LOSS BY EVAPORATION 195 their reach. Therefore, on soils subject to excessive leaching, water may be conserved by use of the roller or other compacting implement, and by such manage- ment as permits the deep subsoil to become more dense. 94. Evaporation.—The second form of soil-moisture loss is by surface evaporation. It has been shown that, in the process of growth, a large volume of water is evaporated directly from the tissues of the plants. In this process it performs useful functions. But a large amount of water is also lost by direct evaporation from the surface of the soil. If the plants which evaporate the soil water are those of the desired crop, the loss is proper and not to be avoided. But it frequently happens that, either before the regular crop is on the land or mixed.with it, are large numbers of worthless plants through which this same moisture loss occurs. This is of course a waste of moisture, and is to be avoided by preventing their growth. It may happen in the spring that the late plowing of land bearing a heavy growth of vegetation permits so great a loss in this way that, unless the subsequent season is one of abundant rain- fall, the regular crop may suffer from the lack of moisture which was stored in the soil, and by timely plowing and preparation could have readily been utilized. In this connection, it should be kept in mind that green manure crops may be directly injurious the first season if they are permitted to grow so late before being turned under as to unduly deplete the soil moisture. In the manage- ment of green manure crops, that optimum point when the excess of water due to heavy spring rain and winter snow has been removed, but the capillary supply not 196 THE PRINCIPLES OF SOIL MANAGEMENT impaired, should be selected. In semi-arid regions, where dry farming—farming without irrigation where it is usually required—is practiced, it is sometimes advis- able to grow but one crop in two years, because the annual rainfall is not sufficient to produce a profitable crop each season. This practice, of course, implies those conservation practices which safeguard the rainfall as it collects, by appropriate tillage methods. The loss of water by direct evaporation from the soil may be excessive, and result in direct reduction of the crop yield. This type of loss is so familiar that examples hardly need be cited. In the results with the Rotham- sted rain gages, about 50 per cent of the annual rainfall was regained in the drainage water. Since the gages bore no crop, the remaining 50 per cent must have been lost by evaporation. And it will be noted that in the summer months under warm temperature this loss was greatest, amounting to 75 per cent of the rainfall. Correspondingly, in the semi-arid and arid sections of the country, where there is little or no drainage, the rain- fall is all lost by evaporation. Investigations indicate that about 70 per cent of the precipitation on the land surface is derived from evaporation from the land sur- face. Even in the humid sections, where the annual rainfall is ample for maximum crop production, the crops are frequently reduced even below the profit point by prolonged periods of dry weather in the growing season, during which the loss from the plants, coupled with the loss from the soil, exhausts the soil supply. If we refer to page 135, we note that the water absolutely needed for crop production, and including the necessary losses CONDITIONS WHICH PERMIT EVAPORATION 197 from the soil, is only a small proportion of the annual rainfall of most of the cultivated sections. These losses are therefore preventable; and that this is true is exemplified by the large difference in average crop yield on those lands where the best conservation prac- tices are in vogue over those where they are neglected. It should be remembered that over the vastly larger proportion of cultivated land area the crop yields are controlled more directly by the lack of water than by the excess of water. It is a common observation that soils which ordinarily give a low yield in seasons of normal or low rainfall give good yields in wet season, indicating how large a dominating factor is the moisture supply. For the moisture concerns not only its direct use as a food and carrier for the plant, but by its influence on solution, and other essential conditions of plant growth, its is a chief dominating factor in growth. Soil evaporation occurs almost entirely at the surface. Exception may be made where evaporation occurs into large, deep cracks in heavy clay soil, which is the primary source of subsoil loss in such cases. If this be prevented, as it may be, the loss will be very small. Since evapora- tion is chiefly at the surface, the nearer the available store of moisture is held to the surface, the larger pro- portionate loss will occur. This principle has its appli- cation in the amount and distribution of the rainfall or irrigation. Frequent small rainfalls are much less effective than less frequent rains in larger amounts. For if the rainfall or irrigation produces only shallow percolation before the water assumes capillary forms, it may be quickly returned to the surface, and lost. 198 THE PRINCIPLES OF SOIL MANAGEMENT Also there is a certain inherent loss in the most careful field practices, which are proportionately greater with small applications of water than with large ones. It has been shown (page 182) that as the capillary films are reduced in thickness the movement becomes in- creasingly difficult and slow. Therefore in a fine-tex- tured or dense soil, where evaporation occurs only at the surface, the top layer may become so dry in warm, clear weather that capillary movement practically ceases. Therefore, loss is also stopped. If now there comes a light rainfall,—sufficient to replenish the super- ficial moisture films, but not enough to produce deep percolation,—the result may be the renewal of capillary movement, which will ultimate in a few days in a greater total loss than would have occurred had there been no rainfall. These results have frequently been observed in practice, and were definitely shown in field moisture studies made by Stewart. In moisture studies of the soil in the open, and under a muslin shade used in grow- ing wrapper tobacco in the Connecticut valley, it was observed that a small rainfall had a much larger effect on the soil-moisture content outside than inside the tent. A rainfall of less than half an inch increased the water in the surface nine inches of the soil outside the tent to a larger extent than could be accounted for by the rain- fall. Careful calculations and observations indicated that the difference represented movement up from the subsoil, due to the renewal of film movement. King has obtained similar results in field studies which he has checked experimentally. This emphasizes the desira- bility of storing water as deeply in the soil as is practi- RETENTION OF WATER BY MULCHES 199 cable, and of giving a few relatively large applications rather than many small ones, in the artificial addition of water. Surface evaporation may be reduced in two ways: (1) By the application of some protective covering to the moist soil. (2) By such surface treatment as will reduce the tendency to evaporation. 95. Mulches.—The protective covering constitutes a mulch. That is, a mulch is any material applied to the ia7 Ure UZFAS. DNF AS Fic. 62. Two types of soil structure. On the right, compact soil, due to the use of the roller. On the left, the same soil, loosened at the surface to form a mulch. surface primarily for the purpose of preventing evapo- ration. It may at the same time fulfil other useful functions, as keeping down weeds and maintaining a more uniform soil temperature, but its primary use is to prevent evaporation. Of course, in so far as the srowth of weeds is prevented, moisture loss from that source is eliminated, and at the same time plant food is conserved for the regular crop. Mulches are of two sorts: (1) Foreign material 200 THE PRINCIPLES OF SOIL MANAGEMENT applied to the surface of the soil. (2) Those composed of the natural soil modified by appropriate tillage. The action of both sorts of material depends on the facts shown on pages 180 and 189; namely, that capillary action may be changed or broken by sufficient change in the texture or structural properties of the material, and, second, that the diffusion of water vapor, even after evaporation has taken place, is exceedingly slow through small irregular pore spaces, such as exist in all materials effective as mulch. Any material is effective as a mulch in proportion as it fulfils these conditions; and their practical application, therefore, becomes chiefly a matter of selecting that material which meets these require- ments, and may be readily applied. Many kinds of material are used as a mulch. Straw, chaff, dead weeds, stubble, leaves, sawdust, manure, boards, canvas, stone, coarse sand—all of these are used, and many other waste materials which may be available. They act as a cover to the moist soil, so that water which is held in the surface of the soil, or is brought up by capillarity, must evaporate into this stagnant and therefore soon-saturated atmosphere; under which con- ditions the loss must be much less than where the vapor is freely removed, and dry air brought in contact with the moist soil. All of these materials are very efficient as a mulch, their efficiency depending upon their thick- ness and porosity. Straw and leaves, when fresh and dry, will reduce evaporation below 10 per cent of the normal, when in a layer three or four inches thick. As they decay and become water-soaked from succes- sive rains, their efficiency decreases; but they retain ARTIFICIAL MULCHES 201 an efficiency of at least 50 per cent for a long period, or until they are so decayed that they acquire decided capillary capacity. A practice based upon this effect is that of growing potatoes under straw. The potatoes are laid upon the surface of the ground, and covered deeply with straw, which keeps the surface soil so moist that the potatoes sprout and will grow a reasonable crop to maturity, when the straw has simply to be raked back and the tubers, clean and smooth, are found on or very near the surface. Leaves, including pine needles, Fic. 63. A very stony soil. Boulders and gravel serve as a mulch, promote drainage, and increase the warmth of the soil. 202 THE PRINCIPLES OF SOIL MANAGEMENT and sawdust, are very effective as a mulch, but some precautions should be observed in their application. For example, the oak is rich in tannic acid, which may be washed out of the mulch into the soil and cause injury to its producing power, by its effect on the growing plant. In some European countries, as well as in a few places in America, stone has been drawn on the soil, particularly in orchard and vineyard culture, to serve as a mulch, and with markedly beneficial effects. Par- ticularly is this true on those lands too steep to permit cultivation. And, as a corollary to this practice, it has been observed in the fruit-growing section of the Ozark Mountains, and doubtless in other regions, that the removal of stone from the land not only permits the soil to become more hard, but also reduces crop yield by increasing the loss of moisture. It is therefore for the farmer to decide whether the inconvenience to tillage or other operations due to the presence of the stone may not be more than offset by their beneficial effects. A layer of two or three inches of coarse sand or fine gravel is a very effective mulch, and is frequently used in green- house practice. The above-mentioned mulch materials are all strictly artificial, and their application is greatly limited, due to the lack of material and the expense involved. They are therefore used only under special conditions. But the second type of mulch is almost universal in its practical availability. Almost any soil may be converted into an effective mulch by proper treatment. This treatment will differ with the character and condition of the soil and the DUST MULCHES 903 climate. Mulches formed from the natural soil are commonly termed “‘ dust mulches,’’ or more expressively “dust blankets.”’ A dust mulch is simply an air-dry layer of the natural soil covering the moist soil below. It may be in a compact condition, but ordinarily it is loose and friable. Its creation is dependent on the prin- ciples explained on pages 172 and 189 concerning capil- lary movement and diffusion of water-vapor. Under arid conditions where the atmosphere is dry and hot, and in free circulation, the surface soil is quickly dried out after an application of water. This drying takes place so rapidly that the capillary films quickly become so thin that movement is stopped, and no more water is brought to the surface. The soil may be ever so hard and compact, but so long as it is kept dry it very effec- tively preserves the moisture below. The more rapid the loss, the more quickly will the mulch condition be created, and therefore the less the total loss of water is likely to be. This has been demonstrated by Bucking- ham in some experiments in which arid climate conditions were created at the surface of a capillary column forty-six inches in height. The soil was a fine sandy loam, the equilibrium distribution of water in which is shown in the curve on page 148. At first, the loss under the arid conditions was very rapid and exceeded the humid conditions, but the rate of loss soon dropped considerably below the humid column, and continued to fall behind during the twenty days of the experiment. This experiment was conducted under the most difficult conditions for creating a mulch, since the soil used was of intermediate fineness and had a large effective capil- 20 4 THE PRINCIPLES OF SOIL MANAGEMENT lary capacity, and, further, it had a full supply of water at the bottom of the column,—conditions seldom found in practice, and certainly not common under arid- climate conditions. The curves of water loss, showing the mulching effect of rapid drying, appear below: 300 100 GRAMS OF WATER EVAPORATED o TIME IN DAYS Fic. 64. Curves showing the relative evaporation of water from two col- umns of the same soil. One was kept in a dry atmosphere at the immediate surface. The other was maintained under normal humid climate conditions of moisture and temperature. For the reasons presented, the moisture supply in arid regions appears to be naturally more effectively conserved than’ in humid regions,—certainly a wise provision. This fact is to be connected with the further one that capillary movement into the deep subsoil is very slow. The mulching effect described above gives further emphasis to the unwisdom of frequent small applications of water to the soil. In humid regions the natural mulching effect is much less marked than in arid regions. If the farmer would produce a soil mulch, he must do it by creating as far as possible the arid conditions. That is, he must bring about such a rapid drying of the surface soil as to convert it into a mulch which will retain the moisture MANAGEMENT OF MULCHES 205 below. Since in humid regions drying is usually slow and capillary movement strong, the process is hastened by loosening the top soil by frequently stirring, in order (1) to hasten the drying of that surface portion to the point where capillarity is stopped, and (2) to reduce its capillary conductivity,—both of which hasten the forma- tion of the mulch. It is for these reasons that a mulch is generally a loose layer of soil. The management of the mulch is evident from the principles involved. It must be kept dry in order to break up capillarity. In humid regions, where frequent rains occur, the mulch may be destroyed. After such a rain, when the soil has reached the proper dryness, it should be again stirred, to renew the mulch. On heavy clay soil in fine tilth, a mulch may be destroyed by very moist foggy weather, or by a number of days of very humid atmosphere, which, by condensation of moisture on the clay, hastens the reéstablishment of capillarity with the subsoil, by which moisture may be pumped up and lost. This is to be overcome by occasional stir- ring, as conditions may require. Another important effect of the mulch on clay is to keep the shrinkage cracks filled up, and thereby prevent the deep drying- out of such soil. When perfectly dry, a coarse sand and a pulverized clay are of almost the same practical efficiency. (See page 190.) It is only when the structure becomes that of coarse clods or stone that the efficiency is greatly reduced. A cloddy surface soil is worse than a smooth surface with no mulch, for the clods are free to evaporate water, and offer small protection to the subsoil. On 206 THE PRINCIPLES OF SOIL MANAGEMENT the other hand, the pulverized clay has so great hygro- scopic and capillary power that its efficiency as a mulch may be readily destroyed by natural climate and soil conditions of common occurrence. It is therefore more Fic. 65. An example of clean, thorough tillage, and the maintenance of an effective ‘dust mulch.” difficult to maintain a dust mulch of clay than of sand. The strong natural mulching tendency of sand may be seen on sand-dunes, where, although the surface is dry and hot, moisture may be exposed by the toe of one’s boot at any season. A perfectly dry dust mulch need not be very deep, to DEPTH OF MULCHES 207 be effective. One inch of sand will permit loss by diffu- sion of less than three inches of water per year, under the most favorable conditions. In practice, however, it is found that two or three inches are usually most effective because of capillary action. And Fortier has concluded from experiments on irrigated soil in California that a ten-inch mulch conserves more moisture than one of less depth. But the efficiency of the ten-inch mulch as com- pared with the four-inch is very much less in proportion to depth, and the latter conserves 75 per cent of the water lost where no mulch was used. Sand mulches may be thinner than clay mulches. King found in Wisconsin that, for corn, cultivation with a small toothed culti- vator to a depth of three inches saved more moisture in fifteen cases out of twenty than did more shallow tillage, but that increase in depth resulted in no corre- sponding increase in efficiency. The sweep or blade type of cultivator (Fig. 137) may be used more shallow than an implement producing ridges. The mulch should be no deeper than is necessary to prevent loss of water, since this top layer is usually most rich in available plant-food, particularly nitrates, and the roots are excluded from it by tillage. Unnecessary depth reduces the root range. Some results from an experiment conducted at Cornell University serve to illustrate the relation of mulches and weeds to soil moisture and crop production in a humid region in a season of good rainfall. The crop grown was maize. Every third plot was a check, and was given normal treatment. The figures show the in- crease or decrease in yield as compared with the nearest check plots. Moisture determinations were made on 208 THE PRINCIPLES OF SOIL MANAGEMENT portions of the plots bearing no crop, but otherwise receiving the same treatment as the remainder of the plot. The table thus shows the moisture conserved or lost by treatment, entirely aside from that transpired . by the crop. TaBLE XXXVII Compari- Increased (+) | Yields ealcu- Soil son soil Or lated to basis | moisture | moisture decreased (—) of 100 on during (basis of 100 yield check plots August on check plots Pounds Per cent Check plot ssc ecr cael. es 100 21.1 100 Weeds removed, but not culényated sec ues: —157 96 18.2 90 Mulched with straw ...... +873 121 250 130 Chesk plot, oo hea] ces . 4. 158 26.8 Memiamsands.....:5.. } Compact 147 93.2 218 THE PRINCIPLES OF SOIL MANAGEMENT The proportionate increase in the water capacity of the sand and decrease of the clay loam is here well shown, and doubtless, if the column had been longer, the compact sand would have had a greater absolute capacity than when loose. Deep plowing is greatly to be re- commended as a practice to increase the moisture capa- city ~of the: sai} Frio. 69. Subsoiler that loosens the subsoil by particularly where raising and breaking it. organic matter is well supplied. It creates a deep soil, and should estab- lish the best conditions for the storage of moisture, as well as food for the plant. If organic matter is not supplied, deep plowing is not advisable on light sandy soil; but on clay soil it is beneficial because of the loosening or granulating effect. The practice of subsoiling aims to loosen up the struc- ture of the deep subsoil without turning the material to the surface. It increases the ease of root penetration, the rate and depth of percolation, and on clay soil it increases the water capacity. Subsoiling is unnecessary and may even be injurious on sandy soil, and on clay soils must be used with discretion. It is difficult to secure the proper moisture condition of clay subsoils for plowing in the spring in time for spring planting. The soil may be in good working condition, or even dry, while the subsoil is wet enough to puddle. On the other SUBSOILING FOR MOISTURE CONTROL 219 hand, if the subsoil gets dry enough to break up, it may remain so loose and lumpy during the remainder of the season that capillarity is largely destroyed, and crops suffer from shallow rooting and lack of moisture. Decrease in crop yields as a result of subsoiling in spring are frequently reported. On the other hand, subsoiling in the fall, although usually more difficult to accomplish, is more likely to result in benefit. The cloddy condition which may be developed is largely broken down in re- gions of heavy winter rain by the saturated condition. Still the structure does not become nearly so compact as before the treatment, and good results. King presents figures which show that, as a result of the application of 1.34 inches of water, the soil which had been subsoiled to a depth of twenty-one inches retained, after a period of four days, 65.6 per cent more water in the surface four feet than the adjacent land not subsoiled. Not only is sub- soiling effective to increase the abso- lute water capa- city, but it may strengthen the capillary or film : movement to such fic. 70. Subsoiler that loosens the subsoil by an extent that an pesels, ma ner. important amount of water is drawn up from the deeper subsoil or from adjacent zones not so treated. A “hardpan” layer below the plow depth may seriously interfere with the upward movement of water and the 220 THE PRINCIPLES OF SOIL MANAGEMENT penetration of roots. This condition may be largely corrected by subsoiling. Coupled with deep plowing and subsoiling, subsur- face packing is often very beneficial. Particularly is this true in early fall and late spring plowing, where the soil is likely to be cloddy and to make poor capillary contact with the subsoil. Spring crops may be greatly injured by this condition. The subsurface packer crushes the clods, presses the furrow slice down more firmly on the subsoil without compacting the surface soil. a ce ft ella ah IA Fic. 71. ‘“‘Clod crusher”’ and sub-surface packer. It leaves a light mulch on the top to hold moisture. Not only is it useful in improving the soil structure under the conditions just mentioned, but it promotes the decay of organic manures and assists plant roots in penetrating into the subsoil below, where they may have a larger moisture and food supply. Increase in the humus content stands next to modifi- cation in texture and structure as a means of increasing the water capacity of the soil in accordance with the prin- ciples explained on pages 144 and 153. It accomplishes IRRIGATION pas this not only through its own large water capacity, but by its favorable influence on the structure of the soil. It should be worked deeply into the soil, in order that its many beneficial effects may be brought to bear on as large a volume as possible. It is especially favored as the adjunct of deep plowing and the use of lime for improving soil condition, particularly clay soil. The means for increasing the organic content of the soil have been discussed. (See page 131.) They include the application of animal manures and other refuse, and the growth of crops for green manure, together with that crop rotation which promotes the accumulation of crop remains, and that type of farming which removes the smallest proportion of the crop from the farm and returns the largest proportion to the soil. 100. Irrigation.—Irrigation is the third method by which the soil moisture may be increased. It is the prac- tice of directly adding water to the soil, to supplement the natural rainfall. It is chiefly identified with the arid and semi-arid sections of the country, where the annual rainfall is small. It is customary to consider a region as having a semi-arid climate when the rainfall is between ten and twenty inches, and arid when it is less than ten inches. These limits are arbitrary and necessarily elastic, because the actual aridity of a region depends on other factors than the total annual rainfall. It depends on the distribution of the rainfall, the climate, particularly temperature, and the character of the soil. While irrigation has been chiefly identified with arid and semi-arid sections (see map, page 137), it is not limited to those regions, and is applicable under any 222 THE PRINCIPLES OF SOIL MANAGEMENT condition where the natural rainfall is deficient at any period of the growing season. Consequently, irrigation is practised even under the very humid climate of Florida, with sixty inches of rainfall, around New York City and Boston, with forty inches of rainfall, and at many other places in the United States and Europe, where a so-called humid climate prevails. In these latter places it is identified with special crops of high value which will justify the expense involved. In France, Ger- many and other European countries, there are extensive areas of grass land which are artificially watered, often with sewage, which adds the element of food supply as well as water. Of course, all greenhouse management in- volves the practice of irrigation. Many engineering problems are involved in the prac- tice of irrigation, and have to do with the collection, storage and application of water to the land. But the principles which govern the application—the method, time and amounts of water—suitable for each crop and soil are purely agricultural considerations, to be han- dled in each case as the local conditions may indicate. The amount of water necessary to be added to pro- duce a full crop constitutes the ‘‘duty,’’ or efficiency, of water. It is the least amount of water which will produce a given yield under a given set of conditions. The ‘duty of water’? depends upon a great many factors; in fact, is limited by as many things as affect the moisture supply of soils in humid regions. The dis- cussion of irrigation which follows presupposes an ade- quate supply.of water, a condition often not fulfilled. For example, the area of the Western States containing CONDITIONS REQUIRING IRRIGATION 223 public lands is 973 million acres, of which Newell esti- mates that about 70,000,000 is of a desert character. At the present time, irrigation is practiced on less than 1 per cent of this area, and the total water supply is estimated to be sufficient for less than 10 per cent of the total area. Fic. 72. Map of the western portion of the United States, showing in black the irrigated land, and in dots the area which may be irrigated if all the avail+ able water supply is utilized. 224 THE PRINCIPLES OF SOIL MANAGEMENT 101. Factors affecting the duty of water.—Eleven factors, as follows, affect the duty of water in irriga- tion: (1) The peculiarities of the crop (see page 134). Some crops require much more water than others for their growth and maturity. Even certain varieties may require much more water than others of the same species. (2) The physical character of the soil. If the applica- tion of water is such that leaching may take place, more water will be lost through sand than through clay. The character of the soil also determines the effective- ness of the mulch, which may be maintained. (3) The character of the subsoil. (4) The frequency of irrigation. (5) Amount and distribution of the rainfall. These last two factors are closely related in their effect on the duty of irrigation water. Their frequency determines the proportion of the water which will be lost by surface evaporation. (See page 198.) (6) The amount and time of applying water. Water . applied in the evening will be more efficient than when applied in the morning, because during the cool night it will have opportunity to diffuse deeply into the soil, where the hot sun of the following day will have less effect upon it than if the water were applied in the morning. (7) The climate. Other things being equal, more water will be required in a warm, windy climate than in one of a cool, quiet atmosphere. This factor, of course, largely determines the rate of evaporation. AMOUNT OF WATER USED IN IRRIGATION 225 (8) Method of applying water. The furrow system is usually more economical of water than the flooding system, because less opportunity is given for evapora- tion. (9) The fertility of the land, as distinguished from its physical properties, determines the duty of water through its influence on the size of crop which may be produced. A large crop is more economical of water than a small one, but a large crop will require a larger total amount of water. (10) The closeness of planting affects the loss of water in much the same way as a large or a small crop: (a) By determining the total amount of water which must be used directly by the plants; and (b) by shading the ground and cutting down temperature agd wind movement more or less, it decreases the loss of water directly from the soil. (11) The tillage practice affects the efficiency of water under irrigation as it does the efficiency of rainfall in humid regions. If lax conservation methods are used, much more water will be needed than where the best tillage processes are applied. For these reasons, it is not possible to specify any definite amount of water which should be used in the practice of irrigation. It varies widely for different sec- tions of the world and, since it is very common to meas- ure the total amount of water supplied at the head of the intake canal,it is largely determined by seepage from the canals and ditches. (See page 134.) The amounts of water which are applied in different irrigation sec- tions are given by different authorities as follows: O 226 THE PRINCIPLES OF SOIL MANAGEMENT TABLE XXXIX Acres irrigated Equivalent to per second-foot inches of water used per ten days Northern India ieee... 60-150 3.96-1.580 By os Pe i cea eee een a 65-— 70 3.66—-3.400 TANG oo os Oa a sas 60-— 80 3.97-2.980 LO i a Mane aed Seeeeatt eoteaet 5 ly aa. acre 60-120 3.97-1.980 San Joaquin Valley, California.... 100-150 2.38—1.580 Santa Clara Valley, California ..., 150-300 1.58— .798 In Sefi, on the lower Nile canals in Egypt, one second- foot is said to be sufficient for 350 acres, as managed. In the humid regions much less water need be added by irrigation, and is necessary only to supplement the rainfall in the drought periods—to fill in the gaps. Ordi- narily only a few inches per season are needed, usually toward the latter part. Dr. Voorhees has compiled the following figures, which show the percentage of years in which there was a deficiency of one inch or more per month in the rainfall, as compared with the average. Tarun Xo One month Two months | Three months Per cent Per cent Per cent New York, 1836-1895 .... 15 42 21 Philadelphia, 1868-1895 .. 88 56 30 In this region, the deficiency is most likely to occur in the summer season. The records show that during one-fourth of the term there is a deficiency of rainfall covering three months. Considering the monthly rain- UNITS OF WATER MEASUREMENT 227 fall to be from two to three inches, a deficiency of one inch amounts to from one-half to one-third of the total, which must be a serious hindrance to crop growth, without the most careful soil management. On light, sandy soils, and with careless tillage in general, the above figures indicate that there may fre- quently be occasion for irrigation. The annual rainfall | i mysss: rea BP BI BIE" BAK ILI Fic. 73. .Flume for measuring miner’s inches. is ample for full crop production, if it could all be utilized. Many units are used in the measurement of water for irrigation. The two most common methods of stating the quantity of water used are: (1) In depth of water over the area, as acre-inches or acre-feet. (2) A given- sized stream flowing through the growing season. The two most common units under the latter system are the second-foot and the miner’s inch. It is frequently esti- mated that a flow of a second-foot of water—one cubic 228 THE PRINCIPLES OF SOIL MANAGEMENT foot per second—through a growing season of ninety days, is sufficient to irrigate one hundred acres. This is sufficient to cover the area 21.3 inches deep, and is equivalent to a little over seven inches per month. (See pages 135 and 137.) The miner’s inch varies in value in different sections. It is most commonly defined as the amount of water which will flow from an opening one inch square under a pressure-head of six inches above the top of the orifice, during a year, and is considered sufficient to irrigate from 5 to 10 acres. It is equivalent to about 1.5 cubic feet per minute, or 21.6 inches over 10 acres in a season, which, it will be observed, is practically the same appli- cation as one second-foot, as stated above. 102. Methods of applying water.—In his book on Irrigation and Drainage, King makes the following cogent statement with reference to the application of water in irrigation practice. ‘‘When water has been provided for irrigation, and brought to the field, where it is to be applied, the steps which still remain to be taken are far the most important in the whole enter- prise,—not excepting those of engineering, however great,—which may have been necessary in providing a water-supply that shall be constant, ample and moder- ate in cost; for failure in the application of water to the crop means utter ruin for all that has gone before.’’ “To handle water on a given field so that it shall be applied at the right time, in the right amount, without injuring the crop, requires an intimate acquaintance with the conditions, good judgment, close observation, skillful manipulation, and patience after the field has METHODS OF APPLYING WATER 229 been put into excellent shape; and just here is where a thorough understanding of the principles governing the wetting, puddling and washing of soils, and possible injury to the crop as a result of irrigation, becomes a matter of the greatest moment.’ (See page 103 et seq.) Mead reports that there are over thirty methods of distributing water in use in the United States. Each of these has its special adaptations as to soil, crop, water supply, climate and land contour. All of these methods may be grouped under four general heads, the further differences being in detail of ae eiion and not in essential principles. These are: (1) Flooding. (2) Furrow distribution. (3) Overhead sprays. (4) Sub-irrigation. 103. Flooding.—Flooding is practiced in _ several ways, and is applied to a much larger area than any other system. There are two fundamentally different types of flooding: (1) One covers the surface of the soil with a thin sheet of flowing water, maintained until the desired degree of saturation has been reached. (2) The other covers the surface with a sheet of standing water, which is allowed to remain until the soil is sufficiently saturated, when any balance is drawn off, or may be dissipated by percolation through the soil, as is fre- quently though unwisely done. The former system corresponds closely with what is termed wild flooding, where the water is distributed by a minute dendric system of ditches, and the remnant gathered by a reversed dendric system of ditches, or by a head ditch at the foot of the slope. The essential point is to keep a thin sheet of water moving over the 230 THE PRINCIPLES OF SOIL MANAGEMENT land until the soil is saturated. The second system agrees with check flooding, in which the water is turned on a nearly level area to a considerable depth. The check, or block, may be a small area—a few square rods on a decided shape, or a large area is possible on very level land. These may be so arranged that the water flows successively from one to the other, perhaps at successively lower levels. The relative advantages of the two types depend on the character and slope of the soil. On gently sloping land of moderately porous character, and not easily washed or puddled, so that the water may be controlled, wild flooding is the most convenient method. Grain fields especially lend themselves to the method. On the other hand, on very level or very steep land the block type must be used. The water is more definitely under control, washing is largely prevented by levees, and puddling is reduced by the almost entire elimination of current. | The flooding system is best adapted to certain classes of crops, as follows: (1) Grain fields. (2) Meadows and hay fields. (3) The soaking of land preliminary to. plant- ing other crops, sometimes termed winter irrigation, where the water-supply is available only in the winter season, and is stored in the soil until crop-growing time. The above crops are adapted to occasional or intermit- tent flooding; but some crops succeed best under a con- tinual flood of water, as in: (4) Rice culture and (5) Cranberry culture. A phase of the flooding system is the basin system sometimes used in orchard irrigation. The advantages of the system are: (1) Ease in hand- ling water. (2) Economy in irrigation works. (3) IRRIGATION BY FLOODING AND FURROWS reg Avoids necessity of tearing up the crop to form large irrigation furrows. The objections to its use are: (1) The large amount of water required. (2) The danger of over-irrigation, with the possible consequent injury from seepage, and the appearance of alkali salts. (3) The impossi- bility of conserving water by appropriate cultivation. (4) On heavy soils possible injury from the crusting and checking of the surface soil as a result of the lack of tillage. (5) Direct injury from flooding some crops, as the potato. 104. Furrows.—Furrow distribution, by which, as the name implies, the water is not applied to the whole surface but is distributed in furrows. The length, size and arrangement of these depends directly on the soil, chiefly its texture. This includes the subsoil as well as the soil. In soils which are porous or easily eroded, the furrows must be shorter than where the opposite conditions prevail, in order that the water may reach the further end of the field before over-wetting the por- tion near the head ditch. That is, in loose, porous soil, head or feeder ditches must be nearer together than on dense, impervious soil. The furrow system is adapted to all intertilled crops. Next to the flooding system, it is used on the largest area, and is adapted to all intensively cultivated crops. Its advantages are that: (1) It conserves water. (2) It is especially adapted to inter-tilled crops. (3) It permits the conservation of water by appropriate cul- tural practices. (4) It avoids injury to crops sensitive to an excess of water. Water should not come in contact 232 THE PRINCIPLES OF SOIL MANAGEMENT with the trunk of trees, or, in general, with the stem of any plant not well shaded. A bright, warm sun in con- _., junction with the excess of OPENING OX? ~water is usually injurious. (5) It 1s the more convenient method to apply to the class of crops to which it is adapted. (6) It more readily permits the avoidance of the injuries due to seepage by avoiding the losses to which that is due. (7) It assists in the con- trol of alkali soils by permit- ting tillage. ae 74. Canvas dam with The supply of soil mois- opening to divide the water in an ture by capillarity is most irrigating furrow. satisfactory to the majority of cultivated crops, and by promoting this the furrow system generally gives better results than flooding. The flooding system has some disadvantages: (1) It is not so economical of water as is to be desired. (2) Much attention must be given to forming the furrows, to the construction of head or supply ditches, to the collection of the overflow water at the end of the furrows, and in the general supervision of the flow of the water over the land to repair broken levees, etc. (3) The water is not applied uniformly. The head of the furrow invari- ably becomes more wet than the lower end. (4) Erosion and puddling occur very readily in cultivated furrows. 105. Overhead sprays.—Overhead spray is used only on very limited areas, and almost entirely in humid _ IRRIGATION BY SPRAYS 245 sections. It has been applied in the growth of Sumatra wrapper tobacco in Florida, and of truck crops near New York, Boston and other large cities. It is therefore used as a very limited supplement to the regular rainfall. It is accomplished by the use of a very thorough piping system with spray nozzles at sufficiently frequent inter- vals to cover the area. These are connected with a rela- tively large pressure-head of water—-at least five pounds is necessary. The advantages of the system: (1) haste in the direct application of water to shallow rooted crops. (2) Convenience in applying water at the desired point. (3) Absence of injury from erosion or puddling the soil. (4) No land wasted in irrigation ditches. (5) Natural climatic conditions developed by such irrigation. The disadvantages of the system are great: (1) The large initial cost of the plant. (2) The high operating expenses ordinarily necessitated to develop the pressure necessary to distribute water from the nozzles, and to maintain the system. (3) The limited capacity of the system. (4) The large evaporation from the spray in the atmosphere, and from the soil and surface of the plants. The spray system is practicable only with special crops under peculiar conditions. 106. Sub-irrigation.—Sub-irrigation often occurs naturally. It is the application of water beneath the surface of the soil. The structure of the land is such that on many low benches and in river bottoms the percolation of water through the soil and fissures of the rock brings it near the surface at these lower levels, 234 THE PRINCIPLES OF SOIL MANAGEMENT where it maintains a fairly constant supply of water to those crops which may be growing on the surface. The ground water is so near the surface in some stream bottoms, lake shores, etc., that this condition prevails. Soils ordinarily poor in their moisture relations become highly satisfactory in such cases. Sandy land is almost ideal in its crop relations, so far as moisture goes, under such conditions. In a limited way it has been attempted to irrigate the soil from beneath the surface by forming under- ground channels of porous pipe, properly graded, into which irrigation water may be turned, which should diffuse through the soil by percolation and capillarity. In some situations, as lawns, truck and fruit gardens, it may be possible to install a drainage system of tile, which may also serve as a means of irrigation. The system has a number of advantages, which in ordinary practice are more than offset by its disad- vantages. Its advantages may be summarized as fol- lows: (1) It is very economical of water. (2) In alkali soil it greatly reduces the surface accumulation of alkali. (3) It insures deep rooting of the crop. (4) It avoids waste land. (5) It avoids injury to the physical condition of the soil. (6) Involves very little super- vision in the application of water. (7) Possibility of the use of the system for drainage purposes. Its disadvantages are: (1) The strong tendency of roots to enter and clog the pipes. (2) The slow diffusion of water by capillarity in dry soil. (3) The expense involved in the installation of a system of pipes ade- quate to irrigate most soils. SUB-IRRIGATION 2350 Plant roots seek the most moist soil which is short of saturation, and therefore they are drawn toward and tend to concentrate around and in the lines of tile, just as roots are found to do where drain tiles carry living water through dry soil. This is the greatest disadvantage of the system. Especially is this true in orchard work. It is more adapted to shallow-rooted annual crops, and to soils of strong rapid capillary power, such as fine sand and coarse silt loam or loam soil. The amount of water to be added at one time must be determined chiefly by the texture and structure of the soil,—or more specifically its water capacity,—and the supply of water available. Under arid conditions, it is generally advisable to apply as much water as can be held within the root zone by capillarity without loss from percolation. Frequent small applications should be avoided, because of the large proportionate loss from surface evaporation. (See page 197.) Also, there is a stronger tendency to the accumulation of alkali salts at the surface, because of the larger evaporation. On the other hand, less frequent large applications of water, particularly under any but the flooding system, where u crop occupies the land, permits the creation and main- tenance of a mulch to conserve moisture; besides which, the deep distribution of the water insures a deep distri- bution of the roots, where they are not only in contact with a larger moisture reservoir, but also with a larger food-supply than is available to shallow-rooted plants. It is a fact of common experience that in arid regions crops generally root deeper than in humid regions. A common accompaniment of irrigation, certainly 236 THE PRINCIPLES OF SOIL MANAGEMENT in semi-arid and arid regions, is the excessive accumu- lation of soluble salts—‘‘alkali salts’’—in the soil. They may become so concentrated as to injure crops or prevent their growth. (See page 307.) In the original condition of such soils they are usually distributed in relatively small amounts through a deep section of soil. But by excessive irrigation, which produces seepage and a general rise in the water-table, aided by those careless tillage methods which permit free evaporation at the surface, these soluble salts become con- centrated in the root zone, and at the surface as an alkali crust. It has frequently happened that land not originally Bia) #5. Middl Didaker plow. Bemes oe seriously “alka- times used in constructing irrigation and line’’ condition has be- drainage ditches. come so by careless management. It is obvious that to avoid this injury there must be (a) conservative irrigation, and (b) the most thorough tillage methods which shall avoid surface evaporation. Where an excess of akali salts exists, they are most successfully removed by means of a deep thorough drainage system, coupled with heavy irrigation which shall wash out of the soil the excess of salts. It is a safe and wise rule to cultivate the soil as soon after applying water as its moisture condition will per- mit without injury, and this should be kept up at fre- quent intervals until an effective dust mulch has been PRECAUTIONS IN IRRIGATION 2a7 created. It has been noted (page 204) that in arid regions soil mulches are relatively more efficient and more easily managed than in humid regions. Soils of intermediate fineness lend themselves most readily to the practice of irrigation. Excessively heavy clay is generally to be avoided, because of (a) the slow diffusion of water, by both capillarity and percolation, and (b) the danger from puddling after an irrigation, unless cultivation is delayed so long that a large amount of water is lost. On the other hand, very light sand should be avoided because of its leachy character, and the great loss of water by percolation or surface evaporation, the former, if a large amount of water is added at once; the latter, if it is added very frequently. But in humid regions it is wise to practice irrigation for crops easily injured by an excess of water except on those light and porous soils which have thorough drainage, because of the possibility of a rainfall following closely upon the application of water, thereby rendering the soil over-wet, to the injury of the crop. On the porous soil the excess quickly drains away. In the Sumatra tobacco region of Florida, for example, where there is a large rainfall, irrigation has been found successful only upon the lighter sandy loam and sand soils. This crop is particularly sensitive to an unfavorable soil condition. Then too, the heavy soil, the clay loam, or clay, has a large water capacity, which makes possible the storage of a large amount of water against the needs of the crop- growing season. Consequently it is on these latter that dry farming of grains is most generally practiced in the Western states. 238 THE PRINCIPLES OF SOIL MANAGEMENT As the demand for produce of high value increases, the maintenance of the moisture supply of the soil by irrigation may well be extended on large areas of soil in so-called humid regions, as well as in arid sections. The highest type of soil-management must seek to utilize the available water-supply for crops in the three ways outlined above, that is, by increasing the water capacity of the soil, by eliminating as far as possible Fic. 76. An example of poor drainage on level clay soil. the losses by percolation and evaporation and, lastly, by supplying any deficiency which may still exist by wise irrigation. 107. Means of decreasing the water content of the soil.—The removal of water from the soil may be accomplished in two general ways. These depend upon facilitating the two types of loss, by percolation and evaporation, described on page 191. They are: (1) Drainage. (2) Surface culture, to hasten evaporation. 108. Drainage by ditches.—Drainage consists essen- DRAINAGE 239 tially in the direct removal of the gravitational water from the root zone of the soil by affording free passages for its percolation and flow. In general, the soil condi- tions requiring drainage may be divided into two groups, which are fairly distinct in the problems which they present. These are: (1) Those lands which are satu- rated with water throughout the year. (2) Those lands which are saturated with water for only brief periods. Into the first group are placed all those lands of an acknowledged swamp character, which not only retain a large part of the water which falls upon their own sur- face, but may receive the water which flows from other lands. Into the second group is put all those wet lands which are saturated for a sufficient period to interfere with the best condition of the soil, or the proper develop- ment of the crop. It represents a very mild or incipient stage of the conditions included in the first group. In the manipulation of soil for the staple upland crops, the establishment of effective drainage is at the foundation of all the other practices which must be employed. If it does not exist, the other farm practices, such as tillage, fertilization etc., can not be applied effectively. An excess of water in the soil has many and far-reach- ing effects upon the soil as a medium for plant growth, especially if this condition is intermittent. The manage- ment of the latter condition is even more crucial than the former. 109. Effects of drainage-——Twelve of the most important effects of drainage are as follows: (1) Firms the soil. (2) Improves the granulation. (3) Increases 240 THE PRINCIPLES OF SOIL MANAGEMENT the available moisture capacity. (4) Improves the aération of the soil. (5) Raises the average temperature. (6) Promotes the growth of desirable organisms. (7) Increases the available food supply. (8) Enlarges the root zone of the soil. (9) Reduces “heaving.”’ (10) Removes injurious salts from “alkali soils.” (11) Reduces erosion. (12) Increases crop yields, and improves sanitary conditions of the region. 110. Firms the soil.—In a saturated soil the particles are held apart and are partially floated by the water, with the result that they afford a poor support for plants, and are largely unable to bear the weight of travel incident to cultural operations. Heavy objects sink into the surface, and become mired as a result of the easy movement of the soil particles from beneath their weight. This movement is greatly facilitated by the lubrication afforded by the water between the particles. It is because of this freedom of movement that a wet soil may readily be “‘puddled,”’ that is, the small par- ticles moved into the spaces between the large ones, producing a more dense mass, a change not possible in dry or even moderately moist soils. 111. Improves the structure.—Drainage improves the granular structure of fine-textured soil. One of the most important factors in soil granulation is alternate wetting and drying. (See page 105.) In a wet soil, this drying and drawing together does not take place. On the other hand, if a granular soil be kept saturated, the crumb structure will be broken down and a bad physical condition results. This is well illustrated by the fact that nearly all swamp soils are in a puddled, or otherwise DRAINAGE AND SOIL STRUCTURE 241 bad physical condition, when first drained. Drainage brings to bear upon the soil all those natural agencies which promote the granular arrangement. In turn, the granular structure, particularly in fine-textured Fic. 77. Section of a 20-year-old tile drain in heavy clay soil. Note the more open structure above the drain. soil, affects the movement and capillary retention of water, the circulation of air, the growth of organisms, the temperature of the soil, and other conditions depend- ent on these, in a manner highly beneficial to the crops generally grown. 112. Increases the available water.—Drainage in- P 242 THE PRINCIPLES OF SOIL MANAGEMENT creases the available moisture capacity of fine-textured soil. This is accomplished through the better granulation and larger porosity which results. The possibilities in this direction are indicated by the effect of structure on the moisture capacity of the soil. (See page 151.) Field experience has many times shown this result to follow drainage. Instead of plants suffering from lack of moisture, as a result of drainage, it is found that they are not only free from the excesses, but that in dry periods the soil is likely. to contain more moisture than the same kind of soil under poor drainage. This is especi- ally true of those soils which are wet only a part of the season. They are subject to great extremes in moisture content. 113. Improves the aération.—Drainage improves the aération of the soil in two ways. (1) It removes the gravitational water from the large pores, thereby permitting the admission of air. (2) Through its effect on granulation it permits the soil to hold a larger volume of air and facilitates its circulation. This also is due to two conditions, especially where the drainage is beneath the surface. The larger pores resulting from granulation ereatly aid the process. And the underground passages, formed by tile or other media, afford channels for the escape of soil air following rain or reduction in baro- metric pressure, and facilitate its readmission when the opposite conditions prevail. The net result is a much larger total change between the outer air and the soil air. This reacts strongly upon the soil organisms and upon the general chemical activity of the soil. 114. Raises the average temperature.—Drainage DRAINAGE AND SOIL TEMPERATURE 243 raises the average temperature of the soil. The specific heat of water is much higher than that of soil, and there- fore the larger proportion of water a soil contains the more heat is required to increase its temperature. (See page 461.) Further, in a wet soil the surface evapo- ration is large, and since the evaporation requires several hundred times as many units of heat as is necessary to raise the same volume of water from the normal temperature to the boiling point, it is clear that the process must consume a large amount of heat. But the heat supplied to any given area of soil is fairly uniform, and consequently, if it is used up in evaporating water, it is not effective to raise the temperature of the soil mass. If the soil contains water which must be removed by evaporation, its temperature will be kept correspond- ingly low; or, what is the same result, the time required to warm the soil will be correspondingly extended. For this reason a wet soil is a “‘late soil,’’ while a well- drained soil is much ‘‘earlier’’ in attaining the tempera- ture necessary for the germination and growth of plants. The practical result of this rapid warming of a well- drained soil is to lengthen the growing season by per- mitting its earlier seeding in the spring, and the later growth of crops in the fall. In some sections of the world, this margin in the length of the growing season deter- mines the growth of certain crops, and materially affects all crops. All of the activities of the soil, both chemical and biological, are favorably affected by the higher temperature. In the peat bogs of England, Parkes found that at a depth of seven inches the drained soil was 15° warmer than the undrained soil, and at thirty-one 244 THE PRINCIPLES OF SOIL MANAGEMENT . inches it was 1.7° warmer. King reports the frequent observation of a difference of 12° between the tempera- ture at the surface of drained and undrained land. 115. Influences the growth of soil organisms.— Drainage promotes the development of the desirable forms of organisms, and hinders the development of the undesirable forms. As will be shown (page 399), the » soil organisms may be divided into two groups, one of which requires free oxygen for their growth, the other does not. These two groups are concerned with different types of chemical change,—the one producing decay the other putrefaction. In proportion as the air is ex- cluded by an excess of water, normal decay is inhibited and putrefaction promoted. The one is beneficial, the other is likely to be injurious. Further, the products of the organisms accumulate in the excess of soil water and sooner or later may kill most of the forms; as is exempli- fied in peat bogs, which owe their origin chiefly to this fact. Not only is the decomposition of organic matter retarded, but the chemical changes in the mineral portion of the soil resulting from these processes are correspondingly reduced by lack of drainage. And most important of all is the stimulation to the formation of nitrates which results from good drainage. The supply of nitrates is often the controlling factor in plant growth, and consequently, in so far as drainage increases this supply, it is directly beneficial. 116. Increases the food-supply.—Drainage increases the available food-supply of the soil in three direct ways: (1) By holding in the soil a larger proportion of avail- able moisture which favors a larger chemical activity DRAINAGE AND THE ROOT ZONE 245 without removing the products from the root zone. (2) Through direct chemical changes which result from good aération. (3) Through the activity of organisms which not only form nitrates but produce carbonic acid and other materials which increase the availability of the mineral portion of the soil. The thoroughness of these chemical changes is well illustrated by the uniform color of a well-drained and well-aérated soil, in contrast to the usually mottled color of poorly aérated and wet soil. Drainage enables the plant-grower to make better use of the food stored in his soil. FU-—-n; Ak = = ij} ae hy TW 4 We ins table between lines of drains. 117. Enlarges the root zone.—Drainage deepens and enlarges the root zone of the soil by the removal of the gravitational water and by the admission of air. Thereby the plant is brought into intimate relation with a much larger volume of soil from which it may draw moisture and food. It is thus enabled to withstand more protracted periods of dry weather; it enjoys a more uni- form climate, and has a larger food-supply, all of which are conducive to a rapid growth and a larger yield. 118. Reduces “heaving.’’—Drainage reduces ‘“heav- ing,” which results from freezing of a wet soil. When water freezes, it expands one-eleventh of its volume. In a saturated soil, this expansion can take place in only one direction—upward—with the result that the 246 THE PRINCIPLES OF SOIL MANAGEMENT soil and consequently the crop is lifted. Shallow-rooted crops are gradually raised out of the ground by repeated freezing when wet, because the soil settled back into Fic. 79. Alfalfa roots raised out of the soil (‘“‘heaved’’) by the repeated freezing of a wet clay. place more quickly than the root. Not only is the plant lifted out of the ground, but many of the smaller roots are broken off, all of which greatly reduces the vitality of the plant. It is most serious on clay soil, because this DRAINAGE AND “HEAVING” 247 texture holds more water and is most likely to contain an excess of water. Drainage reduces this type of injury in two ways: (1) By reducing the amount of water present to freeze. (2) The larger volume of free pore space, due to the removal of part of the water and to the better granulation, permits the expansion due to freezing to be taken up within the mass of the soil, rather than produce a lifting of the surface. Serious ‘‘heaving”’ is always dependent upon an excess of soil water. 119. Removes injurious salts from alkali soils.— Drainage in conjunction with heavy irrigation is the most effective means of removing “alkali salts’ from arid soils. These salts are dissolved in the irrigation water as it passes through the soil, and are then removed in the drainage system beyond any possibility of further injury. By this practice it is possible to reclaim the most pronounced areas of alkali soils to the growth of the most sensitive crops. 120. Reduces erosion.—Drainage reduces erosion due to water. This type of injury results from the flow of water over the surface. Drainage reduces this process: (1) By increasing the absorption of water. (2) By affording channels in which it may be removed without injury, due to a less fall, or in conduits not subject to erosion, such as tile drains. 121. Increases crop yields and improves sanitary conditions.—The direct practical result of all of the above effects is larger and more reliable crop-yields, together with greater ease in all cultural and harvesting operations. . Coupled with the direct economic effect of drainage, 248 THE PRINCIPLES OF SOIL MANAGEMENT is a large improvement in the general sanitary condi- tions of the region, which was recognized long before the economic advantages of the practice, and has gener- ally been sufficient reason for public interest in the prac- tice. It is only within recent years that the economic benefits of drainage have been recognized as of sufficient public concern to warrant regulative legislation. 122. Principles of drainage.—There are two general types of drains: (1) Open, or ‘‘surface drains.”’ (2) Cov- ered, or ‘“‘under drains.’”’ Each of these types has a partic- ular range of usefulness and, while they may be substi- tuted one for the other under ‘some conditions, their respective spheres of usefulness are fairly distinct. 123. Open, or surface drains.—Open or surface drains remove water from both the surface and from the depths of the soil. Their efficiency in removing water from the subsoil depends upon their depth and fall, and upon the level of water in the channel. There are certain conditions to which open surface drains alone are adapted: These are: (1) Where the volume of water to be moved is very large. (2) Where the water table is so near the surface, and the’ fall so slight, that it is not possible to place a drain below the surface. (3) Where the drainage is designed to be for only a short time. As open ditches their efficiency depends on the sur- face flow of water into their channel. They usually tap the low areas where the water accumulates. Some- times, as in river bottoms, they may be arranged regu- larly at intervals, and be of such size as to hold the water which may fall upon the surface during any ordinary METHODS OF DRAINAGE 249 rain, until such time, after the subsidence of a general overflow as it may be removed. They may serve to remove the water accumu ated as the result of an over- flow. In every such case their efficiency depends upon taking advantage of the natural inequalities of the sur- Fic. 80. Surface ditches for drainage in a grain field. Such drains are usually of low efficiency. face of the land. One phase of this practice is to plow the land in narrow beds, so that the frequent ‘‘dead fur- rows”’ serve as surface drains and as temporary storage for the surface water. As sub-surface drains, their efficiency depends upon their depth being sufficient to permit percolation from 250 THE PRINCIPLES OF SOIL MANAGEMENT the adjacent subsoil. This, in turn, is determined by the texture and structure of the soil, and upon all those other factors which determine the efficiency of closed drains, later to be discussed. To be efficient, an open drain should be properly eraded, should have a smooth bottom and sides, should have sufficiently tenacious walls to resist incidental erosion, and should have a shape approximately that of a semicircle, which is the form giving the greatest carrying capacity per cross-sectional area. Since this exact shape is difficult to maintain, it is common in practice to make the depth and bottom width, respec- tively, one-half the width of the top, with sloping sides. The form and grade of the ditch must be governed by the character of the soil. The steepness of the sides will be determined by the ability of the soil to form resistant walls. Clay soil will maintain a much steeper bank than sand. The fall must not be so great as to produce serious erosion. A loam or sand soil is much more suscep- tible to erosion than a clay. The fall should be uniform, in order that there be no undue accumulation of sediment at any point. Sedimentation may be reduced by pre- venting the growth of vegetation in the bottom. As deep-soil drains, open surface ditches have a number of disadvantages, some of which are: (1) They are seldom of sufficient depth. (2) As ordinarily con- structed, they have a small carrying capacity, due to their uneven grade and rough bottom and sides. (3) They are expensive to maintain. (4) They waste much land. (5) They greatly interfere with cultural opera- tions. (6) They may be subject to serious erosion, UNDER-DRAINS 951 124. Covered or under-drains.—Covered or under- drains are any underground channels constructed for the removal of water. Many kinds of material have been used for this purpose. Some of the earlier materials used were brush, stone, poles, boards, and brick. In recent years these have been almost entirely supplanted Fic. 81. Construction of a ditch for tile drains. by pipes made of clay or cement because of the greater permanency and efficiency of the latter. The depth, frequency and size of drains depends on the character of the soil and subsoil, the amount and distribution of the rainfall, the topography of the sur- face, the crop to be grown, the prevalence of under- ground seepage, and the level of the ground water. The system should always be arranged with reference to these conditions. 252 THE PRINCIPLES i jqillll, (ing) tnd a Fic. 82. Laying tile in the bottom of ditch by use of the tile hook. Shows arrangement of tile preparatory to filling the ditch. OF SOIL MANAGEMENT (a) Depth.—The depth of the drain must be such that the water can find entrance before it shall have caused serious injury to the crop. Since water percolates through sand and gravel so much more readily than through clay, drains may be placed much deeper in the former than in the latter. In coarse-textured soil, drains attain their full efficiency almost at once; but in clay, owing to its dense character from long wetness, there is a gradual increase in efficiency through _ several seasons, as the soil becomes better granulated and _ ac- quires other favorable struc- tural properties. In sand, water percolates rapidly into the drain, but in clay this gen- eral movement is greatly re- duced and takes place largely from the sides and top of the drain. In fact, a dense clay soil holds its pores almost full of capillary water, which is not subject to percolation. Under such condi- tions, a large part of the injury comes from water stand- ing on the surface. Here the under-drains must be placed very near the surface, and function chiefly as surface CONSTRUCTION OF UNDER-DRAINS 253 drains. But, as the excess of water is removed, and the soil structure is improved, they assume more fully the function of deep drains by removing water from the joints, or checks, which extend deeply into the soil. Where deep-rooted crops and trees are to be grown, deeper drainage is necessary than where shallow-rooted crops are grown. In gen- eral, it is not desir- able to lower the water-table so much in sandy as in clay soils, because of the less capillary capacity of the former. The water-table should be lowered to from three to five feet below the surface, but it is not always necessary to place tile at this depth, to attain suf- ficiently thorough drainage. Where there is a distinct change from sand to clay, or vice versa, within from two to four feet of the sur-. face, it is usually best Laying double-sole drain- tile by hand. 254 THE PRINCIPLES OF SOIL MANAGEMENT to place the drain on the boundary between the two. If the clay is below, the water will percolate along its surface through the sand and enter the tile. On the other hand, if the clay is underlain by sand, it is easier for the water to percolate downward into the coarse- texture stratum, and through this into the tile, entering from below. (b) Frequency.—There are two general systems of arranging drains: (1) The gridion or regular system. Fic. 84. Two systems of arranging tile drains. Compare the amount of double draining in each system, due to junctions. Note the relative lengths of tile required for the same area under each system. (2) The natural or irregular system. In the first, the drains are arranged at definite regular intervals apart,— this interval depending chiefly on the texture of the soil. This is necessary where the surface is very uniform and the soil very homogenous. It may be applied to a slope as well as to level land. In clay soil the interval must be less than in coarse-textured soil. This is because there is a drainage gradient between the drains. In fine- CONSTRUCTION OF UNDER-DRAINS 255 textured soil the water level rises rapidly away from the drain and reaches the sur- face at no great distance. On sand soil this gradient is much less. The aim must be to have the water level reduced a definite distance below the surface, after a reasonable interval of time follow- ing rainfall, and the drains must be sufficiently frequent to accomplish this. In heavy clay soil this interval may be as small as twenty-five feet, while in coarse-textured soil it may be 200 or 300 feet. Usually, it is best to adopt some minimum interval, and 3 |3'|3" place the first lines of tile at two or more times this interval. If the drainage p aia SF Fie. 85. A more simple system of drains, but one re- quiring more large tile than in Fig.86. does not prove sufficiently thorough, additional drains may be installed with- out affecting the general system. xfe 8 pr . The natural or irregular system is Fic. 86. Drain with minimum number of large tile, but having many turns and branches. designed primarily to collect water from the surface where it has accumulated, or beneath the surface where it comes within the range of the plant roots. Large areas of land are drained by a single line of tile in the low places. Where land is kept wet by seepage, the drains should tap these as near their source as is practicable. The size of drains depends on the 256 THE PRINCIPLES OF SOIL MANAGEMENT Fic.87. The so-called natural or irregular system of arranging drains to remove water from local wet spots. Shading indicates degrees of wetness. volume of water to be handled and on the fall. Where several laterals empty into a main drain, the main must have a capacity equal to their combined flow; but it is not possible to calculate the total or relative sizes with the exactness which is possible in a pressure system of pipes. This is due to the effect of the soil. It acts as a sponge to hold the water, and gives it up gradually. The *sno1iod 81OUI YONUI 1B Sl9Yy}O 9Y} ‘snolAJedult AoA pus peuing-piey aie ainsy oy} Ut eT} [euosexey oy], ‘AB] 0} JUBIUAAUOD YsouI are sedvys [euosexey 10 punoy ‘aI} UreIp Jo sodA} eul0og “gg ‘DIY tats ie a i a oe 258 THE PRINCIPLES OF SOIL MANAGEMENT finer the soil the greater this retentive effect, and con- sequently the less demand there is for drains capable of carrying all of the rainfall in a given short time. Drains run full for only a very small part of the year, and therefore the normal laws of hydraulics are not entirely applicable to them. In a general way, doubling the fall increases the carrying capacity of any given size of tile by one-third. Where the fall is less than 1 per cent, it is unwise to use tile smaller than three inches in di- ameter, because of their strong tendency to clog. Water enters tile al- most entirely through the joints between the sections. Short lengths are therefore better than long ones. Through the walls of even soft brick tile very little water is Fic. 89. Hand tools used in tile- able to percolate. There drain construction. 1, Grade cord; 2, pick; 3, long-handle, round-point shovel; 4 : 7 and 7, types of grading shovel for finish- 1S, therefore, no apprecl ing the bottom of the ditch: 5, spade: 6. able advantage in using ihe banks, Sy: Eyes Htakes: soft tile, while there are many disadvantages,—such as their weakness and lia- _ bility to go to pieces rapidly under alternate wetting and drying, especially if permitted to freeze when saturated with water. Dense, hard-burned tile are most safe to use under average soil conditions. ‘“Silting-up”’ of drains results where the alignment DITCHING MACHINES 259 is bad, the joints too open, or a section is broken. The joints should be fairly snug, but it is not now considered necessary to use collars in ordinary soils. The textures of soil which give most trouble by entering the joints and stopping flow are very fine sand and silt. These materials flow readily when saturated with water. Con- sequently, in laying tile in these materials, precaution must be taken against this. ‘‘Silting-up”’ is most trouble- \ —_ y, a GS NU Lott EEE WE a ma F, S ee = WZ RY Fie. 90. Traction ditching machine. A modern machine for caeuben pecs tile ditches. (See Fig. 91.) some immediately after laying the tile, and before the soil structure has become settled and readjusted. When this has taken place, the tendency to silting-up is small, even in fine sand and silt. In clay and coarse sand it is negligible. This difficulty can be checked or controlled by using some filtering medium around the joints. Straw, leaves, chaff, etc., are excellent and undergo slow decay, coincident with which a resistent structure of soil is ion t ine in opera Fie. 91. Traction ditching mach UNDER-DRAINS AND PLANT ROOTS 261 established. Fine gravel or coarse sand is a more per- manent filtering medium. Plant roots sometimes enter the joints of tile drains, and develop so as to stop the flow of water. This occurs most readily where the tile carries “living water,’’ as where a permanent spring is drained. During dry periods and in naturally well-drained soil, water per- colates from the joints of the tile into the adjacent soil, which conditions at- tract roots and may lead them into the tile at the joints. Depth is not a decided protection against this difficulty unless it be eXcessive. There are many points about the construction of a tile-drain system about which special precaution should be taken. Some of these are: (1) Uniformity of grade. (2) Avoid lead- ing a lateral into a main with a less fall unless silt basins are used. (3) Pro- tection of outlets against -==©= Fic. 92. Ditch cut by the ma- caving and freezing. (4) chine shown in Fig.91. Soil a heavy Protection of the outlet clay. Depth 4% feet. TS ta ep 262 THE PRINCIPLES OF SOIL MANAGEMENT against the entrance of animals. (5) Free flow of water from the outlet. (6) Close joints, which may be more easily attained with round or hexagonal than with Fia. 93. A poorly constructed outlet for a line of drain tile. U or soft tile. (7) Junctions should be made at an acute rather than at a right angle. (8) On hilly land the drain should run with the slope, as far as possible. (9) In general, the fall should be as great as the surface fea- SPECIAL TYPES OF DRAINS 263 tures will permit. (10) Avoid throwing the tile out of alignment in filling the ditch. The chief advantages of covered drains, especially when constructed of tile, are: (1) Permanence. A well- constructed system will last for many decades. (2) Greater efficiency where they are suitable. (3) No waste of land. (4) No interference with cultural operations. (5) Require very little care for maintenance. (6) Less cost over a period of years. 125. Other types of drainage.—Drainage may some- times be accomplished by means of levees. Where land is subject to overflow at either frequent or infrequent intervals, such as river bottoms and tidal marshes, their drainage consists largely in excluding these inundations. Until this is accomplished, any other form of drainage may be useless. Frequently direct drainage may advan- tageously be combined with some form of levee, and for tidal marshes is useful with the aid of the fresh water derived from rainfall and upland drainage, in removing its saltness. Wells or filter basins may be used to drain certain sinks or flat areas having no other outlet. This is pos- sible only where a very porous stratum occurs beneath the soil within a reasonable depth. Usually this is practicable where a clay stratum is underlain by sand or gravel, as occurs in many sections of the country. Wells are constructed through the clay to the porous stratum, and this may be filled with stone or brush as a filtering medium, and covered drains may be emptied into these. 126. Surface culture.—Surface culture may be em- Sd 264 THE PRINCIPLES OF SOIL MANAGEMENT ployed to remove a limited excess of water from the soil. Those practices which may be employed for this purpose are the opposite of those applied in the conservation of water. The most applicable ones are: (1) Rolling. (2) Ridged surface. (3) Growth of plants. Rolling, or any other practice which compacts the soil and strengthens capillary movement of water to the surface, places the moisture in the most favorable position Fia. 94. Water forced to the surface by the closure of the outlet of a tile drain. REMOVAL OF WATER BY PLANTS 265 for evaporation. It would be unwise, as a rule, to roll the soil when it is excessively wet, because of the injury to the structure of the soil which would result. But the Fic. 95. A well-constructed outlet for a line of drain tile. land may be rolled in anticipation of a wet period, which condition of the soil will facilitate the formation of that compact surface which most favors evaporation. In the spring, in regions of cold winters, bare or fallow land has usually settled into this condition, which, if permitted to continue, will most rapidly dry the soil. Ridging increases evaporation by exposing a larger 266 THE PRINCIPLES OF SOIL MANAGEMENT surface. In some sections of the country where the wetness is most serious in the spring, the crops are planted on ridges which are sufficiently raised above the general surface to be drained; and, by the time the roots are ready to penetrate deeply, the excess of moist- ure will have been removed by percolation and evapo- ration. Crops of any sort, inc'uding weeds, green manures and cover-crops, may serve to dry the soil by evaporating as La ods o>, Wie Ss gt eee es oh Gee Fie. 96. The nine foot evener used in the final filling of the ditch by the use of the turning plow after laying drain tile. Care should be exercised in placing the first covering of earth over the tile not to disturb their alignment or break any of the sections. This is best accomplished by hand, and the earth should be carefully pressed around the tile. water from their leaves. It has been seen (page 134) that the amount of water so used is large because of the functional activity of the plants and the large surface which they expose. Growing crops expand the evapo- rating surface of the soil and are especially useful in removing a temporary wetness in the spring. The application of any of the above methods for the removal of water must be guided by the local conditions of soil, season, climate, crop and system of farming. C. PLANT NUTRIENTS IN THE SOIL I. SOLUBILITY OF THE SOIL THROUGH NATURAL PROCESSES Fortunately for mankind, only an exceedingly small proportion of the soil is at any one time soluble in water or in the aqueous solutions with which it is in contact. It is this great insolubility that givés the soil its perma- nence, for, otherwise, in humid regions, it would be rapidly carried away in the drainage water. The portion soluble in the various natural solvents with which it comes in contact furnishes the mineral-food materials for plants. The great mass of soil which is relatively in- soluble is constantly subjected to natural processes which very slowly bring the constituents into solution. Those agents concerned in the decomposition of rock also act upon the soil to bring about its further disin- tegration, and thereby render it more soluble, while added to those are the operations of tillage, which con- tribute to the same end. : The surfaces of the particles alone come into contact with the decomposing agents, and hence it is these por- tions of the particles that are rendered most soluble. The factors that determine how rapidly solution shall proceed are: (1) The amount of surface exposed, which we have seen varies with the size of the particles. (2) The composition of the particles. (3) The strength of the decomposing and solvent agencies. Were it not for this process, there would soon be no mineral food available (267) 268 THE PRINCIPLES OF SOIL MANAGEMENT to plants, as drainage water and the ash of crops carry off relatively large amounts of these substances each year; but in spite of this loss, the soil is able to provide at least some plant-food material for each crop, when called upon by the plant. II. SOLUBILITY OF THE SOIL IN VARIOUS SOLVENTS For purposes of analysis intended to show the amounts of mineral plant-food materials in the soil any one of several different solvents may be used. These solvents differ in strength, and consequently the per- centages of the various constituents obtained from samples of the same soil are different for each solvent. A chemical analysis of a soil is a determination of the amounts of the constituents that have been dissolved in the solvent used. Therefore it will readily be seen that the interpretation of a chemical analysis must depend largely upon the nature of the solvent, and, unless the solvent is equivalent in its action to some pro- cess or processes in nature, the result must be entirely arbitrary. The solvents used have generally been in- tended to show some definite relation of the soil to the food requirements of crops. Upon the accuracy with which this is accomplished depends the value of the chemical analysis. 127. Complete solution of the soil—By the use of hydrofluoric and sulfuric acids, the entire soil mass may be decomposed and all of its inorganic constituents determined. Such an analysis shows the total quantity of the plant-food materials except nitrogen, which SOLUBILITY OF SOIL CONSTITUENTS 269 is never determined in any of the acid solutions, but by a separate process. A deficiency of any particular substance may be discovered in this way, but nothing can be learned as to the ability of the plant to obtain nutriment from the soil. A rock may show as much mineral plant-food material as a rich soil. Such an analysis is used only to ascertain the ultimate limita- tions of a soil or its possible deficiency in any essential constituent. | 128. Digestion with strong hydrochloric acid.— Analy- ses made with hydrochloric acid of 1.115 specific gravity are those usually called ‘‘chemical soil analyses.”’ They are supposed to show the amount of plant food at the time the analysis is made, which is in a condi- tion to be ultimately used by the plant, and the plant- food materials not dissolved by treatment with hydro- chloric acid are assumed to be in a condition in which plants can not use them. It may reasonably be ques- tioned whether these relations hold under field condi- tions. In fact, it is quite certain that some of them do not hold. In other words, while treatment with hydrochloric acid of a given strength marks a definite point in the solubility of the compounds in the soil, it does not bear a uniform relation to the natural processes by which these compounds become available to the plant. 129. Interpretation of results of analysis of hydro- chloric acid solution.—This method of analysis was originally thought to give some indication of both the permanent fertility and the immediate manurial needs of a soil; but for both purposes the accuracy of the 270 THE PRINCIPLES OF SOIL MANAGEMENT deductions are limited by a number of conditions which make it impossible to predict from an analysis how productive a soil may be, or what particular manure may be profitably applied. It is very apparent that the chemical composition of a soil is only one of the many factors affecting its productiveness. Unfortunately, not all of the factors are understood, and consequently these unknown ones cannot be determined either quali- tatively or quantitatively. If it ever becomes possible to determine quantitatively all of the factors entering into soil productiveness in the field condition, the prob- lem will be solved. 130. Permanent fertility, and manurial needs.— Permanent fertility can best be judged by the complete analysis of the soil, but, with the exception of potash, the possible deficiency the constituents likely to be required in manures may be judged from the hydro- chloric acid solution with a fair degree of accuracy. — Conclusions as to the manurial needs of the soil are confined to ascertaining whether any constituent is present in such small amount as to furnish an inadequate supply for crop production. If, for example, a certain ingredient is found to be present in very small amount, it may be concluded that the addition of a manure con- taining this substance would be profitable; but there is considerable difference of opinion among analysts as to what this figure is for each of the ingredients. This minimum amount may vary with certain conditions of soil. 131. Relation of texture to solubility.—The relative amounts of sand and clay in the soil and the distribution INFLUENCE OF TEXTURE ON SOLUBILITY Bid of the fertilizing materials in these constituents will affect the minimum amounts required. Hilgard has shown that the addition of four or five volumes of quartz sand to one of a heavy but highly productive black clay soil greatly increased the productiveness, while diluting the potash content. of the mixture to .12 per cent and the phosphoric acid to .03 per cent. It is evident that in this soil the plant-food materials were in a condition to be easily taken up by the plant when the physical condition of the soil was suitable. If these small amounts of food elements had been distributed in the sand particles as well as in the original clay, the result would’ doubtless have been different. Suppose, for example, that 50 per cent of the potash and phosphoric acid had been in the sand particles and the remainder in the clay, the former which expose much the less surface to dissolving liquids would be proportionately less soluble, and as the minimum quan- tity is approached, as shown by the more dilute soil yielding less than the other, the effect would doubtless have been to decrease the production. (See page 86.) In some soils, particularly those of the arid region, the larger particles may carry much of the mineral nutrients, in which case it is quite evident that a higher percentage of fertility is required than in soils carrying the plant- food material largely in the small particles. 132. Nature of subsoil——The nature and compo- sition of the subsoil is naturally a factor in determining soil productiveness, and must be considered as well as the soil. An impervious subsoil, or a very loose sandy one, will confine the productive zone largely to the top 272 THE PRINCIPLES OF SOIL MANAGEMENT soil, and hence require a greater proportionate amount of fertility. 133. Calcium carbonate.—A determination of the amount of calcium present as a carbonate is important as an aid to the interpretation of an analysis of the soil. Lime not so combined is generally in the form of a silicate, or possibly phosphate. When there is a large amount of calcium carbonate in a soil, the potash, phos- phoric acid and nitrogen are always more readily soluble, and smaller quantities are sufficient for crop growth than where the calcium is not found in this form. The effect of the carbonate of lime upon the nitrogen! com- pounds is to furnish a base for the acids produced in the formation of nitrates and its presence promotes that process. It probably replaces potassium in certain compounds where otherwise it would be secured with more difficulty. It insures the presence of some phos- phates of lime, in which form phosphorus is more soluble than when combined with iron. The form of the manures to be used upon the soil will also depend in large measure upon the presence or absence of calcium carbonate. (See page 349.) For instance, where calcium carbonate is deficient, steamed bone or Thomas slag are more profitable than superphosphate, and nitrate of soda than sulphate of ammonium. Finally, the absence of calcium carbonate indicates the need of liming, and, if the analyses show a considerable amount of potash and phosphoric acid, but practice shows them to be somewhat deficient, it is probable that liming will be all that is necessary, and that manures carrying these 1Not determined in the hydrochloric acid extract. EXTRACTION WiTH ORGANIC ACID 7S substances may be dispensed with. It must be stated, however, that there are cases for which these deductions do not hold, owing to the intervention of other factors. 134. Estimation of deficiency of ingredients.—In a soil in which the other conditions are normal, one would suppose it possible to prescribe, with some degree of accuracy, the content of certain constituents below which a deficiency exists. The use of a manure contain- ing this constituent should therefore be expected to produce beneficial results. However, opinions differ so widely, depending, apparently, upon the soils with which the respective analysts have had to deal, that it is difficult to decide where to set the limit. It is evident that, as the content of any constituent becomes less, the probable need for its application becomes greater, and it thus suggests a practice without assuring its success. 135. Conclusions.—An analysis of the hydrochloric acid extract, therefore, cannot be taken as a guide to the fertilizer needs of the soil, and of itself should not be relied upon; but in connection with other knowledge, particularly that derived from fertilizer tests, it may be useful. 136. Extraction with dilute organic acids. —Other methods used for dissolving soils for analysis depend upon extraction with some dilute organic acid, as citric, acetic, oxalic or tartaric acid. The assumption upon which these methods are based is that the dilute organic acids correspond to the solvent agents in the soil, and thus take from it the amounts of those materials that the plant could take up if it came in contact with all R 274 THE PRINCIPLES OF SOIL MANAGEMENT portions of the soil to the depth represented by the sample analysed. 137. Advantages in showing manurial needs.—The action of each of these dilute acids upon the same soil does not give equal amounts of the various constituents in solution. Citric acid dissolves especially lime, mag- nesia and phosphoric acid, and is the most satisfactory solvent for purposes of analysis. The organic acids naturally dissolve a much smaller amount of material from the soil than does hydrochloric acid. The former acids permit the detection of smaller amounts of easily soluble phosphoric acid and potash than does the latter, larger quantities of soil being used. For example, a chemical analysis of the hydrochloric acid solution is very likely not to show any increase in the phosphorus or potassium in a soil that may have been abundantly manured with these fertilizers, and its productiveness increased greatly thereby. This is because the amount of plant-food material added is so small in comparison with the weight of the area of soil nine inches deep over which it is spread that the increase in percentage may well come within the limits of analytical error. An acre of soil nine inches deep weighs about 2,500,000 pounds. If to this be added dressings of 2,500 pounds phosphoric acid fertilizer containing 400 pounds phosphoric acid, it would increase the percentage of that constituent in the soil only .016 per cent, which difference could not be detected by the analysis of the hydrochloric acid solution. | 188. Usefulness of citric acid.—As shown by Dyer, the use of a 1 per cent solution of citric acid is well EXTRACTION WITH SOLUTION OF CARBON DIOXIDE 275 adapted to show the amount of easily soluble phosphoric acid and potash in certain soils, but for other soils it has failed to give satisfaction in the hands of a number of analysts. Shorey, for instance, finds that it fails utterly for the highly ferruginous soils of Hawaii. It is, doubt- less, better adapted to soils rich in calcium and low in iron and aluminum. The reason urged by Dyer for the superiority of the citric acid over the hydrochloric acid extraction of the soil is that the former gave, in his hands, several times as great a difference in the amounts of soluble phos- phoric acid in soils needing phosphoric manures as com- pared with those not needing them. The application of both the hydrochloric and citric acid methods to a soil may, when used to supplement each other, add greatly to a knowledge of the potential and present productiveness of the soil. There should be present in a soil for cereals and most other crops at least .01 per cent phosphoric acid, soluble in 1 per cent citric acid. A soil containing less than this amount is deficient in phosphoric acid, unless it exists largely in the form of ferric or aluminum phosphate, which is not readily soluble in citric acid, but is fairly available to the plant. Sod land contains organic com- pounds of phosphorus that are easily soluble in the citric acid, but less readily available to the plant; hence such soil should show by analysis more than .01 per cent phosphoric acid, to indicate sufficiency. 139. Extraction with an aqueous solution of carbon dioxide.—As carbon dioxide is a universal constituent of the water of the soil, and without doubt a potent 276 THE PRINCIPLES OF SOIL MANAGEMENT factor in the decomposition of the mineral matter, it has been proposed to use a solution of carbon dioxide as a solvent in soil analysis. The amounts of soil constitu- ents taken up by this solvent are much less than by any of the others heretofore mentioned, but all mineral substances used by plants are soluble in it to some extent. The amount of phosphorus is so small as to make its Fic. 97. The cut-out disc harrow, adapted to hard or stony soil. detection by the gravimetric method difficult. Like other methods employing very weak solvents, it is open to the objection that the extraction fails to remove a considerable portion of the dissolved matter that is retained by absorption, and, as this will vary with soils of different texture, it makes impossible a fair com- parison of such soils by this method. 140. Extraction with pure water.—When soil is digested with distilled water, all of the mineral substances EXTRACTION WITH PURE WATER ae used by plants are dissolved from it, but in very small quantities. It has been proposed to use this extract for soil analysis on the ground that it involves no artificial solvent, the presence or amount of which in the soil is doubtful, but shows those substances which are un- doubtedly in a condition to be used by plants. By determining the water content of the soil and using a known quantity of water for the extraction, the per- centage of the various constituents in the soil water or in the dry soil may be calculated. The substances dissolved from the soil by extraction with distilled water are probably only those contained in the soil-water solution, including a part of the solutes held by absorption. The aqueous extract does not con- tain all of the nutritive salts in solution in the soil water, and hence is not a measure of the fertility held in that form. An undetermined amount of nutrients is retained in the water in the very small spaces and on the surface of the soil particles. It is, however, a fair comparative measure of the content of available nutrients. 141. Influence of absorption.—The quantity of ex- tracted material depends upon the absorptive properties of the soil, and upon the amount of water used in the extraction, or upon the number of extractions. Analyses of the aqueous extract of a clay and of a sandy soil on the Cornell University Farm serve to illustrate the greater retentive power of the former for nitrates. Sodium nitrate was applied to a clay soil, and to a sandy loam soil at the rate of 640 pounds per acre. Analyses of aqueous extract, some ninety days later, showed the following: 278 THE PRINCIPLES OF SOIL MANAGEMENT TaBLeE XLI Kind of soil Fertilizer Bo ee eee AA ai CS he aro, Sa By SE ac Sodium nitrate 7.8 AY Ai tices ate aie ok he eee bes No fertilizer 1.8 AWD MORE 555154 bie Boks 2% kee | Sodium nitrate 150.0 Peay AONE. couric 4, e/g sim <5 So No fertilizer 29.7 There was apparently a much greater retention of nitrates by the clay soil, as shown by a comparison of the fertilized and unfertilized plats on both soils. Schulze extracted a rich soil by slowly leaching 1,000 grams with pure water, so that one liter passed through in twenty-four hours. The extract for each twenty-four hours was analyzed every day for a period of six days. The total amounts dissolved during each period were as follows: TaBLeE XLII Successive extractions it ieee ag Volatile Inorganic WIPE! ee Hn, Mtoe a ete .080 340 195 SEE 11 (ep aaa Glee PDR Ra pas ae .120 Dad .063 Dive A oe eo ie a .261 101 .160 Vigienns a kok: es .203 .083 .120 PIED pr ok ee Ree ee .260 .082 .178 PUM. aera mock ieees .200 OT7 123 It will be noticed that the dissolved matter, both organic and inorganic, fell off markedly after the first extraction, which was larger on account of the matter in solution in the soil water. Later extractions were doubtless supplied largely from the substances held by absorption and which gradually diffuse into the water INFLUENCE OF ABSORPTION ON SOLUBILITY 279 extract, as the tendency to maintain equilibrium of the solution overcomes the absorptive action. With the removal of the adsorbed substances, the equilibrium between the soil particles and the surrounding solution is disturbed, solvent action is increased, and more material gradually passes from the soil into the solution. In this way the uniform and continuous body of extrac- tives is maintained. 142. Other factors.—For purposes of soil analysis, the quantity of water used for extraction must be placed at some arbitrary figure, and the method is open to the objection that it does not represent accurately the soil water solution. Analyses of soils of different types are not comparable, and the water extract cannot be con- sidered to measure the concentration or even the com- position of the solution existing between the root hair and the soil particles. However, for studying some of the changes that go on in the soil, and which are detect- able in the soil-water solution, the method may be used to advantage. III. MINERAL SUBSTANCES ABSORBED BY PLANTS The plant, in its process of growth, withdraws from the soil certain mineral matters that are presented to its roots in a dissolved condition. As the salts in solution are quite numerous, and as the osmotic process by which the absorption is accomplished does not admit of the entire exclusion of any substance capable of diosmosis, there are to be found in the plant most of the mineral constituents of the soil. Some of these are concerned in 280 THE PRINCIPLES OF SOIL MANAGEMENT the vital processes of the plant and are essential to its growth. Others seem to have no specific function, but are generally present. 143. Substances found in ash of plants.—The sub- stances commonly met with in the ash of plants are potassium, sodium, calcium, magnesium, iron, aluminum, phosphorus, sulfur, silicon, and chlorine. In addition to these, nitrogen is absorbed from the soil in the form of soluble salts. The substances known to be absolutely essential to the mature growth of plants are potassium, calcium, magnesium, iron, phosphorus, sulfur and_ nitrogen, while the others are probably beneficial to the plant in some way not yet discovered. Of the substances acting as plant nutrients, each must be present in an amount sufficient to make possible the maximum growth consistent with other conditions, or the yield of the crop will be curtailed by its deficiency. To some extent certain essential substances may be substituted by others, as, for instance, potassium by sodium; but such substitution is probably possible only in some physiological role other than that of an ele- mental constituent of an organic compound. The sub- stances that are likely to be so deficient in an available form in any soil as to curtail the yield of crops are potas- sium, phosphorus and nitrogen, while the addition of certain forms of calcium is likely to be beneficial on account of its relation to other constituents and proper- ties of the soil. It is for the purpose of supplying these substances, and to some extent to improve the mechani- cal condition of the.soil, that mineral manures are used. PLANT-FOOD REMOVED BY CROPS 281 144. Amounts of plant-food material removed by crops.—The utilization of mineral substances by crops is a source of loss of fertility to agricultural soils. In a state of nature, the loss in this way is comparatively small, as the native vegetation falls upon the ground, and in the process of decomposition the ash is almost entirely returned to the soil. Under natural conditions, soil usually increases in fertility; for, while there is some loss through drainage and other sources, this is more than counterbalanced by the action of the natural agencies of disintegration and decomposition, and the fixation of atmospheric nitrogen affords a constant, although small supply, of that important soil ingredient. Fic. 98. A collection of hand-tillage implements. From left to right: 1. Field and garden hoe. 2. Mattock. 3. Weeding-hoe. 4. Stone-hooks. 5. linger-weeder. 6. Grub-hoe. 7. Scuffle-hoe. 8, Garden rake. 9. Spading- fork. 10. Garden trowel, 282 THE PRINCIPLES OF SOIL MANAGEMENT When land is put under cultivation, a very different condition is presented. Crops are removed from the land, and only partially returned to it in manure or straw. This withdraws annually a certain small propor- tion of the total quantity of mineral substances, but, what is of more immediate importance, it withdraws all of this in a readily available form. The following table, computed by Warington, shows the amounts of nitrogen, potassium, phosphorus and lime removed from an acre of soil by some of the common crops. The entire harvested crop is included. TaBLE XLIII : Phos- Crop Yield hy yan Potash Lime gs ss Pounds | Pounds | Pounds | Pounds | Pounds W iteat. io. 30 bus. 172 48 28. 2 21. Barley....... 40 bus. 157 48 35.7 9.2 20.7 6 RE eli 45 bus. 191 55 46.1 11.6 19.4 Maize........| 30 bus. 121 43 36.3 Piste 18.0 Meadow hay..| 14 tons | 203 49 50.9 32.1 12,3 Red clover...| .2 tons 258 102 83.4 90.1 24.9 Potatoes ....| 6 tons (ee 47 76.5 3.4 21.8 SS ANGIDE 6. al. 17 tons 364 192 | 148.8 74.0 | 33.1 145. Amounts of plant-food materials contained in soils.—Comparing the figures given above with those showing the total amounts of the fertilizing constituents in certain soils, it is evident that there is a supply in most arable soils that will afford nutriment for average crops for a very long period of time. The following table shows the amount of nutrients contained in the chief divisions of soil as given on page 30. [IOS JISOdap-199% A O'rF OCS OCP OLE gg 9°0 roe O'ES 0'°0G OLT 0'SS 6 agg | 0 OST 0'0G O'OT OST Te sige | ¢ 0'S8 gc TOT 0'0G ST 9€ 9 O'OT 9°¢ Ttl G6 60 9°0 8 w | WW W W W W W Ge G’¢ ge oie or ol oe aoe. Se: ee ae one Aeyo uel1eq UIBOT UIEO| uel11eq eqopy | 4zIQ | AeIQ | Apueg | ‘pueg | ied IIIX AI III it - A AT * uwnjog | uUINToD | UUINJoD | uLNJoD | UUINJoD | UUINjOD A 9198, | aT erqey, s[IOs osoynuIND es aouel yy A®e]o 4[eseg IIIA uumMyo9 II 919% L s]IOS [VNpIseyYy (O°) Yseq0g oC ee ( oe N) Bpog ieee (O83) wsoUTEy heeecaty comin ec meet (ORD) oull'y T | CO%d) pre s110ydsoyg ee | *spunod uoyyrur ut 4003 -9108 Jod JYySIOM poe}eUITyS ri aa USAIS SI [BIO] CUl uunjog | jo sIsheus o10yM UUINIOD SaNNOg GNVSNOH], NJ “10g dO LOOd-GUOV-ANQ NI GUNIVINOD SLNANLILSNOD GO0Od-INVIg JO SLNQOWY ATTX @14ViL, 7 (283) O'8E WwW ce | sp | -19Z}1MG e800] XI uuinjor ‘[BLIO}BUI 911}Ua 94} JO a1v SaSA[CUB 194}0 [TV OOrT OGL | O8E 0'SE OFT 0°06 0°09 O6¢ | OTP P8 OST OLE O'8E O'6€ | OO9T 0'GS Csl 0'GG 0°08 o9¢ | DOPE | DEL 0°66 O'F% SST 0O'8 oF v9 Lo e¢ qe ee i L'é ce at oD ‘] SSI uotsar Bed l or4O ssooT .| sseo'T Ss90'T i oe wIBo'T IA Ill II *I1 *A «III uumjog | uuINjoD | uUINjoD | uUINTOD | UUINTOD | UUINTOD ITA ®198L IA °198.L s]los }Isodep-pul N19 O19 AaMOKON ere ce o1gO wIeO] TS *II OSL O'TOT O'8% O'¢E 0'0SZ | O'GS8 0';00S | OSST ¢'9T 0'0¢ W W rete ae ‘uu | ACN ABO A®BID TAX IN B.€ uuInjog | uuMyoD | uuIN{oD S[IOS [BIRTH A 198L S]IOS JISOdep-10}% A "SISA[VUB PINK’ OUO[YIOIpAY BUI Sy tea els Meee ee ( Oo) yseyo d eae Shel os ( oe N) Bpog (OSX) BISOUSeIL oa) wie te shel 6; ae (ORD) our] ‘CO%d) prow ou0ydsoyg Coe ae 6 a ***spunod uolj[tur ul yoo -3108 Jed JUSIomM poyeUllysi : * UDAIS SI [BLIO} UL sation =—— SGNQ0g GNVSNOH], NJ “10g JO LOOd-aYOV-ANQ) NI GAENIVEINO() SINDTALILSNO() GOOd-INVTId JO SLNQOWY ponutquoo ‘AT TX Fav, (284) POSSIBILITY OF EXHAUSTING SOILS 285 146. Possible exhaustion of mineral nutrients.— On the other hand, when we consider that the soil must be depended upon to furnish food for humanity and domestic animals as long as they shall continue to inhabit the earth, at least so far as we now know, the very apparent possibility of exhausting, even in a period of several hundred years, the supply of plant nutrients becomes a matter of grave concern. The visible sources of supply, to replace or supplement those in the soils now cultivated are, for the mineral substances, the subsoil and the natural deposits of phosphates, potash salts, and limestone, and for nitrogen deposits of nitrates, the by-product of coal distillation and the nitrogen of the atmosphere. The last of these is inexhaustible, and the exhaustion of the nitrogen supply, which a few years ago was thought to be a matter of less than half a century, has now ceased to cause any apprehen- sion. The conservation or extension of the supply of mineral nutrients is now of supreme importance. The utilization of city refuse and the discovery of new mineral deposits are developments well within the range of possibility, but neither of these promises to afford more than partial relief. The utilization of the subsoil through the gradual removal by natural agencies of the top soil will, without doubt, tend to constantly renew the supply. The removal of top soil by wind and erosion is, even on level land, a very considerable factor. The large amount of sediment carried in streamsimmediately after a rain, especially in summer, gives some idea of the extent of this shifting. This affects chiefly the surface soil and thereby brings the subsoil into the range of root action. 286 THE PRINCIPLES OF SOIL MANAGEMENT IV. ACQUISITION OF NUTRITIVE SALTS BY AGRICUL- TURAL PLANTS All of the salts taken up by the roots of agricultural plants are in solution when absorbed. The movement into the root thus depends upon the presence of moisture, which is the medium of transfer. The root hairs are the great absorbing portions of the plant, and through the cells of their delicate tissues the solutions of the various salts pass by osmotic action. (See Fig. 53.) The nature and quantity of material absorbed is determined by the law of osmosis. From the cells of the root-hairs the dis- solved salts are transferred to other portions of the plant, where they undergo the metabolic processes that deter- mine which constituents shall be retained in the tissues of the plant. The unused ions which remain in the plant juices prevent by their presence the further absorption of those particular substances from the soil water. It thus happens that the composition of the ash of a plant may be very different from that of the substances presented to it in solution. For instance, aluminum, although always present in the soil, in a very slightly soluble form, is either absent or present in mere traces in the ash of most plants. On the other hand, iodine, although present in sea-water only in the most minute amounts, is present in large quantities in the ash of certain marine alge. 147. Selective absorption.—A plant will, in general, take up more of a nutritive substance when presented in large amount, as compared with the other soluble substances in the nutrient solution, than if presented in small amount. Thus, the percentage of nitrogen in ACQUISITION OF NUTRIENTS BY PLANTS 287 maize, oats and wheat may be increased by increasing the ratio of nitrogen to other nutritive substances in the nutrient media. This is also true of potassium and phosphorus, respectively. This fact is accounted for by the maintenance of the osmotic equilibrium at a higher level for a particular ion which is relatively Fic. 99. Showing the intimate relation of root-hairs and soil particles. abundant in the nutrient solution, thus preventing the return of the excess from the plant. 148. Relation between root-hairs and soil-particles.— In a rich, moist soil the number of root-hairs is very great, while in a poor or a dry soil there are compara- tively few. The connection between the root-hairs and the soil-particles is extremely intimate. When in con- tact with the particle of soil, the root-hair frequently almost incloses it, and by means of its mucilaginous 288 THE PRINCIPLES OF SOIL MANAGEMENT wall forms a contact so close as to practically make the solution between the particle and the cell-wall distinct from that between the soil-particles. There has been considerable difference of opinion as to how the plant can obtain its mineral nutrients from a substance so difficultly soluble as the soil. It has, of course, been recognized that the soil-water is aided in its solvent action by a variety of substances that may be normally present in solution, beginning with the gases taken up by the rain in its descent through the atmosphere, and further aided by the carbon dioxide and organic and mineral substance obtained from the soil. It has been held that the plant-roots aid solution of mineral matter by excretion of acids, which act effec- tively as solvents. The well-known root-tracings on limestone and marble have been taken as proof of the excretion of such acids. Sachs and, later, other investi- gators grew plants of various kinds in soil and other media in which was placed a slab of polished marble or dolomite or calcium phosphate, covered with a layer of washed sand. After the plants had made sufficient growth, the slabs were removed and on the surfaces were found corroded tracing, corresponding to the lines of contact between the rootlets and the minerals. In order to test this theory, Czapek repeated the experiments, using plates of gypsum mixed with the ground mineral that he wished to test, and this mixture he spread over a glass plate. Using these plates in the same manner as previously described, Czapek found that, while plates of calcium carbonate and of calcium phosphate were corroded by the roots, plates of alumi- ROOT EXCRETIONS AND SOLUBILITY 289 num phosphate were not. He concludes that if the trac- ings are due to acids excreted by the plant-roots, the acids so excreted must be those that have no solvent action on aluminum phosphate. This would limit the excreted acids to carbonic, acetic, propionic and butyric. Czapek also replies to the argument that the acids pro- ducing the tracings must be non-volatile ones, because of the definite lines made in the mineral, by stating that the excretion of carbon dioxide alone would be sufficient to account for the observations, as it dissolves in water to form carbonic acid, and that carbonic acid is always present in the cell-walls of the root epidermis, from which it does not readily exude. ~Czapek has also shown that liquids having an acid reaction exude from root-hairs, and he attributes the reaction to the presence of acid salts of mineral acids, having found potassium, phosphorus, magnesium, cal- cium and chlorine in this exudate. He has not proven, however, that the exudations were not from dead root- hairs, or from the dead cells of the root-cap. In either case they would have some solvent action, but whether sufficient to make them of importance it is impossible to say. Kunze, who followed up this work, discredits the theory of excretion of acid salts of mineral acids, and attributes the corrosive action of roots to organic acids. In his experiments with 200 species, he found that many plants do not excrete enough acid to be detected by litmus. He attributes to fungi much the greater activity in this respect, and considers them more important in disintegrating the soil than are the higher plants. Ss 290 THE PRINCIPLES OF SOIL MANAGEMENT The present status of experimental evidence on excre- tion of acids other than carbonic by the roots of plants does not admit of any very satisfactory conclusion as to their relative importance in the acquisition of plant-food materials. There can be no doubt, however, that carbon dioxide, resulting from root exudation, and from decom- position of organic matter in the soil, plays a very promi- nent part in this operation. The very large quantity of carbon dioxide in the soil, amounting in some cases to from 5 to nearly 10 per cent of the soil air, or several hundred times that of the atmospheric air, must aid ereatly in dissolving the soil-particles. Whatever may be the concentration of the soil-water, it seems probable that the liquid to be found where the root-hair comes in contact with the soil-particle, and which is separated, in part at least, from the remainder of the soil-water, must have a density much greater than that found elsewhere in the soil. The comparatively rich juices of the plant separated from the soil water only by the delicate cell-walls of the root-hair insures a copious transfer of the constituents of these juices into the intervening water, thus bringing into contact with the soil mineral salts, of which some are doubtless acid salts and also mineral salts of organic acids, and, possibly, some free organic acids. That portion of the soil-water immediately in contact with the soil grain is a much stronger solution than the water further from the soil surfaces on account of the absorptive action of the particles. These solutions, coming in contact with the surface of the soil-particles already subjected to the bacterial and other disintegrating agents of the soil, ABSORPTIVE POWER OF DIFFERENT CROPS 291 may readily be conceived to start an active transfer of mineral substances into the plant. Plants grown in solutions of nutritive salts have few or no root-hairs, but absorb through the epidermal tissue of the roots. If the plant depended upon the pre- pared solution in the soil-water, a similar structure would doubtless suffice. The special modification by which the root-hairs come in intimate contact with the soil- particle, and almost surrounds it, indicates a direct relation between the soil-particles and the plant, and not merely between the soil solution and the plant. New root-hairs are constantly being formed, and the old ones become inactive and disappear. The contact of a root-hair with a soil-particle is not long-continued. Whether the period of contact is determined by the ability of the root to absorb nutriment from the particle is not known. Certain it is that only a small portion of the particle is removed. It may be true that only the immediate surface which had been previously acted upon by the disintegrating agents of the soil, and thus rendered more easily soluble, is affected by the absor- bent action of the root-hairs. 149. Absorptive power of different crops.—As has already been pointed out (page 281), crops of different kinds vary greatly in their ability to draw nourishment from the soil. The difference between the nitrogen, phosphorus and potassium taken up by a corn crop of average size and a wheat crop of average size is very striking. Corn has the longer growing period, but as be- tween oats and wheat, where the growing period is nearly identical, a similar relation exists. 292 THE PRINCIPLES OF SOIL MANAGEMENT The differeace in absorbing power may be due to either one or both of two causes: (1) A larger absorbing system. (2) A more active absorbing system. The former is determined by the extent of the root-hair surfaces; the latter by the intensity of the osmotic action. 150. Extent of absorbing system.—Plants with large root systems may, therefore, be expected to absorb the larger amounts of nutrients from the soil, and such is usually the case, although the extent of the root-system is not necessarily proportional to the total area of the absorbing surfaces of the root-hairs. 151. Osmotic activity.—The osmotic activity of a plant under any given condition of soil and climate depends upon: (1) The rapidity and completeness with which. the plant elaborates the substances taken from the soil into plant substance or otherwise removes them from solution. (2) The extent to which the exudations from the root-hairs act upon the soil particles to in- crease the density of the solution between the root-hair and the soil-particle. The first of these is a function of the vital energy of the plant and its ability to utilize sunshine and carbon dioxide to produce organic matter. It may be com- pared to the property which enables one animal to do. more work than another animal of the same weight on a similar ration. The removal from the ascending water current in the plant of substances derived from the soil is accom- plished in the leaves. By the dissociation of these, ions are constantly furnished for metabolism into materials that may be built into the tissues of the plant. The FACTORS AFFECTING ABSORPTIVE POWER 293 remaining ions are kept in the solution. There is a con- stant tendency to bring the composition and density of the solution into equilibrium, by diffusion and dios- mosis, with the solution between the soil-particle and the root-hair. The rapidity with which the metabolic pro- cess removes a substance from the solution in the plant, therefore, determines the rate at which it ‘is removed from a solution of given composition and density in the soil. Plants making a rapid growth remove more nutri- ents in a given time than those making a slower growth, when the nutrient solution is of a given composition and density. A maize plant, for instance, removes more nutriment from a given solution in one day during its stage of most rapid growth than does a wheat plant during a corresponding stage. Another factor which affects the rate of absorption of salts from the soil is the solvent influence of exudates from the root-hairs. This subject has already been treated (page 287), and it only remains to say that this action apparently varies with different kinds of plants, and probably accounts in no small measure for the dif- ference in the ability of different plants to withdraw salts from the soil. These several factors, which, when combined, deter- mine the so-called ‘‘feeding-power”’ of the plant, are recognized by the popular terms ‘“‘weak-feeder” and “strong-feeder,’’—applied, on the one hand, to such crops as wheat or onions, which require very careful soil preparation and manuring, and, on the other hand, to maize, oats or cabbage, which demand’ relatively less care. In manuring and rotating crops, this difference 294 THE PRINCIPLES OF SOIL MANAGEMENT in absorptive power must be considered, not only to secure the maximum effect upon the crop manured, but also to get the greatest residual effect of the manure upon succeeding crops. Fic. 100. Deep and shallow cultivation for corn. On the right-hand side of the picture the deep cultivator shovels are destroying the upper roots. On the left-hand side the shallow cultivation does not reach the roots. 152. Cereal crops.—These plants possess the power of utilizing the potassium and phosphorus of the soil to a considerable degree, but generally require fertili- zation with nitrogen salts. Most of the cereals, like wheat, rye, oats and barley, take up most of their nitrogen early in the season, before the nitrification processes have been sufficiently operative to furnish a large supply ABSORPTIVE POWER OF CEREALS. 295 of nitrogen, and hence nitrogen is the fertilizer consti- tuent that usually gives best results, and should be added in a soluble form. Wheat, in particular, needs a large amount of soluble nitrogen early in its spring growth. Since it is a delicate feeder, it does best after a cultivated crop or a fallow, by which the nitrogen has been converted into a soluble form. Oats can make better use of the soil fertility and does not require so much manuring. Maize is a very coarse feeder, and, while it removes a very large quantity of plant-food from the soil, it does not require that these be added in a soluble form. Farm manure and other slowly acting manures may well be applied for the maize crop. The long growing period required by the maize plant gives it opportunity to utilize the nitrogen as it becomes available during the summer, when ammonification and nitrification are active. Phosphorus is the substance usually most needed by maize. ) 153. Grass crops.—Grasses, when in meadow or in pasture, are greatly benefited by manures. They are less vigorous feeders than the cereals, have shorter roots, and, when left down for more than one year, the lack of aération in the soil causes decomposition to decrease. There is usually a more active fixation of nitrogen in grass lands than in cultivated lands, but this becomes available very slowly. Different soils and different climatic conditions necessitate different methods of manuring for grass. Farm manures may well be applied to meadows in all situations, while the use of nitrogen is generally profi- table. 296 THE PRINCIPLES OF SOIL MANAGEMENT 154. Leguminous crops.—Most of the leguminous crops are deep-rooted and are vigorous feeders. Their ability to acquire nitrogen from the air makes the use of that fertilizer constituent unnecessary except in a few instances, such as young alfalfa on poor soil, where a small application of nitrate of soda is usually bene- ficial. Lime and potassium are the substances most beneficial to legumes on the majority of soils. 155. Root-crops.—Many of the members of this class of crops will utilize very large amounts of plant- food if it is in a form in which they can use it. Phos- phates and nitrogen are the substances generally re- quired, the latter especially by beets and carrots. 156. Vegetables.—In growing vegetables, the object is to produce a rapid growth of leaves and stalks rather than seeds, and often this growth is made very early in the season. As a consequence, a soluble form of nitrogen is very desirable. Farm manure should also have a prominent part of the treatment, as it keeps the soil in a mechanical condition favorable to retention of moisture, which vegetables require in large amounts, and it also supplies needed fertility. The very intensive method of culture employed in the production of vegetables necessitates the use of much greater quantities of manures than are used for field crops, and the great value of the product justifies the practice. 157. Fruits—In manuring fruits, with the exception of some of the small, rapid-growing ones, it is the aim to maintain a continuous supply of nutrients available to the plant, but not sufficient for stimulation, except during the early life of the tree, when rapid growth ABSORPTION BY SOIL PARTICLES 297 of wood is desired. An acre of apple trees in bearing removes as much plant-food from the soil in one season as does an acre of wheat. Farm manure and a complete fertilizer may be used, of which the constituents should be in a fairly available form, as a constant supply is necessary. V. ABSORPTION BY THE SOIL OF SUBSTANCES IN SOLUTION *- If the brown water extract from manure be filtered through a clay soil not containing soluble alkalies, the filtrate will be nearly colorless. Many solutions of dye stuffs are affected in the same way. Solution of alkali or alkaline earth salts are more or less modified by this operation, the bases being retained: by the soil. Thus when a solution of the nitrate, sulfate, or chloride of any one of these bases is filtered through the soil, a part of the base is absorbed by the soil, while the acid comes through in the filtrate. If these bases are in the form of phosphates or silicates, not only the base is absorbed but the acid as well. 158. Substitution of bases.—Associated with the absorption of the base from solution, there is liberation of some other base from the soil, which combines with the acid in the solution and appears in the filtrate as a salt of that acid. When absorption takes place from solution, the base is never entirely removed, no matter how dilute the solution may be. A dilute solution of potassium chloride filtered through a soil will produce a filtrate containing 298 THE PRINCIPLES OF SOIL MANAGEMENT some calcium chloride or sodium chloride, or both, and some potassium chloride. The more dilute the solution, the larger the proportion retained. Peters treated 100 grams of soil with 250 c.c. of a solution of potassium salts, and found that the potassium of different salts was retained in different proportions, and that the stronger solutions lost relatively less than the weaker. TaBLE XLV ae po (Be 10 normal 20 normal Strength of solution | Grams K20 Grams K:0 absorbed absorbed ME Bias ce meee sh Ne 3124 1990 ee a Weep pen. Leek OLN 3362 2098 6 hee Eh Ube raey Poe anette cree anne tO 5747 3134 The same bases are not always absorbed to the same extent by different soils; one soil may have a greater absorptive power for potassium, while another may retain more ammonia. They seem to be interchangeable, as any absorbed base may be released by another in solution. 159. Time required for absorption.—The amount of absorption depends upon the time of contact between the soil and the solution. While a large part of the dis- solved base is taken up in a short time after being in contact with the soil, the maximum absorption is only effected after considerable time. Ammonia, according to Way, reaches its maximum absorption in half an hour, while Henneberg & Stohmann found that phos- phorus required twenty-four hours to reach the same degree of absorption. PROPERTIES OF ABSORBED SUBSTANCES 299 160. Insolubility of certain absorbed substances.— Although bases once absorbed may be easily displaced by other bases, it is a difficult matter to dissolve them from the soil with pure water. Peters treated 100 grams of soil with 250 c.c. of water containing potassium chloride, of which .2114 grams of eS) were absorbed. The soil was then leached with distilled water, using 125 c.c. of water daily for ten days. At the end of that time .0875 grams of K,O had been removed, or at the rate of 28,100 parts of water to one part of K,O dis- solved from the soil. Henneberg and Stohmann found that it required 10,000 parts of water to dissolve one part of absorbed ammonia from the soil. 161. Influence of size of particles—The surface area of the soil-particles determines to some extent the amount of substance absorbed. For this, and other reasons, a fine-grained soil absorbs a greater quantity of material than a coarse-grained soil. In fact, it was early shown by Way that the absorption phenomenon is largely a function of the silt, clay and humus of the soil. 162. Causes of absorption.—A number of causes have been assigned for the absorption of substances by soils, and there can be no doubt that the phenomenon is not due to any one process. Several distinct causes are now quite generally recognized and, while others that have been suggested may have a part in the result, they cannot all be taken up at this time. The better-known and more important absorption processes are the fol- lowing: 163. Zeolites—As stated on a _ preceding page, 300 THE PRINCIPLES OF SOIL MANAGEMENT Way demonstrated that sand had little absorbing power as compared with clay, and further, that when the zoelitic silicates were removed from clay by digestion with hydrochloric acid, the clay largely lost its power of absorption. Way produced an artificial hydrated silicate of alumina and soda, and Eichorn found natural hydrated silicates or zeolites that removed bases with the substitution of other bases, in the manner of natural soil. A further characteristic of these zeolites is that the replaced base is present in the filtrate in amounts chemically equivalent to the base removed. It has further been shown that the absorptive power of soils is more or less proportional to the amount of acid soluble silicates it contains. The zeolites being rather easily soluble in strong mineral acids, it is held that the bases so combined are more readily available to plants than in most combinations found in the soil, and yet are not readily leached out of it. Soluble bases added to the soil in manures are taken up and held by zeolites, instead of being removed in the drainage water. However, nitric acid, important as it is to agriculture, is not absorbed, and, together with the sulfuric and hydrochloric acid, is quickly but not com- pletely removed from the soil by drainage water. 164. Other absorbents.—Humus, ferric and alumi- num hydrates, and calcium carbonate, exercise absor- bent properties, but to what extent and of what import- ance it is difficult to say. Soils rich in humus, without doubt, owe much of their fertility to the retention by that constituent of a large supply of readily available plant-food material. Many prairie soils that have been ADSORPTION 301 reduced in productiveness under cultivation respond to the application of organic matter in a remarkable manner. Humus in these soils seems to be the chief conserver of readily available plant-food materials. Ferric and aluminum hydrate aid in the retention of acids, notably phosphoric, by forming highly in- soluble compounds. 165. Adsorption.—There is a physical absorption, termed adsorption, due to the concentration of the soil solution in contact with the surface of the particles. The phenomenon is familiarly exemplified in the clari- fying effect of the charcoal filter. This process results in the retention of considerable soluble material in fine- grained soils, that would otherwise be washed out. In the case of nitrates, which are not retained by the zeolites, adsorption is an important factor. (See page 325.) If a solution of a known quantity of nitrate of soda be added to a clay soil, and it is then attempted to extract the nitrate from the soil with distilled water, it will be found impossible to recover a very appreciable per cent of the amount added. While adsorption prob- ably does not account for all of the nitrates retained, there can be no doubt that it plays an important part. Nutritive salts held in this way are readily available to the plant whose root-hairs come in contact with the soil particles. 166. Occlusion.—According to Wiley, clay in a col- loidal state has the property of dissociating to a certain extent potash salts, and entangling the basic ion in the meshes of the colloid structure. How extensive or important this action is has not been demonstrated. 302 THE PRINCIPLES OF SOIL MANAGEMENT 167. Absorption as related to drainage.—The drainage water from cultivated fields in the humid region, and to a less extent in the semi-arid and arid region, except where irrigation is practiced, carries off very consider- able amounts of plant-food material. The loss of this material is due to the operation of the various natural disintegrating agents upon the soil mass, and to the HI mi HTT! ity \ ca “li Za) \\\ | Il co nla Y il N i twa Hy Fie. 101. Wedge: manure i hy lnachiie application of fertilizing materials in a soluble form. The various absorptive properties stand between the natural solubility of the soil and the tendency to loss in drainage, and hold these materials that would otherwise be lost, in a condition in which they may readily be used by the plant. 168. Substances usually carried in drainage water.— However, some material is always lost in drainage water, of which, among the bases of the soil those most SUBSTANCES REMOVED IN DRAINAGE WATER 303 likely to be found are soda, magnesia and lime, and of the acids nitric, carbonic, hydrochloric and sulfuric. Nitric acid and lime undergo the most serious losses. The former may be curtailed to a great extent by keeping crops growing on the soil, during all of the time that nitrification is going on, and if the crop does not mature or if, for any other reason, it is not desired to harvest the crop, it should be plowed under, to return the nitro- gen in the form of organic matter. A crop used for this purpose is called a ‘‘catch crop.’”’ Rye is used quite commonly as a catch crop, as it continues growth until late in the fall, and resumes growth early in the spring, conserving nitrates whenever nitrification may occur, and it may then be plowed under to prepare the land for another crop. Rye also has the advantage of small cost for seed. | The loss of calcium cannot well be prevented, and the use of commercial fertilizers always greatly in- creases such loss. The only remedy is the application of some form of calcium to the soil. 169. Drainage records at Rothamsted.—Drainage water from a series of plats at the Rothamsted Experi- ment Station, which have been manured in various ways and planted to wheat each year since 1852, have been analysed at certain times, and the results of these analyses, as compiled by Hall, give some idea of the loss of salts from cultivated soils. The drainage water was ’ obtained from the tile drains, one of which extended under each plat from one end to the other, and opened into a ditch, so that the water could be collected when desired. The analyses shown in the accompanying table —ouo[® ¢ 4B[q UO Pak, OL |600;/0LZT| 160/ OTS | HIT) TS TOE |S6I | 600 |/OFT| TOT, 266 | F6E/9¢ QTE | FLT) 910} €'82| 60'T | 698 | 9°98) T'9 OOS | TST| 0800/6 LT) 9ST | 2°96 | 60E | 9'FZ OFS |SSl| LTO;E Il) 99) vs |9TE|99 L0Z |6E1|800/LET| PHI | Ver OSE) TZ PSI | #60 | 9'OT OTe + O6t Tog TLE | 69T| 22°0|6'02| ZT 0| 2°68 | F6E| 901 6CE |OFT| 200 |O2T| 16:0 | 106 | T92| 6 OT OV |S°S8 |020|2h72/ PST, FEL | 206); 201 67L | TS |ElLO| FST) 160/ &99 | TIT) ZIT TElx/6°E | S1'0/6°0OT| €9:0 | 24% | 2°01; 0'9 LG¢€ | T9T|/9TO| Lge | T90T | 20d | 2&1 “sng es iss iBS| & 5 = a ~ ee o YF pe a ie #8 /°R |} Be | = |e | fe | 8 a oe bel eet eB Pe; ee |e] a ae es 3 eo ! So wm uol[iu Jed syieg TLIl L°9GG ¥ 10G 9° T6T ee E TPgt TStl € L261 Pv Ist 6'EFT evel T'86 V LPT rN re ae AUHAQARW © | OM HiINOr~OOIOrIr~ CO oO reso Wits NAS Se es ee DMIOHANHTHH A ysejog BISOUse I ant | MO OM MoD RS Pe eS a ee ee ae ADH NON LO HOD uoll jo oprxolag BpOs JO 9}VIPIU “SQ[OOL'T + S[es9uT OT ev erae a) ete ntwthn, whalte erg lis BISoUDBUI ayeyyns + soyeydsoydsodns + s}yes ‘uourue ‘S| OOF FI ei aierie a ePa ls © Tee rae aes 78 P Tees ysejod ayey[ns + soyeydsoydiedns + sq[es ‘uourure ‘sq] OOF SI BT ita arp. weet ee ee epos oyeyjns ++ soyeydsoydiedns + s}[Bs "UOMIUIR ‘Ssq] OOF ZI Pag sh seats + S}[BS “"UMOUTUIR “Sq, OOF IT gg Pe aa SUOTB S}[VS UNIUOUTUIG *Sq] OOF OL "“BPOS JO 9YVIPIU “ST OSS + S[BISUI 6 piece S}[Bs WINTMOWIUI ‘Sq, QO9 + STe1sUTT g pares S}[BS UNMOWIUI “Sq] OOF + S[e19UTL 2 ease Sy[BS UMIUOUIUIe ‘Sq[ OOZ + S[TRIeUT;, 9 6 ke oe eee, 8 we ee we ele, eine) ene AjTuo S[BIOUTTL c pA doy. « Ren bite cage amar aInUBUI ON F pue ¢E Ser ree suo} FT ‘amnueU WIT Z 781d aloe iad aye1 ‘parjdde soinueyy NOILVLG LINGWNIYEdXY GaLSNVHLOY ‘SLVIG LVGHAA Wivdavoug WoOUud YALVM FOVNIVYC AO NOILISOdWO/) IATX @Tavy (304) SUBSTANCES REMOVED IN DRAINAGE WATER 305 were made by Dr. A. Voelcker, and represent the mean of not more than five collections made in December, May and January and April during a period of two years. They can not be regarded as showing accurately the annual removal of salts from the soil but are still sig- nificant. From this table it will be seen that lime is the in- gredient lost in largest amount from this soil and that the character of the manure applied influences this loss to some extent. The sulfates of sodium, potassium, and magnesium have notably increased the loss of lime, as have also the ammonium salts. The loss of lime from all of the manured plats was notably greater than from the unmanured. Potash was not removed in large amount by the drainage water from any of the plats). Ammonium salts with superphosphate and with magnesia occasioned only a slight loss of potash, as did also the absence of manure. The plats receiving mineral manure alone and farm manure lost the greatest quantities of potash. The quantity of sulfuric acid leached from the soil is quite large and highly variable. It is frequently, but by no means uniformly, large on those plats from which lime is removed in large amounts. The plat receiving farm manure lost the largest quantity of sul- furic acid. Phosphoric acid was removed in small amounts and, except in the case of the unmanured plat, those plats losing the least phosphoric acid gave the largest yields. The loss of phosphoric acid seems to be a matter of failure on the part of the crop to utilize it, rather than its liberation by any manurial substance. yy 306 THE PRINCIPLES OF SOIL MANAGEMENT Ammoniacal nitrogen in the drainage water is very small in amount, but nitrate nitrogen is present in amounts sufhcient to make the loss of some concern. The use of sodium nitrate occasioned the greatest loss of nitrogen while ammonium salts and farm manure contributed nearly as much. Forty to fifty pounds of nitrogen per acre may be lost annually in this way, which amount would have a commercial value of from eight to nine dollars. The most serious losses are those of nitrogen and lime, and both are to an extent unavoidable. Potassium and phosphorus, which must also be purchased in ma- nures, are lost only at the rate of a few pounds per acre but had lime been applied to any of these plats, the loss of potassium would probably have been larger. Nitro- gen and phosphorus are best conserved by keeping crops growing on land as much of the time as possible, and the former may also be protected by applying the soluble nitrogen salts only at a time when they can be utilized by crops. The loss of calcium frequently amounts to several hundred pounds per acre annually, and, as the presence of calcium carbonate is essential to a healthy condition, of the soil this loss, particularly from the soil receiving salts like sulfates and chlorides, the bases of which are absorbed by plants in larger amounts than the acids, is likely to result in a very bad condition of the soil. The only method of obviating this is to lime the soil from time to time. 170 Relation of absorptive capacity to productive- ness.—The absorptive capacity of a soil is not so much a measure of its immediate as of its permanent produc- ALKALI SOILS B07. tiveness. It is well known that a very sandy soil responds quickly to the application of soluble manures, but that the effect is confined mainly to one season; while a clay soil, although not so quickly responsive to fertilization, shows the effect of the application much more markedly the second or third year than does the sandy soil. Me- chanical absorption holds the nutritive material in a very readily available condition, while absorption by zeo- litic bodies renders these substances somewhat less readily available. There are also other reasons why the sandy soil is more responsive. It cannot be said that there is a relation between the absorptive capacity of a soil and its productiveness when manured or when nearly virgin, but soil long-cultivated and unmanured frequently show such a relation. King, in working with eight types of soil in different portions of the United States, found that those soils removing the most potassium from solution gave the largest yield of crop. It would not be permissible, however, to adopt this test as a method for determining productiveness in soils. VI. ALKALI SOILS As already explained (page 14), soils are acted upon by a great variety of agencies, which gradually render soluble a portion of the particles. The soluble matter is taken up by the soil water, and in humid regions where a large amount of water percolates through the soil and passes off in the drainage, the soluble matter is found only in small quantity at any time. In arid regions the loss by drainage is slight or entirely wanting, 308 THE PRINCIPLES OF SOIL MANAGEMENT and under such conditions the soluble materials accumu- late in the soil, being transposed downward with the percolating water and upward again with the capillary rise of water during the dry period. The lower soil may at one time contain considerably more soluble salt than the upper soil, while at another time the upper Fie. 102. Bare spot, marking the first appearance of injurious quantities of alkali salts in the surface layer of soil. Utah. soil may contain more of these salts, in which case the solution in contact with plant-roots may, and often does, contain so much soluble matter that vegetation is injured or destroyed. This excess of soluble salts may or may not have a marked alkaline reaction, but in any case produce what are termed alkali soils. KINDS OF ALKALI 309 171. Composition of alkali salts—The materials dissolved in the soil water consist of all of the sub- stances found in the soil, but, as the rates of solubility of these substances vary greatly, there accumulates | a much larger quantity of some substances than of | others. Carbonates, sulfates and chlorides of sodium, | potassium, calcium and magnesium occur in the largest | amounts. Sodium may be present as carbonate, sulfate, | chloride, phosphate and nitrate. Potassium may ea similarly combined. Magnesium is likely to appear as a | sulfate or chloride, and calcium as a sulfate, chloride | or carbonate. In some soils one salt will predominate, | and in other soils other salts will prevail. A base may be/ present in combination with several different acids. The nature of the prevailing salt influences greatly the effect upon vegetation. Table XLVII gives the composi- tion of the soluble salts from a number of alkali soils. 172. White and black alkali—Sulfates and chlorides of the alkalies when concentrated on the surface of the soil produce a white incrustation, which is very common in alkali regions during a dry period, as a result of evapo- ration of moisture. Alkali in which these acids predomi- nate is called white alkali. Carbonates of the alkalies dissolve organic matter in the soil, thus giving a dark color to the solution and to the incrustation, and for this reason alkali con- taining large quantities of these salts is called black alkali. Black alkali is much more destructive to vegetation than is white. A quantity of white alkali that would not seriously interfere with the growth of most crops ‘U0TBIG JUOILIOdX BIUIOFITVO ey} Aq pues siINngjNoUsy jo JuoUTjIvded s9}81G Pez}Uf) eY§ Jo s[log jo NveIng ey} Aq opeul sasAjeue WIOIZ poeTidulo),, . 90% | 068 | IE'FZ | 6 1F | ST'9 | igen o| tons nal rtimee sheeeces | fet Cnn a ee ‘Og | (-S] ‘Opes[Ns umisousey zO'l TO eat ae Tag a MeO ie eral eo TLR 674s ed plata ey a Ea ca Bay iat eae oot ae ‘Od 35 | “en ‘eyeydsoyd wnipog—— €8°8Z | PE'6E | SLPT | 99874 | oo ST°9e | SE ZT) sire | 1O8N “eproryo wuntpog go | SEST | 89°ZE | 8sL | 998T9 pe OT ee er eee “| OS ET | G80 | "ODEN -aenOd aa mere 1Z’8 ye ae sana ere ie | aot NEabhats ie iedee er ae -£ONBN ‘opeazTU UMIPOg “"**" | PS SP | 82°SS | CTSE | LESS 01°29 | PS'OT | " FOg*eN ‘ozyeJ[Ns wNIpPOg ere ore eat a ane os | (Soe pine aye £16 FL'S Micon ee Ronee ECA "nr — | ‘ayeuoqivo umnisseyog & ine (mr coe | IV1G|.09 T | FOo*y ‘oyeyns unisseyog » & neo} "BiG | Seyour | yout qisod | sayoul | seyoul | seyoul | soyoul ’ qaesep | -B| ‘dxq | Ol I-O | seyout| ysnio | -ap el Al ZI ZI yeue eaet | aivyny| eovy | ysntIQ | 9E-ZI | NEXTV | 20BF eovy | pilgy, | puo. a0Bj -wy -OW -1ng -Ing -Ing -099 -1ng BIUIOJ[ED “eau rit : Sarat ae Matra Serer : aeeee on Cunt | TIVITY 40 NOMISOdWO) ASVINGOUTG—I]IATX FAV 41989 jeu -wy nee4 Bid eAel -Of[ eBluIO;eO 219 ‘dx q olen YL, LOOT | TL°% 90°2S | L9° seyoul | youl or T-0 eoey | ysnig -Ing Bue} Uo ‘saul Iq OLS | 28°61 | €6°9 | 9 LEO 62°F | 6V'T sayour | 4sni0 9€-cT | TeV OTT VES | LEST LVET | 8P'9T LST | 616 GL 46.18 | 86S? | C208) ~~ 06'T 0e'sI yisod | sayour | seyout | sayour | soqour oe él GI - oT él aoe} eovy | parqy, | puo Q0Vy -ing | -ang -o0g | -ang oyept puelmMoproyy B,078q *N ‘syIOq puBiy Ag][BA estog "YseM “OD BUIYe A Bige: Wee) 'el fa! (oloren © ‘oO CH N) ‘ayeuoqivo wmnirmouwulry gileh vedere? “aye KSath yy a Sie °OOH™M ‘ayeuoqieoiq + UINISse}og ROW TET ace °FO0H) SIN ‘gyeuoqivolq UINIsoUse]] hire av ares MLNgite Oe 4.8 ®(®OOH) -By ‘ayeuoqiBoIq WINId[eD 'Ogey ‘ovens UNIOTe) pte "STM AA gonial Taos 8! eae oe "OOH -BN ‘eyeuoqieoIq WuNIpog "18D “eplopyo umMI9Te,) Bm GO Rs Loh e (OlESG Ole Je tae 8 i (@) -3]q ‘opluoyyo wnIsouse][ ponuryuod ‘NOILISOdWOQ JO ADVINDOUTG—[JATX WAV] (311) 312 THE PRINCIPLES OF SOIL MANAGEMENT might completely prevent the growth of useful crops if the alkali were black. | | 173. Effect of alkali on crops.—The presence of rela- tively large amounts of salts dissolved in water and brought in contact with a plant cell has been shown by DeVries to cause a shrinking of the protoplasmic lining of the cell, the shrinking increasing with the concentration Fic. 103. Showing plasmolysis of plant cells produced by strong solutions of salts. (a) Normal cells; (6) cell subjected to action of 5 per cent solution of KNO;, showing (z) cell-wall, (p!, p?) plasmatic membranes, (s) vacuole; (c) cell subjected to action of 2.3 per cent solution of KNOs, causing a slight contraction of the plasmatic membranes. of the solution. This causes the plant to wilt, cease growth and finally die. The nature of the salt, and the species and even the individuality of the plant, deter- mine the point of concentration at which the plant succumbs. 174. Direct effect.—The directly injurious effect of the chlorides, sulfates, nitrates, etc., of the alkalies and alkali earths is due to this action on the cell con- tents. The carbonates of the alkalies have, in addition, a corroding effect upon the plant tissues, dissolving the portions of the plant with which they come in contact. EFFECTS OF ALKALI ON CROPS ols 175. Indirect effect.—Indirectly alkali salts may in- jure plants by their influence upon the soil tilth, soil organisms, and fungous and bacterial diseases. 176. Effect upon different crops.—The factors that determine the tolerance of plants to alkali are: (1) The physiological constitution of the plant. (2) The rooting habit. ! The first is not well understood, but resistance varies with species, and even with individuals of the same species. So far as the rooting habit influences tolerance of alkali, the advantage is with the deep-rooted plants like alfalfa and sugar-beets, probably because at least a part of the root is in a less strongly impregnated portion of the soil. Of the cereals, barley and oats are the most tolerant, being able in some cases to produce a fair crop on soil containing one-tenth per cent of white alkali. Of the forage crops, a number of valuable grasses are able to grow with somewhat more than one-tenth per cent of alkali. Timothy, smooth brome and alfalfa are the cul- tivated forage plants most tolerant of alkali,—although they do not equal the native grasses in this respect. Cotton will also tolerate a considerable amount of alkali. 177. Other conditions influencing the action of alkali. —The larger the water content of the soil, the less the injury to plants from alkali; but, should the same soil become dry, the previous large quantity of water would, by bringing into solution a larger amount of alkali, render the solution stronger than it would otherwise have been, and thus cause more injury. The distribution of the alkali at different depths may 314 THE PRINCIPLES OF SOIL MANAGEMENT have an important bearing on its effect upon plants. Young plants and shallow-rooted plants may be entirely destroyed by the concentration of alkali at the surface, when the same quantity evenly distributed through the soil, or carried by moisture to a lower depth, would have caused no difficulty. A loam soil, by reason of its greater water-holding capacity, will carry more alkali without injury to plants than will a sandy one. Certain of the alkali salts exert a deflocculating action upon clay soils, and effect an indirect injury in that way. 178. Reclamation of alkali land.—The alkali salts, being readily soluble, are carried by the soil-water where there is any lateral movement, as frequently occurs where land slopes to some one point. Low-lying lands adjacent to such slopes are thus likely to contain con- siderable alkali, and the “alkali spots’? of semi-arid regions and the large accumulations of alkali in many of the valley lands of arid regions are traceable to this cause. 179. Irrigation and alkalii—In irrigated regions, the injurious effect of alkali is frequently discovered only after irrigation has been practised for a few years. This is due to what is known as a “rise of alkali,’’ and comes about through the accumulation, near the surface of the soil, of salts that were formerly distributed throughout a depth of perhaps many feet. Before the land was irrigated, the rainfall penetrated only a slight depth into the soil, and when evaporation took place salts were drawn to the surface from only a small volume RECLAMATION OF ALKALI LAND 315 of soil. When, however, irrigation water was turned upon the land, the soil became wet for perhaps fifteen or twenty feet in depth. During the portion of the year in which the soil is allowed to dry, large quantities of salts are carried to the upper soil by the upward-moving capillary water. These salts are in part carried down again by the next irrigation, but the upward movement con- | stantly exceeds the downward one. This is because the descending water passes largely through the non-capillary interstitial spaces, while the ascending water passes en- | tirely through the capillary ones. The smaller spaces, | therefore, contain quite a quantity of soluble salt after the downward movement ceases and the upward move- ment commences. In other words, the volume of water carrying downward the salts in the capillary spaces is less than that carrying them upward through these spaces. Surface tension causes the salts to accumulate largely in ~ the capillary spaces, and it is therefore the direction of the principal movement through these that determines the point of accumulation of the alkali. There are large areas of land in Egypt, India and even in France and Italy, as well as in this country, that have suffered in this way, and not infrequently they have reverted to a desert state. There are a number of methods that have been used with more or less success to reclaim alkali land. 180. Underdrainage.—Of the various methods for removing an excess of soluble salts the use of tile drains is the most thorough and satisfactory. When this is used in an irrigated region, heavy and repeated appli- cations of water must be made, to leach out the alkali 316 THE PRINCIPLES OF SOIL MANAGEMENT from the soil and drain it off through the tile. When used for the amelioration of alkali spots in a semi-arid region, the natural rainfall will in time effect the removal. In laying tiles, it is necessary to have them at such a depth that soluble salts in the soil beneath them will not readily rise to the surface. This will depend upon those properties of the soil governing the capillary move- ment of water. Three or four feet frequently suffices, but the capillary movement should first be determined. After drains have been placed, the land is flooded with water to a depth of three or four inches. This is allowed to soak into the soil and pass off through the drains, leaching out part of the alkali in the process. Before the soil has time to become very dry the flooding is repeated and the operation kept up until the land is brought into a satisfactory condition. Crops that will stand flooding may be grown during this treatment, and they will serve to keep the soil from puddling, as it is likely to do if allowed to dry on the surface. If crops are not grown, the soil should be har- rowed between floodings. | The operation should not be carried to a point where the soluble salts are reduced below the needs of the crop, or to lose entirely their effect upon the retention of moisture. 181. Correction of black alkalii—The use of gypsum on black-alkali land has sometimes been practiced for the purpose of converting the alkali carbonates into sul- fates, thus ameliorating the injurious properties of the alkali without decreasing the amount. The quantity of gypsum required may be calculated from the amount NEUTRALIZATION OF BLACK ALKALI 317 and composition of the alkali. The soil must be kept moist, in order to bring about the reaction, and the gypsum should be harrowed into the surface, and not plowed under. Fie. 104. Bromus inermis growing on reclaimed alkali land. When soil containing black alkali is to be tile-drained, ' it is recommended that the land first be treated with gypsum, as the substitution of alkali sulfates for carbo- | nates causes the soil to assume a much less compact condition and thus facilitates drainage, as well as pre-/ venting the loss of organic matter dissolved by the alkali 318 THE PRINCIPLES OF SOIL MANAGEMENT carbonates, and soluble phosphates, both of which are precipitated by the change. 182. Retarding evaporation.—As evaporation of moisture from the surface of the soil is the cause of rise of alkali, it is important to reduce evaporation to a minimum, either in drained or in undrained land. Especially where irrigation is practiced without drainage, it becomes desirable to use as little water as is necessary to produce good crops, and to conserve this to the utmost by checking evaporation from the surface of the soil. The methods used for checking evaporation are the maintenance of a soil or other mulch, and of a good tilth. (See page 195.) In handling alkali spots in the semi-arid region, it is very important to reduce evapo- ration to the smallest amount practicable. 183. Cropping with tolerant plants.—Certain alkali soils that are strongly impregnated with alkali may be gradually improved by cropping with sugar-beets and other crops that are tolerant of alkali, and which re- _ move large amounts of salts. This is more likely to be . efficacious where irrigation is not practiced. 184. Other methods.—Numerous other methods of disposing of alkali or ameliorating its effects have been used or proposed. Among these are the following: (1) ‘‘Leaching,’’ which consists of flooding the surface of the soil for the purpose of carrying the soluble salts down to a depth of three or four feet, where they will not effect the roots of ordinary crops. If natural drain- age exists, this plan is effective and without danger; otherwise evaporation must be reduced to the smallest possible amount. (2) Removal of alkali by scraping the MANURES 319 surface when the salts have accumulated there in time of drought. While this may aid in the work of ameliora- | tion, it is not a final solution of the difficulty. (3) Wash- ing the alkali from the land by turning on a rapidly moving body of water, when the alkali is encrusted on the surface of the soil, has been tried, but with poor suc- cess, as the alkaliis largely carried into the soil, instead of being removed by the water passing over the surface of the land. 185. Alkali spots.—In semi-arid regions, small areas of alkali are frequently found, varying from a few square yards to several acres in size. The quantities of alkali in these are usually not sufficient to prevent the growth of crops in years of good rainfall, but in periods of drought the concentration of the salts and the compact condition they tend to produce combine to injure the crop. The methods already mentioned for treating alkali land are of service on these small areas, and, in addition, the plowing under of fresh farm manure has been found to improve their productiveness. This, with surface drainage, deep tillage and good cultivation, to prevent the soil from drying out, will usually remedy the diffi- culty. Frequently these spots become highly productive under proper treatment. VII. MANURES A manure is any solid substance added to the soil to make it more productive. This it may do: (1) By im- proving the physical condition of the soil, as usually results from the application of lime and the incorporation 320 THE PRINCIPLES OF SOIL MANAGEMENT of organic matter. (2) By favoring the action of useful bacteria, which is one of the most beneficial results of farm manure, and also of lime. (3) By counteracting the effects of toxic substances, as, for instance, the con- version of sodium carbonate into sulfate by gypsum, or the neutralization of acidity, or possibly the removal of toxic organic substances by certain salts. (4) By adding to the soil the nutrient materials absorbed by plants, which results in the case of almost all substances used as manures. 186. Early ideas of the function of manures.— Manures were at one time supposed to pulverize the soil, and the French word maneuvrer, from which the word manure comes, means to work with the hand. This idea probably originated through the observation that farm manure, which was the only manure in use at that time, made the soil less cloddy. It has been argued, notably by Jethro Tull, that as tillage pulverizes the soil it may be used as a substitute for manures. ‘There are, however, conditions aside from tilth that are influenced by manures, and good tilth alone will not suffice to maintain a permanently intensive agriculture. It is true in the United States, as it is in Kurope, that a large consumption of manures goes hand- in-hand with a highly developed and intensive system of farming. } 187. Development of the idea of nutrient function of manures.— While the use of animal excrement on cul- tivated soils was practiced as far back as systematic agriculture can be definitely traced, the earliest record of the use of mineral salts for increasing the yield of HISTORY OF COMMERCIAL FERTILIZERS 321 crops was published, in 1669, by Sir Kenelm Digby. He says, “‘By the help of plain salt petre, diluted in water, and mingled with some other fit earthly substance, that may familiarize it a little with the corn into which I endeavored to introduce it, I have made the barrenest ground far outgo the richest in giving a prodigiously plentiful harvest.’’ His dissertation does not, however, show any true conception of the reason for the increase in the crop through the use of this fertilizer. In fact, the want of any real knowledge at that time of the com- position of the plant would have made this impossible. In 1804, Theodore de Sausure published his chemical researches upon plants, in which he, for the first time, called attention to the significance of the ash ingredients of plants, and pointed out that without them plant-life is impossible, and further, that only the ash of the plant tissue is derived from the soil. Justus von Liebig, in his writings published about 1840, emphasized still more strongly the importance of mineral matter in the plant, and its extraction from the soil. He refuted the theory, at that time popular, that plants absorb their carbon from humus, but made the mistake of attaching little importance to the pres- ence of humus in the soil. He showed the importance of potassium and phosphorus in manures, but, in his later expressions, failed to appreciate the value of nitrogenous manures, holding that a sufficient amount is washed from the atmosphere in the form of ammonia. A true conception of the necessity for a supply of combined nitrogen in the soil was even at that time enter- tained by Boussingault and by Sir John Lawes, although U ee THE PRINCIPLES OF SOIL MANAGEMENT the elaborate experiments conducted by Lawes, Gilbert and Pugh, in 1857, were required to fully demonstrate the fact. Their care in conducting the experiments resulted in their sterilizing the soil with which they experimented, and hence their failure to discover the utilization of free atmospheric nitrogen by legumes. Between 1840 and 1850, Sir John Lawes began the manufacture of bone superphosphate, and, about the same time, Peruvian guano and nitrate of soda were introduced into Europe. The commerical fertilizer industry thus dates from this time. 188. Classes of manures.—While manures are very numerous as to kind, and a certain manure may have a number of distinct functions, they may yet be roughly divided into classes. They will accordingly be treated under the following heads: (1) Commercial fertilizers. (2) Farm manures. (3) Green manures. (4) Soil amend- ments. 189. Commercial fertilizers— Although the commer- cial fertilizer industry is little more than half a century old, the sale of fertilizers in this country amounts to about $50,000,000 annually. Animal refuse and phos- phate fertilizers are exported, while nitrate of soda and. potassium salts are imported. Of the fertilizers sold in 1899, about 70 per cent was consumed in the North Atlantic and South Atlantic states, in an area lying within 300 miles of the seaboard. Nearly one-half of the remainder was purchased in four states, Ohio, Indiana, Alabama and Louisiana. 190. Function of commercial fertilizers.—Primarily the function of commercial fertilizers is to add plant FE y S Ss KJ SSS eee ———— —S . et FE a bay yy. —S—— ly J * im tl ih aaa Mg ill ; Te Mie 4 Bee 7m Lack A (i Hn AT in Wg on He Sma Pe NE i - L5i y Saat i Mn ay H Tog bon PA i Rl aS Fi . 1 De Ex PD, p p . . 1 y _— rw 324 THE PRINCIPLES OF SOIL MANAGEMENT nutrients to the soil, usually in a form more readily soluble than those already present in large quantity. While other beneficial effects may be produced by certain fertilizers, they are usually of secondary import- ance, as compared with the addition of the plant nutri- ents. 191. Fertilizer constituents.—Prepared fertilizers, as found on the market, are usually composed of a number of ingredients. As these are the carriers of the fertilizing material, and as it is upon their composition and solu- bility that the value of the fertilizer depends, a knowl- edge of the properties of these constituents is of interest to every user of fertilizers, and is a valuable aid in their purchase. 192. Fertilizers used for their nitrogen.—Nitrogen is the most expensive constituent of manures, and is of great importance, as it is very likely to be deficient, in soils. A commercial fertilizer may have its nitrogen in the form of soluble inorganic salt, or combined as organic material. Upon the form of combination de- pends to a certain extent the value of the nitrogen, as the soluble inorganic salts are very readily available to the plant, while the organic forms must pass through the various processes leading to nitrification before the plant can use the nitrogen so contained. The inorganic nitrogen fertilizers are sodium nitrate, ammonium sul- fate, calcium nitrate and calcium cyanamid. 193. Sodium nitrate.—This fertilizer now constitutes the principal source of inorganic nitrogen in commercial fertilizers. The salt occurs in the crude condition in Northern Chili, and is believed to be due to the action NITROGEN BEARING FERTILIZERS 325 of soil organisms acting through a very long period, and leaving the product finally in the form of sodium nitrate that has crystalized out of solution in which it has some- time been held. The crude salt is purified by crystalli- zation, and, as put upon the market, contains about 96 per cent sodium nitrate, or about 16 per cent of nitro- gen, 2 per cent of water, and small amounts of chlorides, sulfates and insoluble matter. The cost of nitrogen in this form is from fifteen to eighteen cents per pound. On account of its easy availability, sodium nitrate acts quickly in inducing growth. For this reason it is used much by market gardeners, and for other purposes when a rapid growth is desired. It is the most active form of nitrogen. A light dressing on meadow land in the early spring assists greatly in hastening growth by fur- nishing available nitrogen before the conditions are favorable for the process of nitrification. On small grain it serves a similarly useful purpose where the soil is not rich. Owing to the fact that it is not absorbed by the soil in large quantities, it is easily lost in the drainage water; for which reason it should only be applied when crops are growing upon the soil, and then only in moderate quantity. The continued and abundant use of sodium nitrate upon the soil may result, through its deflocculating action, in breaking down aggregates of soil-particles, thus compacting and injuring the structure. This effect is attributed to the accumulation of sodium salts, par- ticularly the carbonate, as the sodium is not utilized by the plant to the same extent as is the nitrogen. 326 THE PRINCIPLES OF SOIL MANAGEMENT 194. Ammonium sulfate-——When coal is distilled, a portion of the nitrogen is liberated as ammonia, and is collected by passing the products of distillation through water in which the ammonia is soluble, forming the ammoniacal liquor. The ammonia thus held is distilled into sulfuric acid with the formation of ammonium sulfate and the removal of impure gases. Commercial ammonium sulfate contains about 20 per cent of nitrogen. It is the most concentrated form in which nitrogen can be purchased as a fertilizer, having from sixty to eighty pounds more of nitrogen per ton than sodium nitrate. It is, therefore, economical to handle. Its effect upon crops is not so rapid as that of sodium nitrate, but it is not so quickly carried from the soil by drainage water, as the ammonium salts are readily absorbed by the soil. A pound of nitrogen in the form of sulfate has about the same value as the same amount in the form of nitrate. The long and extensive use of ammonium sulfate on a soil has a tendency to produce an acid condition, through the accumulation of sulfates which are not largely taken up by plants. Ammonium sulfate, like sodium Bestel. should not be applied in the autumn, as the ammonia is con- verted into nitrates and leached from the soil in sufficient quantities to entail a very decided loss of nitrogen. There is not likely to be so large a loss of nitrogen from ammonium salts as from nitrates, and, as would naturally be expected, there is greater loss of nitrogen when these salts are used alone than when they are combined with other fertilizing ingredients. LOSS OF SOIL NITROGEN | 327 Hall has estimated the loss of nitrogen from certain drained plats, of the Rothamsted Experiment Station. This estimate is based upon the concentration of the drainage from the different plats, of which there was no record of total flow, but for which the measurements of flow from the lysimeter draining 60 inches of soil were taken, and the total loss of nitrates calculated on this basis. Estimated in this way, the effects of sev- eral different methods of manuring are shown in the accompanying table. TaBLE XLVIII PouNpDs PER ACRE NitrRIc NITROGEN IN DRAINAGE WATER 1879-80 Spring | Harvest Treatment sowing to to spring harvest | sowing NN MMREMSEENL SG) uh Os Leas sy lal. wrote Kear ee ELE es 10.8 Mineral fertilizers only............... 1.6 13.3 Minerals + 400 pounds ammon. salts..| 18.3 12.6 Minerals + 550 pounds nitrate of soda.| 45.0 15.6 Minerals + 400 pounds ammon. salts eae Wh AWCUIOR sy as obras 9.6 | 59.9 400 pounds ammon. salts alone....... 42.9 14.3 400 pounds ammon. salts + sulfate of NE asec tary Arid sx a aleite «d's > 9 16.4 Estimated drainage in inches..... I 4.7 1880-81 Spring | Harvest sOWINg to to spring harvest | sowing 0.6 17.1 O.7 es 4.3 21.4 15.0 41.0 3.4 74.9 7.4 35.2 id 25.0 1.8 18.8 This table, in addition to confirming the statements already made in regard to the loss of nitrogen in drain- age waters, also shows how closely the supply of avail- able nitrogen was used by the crops on those plats, 328 THE PRINCIPLES OF SOIL MANAGEMENT evidently in need of nitrogen fertilization, as these plats lost very little nitrogen during the growing season, while during the remainder of the year they lost nearly as much as did some of the nitrogen manured plats. It also indicates that the loss when nitrate is used is greater than when ammonium salts are applied, as the amount of nitrogen in the 550 pounds of nitrate is really eight pounds per acre more than in the 400 pounds ammonium sulfate, which is not sufficient to account for the difference in the loss. However, half of the nitrate treated plat received no other manure, and produced only a small crop, which would naturally result in a a greater loss by drainage. 195. Calcium cyanamid.—The vast store of atmos- pheric nitrogen chemically uncombined, but very inert, will furnish an inexhaustible supply of this highly valu- able fertilizing element, when it can be, with reasonable economy, combined in some manner that will result in a product commercially transportable, and that will, when placed in the soil, be or become soluble without liberating substances toxic to plants. The importance of the nitrogen supply for agriculture may be appreciated when we consider that nitrates are being carried off. in the drainage water of all cultivated soils at the rate of from twenty-five to fifty pounds and even more per acre, annually, and that nearly as much more is removed in crops. The exhaustion of the supply of nitrogen in most soils may be accomplished within one or two generations of men, unless a renewal of the supply be brought about in some way. Natural processes provide for an annual LIME NITROGEN 329 accretion through the washing down of ammonia and nitrates by rain-water from the atmosphere, and through the fixation of free atmospheric nitrogen by bacteria; but, without the frequent use of leguminous crops, the supply could not be maintained. Farm practice of the present day requires the application of nitrogen in some form of manure, and, as the end of the commer- cial supply of combined nitrogen is easily in sight, there is urgent need of discovering a new source. This has lately been done by combining calcium with atmospheric nitrogen in the forms of calcium cyanamid and cal- cium nitrate. The most successful process for the production of cyanamid consists in passing nitrogen into closed retorts containing powdered calcium carbide heated to a tem- perature of 1,100° C., the product being calcium cyana- mid, and free carbon. CaC,+2 N=CaCN,+C. The free carbon remains distributed in the cyanamid and gives it a black color. A modification of the process provides for the use of lime and coke instead of calcium carbide, but this has not yet been used on a commercial scale. The nitrogen required for the process is obtained either by passing air over heated copper, or by the frac- tional distillation of liquid air. The fertilizer, as placed on the market, is a heavy, black powder with a somewhat disagreeable odor. At present it is not manufactured in America and is not obtainable except in small amounts. Plants for its iicahaie are being promoted, which will doubtless’ 330 THE PRINCIPLES OF SOIL MANAGEMENT result in its being placed on the market in the near future. There are, at present, two calcium cyanamid ferti- lizers being manufactured. One is called lime-nitrogen, and is made in Italy; the other is called nitrogen-lime, and is made in the province of Saxony, Germany. The former contains 15 to 23 per cent nitrogen, 40 to 42 per cent calcium, and 17 to 18 per cent carbon dust. The latter is said to contain somewhat less nitrogen, and to have in it some calcium chloride, which is some- times injurious to plants. The value of calcium cyanamid as a fertilizer has not yet been definitely and conclusively ascertained. The cyanamid must be decomposed before becoming avail- able to the plant. Under favorable conditions, the nitro- gen of the cyanamid is converted into ammonia; but, if the conditions for decomposition are not favorable, the dicyanamid may be formed, which has a poisonous » effect upon plants. Another objection which sometimes obtains is that acetylene is produced from the carbide, which remains: unchanged in the manufacture of the cyanamid. Acetylene is also injurious to plants. By incorporating the calcium cyanamid in the soil eight to fourteen days before the seed is planted, this difficulty may be overcome. It is also important that the cyanamid be plowed under, and not left on or near the surface of the soil, as, under these circumstances, decomposition does not go on properly, and the poisonous action above referred to takes place. Upon heavy soil the value of cyanamid as a fertilizer is not greatly below that of sodium nitrate, but upon CALCIUM NITRATE AOE! sandy soil it ranks much lower. Indeed, it appears to be but poorly suited to use on sandy soils. 196. Calcium. nitrate.—The other process for com- bining atmospheric nitrogen is of even more recent invention than that for the manufacture of calcium cyanamid and, like it, is not conducted on a commercial scale in this country; but, with the vast opportunities for developing electric power which are offered in certain localities, factories for the manufacture of calcium nitrate will soon be established. The process employs an electric arc to produce nitric oxide by the combustion of atmospheric nitrogen, ac- cording to the simple equation: N,+0,=2 NO. A very high power is required for this synthesis, involving a temperature of 2,500° to 3,000° C., and the expense of the operation is determined almost entirely by the cost of the electricity. The nitric oxide gas is passed through milk of lime, giving calcium nitrate. The calcium nitrate produced by this process has a yellowish white color, and is easily soluble in water, but deliquesces very rapidly in the air. This last prop- erty can be overcome by adding an excess of lime in the manufacture, thus producing a basic calcium nitrate, which contains only 8.9 per cent nitrogen. Another way of avoiding the difficulties involved by the deliques- cent property of the nitrate is practiced by the factory at Nottoden, Norway. This consists in first melting the product, then grinding it fine, and packing it in 332 THE PRINCIPLES OF SOIL MANAGEMENT air-tight casks. The fertilizer thus prepared contains 11 to 13 per cent nitrogen. Calcium nitrate contains its nitrogen in a form directly available to plants. It resembles sodium nitrate in its solubility, availability, and lack of absorption by the soil. It may be spread upon the surface of the ground, as it exerts no poisonous action, and does not tend to form a crust, as does sodium nitrate. The relative values of the different soluble nitrogen fertilizers vary with a great many conditions and can ‘be accurately judged only by a large number of tests. At present, both the calcium nitrate and the cyanamid are being produced at less cost per pound of nitrogen than is sodium nitrate, when laid down in the neighbor- hood of the factories in Europe. It seems quite certain that, when the processes have been further improved, the result will be to greatly reduce the cost of the avail- able nitrogen. 197. Organic nitrogen in fertilizers—The commercial fertilizers containing organic nitrogen include cotton- seed-meal, which contains 7 per cent nitrogen, when free from hulls; linseed-meal, with 5.5 per cent nitrogen; castor pomace, having 6 per cent nitrogen; and a number of refuse products from packing-houses, among which there are red-dried blood and black-dried blood, the former having about 13 per cent nitrogen, and the latter 6 to 12 per cent; dried meat and hoof meal, carrying 12 to 13 per cent nitrogen; ground fish containing 8 per cent nitrogen; and tankage, of which the concentrated product has a nitrogen content of 10 to 12 per cent, and the crushed tankage, 4 to 9 per cent; also leather-meal OTHER FORMS OF ORGANIC NITROGEN a35 and wool-and-hair waste, which last two, on account of their mechanical condition, are of practically no value. The meals made from seeds are primarily stock-foods, but are sometimes used as manures. They decompose rather slowly in the soil, owing to their high oil content, and are much more profitably fed to live stock than applied as farm manure. They contain some phosphorus as well as nitrogen. Guano consists of the excrement and carcasses of sea-fowl. The composition of guano depends upon the climate of the region in which it is found. Guano from an arid region contains nitrogen, phosphorus and potas- sium, while that from a region where rains occur con- tains only phosphorus—the nitrogen and potassium having been leached out. In a dry guano the nitrogen occurs as uric acid, urates, and, in small quantities, as ammonium salts. A damp guano contains more ammonia. The phosphorus is present as calcium phos- phate, ammonium phosphate, and as the phosphates of other alkalies. A portion of the phosphate is readily soluble in water. All of the plant-food is thus either directly soluble, or becomes so soon. after admixture with the soil. The composition is extremely variable. The best Peruvian guano contains from 10 to 12 per cent of nitrogen, 12 to 15 per cent phosphoric acid, and 3 to 4 per cent of potash. Guano was formerly a very important fertilizing material, but the supply has become so nearly exhausted that it is relatively unimportant at the present time. Of the abattoir products, dried blood is the most readily decomposed, and therefore has its nitrogen 334 THE PRINCIPLES OF SOIL MANAGEMENT in the most available form. In fact, it produces results more quickly than any other form of organic nitrogen. It requires a condition of soil favorable to decomposi- - tion and nitrification, which prevents its exerting a strong action in the early spring. It should be applied to the soil before the crop is planted. The black dried blood contains from 2 to 4 per cent of phosphoric acid. Dried meat contains a high percentage of nitrogen, but does not decompose so easily, and is not so desirable a form of nitrogen. It can be fed to hogs or poultry to advantage, and the resulting manure is very high in nitrogen. Hoof-meal, while high in nitrogen, decomposes slowly, being less active than dried blood. It is of use in in- creasing the store of nitrogen in a depleted soil. Ground fish is an excellent form of nitrogen, and is as readily available as blood, but has a lower nitrogen content. Tankage is highly variable in. composition, and the concentrated tankage, being more finely ground, under- goes more readily the decomposition necessary for the utilization of the nitrogen. Crushed tankage contains from 3 to 12 per cent of phosphoric acid, in addition to its nitrogen. Leather-meal and wool-and-hair waste are in such a tough and undecomposable condition that they may remain in the soil for years without losing their struc- ture. They are not to be recommended as manures. 198. Fertilizers used for their phosphorus.—Phos- phorus is generally present in combination with lime, iron or alumina. Some of the phosphates also contain PHOSPHATE FERTILIZERS 335 - organic matter, in which case they generally carry some nitrogen. Phosphates associated with organic matter decompose more quickly in the soil than untreated mineral phosphates. 199. Bone phosphate.—Formerly, bones were used entirely in the raw condition, ground or unground. When ground, they are a more quickly acting fertilizer than when unground. Raw bones contain about 22 per cent phosphoric acid and 4 per cent nitrogen. The phosphorus is in the form of tricalcic phosphate (Ca, (PO,),). Most of the bone now on the market is first boiled or steamed, which frees it from fat and nitrogenous matter, both of which are used in other ways. Steamed bone is a more valuable fertilizer than raw bone, as the fat in the latter retards decomposition, and also because steamed bone is in a better mechanical condition. The form of the phosphoric acid is the same as in raw bone, and constitutes 28 to 30 per cent of the product, while the nitrogen is reduced to 14 per cent. Bone tankage, which has already been spoken of as a nitrogenous fertilizer, contains from 7 to 9 per cent phosphoric acid, largely in the form of tricalcium phos- phate. All of these bone phosphates are slow-acting manures, and should be used in a finely ground form, and for the permanent benefit of the soil rather than as an immediate source of nitrogen or phosphorus. 200. Mineral phosphates.—There are many natural deposits of mineral phosphates in different portions of the world, some of the most important of which are in North America. The phosphorus in all of these is in the 336 THE PRINCIPLES OF SOIL MANAGEMENT form of tricalcium phosphate, but the materials asso- ciated with it vary greatly. Apatite is found in large quantities in the provinces of Ontario and Quebec, Canada. It occurs chiefly in crystalline form. The tricalcium phosphate of which it is composed is in one form associated with calcium fluoride, and in the other with calcium chloride. The Canadian apatite contains about 40 per cent phosphoric acid, being richer than that found elsewhere. Phosphorite is another name for apatite, but is chiefly applied to the impure amorphous form. Caprolites are concretionary nodules found in the chalk or other deposits in the south of England, and in France. They contain 25 to 30 per cent of phosphoric acid, the other constituents being calcium carbonate and silica. South Carolina phosphate contains from 26 to 28 per cent of phosphoric acid, and but a very small amount of iron and alumina. As these substances interfere with the manufacture of superphosphate from rock, their presence is very undesirable,—rock containing more than from 3 to 6 per cent being unsuitable for that purpose. Florida phosphates occur in the form of soft phos- phate, pebble phosphate, and boulder phosphate. Soft phosphate contains from 18 to 30 per cent of phos- phoric acid, and, on account of its being more easily ground than most of these rocks, is often applied to the land without being first converted into a superphos- phate. The other two, pebble phosphate and boulder phosphate, are highly variable in composition, ranging SUPERPHOSPHATE 337 from 20 to 40 per cent phosphoric acid. Tennessee phos- phate contains from 30 to 35 per cent of phosphoric acid. Basic slag, or, as it is also called, phosphate slag or Thomas phosphate, is a by-product in the manufacture of steel from pig-iron rich in phosphorus. The phos- phorus present is in the form of tetracalcium phosphate, (CaO),P,0,;. It also contains calcium, magnesium, aluminum, iron, manganese silica and sulfur. On ac- count of the presence of iron and aluminum, and because its phosphorus is more readily soluble than the trical- cium phosphate, the ground slag is applied directly to the soil without treatment with acid. 201. Superphosphate fertilizers.—In order to render more readily available to plants the phosphorus con- tained in bone and mineral phosphates, the raw material, purified by being washed and finely ground, is treated with sulfuric acid. This results in a replacement of phos- phoric acid by sulfuric acid, with the formation of monocalcium phosphate and calcium sulfate, and a smaller amount of dicalcium phosphate, according to the reactions: Ca, (PO,),+2 H,SO,=CaH, (PO,),+2 CaSO, and Ca, (PO,), + H,SO,=Ca,H,(PO,), + CaSO,. The tricalcium phosphate being in excess of the sul- furic acid used, a part of it remains unchanged. In the treatment of phosphate rock, part of the sulfuric acid is consumed in acting upon the impurities present, which usually consist of calcium and magnesium carbonates, iron and aluminum phosphates, and cal- v 238 THE PRINCIPLES OF SOtL MANAGEMENT cium chloride or fluoride, converting the bases into sul- fates and freeing carbon dioxide, water, hydrochloric acid and hydrofluoric acid. The resulting superphos- phate is therefore a mixture of monocalcium phosphate, dicalecium phosphate, tricalcium phosphate, calcium sulfate, and iron and aluminum sulfates. In the superphosphates made from bone, the iron and aluminum sulfates do not exist in any considerable amounts. However, as long as the phosphorus remains in the form of monocalcium phosphate, the value of a pound of available phosphorus in the two kinds of fer- tilizer is the same; but the remaining tricalcium phos- phate has a greater value in the bone than in the rock superphosphate. The superphosphates made from animal bone con- tain about 12 per cent available phosphoric acid, and 3 or 4 per cent of insoluble phosphoric acid. They also contain some nitrogen. Bone-ash and bone-black super- phosphates contain practically all of their phosphorus in an available form, but they contain little or no nitro- gen. South Carolina rock superphosphate contains from 12 to 14 per cent available phosphoric acid, including from 1 to 3 per cent reverted phosphoric acid. The best Florida rock superphosphates contain from 17 per cent downward of available phosphoric acid, part of which is reverted. The Tennessee superphosphates vary from 14 to 18 per cent available phosphoric acid. 202. Reverted phosphoric acid.—On standing, a change sometimes occurs in superphosphates by which a part of the phosphoric acid becomes less easily soluble, and to that extent the value of the fertilizer is decreased. FORMS OF PHOSPHATE 339 This change, known as “‘reversion,’’ is much more likely to occur in superphosphates made from rock than in those derived from bone. It will also vary in different samples,—a well-made article usually undergoing little change, even after long standing. It is supposed to be caused by the presence of undecomposed tricalcium phosphate, and of iron and aluminum sulfates. 203. Double superphosphates.—In making super- phosphates, a material rich in phosphorus must be used, —not less than 60 per cent tricalcium phosphate being necessary for their profitable production. The poorer materials are sometimes used in making what is known as double superphosphates. For this purpose they are treated with an excess of dilute sulfuric acid; the dis- solved phosphorus and the excess of sulfuric acid are separated from the mass by filtering and are then used for treating phosphates rich in tricalcium phosphate and forming superphosphates. The superphosphates so formed contain more than twice as much phosphorus a3 those made in the ordinary way. 204. Relative availability of phosphate fertilizers.— Superphosphates and double superphosphates contain their phosphorus in a form in which it can be taken up by the plant at once. They are therefore best applied at the time when the crop is planted, or shortly before, or they may be applied when the crop is growing. Crude phosphates, on the other hand, become available only through the natural processes in the soil. The presence of decomposing organic matter is a great aid to the decomposition of crude phosphates. Reverted phosphorus, although not soluble in water, 340 THE PRINCIPLES OF SOIL MANAGEMENT is readily soluble in dilute acids. It is now quite gener- ally believed that it furnishes an available supply of phosphorus to the plant. In a statement of fertilizer analyses it is termed “citrate soluble,’’ and this and the “water soluble’’ are termed “ available.”’ The degree of fineness to which the material is ground makes a great difference in the availability of the less- soluble phosphate fertilizers, especially in the ground- rock phosphates, and in ground bone. This material should be ground fine enough to pass through a sieve having meshes one-fiftieth of an inch in diameter. 205. Fertilizers used for their potassium.—The pro- duction of potassium fertilizers is largely confined to Germany, where there are extensive beds varying from 50 to 150 feet in thickness, lying under a region of country extending from the Harz mountains to the Elbe river, and known as the Stassfurt deposits. De- posits have lately been discovered in other parts of Germany. 206. Stassfurt salts——The Stassfurt salts contain their potassium either as a chloride or a sulfate. The chloride has the advantage of being more diffusible in the soil, but in most respects the sulfate is preferable. Potassium chloride has an injurious action on certain crops, among which are tobacco, sugar-beets and pota- toes. On cereals, legumes and grasses, the muriate appears to have no injurious effect. The mineral produced in largest quantities by the Stassfurt mines is kainit. Chemically it consists of mag- nesium and potassium sulfate, and magnesium chloride, or magnesium sulfate and potassium chloride. Kainit POTASH-BEARING FERTILIZERS 341 has the same action on plants as has potassium chloride. It contains from 12 to 20 per cent of potash, and 25 to 45 per cent of sodium chloride, with some chloride and sulfate of magnesium. Kainit should be applied to the soil a considerable time before the crop for which it is intended is planted. It should not be drilled in with the seed, as the action of the chlorides in direct contact with the seed may injure its viability. In addition to the potassium added to the soil by kainit, there are also in this fertilizer magnesium and sodium. The magnesium may be objec- tionable if there is much already present in the soil. (See page 350.) Sodium may to some extent replace potassium in the soil economy, and in that way may be beneficial. Silvinit contains its potassium both as chloride and as sulfate. It also contains sodium and magnesium chlorides. Potash constitutes about 16 per cent of the material. Owing to the presence of chlorides, it has the same effect on plants as has kainit. The commerical form of potassium chloride generally contains about 80 per cent potassium chloride, or 50 per cent potash. The impurities are largely sodium chloride and insoluble mineral matter. The possible injury to certain crops from the use of the chloride has already been mentioned. For crops not so affected, potassium chloride is a quick-acting and effective carrier of potassium, and one of the cheapest forms. High-grade sulfate of potassium contains from 49 to 51 per cent of potash. Unlike the muriate, it is not injurious to crops but is more expensive. 342 THE PRINCIPLES OF SOIL MANAGEMENT There are a number of other Stassfurt salts, consisting of mixtures of potassium, sodium and magnesium in the form of chlorides and sulfates. They are not so widely used for fertilizers as are those mentioned above. 207. Wood ashes.—For some time after the use of fertilizers became an important farm practice, wood ashes constituted a large portion of the supply of potas- sium. They also contain a considerable quantity of lime and a small amount of phosphorus. The product known as unleached wood ashes contains 5 to 6 per cent of pot- ash, 2 per cent of phosphoric acid, and 30 per cent of lime. Leached wood ashes contain about one per cent of potash, 14 per cent of phosphoric acid, and 28 to 29 per cent of lime. They contain the potassium in the form of a carbonate, which is alkaline in its reaction, and may be injurious to seeds when in large amount. They are beneficial to acid soils through the action of both the potassium and calcium salts. The lime is valuable for the other effects it has on the properties of the soil. (See page 348.) 208. Insoluble potassium _ fertilizers.—Insoluble forms of potassium, occurring in many rocks, usually in the form of a silicate, are not regarded as having any manurial value. Experiments with finely ground feldspar have been conducted by a number of experi- menters, but have, in the main, given little encourage- ment for the successful use of this material. An insoluble form of potassium is not given any value in the rating of a fertilizer, based upon the results of its analysis. 209. Fertilizer practice.—The purchase and use of commercial fertilizers is an art that requires some BRANDS OF FERTILIZERS 343 technical knowledge for its efficient conduct. There are many fertilizing materials put up under numerous brands that must be selected from and applied to a great variety of crops grown on innumerable types of soil. The result is that an economical fertilizer practice is difficult to establish, and the use of fertilizers is usually conducted in an entirely empirical manner. 210. Brands of fertilizers —Each manufacturer or compounder of commercial fertilizers places on the market a number of brands of fertilizers that have some trade name, frequently implying the usefulness of the fertilizer for some particular crop, but without reference to the character of the soil on which it is to be used. Each brand of fertilizer is usually composed of several of the constituents that have been described. If those sub- stances are used that are difficultly soluble, the ferti- lizer is not so valuable as if composed of easily soluble substances. The solubility, as well as the percentage of each ingredient of the fertilizer, should be known by the purchaser. ; A fertilizer is known in the market as a high-grade or a low-grade product, depending upon the percentage of fertilizing constituents that it contains. Low-grade fertilizers are cheaper than high-grade merely because they contain less plant-food, although the price per pound of plant-food may be no less,—and, in fact, is usually more. The low-grade product is encumbered with a large amount of inert material, that adds to the cost of transportation and handling, without adding to the value of the fertilizer. For these reasons, the high- grade material is almost always the cheaper fertilizer, 344 THE PRINCIPLES OF SOIL MANAGEMENT A ton of low-grade fertilizer may contain 500 or 600 pounds more inert material than a high-grade fertilizer, upon which freight must be paid, and which must be hauled from the station and spread upon the field. 211. Fertilizer inspection.—Some thirty states have enacted legislation providing for the inspection and con- trol of the sale of commercial fertilizers. Each package of fertilizer must bear a certificate stating the percentage of nitrogen, phosphoric acid and potash, and more or less information in regard to the forms in which these are held and their rates of solubility. This must be guaran- teed to be correct by the manufacturer. The guarantee does not always state the percentage of nitrogen (N), phosphoric acid (P,O;), and potash (K,O), but often uses other terms that imply the presence of these substances, but so combined that the percentage of the carrier is larger,—as, for instance, ammonia, bone phosphate and sulfate of potash. To convert one term into another, factors have been devised which greatly simplify the process. Per cent ammonia X .8235 = per cent nitrogen (N.) Per cent nitrate of soda X .1647 = per cent nitrogen (N). Per cent bone phosphate X .458 = per cent phosphoric acid P.O): Per — soc of potash X .632 = per cent potash (K,O). Per cent sulfate of potash x .54 = per cent potash (K,O). 212. Trade values of fertilizers.—It has been custom- ary for the authorities charged with fertilizer inspection in the states concerned to adopt each year a schedule of trade values for nitrogen, phosphoric acid and potash, in each of the various forms in which they appear in TRADE VALUE OF FERTILIZERS 345 ' fertilizers. These values are based on the cost of the unmixed constituents, if purchased in wholesale lots from the manufacturer, and are secured by averaging the wholesale prices per ton of all the various fertilizer supplies for the six months preceding March 1, to which is added about 20 per cent of the price, to cover cost of handling. The trade values for 1907 were as follows: Value per pound Cents Pepremeris it items se! ie CE eto. Cd wks ate hdd ide < tS 18.5 Nitrogen, inmamimonnn salts .$6. 020.255}. Dank ches 1 5) Organic nitrogen, in dried and finely ground fish meat and blood, and in mixed fertilizers ............. 20.5 Organic nitrogen, in finely ground bone and tankage. . 20.5 Organic nitrogen, in coarsely ground bone and tankage.15.0 Phosphoric acid, soluble in water .................. 5.0 Phosphoric acid, soluble in ammonium citrate ....... 4.5 Phosphoric acid, insoluble, in fine bone and tankage.. 4.0 Phosphoric acid, insoluble, in coarse boneand tankage . 3.0 Phosphoric acid, insoluble, in mixed fertilizers........ 2.0 Phosphoric acid, insoluble, in finely ground fish, cotton- seed meal, castor pomace and wood-ashes ...... 4.0 MMR A PEMABIARE Sleds 0 Gl ew 26.236) be made available in this way. The use of calcium salts may also render phosphorus more useful, probably by supplying a base more soluble than iron or alumina with which in soils deficient in calcium the phosphorus might otherwise be combined. Boussingault, as quoted by Storer, found that the addition of lime to a clover crop increased greatly the calcium, potassium and phosphorus contained in the crop. 350 THE PRINCIPLES OF SOIL MANAGEMENT TaBLe IL Kilos per hectare | Phos- Lime Potash phoric acid Crop not limed (first year) ........ 32.2 26.7 11.0 Crop limed (first year) .....:..:.+. 79.4 95.6 24.2 Crop not limed (second year) ...... 32.2 28.6 7.0 Crop limed (second year) .......... 102.8 97.2 22.9 Calcium salts may also increase greatly the rate at which nitrogen becomes available by its effect upon bacterial action, as before explained. 220. Effect on toxic substances and plant diseases.— Free acids are toxic to most agricultural plants. Some plants are much more sensitive than others. Clover and alfalfa, for instance, should have a slightly alkaline medium for their best growth, and any acid is very injurious. Calcium salts in neutralizing acidity remove this toxic condition. Certain toxic substances of an organic nature are also said to be rendered innocuous by the presence of calcium carbonate. Magnesium salts, when present in excess, May exert a toxic action upon plants. The relative proportion of calcium and magnesium, accord- ing to Loew, determines whether or not magnesium is toxic. The exact limits of the ratio of magnesium to calcium beyond which the former is toxic depends upon the combinations and solubilities of the two, and also upon the crop grown. An actually greater amount of magnesia, as shown by a strong hydrochloric acid diges- LIME AS A SOIL AMENDMENT 351 tion analysis, is not present in very fertile soils of any region, according to Loew. If injury from magnesium is suspected, the obvious means of correction is to increase the proportion of calcium by its addition in some form. The use of limestone, ground or burned, that contains a large percentage of magnesium may be injurious to some soils, as may also those Stassfurt salts containing magnesium. The presence of soluble calcium, with its effects upon the soil, retards the development of certain plant diseases, like the “‘finger and toe”’ disease of the cruci- fere. On the other hand, it may promote some diseases, as, for instance, the potato “‘scab.’’ 221. Forms of calcium.—Calcium is used on the soil in the form of calcium oxide, or quicklime (CaQ), water-slaked lime (Ca(OH),), air-slaked lime (CaCQ,), eround limestone (also a carbonate), and calcium sulfate, or gypsum (CaSO,, 2H,O). The application of any of these is usually called liming the soil, although gypsum does not serve exactly the same purpose as do the other forms. Owing to differences in the molecular weights of these compounds of calcium, it requires more of some forms than of others to furnish the same amount of calcium. Approximately equivalent quantities of some of the common forms when fairly pure are: C1 SUT ORS RA SE Se oe se ome ay Oa ee 56 pounds Orem rer at eS ek to ee 74 pounds Air-slaked lime, marl and ground limestone. . . .100 pounds Caustic lime, or the hydrate, when added to the soil, eventually assume some of the more insoluble forms of 352 THE PRINCIPLES OF SOIL MANAGEMENT combination or remain as the carbonate, never being present as the oxide. It is always desirable to have present in the soil at least a small amount of calcium carbonate. 222. Caustic lime.—Quicklime and water-slaked lime have a markedly alkaline reaction, and hence neutralize quickly any acidity that may exist in the soil. They act also quickly in liberating plant-food, particularly nitro- gen. Some soils respond more rapidly to quick- or water- slaked lime than to carbonate of lime, especially when the carbonate is in the form of marl or ground limestone, in which cases it is never in such a finely pulverized con- dition. The use of the caustic forms of lime has been said to result in the loss of nitrogen by the decomposition of organic compounds. Upon clays, the granulating effect of caustic lime is more marked than that of the carbonate, and for this reason the former has a distinct advantage for use on heavy clay. An occasional moderate dressing is, for the same reason,. better than a heavy dressing given less frequently. 223. Carbonate of lime.—Air-slaked lime has the advantage of being in a finely divided condition, and does not produce the injurious action upon organic matter attributed to caustic lime. Its effect upon the granulation of clay soils is probably less pronounced than that of caustic lime. Marl differs from air-slaked lime principally in its property of being in a less finely pulverized condition. It acts less quickly than does caustic lime. Owing to the fact that marl deposits differ greatly in the compo- FORMS OF LIME AND CROP. VALUE 353 sition of their products, it is well to know the quality of the material before purchasing it. The carbonate of lime in marl may vary from 5 or 10 to 90 or 95 per cent in different samples. Ground limestone has been used as a substitute for marl. It is very important that it be finely ground, as upon the comminution of the material much of its effi- ciency depends. As there was some question as to the value of ground limestone, experiments in which it was compared with caustic lime have been conducted at some of the experiment stations. These have, in the main, given results very favorable to finely ground lime- stone. Frear reports tests in which plats treated with slaked lime, at the rate of two tons per acre once in four years, were compared with plats treated with ground limestone, at the rate of two tons per acre every two years. The records, at the end of twenty years, show that in every case the total yields were greater on the plats receiving ground limestone. After the treatment on these plats had been continued for sixteen years, a determination of nitrogen showed the upper nine inches of soil on the limestone-treated plats to contain 2,979 pounds of nitro- gen per acre, and the slaked-lime plats to contain 2,604 pounds. It may be inferred from these figures that the slaked lime caused a greater destruction of organic matter than did the limestone. Patterson also conducted experiments for eleven years with caustic lime produced by burning both stone and shells, and the carbonate of lime in ground shells and shell marl. The average crops of maize, wheat Ww 354 THE PRINCIPLES OF SOIL MANAGEMENT and hay were all larger on the carbonate-of-lime treated plats. 224. Sulfate of lime.—Gypsum, in which form calcium sulfate is usually applied to soils, is effective in liberating potash, and possibly other substances, from the more difficultly soluble combinations. Its action in improving tilth is less marked than that of caustic lime, or of the carbonate. Whether it eventually contributes to the presence of carbonate of lime is a matter regarding which there is still a difference of opinion. It has the disadvantage of introducing into the soil an acid radical, which is removed by plants only in small amounts, and which tends to produce an acid condition of the soil. On the whole, gypsum is not an adequate substitute for, nor so desirable a form of, calcium as the oxide, hydroxide or carbonate. 225. Common salt.—Sodium chloride has a marked effect upon some soils, but wherein its effectiveness lies is not well understood. The addition of sodium and of chlorine as plant constituents is clearly not the reason, as these substances are always present in soils in avail- able form far in excess of their requirements. The effect of sodium chloride upon clay-bearing soils is to liberate certain plant nutrients, among which are calclum, magnesium, potassium, calcium and_ phos- phorus. This action, although limited in amount, is, in some cases at least, partly responsible for the bene- ficial action of common salt. The structure of the soil is improved by the applica- tion of sodium chloride, just as it is by lime,—although usually not to the same extent. OTHER SOIL AMENDMENTS 355 Another effect of salt is to conserve and distribute soil moisture. Its conserving action is probably due to an increase in the density of the soil-water solution re- tarding transpiration. The film movement of water is likewise increased by the presence of salt in the solution, and in this way the upward movement of bottom water is facilitated, and the supply within reach of the roots maintained in time of drought. It is not all soils, however, that are benefited by salt, its usefulness not being of such wide application as that of lime. Certain crops, as previously mentioned (page 340), are injured by the presence of chlorine. 226. Muck.—The effect of muck is to change the structure of soils; making heavy clay soils hghter and more porous, and binding together the particles of a sandy one. Both classes of soils, but particularly the sandy type, have a greater water-holding capacity after treatment with muck, owing to its great absorptive power, amounting to 70 per cent or more of its own weight. (See page 153.) It is to its content of organic matter that the physical effects of muck are due. Muck contains 1.0 to 2.0 per cent of organic nitrogen, calculated to dry matter which does not readily undergo ammonification. The addition of farm manure which ferments readily, and of lime, serves to hasten ammoni- fication. Its use as an absorbent in the stable fits it well for use on the land. Very large applications of muck are necessary when it is used to improve the structure of the soil. From ten to forty or fifty tons per acre are frequently applied. 356 THE PRINCIPLES OF SOIL MANAGEMENT 227. Factors affecting the efficiency of fertilizers.— The potentially available nutrients in a soil, whether natural or added in manures or fertilizers, are only in part utilized by plants, and the extent of their utilization depends upon the operation of certain limiting factors. This is a very important consideration in the manuring of land, for under conditions as they frequently exist the use of fertilizers is wasteful and extravagant. The factors within the control of man that effect the availability of fertilizing material are the following: (1) Soil moisture content. (2) Soil acidity. (3) Organie matter in the soil. (4) Structure or tilth of the soil. An undesirable condition of any one or more of these factors is a very common and apparent occurrence, and yet fertilizers are expected to produce profitable returns, in spite of these adverse conditions. It must be remem- bered that fertilizers are primarily only nutrient materials, and that the supply of nutrients is only one of the con- ditions that influence plant growth. Furthermore, an economical use of fertilizers requires that they merely supplement the natural supply in the soil, and that the latter should furnish the larger part of the soil material used by the crop. Finally, most fertilizers are ren- dered more or less difficultly soluble, or in some cases practically insoluble in pure water, by the absorptive properties of the soil, and the release of these sub- stances for plant use depends to a great extent upon the factors mentioned above. For instance, when a potassium fertilizer, as potas- sium sulfate or chloride, is placed in the soil, a consider- able portion of the potassium is (page 297) fixed by ab- EFFICIENCY OF FERTILIZERS 307 sorption as one of the bases in a poly-silicate, and thus held in a condition very sparingly soluble in pure water. Other reactions take place, and a portion of the potas- sium in some form is doubtless mechanically held by the soil particles. While this added potassium is more readily obtained by plants than that contained naturally in many soils, it must become available largely by the processes by which the natural supply is rendered soluble. Ammonium sulfate undergoes a somewhat similar pro- cess, while the nitrate of soda remains in a soluble form. It is evident, therefore, that the conditions which contribute to the natural fertility of the soil also apply to that added as fertilizers, with the possible exception of the nitrate. Phosphate fertilizers may be rendered practically insoluble in pure water, when added to the soil, and in the presence of a large amount of iron and aluminum it forms more or less ferric and aluminum phosphate, which becomes soluble very slowly, even under the action of soil-water and plant-roots. When converted into tricalcium phosphate, the phosphorus becomes soluble more readily; but, in any case, its rate of solu- bility depends upon those conditions which are most favorable to the solubility of the natural soil phosphates. It is generally recognized that a sandy soil responds more promptly to the application of fertilizers than does a clay soil. There may be two reasons for this: (1) Absorption may not be so complete both on account of the particles being larger, and because in many sandy soils the particles are largely composed of quartz, which does not have the property of forming combinations 358 THE PRINCIPLES OF SOIL MANAGEMENT with bases as does clay. (2) Drainage and aération are likely to be better, as are all those conditions that con- duce to solubility of plant-food. For these reasons, a sandy soil generally gives larger returns the first year from the application of manures, but shows less effect in subsequent years unless the treatment is repeated. Clay soils are, for these reasons, more likely to involve a wasteful use of fertilizers than are sandy soils, except in respect to loss of nitrogen in drainage, in which the sandy soil is more likely to be at fault, especially if there is no crop on the land. 228. Soil-moisture content.—Soils in a humid region commonly suffer from an excess of water in the spring, and a deficiency in the summer. Cereals and many other crops require the largest quantity of water at the time of heading and blossoming, and the largest production of crop can be secured only where the supply is adequate at that time. It is safe to say that in the great majority of cases crops raised, even in the humid region, suffer at some time from a deficient water-supply. On the other hand, it is well known that crops, almost without excep- tion, suffer either by lateness of planting, or by delayed early growth from an excess of moisture in the spring. A control of the soil-moisture supply should, there- fore, remove the excess of moisture in a time of large rainfall, and conserve it in time of drought. There are three means that may be employed to bring this about: (1) Drains, especially by means of tile. (2) Use of green manures or other organic matter. (3) Good tillage. (See page 190.) Viewed purely from the standpoint of soil fertility, EFFICIENCY OF FERTILIZERS 359 tile drainage does much to increase crop production, and to effect economy in the use of fertilizers. The rela- tion of soil drainage to soil fertility may be summarized as follows. (See, also, page 239.) (1) Aération provided by the removal of water ereatly facilitates nitrification. This relieves the con- stant necessity for the use of soluble nitrogen fertilizers, and makes it possible to rely largely upon the use of leguminous crops for nitrogen fertilization. Aération also renders the other fertilizing constituents of the soil more easily soluble. (2) By quickly removing the excess moisture in the early spring, and thus increasing the length of the grow- ing period, plants secure more nutriment, there is a cor- responding increase in the length of time in which nitri- fication can take place, also in other action brought about by aération. Available nitrogen thus produced at an early period in the crop growth is more effective than a later supply would be. (3) By removing an excess of water from the soil, a larger proportion of the available fertility, both natural and that added in manures, is absorbed by the crop. This is because the solution.is less dilute, and conse- quently a larger amount of mineral nutrients pass through the plant by transpiration. 229. Soil acidity.—An acid condition of the soil renders ineffective a large proportion of the fertilizing material that might otherwise be available. A good illustration of this is the comparison of the crops grown on acid soil when treated with lime with a similar soil not so treated. The size of the crop on contiguous plats 360 THE PRINCIPLES OF SOIL MANAGEMENT has been increased several hundred per cent by the use of lime at a number of the Experiment Stations. The amount of the acidity determines the injury it occasions. There is always a great waste of fertilizers when they are added to an acid soil. The acidity should be corrected by the application of lime, in order that manuring shall be most effective. There are several ways in which an acid condition of the soil operates to render ineffective the natural and applied fertility. (1) Bacteria which are concerned in the processes of rendering plant-food available do not usually thrive in an acid media, preferring a neutral or slightly alka- line condition. Acidity for this reason checks nitrifi- cation, as well as the bacteriological processes by which phosphorus is rendered soluble. (2) Bacteria concerned in the acquisition of atmos- pheric nitrogen in symbiosis with legumes are greatly injured by an acid condition of the soil. Nitrogen con- servation, one of the most important features of the use of legumes for green manuring, cannot be effectively carried out on an acid soil. (3) The liberation of potassium from zeolitic combi- nations is best effected only where there is a basicity that will permit the replacement of one base by another. The presence of at least a small amount of calcium car- bonate in the soil is essential for this, as it is for many other desirable processes, and an acid condition of the soil means that no basicity exists. (4) Lime, when present in large amount, reacts with the very insoluble phosphates of iron and alumina, EFFICIENCY OF FERTILIZERS 361 and by producing phosphate of lime, renders the phos- phoric acid more available for the plant. 230. Organic matter.—The ways in which organic matter contributes to economy in the use of fertilizers are: (1) By improving the soil structure. (2) By con- serving moisture. (3) By producing through decompo- sition carbon dioxide which, dissolved in water, is a weak but continuously acting solvent of the mineral fertilizers; also by forming organic acids that act in a similar way. (4) It furnishes a source of food and energy for bacteria, which aid in rendering soluble the absorbed fertilizing constituents. It is particularly in rendering available to plants the more difficultly soluble phosphate fertilizers that organic matter directly aids in making fertilizers more effective. Farm manure is undoubtedly the best all-round ferti- lizer to be had. In addition to adding organic matter and certain mineral plant-food materials, it introduces into the soil, and furnishes a favorable medium for the growth of large numbers of bacteria that are of great value in rendering available the plant nutrients contained in soils. The use of raw or untreated phosphates to replace superphosphates in soil manuring has received much attention in Germany and to some extent in this country in recent years. Raw phosphates, being much more difficultly soluble than the superphosphates, do not, under most conditions of the soil, give as marked returns. On the other hand, the raw phosphate has the advantage of being very much cheaper, and of not con- taining sulfuric acid. The extent to which raw phosphates will become available in the soil depends largely on the 362 THE PRINCIPLES OF SOIL MANAGEMENT extent of decomposition of organic matter. A soil poor in humus, and which has not been treated with farm manure or green manure, is not likely to respond very strongly to an application of raw phosphate. The fact that superphosphate is available under these conditions is likely to lead to its use without any attempt to im- prove the humus-content of the soil, and thus increase those difficulties that arise from a deficiency of organic matter. It is this condition that makes it necessary to constantly increase the dressings of fertilizer in order to maintain productiveness. Experiments by Thorne have shown that the use of farm manure in conjunction with raw phosphates serves to increase greatly the availability of the latter. In these experiments stall manure was used at the rate of eight tons per acre, in one case alone, and in another in connection with 320 pounds of rock phosphate. The manures were applied to clover sod, and plowed under for maize in a rotation of corn, wheat and clover. In the following table, average yields from the manured plats and from the unmanured ones are given. TABLE L EFFECT OF STALL MANURE ON AVAILABILITY OF Rock PHOSPHATE Average Average Average yieldeleven| yield yield crops ten crops |seven crops maize wheat ay Bushels Bushels Tons Stall manure, 8 tons per acre....... 57.7 20.3 1.6 Stall manure, 8 tons per acre and rock phosphate, 320 pounds per PERS soot it sa: Weeds hr aba eee hee 64.0 25.6 2. ; 1 EFFICIENCY OF FERTILIZERS 363 It will be seen from this table that the combination of stall manure and rock phosphate produced larger crops than did the same quantity of stall manure alone; from which it may be fairly concluded that, under these conditions, the raw phosphate becomes available to an extent sufficient to make its use practical. Whether raw phosphate can be used without supplementing them with superphosphate will depend upon the natural fertility of the soil and the amount of decomposing organic matter it contains. 231. Structure or tilth of the soil.—Tillage aids the plant in several ways to obtain nutrients from ferti- lizers added to the soil: (1) By promoting aération. (2) By permitting the plant-roots to come in contact with a large area of soil. (3) By conserving moisture in time of drought. 232. Cumulative need for fertilizers.—It is often remarked that on fertilized soils there is a gradually increasing need for greater quantities of fertilizers. This is doubtless the case in many instances, and arises from neglect of other factors affecting soil productive- ness. As we have seen, certain fertilizers induce a loss of limefrom the soil, which, if allowed to continue, ~equires an increased amount of fertilizer to maintain the yield of crops. Organic matter is allowed to decrease and this, as well as loss of lime, causes the soil to become compact and poorly aérated, and so, one bad condition leading to another, crops become poorer in spite of ores applications of fertilizer. 233. Farm manures.—The original components of farm manure are the solid excreta from the animal, the 364 THE PRINCIPLES OF SOIL MANAGEMENT urine, usually from the same animal or animals, and the litter used as bedding and also for the purpose of absorb- ing the liquid manure and to render the whole easier to handle. As these constituents differ greatly in their physical and chemical properties, the proportions in which they exist affect appreciably the properties of the manure. nel aanibainenneanannit anaasnmemndnes steemeeseiemaentmaaiieeeeasemanteeeeeeeaa 7 — qs saree —— * - ey c z san * a fi 2 EX ae ar ao : sexe aa il SPITS: hee ° 4 9 Hine bets 2 Fic. 106. A striking example of waste of manure. Leaching and fermentation will remove over half of its value in six months. 234. Solid excreta.—The solid excreta furnishes most of the body of the manure, and as it is already in a stage of partial decomposition, and in a condition both physi- cally and chemically to favor the further processes of decomposition, it is largely to this constituent that the fermentative action of manure is due. It is particularly valuable for the effect it has upon the physical condition of the soil and. the encouragement it gives to decompo- sitlon processes. Chemically, it is not so valuable as the liquid excreta. FARM MANURES 365 It represents, in part, the food materials that have passed undigested through the alimentary canal, and also the secretions this has received on the way, and these substances are not all held in a soluble form, as are those in the urine. Stoeckhardt states the composition of the solid excreta of different farm animals to be as follows: TaBLe Lil | Composition of dry matter Water Nitro- gen Alkalies os- phorie acid Per cent | Per cent | Per cent | Per cent Eigiece (winter 100d) .......... 76 2.08 1.45 {25 Cows (winter food) ............ 84 1.87 1.56 0.62 Swine (winter food)............ 80 3.00 2.20 2.50 Sheep (two pounds hay per day).| 58 1.78 1.42 0.71 Calculated to 1,000 pounds of solid excrement, these figures show the following number of pounds of each constituent. TaBLE LII Ey pies Water eg phoric Alkalies Pounds | Pounds | Pounds | Pounds MERIT tatty ae bk aie oe as foo iB 3.5 3.0 DUET OEM ae Bas SO i vis y 840 ow 2.0 1.0 LM leapt RRL ee Es i ar 800 6.0 4.5 5.0 eR gh Rte SIs See’ oS Bae PD 6.0 3.0 The smaller percentage of water in the sheep excre- ment makes it, pound for pound, the richest of any. Next 366 THE PRINCIPLES OF SOIL MANAGEMENT to it stands hog excrement, and cow excrement is the poorest in fertilizing materials. 235. Urine.—The urine represents a portion of the food which has been digested by the animal and excreted as a waste product through the kidneys. The proportion of the nitrogen and mineral matter retained by the tis- sues depends upon the age of the animal and upon the nature of the food. An animal receiving a large amount of easily digestible nitrogenous food excretes more nitro- gen in the urine than a poorly fed animal. The composition of urine, as given by Stoeckhardt is as follows: Taste LITt Composition of dry 2 matter Water : Phos- Nibror phoric | Alkalies g acid Per cent | Per cent | Per cent | Per cent Horse (hay and:oats) .< 2.04.42. 89.0 10.9 trace Cow (hay and potatoes)........ 92.0 10.0 | trace | 17.5 Swine (winter food)............ 97.5 12.0 5.0 8.0 Sheep (two pounds hay per day) .| 86.5 10.4 3.7 14.9 These figures show the following number of pounds of each constituent in 1,000 pounds of urine. TaBLEeE LIV : Phos- Water N i phoric | Alkalies g aci Pounds | Pounds | Pounds sis aries 1 | TT oT an eee CYP eR RE erie ty Ne ot 890 12 CW ee. ee CR OU Re at ae 920 8 eee 14 SNP AaRe” 8 sks gt as Cand we Blots tees 975 3 1.25 2 SECEGD es: & pounce Ron tins ina eed bation one 865 14 0.50 20 COMPOSITION OF ANIMAL MANURES 367 The liquid excreta of the sheep contains in a given quantity more fertilizing material than that of any of the other animals. Comparing the solid and liquid excreta of these animals as a whole, it will be seen that, in general, the urine is richest in nitrogen and alkalies, while the solid excrement is richest in phosphoric acid. The amount and composition of the urine is more constant than that of the solid excrement. Both are influenced by the character and amount of feed, but the urine much less so than the solid excrement. Experi- ments conducted at the Rothamsted Experiment Sta- tion have shown that from 57 to 79 per cent of the total nitrogen of the food is excreted in the urine, and from 16 to 22 per cent in the solid excrement. 236. Litter—The use of a bulky absorbent, lke straw, sawdust or leaves, is almost universal where live stock are kept in a stable. This is useful in providing a soft bed for the animal, in absorbing the liquid excre- ment, in lightening the manure, making it easier to handle, less likely to undergo undesirable fermentation, and more effective in improving the physical condition of heavy soils. Straw is the absorbent usually used, and is, all things considered, the most satisfactory. It decomposes readily in most soils and, in decomposing, adds to the soil considerable fertilizing material. Of the different kinds of straw, oat straw has the greatest fertilizing value. A ton of oat straw contains about 16 pounds nitrogen, 4 pounds phosphoric acid, 26 pounds of potash, and 9 pounds of lime. As this is more nitrogen and 368 THE PRINCIPLES OF SOIL MANAGEMENT potash than is contained in a ton of average manure, the use of this absorbent increases the fertilizing value of the manure. It is, however, undesirable on some soils to have a very large proportion of straw, on account of its effect in retarding decomposition. Sawdust and shavings are sometimes used, but, while they are good absorbents, they decompose very slowly in the soil, making them objectionable on light soils, and they have practically no plant-food materials. Dry leaves absorb well, and decompose satisfactorily in the soil. They do not add much fertility. 237. Manures produced by different animals.—There is a great difference in the amount and value of manure produced by different kinds of live stock. This is due to a number of causes, among which are the size of the animal, the nature of its food, and the mechanical con- dition in which the digestive processes leave the solid excrement. The differences affect not only the amount of fertilizing constituents in the manures, but, what is of more importance, they determine the nature and rapidity of the decomposition processes, and hence affect the loss of manurial substances and the value of the manure as a fermentive agent in the soil. 238. Horse manure.—A well-fed, moderately worked horse will produce from 45 to 55 pounds of excrement per day, of which from 12 to 15 pounds consists of urine. The straw used for bedding will amount to from 4 to 6 pounds. Roberts has computed the value of the excre- ment to be nearly one-half the cost of the food, while from Wolff’s tables, based on a large number of determi- nations in Europe, the combined solid and liquid excreta COMPOSITION OF ANIMAL MANURES 369 contains the following average percentages of the organic matter, nitrogen and mineral substances originally present in the food consumed: Per cent DS rer FAVE ost sh pwr oie a's 6 Seen, WN aie sale 33.90 IARI a weck nk NOR SARS Piet sinh oll cm nigh ian eller dere 39.50 WUIIGUM PIL DSURMICE eid 2 Una e ac bar's ihe Aas eee. & 56.25 In Robert’s calculations, the value of the manure is based entirely upon its content of nitrogen, phosphoric acid and potash, valued at 15 cents, 7 cents and 4.5 cents, respectively. It is difficult to get a true idea of the value of animal manure, as its content of fertilizing substances is only a part of its manurial value, of which its physical and bacteriological effects upon the soil are extremely important. ' Horse manure has the fibrous matter of the food less well broken down than has cow manure, and this, with its lower water content, produces a light, easily ferment- able substance that readily loses its nitrogen, which passes off as ammonium carbonate. The dry fermen- tation, indicated by a whitish appearance of the interior of the manure heap and a slight smoke, is the cause of this loss. The values calculated for the excrement are never realized in practice because of the losses that occur between the stable and the field. To preserve horse manure to the best advantage, it should be mixed with cow manure,—the wet, compact character of which lessens the amount of fermentation by changing the physical condition of the manure. 239. Cow manure.—A mature cow, given good feed, will produce from 60 to 90 pounds of excrement daily, x 370 THE PRINCIPLES OF SOIL MANAGEMENT depending upon the weight of the animal. Of this 20 to 35 pounds is likely to be urine. Even the solid excreta contains a large percentage of water, and, accord- ing to Boussingault, only about one-eighth of the total excreta is dry matter. The very watery nature of cow excreta causes it to require a large amount of litter. In spite of the lighten- ing effect of the litter, it decomposes slowly as compared with other manures. When applied alone to the soil, action is slow, but it is prolonged over a considerable number of years. The loss of ammonia in the decomposition processes is much less than with horse manure. The admixture of other manures adds much to the rapidity of fermen- tation and to the ease of handling. The percentage of organic matter, nitrogen and min- eral substances contained in the food of cattle that appear ultimately in the excrements are as follows: Per cent (Batre VL ita: eee ee ae ae ee en Oem e bene 27 PY OTL 9 Oooo ess wv ods whe eer aia 42 PUG A TIMEUOL oc 2. chs Dccu ac aye iale atiia oo aLaarcaey eee 50 This corresponds fairly well with the percentage for horse manure, and would justify the belief that the value of the manure would hold about the same ratio to that of the food as in the case of the horse. 240. Swine manure.—The quantity of excrement voided by swine varies greatly even for mature animals, the amounts per 1,000 pounds live weight varying from less than 50 to more than 100 pounds per day. A more concentrated ration produces less excreta, but causes COMPOSITION OF ANIMAL MANURES ort it to be much richer in fertilizing ingredients. Roberts calculated the value of the manure produced in one year by a 150-pound pig fed on a highly nitrogenous ration to be $3.24, and that of a pig of similar weight fed on a carbonaceous ration to be $1.84 for the same period. The manure of swine is wet, but not quite so much so as cow manure. According to Boussingault, about one- sixth of the solid excrement is dry matter. It decomposes slowly. As the urine contains by far the larger part of the nitrogen, it should be saved. 241. Sheep manure.—The total amount of excre- ments voided by mature sheep is from 30 to 40 pounds per 1,000 pounds of live weight, of which about one- fourth is dry matter. Although drier than horse manure and generally richer in nitrogen it is less likely to lose that constituent by fermentation, as the compact nature of the solid excreta is not so favorable to rapid decom- position as is the physical structure of horse manure. It is however, when placed in the soil, a readily acting manure and is frequently used by gardeners for that reason. To obtain the best results, it should be mixed with horse and cow manure. 242. Relative values of animal manures.—Extensive experiments conducted by Roberts, Wing and Cava- naugh at Cornell University Experiment Station, with sev- eral different kinds of animals fed on the common Ameri- can feeds, but perhaps in somewhat heavier rations than the average, and kept under normal conditions, may well be taken to show the relative values of animal manures, although the absolute values may be somewhat above 372 THE PRINCIPLES OF SOIL MANAGEMENT the average. In calculating the values of the manures produced by these animals, nitrogen is reckoned at fifteen cents per pound, phosphoric acid at six cents, and potash at four and one-half cents. The composition, amount and value of the manures without litter are given in the following table. TaBLE LV CoMPOSITION, AMOUNT AND VALUE OF MANURES (WITHOUT LITTER) FROM DIFFERENT ANIMALS Pounds ingredi- Production Percentage compo- ents per ton ig per 1,000 sition mate s aes Kinds of ® live stock 3 : 5 : e di $|s)20/ 9 | 8 |2e| 414 /E8) 38 Sos pee!) S | Beate ie ‘ e a ON ial es aa] Pg Horses . 48.70} 0.49 | 0.26 | 0.48 | 9.00) 5.20 9.60/$2.21 48.8 $27.74 Come aici; 75.25} 0.43 | 0.29 | 0.44 | 8.60) 5.80 | 8.80; 2.02 74.1 | 29.27 Calves .... |77.73) 0.50 | 0.17 | 0.53 |10.00) 3.40 |10.60} 2.18 67.8} 24.45 SWite. 2 74.13] 0.84 | 0.39 | 0.32 16.80] 7.80} 6.40} 3.29 83.6} 60.88 Sheep..... 59.52) 0.77 | ... | 0.59 {15.40} 7.60 deca 3.30 34.1 | 26.09 243. Poultry manure.—The droppings of poultry are nearly twice as valuable, pound for pound, as cow manure, when calculated on the value of the nitrogen, phosphoric acid and potash they contain. It is in the former constituent particularly that poultry manure is rich. A thousand pounds live weight of fowls produce from thirty to forty pounds of droppings daily. These contain when fresh between 50 and 60 per cent of water and over 1 per cent of nitrogen. The nitrogen is largely present as ammonium compounds. It quickly undergoes fermentation, with loss of nitrogen. Lime or alkalies COMPOSITION OF ANIMAL MANURES Ode decompose the ammonium compounds ‘with liberation and loss of free ammonia. _An absorbent, such as land plaster, superphosphate, kainit or dry earth will greatly lessen the loss of nitrogen. Mixing it with other manures is also advisable. When applied to the soil, poultry manure decom- poses rapidly, and is used by market gardeners on account of its rapid action. : 244. Factors affecting the values of farm manures.— The value of animal excrements for manurial purposes depends upon a number of factors, among which are: (1) The relative proportions of solid excrement and urine. (2) The species of animal producing the manure. (3) The age of the animal. (4) The character of the food the animal receives. (5) The use to which the animal is being put. In addition to the factors affecting the excrement, the manure may always be modified by the litter or other absorbent added, and by the method of handling. The effects of solid and liquid excreta, and of the species of animal, have already been discussed. 245. Age of animal.—A young and growing animal requires more nitrogen and phosphoric acid to build bone and muscle than does an animal that has completed its growth. This is taken from the food, and not excreted in the urine or other excretory products, and hence does not appear in the manure. 246. Food of the animal.—Since the large part of the nitrogen phosphorus and potassium contained in the food is contained in either the solid or liquid excrement, it follows that the richer the food in these constituents 374 THE PRINCIPLES OF SOIL MANAGEMENT the more of them the manure will contain. A highly carbonaceous ration produces a poor manure largely because it is low in nitrogen. The manurial value of a food-stuff is generally increased by passing through the animal, provided it can largely be recovered, because the digestion process leaves it in a condition more favor- able to decomposition and to thorough mixing with the soil. 247. Use of the animal.—The amounts of the ferti- lizing constituents recovered in the excrement vary to some extent with the use that is being made of the ani- mal. Animals that are being fattened, or that are pro- ducing milk, divert a portion of the fertilizing constit- uents to their products. Experiments by Laws and Gil- bert with different classes of animals used for different purposes show the following disposition of some of the constituents of the food. As the excrements include the perspiration, the small amount of matter passing off in that form is, of course, not recovered in the manure. TaBLE LVI Nitrogen Mineral matter Contained | Contained Contained | Contained in in in in product | excrement, product | excrement Per cent Per cent Per cent Per cent Borie ah Tesh ons... ks eae None 100.0 None 100.0 Hore ab. work 5. a ees None 100.0 None 100.0 Teri CORI 2 aaa sm, a 24.5 75.0 10.3 89.7 Fattening oxen ......... 3.9 96.1 2.3 97.7 Fattening pigs: .......... 14.7 85.3 4.0 96.0 Fattening sheep ......... 4.3 95.7 3.8 96.2 DETERIORATION OF MANURE 375 It will be seen from these experiments that milch cows divert more of the fertilizing constituents from the manure than do any other class of animal, that fattening pigs divert much more of the nitrogen than do cattle or sheep similarly employed, and that the work of the horse does not affect the composition of the manure. 248. Deterioration of farm manure.—There is always a loss in the value of farm manure on standing. The two processes most operative in bringing this change about are: (1) Fermentation. (2) Leaching. The first of these is a natural process, common to all farm manure, and not occasioned by any outside agencies; the second is due to the running off of the liquid portion of the manure, and to the exposure of the manure to rain. 249. Fermentations.—The fermentations occurring in heaps of farm manure are produced both by aérobic and anaérobic bacteria, that is, by bacteria requiring oxygen for their activity, and by those that do not. The fermentations of the outside of the heap are constantly different from those on the interior, where air does not readily penetrate; but, as fresh manure is thrown upon the pile from day to day, most of the manure first under- goes aérobic fermentation before the anaérobic bacteria begin their work. It is through the action of bacteria on the nitrogen- ous compounds of the manure that loss of value through fermentations occurs. The action of the aérobic bacteria is to convert the nitrogen of the organic matter into ammonia, which, owing to the large formation of carbon dioxid, is partly converted into ammonium carbonate. Both of these substances being volatile, there is danger 376 THE PRINCIPLES OF SOIL MANAGEMENT of their passing off from the heap into the air. The drier the heap, the more apt these substances are to escape. The production of ammonia is very rapid from some of the compounds in farm manure. Urea, in which form the nitrogen of urine is largely found, undergoes con- version into ammonia very rapidly, and some loss in ~ this way is inevitable even under the best management. Chemically the process is a simple one, which may be represented by the following equation: CON,H,+H,0=2 NH,+C0,,. 2 NH, +CO,+H,0=(NH,), CO,. The use of certain preservatives makes it possible to decrease the loss of ammonia from manure. The preservatives are intended to convert the ammonia into a less volatile compound. For this purpose gypsum, kainit, superphosphates and ground phosphate rock are used. The action of gypsum, for instance, in the manure, is to convert ammonia or ammonium carbonate into the form of ammonium sulfate, which is not volatile. The reaction is as follows: (NH,), CO, +CaSO, = (NH,),8O,+CaCoO,. It is customary to sprinkle the preservative in the stall of the animal, where it comes in contact with the excreta aS soon as they are voided. Salts of calcium other than the sulfate, cannot be used, on account of their action in decomposing ammonium salts. The decomposition of proteins forming, among other products, hydrogen sulphide, which becomes oxidized to sulfuric acid, causes a part of the ammonia to natu- WASTE OF MANURE BY LEACHING Der rally take the form of a sulfate, which protects this por- tion from volatilization. The other fermentation resulting in the loss of nitro- gen is due to the action of certain anaérobic bacteria that convert ammonium salts into free nitrogen. Certain of these organisms are able to reduce nitrates to nitrites, and the latter to ammonia, but the greatest loss is doubt- less due to the ammonium salts formed directly from proteins. This process occurs only in the poorly aérated portions of the heap. There does not appear to be as ereat loss of nitrogen through the action of the anaerobic ferments as through the loss of ammonia, which makes it advisable, in practice, to keep the manure heap as compact as possible, and to prevent the heap from be- coming very dry by the application of water in amounts sufficient to keep the heap moderately moist without leaching it. In the arid and semi-arid parts of the coun- try, this is an important precaution to be taken in the preservation of farm manure. 250. Leaching.—When water is allowed to soak through a manure heap and to drain away from it, there is carried off in solution and in suspension a certain quantity of organic and inorganic compounds contain- ing nitrogen as urea, other organic nitrogen in small amounts, ammonium salts and nitrates, some phos- phorus and considerable potassium, with other mineral substances of less importance. The amount of loss to the manure in this way may be very great; and, without doubt, in the humid portions of the country leaching is the greatest source of loss. Protection of manure from the rain is therefore very important. 378 THE PRINCIPLES OF SOIL MANAGEMENT Experiments conaicted by Roberts serve to show the rate and extent of deterioration of manure in a region having a rainfall of about twenty-eight inches in the six months from spring until autumn, during which period the tests were made. The loss arising from fermentation and leaching combined was determined in these experi- ments. Horse manure was lightly packed in a wooden box, not water-tight, surrounded with manure, and left exposed to the weather from March 30 to September 30. Analyses made at the beginning of and at the end of the experiment showed the following: TABLE LVII April 25 September 30 Loss Pounds Pounds Per cent (ares: Weight. 2.2 ec cake oat 4,000.00 1,730.00 57 LAUT Sage Daa ea 19.60 7.79 60. Prospnore atid .. 002.555... 14.80 7.79 47 POSE tay a oee Ree: 36.00 8.65 © 76 At the same time, cow manure was similarly treated, except that 300 pounds of gypsum were mixed with it. This, doubtless, protected some of the nitrogen, and the greater body of material would also decrease loss of all constituents. TABLE LVIII April 25 September 30 Loss Pounds Pounds Per cent isroa weight 2) 020. bn. 10,000 5,125 Dito <5 leieediniee Kee 47 28 41 PROSpNGTIC-BOI 2c. 3.5 cis oe x 32 26 19 Potee Cat eee ea) eee 48 44 8 HANDLING MANURE 379 The greater loss suffered by the horse manure was doubtless due in part to the more rapid fermentation accompanied by volatilization of ammonia, and to its less compact nature making it more permeable to the rain water. Roberts also reports an experiment in which a block of undisturbed manure one foot deep, consisting of both horse and cow excrement mixed with straw and solidly packed by trampling of animals in a covered shed, was exposed from March 31 to September 30 in a gal- vanized iron pan with perforated bottom. The losses were as follows: Loss Per cent ree sri hei ids cela. «oven acai § Bhd 3.2 ame TELS CAO ie aie see ht ae ae phe nhs ena! sl oo. abt 4.7 PPA MES CI Lore tate a Mi A cee aise anh, «te Wi RM eee ee seine RO see 5 39.0 This shows a great saving to both kinds of manure when they are mixed and tramped. The enormous difference in the nitrogen lost, without a corresponding difference in the loss of potash, indicates that the volatili- zation of ammonia, which is greatly reduced by com- pacting, is responsible for a very large share in the deterioration of manure, even in a humid climate. 251. Methods of handling.—The least opportunity tor deterioration of farm manure occurs when it is hauled directly to the field from the stall and spread at once. This is not always possible, and manure must be stored on every farm for longer or shorter periods. In holding manure, the two important conditions are, a sufficient, but not excessive supply of moisture, and a well-com- pacted mass. Water draining away from a manure heap, 380 THE PRINCIPLES OF SOIL MANAGEMENT and a fermentation producing a white appearance of the ‘manure under the surface of the pile (‘fire fanging’’), are both sure indications of unnecessary loss in its ferti- lizing value. : Composting farm manure increases the availability of its fertilizing constituents; but, even when carefully conducted, is accompanied by some loss of nitrogen. The total amount of organic matter is decreased by reason of the decomposition, in which process carbon dioxid and water are formed, part of which escapes, and part remains in the manure. The mineral constituents increase percentagely, due to the loss of organic matter; and the water increases for the same reason, and because it is sometimes added to the compost. The mineral con- stituents are not materially changed in their solubility, but the organic matter becomes more soluble. The nitrogen, after conversion into ammonium salts, is oxidized finally into nitrates, but only in small amounts, and after considerable time. The beneficial effects of composing are only in small part due to the chemical changes in the manure, but chiefly to the good physical condition of the composted material, and to the fact that the operations preliminary to the formation of nitrates have largely been effected in the compost, and when applied to the soil nitrification is rapid. Composting manure with soil, sod, muck or other absorbent material increases the manurial value of the latter by increasing its decay, and therefore its availability, and by reducing loss by leaching. The following analyses, by Voelcker, show the com- position of fresh and rotted farm manure: HANDLING MANURE 381 TaBLe LIX Fresh Rotted NRE al Ot ace hare eg oe eee See 66.17 75.42 Saluble oreanic matter. 22.0) ood. eo 2.48 3.71 DUP OPS ATIC TACO SOI io ine wich pints ayes nn inh 0.15 0.30 Saluble inorganic MALbEr Ws. ...6 ua We. . aes 1.54 1.47 Insoluble organic matter ......... cet eee y 25.76 12.82 Insoluble inorganic matter ................. 4.05 6.58 In applying farm manure to the field, it is customary either to throw it from the wagon into small heaps, from which it is distributed later, or to scatter it as evenly as possible immediately on hauling it to the field. The use of the automatic manure spreader accomplished the latter procedure in an admirable manner. As be- tween these two methods, the advantage, so far asthe conservation of the manurial value is concerned, is with the practice of spreading immediately. When piled in small heaps, fermentation goes on under conditions that cannot be controlled, and that may be very unfavor- able. The heaps may dry out, and thus lose much of their nitrogen; or they are likely to leave the field un- evenly fertilized by leaching into the soil directly under and adjacent to the heap. On the other hand, when spread immediately, little fermentation takes place, as the temperature is generally low and the soluble compounds are leached quite uniformly into the soil. Plowing should follow as closely as possible the spread- ing of the manure, and, except in winter, at which time deterioration is not likely to be great, this can well be done. 382 THE PRINCIPLES OF SOIL MANAGEMENT The amounts and frequency with which farm manure should be applied must depend, to some extent, upon the nature of the farming and upon the character of the soil. Farm manure tends to render all soils more porous and Fic. 107. The wrong way to distribute manure. There is large loss by decay and an uneven growth of crop. light. A naturally light soil may be rendered less pro- ductive by the application of heavy dressings of manure; particularly in a dry climate is this the case. In regions where so-called “‘dry farming”’ is practiced, the return of organic matter to the soil is a great problem, on account of the difficulty in accomplishing its decay PLACE FOR MANURE 383 when plowed under. Composting, or plowing under after it has been applied to sod for several months, or incorpo- rating with a green manure, are methods that must be used with ‘dry farming.”’ Even on heavy soils in a humid region, there is an advantage in applying small dressings of farm manure frequently, rather than large amounts at long intervals. Organic matter decomposes more rapidly when present in the soil in relatively small amounts, and its influence on the solubility of plant nutrients is therefore greater in proportion to the amount of manure used. There can be no doubt that the bacterial flora introduced into the soil by the incorporation of farm manure is an important factor in its usefulness, and when this occurs at frequent intervals it has a marked effect on productiveness. Applications of ten tons to the acre are better than twenty tons at twice the interval. 252. Place in crop rotation.—When a crop rotation includes grass or clover as one of the courses, the appli- cation of farm manure may well be made at that time as a top-dressing. The spreading can be done at times when cultivated land would not be accessible, and the crop of hay will profit greatly. The sod, when plowed, is frequently planted to corn—a crop that is rarely injured by farm manure. On light, dry soils this practice is of advantage, as already explained. Most cultivated crops, with the exception of tobacco, and occasionally sugar-beets, are much benefited by farm manure. Small grains are usually benefited when grown on poer, heavy soils with plenty of rainfall; but in a dry region farm manure should not be applied 384 THE PRINCIPLES OF SOIL MANAGEMENT for these crops, and on rich soils manure is likely to cause small grain to lodge. Farm manure, in judicious amounts, may be plowed under in orchards to great advantage. 253. Functions.—The useful function which farm manures perform in the soil are as follows: (1) To improve the physical condition of the soil by the intro- duction of organic matter, with its favorable influence - on the structure and moisture content. (See page 129.) (2) To add acertain quantity of plant-food in a compara- tively readily available condition. (8) To introduce a new bacterial flora capable of increasing the rapidity of decomposition of organic matter, and of thereby in- creasing the amount of available fertility. 254. Green Manures.—Crops that are grown only for the purpose of being plowed under to improve the soil are called green manures. They may benefit the soil in one or all of four ways: (1) By utilizing soluble plant- food that would otherwise escape from the soil. (2) By incorporating vegetable matter with the soil. (3) Le- guminous crops, when used, add to the nitrogen content -of the soil through the fixation of atmospheric nitrogen. (4) Plant-food from the lower soil may be brought to the surface soil. A large number of crops may be used for this purpose, but certain ones are more useful than others, while the climate determines to some extent which crops should be used. Leguminous crops have the great advantage of acquiring nitrogen from the air. Crops that can be planted in the fall and grow during the cool weather can be utilized when otherwise the land would frequently GREEN MANURES 385 lie bare. Deep-rooted crops usually accumulate a large amount of nutriment from the soil, and considerable from the lower depths. They are therefore useful in bringing plant-food to the upper layer of soil. Succulent crops decompose easily, and dry out the soil less, when plowed under, than do woody crops. Crops with exten- Sive root-systems prevent loss of soluble matter more thoroughly than do plants with small roots. 255. Leguminous crops.—A soil that has become less productive under cultivation, and that must be improved before profitable crops can be grown, receives more benefit from the use of leguminous crops than any other. The legume to use is naturally the one best adapted to the region in which the soil is located. Red clover, mammoth clover and field peas on the soils to which they are adapted in the northern states; alsike clover in the wet soils of that region; cowpeas and crim- son clover in the South, and alfalfa, clovers, soy beans and cow peas in the West, are the principal leguminous green-manuring crops. More recently a positive effort has been made in certain northern states to grow sweet clover (Melilotus alba), which is a vigorous wild legume, as a green manure crop. Marked success has followed its use, but, like alfalfa and the clovers, it requires a soil well stocked with lime. The legumes have the important property of securing nitrogen from the air, which is added to the soil from the decomposition of the tops and roots when the crop is plowed under. The nitrogen contained in a ton of the green crop, when in a condition to plow under, is as follows: Y 386 THE PRINCIPLES OF SOIL MANAGEMENT TABLE LX : Probable . Nitrogen yield per Nitrogen per ton aura per acre Pounds Tons Pounds 10 6 Red or mammoth clover........... 6 0 SRAM ONIVER A mh oa Ged of a ee 9 6 54 ile Cum PT eh eS Co ure 10 5 50 RRUMEN ossisor GE ra ictal cae! side cant gi waate 14 8 112 LNOMEMMAD a Vay eee eee ak woe She oe 8 6 48 BOW SAME ei os tana ee Den 10 6 60 WIEN RAE Bi ook bal whet Gon ecd 11 5 55 Not all of the nitrogen contained in these crops is taken from the air. On soils rich in nitrogen, a consider- able proportion may be obtained from the soil. On poor soils, the proportion derived from the atmosphere is considerably larger. The soils needing the nitrogen most are those that benefit most largely. As the legumes need other fertilizing material in an available form to produce a good yield, mineral ferti- lizers or farm manure should be added to the soil. Especially on run-down land this treatment is profitable. The crops should be plowed under while green and succulent, as they decompose most readily at that stage. On sandy soils and in dry regions, the soil may be rendered so porous by plowing under a crop of dry vegetation that the capillary rise of water is greatly decreased, and the movement of air through the soil causes it to become very dry. The perennial clovers (red, mammoth and _ alsike) and alfalfa do not make a rapid growth after seeding, which is a disadvantage when quick results are desired, COVER CROPS AND GREEN MANURE 387 as on a badly run-down soil. Crimson clover is an annual, and in the central and southern states may be sown in the fall and plowed under in the late spring, thus making use of a period of the year when the soil is most likely to be unoccupied by a crop. Cowpeas, soy-beans and field peas must be grown during the summer months. Vetch promises to be a useful green manure for winter growth in the northern states. 256. Cereal crops.—Where it is desired to keep a crop on the soil during the autumn, winter and spring, for the purpose of utilizing the soluble plant-food, the cereals, especially rye, are useful. Rye has the advan- tage of being an inexpensive crop to seed, besides being very hardy, and capable of growing on poor soil. It furnishes fall pasture, but should not be pastured in the spring if intended for green manure. It is important that it be plowed under while green. Buckwheat, on account of its ability to grow on poor soil, is adapted to use as a green manure, but it must be grown in the summer. D. ORGANISMS IN THE SOIL A vast number of organisms, animal and vegetable, live in the soil. By far the greater part of these belong to plant life, and these comprise the forms of greatest effect in producing those changes in structure and composition which contribute to soil productiveness. Most of the organisms are so minute as to be seen only by the aid of the microscope, while a much smaller proportion range from these to the size of the larger rodents. They may thus be classed as macro-organ- isms and micro-organisms. I. MACRO-ORGANISMS OF THE SOIL Of the macro-organisms in the soil the animal forms belong chiefly to (1) rodents, (2) worms, (3) insects; and the plant forms to (1) the large fungi and (2) plant roots. 257. Rodents.—The burrowing habits of rodents, of which the ground-squirrel, mole, gopher and prairie- dog are familiar examples, result in the pulverization and transfer of very considerable quantities of soil. While their activities are often not favorable to agri- culture, the effect upon the character of the soil is quite beneficial, and analogous to that of good tillage. Their burrows also serve to aérate and drain the soil, and in permanent pastures and meadows are of much value in this way. (388) SOIL MICRO-ORGANISMS 389 258. Worms.—The common earthworm is the most conspicuous example of the benefit that may accrue from this form of life. Darwin, eas the result of care- ful measurements, states that the amount of soil passed through these creatures may, in a favorable soil in a humid climate, amount to ten tons of dry earth per acre annually. The earthworm obtains its nourishment from the organic matter of the soil, but takes into its alimentary canal the inorganic matter as well, expelling the latter in the form of casts after it has passed entirely through the body. The ejected material is to some extent disintegrated, and is in a flocculated condition. The holes left in the soil serve to increase aération’and drainage, and the movements of the worms bring about a notable transportation of lower soil to the surface, which aids still more in effecting aération. Darwin’s studies led him to state that from one-tenth to two-tenths of an inch of soil is brought to the surface of land in which earthworms exist in normal numbers. Instances are on record of land flooded for a con- siderable period so that the worms were destroyed, and the productiveness of the soil was seriously impaired until it was restocked with earth-worms. Wollny conducted experiments with soil, in one case containing earthworms, and in another destitute of them. Although there was much variation in his results, they were in every case in favor of the soil containing the worms, and, in a number of the tests, the yield on rich soil was several times as great as where no worms were present. 390 THE PRINCIPLES OF SOIL MANAGEMENT Earthworms naturally seek a heavy, compact soil, and it is in soil of this character that they are most needed, on account of the stirring and aération they effect. Sandy soil and the soils of the arid regions, in which are found few or no earthworms, are not usually in need of their activities. 259. Insects.—There is a less definite, and probably less effective, action of a similar kind produced by insects. Ants, beetles, and the myriads of other bur- rowing insects and their larve effect a considerable movement of soil particles, with a consequent aération of the soil. At the same time they incorporate in the soil a considerable amount of organic matter. 260. Large fungi.—The larger fungi are chiefly con- cerned in bringing about the first stages in the decom- position of woody matter, which is disintegrated through the growth in its tissues of the root-mycelia of the fungi. These break down the structure, and thus greatly facilitate the work of the decay bacteria. Action of this kind is largely confined to the forest and is not of much importance in cultivated soil. Another function of the large fungi is exercised in the intimate and possibly symbiotic relation of the fungal hyphe to the roots of many forest trees, in soil where nitrification proceeds very slowly, if at all, for nitrates are apparently never present in forest soils. This enveloping system of hyphe, which may consist of masses in a definite zone of the cortex, with occasional filaments passing outward into the soil, or which may surround the root with a dense mass of interwoven hypha, is called mycorhiza. SOIL MICRO-ORGANISMS 391 The cereal, cruciferous, leguminous and solanaceous plants are not associated with mycorhiza. Mycotropic plants are usually those that live in a humus soil filled with the mycelia of fungi. It is thought that the mycorhiza aid the higher plants to obtain nutri- ment that they must strive for in competition with the fungi. Mycotropic plants are also able to grow with a very small transpiration of moisture, as is well known to be the case with many conifers; and this restricted transpiration would doubtless result in lack of nutri- ment were it not for the assistance of the mycorhiza. 261. Plant roots.—The roots of plants assist in pro- moting productiveness of the soil both by contributing organic matter and by leaving, upon their decay, openings which render the soil more permeable to water and which also facilitate drainage and aération. The dense mass of rootlets, with their minute hairs that are left in the soil after every harvest, furnish a well-distributed supply of organic manure, which is not confined to the furrow slice, as is artificially incor- porated manure. The drainage and aération of the lower soil, due to the openings left by the decomposed roots, are of the greatest importance in heavy soil, and the beneficial effects of clover and other deep- rooted plants are due in no small measure to this function. II. MICRO-ORGANISMS OF THE SOIL Of the micro-organisms commonly existing in soils, the great majority belong to plant rather than‘ 392 THE PRINCIPLES OF SOIL MANAGEMENT to animal life. Of the latter, the only organisms of economical importance are the nematodes, whose injurious effect upon plant growth is accomplished through the formation of galls on the roots, in which the young are hatched and live to sexual maturity. 262. Plant micro-organisms.—The microscopic plants of the soil may be classed as slime-molds, bacteria, fungi and alge. 263. Plant micro-organisms injurious Fic. 108. a sed eee Nematodes enter to higher plants.— Injurious ~° plant Pe POOL, micro-organisms are confined mostly to fungi and bacteria. They may be entirely para- sitic in their habits, or only partially so. They injure plants by attacking the roots. Those attacking other portions of plants may live in the soil during their spore stage, but these are not strictly micro- organisms of the soil. Some of the more common dis- eases produced by soil organisms are: Wilt of cotton, cowpeas, watermelon, flax, tobacco, tomatoes, etc., damping-off of a large number of plants, root-rot, galls, ete. These fungi or bacteria may live for long periods, probably indefinitely, in the soil, if the conditions necessary for their growth are maintained. Some of them will die within a few years if their host plants are not grown upon the soil, but others are able to maintain existence on almost any organic substance. Once a soil is infected, it is likely to remain so for a long time, or indeed indefinitely. Infection is easily PLANT MICRO-ORGANISMS 393 carried. Soil from infected fields may be carried on implements, plants, rubbish of any kind, in soil used for inoculation of leguminous crops, or even in stable manure containing infected plants, or in the feces resulting from the feeding of infected plants. Flooding of land by which soil is washed from one field to another may be a means of infection. Prevention is the best defense from diseases pro- duced by these soil organisms. Once disease has pro- cured a foothold, it is practically impossible to eradi- cate all its organisms. Rotation of crops is effective for some diseases, but entire absence of the host crop is more often necessary. The use of lime is beneficial in the case of certain diseases. Chemicals of various kinds have been tried with little success. Steam- sterilization is a practical method of treating green- house soils for a number of diseases. The breeding of plants immune to the disease affecting its particular species has been successfully carried out in the case of the cowpea and cotton plants and can doubtless be accomplished with others. 264. Plant micro-organisms not injurious to higher plants.—The vegetable micro-organisms of the soil all take an active part in removing dead plants and animals from the surface of the soil, and in bringing about the other operations that are necessary for the production of plants. The first step in the preparation for plant growth is toremove the remains of plants and animals that would otherwise accumulate, to the ex- clusion of other plants. These are decomposed through the action of organisms of various kinds, the inter- 394 THE PRINCIPLES OF SOIL MANAGEMENT mediate and final products of decomposition assisting plant production by contributing nitrogen and certain mineral compounds that are a directly available source of plant nutriment, and also by the effect of certain of the decomposition products upon the mineral substances of the soil, by which they are rendered soluble and hence available to the plant. Through these operations the supply of carbon and nitrogen required for the production of organic matter is kept in circulation. The complex organic compounds in the bodies of dead plants or animals, in which con- dition plants cannot use them, are, under the action of micro-organisms, converted by a number of stages’ into the very simple compounds used by plants. In the course of this process, a part of the nitrogen is sometimes lost into the air by conversion into free nitrogen, but fortunately this may be recovered and even more nitrogen taken from the air by certain other organisms of the soil. The slime molds, bacteria, fungi and alge all play a part in thése processes, but none of them so actively during every stage of the process as do the bacteria. Molds and fungi are particularly active in the early stages of decomposition of both nitrogenous and non- nitrogenous organic matter. Molds are also capable of ammonifying proteins, and even reforming the complex protein bodies from the nitrogen of ammonium salts. Certain of the molds and alge are apparently able to fix atmospheric nitrogen, and contribute a supply of carbohydrates required for the use of the nitrogen-fixing bacteria, BACTERIA OF THE SOIL 395 265. Bacteria.—Of the several forms of micro- organisms found in the soil, bacteria are the most important. In fact, the abundant and continued growth of plants upon the soil is absolutely dependent upon the presence of bacteria, as through their action chemi- cal changes are brought about which result in making soluble both ‘organic and inorganic material necessary for the life of higher plants, and which, in part at least, would not otherwise occur. Bacteria are thus transform- ers, and not producers, of fer- tility in the soil, although, as we shall see later, certain kinds _of bacteria take nitrogen from the air and leave it in the soil. With this exception, however, they add no plant food to the soil. It is their action in render- Fic. 109. Some types of Ing available to the plant ma- soil-bacteria, highly magnified. : : a, Nitrate formers; 6, nitrite. terial already present in the soil Be Gants @ Gaon: that constitutes their greatest f, Closteridium pasteurianum. present eta crop-produc- tion. It is to their activity in conveying nitrogen from the air to the soil that we are indebted for most of our supply of nitrogen in virgin soils. It is not usually the entire absence of bacteria from the soil that is to be avoided in practice, for all arable soils contain bacteria, although sometimes not all of the desirable forms; but, as great bacterial activity is required for the large production of crops, 396 THE PRINCIPLES OF SOIL MANAGEMENT the practical problem is to maintain a condition of soil most favorable to such activity. 266. Distribution.—Bacteria are found almost uni- versally in soils, although they are much more numer- ous in some soils than in others. A number of investi- gators have stated that in soils from different locali- ties and of different types that they have examined, the numbers of bacteria were proportional to the productiveness of the soils. The number of bacteria present has, in some cases, been shown to be propor- tional to the amount of humus contained in the soil. It is natural to expect that within certain limits both of these findings will hold. The conditions ob- taining in a productive soil are those favorable to the development of certain forms of bacteria, and these kinds constitute a very large proportion of those gen- erally found in soils. However, there is evidence that comparatively unproductive soils may contain a large number of bacteria which are presumably not favorable to plant-growth. Samples of soil taken from certain productive and relatively unproductive portions of a field on Cornell University farm contained a larger number of bacteria in the poor soil, although the two soils were equally well drained, and the good soil had slightly more organic matter. They had also received practi- cally the same treatment during the preceding few years. Character of Number of bacteria soi per gram of dry soil CME ieee oo cook's Wi ee a ee eee ke aires eine 1,200,000 POE skis aie Pe sinks be ea 9 oe oe ae le ee 1,600,000 ABUNDANCE OF SOIL BACTERIA 397 After wheat had been growing for two months on these soils in the greenhouse, and maintained at the same moisture content, they were again sampled. Character of Number of bacteria i per gram of dry soil TPM ARUN Say BY SN IO A i a, iN hom 760,000 CUT PS RRS a ere ete 5 2 Mod Sek he eles ee nena Ie eg 1,120,000 Another reason why this relation between the number of bacteria and soil productiveness does not hold is that those bacteria having the same functions in relation to plant-food do not always have the same physiological efficiency. In other words, they do not have the same virulence, a small number in some cases being able to bring about the same changes that in other cases require a much larger number. Bacteria are found chiefly in the upper layers of soil, although not at the immediate surface of the ground. The layer between the first and sixth or seventh inches contains, in most soils, the great bulk of the bacteria present. Below that depth they de- crease in numbers, and below a depth of six to eight feet there are usually none. 267. Numbers.—The number of bacteria in any soil will naturally vary with the conditions that favor or discourage their growth. In sandy soils, forest soils, desert soils, acid soils, waterlogged soils and soils low in humus, the bacteria are either absent or very few in numbers. In soils very rich in organic matter, especially where animal manure has_ been applied, or where a carcass has been buried, the num- ber becomes very large, as many as 100,000,000 per 398 THE PRINCIPLES OF SOIL MANAGEMENT gram having been found; while in soil of ordinary fertility and tilth the numbers range from 1,000,000 to 5,000,000 per gram. The extreme rapidity with which reproduction occurs makes it possible for the number to increase enormously when conditions are favorable for their growth. While, therefore, very few bacteria are present in soils of the northern states during the winter, the number increases with great rapidity in the spring. Marshall Ward has shown that in the mild winters in England some soil bac- teria at least continue their activity throughout the winter. In the southern states of ‘America the same is doubtless true. The following table shows the number of bacteria per gram of soil found in different parts of the United States during some portion of the growing season: TaBLeE LXI Investi- State Soil Crop gator Number Delaware. 25.95.32. Grass, 12 yrs. | Chester 425,000 Pralagaine spa oy sce ld 2 _ Grass, 4 yrs. | Chester 425,000 Delawareoi sk cs Clover, follow- | Chester | 1,880,000 ing fallow Delaware. eo. eins Woodland Chester 70,000 Delaware ..| Rich garden Vegetables Chester | 1,860,000 Kansas .... Pana 07 ON eS ee Mayo & | 33,931,747 (humus 2.19%) Kinsley Kansas’. ... ae OR es eer Mayo x 53,596,060 (humus 3.07%) Kinsley Kaupas.; 3 sch). -D pin galls abe fe whe ees Mayo & 78,534 gumbo subsoil Kinsley ‘Kansas’ ¥.)). eam, dow ne) yo eee Mayo x 8,543,006 humus Kinsley Katies. 5.) bose, low ini oe Mayo & | 3,192,131 humus Kinsley SOIL BACTERIA, CONDITIONS FOR GROWTH 399 268. Conditions affecting growth.—Many conditions of the soil affect the growth of bacteria. Among the most important of these are the supply of oxygen and moisture, the temperature, the presence of organic matter, and the acidity or basicity of the soil. 269. Oxygen.—All soil bacteria require for their growth a certain quantity of oxygen. Some bacteria, however, can continue their activities with much less oxygen than can others. Those requiring an abundant supply of oxygen have been called aérobic bacteria, while those preferring little or no air are designated anaérobie bacteria. This is an important distinction, because those bacteria which are of the greatest benefit to the soil are, in the main, aérobes, and those bac- teria that are injurious in their action are chiefly anaérobes. However, it seems likely that an aérobic bacterium may gradually accommodate itself within certain limits to an environment containing less oxygen, and an anaérobic bacterium may accommodate itself to the presence of a larger amount of oxygen. Thus a bacterium may be most active in the presence of an abundant supply of oxygen; but, when subjected to conditions in which the supply is small, growth continues, but with lessened vigor. The term facultative bacteria has been used to designate those bacteria that are able to adapt themselves to considerable variation in oxygen supply. The structure, tilth and drainage of the soil consequently determine largely whether aérobic or anaérobic bacteria shall be most active. 270. Moisture.—Bacteria require some moisture 400 THE PRINCIPLES OF SOIL MANAGEMENT for their growth. A notable decrease in the moisture content of the soil may temporarily decrease the number of bacteria by limiting their development to the films of moisture surrounding the particles. With a decrease in the moisture content of any soil, there occurs an increase in the oxygen in the interstitial spaces. Those bacteria thriving in the presence of oxygen are thereby favored, and the character of the bacterial flora is correspondingly changed. When the soil remains saturated, or nearly so, for any consider- able period, the anaérobic forms assert themselves, and the usually beneficial activities of the aérobic bacteria are temporarily suspended. The most favor- able moisture conditions for the activity of the most desirable bacteria is that found in a well-drained soil. 271. Temperature.—Soil bacteria, like other plants, continue life and growth under a considerable range of temperature. Freezing, while rendering bacteria dormant, does not kill them, and growth begins slightly above that point. Warrington has shown that nitri- fication goes on at temperatures as low as 37° to 39° Fahr. It is not, however, until the temperature is considerably higher that the functions of any of the soil bacteria are pronounced. From 70° to 110° Fahr. - their activity is greatest, and it diminishes perceptibly below or above those points. The thermal death points of most forms of bacteria is found at some point between 110° and 160° Fahr., but the spore forms even resist boiling. Only in some desert soils does the natural temperature reach a point sufficiently high to actually destroy bacteria, and there only in the SOIL BACTERIA, CONDITIONS FOR GROWTH 401 upper surface. In fact, it is seldom that soil tempera- tures become sufficiently high to curtail bacterial activity. 272. Organic matter.—The presence of a certain quantity of organic matter is essential to the growth of most, but not all, forms of soil bacteria. The or- ganic matter of the soil, consisting as it does of the remains of a large variety of substances, furnishes a suitable food-supply for a very great number of forms of organisms. The action of one set of bacteria upon the cellular matter of plants embodied in the soil produces compounds suited to other forms, and so from one stage of decomposition to another this con- stantly changing material affords sustenance to a bacterial flora the extent and variety of which it is difficult to conceive. Bacteria not only affect the or- ganic matter of the soil, but, in the case of certain forms, their activities produce changes in the inorganic matter that cause it to become more soluble and more easily available to the plant. A soil low in organic matter usually has a lower bacterial content than one containing a larger amount, and, under favorable conditions, the beneficial action, to a certain point at least, increases with the content of organic substance; but, as the products of bacterial life are generally injurious to the organisms producing them, such factors as the rate of aération and the basicity of the soil must determine the effectiveness of the organic matter. 273. Soil acidity.—A soil having an acid reaction makes a poor medium for the growth of bacteria. A Z 402 THE PRINCIPLES OF SOIL MANAGEMENT neutral or slightly alkaline soil furnishes the most favorable conditions for bacterial growth. The activi- ties of many soil bacteria result in the formation of acids which are injurious to the bacteria themselves, and, unless there is present some basic substance with which these can combine, bacterial development is inhibited by their own products. This is one of the Fie. 110. Spring-toothed walking cultivator. For thorough, shallow tillage. reasons why lime is so often of great benefit when ap- plied to soils, and especially to those on which legumi- nous crops are growing. For the same reason, the presence of lime hastens decay of organic matter in certain soils, and the conversion of nitrogenous ma- terial with a minimum loss into compounds available to the plant. As showing the value of lime in the process of nitrification, it has been pointed out that in the presence of an adequate supply of lime the availability of ammonium salts is almost as high as FUNCTIONS OF SOIL BACTERIA 403 that of nitrate salts, but where the supply is insufficient the value of ammonium salts is relatively quite low. 274. Functions of soil bacteria.—Bacteria have a part in many of the processes of the soil which greatly affects its productiveness. It has become customary to refer to the changes produced by certain forms of bacteria as their function in contributing to soil-productiveness. 275. Decomposition of mineral matter.—Certain bacteria decompose some of the mineral matter of the soil and render it more easily available to the plant. While the nature of the processes and their extent are not known, there is sufficient evidence to justify the above statement. It is well known that several forms of bacteria are instrumental in decom- posing rock, and that sulfur and iron compounds are acted upon by other forms. Again, the much greater efficiency of difficultly soluble phosphate fertilizers, when used in conjunction with a quantity of organic matter, is evidence of the relation of bacterial action to the decomposition of mineral substances. Stocklasa has shown that, when B. megatherium and B. fluor- escens are added to soil fertilized with insoluble phosphates, plants grown thereon take up a larger amount of phosphorus than those on uninoculated soils. Organic acids and carbon dioxid are constantly produced by soil bacteria. These in soil water are weak but ever-acting solvents, the effect of which must in the end be considerable. It seems likely, however, that there is a more direct effect of certain 404 THE PRINCIPLES OF SOIL MANAGEMENT bacteria upon mineral matter than merely the solvent action of these acids. That rock may be disintegrated through the action of bacteria has been already com- mented upon. Although it has not yet been demon- strated, bacteria such as are capable of decompos- ing rock may, in all probability, exist in the soil where their activities result in the ‘“‘ weathering”’ that always goes on in soils even when no organic mat- ter is present. It has been suggested that carbon dioxid dissolved in water may act on the very difficultly soluble tri- calcium phosphate, producing di-calcium phosphate, a more soluble form, and calcium bicarbonate, thus: Ca,(PO,), +2CO, +2H,O0—Ca,H,(PO,),+Ca(HCO,), The calcium bicarbonate thus produced, as well as that derived from other sources, may then act on the double silicates of aluminum and one of the alkalies, thus: K,O. Al,O,. 6 SiO, + Ca(HCO,),=Ca0. Al,O,. 6 SiO, +2 KHCO, There is then another nutrient rendered available to the plant. It has been shown by Van Delden and by Nadson that several forms (M. desulfuricans, M. estuarii, Proteus vulgaris and B. mycoides) are able to reduce sulfates, while transformations of iron, silicon and calcium are effected by Proteus vulgaris. 276. Decomposition of non-nitrogenous organic matter.—The organic matter commonly decomposed in soils contains a large proportion of compounds FUNCTIONS OF SOIL BACTERIA 405 containing no nitrogen. The non-nitrogenous sub- stances decompose quite rapidly, and the organic nitrogen disappears less rapidly than the carbon, hydrogen and oxygen of organic bodies. Humus always contains a higher percentage of nitrogen than do the plants from which it is formed (page 123). The non-nitrogenous substances consist of cellulose and allied compounds forming the cell-walls of plants, and the carbohydrates, organic acids, fats, etc., con- tained in them. The dissolution of cellulose is brought about by the action of the enzyme cytase secreted by a number of fungi, and is also probably accomplished by the Bacillus amylobacter, but whether through the secretion of an enzyme is not known. Other bacteria have been reported to secrete a cytase that acts on certain constituents of the cell-wall. It is probable that numerous organisms capable of fermenting cellu- lose and allied substances exist in the soil, which decomposition they accomplished through the pro- duction of cytase. ; The effect of cytase upon cellulose and other fiber is to hydrolyse it with the formation of sugar, as glu- cose, mannose, zylose, aribinose, etc. Starch is converted into glucose by a ferment (diastase) either present in the plant itself or possibly secreted by fungi or bacteria. All the sugars are finally converted into organic acids which may combine with mineral bases. Distinct organisms have been isolated that can utilize for their development formates, acetates propionates, butyrates, etc., the final product being 406 THE PRINCIPLES OF SOIL MANAGEMENT carbon dioxid and water. Thus, step by step, the non- nitrogenous matter incorporated in the soil is carried by one and another form of organisms from the most complex to the simplest combinations. The final product of the decomposition of carbon- aceous matter being carbon dioxid, there is a return to the air of the compound from which the carbon of the decomposing substance was originally derived. In the plant, unless it is saprophytic, the carbon of the tissues comes directly from the carbon dioxid of the air, from which more complex carbon-bearing compounds are produced and utilized in its functions or in its tissues. A portion of the carbon is returned to the air by the plant in the form of carbon dioxid, the remainder is retained by the plant, and may be returned by the process of decay, or may be consumed by an animal, and, as the result of its physiological processes, either exhaled as carbon dioxid or deposited in the tissues to be later decomposed and converted into carbon dioxid. The soil is thus the scene of at least a part of the varied transformations through which carbon is continually passing, as it is utilized by higher plants, animals, bacteria and fungi. The non-nitrogenous organic substances in their various stages furnish food for a large number of bacteria, among which are those concerned in the decomposition of mineral matter and in the processes of nitrification and nitrogen-fixation. There are, there- fore, two ways in which these substances are of great importance in soil fertility: (1) As a source of organic acids, (2) As a food-supply for useful soil bacteria. DECAY BACTERIA 407 277. Decomposition of nitrogenous organic matter. —The decomposition of nitrogenous organic matter is accomplished by a series of changes from one compound to another, as we have seen was the case with the non- nitrogenous materials. The final products are carbon dioxid, water, and usually some hydrocarbon gases resulting from the carbon and hydrogen of the organic \ Fic. 111. The large-shovel riding cultivator. matter, and also some hydrogen sulfide or other gas containing sulfur or a final oxidation of the sulfur of the proteids into sulfates, while the nitrogen is ulti- mately converted into nitrates, or into free nitrogen, although a portion of the original nitrogen some- times escapes into the air in the intermediate stage, ammonia. The processes will be discussed under the following heads, which represent certain more or less definite stages in the decomposition: (1) Decay and putre- 408 THE PRINCIPLES OF SOIL MANAGEMENT faction. (2) Ammonification. (38) Nitrification. (4) Denitrification. 278. Decay and putrefaction.—Decomposition of the nitrogenous organic matter of the soil, consisting largely of the proteins, begins with either one of two processes—decay or putrefaction. Decay is produced by aérobic bacteria, and naturally occurs when the conditions are most favorable for their development. When the conditions are otherwise, the growth of these bacteria is checked, and then further decom- position would be extremely slow were it not for the other process—putrefaction. Putrefaction is produced by anaérobic bacteria. In the same body, and conse- quently in the same soil, decay and putrefaction may be in progress simultaneously, decay taking place on the outside and on the surfaces of other parts exposed to the air, while putrefaction occurs on the interior, where the supply of oxygen is limited. By means of the two processes, decomposition is greatly facilitated. Decay produces a very rapid and complete decom- position of the substance in which it operates, most of the carbon and hydrogen being quickly converted into carbon dioxid and water, and the nitrogen into am- monia and probably some free nitrogen. The latter is possibly due to the oxidation of ammonia, thus 4 NH,+3 0,=6 H,0+2N,. The sulfur of the proteins finally appears in the form of sulfates. What the intermediate products are has not been determined, but in the decay of meat, where there was PUTREFACTION BACTERIA 409 an abundant supply of oxygen, succinic, palmytic, oleic and phenyl-propionic acids have been found. Putrefaction results in a large number of complex intermediate compounds and proceeds much more slowly. Many of the substances thus produced are highly poisonous and most of them have a very offensive odor. They may be further broken down by decay when the conditions are suitable, or by a continuation of the process of putrefaction. In either case, the poisonous properties and the odor are removed. In the process of decomposition of organic matter two classes of substances are produced: (1) Those which have been excreted or secreted by the bacterium, and therefore have passed through the metabolic processes of the organism. (2) Those that have been formed because of the removal of certain atoms by bacteria or enzymes from compounds, thus necessi- tating a readjustment of the remaining atoms and the consequent formation of a new compound. Putrefaction is carried on by a large number of forms of bacteria, the resulting product depending upon the substance in process of decomposition, and upon the bacteria involved. Some of the characteristic, although not constant products, formed in the putre- faction of albumin and proteins are albumenoses, pep- tones, and amino-acids, followed by the formation of cadaverin, putrescin, skatol and indol. Where an abundant supply of oxygen is present, or where a sufficient supply of carbohydrates exist, these sub- stances are not formed. There are many other products of putrefaction, including a number of gases, as carbon 410 THE PRINCIPLES OF SOIL MANAGEMENT dioxid, hydrogen sulfide, marsh gas, phosphine, hy- drogen, nitrogen, etc. It will be noticed that these changes, like those occurring in the non-nitrogenous organic matter, involve a breaking down of the more complex com- pounds and the formation of simpler ones; that a very large number of bacteria are concerned in the various steps, while even the same substances may be decom- posed and the same resulting compounds formed by a number of different species of bacteria. Present-day knowledge of the subject does not make it possible to present a list of the bacteria con- cerned in each step, or to name all of the intermediate products formed; but for the student of the soil the principal consideration is a knowledge of the circum- stances under which the nitrogen is made available to plants, and the conditions which are likely to result in its loss from the soil. 279. Ammonification.—Decay and _ putrefaction may be considered as a continuation of ammonification, or the latter process as the beginning of the former. Ammonification, as its name implies, is that stage of the process during which ammonia is formed from the intermediate products. Like the other processes of decomposition, there are many species of bacteria capable of forming am- monia from nitrogenous organic substances. Differ- ent forms display different abilities in converting nitro- gen of the same organic material into ammonia, some acting more rapidly or more thoroughly than others. In tests by certain investigators where the same bac- AMMONIFICATION 411 teria are used upon different substances, the order of their efficiency is changed with the change of sub- stance. It seems likely, therefore, that certain forms are most efficient when acting on certain organic com- pounds. That, in other words, each species is best adapted to the decomposition of certain substances, while capable of attacking others, although less effec- tively. Among the bacteria producing ammonification are B. mycoides, B. subtilis, B. mesentericus vulgatus, B. janthinus and Proteus vulgaris. Of these, B. mycoides has been very carefully studied, and the findings of Marchal may be taken as representative of the process of ammonification. He found that when this bacterium was seeded on a neutral solution of albumin, ammonia and carbon dioxid were produced, together with small amounts of peptones, leucin, tyrosin, and formic, butyric and proprionic acids. He concludes that in the process, atmospheric oxygen is used, and that the carbon of the albumin is converted into carbon dioxid, the sulfur into sulfuric acid, the hydrogen partly into water, and partly into ammonia by com- bining with the nitrogen of the organic substance. He suggests that a complete decomposition of the al- bumin occurs according to the following reaction: | C,H, 13N129Ox +770,=29 H,O +72CO, +SO,+18NH,. The greatest activity occurred at a temperature of 86° Fahr., and as low as 68° Fahr. action was quite strong. Access of an increased amount of air, produced by increasing the surface of the liquid, increased the 412 THE PRINCIPLES OF SOIL MANAGEMENT rate of ammonification. A slightly acid reaction in the liquid produced the maximum activity, but in a neu- tral or even slightly acid medium the process was continued, although much less actively. He found that B. mycoides was also capable of ammonifying casein, fibrin, legumin, glutin, myosin, serin, peptones, creatin, leucin, tyrosin and asparagin, but not urea and ammonium salts. 280. Nitrification.—Some agricultural plants can utilize ammonium salts as a source of nitrogen. This has been determined for maize, oats, barley and po- tatoes. Other plants, such as beets, show a decided preference for nitrogen in the form of nitrates. Whether any of the common crops can thrive as well on ammo- nium salts as upon nitrates has not been finally demon- strated. In all arable soils the transformation of nitrogen does not stop with its conversion into am- monia, but proceeds by an oxidation process to the formation of first nitrous and then nitric acids. This may be considered to proceed according to the fol- lowing equations: 2NH, +30, =2HNO,+2H,0. 2HNO, + 0, =2HNO,,. The acid in either case combines with one of the bases of the soil, usually calcium, so that we have calcium nitrate resulting. Each of these steps is brought about by a distinct bacterium, but they are closely related. Collectively they are called nitro-bacteria. Nitrosomonas and Nitrosococcus are the bacteria concerned in the NITRIFICATION 413 conversion of ammonia into nitrous acid or nitrites. The former are supposed to be characteristic of EKuro- pean, and the latter of American soils. They are sometimes referred to as nitrous ferments. Nitrobacter are those bacteria that convert nitrites into nitrates. They are also designated nitric ferments. There seem to be some differences in bacteria from different soils, but the differences are slight, and the conditions favoring their actions are similar. It is also true that the conditions favoring the action of Nitrosomonas and Nitrobacter are similar, and they are generally found in the same soils, although some experiments show that, in the same soil, nitrites may sometimes accumulate, indicating conditions more favorable to the development of the Nitrosomonas bacteria. The formation of nitrates usually follows closely on the production of nitrites, so that there is rarely more than a trace of the latter to be found in soils. A soil favorable to the process of nitrification is usually well adapted to all of the processes of nitro- gen transformation. Marked differences have been found in the nitri- fying power of bacteria from different soils. Highly productive soils have generally been found to contain bacteria having greater nitrifying efficiency than those from less productive soils, but this may not always be the case, as other factors may limit the productive- ness. 281. Effect of organic matter on nitrification.— A peculiarity in the artificial culture of nitrifying bacteria is that they cannot be grown in artificial 414 THE PRINCIPLES OF SOIL MANAGEMENT medium containing organic matter. This property for a long time prevented the isolation and identifi- cation of these organisms, as it was hardly conceivable © that organisms living in the dark, where energy can- not be obtained from sunlight, could exist without using the energy stored by organic matter. It has been suggested, in explanation of this, that the energy -_ 5 SOIL BS 120 > s NITRATES P.P.M. DRY SOIL S.6 8 MOISTURE PERCENT. , SOIL TEMPERATURE °F. TAKEN 4.80 P.M. o 8 MAY JUNE JULY 19 908° SEPTEMBER OCTOBER Fic. 112. Curves showing the relation the moisture and temperature of the soil to the formation of nitrates which are given in parts per million of dry soil. Depth of sampling, eight inches. These curves bring out clearly the fact that the warmer soil temperature, combined with a moderately high soil mois- ture content favors the formation of nitrates. produced by the oxidation involved in the process of nitrification, makes possible the growth of the or- ganisms under these, apparently impossible, condi- tions. Some experimenters report having grown nitrobacteria in organic media, but it is ‘generally believed, at present, that this is not possible, and that there has been some error in their work. The presence of peptone in the proportion of 500 parts per million completely prevents the develop- NITRIFICATION 415 ment of nitrobacteria and one half that quantity checks it, while 150 parts of ammonia per million has a similar effect. In a normal soil, the quantity of soluble am- monium salts is well below this amount, as must also be that of soluble organic matter. In confirmation of the inhibiting effect of organic matter on the nitrobac- teria, cases have been reported of soils very rich in organic matter in which no bacteria of this type occur. It has also been stated that very heavy manuring with organic manures results in decreased nitrification in the soil. While this may be true where farm manure is used in the quantities sometimes applied in garden- ing operations, it is not likely to occur in soils on which ordinary field crops are grown. The principle is well illustrated by the dry-earth closet. Manure mixed with earth in relatively small proportions and kept aérated by occasional mixing undergoes a very thorough decom- position of the manure but without any corresponding increase in nitrates. On the other hand, under field con- ditions, manure used in relatively small amounts does not undergo this serious loss. The application of twenty tons of farm manure per acre to sod on a clay loam soil for three consecu- tive years, at Cornell University, resulted in a larger production of nitrates on the manured soil than upon a contiguous plat of similar soil left unmanured. This was true during the third year of the applications, when the land was in sod, and also the fourth year when no manure was applied to either plat, and when both were planted to corn, as may be seen from the following table: 416 THE PRINCIPLES OF SOIL MANAGEMENT TaBLE LXII.—NuitTRATES PRODUCED ON HEAVILY MANURED AND ON UNMANURED SOIL NOs; in parts per million, dry soil ¢ Twenty tons ma- Unmanured soil | nure per acre for three years Land in timothy— . PAID UE eee cos th at pss aes gd srg a ak Gates 8.2 21.0 LT SR EN GRE a aa gee 4.1 4.6 US: Motes Beds cas a he er, Bod vas oe 4.5 ay aN Sa ct we Ray ae ots eels 2.0 40 Pen SO eA eS te 2.4 2.0 GG ooh bela ete Ah. SE 0.8 | Be Oe ee es asc a 13 3.0 MER Es eres Sanki= beds Gs gone ads 22 2.8 Puli BA ee ee easel se aaa g 1.8 3.0 Land in maize— DU RP Ak erie tal cn yh ae be 17.5 20.1 ARERR BS ech ots hacaod eee beans 42.8 79.3 aretha SA ee ctor Ar nie 50.0 105.0 sty GNA aah of ie a Sh eke ee 195.0 304.0 282. Effect of soil aération on _ nitrification.— Probably the most potent factor governing nitrifi- cation in the soil is the supply of air. In clay and even in loam soils, the tendency to compactness is such as to exclude air sufficient to enable nitrification to proceed as rapidly as desirable unless the soil be well tilled. Columns of soil eight inches in diameter and of the same depth were removed from a field of clay loam on Cornell University farm, and carried to the greenhouse without disturbing the structure of the soil as it existed in the field. At the same time, simi- lar-sized vessels were filled with soil dug up from a SOIL CONDITION AND NITRIFICATION 417 spot nearby. These may be termed unaérated and aérated soils. Both were kept at the same temperature and moisture content in the greenhouse, but no plants were grown upon them. The production of nitrates was as follows: TaBLeE LXIII Nitrates in dry soil, parts per million Date of analysis Unaérated soil Aérated soil When taken from field .......... 3.2 3.2 After standing one month....... 4.2 17.6 After standing two months...... 9.0 45.6 283. Effect of sod on nitrification.—Nitrification proceeds slowly on sod land, especially if the soil is heavy. On the same type of soil as that used in the experiment last described, the average quantities of nitrates for each month of the growing season in the surface eight inches of sod land as compared with maize land under the same manuring were as follows: TaBLeE LXIV Nitrates in dry soil, parts per million Month ih Riot aa Sod land Maize land EO Pr Ae ieee per irarny 8.9 ae TE Pca te wight: Ray tw css 3.0 wg MEE Rk, Sa ha. Rhee Seid 2-0 2.4 40.3 I Merce ee he wu en eons ak - 4.0 194.0 ee gg RC ee Oe Se 5.4 186.7 418 THE PRINCIPLES OF SOIL MANAGEMENT The amount of nitrogen removed by the maize crop was greater than that removed by the timothy, consequently the greater amount in the former soil can not be due to the effect of the crop. So far as the conservation of nitrogen is concerned, sod is an ideal crop, for nitrates are formed very little faster than they are used, and are not carried off in large amounts by the drainage water. In the corn land as much as 500 pounds of nitrates were present in the first twelve inches of one acre, or fully five times as much as was used by the crop. 284. Depth at which nitrification takes place.— Warington concluded from his experiments that nitrification takes place only in the surface six feet of soil. Hall has pointed to the fact that no more nitrates were leached from the 60-inch lysimeter at Rotham- sted than from the one 20 inches deep; which is very good evidence that in that particular soil nitrification does not take place below 20 inches from the surface. In more porous soils, however, nitrification probably extends deeper, especially in the rich and porous subsoils of the arid and semi-arid regions. . In all probability, nitrification is largely confined to the furrow slice, where the opening up of the soil by tillage has provided the necessary air, and where the temperature rises to a point more favorable to the action of nitrifying bacteria. The results from the aérated and unaérated soils cited above represent the differ- ences that doubtless exist between the furrow slice and . the subsoil so far as nitrification is concerned. 285. Loss of nitrates from the soil.—Nitrogen hav- SOIL CONDITION AND NITRIFICATION 419 ing been converted into the form of nitric acid, it im- mediately combines with available bases in the soil forming salts, all of which are very easily soluble, and which are carried in solution by the soil water. In a region of large rainfall, the removal of nitrates in the drainage water is very rapid. Hall states that nitrates formed during the summer or autumn of one year are practically all removed from the soil of the Rotham- sted fields before the crops of the following year have advanced sufficiently to utilize them. It was formerly customary to fertilize with ammonium salts in the autumn, but the drainage water showed on analysis such a large quantity of nitrates during the months intervening between the time of fertilizing and the opening of the growing season that the practice was discontinued. In regions of less rainfall or of greater surface evaporation, the loss in this way is less, reaching a 420 THE PRINCIPLES OF SOIL MANAGEMENT minimum in an arid region when irrigation is not prac- ticed. Under such conditions, there is a return of ni- trates to the upper soil, as capillary water moves upward to replace evaporated water. In fact, wherever evaporation takes place to any considerable extent, there is some movement of this kind. The need for catch crops to take up and preserve nitrogen is there- fore greater in a humid region than in an arid or semi- arid one. An arrangement of crops that allows the land to stand idle for some time, or a crop that requires intertillage, as does maize, fails to utilize all of the nitrates produced, and promotes the loss of nitrogen in drainage water. 286. Denitrification —The nitrogen transforming bacteria thus far studied have been those that cause the oxidation of nitrogen as the result of their activi- ties. We may now consider a number of forms of bac- teria that accomplish a reverse action. The several processes involved are commonly designated by the term denitrification, and comprise the following: (1) Reduction of nitrates to nitrites and ammonia. (2) Reduction of nitrates to nitrites, and these to elementary nitrogen. The number of organisms that possess the ability to accomplish one or more of these processes is very large,—in fact greater than the number involved in the oxidation processes,—but, in spite of their numbers, permanent loss of nitrogen in ordinary arable soils is unimportant in amount, although in heaps of barnyard manure it may be a very serious cause of loss. Some of the specific bacteria reported to bring about DENITRIFICATION 421 denitrification are: B. ramosus and B. pestifer, which reduce nitrates to nitrites; B. mycoides, B. subtilis, B. mesentericus vulgatus and many other ammonification bacteria which are capable of converting nitrates into ammonia. Bacterium denitrificans alpha and Bacteriwm deni- trificans beta reduce nitrates with the evolution of gaseous nitrogen. In addition to these nitrate-destroying bacteria, there are other bacteria which also utilize nitrates; but, like higher plants, they convert the nitrogen into organic nitrogenous substances. However, as they operate in the dark and cannot obtain energy from sunlight, they must have organic acids or carbohy- drates as a source of energy. While these bacteria cannot be considered to be denitrifiers, they help to deplete the supply of nitrates when conditions are favorable for their development. What these condi- tions are is not well understood, nor can any estimate be made as to the extent of their operations. Most of the nitrifying bacteria perform their func- tions only under a limited access of oxygen, while others can operate in the presence of a more liberal supply; but, in general, thorough aération of the soil practically prevents denitrification. Straw and dung apparently carry an abundant supply of denitrifying organisms, and also furnish a supply of carbohydrates which favors their action, so that stable manure is very likely to undergo denitrification, and straw or coarse stable manure are conducive to the growth of denitrifying bacteria in the soil. 422 THE PRINCIPLES OF SOIL MANAGEMENT Under ordinary farm conditions, denitrification is of no significance in the soil where proper drainage and good tillage are practiced. Warington showed that, if an arable soil be kept saturated with water to the exclusion of air, nitrates added to the soil are decom- posed, with the evolution of nitrogen gas. As lack of drainage is usually most pronounced in the early spring, when the soil is likely to be depleted of nitrates, it is not likely that much loss arises in this way unless a nitrate fertilizer has been added. Of the many diffi- culties arising from poor drainage, denitrification of an expensive fertilizer may be very considerable item. The addition of a nitrate fertilizer to a soil receiving stable manure is not likely to result in a loss of ni- trates unless the dressings of manure have been ex- tremely heavy. Hall states that at Rothamsted, where large quantities of nitrate of soda are used every year in connection with annual dressings of farm manure, the nitrate produces nearly as large an in- crease when added to the manured as when added to the unmanured plat. There appears, in other words, to be no loss of nitrate by denitrification. It is possible to reach a point in manuring where denitrification may take place. Market gardeners sometimes reach this point where fifty tons or more of farm manure, in addition to a nitrate fertilizer, are added to the soil. Plowing under heavy crops of green manure may produce the same result. In either case, the best way to overcome the difficulty is to allow the organic matter to partly decompose before adding the fertilizer. The removal of the easily NITROGEN FIXATION BY BACTERIA 423 decomposable carbohydrates needed by the denitri- fying organisms decreases or precludes their activity. 287. Nitrogen fixation through symbiosis with higher piants:—It has long been recognized by farmers that certain crops like clover, alfalfa, peas, beans, etc., improve the soil, making it possible to grow larger crops of cereals after these crops have been upon the land. The benefit was, within the past century, traced to an increase in the nitrogen content of the soil, and the specific plants so affecting the soil were found to be, with perhaps a few exceptions, those belonging to the family of legumes. It has furthermore been demon- strated that these plants utilize, under certain con- ditions, the uncombined nitrogen of the atmosphere, and that they contain, both in the aérial portions and in the roots, a very high percentage of nitrogen. In consequence, the decomposition of even the roots of the plants in the soil leaves a large amount of nitrogenous matter. 288. Relation of bacteria to nodules on roots.— It has also been shown that the utilization of atmos- pheric nitrogen is accomplished through the aid of certain bacteria that live in nodules (tubercles) on the roots of the plants. These bacteria acquire the . free nitrogen from the air in the soil, and the host plant secures it in some form from the bacteria or their products. The presence of a certain species of bacteria is necessary for the formation of tubercles. Legumi- nous plants grown in cultures or in soil not containing the necessary bacteria do not form nodules, and do not utilize atmospheric nitrogen, the result being that 424 THE PRINCIPLES OF SOIL MANAGEMENT the crop produced is less in amount and the percentage of nitrogen in the crop is less. It has for some years been the belief that the or- ganism which produces the nodules and utilizes the uncombined nitrogen is the Pseudomonas radicicola, Fia. 114. Nodules on the roots of an alfalfa plant Bacteria live in these nodules, or tubercles, and have the power of utilizing the free nitrogen of the air in their growth. but this has very lately been called in ques- tion. The nodules are not normally a part of leguminous plants but are evidently caused by some irritation of the root surface, much as a gall is caused to develop on a leaf or branch of a tree by an insect. In a culture containing the proper bacteria, the prick of a needle on the root surface will cause a nodule to form in the course of a few days. The entrance of the bacteria is effected through a_ root-hair which it penetrates, and may be seen as a filament extending the entire length of the TUBERCLE BACTERIA 425 hair, and into the cells of the cortex of the root, where the growth of the tubercle starts. Even where the causative bacteria occur in cultures or in the soil, leguminous plants may not secure any atmospheric nitrogen, or perhaps only a small quantity, if there is an abundant supply of readily available combined nitrogen upon which the plant may draw. The bacteria have the ability to utilize combined nitrogen as well as uncombined nitrogen, and prefer to have it in the former condition. On soils rich in nitro- gen legumes may, therefore, add little or no nitrogen to the soil, while in properly inoculated soils deficient in nitrogen an important gain of nitrogen results. While P. radicicola has been considered the organism common to all leguminous plants, it is now known that the organisms from one species of legume are not equally well adapted to the production of tubercles on each of the other species of legumes. They show greater activity on some species than on others, but do not develop so successfully on any species as on the one from which the organisms were taken. It was quite generally believed at one time that the longer any species of legume is in contact with the organisms from another species the more active they become, and the greater the utilization of atmospheric nitrogen. Considerable doubt has been cast upon this view in recent years, and it is now generally conceded that the bacteria of certain legumes are not capable of inoculating certain other species of legumes. 289. Transfer of nitrogen to the plant.—It has been shown by several investigators that bacteria 426 THE PRINCIPLES OF SOIL MANAGEMENT from the nodules of legumes are able to fix atmos- pheric nitrogen even when not associated with legumi- nous plants. There would seem to be no doubt, there- fore, that the fixation of nitrogen in the tubercles of legumes is accomplished directly by this organism, and not by the plant itself, or through any combina- tion of the plant and organism,—both of which hy- potheses have been advanced. The part which the plant plays is doubtless to furnish the carbohydrates required in large quantities by all nitrogen-fixing organisms and which the legumes are able to supply in large amounts. The utilization of large quantities of carbohydrates by the nitrogen-fixing bacteria in the tubercles may also account for the small proportion of non-nitrogenous organic matter in the plants. How the plant absorbs this nitrogen after it has been secured by the bacteria is less well understood. Early in the growth of the tubercle, a mucilaginous substance is produced which permeates the tissues of the plant in the form of long, slender threads, and which contain the bacteria. These threads develop by branching or budding, and form what have been called Y and T forms known as bacteroids, which are peculiar to these bacteria, and not produced by them when grown in the media of the laboratory. The threads finally disappear, and the bacteria diffuse themselves more or less, through the tissues of the root. What part the bacteroids play in the transfer of nitrogen is not known. It has been suggested that in this form the nitrogen is absorbed by the tissues of the plant. It seems quite likely that the nitrogen compounds SOIL-INOCULATION 427 produced within the bacteria cells are diffused through the cell-wall and absorbed by the plant. In a recent report, De Rossi states that Pseudo- monas radicicola is not the causative agent in the fixation of nitrogen in the nodules of leguminous plants, and that he has isolated other bacteria that do possess this property. These bacteria produce the Y and T forms in artificial media, which is in itself an indication of their identity with the bacteria concerned in nitrogen-fixation. De Rossi’s work may also explain why what was formerly considered to be one form of bacterium, Pseudomonas radicicola, common to all leguminous plants, is not capable of inoculating one species of legume when transferred from another. It may be that there are a number of different forms, each adapted to certain species of legumes. 290. Soil-inoculation for legumes.—The possibility of securing a better growth of leguminous crops on soils not having previously grown such a crop success- fully, was conceived immediately following the dis- covery of the nitrogen-fixing bacteria. Extensive experiments showed the practicability of inoculating land for a certain leguminous crop by spreading upon its surface soil from a field on which the same crop is successfully growing. It is manifestly much better to apply the organisms or a certain species of legume from a field having grown the same species than to attempt to use organisms from another species of le- gume. The fact that soil-inoculation by means of soil from other fields may possibly transmit weed seeds and fungous diseases, and also necessitates the trans- 428 THE PRINCIPLES OF SOIL MANAGEMENT portation of a great bulk and weight of material, has led to numerous efforts to inoculate soil by means of pure cultures. The pure culture may also make it possible to bring to the soil bacteria of greater physio- logical efficiency than those already there. The first attempt at inoculation by pure cultures was made in Germany, the cultures being sold under the name of “ Nitragin.’’ Careful experiments made with this material previous to the year 1900 did not show it to be very efficient; but, of recent years, improve- ments in the method of manipulating the cultures have resulted in much greater success. In “ Nitragin,”’ the medium used for growing the organisms is gelatin, and, before use, this was formerly dissolved in water; but now a solution of greater density is used in order to prevent a change of osmotic pressure, which may cause plasmolysis and result in the destruction of the bacteria. Within recent years, a number of cultures for soil- inoculation have been offered to the public. The first of these utilized absorbent cotton to transmit the bacteria in a dry state from the pure cultures in the laboratory to the user of the culture, who was to prepare therefrom another culture to be used for inoculating the soil. Careful investigation of this method showed that its weakness lay in drying the cultures on the absorbent cotton which frequently resulted in the death of the organisms. More recently, liquid cultures have been placed on the market in this country, but they have not yet been sufficiently well tested to prove their efficiency. It is undoubtedly NON-SYMBIOTIC NITROGEN FIXATION 429 only a question of time until a successful method of inoculating soil from artificial cultures will be found. In the meantime, inoculation by means of infested soil is the most practical method. 291. Nitrogen-fixation without symbiosis with higher plants.—If a soil be allowed to stand idle, either without vegetation or in grass, it will, under favorable moisture conditions, in the northern states, accumu- late in one or two years an appreciable amount of nitrogen not present at the beginning of the period. At the Rothamsted Experiment Station, one of the fields in volunteer plants, consisting mainly of grass without legumes, gained in the course of twenty years about twenty-five pounds of nitrogen per acre, annually. According to Hall, the nitrogen brought down by rain would account for about five pounds per acre per annum, and dust, bird-droppings, etc., for a little more. As pointed out by Lipman, there must also have been a greater total accretion of nitrogen during the twenty years than appears in the final result, as considerable must have been lost through removal of nitrates in drainage and escape of nitrogen in the ordinary processes of its transformation. 292. Nitrogen-fixing organisms.—Direct experi- ment has shown that certain bacteria have the ability to utilize atmospheric nitrogen and to leave it in the soil in a combined form. A_ bacillus—Clostridiwm ‘pasteurianum— was first found to produce this result. Later, a commercial culture called ‘‘ Alinit’’ was placed on the market in Germany, which culture it was claimed contained Bacterium ellenbachensis, with which the 430 THE PRINCIPLES OF SOIL MANAGEMENT soil was to be inoculated, and that a large fixation of atmospheric nitrogen would result. A number of tests of this material failed to show that it caused any marked fixation of atmospheric nitrogen. A number of other nitrogen-fixing organisms have since been discovered. There are: (1) Several members of the group designated Azotobacter, which are aérobic bacteria, and which some investigators hold to be capable of fixing atmospheric nitrogen when grown in pure cultures, and others believe to be able to do so, at least in large amounts, only in the presence of certain other organisms. (2) Mem- bers of the Granulobacter group, which are large spore-bearing bacilli of anaérobic habits. (3) B radiobacter, which appear to be closely related to or identical with the B. radicicola of legume tubercles. The latter has been shown to be able to fix atmospheric nitrogen even when not growing in symbiosis with legumes. There are doubtless many other nitrogen-fixing organisms ‘still to be discovered. A peculiarity of these nitrogen-fixing organisms is their use of carbohydrates, which they decompose in the process of nitrogen-fixation. They secure more atmospheric nitrogen when in a nitrogen-free medium. The presence of soluble lime or magnesium salts, es- pecially carbonates, is necessary for the best per- formance of the nitrogen-fixing function, as is also the presence of a somewhat easily soluble form of phosphorus. They are exceedingly sensitive to an acid condition of the soil. NITROGEN-FIXATION IN PURE CULTURES 431 293. Mixed cultures of nitrogen-fixing organisms.— Mixed cultures of the various organisms mentioned fix larger amounts of nitrogen than do the pure cultures of any one of them, while some forms are incapable of fixing nitrogen in pure cultures. Certain alge, par- ticularly the blue-green alge, aid greatly in promoting growth and nitrogen-fixation by these organisms. This they probably do by producing carbohydrates, which are used by the bacteria as a source of energy for nitrogen-fixation, the bacteria furnishing the alge with nitrogenous compounds. To what extent the relation is symbiotic is not known at present, but it seems probable that a relation may exist similar to that between leguminous plants and the nitrogen- gathering bacteria in their nodules. 294. Nitrogen-fixation and denitrification antagonis- tic.—Nitrogen-fixation and denitrification are reverse processes. The former is, for most bacteria, favored by an abundant air-supply and a moderately high temperature. Thus, at 75° Fahr., fixation was rapid; at 59° Fahr., it was decreased, and at 44° Fahr, there was none. Denitrification is favored by a some- what limited supply of oxygen. There is no reason to believe that the practical importance of nitrogen-fixation without legumes is equal, under the most favorable conditions, to that with legumes. A further knowledge of the organisms effecting fixation and of their habits will doubtless make possible a greater utilization of their powers, to supplement the use of legumes, as a source of com- bined nitrogen in the soil. EK. THE SOIL AIR I. FACTORS DETERMINING VOLUME The amount of air that soils contain varies with different soils, and in any one soil it varies with cer- tain changes to which it is subject from time to time. The factors affecting the volume of air in soils are: (1) The texture. (2) The structure. (3) The organic matter. (4) The moisture content. 295. Texture.—The size of the soil particles affect the air capacity of the soil in exactly the same way as it does the pore-space (see page 92), since the two are identical. A fine-textured soil in a dry condi- tion would, therefore, contain as large a volume of air as a coarse-textured one, provided the particles were spherical and all of the same size. Under the conditions actually existing in the field, those soils composed of small particles generally possess the larger air-space. 296. Structure.—The volume of air in a water-free soil being identical with the pore space, the formation of aggregates of particles is favorable to a large air volume. The volume of air in any soil, therefore, changes from time to time; and particularly is this true of a fine-grained soil, in which the changes in structure are greater thanin a soil with large particles. A change in soil structure may greatly alter the volume of air con- tained, by altering the pore space, thereby influencing the productiveness. Clay is most affected in this way. (432) THE SOIL ATMOSPHERE 433 297. Organic matter.—Organic matter being more porous than any size or arrangement of mineral particles, the effect of that constituent is always to increase the volume of air. While this is generally beneficial in a humid region, it is often very injurious in an arid one. Unless sufficient water falls upon the soil to wash the soil particles around the organic matter and to maintain a supply sufficient to promote decomposition, the pres- ence of vegetable matter leaves the soil so open that the capillary rise of moisture is interfered with, and the large movement of air keeps the soil dry, with the result that the portion of the soil layer mixed with and lying above the organic matter, is too dry to germinate seeds or support plant growth. 298. Moisture content.—It is quite evident that the larger the proportion of the interstitial space filled with water the smaller will be the quantity of air contained. This does not necessarily mean that the higher the per- BB 434 THE PRINCIPLES OF SOIL MANAGEMENT centage of water in the soil the smaller the volume of air, as the amount of pore space determines both the water and the air capacity. A soil with 30 per cent moisture may contain more air than one with a water content of 20 per cent because of the tendency of mois- ture to move the soil particles further apart. In soils in the field, the average diameter of the cross- section of the pore space is the most potent factor in determining the volume of air. Small spaces are likely to hold water, while the larger ones, not retaining water against gravity, are filled with air. In a clay soil, the volume of air is increased, other things being equal, by the formation of granules, and decreased by deflocculation or compaction. II. COMPOSITION OF SOIL AIR The air of the soil differs from that of the outside atmosphere in containing more water vapor, a much larger proportion of carbon dioxid, a correspondingly smaller amount of oxygen, and slightly larger quantities of other gases, including ammonia, methane, hydrogen sulphid, etc., formed by the decomposition of organic matter. 299. Analyses of soil air.—The composition of the air of several soils, as determined by Boussingault and Lewy, is quoted by Johnson in the table on the follow- ing page. There are several factors influencing the composition of the soil air, those of greatest importance being the production and the escape of carbon dioxid, while of COMPOSITION OF SOIL AIR 435 TABLE LXV Volume in one Composition of 100 parts acre of soil to res depth of 14 inches soil-air by volume Character of soil Air Carbon | Carbon r Nitro- dioxid dioxid Oxygen gen Cn. tt. "Cutt. Sandy subsoil of forest..| 4,416 14 | 0.24 Ds of saint Loamy subsoil of forest.| 3,530 28 4. 0.79 19.66 | 79.55 Surface soil of forest....| 5,891 Oe 0.87 19.61 | 79.52 5 Ge) | a hier ane 10,310 71 | 0.66 | 19.99 | 79.35 Soil of asparagus bed not manured for one year.| 11,182 86 | 0.74 | 19.02 | 80.24 Soil of asparagus bed freshly manured ..... 11,182 172 | 1.54 | 18.80 | 79.66 Sandy soil, six days after manuring ...... 11,783 257 | 2.21 Sandy soil, ten days after manuring (three days Seay ee. SP ee 11,783 | 1,144 | 9.74 | 10.35 | 79.91 Vegetable mold compost | 21,049 772 3.64 | 16.45 | 79.91 less influence is the excretion of carbon dioxid and utili- zation of oxygen by plant roots. 300. Production of carbon dioxid as affecting com- position.—Although the formation of carbon dioxid in the soil depends upon the decomposition of organic matter, it is not always proportional to the quantity of organic matter present. The rate of decomposition varies greatly, and where this is depressed, as is some- times seen in muck or forest soils, the content of carbon dioxid is low. A high percentage of organic matter is in itself likely to prevent a proportional formation of carbon dioxid by the accumulation of the gas inhibiting further activity of the decomposing organisms. 436 THE PRINCIPLES OF SOIL MANAGEMENT Ramann states that the percentage of carbon dioxid in the soil air has the following relations: The carbon dioxid increases with the depth. In general the percentage of carbon dioxid rises and falls with the temperature, being higher in the warm months and lower in the cold months. Fic. 116. Dise cultivator fitted with fenders. Changes in temperature and air pressure change the percentage of carbon dioxid. In the same soil the content of carbon dioxid varies ereatly from year to year. An increase of moisture in the soil increases the per- centage of carbon dioxid. The amount of carbon dioxid varies in different parts of the soil. 301. Escape of carbon dioxid as affecting composition. FUNCTION OF THE SOIL AIR 437 —The movement of carbon dioxid from the soil depends chiefly upon diffusion into the outside atmosphere. The conditions governing diffusion, which will be dis- cussed later (page 439), therefore largely determine the rate of loss of carbon dioxid from the soil. 302. Effect of roots upon composition.—The absorp- tion of oxygen and excretion of carbon dioxid by roots has a real, but as yet unmeasured influence upon the composition of the soil air. It is worthy of note, however, that the carbon dioxid thus excreted is in a position where its aqueous solution can be of the greatest benefit to the plant in its solvent action upon the soil, as it is in direct contact with the absorbing portion of the roots. III. FUNCTIONS OF THE SOIL AIR Both carbon dioxid and oxygen as they exist in the air of the soil have important relations to the processes by which the soil is maintained in a habitable condition for the roots of plants. Deprived of these gases, the soil would soon’reach a sterile condition. 303. Oxygen.—An all-important process in the soil is that of oxidation, because by it the organic matter that would soon accumulate to the exclusion of higher plant life is disposed of, and the plant-food materials are brought into a condition in which they may be absorbed by plant-roots. The presence of oxygen is essential to the life of the decomposing organisms and to the complete decay of organic matter. Through this process, roots of past crops, as well as other organic matter that has been plowed under, are removed from the soil, 438 THE PRINCIPLES OF SOIL MANAGEMENT The process of decay gives rise to products, chiefly carbon dioxid, that are solvents of mineral matter, and leaves the nitrogen and ash constituents more or less available for plant use. Oxygen is also necessary for the germination of seeds and the growth of plant-roots. These phenomena, although not involving the removal of large quantities of oxygen, are yet entirely de- pendent upon its presence in considerable amounts. 304. Carbon dioxid.—The solvent action _ eee of carbon dioxid Fig. 117. Hand cultivator, or wheel hoe, with is 1ts most 1m- attachments. port ant fune- tion in the soil. By its solvent action it prepares for absorption by plant-roots most of the mineral substances found in the soil. Although a weak acid when dissolved in water its universal presence and continuous formation during the growing season results in a large total effect. Carbonic acid dissolves from the soil more or less of all the nutrients required by plants. The amounts so dissolved are appreciably greater than those dissolved in pure water. The constant formation of carbon dioxid by decomposition of organic matter keeps this solvent continually in contact with the soil. Carbon dioxid serves a useful purpose in combining MOVEMENTS OF THE SOIL AIR 439 with certain bases to form compounds beneficial to the soil. Particularly is this the case with calcium carbo- nate, which is of the greatest benefit to the soil in main- taining a slight alkalinity very favorable to the develop- ment of beneficial bacteria and to the maintenance of good tilth. When combined as sodium or potassium carbonate in considerable quantity, as in certain alkali soils, a very injurious action upon plant-roots, and upon soil-struc- ture results. Upon plants it acts as a direct poison. (See page 312.) The effect upon soil structure is to de- flocculate the particles producing the separate grain or compact arrangement. (See page 116.) IV. MOVEMENT OF SOIL AIR There is a constant movement of the air in the inter- stitial spaces of the soil, and an exchange of gases between the soil atmosphere and the outside atmosphere, as well as a more general but probably less effective, movement of the air out of, or into the soil, as the controlling conditions may determine. The movement may be produced by any one or more of the following phenomena: (1) Gaseous diffusion. (2) Movement of water. (3) Change of atmospheric pressure. (4) Change of temperature in soil or atmos- phere. (5) Suction produced by wind. 305. Diffusion of gases.—The wide difference in the composition of soil and atmospheric air gives rise to a movement of gases due to a tendency for the external and internal gases to come into equilibrium, According 440 THE PRINCIPLES OF SOIL MANAGEMENT to Buckingham, the interchange of atmospheric and soil air is due in large measure to diffusion. The rate of movement of the soil air due to diffusion is dependent upon the aggregate volume of the interstitial spaces, and not upon their average size. Thus it is the porosity of the soil that influences most largely the dif- fusion of the air from it, and consequently the size of the particles is not afactor, but good tilth permits diffusion to take place more rapidly than does a compact condi- tion of soil, as the volume of the pore space is thereby increased. Compacting the soil in any way, as by rolling or trampling, has the opposite effect. 306. Movement of water.—As water, when present in a soil, fills certain of the interstitial spaces, it thus decreases the air space when it enters the soil and increases it when it leaves. The downward movement of rain-water produces a movement of soil air by fore- ing it out through the drainage channel below, while at the same time a fresh supply of air is drawn in behind the wave of saturation, as the water passes down from the surface.. The movement thus occasioned extends to a depth where the soil becomes permanently saturated with water. Twenty-five per cent of the air in a soil may be driven out by a normal change in the moisture content of the soil. 307. Changes in atmospheric pressure.—Waves of high or low atmospheric pressure, frequently involving a change of .5 inches on the mercury gage, cross the continent alternately every few days. The presence of a low pressure allows the soil air to expand and issue from the soil, while a high pressure following, causes the out- FACTORS AFFECTING SOIL AERATION 441 side air to enter in order to equalize the pressure. An appreciable, but not important movement of soil air is produced in this way. The size of the interstitial spaces is more potent than their volume in effecting soil ventilation by this and the following methods. 308. Changes in temperature.—A movement of soil air may be induced by a change of temperature in the atmosphere or in that of the soil itself. Changes in atmos- Fic. 118. The hillside plow. The hinged share and moldboard permit con- tinuous plowing on one side of the land. pheric temperature act in the same way as do changes in atmospheric pressure; in fact, it is the effect of tem- perature upon air pressure that causes the movement. Like the movement due to atmospheric pressure, it is not great; but where the soil immediately at the sur- face of the ground attains a temperature of 120° Fahr. at mid-day, as occurs in the corn-belt, the movement must be appreciable. The diurnal change in soil temperature decreases rapidly from the surface downward, due to the absorp- tion and slow conduction of heat. (See page 455.) At the Nebraska Experiment Station, the average diurnal range for the month of August, 1891, was as follows: 442 THE PRINCIPLES OF SOIL MANAGEMENT D1uRNAL RANGE oF AIR AND SoIL TEMPERATURES Degrees Fahr. Air S Test anove. ground: 6s. ys oss nse oe etenea eet 14.4 Soil 4 mel below eirtee: ses lie oan ce es eee 17.9 Soil: 3 inches halowipurieee: sis si ose ec ee 14.8 Sorl:G inehed below auriace: 6 i660 ocd fio ew oe esl ee 9.2 PGi D-IWMeNee WClOW BUTINCE ov .s6 can a er 2 Fe mos saosin ra - ee ee rapa’ - - = Bast # pe CROP-ROT ATION 503 certain types of soil. Cherries and peaches succeed best on a lighter soil than apples may be best grown on. Muck soils are eminently adapted to the growth of celery, onions, etc. With the extension of careful soil and crop surveys, these relations are becoming better known and are extending from groups of plants to species and varieties of plants. By the same methods our informa- tion concerning these relations must be extended until the production of crops rests upon definite knowledge of the plant requirements on the one hand, and the soil capacity and the means available to alter the soil environment on the other hand. Really intelligent hus- bandry can rest only upon the basis of exact knowledge concerning these two groups of facts and principles. V. RELATION OF SOIL PRODUCTIVENESS TO CROP- ROTATIONS At an early time in the development of agriculture, it was understood that a succession of different crops upon any piece of land gave better returns than one crop raised continuously. The plan of changing the crops grown each year thus became customary, and the universality with which it was practiced by Euro- pean peoples shows that its value must have been dis- covered independently in many communities, as ideas, particularly agricultural ones, traveled very slowly in the middle ages. In Great Britain and some of the countries of Europe, crop rotations have been most systematically and effec- tively developed. This has been the natural result of 504 THE PRINCIPLES OF SOIL MANAGEMENT the incentive arising from diminishing productiveness of the soil consequent upon long-continued cultivation, coupled with an increasing population. Countries having undepleted and uninfested soil, or an unpro- gressive people, have done little with crop-rotations. Another condition that discourages the use of crop- rotation is the suitability of a region to the production of some one crop of outstanding value, combined, per- haps, with a relatively cheap supply of fertilizing ma- terial. The abundant use of fertilizers may postpone for a long time the recourse to crop rotations. 356. Principles underlying crop-rotation.—There are many benefits to be derived from a proper rotation of crops that are not directly concerned with soil-produc- tiveness. The practice of crop-rotation must depend upon certain principles in soil management, some _of the most prominent of which are mentioned below, and are modified by climatic, topographic, geographic and economic features, and sais other factors, that cannot be treated here. 357. Nutrients removed from the soil by different crops.—Some crops require large amounts of one fertilizing constituent, while others take up more of another. As before pointed out (see page 294), cereal crops are able to utilize the potassium and phosphorus of the soil to a considerable degree but have less ability to secure nitrogen. They are, therefore, usually much benefited by the application of a nitrogenous manure and leave a considerable residue in the soil. A number of other crops, as, for instance, beets and carrots, can utilize this residual nitrogen. Grasses remove compara- PRINCIPLES OF CROP-ROT ATION 505 tively little phosphoric acid. Potatoes remove very large amounts of potassium. A rotation of crops is, therefore, less likely to cause a deficiency of some one constituent than is a continuous growth of one crop, and it utilizes more completely the available nutrients. 358. Root systems of different crops.—Some crops have roots that penetrate deeply into the subsoil, while others are only moderately deeply rooted, and others quite shallow-rooted. Among the deeply rooted plants are alfalfa, clover, certain of the root crops, and some of the native prairie grasses. Representing those having moderately long roots, are oats, maize, wheat, meadow fescue, grass, etc., and among those having shallow roots are barley, turnips and many of the cultivated grasses. As plants draw their nourishment from those portions of the soil into which their roots penetrate, the deeper soil is not called upon to provide food for the shallow- rooted crops, and the deep-rooted crops remove rela- tively less of the nutrients from the surface soil. It therefore happens that a rotation involving the growth of deep- and shallow-rooted crops effects, by utilizing a larger area of the soil, a more economical utilization of plant nutrients than would a continuous growth of either kind. 359. Some crops or crop treatments prepare food for other crops.—It is quite evident that the growth of leguminous crops, even when not plowed under, leave in the soil an accumulation of organic nitrogen trans- formed by bacteria from atmospheric nitrogen. This, in the natural course of decomposition and nitrification, becomes available to cereal or other crops that may follow 506 THE PRINCIPLES OF SOIL MANAGEMENT in the rotation. The presence of a grass crop upon the land for several years favors the action of non-symbiotic nitrogen-fixing bacteria, as already explained (see page 429). The grass crops also leave a very considerable amount of organic matter in the soil, which by its gradual decomposition contributes both directly and indirectly to the supply of available nutrients. As the organic matter left by the legumes and grasses decomposes slowly, these crops should be followed by a coarse feeding crop, like corn or potatoes, and one which is at the same time a cultivated crop, as are these. Stirring the soil at intervals during the summer greatly facilitates decomposition, and leaves a supply of easily available food for more delicate feeders, like wheat or barley, that may follow the cultivated crop. The intro- duction of cultivated crops in the rotation thus serves to prepare food for the non-cultivated ones. Although practical difficulties sometimes make it impossible to follow the cultivated crops with winter wheat, the prac- tice, where proper preparation of the seed-bed is pos- sible, is a good one. 360. Crops differ in their effect upon soil structure.— Plants must be included among the factors affecting the arrangement of soil particles. The result of practi- cally all root growth is to improve the physical condi- tions of the soil, to a greater or less degree. In general, crops with rather shallow and very fibrous roots are most beneficial, at least to the surface soil. Millet, buck- wheat, barley, and to a less extent wheat, leave the soil in a friable condition. It is upon heavy soils that this property is most beneficially exercised. *ajsnonuiyuo0o peddoio ueeq pey 4J9] 94} UO qeyy, “SIveA 9014} 10} S8BIS Ul useq pey oinjord 94} jo 443 ey} UO pue ey, -doio oziem Supesoons UO pos JO yOoHo BUMOYS “LCT “O17 508 THE PRINCIPLES OF SOIL MANAGEMENT Tap-rooted plants, and others with few surface roots, do not exhibit this action. Alfalfa and root crops are likely to leave the soil quite compact as compared with the crops mentioned above. The effect of sod is generally beneficial, and this is one of the reasons for using a grass crop in a rotation. 361. Certain crops check certain weeds.—By rotating crops, the weeds that flourish during the presence of one crop upon the land may be greatly checked by succeed- ing crops. Some weeds are best destroyed by smothering, for which purpose small grain and notably corn or sor- ghum sown for fodder are effective. Others are most injured by cultivation, to accomplish which the hoed crops are needed; while others can best be checked by the presence of a thick sod on the ground for a number of years. In the warfare against weeds that must be carried on wherever crops are raised, the use of different crops involving different methods of soil treatment is of great service. - 862. Plant diseases and insects checked by removal of hosts.—Many plant diseases and many insects spend their resting stages and larval existence in the soil. A continuous growth of any one crop upon the soil favors the increase of these species by providing each year the particular plant upon which they thrive. A change of crops, by removing the host plants, causes the destruction of many diseases and insects through their inability to reach their host plants. A long rota- tion, such as is frequently used in Great Britain, is particularly effective in eradicating those diseases that persist in the soil for a number of years. In the case of REASONS FOR CROP-ROTATION 509 diseases that affect more than one species of plant, as does the beet and potato scab, there is need for special care in arranging the rotation. Such considerations may frequently make it desirable to change the plan of a rotation. Another feature of the relation of crop rotation to plant diseases is that the more thrifty growth obtainable under rotation assists the crop to withstand many dis- eases. 363. Loss of plant-food from unused soil.—A system of crop-rotation permits a more constant use of the land than is possible with most annual crops. As a soil bearing no crop upon it always loses more plant- food than one bearing a crop, it is thus possible, by a well-chosen rotation, to save plant-food that would otherwise be lost. 364. Accumulation of toxic substances.—That the soil frequently contains organic substances that exert an injurious effect upon the growth of certain plants is indicated by recent experiments and was surmised by some early writers upon the subject. De Candolle was probably the first to advance the idea in 1882. He suggested that at least some plants excrete from their roots substances that are injurious to themselves, although harmless or even beneficial to other plants. This he considered one of the reasons for the failure of many crops to succeed when grown continuously upon the land, while that same soil may be productive under a rotation of crops. Liebig, in his first report to the British Association in 1840, made a similar statement. Recently, Pouget and Chonchak, working with alfalfa 510 THE PRINCIPLES OF SOIL MANAGEMENT soils, have reached the conclusion that alfalfa plants excrete a toxic substance which, gradually accumu- lating in the soil, injuriously affects the growth of alfalfa plants. Whitney, Livingston, Schreiner and their associates conclude that certain soils contain toxic substances of organic nature which may be produced by plant roots, or possibly by certain processes of de- composition of organic matter. They have isolated from soils organic compounds that are poisonous to plants. It is found, for instance, that cumarin, which is a normal constituent of sweet clover (Medicago alba, L and M., officinalis, P), may be obtained from certain soils, and that it is toxic to wheat seedlings,—from which it may be supposed that it is more or less toxic to other plants. Dihydroxystearic acid was isolated from certain soils by Schreiner and Shorey, who found that it is acid to litmus and decomposes BaCO, and CaCO,, forming the corresponding salts. The extracts of the soil containing this substance were toxic to wheat seedlings. The relation of soil acidity and soil toxicity is thus suggested. ; Working with different media in which wheat and other seedlings were grown, it was shown that, where the nutrient solutions were very dilute, so as not to enable the plant to overcome the effects of small quan- tities of toxic matter, the wheat plants grew much better when following other plants; and that, in spite of a renewal of the supply of nutrients, the wheat plants grew less well when one crop succeeded another. The cause of the lessened growth was attributed to the CROP ROTATION AND TOXIC MATERIALS 511 excretion from the plant roots of substances which, while more or less toxic to other plants, are especially so to plants of the same species. Although there are yet many phases and details of this subject to be worked out, there seems to be some relation between the presence in the soil of organic substances poisonous to plants and the continuous growth of one crop; and this may be considered to be one reason for the benefit derived on some soils, at least, from the practice of crop-rotation. INDEX PAGE Absolute specific gravity of soil ... 94 Absorption by the soil...........297 Causes of . Phat mrier Effect of adaarption .> eee SSO Effect of aluminum hydute oe 500 Effect of calcium carbonate.... .300 Effect of ferric hydrate.........300 Biteet OF MUMUSls fue ss oe nkcs Sees 300 Effect of size of particle........299 HHTeECH Ob ZEOLITES: .fecude at te cies 299 Influence in soil analysis........ 277 Insolubility of absorbed sub- SUM CES ei crests cicca es of 6 cee 299 MOCO TO Lists, hahah 3) ere hte acne cheers 301 Relation to drainage........... 302 Relation to productiveness ..... 306 Me CrEGUITCU ee oo aie tiaps aie oes 297 Absorption of nutrient salts ...... 286 Absorptive, physical............. 102 Absorption properties of humus. .128 Abundance of common minerals.. 8 Acidity of soil, effect of ammonium SUlTUhE er we tecie See kd tirana OnO TEMA PETEL C0 thd cS eg eT A a 349 Effect on availability of fertiliz- Ree Ae, oben cde ae ekeaue, ee 360 Effect on availability of phos- PLOTS heir cians ieee etek ate 361 Effect on bacteria........,....360 Effect on liberation of ee sium. fot . 360 In relation to ‘bacteria, ie 401 Acme harrow, efficiency xe Ste. 5 sae Adaptation of crops to soil, exam- pelkest | Pale EN oe ae a 503 Part in soil management........ 465 Maso PAClOre UM; ..)5 s+. ste doves 499 To soil, philosophy ............497 To soil, lack of knowledge..... 501 Adjustment of soil moisture....... 170 Adobe soil, relation to wind forma- ACNE A este ane Mes My foot cits Sade Stalk 62 Adsorption by the soil...........301 AreGh On Nitrates... el. eee ss 301 Relation to plant nutrition... .301 PAGE PROLGHYTOCKS) oo s.atee ect roe 11514 fEolian soils, ng Sane Ole ee 60 Composition of . Si cider rake Oe Relation to loess . ae 60 Aération, effect on availabilie of PELUUIZETS = Fe07 costes eee ae ee 359 Effect of drainage on..........242 Effect of nitrification..........416 Agencies of rock decay........... 14 Plants-and animals......... 28 Agricultural classes of soil..... 74, i Air (oxygen) of soil, as factor in plant erow thet. soe eae 1 Circulation of, affects soil tem- DCTAUUTE too c0e ens Soe) eee 461 Air of soil, effect of on percolation. 167 AITO GHEVSO lax epenearoe-« 2 etme 432 ANALYSES rat .5 caterer tie cto teat aes 434 Compositions ccsece ot eee 434 Carbon dioxide in: (oss . 2. 438 Effect of carbon dioxide produc- OMG MN are usta eevee od rete 435 Effect of cropping on ........% 447 Effect of irrigation on......... 447 Effect of manures on.......... 444 Effect of organic matter on... .433 Effect of roots on composition. .437 Effect of soil moisture on...... 433 Miect; of structure. <2 .../.<,0:20.5 432 Eifect of texture. 4c2. 8505. 6 432 Effect of ‘tillase Om sic = 3% ce 444 Effect of underdrainage on... .445 Escape of carbon dioxide.. ....436 BAGUIO Ma os deseo Ae ate crete tens 437 Modifying volume and move- LACUS ah FR ees aA Be POE ee eae, a: 443 Movements . : UNS cease Movement due hice atmospheric pressure. : . .440 Movement dine io gaseous “dif- EUS IOI fo 5 sw as Svany 2S ovo eee 439 Movement due to temperature .441 Movement due to water....... 440 Movement due to wind........ 443 GySIOATION =. 5 crsalchee monn eee 437 GG (513) 514 INDEX PAGE PROTA a eee hartyss a ol nent tte & 394 PAVNTIN ER tz ahicatasorateie ane al A ints ake ete 429 Alkalies, carbonate of, affect struc- DULG) eis s12) nae pPmrettiarcus Reet Ace 118 Alkali, relation to irrigation...... 230 Alkali salts, relation of drainage to DRMMO VAN iirc cee ee 247 PUA ROMS ait So ae 176 Influenced by fertilizers ....... 182 Measurement: Of). 205.00: a0n os a Modified by auies Se Ay Ge 183 Of water. : PoP ac es, Under cloth Reuit:. pete eke. Is” Capillary water, character and amount of . .144 Distribution aifestad by guivity, 148 516 PAGE Capillary water, relation to texture 144 Relation to structure........... 151 Supplies plants.. So . 142 Carbonates, of alkalies, affect soil structure. .118 Carbon, as plant-food element.. 3 Carbon? im htimisl. ee we eee “123 Carbon dioxide in relation to or- PRTG MAGE LS ctu. ar a crase ere wy he 361 Carbon dioxide in soil air......... 438 Carbonate of calcium, effect on soil.352 Case-ardenin gine wisrescs he es ee 101 Caustic lime, effect on soil......... 352 Cellulose, decomposition by bac- teria . Hee Ride each piety es 4015 Comentation, of granules Pace LOG Cementing materials. Meee HOO Cereal crops, absorption ‘ot nutri- CUUSAM eS Pe ee re Rhee eee tee 294 AS STEEN IMANUTES:.. 00.5%... Oot Chain harrow2se OL... an. a. 20808 486 Chamberlin and Salisbury, char- SCteRr Or miInerals:.cc.0.0050: 8 Characteristics of minerals ....... 8 Characteristics of the soil ........ 2 Checking and formation of gran- UTLGS ee ecet ett Otc oe? oral a pnt ae 106 And moisture content......... 106 Checekmerot soll enn eee eS Relation to evaporation........ 99 Relation tovdrylngs: ..2 2.5.2. 106 Relation to weakness.......... 106 Chemical, agencies of rock decay.. 14 Chemical analysis of soil, complete solution . . .268 Extraction by “distilled water. .276 Interpretation .. Ria ee net g Be PAT AU Manunalimeedsits 2525 oo. 270 Permanent fertility ............ 269 Strong hydrochloric acid....... 269 Use of carbon dioxide for...... 275 Use of organic acids............ 273 Chemical composition of soils.... 30 Chemical decay of rocks, decom- position . ge Sok Ais aerial fe! Chemical effects of organic matter.131 Chemical precipitates, rocks...11, 12 Chemical processes in soil, depend= ent on temperature........... 451 Chemical properties of arid and Jcyb Gna bto las s)l tae tenia oe heme 64 Chert, influence on soil formation. 40 Chief groups’ of soils’: 5... 225... (67 INDEX PAGE Citric acid, use in soil analysis... .274 Clark, abundance of minerals.... 9 Proportion of element in earth’s CTUSG Sas: God els. ble ee er 4 Classes of manures)... 0. .0 see hee 322 Doll FExtwrsl’ Aya ec oon ee 74, 76 Number of particlesin......... 82 Classification of rocks......... LOPE Classification of soils............ 30 Classification of soil textural..... 70 Clay soil: 25.4 See eee eee 74 Clay soil, evaporation in checks. .197 Organic matter in)... 2...) eee Ls Climate, influence on percolation .193 Humid conditions requiring ITTISACION. 22 sale OM a eee 226 Relation to irrigation practice. .224 Clod-crushers, types of.......... 489 Clod, relation granule... a » SI Cloth tent, effect on soil moisture: 214 Cohesiveness of soil. ............. 98 Cold and heat, agency of rock GeCAY’ 250 ase t Ooo Meee 18 Cold soils, meaning of........... 462 Colloidal clay and plasticity...... 97 Colluvial soils, characters of..... 45 Colorsof soiliic 20a. nee 101 Color of soil, affected by humus. . .130 Effect on temperature......... 456 Commercial fertilizers........... 322 Constituents). 2a5¢40.4008 een ee 324 Funetion 0.0 tc. Sa eee Compacting soil, importance of drainage in. Rar ss ( Composition of alluvial soils. . 52; 56 Arid and humid soils.......... 65 Atmosphere: 25 2.)..2s 4 oo eee 16 Effect of roots on composition .437 Escape of carbon dioxide...... 436 Glacial soils: 23452). ee eee 57 Marine'soilsi 00). oe een 49, 50 Residual soils . rs oS ee Rocks and residual sails. a see 32 Soil air. a oh 6 Oe eee Soil air, Effect of ‘earbon dioxide production on. eed .435 Soil-forming minerals eee i: v4 Soil) separates’). ..): 200. sete eens Soil, relation to’ rock......°2.. esi Soil, relation to texture ....... 87 Soils, chemical......... Slayeeene 30 Wind-formed soil. 22025 ee 63 Composting manure............. 380 , | : : INDEX ikZ PAGE Computation of value of fertiliz- GTS sercngihes Meters kee ne ane cate nates 345 Conditions affecting growth of DaACteniatad scsi eh tes sie 399 Conditions affecting structure ....103 Conditions requiring irrigation... .221 Conductivity of heat by soil...... 459 Conduction of heat, effect on tem- DETAUUTG sae an ee ouster 452 Constituents; of 80S... 3.2... 22. 5. (69 Constituents of soil, organic ..... 119 Control) Offerosioni is jas oe = tee Boca 34, 36 Engineering in irrigation........ 222 Erosion, agencies causing........ 492 By water, conditions permitting 494 Controlrore 2s. soe Boas eae Relation of drainage to........ 247 Evaporation .. . 164 Evaporation, affected by ‘checking 99 Affectéd’ by winds... . css = 213 At Rothamsted’....c. sec. es L9G Effect of on soil temperature. . .461 PAGE Evaporation, from weeds and green MMATUTC | os cas cid) 0 ae SRO 195 From soil, wastes water........ 195 Occurs at surface............. 196 Prevented bys, 2.5: 0's sine ame Prevented by special treatment. 213 Proportion of rainfall lost in United States...............196 Relation to irrigation.......... 197 Relation to mulch formation. ..198 Ridge culture to prevent...... 216 Excreta, solid of manure........ 364 Exhaustion of mineral nutrients. . 285 Exhaustion of nitrogen.......... 328 Exhaustion of plant food......... 285 Expansion, of minerals and rock by heat: io e266 250 cee 19, 20 Soil due to: water. .%\.") 5 seuraee 162 Factors in plant growth.......... 1 Factors which determine soil tem- DeratliTre.< so7.)- =. ace eee tee 453 Failyer table, composition of soil SEDBTAUCN SS ssc oe ees ates 86 Fall plowing@c2 a: ses- cts oe eee 210 Farm manures... s50. 2 2) eee 363 Fermentations of manure........ 375 Ferric hydrate, effect on absorp- TON sin oleate it eee 300 Fertility of land, relation to irri- PatiOn. es ow ee le eee 225 Fertilizer, brands:...... . 2. sme 343 Ammonium sulfate............ 326 Availability of phosphates..... 339 Basie’ SISg ci. arses © ove eet ee 337 Bone phosphate...............d00 Bone tankage:.....2..2..0...2. soou Calcium cyanamid)...... 2.05...) 328 Calcium ‘nitrate... 52... .sseen 331 Commercial). >.: 2. 2a...) ees 322 Computation of value.......... 345 Constituents.. ... oe ieee Containing phosphorus - a bSL See 334 Cumulative need for. -. >... -e 363 Double superphosphates....... 339 Dried’ bloud'Ss.. 2). ss se eee 333 Dried meat. AR tans eet) c-:! Effect of anit acidity on availa- DILYS oe se ae eee 359 Effect of soil moisture on availa- Dility 3 Os sec. sant cre ee 358 Factors affecting efficiency..... 355 Function}. 0.252008 one eee 322 a ta ee eS Ss INDEX 519 PAGE PAGE Pertilizer®; Guand vecasecd i cciew ns 333 Food supply in soil, affected by 18 al yf gs 0 ae ae AI ener Gna 343 GraINBRe Sree acc tiene 44 HOOLMealyee sacck eevee epare oar 334 Food of animal, effect on value of In relation to organic matter ...361 TYAN. Coa ee eae he BY (5, Insoluble potassium .......... 342 Force of frost information ....... 20 IMSDOCUIOW. ctoncrccke wae ak a eaten 344 Formation of soils, elements lost WOE cobs. er es ae ee 341 RE Se Be Ev NUR Water: 34, 36 TGMEe=nitrOPeN) s/s ele 2 ene ae 330 ROrms!Gt Boles. 2 tinc.c onc te eee 141 EWA OTAGO ac, ho die he varee si eho 343 Friction, effect on movement of . Methods of applying........... 347 WRCCE cis cae ot ysis eae Ce 172 Mineral phosphates............ 335 Friction determined by texture. ..172 Mixing on the farm............ 346 Determines capillary efficiency .180 Miuisiate of potadl...... 2. 6. 0: 341 In movement of soil moisture, Nitrocenvlimerenc 255025 52 4 els 330 time ClEMENG so. s)shbec ese She 172 Organic nitrogen in............ 332 In moisture movement, relation Part in soil management ...... 465 ton ches te. cs ae ee 182 j 232 HUTTE aR eee or eer Pe Sane 342 Retards movement of moisture .180 Reverted phosphoric acid...... 338 Frost, force of in disintegration... 20 CSE LOLDAAIID 2 Sees SDR Rs eae ne aA 341 Fruits, absorption of nutrients. ..296 SOGWIMMMNGEALE «5. ho hoe ees « 324 Functions of manures........... 384 COREE STSTTLUWELBGEEN 0 Rs Bens Ae au ge gino 340 PON CHONS OF SOs stele ce see 1 SleaMmeGubOne! «a. .c0 c. sas 606 3p Dolan peace ar isc ere erate 437 Sulfate of potash ......... 5. .«6 341 Sol bactenisteneis. < hsas te cee 403 Superphosphates.............. BBY h Water in soi: and plant........ 133 BRCATNCHIRE SS oot os) ha Pevceerors Siaee ce 334 Fungi, large, effect on the soil... .390 PRTAGE VALUE! o,5 osc. isitce chee 8 344 Microscopic, in the soil......... 392 Used for their nitrogen........ 324 Furrow back, meaning of........ 475 Used for their potassium...... 340 Dead, meaningsol .: 2.50.2 vee 475 RUCGGUASNES SRA: ce = .0e cele sts coach 342 Irrigation, conditions and crops Fertilizing, for cereal crops...... 295 FOS UNCUT AMES) taney oe RRP ater ise 231 BRANT IETODS canes ee ek heccinee ee 296 Irrigation, disadvantage of..... 231 “QUETSIE (Gide rene Ly ORR RE 295 Irrigation, principles of ........ 231 Leguminous crops............. 296 Proper width and depth of..... 472 ERCERDRCEOLIS efor Ae es carer ste aes 296 Breretalesircy: ect ist ais cree 296 Gallagher, expansion of soil by Field soil, surface area .......... 83 OW A GE Esavanstncra sti, a1 oye ca tarepean eye vee Available water in............ 157 On SOU SHTIMIKAGE)s -. co7. ws dla spals 98 MMMNYWRWADLGI Se csc hero Ws ic vale cw scouts 146 Soil moisture and physical prop- Film movement of water......... 169 CLUES re Mics ts es Sete Be hase 156 WA aIA ZESTRDSULES 220 sera es eg, oes ea 184 Geological classification of soils... 30 Film water and structure........ 105 Gevnlofy. NOtASQUS..% cic <.-cys stele 2 Film moisture, renewal of wastes Relation to soil study.......... 2 WELLE M ans A RE eRe eee 198 Georgeson, on effect of manure on Flocculation, affected by soluble SOL temperditure... «.)-% ses «i 464 SPDILNG) AS ices eRe ae eee 116 Germination, effect of soil tempera- Produced by carbonate of lime.352 MULTE! Ollie ot: lereva fa hremeen arene sett 448 Produced by caustic lime...... 352 Gilbert, and Laws, water used by Relation to structure......... 116 DISWESias ao hereae sicioe ce chia aenaiere 134 Flooding in irrigation practice. ...229 Glacial ice, agency in rock decay.. 27 Crops and conditions permitting 230 Influence on topography...... 28 Disadvantages of ..............231 Glacial soils, character of........ 54 Food, in soil, as factor in plant Chemical character of......... 56 ALU R ALE Ts fog Bea ne ee TAR ROR Be Lae COMMPORITIOD OL «oes woe sieale 57 520 INDEX PAGE Glacial soils, modified by water .. 59 Occurrence of. bthareteter tae) (OO Physical character of . PALS Oe Relation to underlying Pontes .95,'60 Grain, separate, structure......... 89 Granular struetume ok4 ok wis his el 91 Granulation, relation to texture... 92 Due to-ice crystelse<. seek eee 108 Relation to soil moisture........ 156 Granules, cementation of........ 106 Relation to checking.......... 106 Grass crops, absorption of nutri- CNIS chen ees eee Oe Ee 295 Protection to surface.......... 113 Gravitational water............. 160 ee ce carats A eae Injurioys tO:Crops <0. i060... 2-163 Movement of Hee 0) Pee eet eke 165 Relation to porosity...........161 Relation to texture. ; Gl Water, affected by eeseulntion: 164 Gravity, affects capillary distribu- 1010 ean Wee a ae nT aoe Pe 148 As agency of soil transportation. 45 Green IMANUTES sis pees gy hele 384 Green manures, and humus supply.132 CRTERL.CTODS — cect oe ean 387 Leguminous Crops.............080 May be injurious): ct... 03 OD Ground limestone, effect on soil. . .353 Growth of plants, influence of tem- PCLALULE! Os. son atenedeve ci. asics 449 Growth, requirementsof plantsfor. 1 Guano; Composition.......-....: 333 Gypsum, effect on soil .......... 354 Hall, effect of sodium nitrate on structure. SUES Hardpans, broken, up “by subsoil- ANS ES Sees hese Ree LO Hardpan soil, objections to ...... 475 Hard surface soil, repels rain water. nat bein oe dea aca eel Harrow, as ‘cultivator ae een eee 478 COUCH CHAM Ase ac kis sent cisteyaeiern s 486 EE CStOL aie cae ctereks the Pirersbele 482 Use in mulching land........... 209 Heat and cold, agency of rock de- cay. . re ATC aN es: Frost Rovio + on rock. Soe Ae OEE 20 Mechanical action of........... 19 Heat, increases solvent action.... 19 Heat of the soil, functions of..... 448 PAGE Heat of soil as factor in plant BTOWLIE ssc c5.5s.5'onis ols nee eee 1 See, also, Temperature. Heat, specific, of soil and water. ..455 Heaving, relation of drainage to.. .245 Hellriegel, best soil moisture con- OTN ie ose os os ie, She cha: Ohara 156 Water used by plants.......... 134 Henneberg and Stohmann, experi- ments with soil absorption. . .297 High grade fertilizers........... 343 Hilgard, nitrogen in humus...... 123 Volume weight humus........ 128 Hillside plow, advantages of..... 475 Hoof. meal’. } 2.05 #2 s.ia40 22 see 334 Horizontal movement of water. ..172 Horizontal movement under field CONGIIONG bis ine sisic, ove 0 2 Horse: manure’... ..0 2. eee 368 Hosmer and Whitney, soil moisture157 Humates. oe PM ke 2 ee Humid add! arid soils 35th e ee 64 Conditions, ipa of mulch.198 Properties........ ae of Humid climate, requirements of irrigation in. «6 dale cle een Organic inatters in. ate wre Lae Regions, ditiealty: ‘of keeping MULCH. cine Oe oan ee 204 Soils, composition Of /2 2... 65 Humus, defined’...22:. i... see mee Hummus; Carboni.) st... «see 123 Affects water capacity......... ees Effect on absorption ...2.... oe 300 Effect on color and temperature OF SOM SSS lcseeeoee eleven 457 Effect: on structure... oi... 0.00.8 ee Nitrogensin'’. 222 oeb... ce , >, Ets Wine om 134 Leaching of manure ............ old Oreanicamathers. asl nate os ek 27 Leaf mold. lente ait ays tok. Mem Legumes, Eaters on roots BEE A 423 Leguminous crops for green ma- nure. : ire .385 Absorption of nutrients ULAR a 296 Legumes, inoculation of soil for. . .427 Legumes, inoculation of soil for. . .425 Levees used in drainage......... 263 Level culture, generally best..... 216 Lime, carbonate effect on soil... .352 As cementing material........ 100 Lime, caustic effect on soil....... 352 iect) on humus... 2s. «6285 127 Effect on plant diseases........ 350 Effect on soil bacteria......... 348 Mech On -AtiiCtUre.< <.u.0)ss Gees 116 Bifect On -tilbhs..s a5 ats aote ee 348 Effect on toxic substances..... 350 Forms of, in relation to structure 117 Ground limestone, effect on soil .353 Liberation of plant food....... 349 Ne -MUETOREM: s sis. soe7s occa e eee 330 Lime, relation to magnesium..... 350 As a soil amendment.......... 348 PAIMESTON eG SOUS yess pau. crater aie 37 Lister, conditions where useful... .485 522 INDEX PAGE Loess, composition of ..... ...... 63 Physical characters of......... 61 Relation to wind formation.... 60 oem eembernin Gites. jon. 0 aus c's. ecto mc 61 Loose top soil absorbs rainfall... .217 Loss of nitrates from soil........ 418 Watermtron: sols: ek le 164 Loughridge, table, composition SOU SEHATAUESt a. a... 2 5s sss oe OO Low-grade fertilizers............ .343 Macro-organisms of the soil...... 388 Maintenance of organic matter. ..131 Magnesium, as plantfoodelement. 3 Magnesium, relation tolime....... 350 Management of dust mulch....... 205 External factors in............463 Mulches, summarized..........210 Soiland Texburewcichs cade sien 80 Soil moisture, highest type of. .238 MSiTIUTOR SM cece coco en De itoe etnwe eke 319 Manure, early ideas of function. . .320 As affected by food of animal. . .373 As affected by use of animal... .374 As affected by age of animal... .373 Conrposting: is... os PAROS 380 Conservation of ammonia....... 376 Deteénorationvos s...2i55000 8456 375 Different classes.............. Se Effect on volume and movement Ol SOUsAIT cache esis 444 Factors affecting value......... 373 Farm, formation of ammonia. . .376 Farm, loss of free nitrogen...... 377 HermentahiansyOL..: ss screen ale 315 For cereal crops .......... 295, 387 POMPQTASS CLOPSe os hae eee ete 295 For leguminous crops.......... 296 FOMrOOt TOPS as.ccincie sre ede 296 Eorivepetables’s. 22.0402 soak From animals, relative values. .371 Eiri DOULEY .2.....4. same 70 Decay, of rocks, disintegration.. 14 Support by soil as factor in plant srowih sis 3 3 chs cise eee 1 Meeker harrow, efficiency of...... 484 Merrill, composition of residual SOUS ond a es oa Oe 33 Example of atmospheric disin- tefrationy.. 65.) ks ee 18 Examples of expansion of rock.. 20 Method of calculating loss of rocks in:decay./s:..— . seca 31 Table, composition soil separates 84 Metamorphic rocks............ 11, 14 Micro-organisms, plant.......... 392 Micro-organisms in the soil...... 391 Miners’ inch, defined............ 228 Minerals, characteristics of...... 8 Absorbed by crops... ....2 ene 291 Amounts removed by crops... .281 Composition of important soil forming 5. 5.0.)504.4 ae eee eee Constituents of soil, absorption by TOOTS hha alt eee 279 Deficiency i«daie.sd acne wee 273, 280 a INDEX 523 PAGE Minerals, exhaustion of.......... 285 Groups Gl soca} aoe olcne oma 5 Important soil forming........ 4 Matter, decomposition by bac- NORAD ae oa ne & manta nex Se Se Nutrients, amounts contained INESOMS ieee is cc bicis wereld ae ee 282 Phosphates, composition . ..335, 336 Relative abundance of......... 8 Table of chemical and physical Hropertiessc.4).as...e6. 44 eee 6,7 Minimum capillary content and wilting .. ee ere a neces ave ligyps Minimum moisture content ee sto s E55 Mixing fertilizers on the farm... .346 Moisture in soil, as factor in plant PLOW UN ioe Sas ae 1 Affected by manures.......... Za As related to soil air.......... 433 Capacity of soil effect of texture AUGSUTMUCtULC «05.5 oss eek aes 216 Capillary fOrm 1.0. - oe cea es 144 Content and structure.........105 SUEITEEGUULE: clos Oc kcb ss cata ar eee 190 Crvtiealcontent. .<.4:."0% ssc s es 155 Decreasing loss of............ 191 Diffusion of vapor through soil.190 Effect of early spring plowing. .211 HeChTOL Salts. s'. scr 2 se ee 355 Effect of structure on move- EMESIS eetetens ate atete 3 cue oy ani e Brailes 182 ifect On porosity .......0..5. 2 162 BHeEtFOL Len ON. aoc come. 214 Effect on heat conductivity... .460 Effect on soil temperature..... 461 Forms and availability........ 141 Gravitational form............ 160 Hiyszroscopic form ... 55.3 54. Y: 143 Increased loss through rainfall.198 Maximum content............. 155 Means of decreasing.......... 238 Minimum content.............155 Of soil, adjustment of......... 170 Prevention of percolation...... 191 Relation to bacteria.......... 399 Should be stored deep......... 198 Special treatment to prevent BPORDOrAINON stick. bine ose. 213 Used by different crops........ 185 Use of hydrostaticform........ 194 See Water. Modification of structure........ 104 Soil temperature means....... 463 PAGE Modification of structure, texture. 87 Molds, slime se. <2 ee 394 Moldboard, relation of shape to character of soil............ 472 Sok airs en ere lee pee Sener hres 439 Soil air, methods for modifying. 443 Soil moisture, affected by damp- WN Ihc hin tisk Me haere Re eae 175 Soil moisture, due to texture. . .172 Soil moisture supplemented by EQOUR eS ota a cao aletatpna tT wus ees 174 Soil moisture, thermal..........189 Water, affected by friction ....127 Water affected by solution..... Ve Water, affected by structure. ..182 Water by soil, lack of data on. .185 Water horizontally............172 Wraterdinitsollesis6- se eee oka ee 165 1S Yc) Seep ae oS ol a a Rye 355 Miurcis (GeHned nt eae abc. aoe 121 Ammonia extract, effect onstruc- TUIDG es ee esate ph iie oe kee oe 115 Composition. . oF ee eens ao. Crude, effect on 1 structure. aria 355 Organic matter in. FT ey tee Effect on soil mnlavare. Ra heen Boo HormatienOb< .470% <3 ecto e ee 41 Quantity added to soil........ 355 Mulches, principles of ............ 199 Depend on rapid evaporation . .198 Depend upon preventing diffu- RIO oe So a Ore he se omen 189 Depth of . . 207 Eicciwcueet delenit ‘by REVO CUO ores arch ale Rieee es este nto 182 Effect on structure............ 119 Example of effect, Cornell Uni- VGESIUVic fais Stes e et eee dire 207 Equalize soil moisture......... 198 Implements for creating....... 207 Importance of texture.........205 RAIN BNOR alate heise el sreacvnse Sea 199 Management of dust. eR. s2US Management of, eannriaedl yA May be compact soil.......... 205 Most effective in arid regions. . . 204 Natural formation in arid and ugrrtid Glimisites\..c. . fislerae.c-s os 198 Relation to irrigation practice. .236 To prevent wind erosion ....... 496 When may be formed by roller .487 524 INDEX PAGE PAGE Mulching, grain fields.......... '. 208 Organic matter, amount in soil. ..124 Plow lnanth = sioenot ans aaeie ton eee Absorptive properties.......... 128 Muniate'of potash)... ./24 a 341 Affects water capacity..... 153, 361 And raw phosphates...........361 Nature, method of tillage........ 18 As coloring material........... 101 Nematodes in the soil........... 391 Composition +... «.:.m< + oe IZt Nitrogen, as plant foodelement... 3 Derivation: Of 2. 5. 3)24.4 see 128 INDGr ont fe tected rete aie ete 428 Organic nitrogen in fertilizers... .332 Nitrites, reduction to free nitrogen420 |* Organic soils...................4. 43 INDLTO=DACLCTAS none cae ses alete hee 412 Organisms in the soil............ 388 Nitrobacten 2x 2css-: hea ters eisioe 413 In soil, effect of drainage on... .244 INItrOSOCOCEUBiA 2 ee ict este ae rae Macro=, im the soil .22 255s 388 NrtrosomoOnas 4 4.0. on sao eee Micro=, in ‘the soil...4..; eee 391 Nitroussferments.trsc.s factors» 413 Of soil, importance of tempera- Nobbe, on germination and tem- ture fors<. ics So eee 450 perature..... UIT AS EVER SCOP, 449 Osmotic equilibrium in plants... .287 Nodules . : Pee rae es Outlet of underdrains, importance Nodules, ‘tpaantee ‘of ‘nitrogen to 70) IRE OEMS SIS ee 261 Plantes ss) besavccosere ees 425 Oxygen, as plant food element.... 3 Number of bacteria in soil....... 397 Relation to soil bacteria........399 Particles, calculation .......... Sit Oxidation, a function of soil air. . .437 Particlesmnasowiss x2 Sano sare 81 Nutrient salts, absorption of..... 286 Packers and crushers..........-.. 486 Selective absorption...........2S86 Packing of subsoil, benefits of... .212 Occlusion, relation to soil absorpt’n301 Oily substances on soil particles affects capillarity........... 183 Open drains, advantages and dis- advantages Of ..:.3.5........250 Construction Of xccqemi ete lets 250 Conditions permitting......... 248 Organic acids, use for soil analysis .273 Organic constituent of soil....... 119 Parkes, effect of drainage on soil tEMPELAtULels\é/. = 193 PYOPErbIeR Oke ive tears ae ee 97 Rothamsted figures on........ 192 BIOWS? EV DESL Obi ace el-e ciel Sree ear lee 471 Phosphate fertilizers............. 334 Attachments for uses.......... 476 Physical agencies of rock aay .. 14 Efficiency of depends on....... 470 Absorption .. ; .102 Effect on soil structure.........111 Character of soil, relation to. irri- 15 GUST (RRR PRR er aera ee enh tet een 0 875" PaO Mme. cieieieec SNteioe ate 224 MG E OlACTLONC. neers tycieeess sees 469 Chief groups of soil............. 66 Moldboard, adaptation to soil. .471 Effects of organic matter....... 129 Relation of use to soil moisture .470 Of arid and humid soil..... 64, 79 LS Ollbs cc cess c uksoemne ne eens het A477 (OP S(Ty LS Fe oa eee ica Ea fam marge eet 68 Plowing deep, advantages of..... 218 Processes in soil, relative to tem- Relation to humus supply ....218 WEUAOULO, 2 ins woe Shae Goel vsed tie 431 Pliow-land: mulching’. «2... ...... 209 Properties of soil-forming miner- Plow-sole, character of...........474 CEILS) SHER, Ce ES eee oo ea CER Hae Hone spacenm sll, se. cen. sama 93 Properties of soil most suited to Diameter of individual........ 94 flutter eh EDIN hroyantincsa cera alekacs rea 237, Porosity of rocks. eRe ea sek Pes ws 7.1) Piedmont soils. : nee. 2210) Affected by Aioisture . ere Fest Git 162 Planker, drag or ew, efficiency of 489 Calemlartons Of sere os-0) ote entre Se 92 Plants amount of water used by . .133 ChE SO1 lence erie os 2) chara es 92 And animals, oe in rock Potassium fertilizers.............340 decay .. ce Ahh tele Potato growing, straw mulches in. 202 Plant food, Slenments net EA ey lh Harvester, as cultivator........ 486 As factor FIA gee ON AT 0 Rta PP UE Wie 1 Potts, figures on heat conductivity Derived from rocks . Le ea eae: COV = CON (pests et aE NS A gs 2) 459 Derived from air and: water. ese aa Poultry MIaAMWres < alec. «si oes eee Diseases, effect of lime......... 350 Practices used in soil management .465 Elements, abundance of. 4 Practices in soil management, pri- Elements in soil, abundance. 68, 282 mary and secondary functions [Bshraittstion: Oso. vie es ess aecese Os 285 (CLE DRS Ese ig eat atte AAD coe Mat ttl 465 NEOUS FOL cred sics tm oven dada coal ede 3 Pressure of air, effect on percola- In the soil, amounts removed by LOT rete eis careless sich ats, ekenslat stele 168 POTS Aci oA og kay aie ehe PA OMLIE re yrs coe 281 IPMN Ary, MUIMeTALS ohh. ec e ve eters 5 Relation to crop rotations...... 509 Process of atmospheric rock decay. 16 Plant growth, factorsin......... 1 Productiveness of soil depends on. 36 Influence of soil temperature on 449 Plants, injured ay aaa water. 2 Phos .163 ae in the Soil, ay he 392 Physiological requirements in PUTO RION . Sceyieiscpins stitehenatace.< 499 Requirements for growth...... 1 Result of the inherent Saas of seed. ens Result of Erivironvbont. BE Rs one 1 Roots, effect on the soil........ .391 Roots, effect on soil structure...113 In relation to crop rotations. .. .503 PrOpeRMes OL SOM a. be hay. eto cies 68 Properties of soil separates....... 80 Par alecdestruC hire. von '+ 6 sina eve 90 Puddled soil, changed by lime... .117 Danger from subsoiling....... 478 Movement of water in......... 182 Pulverization, action of plow in. . .469 PTE NEURCHION at co. uta tite,.ci's0ayiene ecarer ovals 408 Quinke estimates molecular attrac- ORM eyS ERO a oare cae rer cea tt a ior sets 146 526 INDEY PAGE PAGE Rainfall, United States, map of . .137 Roots, effect on composition of soil Effect ORBULUCTUTE:: «,./c anew nts 119 BAY ein. visin ls bos dis a 437 Relation to irrigation practice ..222 Excretion of acids. afa . 290 When small, may cause loss of WW RUT copii bikt ecru. custetans Perey el orate 198 Rains, gentle; BESt. ....- Sccujl sss eo Raw phosphates and organic mat- 12) Reg Ss Eon tees pec mete ey aan 361 Reclamation oi alkali soil by drain- BLO. ick dacs ae eye. x eee eee 247 Reduction of nitrates to nitrites. .420 Nitrates to ammonia........... 420 Nitrites to free nitrogen ....... 420 Relation of lime to magnesium... .350 Residual soils. eae Peis. Wo eewi Charactetistios ‘of section Bnet. 40 Proportionate loss of elements in formation, table.......... 34 PWExGURG OL na tea elec at eres 41 Reverted phosphoric acid......... 338 Ridge culture,effect on evaporation 216 Ries~ on“ piasti@ity + «27. 01k see 97 Rise: Of alkali Wiv.o 3 kee some 314 Roberts, Plow Soles caine oe oe 474 Rodents effect on the soil ....... 388 Rocks, as ‘sourt@ of soil.......... 2 Aggregates of minerals......... 10 AnGite proaguets.(...'¢ 5. eae 2 AOUEOUS Stent sales whine: a ip Wee U2} ClassinGakiGi Obs .2.c-1. «= ott «ote 10 Decay, agencies of ............. 14 Decay, atmospheric........... 16 Decay, by solution............ 22 Decay, iceaSagency.......... Di. Decay, type of and composition of soil. bike 36 Decay, type of EeeT texture ae BO eee Oe eee eee s 36 Expansion due to heat......... 20 Igneous .. ee oreert aoe Wea |) Important soil-forming Alois Satta 9 IPOTOSIEVOE brie iate eho. Gee 21 Roller, conditions where effective .487 And packers, typesof ......... 486 Effect on soil temperature...... 459 Relation to percolation........ 194 When used to mulch soil........ 487 Roots, absorbing system.......... 292 Absorption of mineral matter... 277 As related to crop rotations... .505 Crops, absorption of nutrients. .296 Conditions where enter drains Se TA ite Pherae 253, 261 Hairs, relation to soil particles. . 287 Of plants, strike deep in drained BOW; o5.0s bs Saghevn we 5 2 ote 245 Qsmotic activity: i...... dane 292 Osmotic equilibrium in........ 287 Plants, effect on the soil... .391, 113 Rotation of crops... -.... .4 eee 503 Rotation of crops, principles of. . .504 Effect on soil structure.........506 Nutrients removed by......... 504 Part in soil management....... 465 Place\ioi manurein..- > eee 383 Relation to diseases and in- S6CtS \. 26 ase cs soe 508 Relation to loss of plant food .. .509 Relation to toxic substances. . .509 Relation to weed growth...... 508 Root systems of different crops.505 Some crops prepare food for Others’. g.2/.'6.2 ts eae 505 Rothamsted, figures on evapora- TON «kG 5 Ae 4 oni Se ee 196 Tables of percolations.......... 192 Rubbish, covering by plow.......476 Salisbury, and Chamberlin, char- acter of minerals............ Sachs, experiments on solvent ac- tion Of TOOtS. si so eee 288 Salt, effect on soil) 2... ts.s-e ene 354 Sand-dunes, damage by.......... 497 Naturally muleched.........:.- 206 Sandstone souls... .. 4. us see 39 Sandy BO ss c-clhciciaels cla c.cta ee 74 Sandy soil, organic matter in ...... 12 Sanitary conditions, effect of drain- AMS ON sh oiin.t ks lee sie hae 247 Saturation, total water for....... 161 And gravitational water....... Wave of in soil, useful ......... 194 Sawdust as litter in manure...... 368 Schubler, figures on effect of color on temperature <... .2..4.ee 457 On soil shrinkage. J... 2. «cums 98 Season, length of increased by Grainage . . 24... + +0 nee 243 Secondary minerals.............- 5 Sedimentary rocks..........-- 11,12 Sedentary soils... 25.0305 os serene 30 Sedentary soils, divisions of...... 31 INDEX PAGE Sediment, in water of chief rivers.. 26 Seeder types of cultivators........ 485 Selective absorption of nutrient salts. . , . .286 Semi-arid soils, composition GE is 65 Separate grain structure......... 89 Separates, properties of soil. ..... 80 Series, soil, defined... 78 SEALE IETIPMTION <6 vo. 6 s.cfesinw.cte «1s 222 ‘STREET Te aes Greene ee eigiek STAs e 39 Shapes of soil particles........... 7 Sheep manure. oeAtE sere! Silica as cementing santerial Et Sebastes 101 Silting up of tile drains.......... 258 SMAI h ers veer seine seoier teas ts 341 Size of particle, influence on soil MVROVUMON sass Hees Sociehies s -2O0 SWIC CIMOLUS has oe oicte eelctis ewes 394 Slope of soil, influence on tempera- CUESAS SOc ALAR ae ee 458 Shrinkage: Ol SOM sass: Gees dees ne OS Sod, effect on nitrification........ 417 ‘Sar Ts re) 324 Sodium nitrate, composition of. . .325 Deflocculating action.......... 325 Effect on structure............. 118 Effect on plant growth........ 325 WEED AEAUION c six ovetas. s). .:4 noe 280 Straw as litter in manure.......... 367 Packer.. «9 a Straw mulches, in potato growing. 201 Packing necessary i in 1 subsoiling. 220 Stream-formed soils........!.... 47 Sub-surface packing........... 212 Structure of soil, defined........ 88 Sulfate of lime, effect on soil ..... 354 Structure, conditions affecting... .103 Sulfate of potash:,. 2, «esse 341 Affected by animal life........ 118 Sulfur, as plant-food element ..... 3 Affected by carbonate of lime. .352 Sunshine distribution of in United Affected by caustic lime....... 352 States... i avida estes see ee ee 452 Affected by crop rotations..... 506 Relation to soil temperature 452, 453 Affects capillary water........ 151 Superphosphates, composition of .338 Affected by organic matter....114 Hertilizers) v.i2 33.605 6 > ors «ee 337 Affected by rainfall........... 119 Manutacture of)... .. seen 337 Affected by soluble salts....... 116 Supply of soil water. |... -..2 ee eee 136 Affected by surface covering. ..119 Surface area, in field soils......... 83 And moisture content......... 105 Calculation. of... ::... 20 eee 83 Crumb. a. SNORE LOE Relation to absorption..,..... .103 Effect on Se ME ee mov vameat. .182 Relation to texture.......... 82 Heat conductivity ........... 459 Surface covering, influence on struc-~ Percolation w ae 154 Way, experiments with soil absorp- GOUT wie Verse Bs, 2.2 aioe ee ee 298 Weed, defined #5 s2c0.5.2> soe .489 Control of, principles.......... 490 Deplete soil moisture.......... 195 Early and late tillage to kill... .491 How, Injdnous’. >... <0 ee eee 490 Implements useful to kill...... 492 Relation to crop rotation....... 508 Removal of saves water....... 216 Special methods of control..... 492 Weeders, type of cultivator.......483 Weight of soil . : oan ee Weight of soil, ee cubie foot. 96 Per acre-foot . wale . 96 Weight of oreame tintter in soil, .128 Weight of peat and muck........ 128 Wet soil, organic matter in .......125 Whitetalkalt 32.5 «> .