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Mi “ oe f sae ore i} 4s Erebeet by t ones poe ePad > if ebeberk koa ate ; ay } beatae! vain q \ Ho ¥ t ; Yee ablaee ' ryt ee - th Ht ne te ee ester tees 1 ui th 4] Pant be] ae gl bys op wbtoton phaser tees th Pair aint ted petites ’ ” bist isi riebteese ites iC Batt Ga ie} ey - ATE re tp 0 rt 2 sree mt ” . i, Tobe a printstrpet ro ee ” tat Dedede OA oboe aurautt ’ yee petty riet Vater rd me bee rr W Ee O nN 2) 0 i ee THEIR FORMATION, PROPERTIES, COMPOSITION, AND RELATIONS TO CLIMATE AND PLANT GROWTH IN THE HUMID AND ARID REGIONS BY E, W. BIEGARD, Px.) LED, PROFESSOR OF AGRICULTURE IN THE UNIVERSITY OF CALIFORNIA, AND DIRECTOR OF THE CALIFORNIA AGRICULTURAL EXPERIMENT STATION slew Alovk DHE MACWIRMAN COMPANY LONDON: MACMILLAN & CO.,, Lr. 1906 MIEKARY of CONGRESS Two Covies Received ear JUL 30 1906 Capyrent Entry 30,1906 LASS Q RAC. No, ys2ost — P COPY A, COPYRIGHT, 1906, By THE MACMILLAN COMPANY. Set up and electrotyped. Published July, 1906. Nortyood ¥ress : Berwick & Smith Co., Norwood, Mass., U.S.A. hy SUMMARY OF CHAPTERS. I, ORIGIN AND FORMATION OF SOILS. Introduction. Chapter I. 4 0G ss yey CG OV ac Wis Physical Processes of Soil Formation. Chemical Processes of Soil Formation. Chief Soil-forming Minerals. The Various Rocks as Soil-Formers. Minor Mineral Ingredients of Soils. Mineral Fertilizers. Minerals Injurious to Agriculture. 2. PHYSICS OF SOILS. Chapter VI. Hi VII. sf VIII. s* IX. ac De s XI. es XII oH XIII < XIV ss XV. i XVI. : XVII. Physical Composition of Soils. Density, Pore Space, and Volume-Weight of Soils. Soil and Subsoil ; Causes and Processes of Differen- tiation ; Humus. Soil and Subsoil ; Organisms Influencing Soil-Con- ditions. Bacteria. Soil and Subsoil in their Relations to Vegetation. Water of Soils; Hygroscopic and Capillary Moisture. Water of Soils; Surface, Hydrostatic, and Ground- water ; Percolation. Water of Soils ; Conservation and Regulation of Soil Moisture. Irrigation. Absorption by Soils of Solids from Solutions. Absorp- tion of Gases. The Air of Soils. Colors of Soils. Climate. Relations of Soils and Plant-Growth to Heat. 3. CHEMISTRY OF SOILS. Chapter XVIII. ibe XIX. “ XX. e XXI. ee XXII. UGE O-G08& Physico-Chemical Investigation of Soils in Relation to Crop Production, Analysis of Virgin Soils by Extraction with Strong Acids, and its Interpretation. Soils of Arid and Humid Regions. Soils of Arid and Humid Regions continued. Alkali Soils, their Nature and Composition. Utilization and Reclamation of Alkali Lands. ili iv SUMMARY OF CHAPTERS. 4. SOILS AND NATIVE VEGETATION. Chapter XXIV. Recognition of the Character of Soils from their Native Vegetation. Mississippi. os XXV. Recognition of the Character of Soils from their Native Vegetation. United States at large, Europe. he XXVI. Vegetation of Saline and Alkali Lands. TABEE, OF CONTENTS. RAGEOA CHS Pare parct ar cesitete rer cte ekoverae ere metas 5 eR RSS ean ne tear etenea arenes xxili INTRODUCTION, xxix.—Definition of Soils, xxix.— Elements Constituting the Earth’s Crust, xxix.—Average Quantitative Composition of the Earth’s Crust, xxix.--Clarke’s Table, xxx.—Oxids Constitute Earth’s Crust, xxx. —Elements Important to Agriculture ; Table, xxxi.—The Volatile Part of Plants, xxxii. CHAPTER I. AGENCIES OF Sorl, FORMATION, 1.—I. Physical Agencies, 1.—Effects of Heat and Cold on Rocks, 1.—Unequal Expansion of Crystals, 2.—Cleay- age of Rocks, 3.—Effects of Freezing Water, 3.—Glaciers ; Figure, 3.— Glacier Flour and Mud, 4.—‘‘ Green’’ and ‘‘ White’’ Rivers, 4.— Moraines, 5.—Action of Flowing Water, 5.—Enormous Result of Cor- rasion and Denudation, 6.—Effects of Winds, 8.—Dunes, 8.—Sand and Dust Storms in Deserts, Continental Plateaus and Plains, 8.—Loess of China, 9.—Migration of Gobi Lakes, 9.—Classification of Soils, 10.— Their Physical Constituents, 10.—Sedentary or Residual Soils, 11.— Colluvial Soils, 12.—Alluvial Soils. Diagram, 12.—Character of these Soil Classes, 13.—Richness of Flood-plain and Delta Lands, 14.—Low- ering of the Land Surface by Soil Formation, 15. CHAPTER II. CHEMICAL, PROCESSES OF SOIL FoRMATION, 16.—2. Chemical Disintegra- tions or Decomposition, 16.—Ingredients of the Atmosphere, 16.—Effects of Water ; of Carbonic Acid, 17.—Carbonated water a universal solvent, 17.—Ammonic carbonate, effect on silicates, 18.—Action of oxygen ; on ferrous compounds, 18.—Action of Plants and their Remnants, 19.—A. Mechanical ; Force of Root Penetration, 19.—. Chemical ; Action of Root Secretions, 19.—Bacterial Action, 20.—Humification, 20.—Cauwses Influencing Chemical Action and Decomposition, 21.—Heat and Mois- ture, 21.—Influence of Rainfall on Soil-Formation, 22.— Leaching of the Land, 22.—Residual Soils, 22.—Drain Waters ; River Waters. ‘Tables of Solid Contents, 22,—Amount of Dissolved Matters Carried into the Sea ; Amount of Sediment, 24.—Sea Water, Composition of ; Waters of Land-locked Lakes, 25.—Results of Insufficient Rainfall; Alkali Lands, 28. Vv vi CONTENTS. CHAPTER III. ROCK- AND SOIL-FORMING MINERALS, 29.—Quartz, quartzite, jasper, horn- stone, flint, 29.—Solubility of silica in water ; absorption by plants, 30. —Silicate Minerals, 31.—Feldspars, their Kaolinization, 31.—Formation of Clays, 33.—Hornblende or Amphibole, Pyroxene or Augite, 33.— Their Weathering and its Products, 33.—Mica, Muscovite and Biotite, 35.—Hydromica, Chlorite, 35.—Talc and Serpentine ; ‘‘ Soapstone ’’, 36. The Zeolites ; Exchange of Bases in Solutions, 36.—Importance in Soils, in Rocks, 38.—Calcite, Marble, Limestones ; their Origin, 39.— Impure Limestones as Soil-Formers, 40.—Caves, Sinkholes, Stalactites, Tufa, 41.—Dolomite ; Magnesian Limestones as Soil-Formers, 42.— Selenite, Gypsum, Land Plaster; Agricultural Uses, 42.—Iron Spar, Limonite, Hematite, Magnetite, 44.—Reduction of Ferric Hydrate in Ill-drained Soils, 45. CHAPTER IV. THE VARIOUS ROCKS AS SOIL-FORMERS, 47.—General Classification, 47.— Sedimentary, Metamorphic, Eruptive, 47.—Sedimentary Rocks; Lime- stones, Sandstones, Clays, Claystones, Shales, 47.—Metamorphic Rocks : Formed from Sedimentary, 48.—Igneous or Eruptive Rocks, Basic and Acidic, 49.—Generalities Regarding Soils Derived from Various Rocks, 49.—Variations in Rocks themselves. Accessory Minerals, 50.— Granites ; not always True to Name ; Sierra Granites, 51.—Gneiss. Mica- schist, 51.—Diorites, 51.—Diabases, 51.—Eruptive Rocks ; Glassy ones Weather Slowly ; Basaltic Oxidize Rapidly, 52.—Red Soils of Hawaii, Pacific Northwest, 52.—Trachyte Soils ; Light-colored, rich in Potash, Rhyolites generally make Poor Soils, 53.—Sedimentary Rocks, 53.— Limestones, 53.—‘‘ A Limestone Country is a Rich Country,’’? 53.— Residual Limestone Soils; from ‘‘Rotten Limestone’’ of Mississippi; Table, 54.—Shrinkage of Surface, 55.—Sandstone Soils, 55.—Vary According to Cement, and Nature of Sand, 55.—Calcareous, Dolomitic, Ferruginous, Zeolitic, 56—Clay-sandstones, Claystones, 57.—/Vatural Clays, 57.—Great Variety, Enumeration and Definition, 58.—Colors of Clays, 58,—Colloidal Clay, Nature and Properties, 59.—Plasticity ; Kaolinite Non-plastic, 59.—Causes of Plasticity, 60.—Separation of Colloidal Clay, its Properties, 61.—Effects of Alkali Carbonates on Clay, 62. CHAPTER V. THE MINOR MINERAL INGREDIENTS OF SOILS ; MINERAL FERTILIZERS, 63. —Minerals Injurious to Agriculture, 63.—/J/inerals used as Fertilizers, 63.—Apatite ; Phosphorites of the U. S., Antilles, Africa, Europe, 63.-—— Phosphatic Iron Ores, ‘‘ Thomas Slag,’’ 64.—Animal Bones ; Composi- tion and ‘Agricultural Use, 64—Vivianite, Dufrenite, 65.—Chile Salt- peter, 66. Occurrence in Nevada, California, 66.—Origin of Nitrate Deposits, 67.—Intensity of Nitrification in Arid Climates, 68.—Potash Minerals, 68.—Feldspars not Available, 68.—Depletion of Lands by Manufacture of Potashes, 69.—Discovery of Stassfurt Salts, 69.—Origin CONTENTS. vii of these Deposits, 70.—Nature of the Salts, 71.—Kainit, 71.—Potash Salts in Alkali Soils, 72.—Farmyard or Stable Manure ; Chemical Composition, Table, 72.—Efficacy largely due to Physical Effects in Soils, 73.—Green-manuring a Substitute for Stable Manure, 74.—Ap- plication of Stable Manure in Humid and Arid Climates, 74.—J/ine- vals Unessential or Injurious to Soils, 75.—Iron Pyrites, Sulphur Balls, 75. Occurrence and Recognition. Remedies 75.—Halite or Common Salt, 76.—Recognition of Common Salt, 76.—Mirabilite or Glauber’s Salt ; in Alkali Lands ; not very Injurious, 77 —Trona or Urao ; Car- bonate of Soda, ‘‘ Black Alkali,’’ 77. Injury Caused in Soils, 78.— Epsomite or Epsom Salt, 78.—Borax, 79.—Soluble Salts in Irrigation Waters, 79. CHAPTER VI. PHYSICAL COMPOSITION OF SoILs, 83.—Clay as a Soil Ingredient, 83.— Amounts of Colloidal Clay in Soils, 84.—Influence of Fine Powders on Plasticity, 85.—Rock Powder ; Sand, Silt and Dust, 86.— Weathering in Humid and Arid Regions, 86.—Sands of the Humid Regions, 86.— Sands of Arid Regions not Sterile, 86.—Physical Analysis of Soils, 88. —Use of Sieves. Limits, 88.—Use of Water for Separating Finest Grain- Sizes, 89.—Elimination of Clay by Subsidence and Centrifugal Method, Hydraulic Elutriation, 90..—Schone’s Instrument, go.—-Churn Elutriator with Cylindrical Tube, 91.—Figures of Same, 91.—Yoder’s Centrifugal Elutriator, 92,—Number of Grain-sizes Desirable, 93,—Results of such Analyses, 93.—Physical Composition Corresponding to Popular Desig- nations of Soil-Quality. Table, 96.—Number of soil-grains per Gram, 99.—Surface Offered by various Grain-sizes ,99.—Influence of the several Grain-sizes on Soil Texture, 100.—Ferric Hydrate, its Effects on Clay, 1oo.—Other Substances, 101.—Aluminic Hydrate, 101.—Influence of Granular Sediments upon the Tilling Qualities of Soils, 102.—‘‘ Phy- sical ’? Hardpan, 103.—Putty Soils, 103.—Dust Soils of Washington ; Table, Physical Analyses of Fine Earth, 104.—Slow Penetration of Water, 105.—Effects of Coarse Sand, 105. CHAPTER VII. DENSITY, PoRE-SPACK AND VOLUME-WEIGHT OF SOILS, I107.—Density of Soil Minerals, 107.—No Great Variation, 107,—Volume-weight most Im- portant, 107.—Weight per Acre-foot, 107.—Air-space in Dry Natural Soils. Figure, 108.—May be Filled with Water, 108.—Effects of Tillage. Figures, 1o9.—Crumb or Flocculated Structure ; Cements, I1o9.—How Nature Tills, 111.—Soils of the Arid Regions; do not Crust, 112.— Changes of Soil-Volume in Wetting and Drying, 112.—Extent of Shrinkage, 113.—Expansion and Contraction of Heavy Clay Soils. Figure, 113.—Contraction of Alkali Soils on Wetting, 114.—‘‘ Hog Wallows,”’ 114.—Physical Analyses of such Soils. Table, 115.—Crumb- ling of Calcareous Clay Soils on Drying, 116.—Yazoo Bottom, Port Hudson Bluff, 116.—Loamy and Sandy Soils, 117.—Formation of Sur- face Crusts, Physical Analyses, 117.—Effects of Frost on the Soil ; Heaving ; Ice-flowers, 118. vill CONTENTS. CHAPTER VIII. Soir, AND SUBSOIIL,; CAUSES AND PROCESSES OF DIFFERENTATIATION Humvus, 120.—Soil and Subsoil ill-defined, 120.—7he Organic and Or- ganized Constituents of Soils, 120.—Humus in the Surface Soil, 120.— Soil and Subsoil; Causes of their Differentiation, 121.—Ulmin Sub- stances or Sour Humus, 122.—Sour Soils, 122.—Cultivation Induces Acidity, 123.—Humin Substances, 123.—Porosity of Humus, 124.— Physical and Chemical Nature of the Humus Substances. Table, 124. —Chemical Nature, 125.—Progressive Changes and Effect on Soils, 126. —The Phases of Humification, Wood to Anthracite; Table, 127.— Amounts of Humus and Coal formed from Vegetable Matter, 128.— Figure, From Port Hudson Bluff, 128.—Conditions of Normal Humifi- cation, 129.—Eremacausis in the Arid Regions, 129.—Black Earth of Russia ; Kosticheff’s Table, 130.—Losses of Humus from Cultivation and Fallowing, 131.—Estimation of Humus in Soils; Unreliability of Combustion Methods, 132.—Grandeau Method, ‘‘ Matiére Noire,’’ 132.— Amounts of Humus in Soils, 133.—Humates and Ulmates, 134.—Mineral Ingredients in the Humus, 134.—Functions of the Unhumified Organic Matter, 135.—The Nitrogen Content of Humus, 135.—Table for Arid and Humid Soils, 136.—Decrease of Nitrogen Content in Humus with Depth, 138.—Table, Russian River Soils, 139.—Influence of the Original Material upon the Composition of Humus, 139.—Table of Snyder, 139.— Effect of Humus in rendering Mineral Plant Food Available, 140. CHAPTER TX: Sor AND SUBSOII, (continued) , 142.—ORGANISMS INFLUENCING SOIL-CONDI- TIONS. BACTERIA, 142.—MVicro-organisms of the Soil. Bacteria, Moulds, Ferments, 142.—Numbers at Various Depths, given by Early Observers, 142.—Investigations of Hohl; Mayo and Kinsley. Tables, 143.—Multi- plication of the Bacteria, 144.—Aerobic and Anaerobic Bacteria, 144.— Food Materials required, 145.—Functions of the Bacteria, 145.—Nitrify- ing Bacteria. Figures, 146.—Conditions of their Activity. Table, 146. —Effects of Aeration and Reduction, 147.—Unhumified Organic Matter does not Nitrify, 148—Unhumified Vegetable Matter, Functionsin Soils, 148.—Denitrifying Bacteria. Figures, 148.—Ammonia-forming Bacte- ria. Figures, 149.—Alinit, 149.—Effects of Bacterial Life on Physical Soil Conditions, 149.—Root-bacteria, or Rhizobia of Legumes, 150.— Figures of Root Excrescences and Corresponding Bacteroids, 152.— Varieties of Forms, 154.—Mode of Infection, 154.—Cultural Results, 155.—Jlable Showing Increased Production by Soil Inoculation, 155.— Other Nitrogen-absorbing Bacteria, 156.—Distribution of Humus in the Surface Soil, 157.—Fungi, Moulds and Algae, 157.—Animal Agencies— Earthworms, Insects, Burrowing Quadrupeds, 158. CHAPTER X<. SOIL AND SUBSOIL IN THEIR RELATIONS TO VEGETATION, 161.—Physical Effects of the Percolation of Surface Waters, 161.—Chemical Effects ; Calcareous Subsoils and Hardpans, 161,—‘‘Rawness” of Subsoils in CONTENTS. ix Humid Climates, 162.—Subsoils in the Arid Region, 163.—Deep Plow- ing and Subsoiling in the Arid Region ; examples of Plant growth on Subsoils, 164.—Resistance to Drought, 167.—Root System in the Humid Region, 168. Figures of the Root System of an Eastern ( Wis- consin) Fruit Tree, 168.—Comparison of Root Development in the Arid and Humid Regions, 169.—Prune on Peach Root, 169.—Adapta- tion of Humid Species to Arid Conditions, 169.—Grapes, 170.—Ken- tucky and California Maize, 175, 176.--Hops, 172.—Deep Rooting in the Arid Region, 174.—Goose Foot and Figwort, 174.—Jmportance of Proper Substrata in the Arid Region, 175.—Injury from Impervious Substrata, Figure, 177.—Faulty Lands of California, Figure, 178.— Shattering of Dense Substrata by Dynamite, 181.—Leachy Substrata, 182.—‘‘ Going-back ” of Orchards, 182.—Hardpan, Formation and Varieties, 183.—Nature of the Hardpan Cements, 184.—Bog Ore, Moor- bedpan and Ortstein ; Calcareous and Alkali Hardpan, 184.—The Causes of Hardpan, 185.—‘‘ Plowsole,’’ 186.—Marly Substrata, 186. CHAPTER XI. THE WATER OF SOILS. HYGROSCOPIC AND CAPILLARY MOISTURE, 185.— General Properties, 188.—Physical Factors of Water compared with other Substances. Table, 188.—Capillarity or Surface Tension, 189.— Heat Relations, 190.—Density, 190.—Specific Heat and its Effects, Igo. Ice, 191.—Vaporization, 191.—Solvent Power, 191.—Water-requirements of Growing Plants, 192.— Evaporation from Plants in Different Climates, 192.—Relations between Evaporation and Plant Growth. Table, 193.— Fortier’s Experiments. Figure, 194.—Different Conditions of Soil Water, 196.—Hygroscopic Water in Soils ; Table, 196.—Influence of Temperature and Air-Saturation, 197.—Utility of Hygroscopic Water to Plant Growth, 199.—Mayer’s Experiments, 200.—Summary, 200.— Capillary Water, 201.—Ascent of Water in Soil-Columns. Table, 202. —Ascentin Uniform Sediments. Figure, 204.—Maximumand Minimum Water-holding Power, 207.—Capillary Water held at different Heights in a Soil Column. Table, 208.—Capillary Action in Moist Soils, 210.— Proportion of Soil Moisture Available to Plants, 211.—Moisture Require- ments of Crops in the Arid Region, 211.—Tables of Observations in California, 214. CHAPTER XII. SURFACE, HYDROSTATIC AND GROUND WATER. PERCOLATION, 215.— Amount of Rainfall, 215.—Natural Disposition of Rain Water, 216.-- The Surface Runoff, 216.—Washing-away and Gullying inthe Cotton States, 217.—Injury in the Arid Regions, 219.—Deforestation, 219.— Prevention of Injury to Cultivated Lands from Excessive Runoff, 220. Absorption and Movements of Water in Soils, 221.—Determination of Rate of Percolation. Diagram, 221.—Summary, 224.—Influence of Var- iety of Grain-sizes, 224.—Table of King’s Experiments, 224.—Percola- tion in Natural Soils. Figure, 225.—Ground or Bottom Water, 227.— Lysimeters, Surface of Ground Water; Variations, 227.—Depth of x CONTENTS, Ground Water most Favorable to Crops, 228.—Moisture Supplied by Tap Roots, 229.—Reserve of Capillary Water, 229.—Injurious Rise of Bottom Water from Irrigation, 230.—Consequences of the Swamping of Irrigated Lands ; Prevention, 231.—Permanent Injury to certain Lands, 231.— Reduction of Sulfates, 232.—Ferruginous or Red Lands, 233. CHAPTER air. WATER OF SOILS ; THE REGULATION AND CONSERVATION OF SOIL MoIst- URE; IRRIGATION, 234.—Loosening of the Surface, 234.—Effects of Underdrains ; Rain on Clay Soils, 235.—Winter Irrigation, 236.— Methods of Irrigation, 236.—Surface Sprinkling, 237.—Flooding, 237. —Check Flooding. Furrow Irrigation, 237, 238.—Figure Showing Pen- etration, 239.—Figure Showing Faulty Irrigation in Sandy Lands, 239. —Distance between Furrows and Ditches, 241.—Irrigation by Lateral Seepage, 242.—Basin Irrigation of Trees and Vines; Advantages and Objections, 243.—Irrigation from Underground Pipes, 245.—Quality of Trrigation Waters, 246.—Saline Waters ; Figures of Effects on Orange Trees, 246.—Ljimits of Salinity, 246.—Mode of Using Saline Irrigation Waters; Apparent Paradox, 249.—Use of Drainage Waters for Irrig- ation, 250.—‘‘ Black Alkali ’’ Waters, 250.—Variations in the Salinity of Deep and Shallow Wells, 250.—Muddy Waters, 251.—7he Duty of Irrigation Waters, 251.—Causes of Losses, 252.—Loss by Percolation. Figure, 252.—/vaporation, 253.—Tables Showing same at California Stations, 255.—Evaporation in Different Climates; Table, 255.—Evapo- ration from Reservoirs and Ditches, 257.—Prevention of Evaporation ; Protective Surface Layer, 257.—Illustrations of Effects of Tillage ; Table, 258.—Evaporation through Roots and Leaves, 262.—Weeds waste Moisture, 264.—Distribution of Moisture in Soils as Affected by Vegetation, 264.—Forests and Steppes, 265.—Eucalyptus for Drying Wet Lands, 265.—Mulching; Effects on Temperature and Moisture, 266, CHAPTER XIV. ABSORPTION BY SOILS OF SOLIDS FROM SOLUTIONS. ABSORPTION OF GASES, AIR OF SOILS, 267.—A bsorpition of Solids, 267.—Desalation, 267.—Deco- lorization, 267.—Complexity of Soil-Action, Physical and Chemical, 268.—‘‘ Purifying ’’ Action of Soils on Gases and Liquids, 269.—Waste of Fertilizers, 269.—Variation of Absorptive Power, 270.—Generalities Regarding Chemical Action and Exchange, 270.—Drain Waters, 271.— Distinctions not Absolute, 272.—Absorption or Condensation of Gases by the Soil, 272.—Proof of Presence of Carbonic and Ammonia Gases in Soils, 273—Absorption of Gases by Dry Soils. Figure, 274.—Composi- tion of Gases Absorbed by Various Bodies from the Air. Table, 275. —Discussion of Table, 277.—T7he Air of Soils, 279.—Empty Space in Dry Soils, 279.—Functions of Air in Soils, 279.—Insufficient and Ex- cessive Aeration, 280.—Composition of the Free Air of Soils, 280.—Car- bonic Dioxid vs. Oxygen, 281. —Relation to Bacterial and Fungous Activity, 281.—Putrefactive Processes, 282. CONTENTS. xi CHAPTER XV. CoLors oF SOILS, 283.—Black Soils, 283.--‘‘ Red” Soils, 284.—Origin of Red Tints, 285.—White Soils, 285.—Differences in Arid and Humid Regions, 286.—White Alkali Spots, 286. CHAPTER XVI. CLIMATE, 287.—Heat and Moisture Control Climates, 287.—Climatic Con- ditions, 287.—Ascertainment and Presentation of Temperature Condt- tions, 288.—Annual Mean not a Good Criterion, 289.—Extremes of Temperature are most Important, 289.—Seasonal and Monthly Means, 289.—Daily Variations, 290.—7he Rainfall, 290.—Annual Rainfall not a Good Criterion, 290. Distribution most Important, 290.— Winds, 291. —Heat the Cause of Winds, 291.—Trade Winds, 291.—Cyclones, 292. Influence of the Topography on Winds; Rains to Windward of Mountains, Arid Climates to Leeward, 293.—General Distribution of Rainfall on the Globe. Figure, 294.—Ocean Currents, 295.—The Gulf Stream, 295.—The Japan Stream, 296.—Contrast of Climates of N. W. America, 297.—Continental, Coast and Insular Climates, 297.—Subtropic. Arid Belts, 298.—Utilization of the Arid Belts, 299. CHAPTER XVII. RELATIONS OF SOILS AND PLANT GRowTH TO HEAT, 301.—Temperature of Soils, 301.—Water Exerts Controlling Influence, 301.—Cold and Warm Rains, 302.—Solar Radiation, 302.—Penetration of the Sun’s Heat into the Soil, 302.—Change of Temperature with Depth, 303.—Surface Con- ditions that Influence Soil Temperature, 303.—Heat of High and Low Intensity, 304.—Reflection vs. Dispersion of Heat, 304.—Influence of Vegetation, and of Mulches, 305.—Influence of the Nature of the Soil- Material, 306.—Influence of Evaporation, 307.—Formation of Dew, 307. —Dew rarely adds Moisture, 308.—Dew within the Soil, 308.—Plant Development under Different Temperature-Conditions, 309.—Germin- ation of Seeds; Optimum Temperature for each Kind, 309.—Artificial Heating of Soils ; by Steam Pipes or Water, 310. CHAPTER XVIII. PHYSICO-CHEMICAL INVESTIGATION OF SOILS IN RELATION TO CROP Propuction, 313.—Historical Review of Soil Investigation, 313.— Popular Forecasts of Soil Values, 313.—Cogency of Conclusions Based upon Native Growth, 314.—Ecological Studies, 315.—Early Soil Surveys of Kentucky, Arkansas and Mississippi, 316.—Investigation of Cultivated Soils, 316—Change of Views, 317.—Advantages for Soil Study offered by Virgin Lands, 318.—Practical Utility of Soil Analysis ; Permanent Value vs. Immediate Productiveness, 319.—Physical and Chemical Conditions of Plant Growth, 319.—Condition of Plant-food Ingredients, in the Soil, 319.—Water-soluble, Reserve, and Insoluble Part, 320.— Hydrous or ‘‘ Zeolitic ’’ Silicates, 321.—Recognition of the Prominent Chemical Character of Soils, 322.—Acidity, Neutrality and Alkalinity, Xll CONTENTS. 322.—Chemical Analysis, 323.—Water-Soluble and Acid-Soluble Por- tions most Important, 324.—We cannot Imitate Plant-root Action, 324 Cultural Experience the Final Test, 324.—Analysis of Cultivated Soils, 325.—Methods of Analysis, 325.—Zhe Solvent Action of Water upon Soils, 327.—Extraction of Soils with Pure Water, 327.—Continuous Solubility of Soil Ingredients. Tables, 328.—King’s Results. Table, 329.—Composition and Analysis of Janesville Loam, 331.—Solubility of Soil Phosphates in Water, 332.—Practical Conclusions from Water Extraction, 332.—Ascertainment of the Immediate Plant-food Require- ments of Cultivated Soils by Physiological Tests, 333.—Plot Tests; their uncertainties. Diagram, 334.—Crop Analysis as a Test of Soil Character, 337.—Chemical Tests of immediately Available Plant Food ; Dyer’s Method, 338. CHAPTER XIX. ANALYSIS OF VIRGIN SOILS BY EXTRACTION WITH STRONG ACIDS AND ITS INTERPRETATION, 340.—Loughridge’s Investigation on Strength of Acid and Time of Digestion, 340.—Writer’s Method, 342.—Virgin Soils with High Plant-food Percentages are always Productive. Table, 343.—Dis- cussion of Table, 343.—Low Plant-food Percentages not always Indica- tion of Sterility, 346.—What are ‘‘ Adequate’’ Percentages of Potash, Lime, Phosphoric Acid and Nitrogen, 347.—Soil-Dilution Experiments, 347.—Table of Compositions, 350.—Figures of Plants and their Root- Development, 351.—Limitation of Root Action, 351.—Lowest Limits of Plant-food Percentages and Productiveness Found in Virgin Soils, 353. Limits of Adequacy of the Several Plant-food Percentages in Virgin Sotls, 353.—Lime a Dominant Factor in Interpretation, 353.—Potash, 354.—Phosphoric Acid, 355.—Action of Lime and Ferric Oxid, 355.— Table of Hawaiian Ferruginous Soils, 356.—Unavailability of Ferric Phosphate, 356.—Nitrogen, 357.—Nitrification of the Organic Matter of the Soil, 358.—Analysis of Soil from the Ten-Acre Tract at Chino, Cal., 358.—Experiments and Results; Matiére Noire the Only Guide, 360.—What are Adequate Nitrogen Percentages in the Humus ? 360.— Table of Humus and Nitrogen-Content of Californian and Hawaiian Soils, 361.—Confirmatory Experiment. Figure, 362.—Data for Nitrogen- Adequacy. Table, 363.—/ufluence of Lime upon Soil Fertility, 365.— *“A Lime Country is a Rich Country,’’ 365.—Effects of High Lime-Con- tent in Soils, 365.—Table of Soils showing Low Phosphoric Acid with High and Low Lime-Content, 366.—What are Adequate Lime-percent- ages? Differ for Light and Heavy Soils, 367.—Table Showing Need of High Lime Percentages in Heavy Clay Soils, 368.—European Standards for Land Estimates, 369.—Maercker’s Table, 369. CHAPTER XX. SOILS OF THE ARID AND HumiIp REGIONS, 371.—Composition of Good Medium Soils ; Table, 371.—Criteria of Lands of the Two Regions, 371. —Tables of Soil-Composition in Both Regions, 372.--Soils of the Humid Region governed by Time, 374.—Soils of the Arid Region Governed CONTENTS. Xlll by Moisture, 374.—Lime and Magnesia Uniformly High in Arid Soils, Despite Scarcity of Limestone Formations; Potash also High, 374.— General Comparison of the Soils of the Arid and Temperate Humid Regions, 375.—Basis of Same, 376.—New Mexico and Analysis of Soil, 376.—General Table, 377.—Discussion of the Table, 378.—Lzme ; Sum- mary of Physical and Chemical Effects of Lime Carbonate in Soils, 378. Discussion of Summary, 379.—MWagnesia : Its role in Plant Nutrition, 381.—Manganese: Its Stimulant Action, 383.—Z7he ‘‘ Znsoluble Res- idue’’ or Silicates, 384.—Soluble Silica and Alumina, 384.—Analysis of Clay from Soil, 385.—Difference in Sand of Arid and Humid Regions. Table, 386.—Soluble Silica or Hydrous Silicates more Abundant in Arid than in Humid Soils, 388.—Aluminic Hydrate. ‘Table, 389.—Retention of Soluble Silica in Alkali Soils, 391.—/ervic Hydrate, 392.—Phosphoric Acid, 392.—Sulfuric Acid, 394.—/fotash and Soda, Retained more in Arid Soils, 394.—Arid Soils Rich in Potash, 395.—Hwmus, Low in Arid Soils, but Rich in Nitrogen, 396.—The Transition Region, 397. CHAPTER XXI. SOILS OF ARID AND HUMID REGIONS CONTINUED, 398.—Soz/s of the Tropics, 398.—Humus in Tropical Soils, 399.—Investigations of Tropical Soils, 4o1.— Soils of Samoa and Kamerun, 402.—Soils of the Samoan Islands, 403.—Soils of Kamerun, 404.—Sozls of Madagascar, 405.—Soils of India, 410.—The Indo-Gangetie Plain, 411—-The Brahmaputra Al- luvium in Assam, 413.—Black Soils of Deccan, 414.—Red Soils of the Madras Region, 415.—Laterite Soils, 416.—/ufluence of Aridity upon Civilization, 417.—Preference of Ancient Civilizations for Arid Coun- tries, 417.—Irrigation Necessitates Co-operation, 419.—High and Per- manent Productiveness of Arid Soils Induces Permanence of Civil Organization, 419. CHAPTER XXII. ALKALI SOILS, THEIR NATURE AND COMPOSITION, 422.—Alkali Lands vs. Seashore Lands, 422.—Origin, 422.—Deficient Rainfall, 423.--Predom- inant Salts, 423.—Geographical Distribution, 424.—Their Utilization of World-wide Importance, 424.—Repellent Aspect, Plate, 424.—-Effects of Alkali upon Culture Plants. Figures of Apricot Trees, 426.—Nature of the Injury, External and Internal, 426.—Effects of Irrigation, 428.-- Leaky Irrigation Ditches, 429.—Surface and Substrata of Alkali Lands, 429.—Vertical Distribution of the Salts in Alkali Soils, 429.—How Native Plants Live, 430.—Figures of various Phases of Reclamation, 431.—Upward Translocation from Irrigation, 433.—Distribution of Al- kali in Sandy Lands, 433. In Heavier Lands, 436.—Salton Basin or Colorado Delta, 436.—Diagram of Alkali Distribution in Same, 438.— Horizontal Distribution of Alkali Salts in Arid Lands, 439.—Alkali in Hill Lands, 439.—Usar Lands of India, 440.—‘‘ Szek ’’ Lands of Hungary, 440.—Alkali Lands of Turkestan, 441.—Composition and Quantity of Salts Present, 441.—Nutritive Salts, 441.—Black and White Alkali. Tables, 442.—Estimation of Total Alkali in Land, 444.—Composition of xiv CONTENTS, Alkali Soils as a whole. Tables, 445.—Presence of much Carbonate of Soda, 448.--Cross Section of an Alkali Spot. Table, 448.—/eactions between the Carbonates and Sulfates of Earths and Alkalies. Figure of Curve, 449.—Inverse Ratios of Alkali Sulfates and Carbonates. Dia- grams, 451.—Exceptional Conditions, 453.—Summary of Conclusions, 453: CHAPTER XXIII. UTILIZATION AND RECLAMATION OF ALKALI LAND, 455.—Alkali-resistant Crops, 455.—Counteracting Evaporation, 455.—Turning-under of Sur- face Alkali, 456.—Shading, 457.—Neutralizing Black Alkali, 457.— Removing the Salts from the Soils, 458.—Scraping off, 458.—Leaching- Down. Figure, 459.—Underdrainage, the Final and Universal Remedy for Alkali, 460.—Possible Injury to Land by Excessive Leaching, 462. —Difficulty in Draining ‘‘ Black ’’ Alkali Land, 462.—Swamping of Al- kali Land, 463.—Removal of Alkali Salts by Certain Crops, 463.— Tolerance of Alkali by Culture Plants, 463.—Relative Injuriousness of the several Salts. Effects on Sugar Beets, 464.—Table of Tolerances ; Comments on same, 467.—Saltbushes and Native Grasses. Australian Saltbushes, 469.—Modiola ; Native and Cultivated Grasses, 469.—Other Herbaceous Crops, 472.—Legumes, 472.—Mustard Family, 473.—Sun- flower Family, 473.—Root Crops, 474.—Stem Crops, 475.—Textile Plants, 475.—Shrubs and Trees, 475.—Vine, Olive, Date, Citrus Trees. Deci- duous Orchard Trees. Timber and Shade Trees, 475.—Inducements toward the Reclamation of Alkali Lands, 481.—Wheat on Reclaimed Land at Tulare ; Figure, 482.—Need of Constant Vigilance, 484. CHAPTER XXIV. THE RECOGNITION OF SOIL CHARACTER FROM THE NATIVE VEGETATION ; MISSISSIPPI, 487.—Climatic and Soil Conditions, 487.—Natural Vegeta- tion the Basis of Land Values in the United States, 488.—Investigation of Causes Governing Distribution of Native Vegetation, 488.—Investiga- tions in Mississippi, 489.—Vegetative Belts in Northern Mississippi, 490.—Sketch Map of Same, with Tabulation of Lime Content and Native Vegetation, 490.—Lime Apparently a Governing Factor, 492.— Soil Belts in Southern Mississippi, 493.—Vegetative and Soil Features of Coast Belts. Diagram, 495.—Table of Plant-Food percentages and Native Growth, 496.—Definition of Calcareous Soils, 496.—Differences in the Form and Development of Trees, 498.—Forms of the Post Oak. Figures, 498.—Forms of the Black Jack Oak. Figures, 500.—Charac- teristic Forms of other Oaks, 502.—Sturdy Growth on Calcareous Lands, 502.—Growth of Cotton, 503.—Lime Favors Fruiting, and compact Growth, 504.—Physical vs. Chemical Causes of Vegetative Features, 505.—Lowland Tree Growth, 506.--Contrast between ‘‘ First” and ““Second’’ Bottoms, 506.—Tree Growth of the First Bottoms. The Cypress, 507.—Figures of Swamp and Upland Cypress, 508.—Other Lowland Trees, 509.—General Forecasts of Soil Quality in Forest Lands, 509. CONTENTS. XV CHAPTER XXV. RECOGNITION OF THE CHARACTER OF SOILS FROM THEIR NATIVE VEGE- TATION. UNITED STATES AT LARGE, EUROPE, 511.—Forest Growths outside of Mississippi ; Alabama, Louisiana, Western Tennessee, and Western Kentucky, 511.—North Central States East of the Mississippi River, 513.—Upland and Lowland Vegetation in the Arid and Humid Region, 515.—Forms of Deciduous Trees in the Arid Region, 516.— Tall Growth of Conifers, 517.—Herbaceous Plants as Soil Indicators, 517.—Leguminous Plants Usually Indicate Rich or Calcareous Lands, 518.—European Observations and Views on Plant Distribution and its Controlling Causes, 519.—Composition of Pine Ashes on Calcareous and Non-calcareous Lands. Table, 520.--Calciphile, Calcifuge, and Indifferent Plants, 521.—Silicophile vs. Calciphile Flora, 523.—What is a Calcareous Soil ? 524.—Predominance of Calcareous Formations in Europe, 525. CHAPTER XXVI. THE VEGETATION OF SALINE AND ALKALI LANDS, 527.—Marine Saline Lands, 527.—General Character of Saline Vegetation, 527.—Structural and Functional Differences Caused by Saline Solutions, 528.—Absorp- tion of the Salts. Table, 529.—Injury from the Various Salts, 531.— Reclamation of Marine Saline Lands for Culture, 533.—7he Vegetation of Alkali Lands, 534.—Reclaimable and Irreclaimable Alkali Lands as Distinguished by their Natural Vegetation, 534.—Plants Indicating Irreclaimable Lands, 535.—Tussock Grass; Bushy Samphire ; Dwarf Samphire ; Saltwort ; Greasewood ; Alkali Heath ; Cressa; Salt Grass, 536.—Relative Tolerances of the different Species ; Table, 549. APPENDICES. A.—Directions for taking Soil Samples, issued by the California Experiment Station, 553. B.—Summary Directions for Soil-Examination in the Field or Farm, 556. C.—Short Approximate Methods of Chemical Soil-Examination Used at the California Experiment Station, 560. General Index, 565. Index of Authors referred to, 591. PREPACE. Tus volume was originally designed to serve as a text- and reference book for the students attending the writer’s course on soils, given annually at the University of California, who complained of their inability to find in any connected treat- ise a large portion of the subject matter brought before them. As all these students had preliminary training in physics, chem- istry and botany, no introductory chapters on these general subjects were necessary or contemplated; the more so as good elementary treatises embracing the needful preparation are now numerous. As time progressed, however, outside demands for a book embodying the writer’s soil studies in the humid and arid regions, especially the latter, became so numerous and pressing that the scope of the work has gradually been much enlarged to conform to these demands; and this, rather than com- pleteness of detail, when such detail can be found well given elsewhere, has been the guide in the necessary condensa- tion of the whole. To give the entire subject matter full eluci- dation, would require several more volumes. It may not be unnecessary to explain at the outset why and how this treatise deviates in many respects from previous pub- lications on the same general topic. From boyhood up it has fallen to the writer’s lot to be almost continuously in more or less direct contact with the conditions and requirements of newly settled regions, as well as with those hardly yet invaded even by the pioneer farmer; where the question of cultural adaptation was yet undetermined or wholly in the dark. Being during his active life constantly called upon in his official capa- city to give information and advice to pioneer farmers or in- tending settlers in regard to the merits and adaptations of virgin soils, the writer’s attention was naturally and forcibly directed toward soil investigation as a possible means of determining, beforehand, the general prospects and special features of agri- XV11 Xviil PREFACE. culture in regions where actual experience was either non-exis- tent or very brief and partial. In the pursuit of these studies he has been favored by exceptional opportunities, extending over a varied climatic area reaching on the south from the Gulf of Mexico to the Ohio, across to the Pacific coast, and to British Columbia on the north. That a systematic investiga- tion of soils over so large an area, covering both humid and arid regions, should lead to some unexpected and novel re- sults, is but natural; and it is the discussion of these results in connection with those obtained elsewhere, and with some of the prevailing views based thereon, that must serve as the justification for the present addition to an already well- stocked branch of literature. From the very beginning of the scientific study of agricul- ture, the investigation of soils with a view to the d@ priori de- termination of their adaptation, permanent value, and best means of cultural improvement, has formed the subject of continuous effort. It is not easy to imagine a subject of higher direct importance to the physical welfare of mankind, whose very existence depends on the yearly returns drawn by cultural labor from the soil. It is certainly remarkable that after all this long-continued effort, even the fundamental principles, and still more the methods by which the object in view is to be attained, are still so far in dispute that a unification of opinion in this re- spect is not yet in view; and a return to pure empiricism is from time to time brought forward to cut the Gordian knot. While this state of things is primarily due to the intrinsic complexity and difficulty of the subject itself, it has unquestion- ably been materially aggravated by accidental, partly historic conditions. Foremost among these is the fact that until within recent times, soil studies have borne almost entirely on lands long cultivated and in most cases fertilized: thus changing them from their natural condition to a more or less artificial one, which obscures the natural relations of each soil to vege- tation. The importance of these relations is obvious, both from the theoretical and from the practical standpoint. From the former, it is clear that the native vegetation represents, within the climatic limits of the regional flora, the result of a secular PREFACE, xix process of adaptation of plants to climates and soils, by nat- ural selection and the survival of the fittest. The natural floras and sylvas are thus the expression of secular, or rather, millennial experience, which if rightly interpreted must convey to the cultivator of the soil the same information that other- wise he must acquire by long and costly personal experience. The general correctness of this axiom is almost self-evi- dent; it 1s explicitly recognized in the universal practice of settlers in new regions, of selecting lands in accordance with the character of the forest growth thereon; it is even legally recognized by the valuation of lands upon the same basis, for purposes of assessment, as is practiced in a number of States. The accuracy with which experienced farmers judge of the quality of timbered lands by their forest growth, has justly excited the wonder and envy of agricultural investigators, whose researches, based upon incomplete theoretical assump- tions, failed to convey to them any such practical insight. It was doubtless this state of the case that led a distinguished writer on agriculture to remark, nearly half a century ago, that he “ would rather trust an old farmer for his judgment of land than the best chemist alive.” + It is certainly true that mere physico-chemical analyses, un- assisted by other data, will frequently lead to a wholly errone- ous estimate of a soil’s agricultural value, when applied to cul- tivated lands. But the matter assumes a very different as- pect when, with the natural vegetation and the corresponding cultural experience as guides, we seek for the factors upon which the observed natural selection of plants depends, by the physical and chemical examination of the respective soils. It is further obvious that, these factors being once known, we shall be justified in applying them to those cases in which the guiding mark of native vegetation is absent, as the result of causes that have not materially altered the natural condition of the soil. It is probable that, had agricultural science been first de- veloped in regions where the external conditions permitted the carrying-out of such a course of investigation, instead of in the abnormally temperate, even and humid climate of middle 1“The Soil Analyses of the Geological Surveys of Kentucky and Arkansas.” S. W. Johnson in AM, JOUR. SCZ, Sept. 1861. XX PREFACE. Europe, with its long-cropped, worn fields, and very predomi- nantly calcareous soils, the present condition of this science might differ not immaterially from that actually existing. As a matter of fact, it has attained its present state under very disadvantageous external conditions, which frequently necessi- tated a recourse to highly complex and laborious methods and artificial appliances, for the establishment and maintenance of the conditions which elsewhere might have been found abundantly realized in nature; thus permitting, by the multi- plication of observations over extended and widely varied areas, the elimination and control of accidental errors of experiment and observation. Just as in historical geology the subdivisions of formations observed and accepted in Europe formed for many years a pro- crustean bed upon which the facts observed elsewhere had to be stretched, so in the domain of soil physics and chemistry, and even in vegetable physiology, the observations made in the really exceptional climates and soils of middle Western Europe, have often erroneously been construed as constituting a general basis for unalterable deductions. The rapid extension of civilization and the carrying of minute scientific research into other regions, now rendered possible by the improved means of communication, has shown the one-sidedness of some of the views prevailing heretofore, inasmuch as they are really applicable only to accidental and rather exceptional conditions. It is therefore one object of this volume to present and discuss summarily the facts of physical and chemical soil con- stitution and functions with reference to the additional light afforded on the wider basis, embracing both the humid and the arid regions; of which the latter has, as such, received but scant and desultory attention thus far, to the detriment of both the work of the agricultural experiment stations and of agricul- tural practice. The book therefore includes the discussion both of the methods and results of direct physical, chemical and botanical soil investigation, as well as the subject matter relat- ing to the origin, formation, classification and physical as well as chemical nature of soil, usually included in works on scien- tific agriculture. In the presentation of these subjects, it has been the writer’s PREBACE: Xxl aim to reach both the students in his own classes and in the agricultural colleges generally, as well as the fast increasing class of farmers of both regions who are willing and even anxious to avail themselves of the results and principles of scientific investigation, without “shying off” from the new or unfamiliar words necessary to embody new ideas. It would seem to be time that the latter class, and more especially those constituting farmers’ clubs, should learn to understand and appreciate both the terms and methods of scientific reason- ing, which are likely to form, increasingly, the subjects of in- struction in the public schools. But in order to segregate to some extent the generally intelligible matter from that which requires more scientific preparation than can now be generally expected, it has been thought best to use in the text two kinds of type; the larger one embodying the matter presumed to be interesting and intelligible to the general reader, while the smaller type carries the illustrative detail and discussion which will be sought chiefly by the student. As regards the chemical nomenclature used in this volume, the writer has not thought it advisable to follow the example set by some late authors in substituting for the well-known names of the bases and acids, those of the elements, and still less, those of the intangible ions. Any one who has taught classes in agricultural chemistry will have experienced the difficulty and loss of time unnecessarily incurred in the inces- santly recurring transposition of terms, and complication of formule, serving no useful purpose save that of academic con- sistency. It is of at least doubtful utility to present to the farmer, e. g., the inflammable and dangerous elements phos- phorus and potassium as prime factors in the success of his crops, and of healthy nutrition. Inasmuch as all the elements are presented to and con- tained in the plant in compounds only, and these compounds are themselves, in the dilute solutions used by plants, known to be largely dissociated into their basic and acid groups, it seems to be most natural to present them under the corresponding, even if not absolutely theoretically correct names of acids and bases, to which the farmer and the trade have been accustomed for half a century. Upon these considerations the long-used designations of potash, soda, lime, phosphoric, sulfuric, nitric XXii PREFACE. and other acids and bases have been retained in this volume, adding the chemical formula where, as in analytical statements, a doubt as to their meaning might arise. Assuredly, the diffu- sion of scientific knowledge should not be needlessly hindered by the adoption of a pedantic mode of presentation. The great breadth of the subject of this volume has ren- dered inadvisable any such extended bibliography, such as it has of late become customary to add to works of this kind. References have therefore been restricted to publications specially discussed, and to such as are not widely known on account of limited circulation. The author’s warmest acknowledgments are due to Professor R. H. Loughridge, of the University of California, for effi- cient and sympathetic assistance, both in the revision of the manuscript, and active personal help in the preparation of the illustrations. Without his cooperation the preparation and publication of the volume would have been much longer de- layed. Acknowledgments are also due for helpful suggestions and criticism to Professors L. H. Bailey, of Cornell University, F. H. King, of Wisconsin, and Jacques Loeb of the University of California. E. W. HILGARD. BERKELEY, CALIFORNIA, November 15, 1905. INTRODUCTION: Definition of Soils—In the most general meaning of the term, a soil is the more or less loose and friable material in which, by means of their roots, plants may or do find a foot- hold and nourishment, as well as other conditions of growth. Soils form the uppermost layer of the earth’s crust; but the term does not indicate any such definite average texture as is sometimes implied by its popular use to designate certain loose, loamy materials found in older geological formations. We do find in these, not unfrequently, layers that in the past have served to support vegetation, as evidenced by remains of plants found therein. But as a rule, such ancient soils are much compacted and otherwise changed, and would not now be capable of performing the office of plant nutrition without previous, long-continued exposure to the same agencies by which all soils were originally formed from pre-existing rocks. Within the latter category must be included, in scientific par- lance, not only the hard rocks known as such in daily life, but also such soft materials as clay, sand, marls, etc., which often compose, partially or wholly, the bodies of wide-spread geo- logical formations. Elements Constituting the Earths Crust-——More than seventy elementary substances have been found within the portion of the earth accessible to man; most of these are present only in very minute proportions; of those occurring in relatively considerable quantities, a list showing their approximate pro- portions is given below. Average quantitative composition of the Earth’s Crust.— The total thickness of the outer shell of the earth, thus far known to us, does not exceed about 95,000 feet, as observed in the accessible rock deposits. Estimates of the proportions in which the more abundant elements contribute to the com- position of these constituent rocks, have repeatedly been made. The latest and most widely accepted of these, by F. W. Clarke, of the U. S. Geological Survey, is given herewith. It in- xxiii XXIV INTRODUCTION. cludes the constituents of the sea and atmosphere as well; these two constitute about 7 per cent of the whole, 93 per cent being solid rocks. RELATIVE ABUNDANCE OF THE ELEMENTS TO A DEPTH OF TEN KILOMETERS, SoLip CRUST OCEAN MEAN, (93 PER CENT). (7 PER CENT). INCLUDING AIR, OXY PEN ew cnicleiclels eles cieleiere ole ois 47.2 85:79 49.98 SUICON .. eee e eee weer senor AOA acogeoscaenb00C 25.30 iMiviatieybOon 5 Gopcon oe dao Gono Od Poss sdngananveboooc 7.26 NinOMsets eh croc conte iscraern stole oiesks Bort ogadasceedaon0c 5-08 (CANCE boacnoGemsooocaougDO 7a 0.05 Bg Via PNESIUM ayn ciciceiericieielereisicislele 2.68 0.14 2.50 Sodium trem ao errr eieee 2.36 1.14 2.28 Potassium). cisic ciefecie\s «i011 n0)«)- 2.40 0.04 2223 Ely TOG eMe\sclatolatelteksvelaieielteiete 0.21 10.67 0.94 AMEN 6 oéoodanaoandocuos Meee iaodoseoes a poaC 0.30 (Carbone weiss ier 0.22 ©.002 0.21 (Elnora soo doplcogasog DusooudT 0.01 2.07 0.15 Phosphorus........ sQd000 3006 QUO a dovsdidasacndgac 0.09 Mam anes erenrl-telercielefecleretetoniers Os OSH Ti ereprereternte torre 0.07 Sih lite os. bsaonospoadooauens 0.03 0.09 0.04 Ba MANITNevadele eteyerciatejeieforeleereled-rere OnOR et coudignoods S0H06 0.03 INITETO GEM! .F<1055)2.5isio\ eis eis etete ee eietraes ololo eters atenelaieteN ei sterat era sIoreets 0.02 FEDIITO TAM ayes 1 s0- /avorescrsie eiateioieereneeners Ch} s a eo clncnes ado cae 0.02 ElibcornbithWasroaoun cedan docu 0.01 soougedbososeDs 0.01 It will be noted that one-half of the total consists of oxygen, and that nearly 86% (or 47.29% of the 49.98%) of this amount is contained in the solid rocks; nearly 2.50% of the remainder in sea and other water; and .41% in the atmosphere, in the free condition, in which it serves for the respiration of animals and plants, and for the various processes of slow and rapid combustion, or “ oxidation.’’ This relatively small pro- portion of the whole, is, nevertheless, the most directly im- portant for the maintenance of organic life. Oxids Constitute Earth's Crust—The vast predominance of oxygen in the above list suggests at once that most of the other elements must exist in combination with it, 7. e., as “oxids.” H. S. Washington! has lately revised the esti- mates heretofore made, on the basis of a very large number of analyses made by him and others, of rocks within the United States, and gives the following table; alongside of which is placed a revised estimate by Clarke, which also includes rocks from abroad; both being given in terms of oxids of the several elements. 1U.S. Geol. Survey, Professional Paper No. 14, p. 108. INTRODUCTION. XXV WASHINGTON. CLARKE. DULL Coemeratoneteleleteretelela/eretatetelarefareateicleiereronnre SiO, 57-78 59.89 AMhiniViNe)s Sho oS boowooKoUGUbuoenGodadc Al,O, 15.67 15.45 Peroxidwof wr omiaasiereisiaes sire Olsiaceteneiavee Fe203 Bai 2.64 PirOu@paiel Gi IWIN ».nooo0dogcnbsba6 oe FeO 3.84 3.53 INEEINESIET Ss Go aencdhoaDo0SDOodeDNO Oc MgO 3.81 4.37 ILI. cogcbd ondosooou Us ood oHODCONS CaO 5-18 4.91 SOGE -caoisctvodooavededogoun0 Ose banc NagO1 3.88 3:50 IPGIBIE No ooo sodcogapuoeocuCoUUCOGODEST K20 Sits) 2.51 Waliony ESI > oobGbhoe coda dbocoscclbas H20+ 1.42 Wa52 Wistar macidenientec occ satetie nce earers H,O— 36 .40 liGinas Sih wGh Ma posasbioeelaooe gape WEISin 1.03 .60 Phosphoric acid........ , REGS P205 .37 =22 Man canesereroOtOxid ariel oi-ttelerl sists MnO .22 .10 The salient point which at once attracts attention in these tables is the great predominance of the oxid of silicon—silica, silicic acid, quartz, etc..—over all other substances. While quartz occurs alone in enormous masses, as will be shown later, probably the greater proportion is found in combina- tion with other oxids, notably those of aluminum, calcium, iron, magnesium, and the alkali metals potassium and sodium. Chlorin and fluorin, however, do not occur as oxids.? The Chemical Elements Important to Agriculture.—Of the numerous elements known to chemists, only eighteen require mention in connection with either soil formation or plant growth; and of these only thirteen or fourteen participate in normal plant growth. They are the following: METALLIC ELEMENTS. NON-METALLIC ELEMENTS. Potassium Carbon Sodium Hydrogen Calcium Oxygen Magnesium Nitrogen Iron Phosphorus Manganese Sulphur Aluminum Chlorin Titanium Fluorin Todin Silicon. Of this list, titanium, though a very constant ingredient of 1 A trifling amount of chlorin is found oxidized in the form of sodium perchlor- ate, in the nitre deposits of Chile. XXV1 INTRODUCTION. soils in the form of titanic dioxid, is not known as performing any important function in soils, and is not, so far as known at present, ever taken up by plants. Aluminum, in the form of its compounds with oxygen and silicon, is a very prominent and physically very important soil ingredient, but does not, apparently, perform any direct function in plant nutrition, and is absent from their ash, except in the case of some of the lower plants (horsetails and ferns). Iodin appears to be normally present in all seaweeds, and occurs in traces in some land plants. Fluorin is a normal in- gredient of animal bones, and its presence in plant ashes is often easily shown. The remaining fourteen, however, are always present in plants; carbon, hydrogen, oxygen and nitro- gen forming the volatile or combustible part, while the rest occur in the ashes. It is true that other elements, or rather their compounds, are sometimes found in plants, being taken up by them from solu- tions existing in the soil. Thus the alkalies caesium and rubi- dium, also barium, strontium, zinc, copper, boron and some others, may be absorbed when present in soluble form. But they are neither necessary nor beneficial to plant economy, and when in considerable amounts are harmful. Thus fifteen ele- ments, ommiting iodin and titanium, alone require discussion. The Volatile Part of Plants, as already stated, consists of carbon, hydrogen, oxygen and nitrogen. Of these, car- bon is obtained by the plant exclusively from the carbonic (dioxid) gas of the air; hydrogen and oxygen, from the soil in the form of water; nitrogen, directly from the soil but in- directly also from the air, through the agency of certain bacteria. The ash ingredients of course are all derived from the soil through the roots, and must all be present in the lat- ter in an available form, to a sufficient extent to supply the demands of vegetation. The Agencies of Soil Formation+—With respect to their mode of formation, soils may be defined as the residual product of the physical disintegration and chemical decomposition of rocks; with, ordinarily, a small proportion of the remnants of organic life. The agencies producing these changes are those classed under the general term “ atmospheric’”’ or ‘“ meteoro- INTRODUCTION. XXVil logical; ”” they include therefore the action of temperatuye— heat and cold—that of water, and that of air and its ingre- dients. In popular parlance, it includes the processes of weathering; nearly the same processes are involved in the “ fallowing”’ of soils. PART. I: ‘THE ORIGIN AND FORMATION OF SOILS. CHAPIN RE THE PHYSICAL PROCESSES OF SOIL FORMATION. SINCE the physical and mechanical effects of the agencies mentioned above usually precede, in time, the chemical changes, which are materially facilitated by the previous pulverization of the rocks, the former should be first considered. Effects of heat and cold on rocks.—Most rocks are aggre- gates of several simple minerals; a few only (limestone, quartzite and a few others) expand or contract alike in all their parts. Of the minerals composing the compound rocks, scarcely any expand to exactly the same extent under the in- fluence of the sun’s heat, especially when their colors differ ; nor, in the great majority of cases, does one and the same mineral expand alike in all three directions. It follows that at each change of temperature there is a tendency to the forma- tion of minute fissures between adjacent crystals or masses of different simple minerals; and especially in the case of large crystals of certain kinds, this action alone will gradually result in the disruption of the rock surface, so that individual crystals may be detached with little difficulty. ~ In any case, the cracks so formed are gradually widened by a frequent repetition of the changes of temperature, coupled wih access of air, water, dust, and the rootlets of plants; all of which brings about a gradu- ally increasing rate of surface crumbling. This is especially conspicuous at the higher elevations of mountains, where the temperature changes are very great and abrupt; and also in the clear atmosphere of deserts, where owing to the extent and suddenness of temperature- changes between day and night, caused by the free radiation of heat into the clear sky, even homogeneous pebbles are known to be almost explosively dis- rupted in the mornings and evenings of clear days. I 2 SOILS. Such effects may often be strikingly observed on small sur- faces of compound crystalline rocks, such as granite, exposed on glaciers, where the daily changes of temperature are often extreme, viz., from below the freezing point to as much as 130 degrees Fahr. (54.4 degrees C.). In such cases one may sometimes scoop off the disintegrated rock by the handful, while yet the mineral surfaces are almost perfectly fresh. On a larger scale, the disruption and scaling off of huge slabs of granite, and rocks of similar structure, may be observed in southern California on the southwestern side of rock ex- posures, where slabs from a few inches to ten and more feet in length and eight or ten inches thick, have slid off, perhaps still leaning against the parent rock, which has been rounded off by a succession of such events into the domelike form so characteristic of granite mountains. Merrill * reports similar exfoliations to occur especially on the peninsula of California, on Stone Mountain in Georgia, and elsewhere. A striking exemplification of: the effects of frequent and rapid changes of temperature on rocks, and of humid and dry climates as well, is seen in the case of the great monoliths of Egypt, one of which now stands in the Central Park, New York. In the quarries of Syene in Upper Egypt, where most of these monoliths were obtained, the rough blocks that were in progress of quarrying when the work was abandoned, quite two thousand years ago, still show an almost perfectly fresh surface; and the same is true of the finished obelisks in Lower Egypt, where both the changes of temperature and the rain- fall are somewhat greater. It is a matter of public note that one of ‘ Cleopatra’s Needles’ which was set up in Central Park nearly thirty years ago, but originally erected at Helio- polis on the Nile, is in great danger of destruction from the influence of a totally different climate, in which both the temperature changes and the rainfall are much more frequent and severe than in Egypt. The large crystals of feldspar and quartz which compose the (syenite) rock material have had fine fissures formed between them by often-repeated expansion and contraction ; which when filled with water and subsequently r ! See Rocks, Rock-weathering, and Soils, page 246; also paper on Domes and Dome Structure, by G. K. Gilbert, in Bulletins of the Geol. Society Am., Vol. 15, Pp- 29-36. THEVPHYSICAL PROCESSES: OF SOIL FORMATION. 3 changed to ice, the latter's expansion in freezing (see below) has still farther enlarged them and caused a scaling-off, which threatens to obliterate the hieroglyphic inscriptions. Thus temperature-changes and a rain followed by freezing may in a few days produce a greater effect than a thousand years of Egyptian climate. Cleavage of rocks.—Many kinds of rocks have definite direc- tions of ready cleavage. The most common and obvious cases of this kind are schists, slates and shales, cleaving readily into plates or irregular flat or lens-shaped fragments. Such struc- ture greatly favors disintegration, especially when the layers are on edge at steep angles. But there are other apparently structureless, massive rocks, particularly basalts and other eruptive rocks related to them, as well as many sandstones and claystones, that have a strong tendency to cleave into more or less definite forms when struck; such as columns or prisms, square, six-sided or diamond-shaped blocks, ete. Similar forms are naturally produced in them under the influence of changes of temperature; by the formation of minute cracks at first, then enlargement of these by the several agencies already mentioned. Effects of freezing water.—The irresistible force exerted by the expansion of water in freezing, amounting to about 9 per cent of its bulk, is a powerful factor in widening and deep- ening fissures and cracks of rocks; not uncommonly, whole masses of rock are rent into fragments by this agency, which is one of the most common causes of “rock falls’? on the brink of precipices. By the freezing process cracks and crevices are enlarged, and the surfaces exposed to weathering are still farther increased; and the rock fragments or soil particles are loosened and rendered more liable to be removed from the original site, whether by gravity, wind or water. Glaciers.—Ice in the form of the glaciers that descend from mountain chains (see figure 1), and of the moving ice sheets that have covered large portions of North America and Europe in past ages and now cover Greenland and the South Polar con- tinent, exerts a most potent action in abrading and grinding even the hardest rocks; not so much by the direct friction of the moving ice itself, as by the cutting, scoring, grinding and crushing action which the stones imbedded in the ice, or carried 4 SOILS. and shoved by it, exert upon the rocky channels in which the ice stream moves, as well as upon each other. The product of this grinding process is largely very fine (hence “ glacier flour’’), so that it remains suspended in the water of the glacier-streams until their velocity is permanently checked when reaching a plain or lake. This suspended stone-flour imparts to the glacier streams their distinctive character of ‘““white rivers,” as contradistinguished from the clear, dark green rivers” that have their origin outside of glaciated “ee Fic. 1.—Zermatt Glacier (Agassiz). areas. This difference can be readily observed in traveling along any of the glacier-bearing mountain chains of the world, and is frequently expressed in the names of the streams. The physical analysis of mud from the foot of Muir glacier,* Alaska, at its sea front, made by Professor Loughridge, shows the prevalent fineness of the materials brought down by the glacier waters. 1 Collected by Dr. W. E. Ritter of the University of California. LHe PEYSI€ AL PROCESSES OF SOIL; FORMATION, 5 PHYSICAL COMPOSITION OF GLACIER MUD. MATERIAL. DIAMETER. PER CENT. (Cle Woiad decd os ogo udeeceouuTEuD. ? 16.57 | IME SIE orso cep toe mod onenpeElS 0023 — .o16 mm. 53-74 § 19:31 IMME Sills oo ctsodeno oe clbouceseaagc .o16 to .025 mm. 4.38 Mie cian silts sis cota nieve rtsveress sence .025 to .036 mm. 7.06 Coarse: Sills ogenboapbosenauSoacT .036 to .047 mm. 5-91 G@Warseusil tere sina teers Taso .047 to .072 mm.i 3.76 IMG S SA) GIN. ete ote lavsTove sco slate iS eevers 072) tO)-02s min 1.14 Mediumysands. cece cm sc cece 7 “YWey pile) sorhan 1.56 AIO tale seteie eee sl ep aue neds eee Wales ua witpare Vaya ats Aare o hioseecvee toate 04.12 It will be noted that over 70 per cent of this mud consists of extremely fine, wholly impalpable materials; but little of which is true clay. The fineness of the glacier-flour renders it peculiarly suitable for the rapid conversion into soil, and such soils are usually excellent and remarkably durable. ~The great and lasting fertility of the soils of southern Sweden is traced directly to this mode of origin, and doubtless the great American ice sheet of glacier times is similarly concerned in the high quality of the soil of our “north central” states, from the Ohio to the Great Lakes and the Missouri. The accumulations of rocks and debris of all sizes in the “moraines ” or detrital deposits of glaciers and ice-sheets form another class of glacier-made lands which cover extensive and important agricultural areas (drift areas), both in the old and new worlds. Such lands are undulating or slightly hilly, and the soil usually contains imbedded in it stones of a great variety of kinds and sizes, partly angular, partly rounded and polished by friction. Of course the frequent and violent changes of temperature occurring on the surface of a glacier, aid materially in reducing the rocks carried by it to the con- dition in which we find the material of the moraines; which commonly form lateral or cross ridges in valleys formerly occupied by glaciers. Action of flowing water.—The action of flowing water is doubtless at this time the most potent mechanical agency of soil formation. From the sculpturing of the original simple forms in which geological agencies left the earth’s surface 5 SOILS. into the complex ones of modern mountain chains, to the formation of valleys, plains, and basins out of the materials so carried away, its effects are prodigious. The torrents and streams in carrying silt, sand, gravel and bowlders, according to velocity and volume, do not merely displace these materials ; the rock fragments of all sizes not only score and abrade the bed of the rill or stream, but by their mutual attrition produce more or less of fine powder similar to that formed by glacier action; usually more mixed in its ingredients than the former, because derived from a wider range of drainage surface. In Fic. 2.—Erosion of Hawaiian Hills, near Honolulu. (Phot. by H. C. Myers.) the glacier stream itself, it is easy to trace the gradual transi- tion from the sharp stone fragments lying in the water as it issues from the terminal ice cave at the lower end of the glacier, to the rounded shingle found a few miles below. On slopes where water flows only during rain or the melting of snow, the same erosive effects may be seen as between the heads of ravines and their outlets. (See figure 2,) It is there too that the surprisingly rapid cutting-out of channels by the aid of water charged with rock fragments or gravel, can readily be observed, and the enormous power of water erosion convincingly shown. In the United States the stu- pendous gorges of the Columbia and Colorado rivers, the THE PHYSICAL PROCESSES OF SOIL FORMATION. 7 former cut to a depth of over 2000 feet into hard basalt rock, the latter to over 5,000 feet, partly into softer materials, partly into granite, are perhaps the most striking examples of this power; the manifestations of which can, however, be as con- vincingly seen in thousands of minor rivers and streams. All the materials so carried off from the higher slopes are finally deposited on a lower level; whether only a short distance away on a lower slope (colluvial soils), or farther away in the flood plain of streams, rivers, or lakes (alluvial soils). «Other things being equal, the finest materials are of course, carried farthest, and often into the sea; in which, however, they can- not long remain suspended, but are quickly thrown down, forming river bars, flood plains, and deltas. « The fineness of the material of delta soils, like that of those made from glacier flour, insures them the same advantage, viz. great fertility and durability. It is calculated that the Mississippi River carries into the Gulf of Mexico annually some 7469 millions of cubic feet of earthy deposits, which would fill one square mile of surface to the height of 268 feet, or would cover that number of square miles to the depth of one foot. Fic. 3.—Cliffs and caves on sea-beach at La Jolla, Calif, showing effects of Wave action. W ave-Action.—The powerful effects of the beating of waves upon abrupt shores of seas or lakes are in evidence all over the world, and these effects are so characteristic that they can be recognized even where no sea or lake exists at present. Gravel and sand are carried in the surf and serve as grinding ma- terials, wearing even the hardest rocks into grooves, rills, chan- 8 SOILS. nels and caves, defining sharply the varying degrees of hard- ness or tough resistance in different parts of rocky cliffs; frequently undermining them and causing extensive rock-falls. The latter then serve for a time to break the violence of the waves’ onset, and may even cause permanent shore deposits to be formed under their lee. Such deposits are very generally formed on gently sloping beaches, and as the water gradually recedes, sometimes by elevation of the ground, beach lines or beach-terraces are left, which indicate the successive levels of the lake or sea. Such old beach lines or terraces and level-surfaced “ buttes ’’ in the Great Basin country, and ‘bench lands” elsewhere, show in their structure the characteristic lines of wave-deposition. Effects of Winds.—The action of winds in transporting soil particles (dust and sand) is familiar; and the accumulations that may be formed under the influence of regular, continuous winds are sufficiently obvious on lee shores having sandy beaches, inland of which the formation of sand dunes at times assumes a threatening magnitude. Where winds are irregular, frequently reversing their direction, of course the local effects will be less obvious, and the transportation of material actually occurring will often not be noticed. Yet there can be no doubt of the importance of wind action in soil formation, and there are cases in which no other agency can explain the facts ob- served over widely extended areas. This is especially true with regard to the soil masses of the high plains or plateaus of the dry continental interiors, where not only the regularity of the prevailing winds, but also the structure (or absence of struc- ture) and pulverulent character of the soil itself, renders this the only rational mode of accounting for its presence where we find it. The effects that may be exerted by regular winds are well illustrated in the plains and deserts of Africa as well as those of central Asia. Here we find a distinct subdivision of the desert (rainless) areas into the stony, from which the wind has swept all but the bedrock and gravel and where scarcely any natural growth, and certainly no cultivation is pos- sible in the almost total absence of soil. The next subdivision is the sandy desert, to leeward of the stony area, where the winds are less violent and regular, and where, therefore, the sand has been dropped THE -PHYSICAL PROCESSES, OF SOIL FORMATION: 9 and is wafted back and forth by “sand storms,” the surface being covered with moving sand dunes. Still farther to leeward we find the region in which the finer portions of the desert surface has been deposited ; here we have “dus/ storms”’ so long as the land is not irrigated ; but the application of water renders the soil abundantly fruitful. Such is the case of the Oases and fertile border-lands of the Sahara and Libyan deserts. In the cultivated portions of the Mojave and Colorado deserts in California, plowing of the land during a dry time is not uncommonly followed by a bodily removal of the loosened soil to neighboring fields, sometimes leaving a gravel surface behind. Such “ blown-out lands’ exist naturally at numerous points in the Colorado desert. Sven Hedin (Central Asia and Tibet, Vol. II,) shows that from the effects of the violent storms that prevail in the Gobi or Takla Makan desert, Lop-nor lake, the sink of the Tarim river, has in the course of time shifted its bed as much as fifty miles in consequence of the excavation of the southern part of the desert by the wind; while the sand so blown out, together with the deposits from the rivers, now tends to fill up the present (southern) lake, which is gradually returning northward toward its original site, now a desert, but around which formerly a dense population existed. The great plains of North America, the pampas of South America, the plateaus of Mongolia and especially the fertile loess region of northwestern China, are also cases in point. The dense dust storms of these regions are familiar and un- pleasant phenomena, which are often observed even by vessels at sea off the east coast of South America, where the dust-laden “pamperos ”’ at times compel them to proceed with the same precautions as in a fog; and the same is true of the northeast winds blowing off the Sahara desert on the west coast of Africa. The effects of windstorms carrying sand in the erosion of rocks are very obvious and striking in many parts of the world; nowhere probably as much so as on the great plains of western North America, where the geological composition of the ‘‘ bad lands’ is frequently impressed upon the rock surfaces very prominently. The strikingly grotesque forms are frequently 10 SOILS, brought out in this way, especially in the case of “ mush- room ” rocks, where a hard stratum has remained as a covering while softer layers underneath have been worn away. The illustration annexed shows such a case on the plains of Wyom- ing as figured in the Report of the U. S. Geological Survey, on the Central Great Plains, by N. H. Darton. Striking ex- amples of the same effects are seen on the shores of Lake Michigan in the Grand Traverse region, where the rocky cliffs are visibly worn away and carved under the influence of the regular ‘ sand-blasts’’ of northwest winds. On a smaller scale the effects of these sand-blasts may be noted in the cob- Fic. 4.—‘ Mushroom rocks,” produced by Wind action, Wyoming. (Darton.) ble-deserts, where we frequently find the cobbles worn away on the windward side in a very characteristic manner; the lee side remaining rounded and smooth, while the structure of the rock is strongly outlined on the windward side. CLASSIFICATION TORS SOnes: The physical Constituents of soils are thus, in the most gen- eral terms, first, rock powder (“‘sand’’) more or less changed PoE SPAY SICAL PROCESSES OF SOILsFORMATION: II by weathering; second, clay, as one of the chief results of the weathering process of silicate minerals; and thirdly, humus, the dark-colored remnant of vegetable decay. According to the obvious predominance of one or the other of these primary ingredients, soils are popularly, in the most general sense, classed as “heavy” and “light’’; the former term corre- sponding as a rule to those in which clay forms a prominent ingredient, while sandy and humous or “ mold” soils usually fall under the latter designation, because of their easy tillage. For practical purposes these subdivisions are both convenient and important, and they form the ordinary basis of land class- ification. Beyond these, the degree of fineness of the rock de- bris, and their physical and chemical constitution, determine distinctions such as gravelly, sandy, silty, loamy, calcareous, siliceous, magnesian, ferruginous, and others of less general application, though locally often of considerable importance. For the purposes of discussion and definition, however, an- other basis of classification 1s needed, which essentially con- cerns both the origin and the adaptations of lands. UPLAND Plateau “Scab ~ ‘ Sedentar, Soil iE LOWLAND Alluvial Flood Plains nch (afm selina Se Fic. 5.— Diagram illustrating the genetie relation of different svil classes to each other. 1. Sedentary Soils —When soils have been formed without removal from the site of the original rock, by simple weather- ing, they are designated as sedentary, or residual soils, or “soils in place.” In the case of these, the original rock under- lies the soil or subsoil at a greater or less depth, according to the intensity and duration of the weathering process, and is usually more or less softened and decomposed at the surface where it meets the soil layer. The latter of course bears some of the distinctive characters of the parent rock, and its composi- tion and adaptations may, in a measure, be directly inferred from that origin. Such soils usually contain, especially in their lower portions, some angular fragments of the parent rock. In ie SOILS. some cases sedentary soils may have been partially derived from rocks that have been removed from above the present country rock by erosion, and in that case fragments of such vanished rock may also be present. Sedentary soils are most commonly found on rock plateaus. and on slopes or plains underlaid by rock strata of but slight inclination, where the velocity of the “ run-off” rainfall is not sufficient to dislodge the rock debris. Extended areas of such soils exist in the granitic areas of the southern Alleghanies, in the “ black prairies’ of the Cotton States, and on the “ basal- tic’ plateaus of the Pacific Northwest. 2. Colluvial Soils—When the soil mass formed by weath- ering has been removed from the original site to such a degree as to cause it to intermingle with the materials of other rocks or layers, as is usually the case on hillsides, and in undulating uplands generally, as the result of rolling or sliding down, washing of rains, sweeping of wind, etc., the mixed soil, which will usually be found to contain angular fragments of various rocks, and is destitute of any definite structure, is designated as a colluvial* one. Colluvial soil masses are frequently sub- ject to disturbance from landslides, which are usually the result of water penetrating underneath, between the soil mass and the underlying rock, or sometimes simply of complete satur- ation of the former with water. Aside from such catastrophic action, they commonly have a slow downward movement in mass (creep), which ordinarily becomes perceptible only in the course of years; most quickly where there are heavy frosts in winter, which act both by direct expansion, and by the state of extreme looseness in which the soil mass is left on thawing. Colluvial soils form a large portion of rolling and hilly up- lands, and are of very varying degrees of productiveness. 3. Alluvial Soils—When soils are the result of deposition by streams, the material having been gathered along the course 1 The term “overplaced,” used for such soils in late memoirs of the U. S. Geo- Jogical Survey, is at least superfluous, in view of the perfectly understood term already in general use, and does not seem to commend itself for adoption by any special or superior fitness; nor does the suggestion of Shaler (The Origin and Nature of Soils, r2th Rep. U.S. Geol. Survey) to include the colluvial soils within the alluvial class, commend itself either from a theoretical or practical point of of view, since but few useful generalizations can apply to both classes. DHE PHYSICAL PROCESSES OF SOIL, FORMATION. 13 of the stream from various sources and carried to a distance before being deposited, the soil is designated as alluvial. These are the soils of the valleys, flood-plains, and sea- and lake-borders, past and present. Being of mixed origin, their general character may vary from one extreme to the other, both as regards physical and chemical composition. Since, moreover, they represent the finer portions of the soils of the regions drained by the watercourses, alluvial soils are as a rule of a fine texture; and as representing the most advanced de- composition products of the parent rocks, they are usually preéminently fertile. This is proverbially true of the flood- plains of rivers, and still more of their deltas—the bodies of lands formed near their outlets into seas or lakes. Character of these soil-classes—Sedentary soils are as a matter of course, other things being equal, dependent entirely on the parent rock for their specific character; and taking into consideration the various rocks (usually one or few) from which they may have been derived, nearly the same is true of colluvial soils, except that a portion of the clay and finest pul- verulent matters may in their case be carried down on the lower slopes and into the valleys and streams, by the hillside rills. According to the calculation of Merrill (Rocks, Rock-weathering, and Soils, p. 188) granite when transformed into soil z7thout loss would increase in weight by 88 %; more than doubling its bulk. More usually, the leaching process dmznishes their volume as compared with the parent rock. Alluvial soils are also of course to a certain extent de- pendent upon the character of the rocks and surface deposits occurring within the drainage area of the depositing stream. Asa rule their composition is much more generalized ; but their character as to the relative proportions of sand and clay is essentially dependent upon the velocity of the water current. Thus in the upper portions of valleys, where the slope is relatively steep and the velocity therefore high, a large pro- portion of cobbles and gravel is often present in the deposits, sometimes to the extent of rendering cultivation impracti- cable, or at least unprofitable. As the slope and velocity de- 14 SOILS, crease, first coarse and then fine sand will be the prominent component of the deposited soil; while still lower down, in the region of slack water, the finest sand or silt, together with clay, will predominate. According to Hopkins,* flowing water will, at a velocity of three inches per second, carry in suspension only fine clay (and silt); at eight inches it will carry sand as large as linseed. At one and one-third inches, it will move pebbles one inch in diameter; and at a velocity of two inches per second, pebbles of egg size are moved along the stream bed. Since the velocity of streams subject to freshets will vary greatly from time to time, deposits of very different grain will in such cases be found alternating with one another in the soil stratum of the flood plain. In fact, this alternation and the more or less stratified structure resulting therefrom, is the distinguishing mark of alluvial soils as such. It is true that this peculiarity is also sometimes found in the case of lands now lying far above the flood-plains of present rivers; but this is due to the elevation of the land or the depression of the river channels at a former period, prior to which such lands (commonly known as river terraces, benches or second bottoms) were formed. The same is true of lake terraces (‘“ mesas’’), which cover enormous areas in some parts of the world, more particularly in western North America. It must nevertheless be remembered that such alluvial terrace or bench soils differ in some respects from the modern alluvials, on account of their long exposure to atmospheric action alone; one result of which is that they are usually much poorer in humus, and therefore of lighter tints, than the more modern soils of alluvial origin. Other differences will be adverted to hereafter. As a matter of course the above distinctions, especially between colluvial and alluvial soils, cannot be rigorously maintained in all cases. There are transitions from one class to the other, so that it is sometimes optional with the observer to which of the two classes a particular soil may be considered as belonging. On the lower slopes of the hills bordering alluvial valleys the colluvial slope-soil may often be found alternating with the alluvial deposits, or bodily 1 Geikie, “ Text-book of Geology, 3d ed. Phe PHYSICAL PROGESSES: OF SOIL FORMATION. 15 washed away to be redeposited as alluvium at a greater or less distance. One characteristic of the flood-plain lands of all the larger rivers, and more or less of all streams subject to periodic overflows, is that the land immediately adjoining the banks is both higher and more sandy than are the lands farther back from the stream. The cause of this phenomenon is that as lateral overflow diminishes the velocity of that flow, its coarser portions are deposited near the river banks, while the finer particles are carried farther away, until finally only the finest —clay-substance—reach the lagoons or lakes filled with the overflow or back-water, and are there in the course of time deposited as heavy clay “swamp” soils. The same occurs where rivers empty into lakes or the sea; and these slack-water or delta lands are, as a rule, the most productive on the river's course. The continued productiveness of alluvial soils 1s more- over in many cases assured by the deposition, during overflows, of fresh soil-material brought down from the head waters of the streams. The Nile, and the Colorado river of the West, illustrate this point. Lowering of the land-surface by soil formation.—It is evident that the soil-forming agencies must in the course of time materially affect both the surface conformation and the absolute level of the land. The sharp pinnacles and crests of rock are abraded into the rounded forms now characterizing our uplands and lower ranges of hills and mountains; and it is estimated that, e. g., the general level of the drainage basin of the Mississippi river is lowered about one foot in 7.000 years, the material being carried into the lowlands and the sea. CHAP CEH Ra ith THE CHEMICAL PROCESSES OF SOIL FORMATION. Chemical Disintegration, or Decomposition. Ir may be said that in general, the physical agencies of dis- integration are most intensely active in the dry or arid regions of the globe, while chemical processes of decomposition are most active in humid climates. The chemical decomposition of rocks is primarily due to the action of the atmosphere, the average composition of which may be stated as follows: VOLUME PER CENT. WEIGHT PER CENT. UN IEEO DENG o, alps eel Gt [ee sel Balen | et ee eke 60z | goz | Sgr | ghz | gkz en ay “pues a Es "SANWId/(}) IddISSISSIJ DURMONOUOOGIO yd e{o) GAN EY | sees (Qolz+0j=L+) ainjsloyy d1dossoiZ A} £z00'o> Fn EY <1 Sz‘o> oro* Sz‘o gio So $zor re I g£o° WIS z Lro: / zLo- 8 ci | gt gt | ze of: pseieletain pues tg os: 1-S° Sey seleieienine FT1C) 28 ae ae 63 o ad : *S[PLIO}LYY jo uolj}eusisoq ~ es i3or a= o = » sans RES + |\ate oy po ( ‘STIOSHNS GNV SITIOS AO SHSATVNV ‘TIVOISAHd PHYSICAL COMPOSITION OF SOILS. 99 Number of soil grains per gram.—lIt is of some interest to consider the number of grains of different sizes that may be contained in, e. g., a gram of soil. If for this purpose we as- sume all the soil grains to be spherical, we shall obtain the minimum figures, for most other shapes will pack more closely. King (Physics of Agriculture, p. 117) calculates such figures for different grain-sizes, assuming the density to be that of quartz (2.65), with the result that while with a diameter of one millimeter (1-25 inch) the number of grains would be 720, and with one-tenth of a mm. 720,000; if made of the finest particles only, viz., one thousandth of a mm., the number would be 720,000 billions. Probably few of the clayey soils we ordinarily deal with are of this order; it is doubtless approached in certain fine plastic clays. Surface afforded by various grain-sizes—The amount of surface afforded by a similar amount of soil must naturally be considered in this connection, since upon it depends not only the amount of moisture which the soil may hold in the form of superficial films, but also the extent of surface upon which the weathering agencies as well as the root hairs of plants may act. Quoting again from King’s work, we find on the same premises given above for the number of grains, that their surface would in the case of grains of one mm. diameter be eleven square feet per pound (about half a pint) of material; while in the case of the finest grade we should have 110,538 square feet, or more than two and a half acres. From actual experiments made with the flow of air through various soils, King calculates that while in ordinary loam soils the total surface is about an acre per cubic foot, in fine clay soils it rises to as much as four acres. If we imagine this large surface to be covered with even a very thin film of water, it is readily seen how large an amount may be present in a cubic foot of moist soil. E. A. Mitscherlich (Bodenkunds fiir Land-und-Forstwirthe ; Berlin, 1905) attributes to the surface offered by the soil particles supreme importance in determining the productiveness of soils. According to him the internal soil-surface determines directly the ease with which roots can penetrate the soil; and he proposes the determination of this factor by means of the heat produced in wetting the soil ( “ Benet- 100 SOILS. zungswarme”’ ), measured in a calorimeter, as a substitute for all methods of physical soil analysis, which are vitiated by the varying shapes and densities of the particles; while his method gives directly the actual surface. To the consumption of energy required by difficult penetra- tion he attributes most of the differences in production, and hence re- fers to the internal soil-surface as governing nearly all the other physi- cal factors. The introduction of many arbitrary assumptions, and the failure to show that the admitted inaccuracy of the ordinary mechanical soil analyses are of any practical importance, greatly detract from the cogency of the rigorous mathematical discussion carried through his work by Mitscherlich. Influence of the several grain-sizes on soil texture —Un- doubtedly the most potent of all the sediments appearing in the above table in influencing soil texture, is the “clay.’’ That the materials included under this empirical designation may vary considerably in different soils, has already been sufficiently insisted on; and it is doubtful that in the present imperfect state of our knowledge of the functions of the several physical grain- sizes, we would be much wiser were we to go to the extreme advocated by Williams (Forsch. Agr. Phys., vol. 18, p. 225, ff), of determining with precision the actual amount of such ex- tremely fine clay particles as cease altogether to obey the law of gravity when once suspended in water. It is at least doubt- ful that the essential property of adhesive plasticity belongs only to these, for this property doubtless increases gradually as the size diminishes, although unquestionably not a mere function of the latter, since it belongs only to the hydrated silicate of alumina. Ferric Hydrate.—Probably the body which most commonly modifies materially the adhesive and contractile properties of the clay substance, is ferric hydrate ; the more as on account of its high density it tends to exaggerate materially, in many cases, the apparent content of true clay, and the estimate of the soil’s plasticity based upon it. A good example in point is the case of soil No. 246 (Miss.) of the above table. This is a heavy clay soil, yet not excessively adhesive; scarcely as much so as No. 230 (Miss.), the heavy gray “flatwoods”’ soil, and not nearly as “ sticky’? when wet as No. 173 (Miss.), the prairie sub- soil, although containing apparently 15 % more clay than the former, PHYSICAL COMPOSITION OF SOILS. IOI and 7 % more than the latter. But No. 246 is a highly ferruginous clay, in which the ferric hydrate isin a very finely divided condition, and materially influences the physical qualities of the clay substance. Were it all accumulated in the “clay,” it would diminish the percen- tage of true clay by 11.75%, reducing the clay-percentage to 28.5% which accords more nearly with the soil’s only moderate adhesiveness, and not excessively heavy tillage. But it must be remembered that the iron oxid shown in the analysis is not nearly always in this finely diffused condition. Frequently it incrusts the sand grains; quite commonly it forms small concretions of limonite, which themselves act as sand grains; and again, it may be present in the form of “ black sand ” or magnetic oxid, as is commonly the case in California and on the Pacific slope generally. To take this point properly into account, therefore, it would be necessary to determine the amount of ferric hydrate actually present in the “clay” as separated by subsidence of the granular constituents. Other substances.—The circumstance as well as the inevi- table presence of other modifying substances, clearly shows the desirability of being enabled to examine the physical properties of this “clay” directly, by collecting its entire amount as ob- tained in analysis, instead of merely determining it by weighing fractional portions. When this is done the analysis is much more valuable as indicating the true tilling qualities of the land. The increase of bulk suffered by this substance after wetting, is a very fair index of its content of true clay, and is preferable to the chemical analysis proposed by some investi- gators. For it is quite impossible to distinguish the silica and alumina derived from the kaolinitic substance proper, from that which is due to the decomposition of zeolites. It is possible, however, to determine the possible maximum of the kaolinite ingredient by taking into consideration the quantitative ratio according to which silica and alumina com- bine to form it, viz., approximately 46% of the former to 40 of the latter, the rest being water. By using this calculation we can often demonstrate clearly the presence in the “clay” of considerable amounts (up to 33%) of aluminic hydrate; since no zeolitic mass can contain as much alumina as does kaolinite, Whether the aluminic hydrate be in the form of gibbsite, 102 SOILS. bauxite, disapore,’ or in the gelatinous state, the nature of the soils containing it proves that it is totally destitute of plasticity and adhesiveness; and this consideration will often serve to explain the fact that soils showing in their chemical analysis high percentages of alumina, nevertheless show quite low de- grees of plasticity, adhesiveness and water absorption. What part it may take in modifying the physical properties of the soil we can thus far only conjecture. Influence of the granular sediments upon the tilling qualities of Soils.—Considering the granular sediments by themselves, in the absence of clay, it may be stated in a general way that while in a moist condition they flocculate sufficiently to pro- duce a fair tilth, they will nevertheless on drying collapse into a close arrangement resulting from the single-grain structure. The form of the grains being angular instead of rounded, they are apt to form a very closely packed mass far from suitable to vegetable growth; as will be seen by an example taken from one of the culture stations of the University of California, from a piece of land which on the surface would be called a very sandy loam, but after we descend increases in its content of fine grains until at a depth varying from eighteen inches to three feet we find what appears to be a hardpan, which is equally impervious to roots and water and causes the water to stagnate to such an extent that after heavy rains the land becomes so boggy as to render plowing almost impossible with- out endangering the team. A close examination of this hard- pan shows that, unlike others, it is devoid of any cement, and when taken out can be readily crushed between the fingers, and softens in water, but does not become plastic. Its impervious- ness is therefore due solely to the close packing of the sand grains, for it contains practically no plastic clay, and under the microscope the grains are seen to be angular-wedge-shaped and composed of the remnants of granite. The physical analysis shows the following result: ‘Bauxite is not only the most abundant of the three hydrates of alumina known to occur naturally, but also stands nearly midway between the two others in its water content, viz., alittle over 25°/,; that of diaspore being nearly 15°/,, gibbsite about 35°/.. PHYSICAL COMPOSITION OF SOILS. 103 MECHANICAL ANALYSIS OF HARDPAN, Designation. Diameter. Percentage. .50 mm 10.93 ogo), 21.2 SABGeiideiwa cle, sla selec ar 7.5 aie. aU 7.2 | (072i 9.63 Koyitgp Se 12.00 SUE soooccucosdeDoonds .036 “ 7.19 O2)\5ure 1-2 fOlOus 14.20 pa layeedereettortectarellelereisy- ? 8.64 It is doubtful whether this condition of things can be remedied by the usual measure of breaking up the hardpan either by hand or by means of giant-powder blasting. Ex- perience seems to show that the effect is only temporary, and that in the course of time, by the action of the percolating waters, the particles settle back into their original impervious condition. It is just possible, however, that if once penetrated by roots, the intervention of these would permanently destroy the close structure, so as to make this a fair subsoil for the growth of trees and other plants. The writer is not aware that this kind of purely physical hardpan without cement has ever been observed elsewhere. This physical condition is doubtless responsible for two other phenomena, viz., the “ putty soils,’ and also certain difficulties experienced in irrigation. “ Putty Soils” is the name popularly given in the Cotton States, and probably elsewhere, to soils usually occurring in low ground and also known as “ cray-fishy.’’ They consist of very uniform, powdery sediment, with little or no coarse sand and still less of clay to render them coherent. When wet these soils behave precisely as would glazier’s putty, adhering to the surface of even the best-polished plowshare, so that no furrow- slice can be turned and the plow is soon dragged out of the ground. Ata very closely limited condition of moisture such lands may plow fairly well; but when this limit is passed in the least (as sometimes happens in the course of a single day), it turns up only hard clods, which in a few hours of sunshine become so hard that no instrument of tillage short of a sledge- 104 SOILS. hammer will make any impression upon them. The physical analysis of these usually gray soils shows that they contain only a trifling amount of clay; perhaps 1 or 2%, playing the part of linseed oil in making putty out of whiting. Even the addi- tion of lime does not help such soils much, because there is little or no clay to flocculate. They are, as a matter of fact, among the most refractory lands the farmer has to deal with. A soil showing similar behavior, though not quite as extreme as in the case of the Gulf or Cotton States’ soils in question, occurs at the culture substation at Paso Robles, California, and is probably closely correlated to the physical hardpan re- ferred to above. The physical analysis of this soil yielded the following result: MECHANICAL ANALYSIS OF SOIL. Designation. Diameter. Percentage. .50 mm. 14.24 : BGOiie 15.17 San dipaeiis terse ceetorets Bae 388 atgg 5.60 { LO 2Naies 6.75 | 047“ 8.35 Silikes cicoson osda0d0¢ } 036 “ 8.55 fayaigy 6.03 f OLOWN cs 17.77 Wi Clery? eccucne womegoone ? 7.50 It would seem the best and almost only remedy to be ap- plied to such soils as these is the introduction of vegetable matter or green-manuring, by which their texture is loosened: for the hauling of mere clay upon the land would hardly ac- complish the purpose intended, within the limits of farm economy. Dust Soils, which during the dry season are even in their natural condition so loose as to rise in clouds and render travel very uncomfortable, are not uncommon in arid countries, e. g., in Washington and adjacent parts of Oregon, on the uplands bordering the Columbia, Yakima and Snake rivers. The physical analyses of three of such soils, given in the table be- low, will convey some idea of their peculiarities in this respect. ee eee S| eee PHYSICAL, COMPOSITION OF SOILS: 105 PHYSICAL ANALYSIS OF DUST SOILS. Hydr. Value. Diameter. No 17. | No. 37. |No. 79. CEs o0nssc0805 <.0023. mm. <.10—? 93 3.59 1.27 <.25 mm. O10 30.93 13.06 32.29 Silt 25 tOle5 o16 3-20 5.82 12.75 ie eae tO 220 025—.047 7.18 27.37 37-51 2.0 to 8.0 .047.—.120 21.88 43-78 10.92 SHiNGlo6 a dab eee 8.0 to 64.0 I2— .50 32-39 49.57 3-97 Tess ooSclleses oodamasbouollopoe cooucoededs 96.57 98.18 98.72 Slow penetration of Water—Soils of this class are wetted with extreme slowness by irrigation water; so that when first taken under cultivation it sometimes takes twenty-four hours to soak the land for twelve inches in each direction. Irrigation furrows must be placed very close together and in large num- bers, in order to ensure the wetting of the soil so that the crop shall not suffer from lack of moisture at a distance of two or not more than three feet. Where the irrigation furrows are drawn farther apart a fine stand of grain may be seen within eighteen inches of the same, while farther away the crops may be dying from lack of moisture. This difficulty is by no means infrequent in the arid region, and is difficult to overcome except by frequent and thorough tillage, which gradually increases the rapidity of water-penetration; as has been shown in the soils of the alluvial prairies of the Yakima country in the State of Washington. It is necessary, however, to take care that they shall always contain an adequate amount of humus or vege- table matter, in order to prevent re-consolidation by the burn- ing-out of the humus during the warm, rainless season. There is an unmistakable resemblance between these dust soils of the Northwest and the “ putty ” soils mentioned above; both showing a very low percentage of clay with a relatively large amount of the finest sediments, with a sudden downward break of the curve before the coarser grain-sizes are reached. It would seem as though the absence of these intermediate gtains favors the close packing of the fine sediments in the interstices of the coarse ones, thus bringing about the imper- viousness, which is the chief obstacle to their cultivation. Effects of coarse Sand.—Coarse sand intermingled with heavy clay soils has but little effect in improving the tilling qualities, unless carried to such excess as renders it financially a 106 SOILS. impracticable. In actual practice it is frequently possible to improve such soils by properly distributing upon them the washings of the adjacent hills, which will always carry sands of many grades; and when it is intended to improve garden land by hauling sand it is important to choose the latter so as to complement the deficient grain-sizes of the soil. The sand of wind drifts or dunes is generally well adapted to such improve- ment, being, as Udden? has shown, of a fairly definite com- position of sufficiently wide range of grain-sizes for the pur- pose. The effects of humus in modifying soil texture are discussed farther on. 1 The Mechanical Composition of Wind Deposits, Bull. No. 1, Augustana Library Publications ; 1898. CriAG BER Vit. THE DENSITY AND VOLUME-WEIGHT OF SOILS. AsIpE from the humus-substances the specific gravity of the common soil constituents, taken individually, do not vary widely; kaolinite. being the lightest (2.60), feldspar next (2.62) ; then quartz (2.65), calcite (2.72). Mica and horn- blende range (according to their iron contents) from 2.72 to over 3.0. The average specific gravity of soils of ordinary humus content only will thus range between 2.55 and 2.75; sandy soils approaching very closely to that of quartz alone. V olume-W eight.—The specific gravity of the soil is, how- ever, of little practical consequence compared with the “ volume- weight,” 1. e., the weight of the natural soil as compared with an equal bulk of water. A cubic foot of water weighs 62% pounds; a similar volume of soil usually weighs more, but in the case of peaty lands may actually (when dry) weigh less. The extreme range is from 110 pounds for calcareous, and somewhat less for siliceous sand, to as little as 30 to 50 pounds in the case of peaty and swamp soils. It may be conveniently remembered that while average arable loams range from 80 to about 95 pounds per cubic foot, “ heavy ”’ clay soils range from 75 pounds down to 69, observed by the writer in the case of certain alluvial soils, poor in humus,’ of the Sacramento river, California. Manured garden soils, and the mold surface soil of deciduous forests, generally contain so much humus as to depress their weight considerably, varying according to their state of tilth from 66 to 70 pounds per cubic foot. Weight per acre-foot.—As for practical purposes and calcu- lations it is often desirable to know approximately the weight in pounds of an acre (43,560 square feet) one foot deep, it is convenient to remember that in the case of sandy land, this weight (per “ acre-foot’”’) may be assumed at four millions of pounds; for loams, at 3% millions; for clay lands, 3%4 1 This remarkable soil seems to have been derived from the finest “slickens ” of the hydraulic gold mines. 107 108 SOILS, millions; for humus or garden land and woods earth, about 3 millions of pounds; for reedy swamp and peaty lands, 2 to 2% millions. The loose tilth and humus-content of the surface soil will in general cause it to weigh less, bulk for bulk, than the underlying subsoil, even when the latter is more clayey; moreover, the continuous pressure from above will tend to consolidate the subsoil and substrata. Waring- ton (Phys. Properties of Soils, pp. 46, 47) gives interesting data on this point from the Rothamstead fields, as follows : Old pasture, first nine inches. . . . . 71.3 pounds per cub. ft. Same, fourth do. do.. . cpak OZes eras eer ee Arable lang, mirst i jidos dott. Wien) is) (ay, eich oe4iny e TG Same, fourth do: tadons: ivceok Se elon alt 6 ME! Do By The influence of humus and unhumified organic matter, as well as of tillage, in diminishing the volume-weight of soils is here strikingly shown. Air-space in Natural Soils —The differ- ence between the specific gravity as usually determined, and the volume-weight of soils, is of course caused by the large amount of air contained in them when dry, but which in wetting them is partially or wholly re- placed by water. Theoretically, assuming all soil grains to be globular, and packed as closely as possible (in oblique order), the space not filled by them would be the same for all sizes, whether that of marbles, or so min- ute as to be hardly felt between the fingers ; and would be 25.95 per cent of the soil volume. If the same globular particles were packed as loosely as possible, 7. e., in square instead of oblique order (see figures 10 and 11), the vacant space would be 47.64 per cent. If however we imagine each sphere to be itself composed of a num- Se REE 2 ee ber of smaller ones, the empty space will arrangements of soil particles, Obviously be greatly increased, to an ex- 1 King, Physics of Agriculture, p. 116, ff. THE DENSITY AND VOLUME-WEIGHT OF SOILS, 109g tent proportionate to the diminution of solid mass thus brought about. The pore-space might in that case, with the oblique arrangement of the globules as shown in Fig. 10, be as high as 74.05 per cent. But since the soil particles may be of all shapes and sizes within the same soil, and usually fit much more closely than would globular grains, the empty space rarely approaches (only in certain alluvial soils and in loose mulches) to the figure last named. In sandy soils it may fall as low as 20%, and in coarse gravelly soils even as low as 10%. Most cultivated soils range between 35 and 50% of empty space. Effects of Tillage-—That these figures can be only approxi- mations is obvious from the consideration that one and the same soil will vary materially in its volume-weight according to its temporary condition of greater or less compactness. After land has been beaten by winter rains, its volume-weight will be found to have materially increased from the well-tilled condition brought about by thorough cultivation. This differ- ence is strikingly seen when, in plowing, the height of the ground on the land side is compared with that of the turned furrow-slice in well conditioned loamy land. This loose con- dition is called filth, and it results from the formation of relatively large, complex crumbs? or floccules, between which there are large air spaces that were wholly absent in the un- tilled land; the floccules themselves being also more loosely aggregated than was the case before tillage. Crumb or Flocculated structure.—Figure 11 illustrates the difference between the unplowed land, consolidated especially on the surface by winter rains, and in its upper portion con- sisting largely of single grains; while the plowed land, toward which the furrow-slices have been turned, is greatly increased in height and volume and consists almost wholly of variously- shaped and-sized aggregates or floccules, loosely piled upon one another and separated by large interspaces. The increase 1 The word crumbs, which is generally understood as meaning a relatively large, loose aggregate, seems preferable to the word kernels, suggested for the same by King (Physics of the Soil, p. 110). Kernels are understood to be bodies rather more solid than the surrounding mass, and do not convey the idea of loose aggre- gates. The word “ Kriimelstructur” (crumb-structure), adopted by Wollny for this phenomenon, has both fitness and priority in its favor. 110 SOILS. in volume from consolidated clay to crumb-structure is given by Fic. 11.—Land before and after plowing. The compactness of the soil is indicated by the density of dotting. Before plowing there is a compact surface crust (s), below which the soil becomes less and less compact as we go deeper. After plowing we find the soil (fs, furrow-slice) converted into a loose mass of crumbs (floccules), with increase of bulk. Compacted plow-sole at pl Wollny (Forsch., vol. 20, p. 13, 1897) at 41.9%, to powder as 33%. On moistening dry clay increased 36.9%, quartz powder 8.01%. When land is plowed in the proper moisture-condition the crumbs of floccules are held together by the surface tension of the capillary films (menisci) of water at the points of contact. In the case of sands, the crumbs will collapse into single grains when- hie sana saleramb, magsied (© ever the water-films evaporate, un- posed. The particlesare held together by less some cementing substance was ie warmers usacaetishaisot dissolved or suspended inthe between the particles represent air. water. (See figure 12)% Lime carbonate is one of the substances most commonly found per- manently cementing the floccules; hence the ready tillage of most calcareous soils, and especially the loose texture of the “loess” of the western United States, and of Europe and Asia. In these deposits we find sandy and silt aggregates or concretions ranging from ten or more inches in length (loess puppets) to microscopic size, held together by lime carbonate, but collapsing into silt and sand when the material is treated with acid so as to dissolve the cement. The rough surfaces of these aggregates, gripping into each other, explain the stability of the steep loess cliffs in the United States, as well as in northeastern China, as observed by Von Richthofen and Pumpelly. Clay is most frequently the substance which imparts at least temporary stability to the crumbs and crumb-structure; this is THE DENSITY AND VOLUME-WEIGHT OF SOILS. q11 one of its most important functions in soils, as it serves to maintain tilth once imparted by cultivation, even after the land dries out. Beating rains, and cultivation while too wet, will in this case of course destroy the crumbs and the loose tilth. Other substances which greatly aid the maintenance of tilth are the several humates (of lime, magnesia, iron), which when fresh are colloidal (jelly-like) like clay itself, but unlike the latter, when once dried do not resume their plastic form by wetting (Schloesing). The crumbs thus formed are there- fore quite permanent and contribute to the looseness of soils rich in humus. One part of lime humate is said by Schloesing to be equal in cementing power to eleven parts of clay. Silica, silicates and ferric hydrate are sometimes found cementing soil crumbs, wholly or in part. The importance of the ready penetration of air, water and roots thus rendered possible is obvious; and the question arises how it happens that wild plants are able to do without tillage. How Nature Tills——When we examine the undisturbed soil of woods or prairie in the humid region, we will as a rule find the natural surface soil in a very good condition of tilth; the obvious cause being the presence in it of an abundant network of surface roots and rootlets of grasses and herbs, which in connection with the fallen foliage prevent the beating and com- pacting of the soil surface; which can be seen to happen before the observer’s eyes whenever a heavy rain falls on a bare land surface, however well tilled. Crusting of Sotls—In some soils, especially of the Gulf States, the beating of rain followed by warm sunshine so effectually compacts the surface that in the case of taprooted plants like cotton, it becomes necessary to cultivate after each rain, so as to break the crust that would otherwise not only prevent the proper circulation of air, but would also serve to waste the moisture of the land. The same land in the wild condition suffered no such change, being protected by the native vegetation, and by fallen leaves. (See chapt. 8). Soils of the arid region.—In the regions of deficient rain- fall the conditions are modified in several respects. Grass sward rarely exists, nearly all grasses assuming the habit grow- ing in tufts or bunches some distance (a foot or two) apart; 3 SOILS. hence the name of “ bunch grass ’’ commonly used, which how- ever means not any one definite kind of grass, but serves to distinguish the grasses of the uplands from those of the moist lowlands, where true sward may be found. Between these bunches of grass the soil is fully exposed, and being free from roots and leaf-covering is compacted, unless its nature 1s such that the usually gentle rains do not produce a serious crusting of the surface. That such is actually the predominant nature of the soils formed under arid influences has already been stated; and thus the hard-baked soil-surface so often seen in the Eastern United States in unplowed bare land, or during the prevalence of a drought, is rarely seen in the arid region. The clay lands that do exist are usually sufficiently calcareous to possess the property of “ slaking ” into crumbs whenever wetted after dry- ing. But where this is not the case, the stony hardness brought about by the long dry and warm season is long in being re- moved by the winter rains. Charges of soil-volume on wetting and drying.—The be- havior of colloidal clay in the above respects has already been described above (see chapt. 4, page 59). It is obvious that whenever soils contain a large proportion of such clay, their behavior on wetting and drying will approximate to those of the pure clay. This is exemplified in the heavy clay, or so- called ‘prairie soils”? of the United States, which when thoroughly wetted in spring will, during a dry summer, form wide, gaping cracks. These in the long summers of the arid region may extend to the depth of several feet, with a width of as much as three and more inches at the surface of the ground. This, of course, contributes greatly to the drying-out of the soil to the same depth, and results as well in the mechanical tearing of the root-system of growing plants; sometimes causing the total destruction of vegetation. In some clay soils it happens that after a rain or irrigation, the shrinkage occur- ring upon the advent of warm sunshine will cause the surface crust to so contract around the stem, e. g., of grain, as to con- strict and injure the bark, causing serious injury to the crop. In soils of this character very thorough tillage in preparing for a crop, and the maintenance of a loose surface during its growth, are of course extremely essential. THE DENSITY AND VOLUME-WEIGHT OF SOILS, ake In the arid region it will frequently happen that such soils when not tilled to a sufficient depth, will during the later part of the summer so shrink and crack beneath the shallow-tilled surface layer that the latter will bodily fall into the cracks, ex- posing the roots to all the deleterious influences of mechanical lesion and drying-out. It is thus obvious that the cultivation of such soils should not be undertaken at all by those not nat- urally able and willing to bestow upon them, to the fullest ex- tent, the deep and thorough tillage which is absolutely essential in the utilization of their usually high productive power. Extent of Shrinkage.—TVhe extent of this shrinkage in drying, and subsequent expansion in wetting, have been measured by the writer by the use of the sieve cylinder described below (chapt. 11, p. 209), as serving for the determination of the water capacity of soils. Whena soil of the kind above referred to is placed in the sieve cylinder in the tilled (flocculated) condition, then allowed to absorb its maximum of water and then dried at roo degrees C., the contraction in drying can be very strikingly seen, and its amount measured by filling up the empty space with mercury; then measuring the latter after expelling the surplus by means of a ground glass plate laid on top. The con- traction of several heavy clay soils, thus measured, has been found by the writer to range from 28 to as much as 4o per cent. of the original bulk." The soil thus contracted, when again wetted, does not return altogether to its original bulk, but remains in a more or less compacted condition, like that of a soil which has been rained upon. The expansion and contraction of a heavy clay soil on wet- ting and drying are well illustrated in the figure below, in which the soils are shown in the shallow cylinder which serves for the determination of water-holding power (see chapt. 11, p. 209). The middle figure shows in profile the expansion of a dry, pulverized “ black adobe,” struck level, when allowed to absorb its maximum of water; it rises above the rim of the sieve-box to nearly the half height of the latter. The outside figure to the right shows the same soil after drying; that to the left, a red clay soil similarly treated. It is easily seen that these variations in volume may bring about very marked results in 1 Wollny (Forsch. Vol. 20, p. 13 ff, 1897) records similarly high shrinkages in his experiments. 114 SOILS, the fields; the surface of which, apart from the cracks usually formed, may be several inches lower in the dry season than during wet weather. Rep Cray So!t. Brack “ Apose ”' CLay SOIL. Fic. 13.--Expansion on Wetting and Contraction on Drying of heavy clay soils. Contraction on Wetting.—In the case of alkali soils contain- ing much carbonate of soda, a very notable contraction occurs in wetting the loose, dry soil. The cause is here obviously the collapse of the crumbs, formed in dry tillage or crushing, into single grains, closely packed. The same result is observed in the naturally depressed “ alkali spots”’ (see chapt. 22). “ Hog-wallows.’—In the field the wetting of cracked clay soils produces some very curious effects. The effect of the first light rains usually is to crumble off the edges or angles near the surface, the materials thus loosened falling into the lower portion of the cracks. This is repeated at each success- ive shower followed by sunshine, the crevices thus becoming partly filled with surface soil. When, subsequently, the heavier and more continuous rains wet the land fully, also causing the consolidated mass in the crevices to expand, the latter cannot close on account of the surplus material having fallen into them; the result being that the intermediate portions of the soil are compelled to bulge upward, sometimes for six or more inches, creating a very uneven, humpy surface, well-known in the southwestern United States as “‘ hog-wallows,”’ 4 1 A totally different kind of “ hog-wallows,” occurring in California and the arid region generally, have been described in a previous chapter under the head of Aeolian soils (See chapt. 1, p. 9). a — —— a _ —————<— rl OCS THE DENSITY AND VOLUME-WEIGHT OF SOILS. PES Such a surface is always therefore an indication of an ex- tremely heavy soil, difficult to cultivate; yet embracing some of the most highly and permanently productive lands known in the United States, and in India, where the “ regur” lands of the Deccan are of this character; they have been cultivated without fertilization for thousands of years. The subjoined physical analyses of lands of such extreme character as to be almost uncultivatable will serve to exemplify their physical composition. PHYSICAL ANALYSES OF HEAVIEST CLAY SOILS, No 242 Miss.| No. 643 Cal. Hog-wallows |Black Adobe. soil. Contra Costa Jasper Co. Co. Mississippi. | California. Weight of gravel over 1.2 mm. diameter.......... 8 «~ between 1-2:and 1 mm........... ao ‘ “ Se 8 | se s& humus. BGs |enu5|2ec ne, Ey eae or cena SUB-IRRIGATED ARID SOILS (California). 586|Sandy plains soil, Tulare, Tulare Co............. dod si deka EOL: || ees 1466|Loam soil, Miramonte, Kern Co........... See eeOOl|LO:06 I) 064) 1284|Moist land loam soil, Chino, San Bernardino ‘Gece 1.99 | 10.20] .203 1148|Swale soil, near Paso Robles, San Luis Obispo Co.. iio) || CMOS |] aie 1714|Bench soil, Santa Clara River, Piru, Ventura Co....... 78 | 9.50] .074 77\Alluvial soil, Tulare Lake bed, Tulare Co............. 47 | 9.37] .045 1880|Creek bench soil, Niles, Alameda Co................. 1.19 | 8.90] .109 1903/Sediment soil, Porterville, Tulare Co................. 1.12 | 8.50] .140 168/Alluvial soll, Santa Clara river, Santa Paula, Ventura Co| .84 | 7.99] .067 1760|Green-sage land, Perris Valley, Riverside Co.......... QI | 7.70} .070 506) Alluvial soil, Colorado River, Yuma, San Diego Co....| .75 | 7.47 .050 Foo) Red soil,, Manton, Tehama Cote}. § i. sce ccc a's ae aces 2.00 | 6.86] .137 1758|Alkali soil, Perris Valley, Riverside Co. selesvievs|) -0O | 6:33)|) (07 1963|Sandy loam Soil Wallowsym Glenn Coarse irerieileerse 36 | 6.05] .022 2080|Sandy soil, Santa Maria Valley, Santa Barbara Co.. 1.64 | 5.36] .og0 Average of sub-irrigated arid soils............ 1.06 | 8.38] .099 HUMID SOILS FROM ARID AND HUMID REGIONS (California). 207|Eel River Alluvial soil, Ferndale, Humboldt Co........ 1.25 | 6.96] .085 2319|Alluvial soil, Hupa Valley, Humboldt Co............. 7203) |MO7 Ol meena 213|Marsh soil, Novato, Meadows, Marin Co............. 1.54 | 6.36] .089 1704] Valley soil, Hollister, San Benito Co................. .94 | 5.21] .049 2295| Lule soil, Upper Lake, Lake Co..........:..... meeoa| Hever || ZbGes'|| soy7/7, 110/Alluvial soil, Putah Creek, Dixon, Solano Co.......... Te7ko |e SaleeO72 37|Redwood Valley soil, Pescadero, San Mateo Co....... 2.28 | 3.07 | .070 Average for California........ poncuccdnoaos|| Zou I Geey|). oi Be OTHER STATES. Bolo soil) Michigan’. cies ecene Soe e asiatd ceSeela teats 233.02| 6.08 |22.012 Back-land clay loam, Houma, Louisiana............... 5.07 | 4.20] .218 BY Tatie SOU; OLELON ss 2/5 onz)ae,ohese esi viaisig ereieiarerciete 3 weit scseiatercts 13.84 | 3-49] -483 Sandy prairie soil; Earns Cow mlexasacidecits oclae eels ste 2.13 | 3.66] .184 Average for other States....5...0ccces+s- Visele || ee7hs) |) eeto\s 23/Red soil, Oahu Island, Hawaii (maximum)........ SA Piacy aa (a Reval biter ts) 27|Guava soil, Hawaii Island (minimum)............ soovdl| CHO |) tere || ottyfe) PNVE TAC LO aS SOils,. Oars NS] am srersyajslepeie ose eteveleleveielere’s ¢ 3.01 6.07 | .237 Average of 2 soils, Maui Island....... ettokatetatlenerstetetal= 9.07 | 2.13] .286 Averarelor AlsoilssElawait Islandien. -twers secciseiiece ciel G.l70|) 2254) | erAS Average for Hawaiian Islands......... vieacelt 5-20) “309s .kOo Total for Humid soils, average............. 4.58) 49 4.235 | 1100 2 Introduced only for comparison of the nitrogen percentage in Humus and not included in the average. 138 SOILS. It thus appears that on the average the humus of the arid soils contains about three and a half times as much nitrogen as that of the humid; that in the extreme cases, the difference goes as high as over six to one (see Nos. 37 and 704) ; and that in the latter cases, the nitrogen-percentage in the arid humus con- siderably exceeds that of the albuminoid group, the flesh-form- ing substances. It thus becomes intelligible that in the arid region a humus- percentage which under humid conditions would justly be con- sidered entirely inadequate for the success of normal crops, may nevertheless suffice even for the more exacting ones. This is more clearly seen on inspection of the figures in the third column, which represent the product resulting from the multi- plication of the humus-percentage of the soil into the nitrogen- percentage of its humus; as appears in comparing the respective averages, or Nos. 1167 and 110 and others. An additional consideration is the probable greater ease with which the nitri- fying bacteria can act upon a material so rich in nitrogen. We must not, then, be misled by the smallness of many humus-percentages in the arid region, into an assumption of a deficiency in the supply of soil-nitrogen. Decrease of Nitrogen-Content in Humus with Depth—Since the oxidation of the carbon and hydrogen in the humus-substance, and the consequent increase of its relative nitrogen-content, are manifestly de- pendent upon the presence of air and heat, it is reasonably to be expected that the nitrogen-percentage of the humus should decrease with the depth of the soil. That this is really the case is plainly shown in the subjoined table, which gives the humus-percentages and the nitrogen-content of the humus from the surface foot down to twelve feet, in a soil on the bench of the Russian River, Cal., which is sub-irrigated, and liable to more or less rainfall during the summer. It will be seen that not only does the absolute humus-percentage decrease quite regularly down to seven feet, at which point there evidently was at one time a strong root development, causing a notable increase of the humus-con- tent; from which again there is a regular decrease down to the twelfth foot. It will be noted that the nitrogen-percentage in the humus, while not decreasing with the same regularity as the humus-content itself, yet exhibits a general recession from 5.30 to 1.15 in the ninth foot, to which direct oxidation doubtless never penetrates. SOIL AND SUBSOIL. 139 HUMUS AND NITROGEN-CONTENT OF RUSSIAN RIVER SOIL. Depth in feet. Per cent Humus in |Per cent Nitrogen in} Per cent Humus- soil. Humus. Nitrogen in soil. I 1,21 5-30 064 2 1.16 4.32 .054 3 1.14 3.87 -044 4 NeiLy, 3.76 .044 5 74 2.16 .016 6 60 2.66 .o16 7 “47 2.54 O12 8 78 1.54 O12 9 54 2e2 O12 10 52 Tews .006 II 53 1.51 .008 12 -44 1.81 .008 Influence of the Original Materials on the composition of Humus.—The great variability of the composition of humus formed from different substances is well shown in the sub- joined table, representing the results of experiments made by Snyder,’ who caused various substances to humify by mixing the pulverized material intimately with a soil poor in humus, and allowing the process to continue for a year. At the end of that time the humus formed was extracted by the method of Grandeau, outlined above, and analyzed, with the following results. Oat Green | Wheat Saw- Meat Cow Sugar. | straw. | Clover.| Flour. | dust. Scraps. |Manure. 2 Carboni... - 57-84 54.30 54.22 51.02 49.28 48.77 41.93 Hydrogen...... 3.04 2.48 3.40 3.82 Bons 4.30 6.26 INttrogen«)..... << 08 2.50 8.24 5.02 0.32 10.96 6.16 O@xycenerienc's|) 39:04. | 40.72 34.14 | 40.14 47.07 35-97 45-63 100.00 100.00 100.00 100.00 100.00 100,00 100,00 While it may be questioned whether the process of humifica- tion had in these materials really reached the point of sensible completion in all cases (notably in those of sawdust and cow 1 Bull. No. 53, Minn. Exp’t Station, p. 12, Chem. of Soils and Fertilizers, p. 94. 2'The figures for cow manure are so far out of range with any others thus far observed, that it seems reasonable to suppose that they are influenced by un- changed substances present in the excreta. 5 140 SOILS. manure), the great variability of the products from different materials is very striking. When the nitrogen-content is de- ducted the percentage composition of the products agrees more nearly. Considering that the nitrogen is probably pres- ent in the amid form, it is natural that hydrogen should in a measure vary with it, as in the case of the clover, flour and meat humus. Nitrogen being the most variable ingredient of humus, it seems probable that the variation of the proportion of the humus-amids present is the most potent factor in the variability of the composition of natural soil-humus. Arranging these results in the order of their nitrogen-con- tent as in the table below, we see that the latter approximately corresponds to the original protein-content of the humified sub- stances. Mumusetrom’meat Scraps... 6420 ees 10.96 % Nitrogen. as cP ROTEEM (ClOVER S171 crn se eeyer 8.24 < SEU COW MATTE oo aja ater erclales 6.16 - frawheat HOU se ei.cnis aes 5-05 UY Se ROE SULA Wipe pee atone oe 2.50 ae CEO BSA ALUS Egicse re iosetahe eae Ses 32 While the above data prove the correlation between the first products of humification and the original substance, it must be remembered that subsequently, under proper conditions, the nitrogen-percentage in humus may, in the course of time, in- crease very greatly, even to a proportion considerably above that contained in flesh itself. When we consider that ordina- rily, the latter, and the albuminoid substances generally, decom- pose in contact with air with an abundant evolution of ammonia compounds, sometimes leaving only a little fat (adipocere) behind, it is surprising that the decomposition within the soil should have exactly the opposite result, viz., an accumulation of the nitrogen. The causes of this marked difference are not yet well understood, but it is probably due to the differences in the kinds of bacteria that are active in the two cases. Snyder has also shown that the richer the organic matter humified is in nitrogen, the more energetically it acts in render- ing available the mineral matters of the soil for plant nutrition. SOIL AND SUBSOIL. 141 Correspondingly, Ladd + has shown that with the increase of humus in the soil, there is also a corresponding increase in the amounts of mineral plant-food extracted from the soil by a four per cent solution of ammonia, such as is employed in the Grandeau method of humus-determination. 1 Buil., S, Dakota Station, Nos. 24-32, 35, 47. CHAPTER IX: SOIL AND SUBSOIL (Continued). ORGANISMS INFLUENCING SOIL CONDITIONS; BACTERIA, ETC. MICRO-ORGANISMS OF THE SOIL. INTIMATELY correlated with the humus-substances of the soil, as well as with its temporary contents of the carbohydrates (cellulose, gums and sugars) from which humus is formed, is the multitudinous flora of micro-organisms always present and exercising important functions in connection with the growth of the higher plants. Extended researches by Adametz, Schloesing and Mtintz, Miquel, Koch, Fraenkel, Winograd- sky, Frank and many others, have thrown light upon the im- mense numbers and great variety of minute organisms, es- pecially of the bacterial group, present in soils, and upon their distribution and activities in the same. It has been shown that their numbers are greatest near (although usually not at) the surface, decreasing rapidly downward and generally disappearing wholly at depths between seven and eight feet; the latter depth varying of course according to the nature and porosity of the soil, and both depth and numbers being greatest in summer. Numbers of Bacteria in Soils—Adametz found in one gram of soil, 38,000 bacteria at the surface, 460,000 at ten inches depth; in a loam soil at the surface 500,000, at ten inches 464,- 000 in each gram of earth. Of mould and similar fungous germs there were only 40 to 50 in the same, 6 species being true molds, while four were ferments, including the yeasts of wine and beer. Fraenkel found in virgin land from near Pots- dam, a sudden, marked decrease at depths of from three to five feet ; while in earth from inhabited places within the city of Berlin, considerable numbers were still present at eight and even ten feet, in some cases. In the researches lately made by Hohl at the bacteriological 142 SOIL AND SUBSOIL. 143 station at Liebefeld, near Bern, it was found that in cultivated soils the number of bacteria greatly exceeds the figures given by Fraenkel. He found a gram of moist soil to contain from three to fifteen millions of bacteria. In the cultivated soil of Liebefeld he found 5,750,000, in meadow land 9,400,009, in a manure pile 44,500,000 per cubic centimeter. These figures seem high for so small a quantity of material, but taking the average size of a bacterium, a cubic centimeter might readily contain six hundred millions. (Grandeau, Ann. Sci. Agrono- mique, vol. I, p. 461, 1905). Mayo and Kinsley (Rep. Kansas Exp’t Station for 1902-3) have made elaborate investigations of the numbers and kinds of bacteria found in various soils in Kansas, in connection with different crops. It is noteworthy that in most cases their figures exceed considerably those given by European observers, as they often reach high into the millions, in one case to over fifty millions, per cubic centimeter.! Five fields with different soils were investigated; the land being described as follows: “Field No. 1 is a black loam containing con- siderable humus; field No. 2 is similar to field 1 but contains more humus ; field No. 3 is a thin soil with clay gumbo subsoil ; fields Nos. 4 and 5 are black loams, but not as rich in humus as either No. 1 or No. 2.” The average bacterial contents of the several fields are given as follows : Hield INOwid as: wa eets ek 33,931,747 per cubic centimeter. hey NOS2 G42 ie rae 53,500,000. 7° ost d: CU NODS ito aod eete Toss at sr &¢ SSOIN Os Ale aia jets Rein oR OA BROOOIY, Ell hue it es Ber Obe Si tey sich oe ctav shots LOD 3 Tee, ase a “The crop records of these fields for the past ten years indicate that the crop yield has been (more or less ?) directly proportional to the bacterial content of the soil of each field ; field 2 has produced the largest yield, field 3 the least.” Unfortunately no chemical analyses of any of these soils are com- municated ; but at the request of the writer samples of the soils of the 1 The mode of statement in the paper is not always quite clear as to the manner in which the averages given were calculated. It must be remembered that these data refer to cubic centimeters of soil, or about twice the amount (1 gram) used by European observers. 144 SOILS. first three fields were sent from the Kansas station for humus deter- minations (courteously made by Dr. H. C. Myers), which gave the following results : Field (NOs 1 3:.).4 Sie aire eiata esate 2.19% of Humus. EC TAN Osis Gino sia ees eso 3.07 pu se 6 INOW3 tse ose ess asic elapate 1.85% “ es While these humus-percentages are not directly proportional to the bacterial content, a favoring effect of high humus-content is clearly shown. ‘The bacterial and the humus-content of these soils are sensibly, even if not directly, correlated; which might reasonably be expected, since the organic matter and the humus are the bacterial food. The investigation also showed wide differences in the bacterial con- tent of the same soil when different crops were growing on it. ‘Thus in samples taken on Aug. 15, there were found in the first twelve inches of a black loam soil bearing timothy and clover, 1,380,000, in the same with alfalfa and clover, 21,091,000, with maize from one to over two millions. In soils from the western part of Kansas, the bacterial con- tent of the same crops was much less (as doubtless is the humus-con- tent), and it is noteworthy that the prairie buffalo grass shows through- out a relatively high bacterial content in the first foot of the soil, ranging next to alfalfa. The root bacteria living on the legumes will naturally increase the bacterial content of the soils on which they grow, more than plants which, like maize, do not directly utilize bacterial action. Multiplication of the Bacteria—Marshall Ward and Duclaux have made some special observations in regard to the rapidity with which certain bacteria multiply. Duclaux summarizes the final conclusion thus: taking as a basis the time of 35 minutes for the subdivision into two, which has been frequently observed by Ward, there would be four millions of bacteria produced in twelve hours. ‘The first filaments had plenty of room in a drop culture of one cubic millimeter; but at the end their total volume amounted to the tenth part of the total volume of the drop. At the above rate, making 48 generations in 24 hours, 281,500 billions of organisms would be produced. (Grandeau, Ann. Sci. Agron. Vol. 1, 1905, p. 456). Aerobic and Anaerobic Bacteria——As may readily be in- ferred, the cultural and other surface conditions exert a potent influence both upon the kinds and abundance of the bacteria and molds; since the life-functions of some are dependent upon SOIL AND SUBSOIL, 145 the presence of free oxygen (“aerobic”), while others flour- ish best, or only, in the absence of air (“ anaerobic’), or are able to avail themselves of the presence of combined oxygen, by reduction of oxids present. Their number is found, in general, to be greatest in cultivated lands, and bacteria are there by far predominant over the moulds. On the other hand, the moulds gain precedence in woodlands and meadows, at least so far as air can gain access; while in the deeper layers of the same, as well as in peaty lands, bacterial life is always scanty. This holds particularly in respect to the nitrifying organisms, and others whose life-functions are dependent upon abundant access of oxygen (aerobic). Food Material Required.—All bacteria, like the fungi, are dependent for their development upon the presence of adequate amounts of some organic food-material, best apparently in water-soluble form. In the soil it seems to be chiefly com- pounds of the carbohydrate group, especially various gums derived from the decaying plant substance, or from stable ma- nure; in artificial cultures, glucose is mostly found to be a highly available food. When the decaying substance reaches the state of humus, the latter seems to be available as food only to comparatively few bacteria. The very abundant de- velopment of bacterial life seems to be among the most im- portant effects produced by stable manure upon the surface soil, in establishing good tilth (‘‘ Bodengare”’ in German). Functions of the Bacteria—While there is still much uncer- tainty as to the exact functions performed by most of these bacteria in respect to soil-formation and plant growth, there are several kinds whose activity has been proved to be of the utmost importance in one or both directions; it having been shown that when the soil is sterilized either by heat or anti- septic agents, certain essential processes are completely sup- pressed until the soil is re-infected and the conditions of bac- terial life restored. Probably the chief in importance are those connected with the processes of nitrification and demttrification, bearing as they do upon the supply to plants of the most costly of the three substances furnished by fertilizers. These organisms have been first extensively studied by Winogradsky, while the con- if) 146 SOILS. ditions of their activity have been largely developed by R. Warington. Nitrifying Bacteria.—The conversion of ammonia into ni- trates is accomplished under proper conditions by two or- ganisms, or groups of organ- isms; the first stage being the formation of nitrites by the round, often flagellate cells of nitrosomonas (or nitrosoco- cus). The second, the oxid- ation of the nitrites into ni- trates by very minute rod- shaped bacilli, named nitrobac- teria. The conditions under which these bacteria can act are quite definite in that, aside Fic. 16.—Nitrobacterium. (Winogradsky). from a supply of the nitrifiable substance, a fairly high temperature (24° C. or 75° F.) and a moderate degree of moisture, there must be a free access of oxygen (air); and there must be present a base (or its car- bonate) with which the acids formed by oxidation can imme- diately unite. In an acid medium (“sour”’ soils) nitrifica- tion promptly ceases; as it also does whenever the amount of base present has been fully neutralized. The bases most favor- able to nitrification are lime and magnesia in the form of car- bonates, an excess of which does no harm; while in the case of the carbonates of potash and soda, the amount must be strictly limited. Fic. 15.—Nitrosomonas. (Winogradsky). Conditions of Activity—Dumont and Crochetelle found that up to .25 per cent, potassic carbonate acted favorably on the process ; which was, however, completely stopped by as much as .8 per ct. War- ington has shown that ammonic carbonate similarly prevents nitrifi- cation when exceeding about .37 per ct. Ammonia salts in general appear to be antagonistic to the transformation of nitrites into nitrates. Aside from the carbonates, some neutral salts favor nitrifi- cation very markedly; while others tend to depress it. Deherain found that .5 per cent of common salt suffices to pre- SOILFAND SUBSOIE. 147 vent nitrification altogether, while smaller amounts retard it proportionally. According to Dumont and Crochetelle, potas- sium chlorid acts favorably up to .3 per cent, but at .8 per cent. suppresses nitrification. Earthy and alkaline sulfates, on the contrary, seem to act favorably throughout, at least up to .5 per cent. this is especially true of gypsum, which, according to Pichard, accelerates the process more than any other sub- stance known. ‘Taking the effect of gypsum as the maximum, he found that, other things being equal, the amounts of nitrates formed were as shown in the table below, the effect of gypsum being taken as 100: LON DSN he ekard eects OED. mares yoor euotre deters 100 SOGiegstlbatetwrajcke es S essere aussor, wis se rer ats 47-9 IPOtassiG SUliate mse. scpeca.ccis ols mus he stem clits 35.8 Galeries Carbonate verre -jcishee wus lsuere echereevee 8 juste. Miasmestes Ganonmater srenterciacrare telaicca clei ars tele W205 The above estimates are markedly confirmed by the observations of the writer in the alkali soils of California. In these, nitrates exist most abundantly when the salts contained in the soil are mainly sulfates ; while wherever common salt or sodic carbonate are present in con- siderable amounts, the amounts of nitrate found are notably less. In saline seashore lands nitrates are usually present in traces only. Wollny has moreover shown that the nitrates themselves exert a repressive influence on nitrification. Effects of Aeration and Reduction——While the fostering effect of sulfates upon nitrification is very energetic in well aerated soils, they become injurious whenever by a reductive process in ill-drained lands, the sulfates are reduced to sulfids. Under such conditions the process will in any case be much im- paired. On the other hand, the favoring effect of abundant aeration was strikingly shown in the experiment made by Deherain, in which a cubic meter of soil was left unmoved for several months, while a similar mass was thoroughly agitated once a week during the same time. The proportion of nitrates formed in the latter case was as 70 to 1 formed in the quiescent soil mass. It follows that the intensity of nitrification is essen- tially dependent upon the porosity of the soil; and that it is thus greatly favored in the pervious soil-strata of the arid re- 148 SOILS. gions. It also follows that thorough and frequent tillage and fallowing greatly favor nitrification; thus explaining one of the beneficial results of these operations. At the same time, it is true that we may thus in a short time seriously diminish the reserve stock of nitrogen contained in the soil in the form of humus-amids; and since nitrates are exceedingly liable to be lost from the soil in several ways, such excessive nitrification is to be avoided. Unhumitied Organic Matter docs not Nitrify.—There can be little doubt that the formation of ammonia from the amido- compounds in humus is also the work of bacteria; but this, really the initial phase of the nitrogen-nutrition of plants, has not yet been fully elucidated. That, however, it 1s essentially only the ready-formed humus and not the unhumified debris of the soil which participate in nitrification was shown by the experiments of the writer, see chapter 19. Denitrifying Bacteria——Among the sources of loss of ni- trates in the soil is the action of denitrifying bacteria; some of which cause merely the reduction of nitrates to nitrites and progressively to ammonia, while others cause gaseous nitrogen to be given off from nitrites and nitrates, resulting in their complete loss to the soil. While there are probably several kinds of the latter class, the most rapidly effective is an organ- ism contained abundantly in fresh horse dung, and also on the surface of old straw. This can readily be shown by subjecting a very dilute solution (1-3 per cent.) of Chile saltpeter to the action of fresh horse dung in a close flask, when nitrogen and carbonic dioxid gases are evolved, and in a few days the nitrate has totally disappeared. In the course of time this power of carbonic dioxid gases are evolved, and in a few days the nitrate has totally disap- peared. In the course of time this power of horse-manure disappears; so_ that “rotted manure” is practically free from it and under proper conditions serves nitri- fication so effectively, that in the past it Fic. 17.--Bacillus denitri- has served extensively for the production fcans aE oon) of saltpeter in the “ niter-plantations”’ for the industrial purposes; the material of which was loose SOIL AND SUBSOIL. 149 earth, marl and manure, kept moist and frequently forked over for better aeration. Saltpeter is similarly produced in stables, corroding the mortar of brick foundations. Neverthe- less, it is necessary to avoid the use, either together or at short intervals apart, of Chile saltpeter and fresh manure; the ma- nure if used first should be allowed to remain at least two months in the soil before saltpeter 1s applied. The reduction of nitrates to nitrites and ammonia is brought about by quite a number of bacteria, mostly anaerobic, and such as consume combined oxygen in their development. Thus the butyric ferment, which in the absence of readily reducible compounds evolves free hy- drogen, will in presence of nitrates reduce the latter to nitrites, or form ammonia by addition of hydrogen to nitrogen just set free by reduction. Such reductive processes of course occur chiefly in soils rich in organic matter, or ill-aerated. ‘The ammonia so formed, while at first simply combining with any humus acids present, may in the course of time be itself reduced to the amidic condition, being thereby rendered relatively inert, until again brought into action by ammonia-forming bacteria. Ammonia-forming Bacteria.—A large number of different bacteria appear to be concerned in the formation of ammonia from compounds of the albuminoid group, (and probably from humus). Among these is one of the most common in soils (Bacillus mycoides, root bacillus), which while forming am- monia carbonate in solutions of albumen, is also capable of reducing nitrates to nitrites and ammonia in presence of a nutritive solution of sugar. The “hay bacillus” (B. subtilis), so abundantly developed in hay infusions, and one of the most abundant in cultivated soils, has together with B. ellenbachensis, B. megatherium, B. mycoides, and others, by some been credited with important action in favoring vegetation; so that a fairly pure culture of B. ellenbachensis has been brought out commercially in Ger- many under the name of “ Alinit.”’ Rigorous culture experi- ments made by Stutzer and others have, however, failed to show any general benefit from the use of alinit in infecting either land or seeds. But there is no doubt of the Effects of Bacterial Life on Physical Soil Conditions.—It is apparent that all conditions favoring the life of aerobic (air- needing) bacteria tend also to produce the loose, porous state 150 SOILS, (tilth) of the surface soil so conducive to the welfare of cul- ture plants, designated by German agriculturists as ‘* Boden- Fic. 18.——Bacillus subtilis. (Wollny, after Brefeld. Fic. rg.—Bacteria producing ammoniacal fermentation: A, C. mycoides: B, B. stut- zerz. (From Conn, Agr. Bacteriology.) Fic. 20.—Bacillus magaterium. (From Migula.) gare.’ Whether or not this con- dition is directly due to bacterial processes, as is thought by Stut- zer (Landw. Presse, 1904, No. II) it is assuredly a highly im- portant point to be gained, and is essentially connected with the presence of humus in adequate amounts, which is also a favor- ing condition of abundant bac- terial life. It seems thacetie preference given to the shallow putting-in, or even surface appli- cation of stable manure, existing in Europe, is largely based upon the marked effect upon the loose- ness of the surface soil, generally credited to the physical effect of the manure substance itself, but apparently largely due to the in- tensity of bacterial action thus brought about. ROOT-BACTERIA OR RHIZOBIA OF LEGUMES.—Among the most important bacteria, agricultur- ally, 1s that which enables plants of the leguminous order—( peas, beans, vetches, clovers, lupins, etc. ),—to obtain their supply of nitrogen from the air independ- ently of those contained in the soil. The source of nitrogen to plants was long a disputed question ; it was at first supposed (by de Saussure) that it was ob- tained directly from the soil by the absorption of humus; but this was disproved, and Liebig then contended that it was derived directly from the atmos- SOIL AND SUBSOIL, I51 phere through the ammonia in rain water. This was then shown to be wholly inadequate; and Boussingault proved con- clusively that plants do not take up nitrogen gas from the air. This was subsequently denied by Ville; but investigation at the Rothamstead agricultural station by Lawes and Gilbert definitely confirmed Boussingault’s results. At the same time they also proved very definitely that while grass and root crops deplete the soil of nitrogen, clover and other leguminous crops leave in the soil more nitrogen than was previously present, even when the entire, itself highly nitrogenous, leguminous crop is removed from the land. The improvement of lands for wheat production by rotation with clover had long ago become a practical maxim; but the cause was not understood until, in 1888, Hellriegel and Wilfarth announced that the variously-shaped excrescences or tubercles which had long been observed as frequently deforming the roots of legumes, are caused by the attacks of bacilli capable of absorbing the free nitrogen of the air and thus enabling the host-plant to acquire its needed supply by absorbing the richly nitrogenous matter thus accumulated in the excrescences. The minute rod-shaped organism was named Bacillus radicicola by Beyerinck; Rhizo- bium leguminosarum, by A. Frank, who has published an ex- tensive treatise on the subject.* Microscopic examination of the nodules shows their tissues to contain partly motile, free bacteria, partly others (bacte- roids), which have assumed a quiescent condition, and are of much greater dimensions than those of the motile form. These relatively thick, and- sometimes forked, forms, dif- fering somewhat in each of the group adaptations men- tioned below, constitute the bulk of the cell-contents of the nodules, and ultimately serve for the nutrition of the host- ,7 ZtjMermenie, sti of sal sea plant with nitrogen. When filled with Rhizobia? 1 Uber die Pilzsymbcose der Leguminosen, Berlin, 1890. 2 Original figure from drawing by O. Butler, Asst. in Agr. Dep’t Univ. of California. 152 SOILS, the growth of the excrescence is completed, the swollen, quies- cent bacteroids gradually collapse and become depleted of their nitrogenous substance; and finally the apparently empty husk remains or drops off, carrying with it the minute cocci which in the soil become active bacteria again. The nodules are thus found mainly on the actively-growing roots, and at the time when vegetation and assimilation are most active in the plant. In autumn, or when the plants are in fruit, the roots may be wholly destitute of nodules. Fic. 25.—Square-pod pea.—Tetragonolobus purpureus. Fic. 26.—White Lupin.—Lupinus albus. The adhesion of the nodules to the roots is mostly very loose, and their falling-off when the seedlings are carelessly transplanted, doubtless accounts for much of the difficulty generally found in transplanting legumes when once es- tablished. The figures annexed show the various forms assumed by the nodules in different plants, and with them also the correspond- ing forms of the bacteroids of each. The latter, here shown ND SUBSOIL. SOIL A “WINAT}es WINSIg — vad uapiey —'bz “DIY *‘e}ENIUSp OSeoIpay AI —“49A0/9 Ing fz “Old *BATJES BIOTA. —ydjaA wouWIOD—"zz ‘OL 154 SOILS. magnified about rooo times, are taken from the inaugural dis- sertation of D. Brock on this subject, published at Leipzig in 1891. It appears that the forms of the bacteroids are quite as much varied as are those of the nodules they form. Varieties of Forms.—While these bacilli seem to be normally present in most soils, it seems to be necessary that they should adapt themselves for this symbiosis! with each of several groups of the legumes in order to exert their most beneficial effects. In many soils there appears to exist a “ neutral form, which requires about a season’s time or more to adapt itself specially to the several leguminous groups so that a great ad- vantage is gained by infecting either the seeds or the soil with the forms already adapted, when no similar plant has lately occupied the same ground. Thus the bacillus of the clover root is of little or no benefit to beans, peas or alfalfa, and the root-bacilli of each of the latter are relatively ineffectual when used to infect either of the other groups. The same is true of the bacilli of lupins and of acacias, as applied to leguminous plants of any other groups.? Mode of Infection—The infection is especially effectual when applied to the seeds before sowing; and for that purpose there may be used either the turbid water made by stirring up in it some earth of a properly infected field, or else water charged with a pure culture of the appropriate kind, commer- cially known under the name of nitragin, now manufactured for the purpose. Or else, the field to be sown may be infected by spreading on it broadcast, and promptly harrowing in, a wagon-load of earth per acre from a properly infected field. Such earth must not be allowed to dry, or to be long exposed to light. Specially effective ( ‘virulent’? ) and hardy forms of such bacteria have been produced under artificial culture by Dr. Geo. T. Moore of the U. S. Department of Agriculture. These cultures can be sent by mail on cotton imbued with them, for the infection of seeds. 1“TVjiving together” beneficially ; in contradistinction to parasitism, which is injurious to the host plant. 2 It is asserted by some observers that the root bacilli producing differently- shaped excrescences upon different legumes are distinct species; but this view is not sustained by the experiments of Nobbe and Hiltner, and seems intrinsically improbable. SOIL AND SUBSOIL. 155 It is very important that the bacillus should be present in the earliest stages of the growth of the seedlings ; otherwise the latter will undergo a longer or shorter period of starvation, unless the soil contains, or is furnished with, a sufficiency of available nitrogen to supply their immediate wants. When such a supply is very abundant, the legume crop will sometimes develop no nodules at all; but the best crops appear to be the result of a thorough infection, and abundant formation of the excrescences. Cultural Results—The marked results obtained in certain soils by inoculation with the legume-root bacillus are exempli- fied in the following table, showing results of experiments by J. F. Duggar, at the Alabama Experiment station.? TABLE SHOWING INCREASE OF PRODUCTION BY SOIL INOCULATION. PER ACRE, TOPS. ROOTS. NITROGEN. Ibs. Ibs. Ibs. Value. Hairy vetch, not inoculated.......... 194 387 7 $ 1.05 dowudo:mmnoctlatedsereiiit 1 3045 1452 106 15.90 Crimson clover not inoculated........ 106 206 4.3 65 dot do: winoculateds-4) aces) eae 4040 1452 143.7 21.25 Such marked increases from soil inocculation cannot of course be expected in cases where the soil has previously borne leguminous crops of similar nature and therefore already con- tains the root bacteria. Hence Duggar found no increase of production when inoculating for cowpea, land that had borne that crop two years before and already contained the root bac- teria. In the arid region, where the almost universally calcare- ous soils usually bear a natural growth largely composed of various leguminous plants, inoculation is likely to be less com- monly effective than in the humid region east of the Missis- sippi, where leguminous plants are much less generally present in the native flora. The distinctive agricultural function of supplying nitrogen to the soils on which they grow, renders inexcusable the per- sistence of some writers and teachers in designating all forage plants as “ grasses.” Whatever excuse there may have been for this practice so long as the nitrogen-gathering function of the legumes was unknown, disappears with this discovery, and ? Bull. Ala. Exp’t Station, No. 96, 1808. 156 SOILS. the misleading misnomer should be banished from agricultural publications and lectures, at the very least. Other Nitrogen-Absorbing Bacteriaa—An increase in the nitrogen-content of some soils, aside from the action of legu- minous root-bacteria, has long been observed. As already stated, this increase was at first ascribed to certain green alg often seen to develop on the soil surface; but it has now been shown that the nitrogen-gathering function belongs to at least two bacteria, one of which (Clostridium pastorianum) was discovered by Winogradski, the other (Azotobacter chroococcum) by Beyerinck, and has since been farther in- vestigated by Koch, Krober, Gerlach and Vogel, and last by Lipman and Hugo Fischer. According to the latter it seems likely that Azotobacter chroococcum lives in symbiosis with the green alge, all of which, like the Azotobacter itself, de- velop with special luxuriance on calcareous soils. Lipman (Rep. Agr. Exp’t Station, New Jersey, 1903 and 1904) describes as Azotobacter vinelandii a form somewhat different from the A. chroococcus, the nitrogen-assimilating power of which he tested quite elaborately. He exposed to air pure cultures of 4. vinelandii in nutritive solution containing the proper mineral ingredients, and glucose 20 grams per liter. roo cub. centimeters of this solution was exposed in flasks of respectively 250, 500 and 1000 cc. content, therefore having _ greater surface in the larger flasks. After ten days, the amounts of nitrogen fixed were found to be respectively 1.67, 3.19 and 7.90 milli- grams. When mannite solution was employed instead of glucose, a similar fixation was observed ; and it was also shown that the presence of combined nitrogen in the forms of nitrates or ammonium salts dis- couraged the fixation by the bacillus. It was thus clearly proved that A. vinelandii at least does not need symbiosis with algze to fix atmospheric nitrogen; but experiments with mixed cultures of the above bacillus and another (designated as No, 30 by Lipman) proved that when these two co-operate the absorption of atmospheric nitrogen is nearly doubled. As it is probable that this is the case also with other soil bacteria, the importance of this source of nitrogen to plants is obvious; provided of course that the proper nu- tritive ingredients are present in available form. Lipman shows that among the organic nutrients, besides the sugars, glycerine and the salts of propionic and lactic acids, and probably also others of the same groups, can serve as nourishment to the nitrogen-fixing bacteria. SOIL AND SUBSOIL, Li 9/ DISTRIBUTION OF THE HUMUS WITHIN THE SURFACE SOIL. The uniform distribution of the humus-contents of the sur- face soil, as shown in sections of the same, is by no means easily accounted for. The roots from which its substance is so largely derived are not so universally distributed as to account for it; but least of all can the rapid disappearance of the leaf-fall and other vegetable offal from the surface be accounted for without some outside agencies. Of these, the action of fun- gous vegetation, and of insects and earthworms, are doubtless the chief ones. Fungit.—When we examine a decaying root, we find radiat- ing from it a zone of deeper tint, as though from a colored solution penetrating outward. But since under normal con- ditions humus is insoluble, this explanation cannot stand. Microscopic examination, however, reveals that the outside limit of this zone is also the limit to which the fungous fibrils concerned in the process extend; and as these fibrils are much more finely distributed and much more numerous than the roots of any plant, it is natural that the humus resulting from their decomposition should be more evenly distributed than the roots themselves. Such fungous growth is not, however, confined to dead and decaying roots only. A large number of trees and shrubs, among them pines and firs, beeches, aspen and many others, also the heaths, and woody plants associated with them, appear to depend largely for their healthy development, notably in northern latitudes, upon the co-operation (‘‘ symbiosis”) of fungous fibrils that “infest’’ their roots, enabling them to assimilate, indirectly, the decaying organic (and inorganic) matter which would otherwise be unavailable, and at the same time converting that matter into their own substance. Fun- gous growths thus mediate both the decomposition and rehabilitation of the vegetable debris. The vegetative fibrils (mycelia) of several kinds of molds are constantly present in the soil, and while consuming the dead tissue of the higher plants, spread their own substance throughout the soil mass. The same is true of the subter- 1 Kosticheff, Formation and Properties of Humus; in abstract Jour. Chem. Soc., 1891, p. 611. 158 SOILS, ranean or “root” mycelia of the larger fungi, toadstools, mushrooms, which are commonly found about dead stumps and other deposits of decaying vegetable and animal offal. All these being dependent upon the presence of air for their life functions, remain within such distance from the surface as will afford adequate aeration; the depth reached depending upon the perviousness of the soil and subsoil. In the humid region this will usually be within a foot of the surface, but in the arid may reach to several feet. Ultimately these organ- isms contribute their substance to the store of humus in the land. On the surface of moist soils we frequently find a copious growth of green fibrils, which may be either those of algae, such as Oscillaria, or the early stages (prothallia) of moss vegetation. This vegetation has been credited with absorption of nitrogen from the air, thus enriching the soil; but later researches have shown this effect to be due to symbiotic bacteria (see above p. 156). Animal A gencies.—Darwin first suggested that wherever the common earthworm (Lumbricus) finds the conditions of ex- istence, it exerts a most important influence in the formation of the humous surface-soil layer; and the limitation imposed upon these conditions by the subsoil has doubtless a great deal to do with the sharp demarcation we often find between it and the surface soil. Briefly stated, the earthworm nourishes itself by swallowing, successively, portions of the surrounding earth, digesting a part of its organic matter and then ejecting the un- digested earth in the form of “ casts,” such as may be seen by thousands on the surface of the ground during or after a rain. Darwin (The Formation of Vegetable Mold, 1881), has cal- culated from actual observation that in humid climates and in a. ground fairly stocked with these worms, the soil thus brought uy may amount to from one-tenth to two-tenths of an inch annually over the entire surface; so that in half a century the entire surface foot might have been thus worked over. Aside from the mechanical effect thus achieved in loosening the soil, and the access of air and water permitted by their burrows, the chemical effects resulting from their digestive process, and the final return of their own substance to the soil mass; also their SOLMETANDISUBSOME 159 habit of drawing after themselves into their burrows leafstalks, blades of grass and other vegetable remains, renders their work of no mean importance both from the physical and chemical point of view. The uniformity, lack of structure and loose texture of the surface soil, especially of forests, as compared with subsoil layers of corresponding thickness, 1s doubtless largely due to the earthworms’ work. It has frequently been observed that when an unusual overflow has drowned out the earthworm population of a considerable area, the surface soil layer remains compacted, and vegetation languishes, until new immigration has restocked the soil with them. Again, the humus formed under their influence is always neutral, never acid. Wollny (Forsch, Agr., 1890, p. 382), has shown by direct experimental cultures in boxes, with and without earthworms, surprising differences between the cultural results obtained, and this has been fully confirmed by the subsequent researches of Djemil (Ber. Physiol. Lab. Vers. Halle, 1898). In Wollny’s experiments, the ratio of higher production in the presence of the worms, varied all the way from 2.6 per cent in the case of oats, 93.9 in that of rye, 135.9 in that of potatoes, 300 in that of the field pea, and 140 in that of the vetch, to 733 per cent in the case of rape. Wollny attributes these favorable effects in the main to the increased looseness, and perviousness of the soil to air, and diminished water-holding power. Djemil’s results all point in the same direction ; and he shows, moreover, that the ailegation that the roots penetrate more deeply in the presence of the worms by following their burrows, is unfounded, the descending roots often passing close to and outside of these. The work of earthworms is especially effective in loamy soils and in the humid regions. In the arid region, and in sandy soils generally, the life-conditions are unfavorable to the worm, and the perviousness elsewhere brought about by its labors already exists naturally in most cases. It is stated by E. T. Seton (Century Mag. for June, 1904) that the earth- worm is practically non-existent in the arid region between the Rocky Mountains and the immediate Pacific coast, from Mani- toba to Texas. In the Pacific coast region, however, they are abundant, and do their work effectually. 160 SOILS: Insects of various kinds are also instrumental in producing, not only the uniform distribution of humus in the surface soil, but also the looseness of texture which we see in forest soils especially. Ants, wasps, many kinds of beetles, crickets, and particularly the larvee of these, and of other burrowing crea- tures, often form considerable accumulations, due directly both to their mechanical activity, and to their excrements. The work of ants is in some regions on so large a scale as to attract the attention of the most casual observer. Especially is this the case in portions of the arid region, from Texas to Montana, where at times large areas are so thickly studded with hills from three to twelve feet in diameter, and one to two feet high, that it is difficult to pass without being attacked by the insects. The ‘‘ mounds” studding a large portion of the prairie country of Louisiana seem also to be due to the work of ants, although not inhabited at present. Larger burrowing animals also assist in the task of mixing uniformly the surface soils, and aiding root-penetration, as well as, In many cases, the conservation of moisture. Seton (loc. cit.) even claims that the pocket gophers (Thomomys) in a. great degree replace the activity of the earthworms in the arid region, where they, together with the voles (commonly known there as field mice), exist in great numbers. Of course the work of these animals, as well as that of the prairie dogs, ground squirrels, badgers, etc., 1s incompatible with cultiva- tion. But the effects of their burrows on the native vegeta- tion, and the indications they give of the nature of the subsoil, are eminently useful to the land-seeker. Thus in the rolling sediment-lands of the Great Bend of the Columbia, the observer is surprised to see the “ giant rye grass,” usually at home in the moist lowlands, growing preferably on the crests of the ridges bordering the horizon. Examination shows that this is due to the burrowing of badgers, whereby the roots of the grass are enabled to reach moisture at all times, even in that extremely arid region. CHAPTERS SOIL AND SUBSOIL (Continued) THEIR RELATIONS TO VEGETATION, Physical Effects of the Percolation of Surface Waters.— The muddy water formed by the beating of rains on the soil surface will, in penetrating the soil, carry with it the diffused colloidal clay to a certain depth into the subsoil. We should therefore expect that as a rule every subsoil will be more clayey than its surface soil; and this is found to be almost uni- versally the case in the humid region. Subsoils are therefore almost always less percious and more retentive of moisture, as well as of plant-food substances in solution, than their surface soils, unless these are very rich in humus; and as the finest particles are usually those richest in available plant-food, it follows that subsoils will as a rule be found to contain larger supplies of the latter than the surface soil. Common expert- ence as well as comparative analysis confirm both of these in- ferences so thoroughly, that it becomes unnecessary to adduce examples in this place. On the other hand, the reverse, upward movement of moist- ure caused by surface evaporation tends constantly to bring any soluble salts contained in the soil mass nearer to the sur- face, thus increasing the stock of easily available plant-food in the surface soil. In extreme cases, especially in the arid region, this accumulation of salts may become excessive, and seriously injurious to plant growth. (See “ Alkali Soils, chapters 21, 22.) Chemical effects of Water-Percolation.—The accumulation of plant-food in the subsoil is not, however, due only to the mechanically-carried particles, but also to the ingredients carried in solution from the surface soil and redeposited in the more retentive subsoils. Especially is this true of lime car- bonate, which is dissolved by the carbonic acid formed chiefly II 101 162 SOILS. within the humic surface soil, and is often carried off in amounts sufficient to obstruct drain tiles by its deposition in contact with air (see chapt. 3). In the case of moderate rains, however, it is carried no farther than the subsoil, and is there redeposited, in consequence of the penetration of air, following the water, and causing the carbonic gas to diffuse upward; thus leaving the lime carbonate behind. In the majority of cases this results simply in a gradual enriching of the subsoil in this substance; while the surface soil may become so depleted as to require its artificial replacement by liming or marling. The same general process occurs to a less extent, in the case of magnesia. Calcareous Subsoils—The fact that subsoils are more cal- careous than the corresponding surface soils is often of great practical importance, in enabling the farmer to enrich his de- pleted surface soil in lime by subsoil plowing. The accumula- tion of lime carbonate in the subsoil also tends in a measure to offset the extreme heaviness sometimes resulting from the ac- cumulation of clay. Calcareous Subsoils and Hardpans.—When soils are very rich in lime, and rains occur in limited showers rather than con- tinuously, the lime carbonate dissolved from the surface soil may accumulate in the subsoil so as to either form calcareous “hardpan” by the cementing of the subsoil mass; or it may accumulate and partly crystallize around certain centers and thus form white concretions, known to farmers as “ white gravel.”’ The latter is the form usually assumed in the re- gions of summer rains; while in the arid regions the deficient rainfall causes this substance to accumulate, and calcareous hardpan to form, at definite depths depending upon the maxi- mum penetration of the annual rainfall; sometimes in crystal- line masses of veritable limestone (“ kankar” of India), or sometimes merely as crystalline incrustations loosely cementing the subsoil. “ Rawness”’ of Subsoils in Humid Climates——From the greater compactness of the subsoil which is almost universal in the humid regions, the absence of humus and of the resulting formation of carbonic and humic acids, it follows that its minerals are less subject to the weathering process than are Hen SOIL, AN D-SUBSOIL: 163 those of the surface soil. In the farmer’s parlance, the sub- soil is “‘ raw ” as compared with the surface soil; it is not so suitable for plant-nutrition, and therefore must not be brought to the surface to form the seed-bed, or be incorporated with the surface soil to any considerable extent at any one time, if crop-nutrition is to be normal. It is only in the course of time, by exposure to atmospheric action as well as to that of the humus, and of plant roots, that it becomes properly adapted to perform the functions of the surface soil. Soils and Subsoils in the Arid Region.—But however pro- nounced and important are these distinctions and differences in the humid region, they are found to be profoundly modified in the arid; where, as before stated, the formation of colloidal clay is very much diminished, so that most soils formed under arid conditions are of a sandy or pulverulent type. There is then little or no clay to be washed down into the subsoil, hence there is no compacting of the latter; the air consequently cir- culates freely down to the depth of many feet. Thus one of the most important distinctions between soil and subsoil is to a great extent practically non-existent in the arid region, at least within the depths to which tillage can be made to each; so that the limitations attached to subsoil-plow- ing in the countries of summer rains do not apply to the characteristic soils of the arid regions. Even the distinction in regard to humus is here largely ob- literated by the circumstance, already alluded to, that most of that substance must, in the arid regions, be derived from the decay of roots, which moreover reach to much greater depth in these soils. Hence even in the uplands of the arid region it is common to find no change of tint from the surface down to three feet, and even more. This, like the free circulation of the air in consequence of porosity, tends to render the distinction of soil and subsoil practically useless; since it disposes of the objection to “ subsoiling ”’ based upon the inert condition of the subsoil, which in humid climates so effectually interferes with the welfare of crops unless subsoiling is restricted to a fraction of an inch at a time. These fundamental differences in the soils of the two regions are illustrated schematically in the subjoined diagram, which shows on the left the contrast between clay or clay loam soils, 164 SOILS. in which the depth of the surface soil-sample to be taken is prescribed as nine inches by the rules of the Association of Am. Official Chemists (in the writer's experience it is more nearly six inches as a rule). Alongside of the Eastern soil thus characterized 1s placed a typical “‘ adobe ” soil from the grounds of the California Experiment station, of which a sample show- ing uniform blackness to three feet depth was exhibited at the World’s Fair at Chicago in 1893. At the right is a profile of the noted hop soil on the bench lands of the Russian river, Cal., in which the humus-content was determined down to twelve feet, the humus-percentage being .44% at that depth against 1.21% in the surface foot (see chapt. 8, p. 139). In this and similar soils the roots of hops reach down to as much as fourteen feet without much lateral expansion; as shown in plate No. 31 of this chapter. Similar conditions prevail in the sandy uplands, as, e. g., in the wheat lands of Stanislaus county, Cal., mentioned above. Taking the clay soils as a fair type for comparison, it would seem that the farmer in the arid region owns from three to four farms, one above another, as compared with the same acreage in the Eastern states. Subsoils and Deep-plowing in the Arid Region.—Up to the present time this advantage is but little appreciated and acted upon by the farmers of the arid region. They still instinctively cling to the practice taught them by their fathers, and which is still promulgated as the only correct practice, in most books on agriculture. There are of course in the arid as well as in the humid region, cases in which deep plowing is inadvisable; viz, that of marsh or swamp lands, as well as sometimes in very sandy, porous soils, the cultural value of which often depends essentially upon the presence of a somewhat consolidated, and more retentive subsoil, which should not be broken up. But in most soils not of extreme physical character, it is in the arid region not only permissible, but eminently advisable to plow, for preparation, as deeply as circumstances permit, in order to facilitate the penetration of the roots beyond the reach of harm from the summer’s drought; while for the same reason, subse- quent cultivation should be to a moderate depth only, for the better conservation of moisture, and the formation of a pro- tective surface mulch (see chapter 13). - SOIL AND SUBSOIL. 165 TYPE OF EASTERN SOILS TYPES OF CALIFORNIA SOILS. Up land clay-loam Upland. Bench land. Fic. 27.—Soil Profiles illustrating differences in Soils of Humid and Arid Region. 166 SOILS. It must not be forgotten that there are in the lowlands of the arid region (river swamps or tules, seacoast marshes, etc., ) soils in which surface soil and subsoil are differentiated as fully as in the humid countries; at least so long as they have not been fully drained for a considerable length of time. In swamp areas that have been elevated above the reach of overflow or shallow bottom-water by geological agencies, even the heavy swamp clays are fully aerated down to great depths, and roots penetrate accordingly. Examples of Plant-growth on Arid Subsoils—The fact that in the arid region the surface-soil conditions reach to so much greater depths than in the East and in Europe, is so important for farming practice in that region that experimental evidence of the same should not be withheld. Of such, some cases well established as typical of California experience are therefore cited. It is well known that in the Sierra Nevada of California the placer mines of the Foothills, worked in the early times, have long disappeared from sight, having been quickly covered by a growth of the bull pine (P. ponderosa). Much of this timber growth has for a number of years past been of sufficient size to be used for timbering in mines, and a second young forest is springing up on what was originally the red earth of the placer mines, which appears to the eye as hopelessly barren as the sands of the desert. In this same red sandy earth not unfrequently cellars and house foundations are dug, and the material removed, even to the depth of eight feet, is fearlessly put on the garden and there serves as a new soil, on which vegetables and small fruits grow, the first year, as well as ever. In preparing such land for irrigation by leveling or terracing no heed is taken of the surface soil as against the subsoil, even where the latter must be removed to the depth of several feet, so long as a sufficient depth of soil material remains above the bedrock. The same is generally true of the benchlands; the irrigator levels, slopes or terraces his land for irrigation with no thought of discrimina- tion between soil and subsoil, and the cultural result as a rule justifies his apparent carelessness. It is only where from special causes a con- solidated or hardpan subsoil is brought to the surface, that the land when leveled shows “ spotted”’ crops. Such is the case in some of the ‘“‘hog-wallow” areas of the San Joaquin valley of California, and in SOIL AND SUBSOIL. 167 some cases where by long cultivation and plowing to the same depth, a compact soil-layer or plowsole has been formed, and the land is then leveled for the introduction of irrigation. In these cases a section of the soil mass will usually show a marked difference in color and texture. But, as a rule, in taking soil samples, no noticeable difference can be perceived between the first and the second, and oftentimes as far down as the third and fourth foot. The extraordinary root-penetration of trees, shrubs and taprooted herbs, whose fibrous feeding-roots are found deep in the subsoil and are sometimes wholly absent from the surface soil, fully corroborate the conclusion reached by the eye. ‘The roots of grape vines have been found by the writer at the depth of twenty- two feet below the surface, in a gravelly clay loam varying but little the entire distance. In a similarly uniform and pervious material, the loess of Nebraska, Aughey! reports the roots of the native Shepherdia to have been found at the depth of fifty feet. ! Resistance to Drought.—These peculiarities of the soils of the arid region explain without any resort to violent hypo- theses, the fact that many culture plants which in the regions of summer rains are found to be dependent upon frequent and abundant rainfall, will in California, and in the country west of the Rocky Mountains generally, thrive and complete their growth and fruiting during periods of four to six months of practically absolute cessation of rainfall; when east of the Mississippi a similar cessation for as many weeks will ruin the crops, if not kill the plants. In continental Europe, in 1892, a six weeks’ drought caused almost all the fruit crops to drop from the trees, and many trees failed to revive the next season; while at the very same time, the same deciduous fruits gave a bountiful crop in California, during the prevalence of the usual five or six months’ drought. This was without irri- gation, or any aid beyond careful and thorough surface til- lage following the cessation of rains in April or May, so as to leave the soil to the depth of five or six inches in a condition of looseness perfectly adapted to the prevention of evaporation from the moist subsoil, and of the conduction of the excessive heat of the summer sun. This surface mulch will contain practically no feeding-roots, the paralysis or death of which by heat and drought would influence sensibly the welfare of the growing plant. 1 See Merrill, Rocks and Rockweathering. 168 SOILS. Root-system in the Humid Region.—It is quite otherwise where a dense subsoil not only obstructs mechanically the deep penetration of any but the strongest roots, but at the same time is itself too inert to provide sufficiently abundant nourish- ment apart from the surface soil, which is there the portion con- taining, alongside of humus, the bulk of the available plant- food, and in which alone the processes of absorption and nu- trition find the proper conditions; such as access of air and the Fic. 28.—Root ofan Eastern (Wisconsin) Fruit Tree. (Photograph by Prof F. H. King.) ready and minute penetration of even the most delicate rootlets and root-hairs. The largest and most active portion of the root-system being thus accumulated in the surface soil, it fol- lows that unless the latter is constantly kept in a fair condition of moistness, the plant must suffer material injury very quickly ; hence the often fatal effects of even a few weeks’ drought. The same occurs in the arid region when often-repeated shallow plowing has resulted in the formation of a “ plow- sole’’ which prevents the deep penetration of roots; when a SOLE AND SU-BSOIL: 169 hot “norther” will often in a short time not only dry the plowed soil, but will heat it to such extent as to actually bake the roots it harbors. Under the same weather-conditions an adjoining field, properly plowed, may almost wholly escape injury. Comparison of root development in the arid and hunud regions.—Figures 28, 29 given here show the differences as Fic. 29.—Prune Tree on Peach Root, at Niles, Cal. actually seen in the case of fruit trees as grown in Wisconsin and California, respectively, both in the absence of artificial water-supply. Adaptation of humid species to arid conditions.—Figures, in No. 30, show the root systems respectively of the riverside grape (Vitis riparia) as grown in the Mississippi Valley states, and the natural development as found in the Rock grape of 170 SOILS. Missouri and also in the wild grape vine of California. It will be noted at once that the latter directs its cord-like roots almost vertically from the first, until 1t reaches a depth varying from 12 to 18 inches, where it begins to branch more freely, but still with a strong downward tendency in all. The roots of the riverside grape, on the contrary, tend to spread almost hori- zontally, branching freely at the depth of a few inches and 'RIPARIA Gloire de Montp. § months old. St. Helena, Dec. 1899 € = i uw & = Hi = =) & Fic. 30.—Root Growth of Resistant Grape Vines. manifestly deriving its supply both of plant-food and moisture mainly from the surface soil. It is curious to observe the behavior of this vine when cuttings are planted in California vineyards as a resistant grafting-stock. Its first roots are sent out horizontally, very much as is its habit in the East, so long as the soil moisture is maintained near the surface. But as the season advances, the more superficial rootlets are first thrown out of action by the advancing dryness and heat of the surface soil, and many finally die the first year. SOIL AND SUBSOIL. 171 Not unfrequently the entire root system developed by the up- permost bud perishes; but usually its main roots soon begin to recede from the threatening drought and heat of the surface, curving, or branching downward in the direction of the moist- ure supply, and without detriment to their nutrition because of the practical identity of the surface soil and subsoil. As the portions of the roots near the surface thicken and mature, their corky rind soon prevents their being injured by the arid conditions to which they are subjected; while the root-ends, finding congenial conditions of nutriment and aeration in the moist depths, develop without difficulty as they would in their humid home. Practically the same process of adaptation takes place in every one of the trees, shrubs, or perennials belonging to the humid climates, until their root system has assumed nearly the habit of the corresponding native vegetation. The photograph of the roots of a hop plant, grown on bench lands of the Sacramento river, shows the roots extending to 8 feet depth, but where broken off the main root is still nearly two millimeters in thickness, proving that it penetrated at least two feet beyond the depth shown in figure 31. In the case of native annuals, either the duration of their vegetation is extremely short, ending with or shortly after the cessation of rains; or else their tap roots descend so low, and the nutritive rootlets are developed at such depth, as to be be- yond reach of the summer’s heat and drought. For while it is true that rootlets immersed in air-dry soil may absorb plant- food, this absorption is very slow and can only be auxiliary to the main root system which, instead of terminating in the sur- face soil as in the humid region, will be found to begin to branch off at depths of 15 and 18 inches, and may then in sandy lands descend to from 4 to 7 feet even in the case of annual fibrous-rooted plants like wheat and barley.t In the case of maize the roots of a late-planted crop may sometimes be found descending along the walls of the sun-cracks in heavy clay land 1 Shaler (Origin and Nature of Soils; r2th Rept. U.S. Geol. Survey, p. 311) says: ‘“ Annual plants cannot in their brief period of growth push their roots more than six to twelve inches below their root-crowns ”’ a generalization measurably true for the humid region only. According to F. J. Alway, the roots of cereals penetrate to 5-7 feet in Saskatchewan, also. SOILS: acramento Bench-land Hop Root from S Fic. 31.— SOIL AND SUBSOIL. 173 poorly cultivated ; and it frequently matures a crop without the aid of a single shower after planting. See figures 33, 34. The annexed plate (No. 32) shows the main roots of two native perennial weeds of California, the goosefoot (Cheno- podium californicum) and the figwort (Scrophularia cali- fornica), common on the lower slopes of the coast ranges. The soil was a heavy clay loam or “black adobe” resulting from the weathering of the clay shale bedrock, fragments of which are so abundantly intermixed with the substrata that excava- tion of the roots became very difficult. Yet the main root of the goosefoot went down below the depth of eleven feet. The main root of the figwort, also, was followed below the depth of ten feet without reaching the extreme end. This proves clearly that the great penetration of the goosefoot was not, as might be supposed, due to its bulbous root. Yet such thickening of the root just below the crown is a rather common feature in arid-region plants, and can here be noted even in the figwort, within whose botanical relationship bulbous roots are almost unknown. Any one accustomed to the cornfields of the Middle West, where in the after-cultivation of maize it is necessary to re- strict very carefully the depth of tillage to avoid bringing up a mat of white, fibrous roots, will be at once impressed with the remarkable adaptability of maize to different climatic condi- tions, as exhibited in such cases and shown in figures 33, 34. In southern California, in the deep mesa or bench soils, corn stalks so tall that a man standing on horseback can barely reach the tassel, and with two or three large ears, are quite com- monly grown under similar rainfall-conditions. Importance of proper Substrata in the Arid Region.—The paramount need of deep penetration of roots in the arid region renders the substrata below the range of what is usually under- stood by subsoil in the humid climates, of exceptional import- ance. A good farmer anywhere will examine the subsoil to the depth of two feet before investing in land; but more than this is necessary in the arid region, where the surface soil is often almost thrown out of action during the greater part of the growing season, while the needful moisture and nourish- ment must be wholly drawn from the subsoil and substrata; hale _— . a ets a ate - CO 4 <> - Op Sich. oye —— a a ‘JAOMTL] PUL JOOJISOOL) LIUIOJYLD VAYEN Jo Suyooy-desq— ‘ee “orf ; ease oes Mite Ds cae aa og és Bs : 7 : ‘ 3 eer ; : ‘ oa punter ee ree ane eee eee thn uosod Yayo | 1 SOIL AND SUBSOIL, Fic. 33.—Kentucky Maize, grown in region of Summer Rains. (Photography by A. M. Peter. ) SOMES: “170 in or Irrigation. Grown Without Ra .—California Maize, Fic. 34 y SOLEVAIND SU BSOLE: VZ7 an examination of which should therefore precede every pur- chase of land, or planting of crops. Such examinations are most quickly made by means of a probe con- sisting of a pointed, square steel rod five or six feet long, provided at one end with a loop for the insertion of a cross-handle like that of a carpenter’s auger. ‘The handle being grasped with both hands, the probe is forced into the soil with a slight reciprocating motion, by the weight of the operator; who soon learns how to interpret the varying kinds of resistance, and on withdrawing the probe carefully will generally be able to determine if bottom water has been reached. Should this easy method of examination not convey all the needful information, the posthole auger may be resorted to; and it is desirable that extra (three- foot) rods or gaspipe joints be provided for the purpose of lengthening the probe or auger, when necessary, to nine or twelve feet. It will rarely be necessary to go to the trouble of digging a pit for such exam- inations ; but even this is to be recommended rather than “ buying a ’ cat in a bag”’ in the guise of an unexplored subsoil. Faulty Substrata—A number of examples of “ faulty lands,” 2. e., such as are underlaid by faulty substrata, are given in the annexed diagram Fig. 35; the examples being taken from California localities because of their having been most thoroughly investigated. Similar cases, as well as others not here illustrated, of course occur more or less all over the world. No. 1 shows a case which, though at first sight an aggravated one of a rocky substratum, is in reality that of some of the best fruit lands in the State. The limited surface-soil is very rich, and is directly derived (as a “sedentary” soil) from the underlying bedrock slate. But this it will be noted stands on edge, and the roots of trees and vines wedge their way along the cleavage planes of the slate to considerable depth, deriving from them both nourishment and moisture. Under similar conditions the California laurel, usually found on the banks of streams, grows on the summits of rocky ridges in the Coast Ranges. The case of No. 2 is quite otherwise. Here the shale lies horizontally, and though much softer than the slate of the first column, obstinately resists the penetration of roots; so that the land, though fairly provided with plant-food, is almost wholly r2 Go Naess OP Re NEISA IE AsN DiS = BAe Wray SOILS. im j | \ an wh | I , i i 1)! i as j yy i PN po I 1 bes oe ON iF es Ge eg ye PAST Gan La TTT ~ xX 2 Fic. 35.—Faulty Lands, California. SOIL AND SUBSOIL. 179 useless for cultivation. It is naturally covered with low, stunted shrubs or chaparral; only here and there, where a cleft has been caused by earthquakes or subsidence, a large pine tree indicates that nourishment and moisture exists within the refractory clay stratum, and suggests blasting as a means of rendering the land fit for trees at least. No. 3 is a case similar to that of No. 2, only there is here a dense unstratified mass of red clay, of good native fertility. It is here that the expedient of blasting the tree holes with dy- namite was first successfully employed, in central California. For lack of this, extensive tracts of similar land in southern California, planted to orchards, have completely failed of useful results after three years of culture. No. 4 shows a typical case of calcareous hardpan obstruct- ing the penetration of roots, even though usually interrupted at intervals, because of the formation occurring mostly in swales, along which the sheets lie more or less continuously. Here also, blasting will generally permit the successful growth of trees and vines, whose roots frequently will, in time, wholly disintegrate the hardpan and thus render the land fit for field cultures. The depth at which such hardpan is formed usually depends upon the depth to which the annual rainfall pene- trates. (See below, page 183). Nos. 4, 5, and 6 all illustrate cases of intrinsically fertile, very deep soils, shallowed by obstructions which in the case of No. 4 are hardpan sheets, while in No. 5 the intervention of bottom water limits root penetration, hence restricts the use of the land to relatively shallow-rooted crops, and the use of only a few feet of the profusely fertile soil. Such is the case where bottom water has been allowed to rise too high, through the use of leaky irrigation ditches. No. 6 illustrates a case not uncommon in sedimentary lands, where bottom water is quite within reach of most plants, but is prevented from being utilized by the intervention of layers of coarse sand or gravel, through which the water will not rise; and the roots, while they would be able to penetrate, are not near enough to feel the presence of water underneath and there- fore spread on the surface of the gravel, suffering from drought within easy reach of abundance of water. The “ going- back’ of large portions of orange orchards in the San Ber- Fic. 36.—Almond Tree on Hardpan. Paso Robles Substation, Cal. SOIL AND SUBSOIL. I8I nardino Valley of California has been thus brought about; and unfortunately this state of things is almost beyond the possi- bility of remedy. Injury from Impervious Substrata—The injurious effects of a difficultly penetrable subsoil have already been discussed and are selfevident. When the substratum is a dense clay, the rise of moisture from below being very slow, it can easily happen that the roots cannot penetrate deep enough in time for the coming of the dry season, and that thus the crop will suffer. The case will be still worse when hardpan cemented by lime or silex limits root-penetration, as well as proper drainage. In such cases the culture of field crops often becomes ‘im- practicable, even with irrigation, as its frequent repetition, be- sides being costly, can rarely be commanded. In the case of trees, the limitation of root-penetration results in the spreading- out of the roots on the surface of the impenetrable layer; as shown in figure 36, which exhibits a root-development that would be quite normal in the regions of summer rains, but is wholly abnormal in the arid region, and results in the unpro- fitableness or death of the trees. It has often been attempted in such cases to plant trees in large holes dug deep into the sub- soil and refilled with surface earth and manure. All such at- tempts result in failure, if only because the excavation in- evitably fills with water, which will soak away but very slowly into the dense substrata, and will thus injure or drown out the roots. Besides, the latter will remain bunched in the loose earth, and will thus be unable to draw either moisture or nourishment from the surrounding land. It is absolutely nec- essary to remedy this by loosening the substrata, if success is to be attained. Shattering of Dense Substrata by Dynamite——The per- manent loosening of dense substrata is best accomplished by moderate charges (14 to 34 pounds ) of “ No. 2” dynamite at a sufficient depth (3 to 5 feet). The shattering effect of the ex- plosive will be sensible to the depth of eight feet or more, and will fissure the clay or hardpan to a corresponding extent side- wise. If properly proportioned the charge will hardly disturb the surface; but if this be desired, from 1%to 2% pounds of black powder placed above the dynamite will throw out suffi- 182 SOM: ioe cient earth to plant the tree without farther digging. Where labor 1s high-priced this proves the cheapest as well as the best way to prepare such ground for tree planting; and it has often been found that in the course of time, the loosening begun by the powder has extended through the mass of the land so as to permit the roots to utilize it fully, and even to permit, in after years, of the planting of field crops where formerly they would not succeed. Leachy Substrata-—While we may thus overcome the dis- advantages of a dense subsoil or hardpan, there is another diffi- culty not uncommonly met with 1n alluvial lands, which cannot be so readily remedied. It is the occurrence, at from two to six feet depth, of coarse sand or gravel, through which capillary moisture will not ascend, but through which irrigation water will waste rapidly, leaving the overlying soil dry. Then unless very frequent irrigation can be given, the crop will suffer from drought, unless indeed the gravel itself is filled with bottom water upon which the root-ends can draw. This case is a common one in the larger valleys of the arid region, and in time of unusual drought the sloughs originally existing, but since filled up, will be clearly outlined by the dying crops, while outside of the old channels there may be no suffer- ing. “ Going-back” of Orchards. On such land as this, and on such as has a shallow soil underlaid by an impervious subsoil, trees will often grow finely for three to five years; then sud- denly languish, or turn yellow and die, as the demand of their larger growth exceeds what moisture or plant-food the shal- low soil and subsoil can supply. Enormous losses have arisen from this cause in many portions of the arid region, but more especially in California, owing to the implicit confidence re- posed even by old settlers, and still more by newcomers, in the excellence of the lands, as illustrated by farms perhaps a short distance away, but differently situated with respect to the country drainage and the geological formations. All such disappointments could have been avoided by an intelligent ob- servation of the substrata, either by probing or digging. Im- portant as is such preliminary examination in the region of summer rains, it is a vitally needful precaution in the arid SOIL AND SUBSOIL. 183 region, where the margin between adequate and inadequate depth of soil and moisture-supply is much smaller. When farmers note such distress in the orchard, the first idea usually is that fertilization is needed. ‘This in the almost universally very rich lands of the arid region is rarely the case until after many years of exhaustive cultivation, and is scarcely ever of more than passing benefit in such cases. ‘The first suggestion should always be an examination of the substrata, and especially of the deeper roots; in the diseased or thirsty condition of which the cause of the “die-back”’ or yellowing will commonly be found. Of course no amount of fertilization can permanently remedy such a state of things, arising from impervious substrata, coarse gravel, or shallow bottom water. Hardpan.—By “hardpan” is understood a dense and more or less hardened layer in the subsoil, which obstructs the pene- tration of both roots and water, thus materially limiting the range of the former both for plant-food and moisture, and giving rise to the disadvantages following such limitation, as described in the case of dense subsoils. The hardpans proper differ from the latter, however, in being usually of limited thickness only ; the direct consequence of their mode of forma- tion, which is not direct deposition by water or other agencies, but the infiltration of cementing solutions into a pre-existing material originally quite similar to that of the surface soil. Such solutions usually come from above, more rarely from be- low, and are of very various composition. The solutions of lime carbonate in carbonated water have already been referred to in this connection; as has also the fact that corresponding solutions of silica, associated more or less with other products of rock decomposition (see chapters 2 and 4) are constantly circulating in soils. The surface soil being the portion where rock-weathering and other soil-forming processes are most active, these solutions are chiefly formed there; and according as their descent into the substrata is unchecked, or is liable to be arrested at some particular level, whether by pre-existing close-grained layers or by the cessation of rains, the subsequent penetration of air, and evaporation of the water alone by shal- low-rooted plants, may cause the accumulation of the dissolved matter at a certain level, year after year. Finally there is 184 SOIL. formed a subsoil-mass more or less firmly cemented by the dis- solved matters, sometimes to the extent of stony hardness (lime carbonate in the arid regions, kankar of India), more usually soft enough to be penetrated by the pick or grubbing hoe, and sometimes by the stronger roots of certain plants; but resisting both the penetration and the assimilation of plant food by the more delicate feeding roots. Nature of the Cements.——The nature of the cements that serve to consolidate the hardpan mass 1s substantially the same as those already mentioned in the discussion of sandstones (chapt. 4, p. 55); with the addition of those formed, usually, in connection with siliceous solutions, by the acids of the humus eroup. The latter class of hardpans is especially conspicuous in the case of swampy ground and damp forests, where “ moor- bedpan ” and reddish “ ortstein”’ (the latter particularly devel- oped in the forests of northern Europe, where it has been studied in detail by Muller and Tuxen', are characteristic. The latter gives for a characteristic sample of the reddish hard- pan underlying a beech forest in Denmark a content of from 2.20 to 4.40% of ulmic compounds, and shows that the color is due_to these and not, as had been supposed, to ferric oxid, which is present only in minute quantities. Bog ore, Moorbedpan, Ortstein.—lt is otherwise with moor- bedpan, which often consists of a mass of bog iron ore per- meated or less with humous substances, which impart to it the dark brown tint so often seen also 1n the “ black gravel ”’ spots of badly-drained land. On the whole, however, ferric cements are much less frequently found in hardpans than in sandstones formed above ground. Clay substance washed from the surface into the subsoil by rains (chapter 10, p. 161) always helps materially to render the hardpan impervious when afterwards cemented, a much smaller proportion of the cementing material sufficing in that case to form a solid layer. In such cases however the cement is rarely of a calcareous nature, since lime prevents the diffu- sion and washing-down of the clay. It is mostly siliceous or zeolitic; if the former, acid will have little or no effect upon the solidity of the hardpan; while if zeolitic, acid will pretty 1 See “ Studien iiber die natiirlichen Humusformen,” by Dr. P. E. Miiller. SOIL AND SUBSOIE. 185 promptly disintegrate it. The presence of humus acids in the cements, if not apparent to the eye, is readily demonstrated by immersing the hardpan fragment in ammonia water or a weak solution of caustic soda; when if humus acids are the main cementing substance the fragment will fall to crumbs, or be softened to an extent corresponding to the amount of the humus present. Calcareous hardpan is, of course, readily recognized by its quick disintegration by dilute acid, with evolution of carbonic gas. In “alkali” soils containing sodic carbonate (“black alkali’) there is commonly found at the depth of two or three feet an exceedingly refractory hardpan resulting from the accumulation of puddled clay (see above chapt. 4, p. 62) in the subsoil, or sometimes even on the surface of depressed spots. This hardpan, easily destroyed by the use of gypsum and water, is described more in detail in chapter 22, on alkali soils; it blues red litmus paper instantly. The Causes of Hardpan.—The recognition of the cause of hardpan is of considerable importance to the farmer, because of the influence of the nature of the cement and the causes of its formation upon the possibility and methods of its destruc- tion, for the improvement of the land. It may be said in general that inasmuch as the cause of the formation of hardpan 1s a stoppage of the water in its down- ward penetration, the re-establishment of that penetration will tend to prevent additional induration; moreover, experience proves that whenever this is accomplished even locally, as around a fruit tree in an orchard, the hardpan gradually softens and disappears before the frequent changes in moisture- conditions and the attack of roots. The use of dynamite for this purpose in California has already been referred to; it seems to be the only resort when the hardpan lies at a considerable depth. When it is within reach of the plow, it may be turned up on the surface by the aid of a subsoiler and will then gradually disintegrate under the influence of air, rain and sun. But when the hardpan is of the nature of moorbedpan, containing much humic acid and perhaps underlaid by bog iron ore, the use of lime on the land is indicated, and will in the course of time destroy the hardpan layer. This is the more desirable as in such cases the surface soil is usually completely 186 SOILS. leached of its lime content, and is consequently extremely un- thrifty. Woodlands of northern countries bearing beech and oak are especially apt to be benefited by the action of lime on the “raw, acid humous soil and underlying hardpan, which is commonly underlaid by a leaden-blue sandy subsoil (*‘ Ble1- sand” of the Germans, ‘‘ Podzol”’ of the Russians) colored brown by earth humates and mostly too moist in its natural condition to permit of adequate aeration. These soils are usually of but moderate fertility, and are best suited to forest growth unless somewhat expensive methods of improvement can be put into practice. “ Plowsole.”—An artificial hardpan is very commonly formed under the practice of plowing to the same depth for many consecutive years. The consolidated layer thus created by the action of the plow (hence known as plowsole) acts precisely like a natural hardpan, and is sometimes the cause of the formation of a cemented subsoil crust simulating the nat- ural product. This is most apt to occur in clayey lands, and greatly increases the difficulty of working them, while detract- ing materially from the higher productiveness commonly at- tributed to them as compared with sandy lands. Of course it is perfectly easy to prevent this trouble by plowing to different depths in consecutive years, and running a subsoil plow from time to time. In this case, also, lime will generally be very useful and be found to aid materially in the disintegration of the “ plowsole.” It is hardly necessary to insist farther upon the need of the examination of land to be occupied, for the existence of hard- pan or other faulty subsoil, which may totally defeat for the time being the farmer’s efforts, or make him lose his invest- ment in plantations after a few years. Probing by means of the steel rod described above (p. 177) or boring with a post- hole auger; or finally, if necessary, digging a pit to the proper depth (from four to six feet in the arid region), should precede every purchase of new or unexplored agricultural land. Marly Substrata—Among the causes of failure occasionally found in the case of the “ going-back’’ of orchards, is the SOTL-AN DY SUBSOIEL. 187 occurrence of strongly calcareous or marly substrata, at depths which in the humid region would not be reached by the roots, but in the course of a few years are inevitably penetrated by the roots of trees 1n the arid region. Then there appears a stunt- ing of the growth, and sometimes a yellowing of leaves, or chlorosis, due to the influence of excessive calcareousness at the depth of four or five feet. For this of course there is no remedy except the planting of crops which, like the mulberry, Texas grapes, Chicasaw plum and others, are at home on such lands; which in the Eastern states are naturally occupied by the crab apple, honey locust and wild plums. CHAPTER XE THE WATER OF SOILS. HYGROSCOPIC AND CAPILLARY MOISTURE. WHEN it is remembered that from 65 to over 90% of the fresh substance of plants consists of water, the importance of an adequate and regular supply of the same to growing plants is readily understood. But it seems desirable, before discussing the relations of water to the soil and to plant life, to consider first the physical peculiarities which distinguish it from nearly all other substances known. ‘That it is colorless, tasteless, in- odorous, and also chemically neutral, alone constitutes a group of properties scarcely found in any other fluid. But its special adaptation to its functions in relation to vegetable and animal life are much more fundamental, as is shown in the table of its physical constants as compared with other well-known sub- stances, given below. PHYSICAL FACTORS OF WATER COMPARED WITH OTHER SUBSTANCES (PER UNIT WEIGHT). Capillary ascent in glass tubes Specific Heats. Heat of Evaporation. of one mm. diameter. \iVeliGies Gas dooGoocKancc 14 mm.|Water........ 1.000 Water at 20°C .613 Cal. INICIO coos soongses 6}mimy| iceman. 502 ney G year OMS Cill6 ooboccmc So HMMS oS. boa fy NO MN Gas g5gsocZes) Clay, Glass... .180-.200/Spirits of Tur- Chaxcoaleereee240 PEMEME eel G7es Sy | Ds r - . HEAT RELATIONS. Woods .;.0s550 ¢032 Density. Gold, Lead.... .032-.031 LVN OCMC OSD .096 Water at o° C. (freezing (Steels yosersrrere 119 Dts) bpaie:s tease -... .99988 Ee Water at 4 (Maximum BicaL of seston. density) ieemeneceeeer 1.00000} Water (Ice)... 80 Cal. Water at 15° C. (ordi- Metalse ce eens=2ou as nary temperature)... .990 Salts, (incl. sili- Ice at o° (freezing pt.). .g2800] cates)......40-63 “ Summarizing the meaning of the data given in the above table with respect to organic life, we see, first, that water rises higher both in the soil and in the tissues of the plant than any 188 THE WATER OF SOILS: 189 other liquid. Second, that as its density decreases in cooling after a certain point is reached, it freezes at the surface instead of at the bottom, as other liquids do; and as solid water (ice) is lighter than fluid water, ice stays at the surface and 1s readily melted when spring comes. Third, since its temperature changes more slowly than that of any other liquid, it serves to prevent injuriously rapid changes of temperature in plants and animals as well as in soils. Its high “heat of fusion” also serves to prevent quick freezing of plant and animal tissues, so that the brief prevalence of a low temperature may be more readily borne. Finally, the large amount of heat absorbed in evaporation of water serves to keep both plants and animals cool under excessive external temperatures which would other- wise quickly destroy life. Capillarity or Surface Tension.—In this table it will be noted, first, that water rises higher in fine (“capillary ’’) or hair tubes than the other fluids mentioned, which fairly rep- resent all others. No other fluid approaches water in the height to which it will rise’ in either soils or plant tissues. Were its capillary factor no higher than, ec. g., that of oil or alcohol, trees could not grow as tall as we find them, and the water supply from the substrata, and all the movements of water in the soil, and hence plant growth, would be similarly retarded. It is easy to verify these differences by immersing a cylinder of clay soil (or a cotton wick) in water on the one hand, and in oil or alcohol on the other. Notwithstanding the greater fluidity of alcohol as compared with water, the latter will be found to fill the porous mass much more quickly. The smaller the diameter of the tube, the higher will the water rise in it, and the greater will be the curvature of its upper surface, to which the rise is sensibly proportional. But in the case of liquids which do not “wet” the walls of the tube (as in that of mercury and glass), the curve (meniscus) is convex, instead of concave, and the liquid is depressed instead of rising. It is in its relations to heat, however, that water is specially distinguished from other substances; and these differences are 1 Excepting only the water-solutions of certain salts, among which common salt, kainit and nitrate of soda are of agricultural interest. Common salt may in- crease the capillary rise to the extent of more than five per cent. 190 SOILS. most vital not only to living organisms, but to the entire econ- omy of Nature. Density.—As regards the density or specific gravity of water (which is by common consent assumed as the unit of com- parison), it will be seen from the “‘ Density ” table that whereas all other bodies contract and become more dense as they grow colder, water has its point of (fluid) ‘“‘ maximum density ” at 4° C. (49°.2 Fahr), and expands as it grows colder, until at o° °C. (32° Fahr.) at solidifies into ice. in /sotdoing, itede. parts still farther from the rule obtaining with all other bodies (excepting certain mixtures, such as type metal) and again ex- pands so as to decrease the density from .g9988 to .g2800; thus causing ice to float on water at the freezing point. Hence water, unlike all other fluids, solidifies first on the surface; and but for this, the thawing of the winter’s ice, which would be formed at the bottom of rivers and lakes, would be deferred until late in summer. The expansion of water in freezing is forcibly illustrated in the bursting of water pipes and pitchers in winter; in the soil, the ice forming in the interstices serves to loosen the compacted land and give it better tilth for the en- suing season. Specific Heat.—Considering next, the column showing the “specific heat ’’ of water as compared with other substances, we see that it exceeds all other known bodies in the amount of heat required to change its temperature; hence again, its heat capa- city 1s taken as the unit to which all others are compared. The figures given in the table show that even ice and steam require for equal weights only about half as much heat (or burning of fuel) to change their temperature (ce. g., I degree) as would liquid water. But earthy matters, such as clay or soil and glass, require only one-fifth as much heat for a similar change; charcoal only about one-fourth as much. But vegetable mat- ter as represented by wood on the one hand, and gold and lead on the other, require only about one-thirtieth as much heat as an equal weight of water; zinc about one-tenth as much, steel somewhat more. It is thus plain that masses of water act powerfully, more than any other substance, as moderators of changes of temper- ature by their mere presence. The body of an animal or plant is protected against violent changes by the presence of EE WAGERS OL SOLES: IgI from 60% to 90% of liquid water, the temperature of which can only be raised or lowered slowly; and the presence of the sea tempers the climates of coasts and islands as compared with the heat or cold occurring in the interior of the continents. I[ce.—Again, it is shown in the table that the heat required to melt ice 1s greater than in the case of any other substance, especially the metals; which when once heated to the fusing point, require only a very little more heat to become liquid. The fusion of salts (including silicate rocks (requires more heat than does that of the pure metals. V aportzation.—In the amount of heat required for its vapor- ization water is also especially pre-eminent, and potent in its influence upon organic life. The table shows that the evapor- ation of water requires six hundred heat units ' as compared with alcohol, requiring only two hundred; while spirits of turpentine, the representative of a large proportion of vegetable fluids, needs but sixty-seven. The practical result is that evaporation of water from the surface of animals and the leaves of plants, is exceedingly effective in preventing excessive rise of temperature, the heat of the sun and air being spent in evaporating the perspiration of animals and plants before an injurious rise of temperature, such as would cause sunstroke in animals, and wilting or with- ering in plants, can occur. But since evaporation is most rapid in dry air, it follows that the cooling effect will be the greater in the arid regions than in the humid. In the latter, therefore, sunstroke is much more frequent than in the fervid regions of the arid west, even though the temperature in the latter may be higher by twenty or twenty-five degrees Fahrenheit. White men who would soon succumb if they attempted to work in the sun in Mississippi or Louisiana when the thermometer stands at 95°F. will experience no inconvenience under the same con- ditions in the dry atmosphere of the Great Valley of California. Solvent Power.—To the exceptional properties of water dis- cussed above, should be added another hardly less important one, viz., that of being an almost universal solvent especially of 1 A heat unit, or “ calorie,” is the amount of heat required to raise the tempera- ture of a unit-weight (pound, kilogram, or gram) of water one thermometric degree. According to the unit-weight and thermometric scale used, the figures will vary, but in this text the basis is understood to be kilograms and the centigrade scale. 192 SOILS. mineral matters, including even those which, like quartz, appear to be most insoluble and refractory (see chapt. 3). The water of the soil is thus enabled to convey to the roots of plants, in solution, all kinds of plant food contained in the soil. It should be noted that distilled (hence also rain-) water is a more powerful solvent, e. g., of glass, than ordinary waters containing mineral matter, and even free acids. Practically, plants take up al/ their water supply from the soil in the liquid form; and hence the soil-conditions with respect to this supply are of the most vital importance to plant growth. The most abundant supply of mineral plant food may be wholly useless, unless the physical conditions of adequate soil-mois- ture, access of air, and warmth, are fulfilled at the same time. On the other hand, comparatively few plants are adapted to healthy growth in soils saturated with water, or in water itself; and but few among these are of special interest from the agricultural standpoint. Water-requirements of Growing Plants——The amount of water contained in any plant at one time, however large, is but a small proportion of what is necessary to carry it through its full development. When we measure the amount of water actually evaporated through the plant in the course of its nor- mal growth, we find it to be several hundred times the quantity of dry vegetable substance produced; varying according to the extent and structure of the leaf-surface, the number and size of the breathing pores (stomata) of the leaves, and the climatic conditions (including specially the duration of active vegetation, and temperature during the same), from 225 to as much as g12 times the weight of the mature, dry plant. The following are extreme figures for water consumption of different plants as reported by different observers, viz., Lawes and Gilbert in England, Hellriegel in northern Germany, Wollny in Southern Germany (Munich), and King in Wis- consin: Wheat, 225 to 359; barley, 262 to 774; oats, 402 to 665; red clover, 249 to 453; peas, 235 to 447; mustard and rape, 845 to 912 respectively; the latter figure being the maximum thus far reported. The highest figures given are throughout very nearly those of Wollny, working in the very rainy climate of Munich. Evaporation from Plants in Different Climates.—It might ———--—“‘ ;wr See THE WATER OF SOILS. 193 be expected that in countries where the air is usually moist, the evaporation will, other things being equal, be less than where it is commonly far below the point of saturation. But the “ suardian cells’ (stomata) of the leaf pores possess the power of regulating, to a certain extent, the evaporation from the leaf-surface in accordance with temporarily prevailing condi- tions, so as to allow free evaporation in moist air, but to pre- vent the writing and drying-up of the leaf in hot and dry air, save in extreme cases. Moreover, plants adapted to arid condi- tions are usually provided with additional safeguards in the form of thick, non-conducting layers of surface cells, or long channels connecting the interior tissue with the breathing- pores on the surface. Often hairy, scaly or viscous coverings serve the same end. On the other hand, when the air is very moist, so as to check evaporation, water is sometimes found secreted in minute droplets around the breathing-pores of the leaves, since its ascent is a necessary condition of nutrition and development. Relation between Evaporation and Plant-growth.—There is not in all cases any direct relation between the amount of evap- oration and plant growth; but experience, as well as numerous rigorous experiments have shown that wider ordinary condi- tions of culture, and within limits varying for different soils and crops, production is almost directly proportional to the water supply during the period of active vegetation. On the basis of Hellriegel’s results, showing that wheat uses (in Germany) about 435 tons, or nearly four acre-inches of water in the production of one ton of dry matter, and assuming the ratio of grain to straw to be 1:1.5, King calculates the following table of probable production under different moisture conditions (Physics of Agriculture, page 140) : YIELD PER ACRE. Number of/Weight of Grain.| Weight of Straw.| Total Weight. Water used. Bushels. Tons. Tons. Tons. Acre-inches. | 15 45 .675 1.125 4.498 20 60 -90 I. 500 | 5.998 25 75 GAs 1.875 7.497 30 290 1.350 2.250 8.997 35 1.05 1.575 2.625 10.495 40 1.20 1.800 3-000 12.000 194 SOILS: S. Fortier has made several series of tests to determine the actual yield of grain crops under field conditions when sup- plied with different amounts of water. Two of these were made at the Montana experiment station in 1902 and 1903, (see reports of these years), in large tanks placed in a field, level with the ground. ‘The results of the last year’s experi- ments are shown graphically in the figure below, from which it will “be seen that ste yield increased quite regu- larly with the amount of water supplied, up to the depth of 36 inches of water. It should be noted that in this case (and as usual) not only the quantity but the quality of the grain was greatly improved as the -water-supply —in- creased, - it beconim7s larger and more uniform in size. Of similar experiments made in the San Joaquin Valley, Californiay ain 1904, Fortier says: + Depth of Irr/gation in Feer a : ; | In e¢x peri menting ar with barley last winter Fic. .—E iments on Cereal production with ra : Sie way i the natural rainfall, various amounts of water (Fortier, Report Mont. Expt. Sta., 1903). which amounted to 4% inches during the period of growth, produced at the rate of nine bushels per acre, while the application of sixteen inches of water increased the yield to twenty-two bushels per acre. In the same case; of wheat, the rainfall, alone, produced straw, but no grain; four inches of additional irrigation water pro- duced a yield at the rate of ten bushels, and sixteen inches of water increased the yield to thirty-eight bushels per acre.” 1“ Water and Forest,” January, 1905. ‘“ The Use of Water,” by S. Fortier _— —_— See THE WATER ©F SOILS. 195 It is thus obvious that, other things being equal and with conditions sufficiently favorable for the growth of crops, the rule as formulated above is verified in practice. Whitney (Bulletin 22, Bureau of Soils, U.S. Dept. Agr.), has carried this rule so far as to claim that in all soils, the moisture supply is the only important factor, and that so long as this is provided for, soil fertility continues indefinitely without replacement of ingredients with- .drawn. ‘The latter conclusion is so thoroughly disproved by experience as well as experiment that it hardly requires discussion here. Whether plants, especially cultivated ones, are capable of adapting themselves to arid conditions so as to be capable of producing satisfactory crops with less water than is actually consumed in the humid region, has not been directly deter- mined. Such is, however, the impression produced by farming experience ; and the fact that among the common weeds of arid California are mustard and rape, cited by Wollny as requiring over three times as much water as does maize for the pro- duction of one part of dry matter, lends color to the supposition that in some manner these, and probably other plants, use more water in humid than in dry climates (see this chapt. p. 212). It is therefore impossible to assign a definite figure for the amount of water required by vegetation at large; and even for one and the same plant, only approximations conditioned upon climatic factors can be given. We can in many cases, how- ever, assign for one plant, or for certain groups of plants, the amounts of water producing the best results (“ optimum ’’) and the least amount (“‘ minimum”) compatible with a paying crop, that must be furnished during the growing season, to produce certain results. For when instead of fruiting, it is desired that the crop should produce the largest possible amount of vegetable substance, as in the case of forage crops, a larger amount of water will usually be serviceable. Different conditions of Soil-Water—Water may be con- tained in the soil in three different conditions, viz. : 1. From absorption of water vapor; Hygroscopic water. 2. Liquid water held suspended between the soil particles so as to exert no hydrostatic pressure; capillary water, or water of imbibition. 1 See Wollny’s experiments, Forsch. Agr. Phys. Vol. 20, p. 58. 196 SOILS. 3. Liquid water seeking its level; bottom, ground or hydro- static water. HYGROSCOPIC WATER. Soils artificially dried so as to deprive them of all their mois- ture, when exposed to moist air absorb water vapor with great energy at first; both the rapidity of absorption and the amounts absorbed, when full time is given, varying greatly with their nature. Sandy soils, broadly speaking, absorb the smallest amounts; while clayey soils, and those containing much humus, or finely divided ferric hydrate, take up the largest proportion. The figure expressing the amount of aqueous vapor absorbed at the standard temperature of 15° Cent., is called the coef- ficient of moisture absorption. For one and the same sub- stance, this coefficient rises as the grain becomes finer, the surface being correspondingly increased (see chapt. 6). The table below indicates the effect of the three substances mentioned in increasing moisture absorption as compared with a very sandy soil from the pine woods of Mississippi, and a gray silt or “dust” soil from Washington, very fine-grained but poor both in humus and ferric hydrate. (For details of the physical composition of the Mississippi soils see table in chapt. 6, p. 93). A highly ferruginous soil from Oahu shows plainly the effect of that substance. . TABLE SHOWING INFLUENCE OF SILT, SAND, CLAY, FERRIC HYDRATE, AND HUMUS ON MOISTURE ABSORPTION. 248 | 79 | 238 | 230 | 246 220 | 215 2) Yn s Gate = - ee 3 aie) we Se eI a Sree ceal et yy tae | ie 2 BA St SO TL Oe a es 0 cs arene oH =) ZO SM} Ye a Ouest S| aS soles | &S$ |4s|as Aolan}s@ibe| oO} 3 oi SS" cae ae ee Raat | ae) ell eel el ee = ° Bale |B")2°) S86) 82 2 [8 %)%|% |) &| % % | bY hb Ely OT VUOIS EINE wteiarestsisielelaleietel> 2.48] 4.92] 9.09] 9.33) 18.60] 19.66)21.00|15.40 OIE 5.5050 GSadtooSodG D065 JoO 2.94) 1.27|74.65|25.48] 28.15 ? Tre 1; Gr ImSre IshyohaNnissscooaveccoos MoOyllon oo st aware WGC) | ACI) Ga acllocs . - leben 55.5 sb Sooo oasoKSUDeoaC 55| -44| 0.00] 50) little 3.33/66. 10/19.83 Finest Silts (oI-.0250 mm.)... 60.10 45-04|23.15/68.60) 40.33 3-94] 8.70 Sands, f. and c. (.0250-.50 mm.)|/31.20/42.40] .20] 4.70|/ 15.61 t 45-66 oe . (70.18 THE WATER OF SOILS, 197 It will be noted that the greater fineness of grain in the Washington dust soil induces a higher absorption of moisture than occurs in the sandy soil from Mississippi, although the latter contains more clay. Comparison of the figure for the Mississippi pipeclay and clay soil with the ferruginous soils, from the same state and from Oahu, indicate plainly the in- fluence of the ferric hydrate in increasing absorption; although in the latter case the clay determination was not made, because of the excess of ferric hydrate. The influence of humus 1s plainly shown in the case of the marsh muck and soil, neither of which contain any appreciable amount of either clay, or fer- ric hydrate in the finely diffused condition. The relatively slight difference in the absorptions of muck and soil is due to the only partial humification of the organic matter in the former, while in the soil the humification is sensibly complete, and the sand forming the body of the material serves to render it more loose. These data, referring to natural materials, while not as com- plete as could be desired, are sufficient to prove the facts, and seem preferable to any artificially devised imitation of their kind. Influence of Temperature, and Degree of Atr-Saturation.— The amount of moisture absorbed varies materially both with the temperature, and with the degree of saturation of the air to which the soil is exposed. Schubler, Knop and other earlier observers, operating with earth exposed to air only partly saturated, and with soil layers of considerable thickness (in watch glasses), found that the absorption decreased as the temperature increased, according to a law formulated by Knop. The writer found that under the conditions established in the experiments of Knop and others, the air was not nearly satur- ated,* so that these determinations are marred by ineliminable 1 It should be understood that it is by no means easy to insure full saturation in any considerable volume of air. It has generally been considered sufficient to cover with water the bottom of the space in which absorption was to occur. The writer found that in order to insure uniform results, it was necessary to cover the entire inner surface of the vessel with wet blotting paper, and even then to exclude carefully all circulation of air by padding the joints with such paper. When only the bottom of the box was covered, samples placed at different levels above the water surface gave dis- cordant results. It was also observed that whenever the thickness of the soil 198 SOILS. faults, the more as the soils used are only designated in general terms, as “ garden soil,” “‘loam,” “ peaty land,” etc., without any definite indication of their actual physical or chemical con- stitution. The writer therefore undertook to correlate these coefficients, determined with respect to. completely saturated air, with the physical composition of certain soils, as deter- mined by means of the methods heretofore described. Some of the data so obtained are given in the table of physical soil composition on page 93, chapt. 6. They have since been extensively supplemented by additional determinations, but without materially changing the coefficients approximately corresponding to the several designations accepted in farm practice. Experiments conducted by the writer have conclusively shown that Knop’s law of decrease of absorption with rise of temperature not only is not true for fz//y saturated air, but must be reversed ; the fact being that the amount of water absorbed by the soil ¢ucreases in a fully saturated atmosphere (i.e., in presence of excess of water) as the temperature rises, at least between 15 and 35 degrees Cent. Thus, fine sandy soil which at 15° absorbed 2% of moisture, took up 4% at 34°; while loam soil absorbing 7 % at 15°, showed nearly 9% at 35°; an increase of 2% in each case. But in partially saturated air® it was found that, as stated by Knop, the amounts absorbed steadily decrease, though not according to the law announced by him. Taking as a unit the moisture absorbed at 15°, it was found that in air three-fourths saturated, 3 of the unit was taken up by the soil; at half saturation, nearly the proportional amount ; but at one-fourth saturation the earths absorb materially more than a similar proportion, being then capable of withdrawing moisture from greatly layer exceeded about one millimeter, a long time was required for full saturation ; during which inevitable changes of temperature would bring about a deposition of dew on the soil, greatly exaggerating the absorptive coefficient. In the chamber used at the California station for soil saturation, dimensions 12 x 18 X 19 inches high, the same soil was exposed on a shelf close to the sur- face of the water, another midway up, a third near the lower surface of the cover; liquid water being in the bottom of the chamber, and the rest covered with wet blotters. It was found that despite these precautions, the lowest soil layer absorbed in the same time as much as 3{°/, more than the uppermost one. 2 The partial saturation to a definite extent was effected by means of solutions of calcium chlorid of different degrees of concentration, according to the de- terminations of Wiillner (Pogg. Ann.). These solutions were placed ina wide, flat dish, over which a layer of soil 1 mm. in thickness was exposed, all being covered with a bell glass lined inside with the same solution, so as to insure equal saturation. THE WATER OF SOILS. 199 ‘ undersaturated air. Since air thus undersaturated occurs not uncom- monly in the arid regions of the world, the fact that the soil cannot be farther dried by such air of the same temperature, is of some practical significance. In view of the highly variable composition of soils and of the doubtless varying hygroscopic properties of their several physical constituents, it is not to be expected that any one nu- merical law will hold good exactly for all kinds of lands. Mineral powders, colloidal clay, ferric hydrate, aluminic hy- drate, the zeolites, humus, and other hydrates known to occur, doubtless each follow a different law in the absorption of mois- ture and gases; so as to modify the hygroscopic properties of the soil in accordance with their relative predominance in each case. (See table of absorption of gases, chapter 14). Utility of Hygroscopic Moisture to Plant-growth.—The early experimenters considered the hygroscopic moisture of the soil to be of very great importance to the welfare of crops. Within the last twenty-five years much doubt has been cast upon this claim, even to the extent of stating that “the hygroscopic efficacy of soils must be definitely eliminated from among the useful properties” (Mayer's Agriculturchemie, vol. 2, p. 131). Yet Mayer himself concedes the cogency of the experiments made by Sachs, which proved that dry soil im- 1E. A. Mischerlich (Bodenkunde fiir Land-und Forstwirthe, p. 156 et al.) claims that all determinations of soil hygroscopicity thus far made are grossly incorrect on account of the dew liable to be condensed on the soil layer from fully saturated air, as the result of slight changes of temperature. He therefore would have all such determination made either in an air-vacuum, or over a 10°/, solution of sulfuric acid. Such dew-formation, however, cannot happen to any appreciable extent under the conditions maintained in the writer’s work, viz, absorption within a thick- walled (two-inch) wooden box of the dimensions given above, and sunk in the ground in a cellar in which the temperature varies only a few tenths of a degree during 24 hours. The soil layer of one millimeter thickness being put down in the morning, the 7 hour absorption period falls at the time of slightly rising tem- perature, as an additional precaution against dew-deposition. Mitscherlich fails, moreover, to show that this source of error produces any wide or serious dis- crepancies except under such long absorption periods as he finds it necessary to use because of the great thickness of his soil layers. It is doubtful whether the limits of errors in soil sampliug do not greatly exceed any of those involved in the writer’s method, and whether such accuracy as is attempted by Mitscherlich is of any practical significance. 200 SOILS. mersed in a (probably not even fully) saturated atmosphere is capable of supplying the requirements of normal vegetation; thus explaining the obvious beneficial effects on vegetation of the summer fogs prevailing in portions of the arid region, e. g., on the coasts of California and Chile. Mayer’s experiments relied upon to prove the uselessness of hygro- scopic moisture to plant growth, were carried out in flower-pots, in which it was plainly shown that the plants wilted before even the visible liquid (capillary) moisture of the earth was entirely exhausted. But this simply proves that under such artificial conditions, plants can- not withdraw moisture from the soil rapzd/y enough for their needs. In zature, and notably in the arid regions, the chief supply of water is received through the deep-going main roots, while the bulk of the active feeding roots of the plant may be surrounded by almost air-dry soil; under which conditions, as Henrici (Henneberg’s Journ., 1863, p, 280) has shown, slow growth and nutrition occurs even in such plants as the raspberry, a native of humid climates. But in the arid region this is the normal condition of the native vegetation through most of the rainless summer. That a higher moisture-coefficient does not necessarily imply that a larger amount of moisture can be withdrawn from the soil by the plants, is undoubtedly true in some, but not in all cases ; for in soils rich in humus, the moisture is more freely shared with the roots than in non-humous, clay lands. The higher moisture-absorption is however of the most un- questionable service in the case of the occurrence of the hot, dry winds that so frequently threaten the entire crops of some regions. In this case the soil containing the greater amount of moisture requires a much longer time to be dried, and heated up to the point of injury to the roots, than in the case of sandy soils of low absorptive power, whose store is exhausted in a few hours and then permits the surface to be heated up to the scalding point, searing the stems and root crowns. That such injury occurs much sooner in sandy lands than in well-culti- vated clay soils, is a matter of common note in the arid region. Summary.—The significance of hygroscopic moisture in connection with plant growth may then be thus summarized: 1. Soils of high hygroscopic power can withdraw from moist air enough moisture to be of material help in sustaining THE WATER OF SOILS: 20% the life of vegetation in rainless summers, or in time of drought. It cannot, however, maintain normal growth, save in the case of some desert plants. 2. High moisture-absorption prevents the rapid and undue heating of the surface soil to the danger point, and thus often saves crops that are lost in soils of low hygroscopic power. CAPILLARY WATER. The liquid water held in the pores of the soil, in the form of surface films representing the curved surface seen in capillary tubes, and therefore tending to cause the water to move upwards, as well as in all other directions, until uniformity of tension is established, is of vastly higher im- portance to plant growth than hygroscopic moisture. It not only serves normally as the vehicle of all plant food absorbed during the growth of the usual crops, but also, as a rule, to sus- tain the enormous evaporation by which the plant maintains during the heat of the day, a temperature sufficiently low to permit of the proper operation of the processes of assimilation and building of cell tissue. Comparatively few plants have roots adapted to healthy ac- tion while submerged in water, excluding them from free ac- cess of the oxygen of the air; and when such roots are formed by plants not naturally growing in water or swampy ground, they differ so far from earth roots in their structure that when transferred to soil they usually die, normal earth-roots being gradually formed instead. Conversely, there is for all land plants a definite time-limit beyond which their roots cannot live, or at least remain healthy, in submersion. Thus grain fields will with difficulty recover from a week’s total submer- sion; while young rice fields will resist considerably longer. When in the resting (winter) condition vineyards will bear submergence for thirty-five and even forty days, deciduous orchards about three weeks; but when in the growing condi- tion, injury is suffered much more quickly. It follows that whenever the soil-pores remain completely filled with water for a length of time, there is danger to the welfare of nearly all plants commonly cultivated in the tem- perate zones. It is therefore important to know how much 202 SOILS. water will bring about this undesirable condition in the dif- ferent kinds of soil. To determine this point we may either employ the deter- mination of pore space by a comparison of the density of the soil constituents (see chap. 7, p. 107) with the volume weight of the soil; or we may measure directly the amount of water required to fill the pore-space. For the latter purpose it is only necessary to measure the amount of water (conveniently flowing from a graduated pipette) which, rising slowly from below in a U-shaped tube so as to expel all the air before it, is required to fill a definite weight or volume of the soil en- tirely full, so as to rise to its surface. We thus ascertain the amount of empty space existing within the soil,’ which in the absence of water will ordinarily be filled by air. In most cultivated soils, as already stated, the air-space con- stitutes about 25% to 50% of their volume; and this space when filled with water represents what is commonly termed their maximum water capacity or saturation point. It is of in- terest to know this, because it has been ascertained from ex- perience that in order that plants may reach their best develop- ment, the capillary water present should not amount to more than 60%, or less than 40% of its maximum water-holding capacity ; thus leaving about half the pore-space filled with air. This optimum, however, varies somewhat for different plants, some, like celery, being more tolerant of excess, and others being more tolerant of a deficiency of moisture, as is the, e. g., egg-plant, originally a desert growth. Capillary Ascent of Water in Soil Columns.—When a col- umn of dry soil (e. g., contained in a glass tube closed with muslin at the lower end) is brought in contact with water, the latter is soon seen to ascend in the soil, wetting it and thus changing its color so as to permit of ready observation of its progress. At first the rise is comparatively rapid, in some cases as much as an inch in one minute; but it soon slows down and after a time ranging from a few days to many 1 Simple as this operation appears to be, it is found to be by no means easy to expel with certainty every small air bubble without resorting to means which would destroy the natural condition of the soil; such as boiling, or the use of the air-pump. These determinations cannot therefore lay claim to great accuracy. THE WATER OF SOILS. 203 months, reaches a maximum height beyond which the liquid water will not rise. The ascent is most rapid, and stops soonest, in coarse sandy soils; it rises most slowly, but in the end considerably higher, in heavy clay soils. The most rapid continuous rise, and ultimately the highest, occurs in salty soils containing but a small _ propor- tion of clay. The maximum height of capillary rise thus far observed, viz. 10.17 feet, was noted in the case of quartz tailings from a stamp mill, ranging from .005 mm. to .oO16 mm. in diameter; but it took about 18 months’ time to reach this maximum. The excessively fine texture of clay opposes great frictional resistance to the movement of the water, and the same is true of the finest silts, which, like clay, remain almost indefinitely suspended in water. But it must be remembered that while pure grains of silt will in wetting re- main unchanged in size, clay particles, and the clay incrusting silt grains, will on wetting swell greatly, and thus fill up the interstices, largely closing them up against the passage of water. These facts are exemplified and graphically illustrated below. The soils selected for this illustration, from California lo- calities, are the following: No. 233. Very sandy soil from near Morano, Stanislaus County. Typical of the noted wheat-growing region of the lower San Joaquin Valley, from northern Merced to Southern San Joaquin Counties; bench or plains lands. First foot. No. 1197. Sandy alluvial soil from near the confluence of the Gila and Colorado rivers, near Yuma. Very deep, light and easily cultivated. First foot, but almost identical to 15 feet. No. 168. Silty alluvial soil from the old alluvium of the Santa Clara River, near Santa Paula, Ventura County. Very deep, very easily tilled; a typical alluvial loam of the arid region. No. 1697. Black adobe or clay soil, from the experiment station grounds, Berkeley. A heavy clay soil, originally a swamp deposit, becoming very tenacious when wet. An ex- cellent wheat soil. The physical analyses of these soils are given below. 204 SOILS. PHYSICAL ANALYSES OF TYPICAL SOILS. Silt. Sand, 2.0 to Clay Fine, Coarse, | 64 mm. <.25 to |.5to2.mm. h. v. SGyemeoe Nava!) cle We No. 233. Morano sandy soil..... 2.82 3.03 3-49 89.2 No. 1197. Gila bottom soil....... 3.21 5-53 15.42 72.05 No. 198. Ventura silty soil...... 15.02 15.24 25.84 45-41 No. 1697. Berkeley adobe soil....| 44.2 25.35 13.47 13.37 The most striking feature in this diagram is the very rapid * and high ascent in the combination of sediments represented by the Gila bottom soil. It outstrips at once both the sandy soil from Stanislaus, which contains a trifle less of clay, and the silt soil from Ventura, from which at first sight it does not seem to differ widely, but which contains considerably more clay. It is doubtless the latter which so greatly retards the motion of the water, as is still farther seen in the case of the clay or adobe soil. It will be noted that on the second and third days, the Gila soil had raised the water nearly twice as high as the adobe, and that it took only 18 hours to raise it nearly the same height as that attained by the Ventura silt in so many days. But it ceased to rise after the 125th day, while the Ventura soil, continuing for 195 days, finally rose 3 inches higher. The adobe also continued its rise, but did not reach the same height as the Gila soil by nearly two inches. There can be no doubt that the energetic and high rise of the latter proves an important factor in the culture of these lands. The coarse sandy soil reached its highest limit, 16% inches, within six days, when the silty Gila soil stood at about double that height. Ascent of Water in uniform? Sediments.—Loughridge has ascertained the rate of ascent of uniform sediments of differ- ent grain-diameters, with the results shown in the diagram 1 The ascent is of course most rapid,in the large tubes almost instantaneous, when the capillary space is entirely clear; but in the complex system of con- nected air spaces in soils, the curved paths and the friction obstruct the move- ment. 2 J. e., uniform between the narrow limits given. THE WATER OF SOILS. 205 Adobe Soil Soil Soil Soil eee Co. Gila River | Ventura } lameda Co, Fic. 38.—Columns showing heights to which water will rise b y capillarity in soils of different Physical composition, and rates of ascent. SOILS. 206 “SIOJSWEIC] JWIIBFIP JO Sjuati[pag [10g ur szsjeA4 Jo asry Arvypideg — ‘ws 240) = 6£ “ory ‘Www pe ae sf % o THE WATER OF SOILS. 207 subjoined, together with the maximum height reached by each. The diagram is very eloquently illustrative of the great differ- ences in the capillary properties of granular sediments of the various grades; and it would seem that it ought to be possible to deduce from it by a somewhat complex formula the rate and height of ascent of water in any soil of known physical composition. In nature, however, the presence of clay and the greater or less degree of flocculation of mixed sediments will always vitiate to a very great extent the results deducible from such calculations ; hence the data conveyed by the obsery- ations of Loughridge must be considered applicable only to granular sediments free from clay and entirely deflocculated. It is curious that in this case the “clay’”’ showed a rise markedly below that of the finest granular sediment, despite the extreme fineness of its particles. This proves plainly that the physical nature of colloid clay is unlike that of the granular sediments; as has been repeatedly mentioned above. Maximum and Minimum of Water-holding Power.—lt 1s clear that at the base of the columns of soils just considered, the maximum of water-absorption of which the soil is capable will have been brought about; while at the top of the same column, the minimum of possible liquid absorption (continu- ous films of water) will exist. The same minimum moisture- condition will be produced when a limited quantity of water 1s placed with a large mass of soil; the moisture will spread to certain limits, until the surface films of water have all acquired uniform tension; and will then cease to extend, except by evaporation and hygroscopic absorption.* It is clear that the same condition will be brought about in the course of time at the top of a soil column in which water has percolated from above; and hence the minimum mentioned, aside from evapora- tion, represents approximately the usual condition of the soil 1 Ad. Mayer (Agriculturchemie 2, p. 141) designates this minimum content of liquid water as the “absolute ” water capacity of the same; but it is not obvious wherein this factor is better entitled to this name than would be the maximum (see Wollny’s Forsch., 1892, p.1.). M. Whitney (Rep. Proceedings Ass’n Agr. Coll. & Exp’t St’ns, Nov. 1904) gives as a new observation the fact that in soils ap- proaching the drought condition water “ does not obey the ordinary physical laws as we recognize them in capillarity.” This evidently refers simply to the well- known phenomenon mentioned above. 208 SOILS. near the surface within a variable time after a rain, or irriga- tion, when the descending water column has attained a length corresponding to the height to which the water would have risen from below in a tube arranged as shown on p. 205. It is therefore a condition of very frequent occurrence in the arid region. Capillary Water held at Different Heights in a Soil Col- umn.—To determine the amounts of water held in the differ- ent portions in columns of soils in which water ascends by capillary rise, the following plan was adopted by the writer in collaboration with Loughridge (Rep. Calif. Sta. 1892-4, p. 99). Instead of glass tubes the soils to be tested were placed in copper tubes one inch in diameter, divided into segments six inches long, and flattened on one side. In the flattened side a slot half an inch wide was left, and glass plates, held in posi- tion by rubber elastics, were cemented on the slotted side by means of paraffin, to prevent a sifting-out of the soil. The short sections can be connected at the ends like joints of stove- pipe, and the earths can be easily introduced in proper, even condition. It was thus possible to gain access to any portion of the column at any time, for the taking of samples. WATER CONTENTS OF SOIL COLUMNS AT VARIOUS HEIGHTS ABOVE WATER LEVEL. No. 233 1197 1679 Height above Water Sandy Soil, Sandy Alluvium, Level. Morano: Gila. adobe bola 47 inches 4.33 42 inches 10.26 36 inches 11.99 30 inches 15.26 24 inches 21.39 10.26 * 18 inches 27.63 29.48 12 inches 3.93 32.48 33-04 6 inches 14.15 35.04 38.47 3 inches 38.49 I inch 24.34 30.64 44.41 Since gravity limits the capillary ascent in a progressive ratio, as shown in diagram 39, itis obvious that the true maximum saturation 1 This figure represents only a temporary condition; the full height of 46 inches was not reached until the 195th day. THE WALTERSOF SOILS: 209 can exist only in a very short (strictly speaking, an infinitesimally short) vertical column. The least practicable height for experimental work being about 1 cm. (? in.), the writer has adopted for the purpose of rapid determination of this factor, the use of a brass cylinder 1 cm. high and of such width as to contain, for the sake of convenience, 25 or 50 cm. of soil. This cylinder has a finely perforated bottom, which may be covered with filter paper ; after being filled with soil which has been struck level, and weighing, it is immersed to 1 mm. depth in dis- tilled water and allowed to rest for an hour ; then quickly dried outside and beneath with filter paper, and again weighed. The amount of water found by difference should for all practical purposes be referred to the volume, not to the weight, of the soil, so as to eliminate the error arising from the varying specific gravity of the latter. In most cases the surface of the soil in the sieve cylinder remains level after wetting; but sometimes it swells so as to rise above its dry level, even to the extent of nearly 30% (see chapter 7, p. 114). This happens especially in strongly ferruginous soils. In the case of “black alkali” soils, in wetting an enormous co//apse sometimes takes place (see chapter 22). If it be desired to determine also the mnimum liquid absorption (see below), the surface of the wet soil is first covered with air-dry soil, to absorb the surplus moisture, and finally with soil previously saturated with hygroscopic moisture ; the added soil being each time thrown off and finally the surface “struck” level with a tense silk thread before weighing. Corrections must be applied for the usual increase in weight, from the addition of soil, and for the hygroscopic moisture. While the minimum of liquid absorption can thus be deter- mined quickly, without awaiting the capillary ascent of a water column, and if sufficient time is given can also be determined in higher columns, as proposed by Mayer (Wollny’s Forsch. Vol. 3), the maximum cannot thus be determined without gross inaccuracy. In determinations made by the writer it was found that the figures for the minima of very different soils (clayey and sandy) of the arid region, differ proportion- ally much less than do the respective maxima. In few of these soils it was found to exceed about 10 per cent, and it scarcely fell below 4 per cent even in very sandy soils. A very deep, sandy soil, which had been irrigated in May, and 14 210 SOILS. upon which no rain had since fallen, showed in July in the second foot, upon which rested ten inches of fully air-dried soil free from vegetation, a water-percentage of eight per cent. Capillary Action in Moist Soils.—In the preceding discus- sion the case of columns of air-dry soils, so common in the arid regions, has been considered. It is obvious that a soil column holding the minimum of capillary water may be of any height; so that when, as happens in the open field, the rain water soaks down beyond the range of capillary rise in a given soil, the upper portions of the latter, above that range, will remain at the minimum of moisture-content so long as it is not depleted by evaporation. King has made extended observations on soil columns ten feet high and moistened throughout the mass. Capillary movement takes place in moist soils much more rapidly than in dry ones, although when sufficient time is given the final adjustment will of course be the same. King’s experiments showed that evapor- ation at the surface of the tenfoot columns caused a sensible depletion of the water content originally existing at the depth of ten feet, in the course of 314 days. While so slow a movement might not be of any benefit during the growth- period of shallow-rooted annual crops, the fact shown is of importance to permanent plantings, as of trees and vines. Another and not so readily intelligible effect observed by King is that when the surface-soil is wetted, moisture may be withdrawn toward the surface from the lower layers. In one experiment he found that when water was applied on the sur- face so as to add two pounds of water to each surface foot in several soils, at the end of 26 hours there had been an increase of three pounds in the same, and a loss of one and three quarter pounds from the second and third feet. The cause of this translocation is probably a “ distillation’ of the subsoil mois- ture toward the cooled soil; the fact that it occurs is of prac- tical interest, since it seems to show that wetting the upper 1 Hall (The Soil, p. 66) gives for the minima in the case of soils examined by him the following figures : coarse sandy soil, 22.2, light loam, 35.4, stiff clay, 45.6, sandy peat, 52.8. These figures are very much higher than for apparently similar materials used by the writer, and the differences exceed those between the maxima given for the same. This discrepancy I am unable to account for. THE: WATER: OF ‘SOILS: 21% portion of the soil by cold rain or irrigation may tend to raise additional supplies from below. At the change of seasons we not uncommonly find, in digging tree holes or wells, a wet streak at from 9 to 18 inches below the surface, caused evi- dently by the condensation of subsoil moisture, at the limit of a cold zone resulting from the penetration of unseasonable tem- perature (‘‘cold snap’) from above. Such movements of soil-moisture by means of evaporation and recondensation within the soil can of course take place even when the mini- mum of liquid absorption has been reached and direct capil- lary movement has ceased. It is, as it were, dew within the soil. Proportion of Moisture Available to Growing Plants.—Not all the capillary moisture contained in soils is available to plants, as can readily be seen from the fact that many plants, especially when growing in pots, begin to wilt while the soil still appears visibly moist. The limit of wilting differs greatly in different plants, and in the open ground it is difficult to as- certain that limit, because the deeper roots continue to supply moisture from moister substrata. Hence potted plants wilt while the soil appears much moister than when the same grow in the field. King+ has determined the amounts of moisture down to 43 inches in a Wisconsin soil in which clover and corn were at the wilting point, as in the following condensed table: Clover. Maize. OY ground. Hirst 2 inches, clay loam............. 8.44 7.03 17.01 Second 12 inches, reddish clay........ 12.84 11.79 19.86 24 to 30 inches, sandy clay............ 13.52 10.84 18.56 AOMOMB INCHES, SANG: ..\ce snes cece 9.53 4.17 15.90 It is plainly shown here that the roots of clover and corn were unable to utilize the higher moisture-content of the sub- soil-clay to the same extent as the smaller amounts present in the surface foot, and in the sandy substrata. Evidently the moisture in the clay soil was more tenaciously retained. 1 Physics of Agriculture, p. 135. 212) SOILS. This is doubtless due, as King shows, to the equal thinness of the moisture film remaining on the soil grains in either case; the number of grains, and therefore the aggregate sur- face holding these films, being much greater in the clay than in sands; hence the higher water content. It is interesting to compare these figures given by King for clover and maize at the wilting-point, and fallow ground adja- cent, with those given by Eckart (Rep. Expt. Sta. Haw. Sugar Planters’ Ass’n., 1903) for those affording good growing conditions for sugar cane on the (highly ferruginous) soils of that station. The plots were irrigated at the rate of one, two and three inches of water per week, allowance being made for the rainfall. Two inches proved, on the whole, to give the best average results for production. The moisture determination of the soil under the two-inch regime gave an average moisture content of 29.13% in the first foot of soil. It is not stated what was the hygroscopic coefficient of that soil, but it was probably very high; in the neighborhood of 21.5%, judging by the determinations made with six Hawaiian soils at the California Station. This would indi- cate about 7.63% of free moisture as the optimum for sugar cane. Motsture-requirements of Crops in the Arid Region.— Plants (particularly broad-leaved ones) which have made a brash growth during a period of abundant moisture, will wilt quickly when sunshine returns, and take some time to adapt themselves to the drier conditions. On the other hand, plants accustomed to dry air and scanty soil-moisture, will not wilt or suffer under what would elsewhere be considered very rigorous conditions. Loughridge + has made numerous determinations of moisture in soils in which crops were beginning to suffer, and others on similar soils that were growing normally, and found that in general, not only were the differences in mois- ture content considerably less than in the case above quoted from King’s observations, but that the amounts of free mois- ture required by various crops in the arid climate of Cali- fornia were surprisingly small. The tables below show the results of observations made by 1 Rept. Cal. Expt. Sta. 1897-08, pp. 65-096. THE WATER OF SOILS. 213 Loughridge during several drought years in California; so ar- ranged as to show the differences of moisture content for the same crop in different soils. It will be observed that in all cases where a crop growing on a clay soil could be compared with the same on a lighter soil, the moisture required to keep the crop in good condition was very much greater in the clay than in the loam or sandy soils. In the case of apples, e. g., 8.3% of water was abundant to keep the trees in excellent con- dition on a loam soil, while on a clay soil holding 12.3% the condition was very poor. That this difference is due in the main to the difference in the hygroscopic-moisture coefficient of the respective soils, is plainly apparent in several cases. It is therefore not the total moisture content, but the free mois- ture present in excess of what is held by hygroscopic absorp- tion, that determines the welfare of the plant. By determining, first, the total moisture in the soils, as taken in the field, then, after allowing them to become air-dry, deter- mining the maximum of hygroscopic moisture they would ab- sorb (see p. 198), Loughridge found by difference the amount of free moisture, or liquid water which must be present in the soil to prevent the crops from suffering. An exceptionally good opportunity for these observations was offered by the dry season of 1898, during which crops suffering and not suffering, on identical lands, could easily be found. The de- terminations were always made for each foot of the upper four feet of the land in the immediate neighborhood of the trees or among the field crops. The first table exemplifies the method of procedure; the second gives the summary of results for the several crops and trees, as calculated from observations made during the season. 214 SOILS. TABLE SHOWING CONDITION OF CROPS ON VARIOUS SOILS UNDER DIFFERENT MOISTURE-CONDITIONS. Per cent Moisture in four feet. Kind of Crop. | Kind of Soil. verses of Br) Mane Total ie F Free per P acre Wheat yan iee vets Very sandy..... ROOT aiccelots Sool) | Als) 1.9 7 56 SOE TS Sctetno my Us Sandy loam). .|Good 2). /3)-\)2 +.) 12.8 5.6 7.2 576 Oy VoaGocdac GIES? Bois Sedicdocc Dead... : 14.1 10.5 3.6 288 Maize ttactthsisisr Clay adobe..... Very good..... 12.9 8.3 4.1 328 cc Miiest fehovencal siete Sandy loamy aloe cree iaeetets 6.1 2.3 3.8 304 Banleyanretrscittete Black adobe.../Wilting........ 10.7 8.8 1.9 152 Sugar Beets....|Black loam..... Good teen. 12.4 5.6 6.8 544 ViANeS\ Hl. yocehicers WoatWarns yack Cosdeseckossee 8.5 5:0 3.5 280 sigikelerctncistorerers Sandy loam(y.f.)|POOKs). clsseieie © <1 1.9 1.5 4 32 Aillmondsiieiiete Moamiiias 600 : 124.9 63-92| 6.72] 29.36]...... Gypsum) dinel ys powered sicrc sicinictelelsisleisiseisioisieie «/eleielsisveifl 00722 Oulmeisisiecieie 80.95! 19-05! 0.00!...... Discussion of the Table—It will be observed that in this table, the largest amount of total gas given off by equal weights of any one sub- stance was in the case of carbonate of magnesia ; but it is. quite probable that in part, at least, this large amount of gas was due to the evolution of carbonic gas from the easily decomposable carbonate ; the more as the analysis of the gases shows over 29% of carbonic gas. But the highest absorption by equal vo/umes of any substance is shown by the ferric hydrate; next to this by the light poplar charcoal, and next by the carbonate of magnesia. The high absorptive power here shown by the ferric hydrate is of great interest in connection with the facts already stated regarding the absorption of moisture and ammonia by ferruginous soils (see page 274, this chapter) ; and the fact that the larger proportion of the gas—as much as 70% in one case—consisted of carbonic gas, is particularly interesting in the same connection. Both in the amount of gas contained, and in the proportion of carbonic gas therein, the ferric hydrate exceeds even peat, the representative of humus in soils. It will, however, be noted that in the garden soil, also, the proportion of carbonic gas is very large, while that of oxygen isvery low. It is curious to note that in very few cases the proportion of oxygen to nitrogen is the same as in the atmosphere ; in most cases the nitrogen predominates considerably beyond its normal proportion, and in two cases, that of 278 SOILS, charcoal and of calcic carbonate (whiting), the gas was found to consist of pure nitrogen. We are forced to conclude that the substances here enumer- ated, as a rule, condense oxygen in smaller proportions than they do nitrogen, or carbonic gas. As regards the carbon monoxid mentioned in the table, it is doubtful that it was con- tained as such in the substance originally examined; it may readily have been formed under the influence of the heat re- quired in expelling the gases from the substances containing organic matter. Among the important results shown in the table, is the comparative determination of the gases in moist, and in dry garden earth, showing that in the moist earth the amount of gas absorbed ranged from less than one-half down to almost one-fourth that absorbed by the dry. The import- ance of these differences in the case of the fallow can readily be appreciated. The changes in the absorptive power brought about by wetting and drying, as shown in the above table, are very insignificant. Inthe case of the charcoal, soil and silt the diminution may fairly be assumed to be caused by the deposition of soluble salts on the surface, partly clog- ging the pores. In the case of the clay as well as in that of the river silt, the inevitable content of organic matter in process of decompo- sition has doubtless influenced the result, as is suggested by the increase of carbonic gas. That prepared chalk should in one case contain ex- clusively nitrogen gas, in the other case mixed gases, seems to indicate a difference in the air to which it is exposed, or in the water employed in its preparation ; the latter case agreeing substantially with the results obtained from the precipitated carbonate. In both (as well as in the carbonates of barium and strontium), the absorption of carbonic gas is very small, or 777. It thus appears that for the condensation of carbonic dioxid gas, ferric and aluminic hydrates are prepotent among mineral substances; while clays, river silts and soils may always be expected to contain relatively large proportions of this gas in absorption. ABSORPTION BY SOILS, 279 PEE PATRI ORS SOLES: The Empty Space in Soils——In dry soils the empty space, usually amounting to from 35 to 50 per cent of its volume, is filled with air;* in moist or wet soils the space unoccupied by water is similarly filled. Hence when soils are in their best condition for the support of vegetation (chap. II, p. 202), about one half of their interstices is filled with water, the other half with air. Actual measurements of the amount of air contained in well-cultivated garden soil have been shown by Boussingault and Levy to range between 10,000 and 12,000 cubic feet per acre, substantially agreeing, therefore, with the above statement. In uncultivated forest soil, on the contrary, they found only from somewhat less than 4000 to 6000 cubic feet of air per acre. Extended observations since carried out by Wollny, Ebermayer, and others have in general confirmed the earlier observations, while adding greatly to their signifi- cance in respect to their relations to plant growth, and to the process of humification and soil-formation. As a matter of course, when water evaporates from the soil in drying, its place is taken by air so far as it is not filled by capillary water drawn from below. Functions of Air in Sotls—That roots require for the per- formance of their vegetative functions the presence of oxygen, has already been discussed; but there can be no question that the higher productiveness of well-cultivated soils is largely due to the greater and readier access of air to the roots. Apart from this direct function, however, the presence of oxygen in the soil serves other important purposes, and among these doubtless the most dominant is the promotion of the oxidation of the organic matter of the soil through the agency of micro- organisms; and more particularly that of nitrification, which chiefly governs the supply of nitrogen to non-leguminous plants. In the case of leguminous plants, the presence of air as a furnisher of nitrogen as well as oxygen is absolutely essential. The injurious effects of insufficient aération of the soil have been repeatedly referred to already (pp. 45, 76). In water- logged soils reductive fermentations are soon set up, and the 1 The normal composition of atmospheric air is given on p. 16, chap. 2. 280 SOILS. nitrates of the soils are reduced partly with the evolution of nitrogen gas, partly to ammonia; while their oxygen is con- sumed to supply the demands of the roots. Ferric oxid is reduced to ferrous carbonate, sulfates to sulfids; thus de- ranging the whole process of plant-nutrition and absorption of plant-food. If continued for any length of time these condi- tions end in the death of the plant. Too much importance can- not therefore be attached to the proper aération of the soil and subsoil. Excessive Aération; Compacting the Soil—On the other hand, excessive aération of the soil may be injurious in caus- ing a serious waste of moisture; especially in arid climates, where the hot, dry winds may readily destroy the germinating power of the swollen seed when the seed-bed is too loose and open, and later may injure or destroy the feeding roots. The abundant growth of grain often seen in the tracks of a wagon carrying the centrifugal sower, when the stand in the general surface is very scanty, is usually due to the consolidation of the seed-bed, and suggests at once the well-known efficacy of light rolling to insure quicker germination and a better stand. Simi- larly, the rolling of grain fields in spring is often the saving clause for a crop in dry years. But such needful consolidation must not, of course, be carried to the extent of creating a sur- face crust which would subsequently serve to waste the subsoil moisture. Hence, the soil-surface should be rather dry when rolling is resorted to. The pressing of the earth around transplanted plants, simi- larly, is a needful precaution, not only with respect to the dry- ing-out of the soil, but also to insure close contact between the roots and the soil. The Composition of the Free Air of the Soil usually differs from the air above, in that besides being saturated with mois- ture, its nitrogen-content is slightly increased (by one-half to over one per cent) ; the oxygen-content on the other hand, is diminished, being in part (sometimes nearly to the extent of one-half of its volume) replaced by carbonic gas, de- rived partly from its secretion by the roots, partly from the oxidation of organic substances. It naturally follows that the richer the soil in the latter, the more carbonic gas will be formed under favoring conditions; so that in freshly-manured ABSORPTION BY SOILS. 281 land the amount of oxygen transformed into carbonic gas will be greatest, while in the surface-soil of ordinary fields, car- bonic gas rarely reaches to as much as one per cent. In all cases, however, the content of carbonic gas in the air of the soil is materially higher than that of the air above it, and thus serves to intensify greatly the solvent and disintegrating effect of the soil water upon the soil materials (see chap. 2, p. 17). The soil-mass itself, however, retains carbonic dioxid with con- siderable tenacity, so that it is not possible to wash it out com- pletely by filtering water through it. When water containing carbonic gas in solution is filtered through the soil, the gas is sometimes completely absorbed, the water passing off free from gas. The presence of free carbonic gas in soils is readily demon- strated by passing through the warmed soil a current of air, which is then made to bubble through lime water; a clouding of the latter, and the ultimate formation of a precipitate of calcic carbonate, proves the presence of the gas, and may also serve to measure its amount. From the fact that the free air in normal soils may contain as much as one-fortieth of its bulk of carbonic gas, besides what may be contained in the condensed form, we may con- clude that this gas is formed within them with considerable rapidity ; for otherwise, in view of the free communication and diffusion with the outer air, such large amounts could not be maintained in the surface-soil. Doubtless a considerable pro- portion of the carbonic gas normally contained in the atmos- phere is thus supplied from within the soil itself. Relation of Carbonic Gas to Bacterial and Fungous Activity. —It has been fully demonstrated by the researches of Koch, Miquel, Adametz, Fuelles, Wollny and others, that the forma- tion of carbonic gas in the soil is not a purely chemical oxida- tion process, but is essentially dependent upon the presence and life-activity of numerous kinds of organisms, bacterial as well as fungous. The crucial proof of this fact is that the presence of any antiseptic diminishes, and if exceeding certain propor- tions completely suppresses, the formation of carbonic gas; while on the other hand all conditions known to be favorable to the life of such organisms, viz., the proper conditions of tem- perature and moisture (varying with different kinds), increase 282 SOILS. the formation of the gas. Such formation is of course, how- ever, conditioned upon the presence of oxygen. In the case of most bacteria, there is a certain limit beyond which the pres- ence of their own product exerts an injurious or repressive effect upon their activity ; so that if the gas accumulates beyond that limit, the rate of its formation decreases despite of other- wise favorable conditions. It follows that the best life-conditions of these organisms (even when anerobic) cannot be fulfilled below a certain limited depth in the soil; and all observations show that their number decreases very rapidly with increasing depth (see chap. 9, p. 142), varying with the perviousness of the soil, but rarely exceeding four or five feet in the humid regions; though doubtless found at greater depths in the arid climates. It is also obvious that the use of any antiseptic or poisonous materials on the field or in the manure pile will tend to disturb and restrain the useful activity of these organisms. Putrefactive Processes——Carbonic gas is formed also, but to a much more limited extent, in putrefactive processes, occur- ring in the absence, or with only limited access, of air or oxygen. These processes likewise are conditioned upon the presence or activity of (largely anerobic) bacteria; but they should not occur in normally constituted, and especially in tilled soils, being as a rule inimical to the growth of cultivated plants (see chap. 9, p. 145). CHAPTER S6V. THE COLORS OF SOILS. THE natural coloration of soils forms a prominent part of the characters upon which farmers are wont to base their judg- ment of land quality; hence the origin and value of soil-colors deserve consideration. Black Soils—From the oldest times down to the present a “rich, black soil” has commanded attention and approval. The black and brown-black colors being almost invariably due to the presence of much humus (very rarely to an admixture of carbon (graphite), of magnetic oxid of iron, or sesquioxid of manganese), it is obvious that the farmers’ judgment coin- cides with a high estimate of the agricultural value of humus. A discussion of this point will be found in another place; but the popular judgment is based quite as much upon the experi- ence had in the advantages that usually accompany the pres- ence of humus. It largely characterizes low grounds, and therefore alluvial lands, whose richness is due to far more gen- eral causes. But the shade of the blackness seen in the soil deserves and usually receives close consideration. If tending toward brown, acid humus or “ sour ”’ land is indicated ; unless indeed the surface soil should be bodily derived from decayed wood, as in the primeval forests. Forest soils in general are usually dark-tinted for some inches near the surface, owing to the presence of leaf mold, and mostly have an acid reaction. But the black tint is equally welcome to the land-seeker when seen outside of alluvial and forest areas. Belts of “ black lands’’ appear on hillsides and plateaus; and these lands, though clearly not alluvial, are also found to be preéminently productive; witness the upland prairies of the western and southern United States. These black soils are always charac- terized by the presence of a full supply of lime in the form of carbonate, under the influence of which the most deeply black humus is formed. In other words, the jet black tint is indica- 283 284 SOILS. tive of calcareous lands; and these, as will be more fully shown below, are almost always highly productive. From both points of view, then, the favorable judgment passed upon black soils by practical men is justified. But it is not necessarily true that soils showing no obvious black tint are poor in humus; for in strongly ferruginous or “red” soils its tint is frequently wholly obscured, though when still visible it gives rise to the laudatory name of “ ma- hogany land,” which every farmer considers a prize. Of course then it would be wholly incorrect to judge of the agricultural value of land from its humus-content alone; for its color may be entirely imperceptible and yet its amount and nitrogen content be fully adequate to the requirements of thrifty vegetation. Gray and even whitish soils very fre- quently fall within this category in the arid region. The black tint is also favorable to the absorption of the sun’s heat, and is therefore conducive to earlier maturity than is to be looked for in light-tinted lands similarly located. Wollny (Forsch. Agr. Phys. Vol. 12, 1889, p. 385), dis- cusses the influence of color on soils in relation to moisture and content of carbonic acid. The results show in general simply the effects due to increase of temperature when the soils are either darker-colored throughout, or made so superficially. “ Red” Soils —Next to a black soil, a “‘ red”’ one will usu- ally command the instinctive approval of farmers. The cause of this preference is not as obvious as in the case of the black tints; but the general consensus of opinion requires an ex- amination of its claims. It is of course easy enough to adduce examples of very poor “red” soils, derived from ferruginous sandstones that supply little else than quartz and ferric hy- drate; the Cotton States supply cogent examples in point, as do also the lower Foothills of the Sierra Nevada of Cali- fornia. It is not, therefore, the iron rust or ferric hydrate that renders the land productive; but its presence is a sign of some favorable conditions. First among these is, that ferric hydrate cannot continue to exist in badly drained soils; a “‘ red”’ soil is therefore a well-drained one, and this is probably one of the chief causes of the popular preference. The “ white land” sometimes seem in tracts otherwise colored with iron, is dis- tinctly inferior in production to the red lands; and examination THE COLORS OF SOILS. 285 will generally show that from some cause, such white lands have been subjected to the watery maceration which proves so injurious (see chap. 3, p. 46, chap. 12, p. 231). That finely-diffused ferric hydrate has a very high power of absorbing moisture as well as other gases of the atmosphere, has been shown in the preceding chapter; it stands in this re- spect next to humus itself, and hence highly ferruginous soils need not contain as much humus as “‘ white”’ soils from this point of view. Like humus, also, it renders heavy clay soils more easily tillable. Origin of Red Tints—Where crystalline rocks prevail, the red tint usually indicates the derivation from the weathering of hornblende; implying also, outside of the tropics, the presence of sufficient lime in the land. Such lands are naturally pre- ferred to those of lighter tints derived from purely feldspathic rocks (see chap. 3, p. 32), although they may be poorer in potash than the latter. But the red tint has also its intrinsic advantages in the more ready absorption of the sun’s heat by the colored than by a white surface. This is probably the chief cause of the higher quality of wines grown on red hillsides in the middle and northern vine districts of Europe, where everything that aids earlier maturity is of the greatest importance. The function of ferric oxid as a carrier of oxygen (chap. 4 p. 45) prob- ably also aids nitrification. “Yellow” lands owe their tint, of course, to smaller amounts of ferric hydrate, but share more or less in the ad- vantages of the “ red.”’ White soils, or more properly those having very light gray tints, are not usually looked upon with favor, especially in the humid region. The causes of the unfavorable judgment cur- rent among farmers in respect to white soils has already been partially explained in the discussion of the black and red tints. The light color means the scarcity or absence of both humus and ferric hydrate, and usually implies that the soil has been subject to reductive maceration through the influence of stag- nant water; reducing the ferric hydrate to ferrous salts, oxidiz- ing away the humus, and accumulating in the form of inert concretions most or all of the lime, iron and phosphoric acid of the soil mass (see chap. 3, p. 46, chap. 10, p. 184). The 286 SOILS. term “ crawfishy,’’ so commonly applied to white soils in the eastern United States, expresses well the usual condition of the white soils of that region; which are very commonly in- habited by crayfish, whose holes reach water a few feet below ground, and are surrounded on the outside by piles of white subsoil mixed with “ black gravel” or concretions of bog iron ore. It is needless to say why such lands cannot command the favorable consideration of the farmer; they cannot as a rule be cultivated without previous drainage, and even after that will usually prove unthrifty, “ raw,” and in immediate need of fertilization by greenmanuring, and the use of phosphates. In the arid region, lands of this character are of rare occur- rence, while (as has been explained above, chap. 8, p. 135), the light gray or “‘ white” tints are there a very common char- acteristic of even the very best soils. It is true that they are poor in humus and in finely diffused ferric hydrate; but their “light” texture renders the presence of humus for this pur- pose less needful, and as stated elsewhere (see chap. 8, p. 135), the high nitrogen-content of arid humus renders a smaller supply adequate for vegetative purposes. As to iron, its presence being more important as a sign of good drainage and aération than directly, its absence from soils of great depth and loose texture is of no consequence; especially when the heat-absorption which it favors is not only not needed, but is usually already in undesirable excess during the hot sum- mers. White Alkali Spots—In the valleys of the arid region, how- ever, very white spots commonly indicate the prevalence of alkali salts, and to that extent are an unfavorable indication; especially when coupled with the occurrence of black rings or spots, which indicate the presence of black alkali or carbonate of soda (see chap. 22). GHAR TE Re Say ae CLIMATE. Heat and Moisture are the main governing conditions of plant growth. Ina preceding chapter the relations of soils and plant growth to water have been considered; in the present one the relations of both moisture and heat to soils and plants will be discussed; and to do this intelligibly to those not making a specialty of such studies, it becomes necessary to introduce, first, a summary consideration of the subject of climate. Climatic conditions control, and to a great extent determine, the industrial pursuits of every country; all the more so as the rapid communication and transportation by means of modern appliances now brings every part of the globe in competition with every other. The question is not now what it may be intrinsically possible to do under certain climatic and geo- graphical conditions, but whether these things can be done with a reasonable prospect of profit and commercial success, in competition with other countries offering more or less of simi- lar possibilities. While it is true that the cost of labor fre- quently enters most heavily into such problems, yet favorable or unfavorable climatic or soil-conditions may in many cases turn the scale. Thus the high price of labor and fuel on the Pacific coast of the United States would at first blush seem to render competition with Europe and the East in the pro- duction of beet sugar commercially impossible; yet exception- ally favorable climatic and soil-conditions concur to turn the scale in favor of California at least, so as to have placed that state at the head of the sugar-producing states of the Union. A general understanding of the climatic conditions which con- cern the United States more or less directly, is therefore need- ful to an appreciation of their agricultural possibilities. Climatic Conditions—The factors usually mentioned as constituting climate are temperature, rainfall and winds. Since the latter two factors, however, are themselves merely 287 288 SOILS. the result of heat conditions, it 1s proper to discuss from the outset the origin and mode of action of heat. TEMPERATURE. The temperature of stellar space outside of the atmosphere is known to be very low. The increasing cold as we ascend to greater heights, is a fact familiar to all. Langley has calcu- lated upon the basis of observations made at the summit and foot of Mount Whitney in California, that the temperature of space lies near 200° Cent. (360° F.) below the freezing point of water; and this would be the temperature near the Earth’s surface, were it not for the surrounding atmosphere. The lat- ter absorbs but a small amount of the sun’s direct heat rays (which are of high intensity), as they penetrate it to the Earth’s surface. But as the earth’s surface is warmed, the heat rays of Jow intensity which it emits cannot pass back through the atmosphere to the sun or to outer space; they are “trapped,” as it were, by the dense air resting near the earth’s surface, which is then warmed partly by the radiation from, partly by direct contact with, the soil. It is to the existence of our atmosphere, then, that the possibility of our animal and vegetable life in their present form is due; and a decrease of the trapping effect on the sun’s heat rays makes itself quickly felt when ascending, either in balloons or on high mountains. Moreover, it is well known to mountain climbers that at great elevations the sun’s heat is extremely intense at noon; even though the temperature may fall to the freezing point at night, owing to the failure of the thin air to prevent the radiation back into space of the heat absorbed during the day. On the high plateaus of the Andes and of Asia, therefore, very ex- treme climates prevail, on account of the great range of tem- perature between day and night. Ascertainment and Presentation of Temperature-Conditions. —The proper understanding of the temperature conditions of any locality or region is by no means a simple matter. Shall we study the daily, monthly, or annual changes of temperature, or the means deduced from either or all of them, in order to gain a clear insight into the climatic conditions that control crop production and health conditions? —e ee CLIMATE. 289 The Annual Mean Temperature not a Good Criterion— Since one and the same figure may result equally from the averaging of two widely divergent data, and from such as are close together, it is clear that the mean annual temperature cannot be a proper criterion of the agricultural adaptations of a country. Thus an average temperature of 60° F. might re- sult, equally, from the averaging of 65 and 55 degrees, or from taking the mean of 15 and 105 degrees; yet the respective cul- tural adaptations would be widely different. Extremes of Temperature are Most Important.—lIt is, on the contrary, rather the extremes of temperature, more par- ticularly of cold, but frequently also of heat, together with the total amount of heat available during the growing season, that determines such adaptation so far as temperature is con- cerned; for no culture plant can be successfully grown where the temperature during winter even occasionally falls for more than a few hours below the point which it can resist; and for each plant there is a certain aggregate requirement of heat to carry it from germination to fruiting. Even different varie- ties of one and the same plant differ materially in the latter respect, so that it is very important that in the selection of varieties to be grown, this factor should be taken into con- sideration. It cannot be too strongly urged that the compari- son of annual means of temperature, so commonly made by promoters of colonization schemes, must not be taken as a guide either in the estimate of cultures in which the immi- grant may desire to engage, or by those in search of a climate adapted to their health-conditions. Seasonal and Monthly Means.—The statement of the mean temperatures of the conventional four seasons—spring, sum- mer, autumn and winter—afford a much clearer conception of climatic adaptations; provided always that the extreme tem- peratures be considered at the same time. With the same un- derstanding, the monthly means are still more instructive; but here again, it is most essential that the distribution and amount of rainfall in each be regarded at the same time, since the most desirable temperature is of no avail without the moisture re- quired for vegetation. In some cases, e. g., that of California, it becomes neces- sary for practical purposes to regard the “ season,” and not oS) 290 SOILS. the calendar year, as the unit or reference for crop production. There the crops depend upon what rainfall may occur from October to May, there being no summer rains of agricultural significance, and outside of irrigated lands, almost all vegeta- tion save that of trees being in abeyance. In India, there are two distinct growing seasons (“‘ kharif”’ and “ rabi’’), corre- sponding to the two “ monsoon ”’ seasons; and no matter how much rain may fall during one, almost total failure may occur in other tropical and arid sections of that country. The Daily Variations are of interest chiefly with respect to health conditions, since most plants are more adaptable in this respect than the average man. RAINFALL. Distribution Most Important.—The summary statements of the annual rainfall are almost equally as deceptive as are those of annual mean temperature, since quite as much depends on the manner in which it is distributed through the year, as upon its absolute amount; and also upon the manner of its fall. Thus Central Montana has the same aggregate annual rainfall as the country surrounding the Bay of San Francisco, viz. about 24 inches; but while in the Franciscan climate this amount of rain falls during one-half of the year, and that the growing season, enabling crops to be grown without irrigation, in Montana the rainfall is distributed over the entire season, so that irrigation is absolutely essential for the successful pro- duction of crops. This so much the more as, while the winter snowfall is very light, the rains of summer are largely torren- tial, running off the surface in muddy floods and giving little time for absorption into the soil. Farther west, in Washing- ton, where grain crops are largely grown without irrigation, the sowing of winter grain is impracticable because the dry summer is immediately followed by the very light snowfall of winter, which falls on dry ground. Fall-sown grain would thus simply lie dormant in the ground through the winter, with great liability to injury from stress of weather in early spring, apart from the depredations of birds and rodents. Hence grain is always sown there in spring only. These examples may suffice to show that summary state- CLIMATE. 201 ments of either temperature or rainfall by yearly means are of little practical interest to the farmer. What he needs to know is whether or not sufficient rains to mature a full crop are likely to fall during the time that the growing temperature prevails ; and what are the minima and maxima of temperature —heat and cold—that his crops will be called upon to endure. WINDS. The third climatic factor mentioned, the winds, though proverbial for their unreliability and inconstancy, are not only very incisive in their action, but also to a considerable extent of very definite local or regional occurrence and signifi- cance. Moreover, their occurrence, direction, temperature and moisture-condition can, in regions whose climatology has been reasonably well studied, be foretold with sufficient accuracy to be of great use to the farmer. Heat the Cause of Winds.—As already stated, the primary cause of all winds is heat, substantially on the principle accord- ing to which draught is created in our domestic fires. The hot air rising creates an indraught from all directions, especi- ally from that which it can most readily come; viz., from the ocean,? or from level lands, rather than across mountain chains. Hence the sea-breeze in the after part of the day, when the land has become heated; while the sea, requiring a much larger amount of heat to change its temperature to a similar extent, remains relatively cool. But at night the earth cools more rapidly than the sea, by radiation; hence toward evening 1 A striking case in point is the regular wind which in summer blows through the “Golden Gate,” a gap in the Coast Range connecting the Pacific Ocean directly with the great interior valley of California, along the bays of San Francisco, San Pablo, and Suisun. The great interior valley and adjacent moun- tain slopes becoming intensely heated during the rainless summer, the ascending air is replaced by a steady indraught from the sea, which is bordered by a belt of cold water causing fogs along the coast. The fogs are quickly dispelled on reach- ing the edge of the valley near the middle of its length; whence steady breezes blow northward and southward, up the valleys of the Sacramento and San Joaquin respectively. These winds, popularly often, but erroneously, called trade- winds, are really “monsoons” similar in their origin to those of India, which, when coming from the sea cause rains, but when from the heated land itself are hot and dry; as in the case of the sirocco of Italy and North Africa, the terral of Spain and the northers of California. 292 SOILS. the sea-breeze dies down, and toward and after sunset the land-breeze takes its place. The principle of this local change of winds, together with the rotation of the earth, the absorption of moisture by air, and the fact that the latter becomes cooler when it expands on rising and warmer when it is compressed by descending, serves to explain all the major phenomena usually observed in connection with winds. The air of the equatorial belt, heated throughout the year, necessarily rises and creates an indraught from both north and south; but since the air thus flowing in has a lower rotary velocity than the earth’s surface ‘at the Equator, it lags behind and so gives rise to northeast and southeast winds, respectively, between the two tropics and the equatorial belt. These regular winds, from the aid they give to commerce in passing from continent to continent, are known as the trade winds. On the other hand, the air that has risen from the hot equatorial belt, cooling by expansion as it rises and flowing northward and southward from the Equator, on descending as it mainly does into the temperate zones, has a higher rotary velocity than the land-surface and so tends to give rise to southwest and northwest winds in the northern and southern hemispheres respectively. At sea, on coasts and in level inland regions to windward of mountain chains, such winds are often quite regular during a portion of the year. Cyclones.—But local disturbances arising from heated land areas or mountain slopes, as well as wide atmospheric changes whose causes are not fully understood, give rise to waves of alternating high and low barometric pressure, largely con- verting rectilinear or slightly curved wind-motion into whirls or “cyclones’’ + ranging from a thousand to over two thou- sand miles in diameter. These in the case of low-pressure waves or centers, toward which the air flows from the outside, revolve in the direction contrary to the movement of the hands 1 This designation is popularly and incorrectly applied to the comparatively limited, but very violent and destructive rotary storms or whirlwinds which originate locally on the heated plains of the Middle West of the United States, and are almost always accompanied by violent electric phenomena. These should properly be called tornadoes. At sea such whirlwinds give rise to waterspouts, in deserts to sand storms. CLIMATE. 293 of a clock, and commonly produce rain in their east portion. A high-pressure wave or center, from which the air naturally flows toward the outside, will usually bring about an “ anti- cyclone” area with fair, and in winter cold (“ blizzard’’) weather, the direction of the whirl being, in this case, the re- verse, or in the same direction as the hands of a clock. Both cyclones and anti-cyclones move in North America from west to east, mostly entering from the Pacific Ocean off the north- west coast and traversing the continent with a slight south- east (or in the case of cold weather almost south) trend, with a velocity of twenty to thirty miles an hour; until upon reach- ing the region of the Great Lakes they generally turn north- eastward and pass into the Atlantic Ocean from the New Eng- land and Canada coasts.—It is upon these general facts, roughly outlined here, that the weather forecasts are in the main based; taking into consideration, of course, the local or regional conditions, topography, etc., which modify the appli- cation of the general rules. In the southern hemisphere, the air-movements substantially correspond to those observed in the northern, so far as not modified by mountain chains; as is especially the case in South America. INFLUENCE OF TOPOGRAPHY. Rains to Windward of Mountain Chains.—The surface fea- tures or topography of the regions traversed by the air cur- rents or winds may materially modify both their direction and their physical condition, especially as to moisture and temper- ature. Mountain chains may deflect them, or, causing the air currents to rise on their slopes, and thus to cool by expansion, the moisture these bring with them from the sea may be partially, or sometimes almost wholly, deposited in the form of rain or snow; chiefly on the windward slopes. Then, continu- ing across the range, the air deprived of most of its moisture cannot readily yield up more; hence the scarcity of rain— “arid climate ”—under the lee of mountain chains; as in the Great Basin between the Sierra Nevada and Cascade ranges on the one hand and the Rocky Mountains on the other, and also on the Great Plains under the lee of the latter. The 294 SOILS. abundant rainfall between the Mississippi river and the At- lantic coast is due to the moist winds coming from the warm waters of the Gulf of Mexico and Caribbean sea, whose access is not interfered with by any cross-ranges of mountains. But the Great Plains lying between the Mississippi and the Rocky Mountains are not within the sweep of the Gulf winds, whose trend is SW to NE; while they are equally out of reach of moisture from the Pacific, all that having been successively de- posited on the intervening mountains; hence their deficient rainfall. Northward of the temperate zone the rainfall generally de- creases as we approach the arctic regions; except where the in- fluence of warm ocean currents to windward creates com- paratively local exceptions, as in the case of Norway and Alaska. Fic. 52.—Composite Curve showing distribution of Rainfall in Europe, Africa and America pro- jected on roo Meridian W. L. The general Distribution of Rainfall on the globe is well shown in the annexed diagram, which is copied by permission of the author from his treatise on the ‘“‘ Evolution of Climates,’ + and represents the mean deduced from data given in the Atlas of Meteorology by J. G. Bartholomew. It is a composite curve derived from the consolidation of four curves showing the distribution of rainfall, viz, on the meridians of 1“ The Evolution of Climates”; by Marsden Manson, July, 1903; also Amer. Geologist, Aug.—Oct. 1897. CLIMATE. 205 20°E.L.; the west coasts of Europe and Africa; the 30th meridian W.L., in the Atlantic Ocean; and the west coasts of North and South America, projected on the plane of the 1ooth meridian W.L. The latter curve corresponds with remarkable closeness to the mean curve here given. “It is not intended that these curves should include the rainfall upon meridians on which the distribution in belts is interrupted by continental influences, and by the irregular oblique belts of rain on the east coasts.” But it presents an admirable generalization upon which, as a basis, the local disturbances may be studied. It will be noted that the maximum of rainfall in the tropi- cal rain-belt lies several degrees to northward of the equator, owing doubtless to the greater land area in the northern hemi- sphere. There is thus, on the whole, a narrower belt of de- ficient rainfall or aridity between the tropical and northern temperate rain-belts, than in the southern hemisphere. The southern temperate rain-belt touches only the extreme ends of South America, Africa and New Zealand; elsewhere on the ocean it has not been sufficiently observed as yet. The zones of rainfall and aridity are, however, known to be subject to seasonal oscillations of several degrees in latitude, owing to the obliquity of the plane of the ecliptic, which shifts its posi- tion upon that of the equator. Ocean Currents.—Since water as a fluid is subject to the same circulatory motions which cause winds, it is to be ex- pected that ocean currents should exist corresponding to those of the air, as characterized in general above. But as water warms so much more slowly than air, its circulation would be comparatively insensible were it not for the effects produced by the air currents upon the surface of the sea, combined, as in the case of the winds, with the effects of the rotation of the earth. Without going into the details of the ocean currents in the tropics, it may suffice to say that owing partly to the moving and warming effects of winds, partly to the natural circulatory motion of the water, two great warm currents flow from the tropics northward, materially modifying what would otherwise be the climates of the coasts they touch. The Gulf Stream.—The current most generally known is the Gulf Stream, flowing partly from the Gulf of Mexico and the Caribbean Sea, partly from outside of the same along the 296 SOILS. chain of the Lesser Antilles, along the southeast coast of the United States (Florida, Georgia and South Carolina); but owing to its greater rotational velocity it is soon, like the winds of the same latitudes, deflected from a northward to a NE. course, which carries it away from the American coast, to impart some of its warmth, (probably mainly through the winds that blow over it), to Great Britain and Ireland, Scandi- navia, and Western Europe generally; while the northern American coast is left to be bathed by the icy polar current flowing from the Arctic through Baffin’s Bay, which carries icebergs far to the south in the way of the transatlantic traffic between the Eastern States and Europe, and causes a differ- ence in climate that is well exemplified in the comparison of the climate of New York with that of Naples, both lying in the same latitude; and similarly of the bleak coast of Labrador with that of Great Britain. The Japan Stream.—On the eastern Asiatic Coast, a warm current originating in the Sunda seas, flows off the coasts of the Philippines and of China and bathes the Japanese islands; hence it is known as the Japanese Current, or Kuro-siro. It is partly this current which, failing to pass into the Arctic through the shallow waters of Behring strait, renders the coast climates of the northwest coast of America so much milder and moister than is that in corresponding latitudes on the east coasts of both continents. Alaska corresponds to Nor- way in its moist, foggy and relatively mild coast climate; Brit- ish Columbia, Washington and Oregon participate in the bene- fits of the tempering influence of the return current of the Kuro-siro. But as this return (‘‘ Alaska”) current passes southward into the warmer seas off the California coast, its influence is reversed; it becomes a cold current in the warm waters of the Pacific, and the warm, moist air of the ocean being carried by the westerly winds across this cold stream which flows along the shore of California, in summer dense fogs are formed, which render navigation difficult and pro- duce a coast climate whose average summer and winter tem- peratures (e. g. at San Francisco) may differ by only a few degrees, viz., 15.5 and 13.0° C. (60 and 56° F.); so thapam change of clothing from season to season is hardly called for. The Alaska Current leaves the immediate coast of California re ye? CLIMATE. 297 off Pt. Conception near Santa Barbara, gradually losing it- self southwestward, but still tempering the tropical heat in the Hawaiian Islands. Hence the coast climate is much warmer and less foggy in southern California; but throughout the State in the interior valleys, screened from the coast winds by the Coast ranges, the temperature in summer may rise several degrees above 100° F. for days together; although, owing to the dryness of the air, the heat is not oppressive. Contrasting Climates in N. W. America.—An even more striking contrast, showing the effects of the warm ocean and air currents, when intercepted by mountain chains, exists on the Pacific coast farther northward, as already mentioned. In Oregon and Washington first the low Coast ranges, and then the higher Cascade mountains, obstruct the eastward progress of the westerly ocean winds. The result is a very heavy rainfall to coastward of and within the Coast ranges, and an almost equally heavy precipitation on the western slope of the Cascades. Standing on the crest of the latter in summer, one may see to westward a rolling sea of clouds, causing almost daily rains; while to eastward the eye ranges over brown or whitish, dusty plains or rolling lands, almost destitute of tree growth and quivering with heat, under a deep blue sky untroubled by clouds for months. A somewhat similar contrast is seen in the Hawaiian islands, which are in the sweep of the subtropical northeast trade winds, and on their windward (eastern) slopes have abundant rains; while on the leeward slopes an almost arid climate pre- vails, calling for extended irrigation. Continental, Coast and Insular Climates.—From what has been said above, the striking differences of climate caused by the position of any region with reference to the sea or other large bodies of water on the one hand, and to mountain chains on the other, can be readily understood; provided of course that the direction of the winds and the trend of the mountain chains be properly taken into consideration. Western coasts in the temperate and subtropical regions will have a relatively even, temperate and moist climate as compared with the in- terior of continents, from which the tempering influence of the sea is cut off by mountain chains. Where no such chains intervene the coast climate may extend far inland. The lat- 2098 SOILS. ter case is that of Europe, where the prevailing westerly winds, warmed by the Gulf Stream, temper the climate as far east as the borders of Russia, and northward to Norway; while to southward the warm waters of the Mediterranean and Black seas temper both heat and cold in Spain, southern France, Italy and the Mediterranean border generally. But to east- ward, in Russia and Siberia, the climate becomes “ conti- nental’’ to an extreme degree, with very cold winters and very hot summers. The same is true of interior North Amer- ica, wherever the continental divide cuts off the tempering in- fluence of the westerly winds; Montana, the Dakotas and the Great Plains states generally being examples. The climate of the Mississippi valley, as stated before, is tempered by the winds blowing from the Gulf of Mexico, but with occasional irruptions of the continental climate (sometimes reaching as far east as the South Atlantic coast) in the forms of cold “blizzards,” from which the coast climates of the Pacific and of western Europe are practically free. The Atlantic coast of North America (including the coast of the Gulf of Mexico), moreover, not unfrequently suffers from the violent cyclonic storms that originate in the Antilles and follow more or less the direction of the Gulf Stream. Islands, differing from continents mainly in their extent, and having a relatively large proportion of coast, naturally have climates controlled essentially by the surrounding ocean. The insular or oceanic climates are therefore, as a rule, more temperate and even than are those of the nearest mainland. It is often said that the climate of western Europe is “ in- sular”’; and owing to its position under the lee of the Gulf Stream, this is eminently true of Great Britain. Subtropic Arid Belts——Where the surface features of the land in relation to the ocean and prevailing winds do not in- terpose special obstacles, we find to poleward of both tropics a climatic belt of greater or less width, in which the annual, or at least the summer rainfall is too small to maintain annual herbaceous vegetation throughout the season, even when the temperature is favorable. These two “arid” belts are best defined in Africa, where the northern one is represented by the Sahara desert, lower Egypt and Arabia, while the south- ern one is exemplified in the Kalahari desert, to northward of CLIMATE. 299 the Cape of Good Hope. The northern belt is continued into Asia Minor, Palestine, Syria and Persia, and is again manifest in northwestern India; but to eastward is stopped by the in- fluence of the great Himalaya range. The plateau countries beyond, in Central Asia, are extremely arid, largely by reason of their high elevation. In Australia the southern arid belt is very strongly defined. In North America, the arid belt is characteristically defined on the Pacific Coast. It embraces all but the southernmost point of the peninsula of Lower California, with about two-thirds of the State of California; thence eastward across Sonora and Arizona to New Mexico and western Texas. But here the influence of the mountain ranges and high plateaus obscures the subtropical belt as such, the arid climate continuing, east of the great Pacific ranges, through Nevada, Utah, Wyoming, Montana, Idaho, and eastern Oregon and Washington nearly to the line of British Columbia on the north, and with gradu- ally decreasing aridity, into Colorado, Kansas, Nebraska, and the Dakotas. In South America the rainless seaward slopes of southern Peru and northern Chile indicate the southern arid belt; but here, the great chain of the Andes intervening, the dry pampas. of Argentina, and the Gran Chaco of southwestern Brazil, like the Nevada basin, though arid would naturally be referred to the moisture-condensing influence of the Andes chain, under the lee of which they lie. From this cause the region of de- ficient rainfall, which on the western coast ends to northward of Santiago de Chile, is east of the Andes continued much farther poleward, as in North America; reaching into Pata- gonia. Utilization of the Arid Belts—While, as already explained, the distribution of the rainfall through the year is nearly as important as its total amount, yet it is evident that even with the minimum of twenty inches of total precipitation as the measure for crop production, a very large proportion of the land of the arid region cannot, even with the most elaborate system of water conservation, be supplied with sufficient water for ordinary crops, and must be otherwise utilized, mainly for pasture purposes. This is rendered practicable to a much greater extent than might be expected, because the rapid transi- 300 SOILS. tion from the rainy to the permanent dry season cures the standing herbage into hay, which affords good grazing during the rainless season. Moreover, the use of drought-resistant, browsing forage plants, both shrubs and trees, serves to sup- plement materially any deficiency in the supply of “ standing hay,” especially in case the rains should toward the end be unduly delayed. The same is true of the dried pods and seeds of native herbage, which in some cases (bur clover, lupins, ete.,) afford highly nutritious additions to the leafy forage. 1See Rept. of the U. S. Commissioner of Agriculture for 1878, pp. 486-488 ; Bull. Nos. 16 and 42, Wyoming Expt. Station; Bull. No. 1so Calif. Expt. Station ; Bull. No. 51, Nevada Expt. Station; South Dakota Station Bulletins Nos. 40, 69, 70,74; Kansas Expt. Station, Bulletin No. 102; New Mexico Expt. Station, Bulletin No. 18; Montana Expt. Station, Bulletin No. 30; and others. CHAPTER XVII. RELATIONS OF SOILS AND PLANT GROWTH TO HEAT. The Temperature of Soils——The rapid germination of seeds, as well as the development of plants to maturity, is essentially dependent upon the maintenance of the appropriate tempera- ture. The temperature most favorable to germination or growth, as well as the degree of tolerance of high and low temperatures, varies greatly with different plants, governing mainly what is known as their climatic adaptation. A knowl- edge of these points with reference to the several crops is therefore of no mean importance to the farmer; for, to a cer- tain extent, he can control the temperature in the soil itself, and he can mostly choose for sowing and planting, the time when the soil shall have the proper temperature for rapid germination or maturity. Asa rule, it is not desirable to have either seeds or seedling plants in the ground for any length of time when the temperature is too low for active vegetation; for while they rest, other, lower organisms (fungi and bac- teria), adapted to low temperatures, may continue in full activity at the expense of the vitality of the crop plant. Water exerts controlling Influence.—Since the capacity of water for heat is approximately five times greater than that of the average soil, equal weights being considered, it follows that the temperature of soil-water must exert a controlling influence over that of the soil. Taking the case of a cubic foot of loamy soil, fully saturated with water, in which one- third of the volume may be assumed to be water: the weight of the dry soil being about eighty pounds per cubic foot, cal- culation shows that the amount of heat required to raise the temperature of the water contained, one degree, will be fully twice as great as for that required for the soil itself. It is thus obvious that the control of soil-temperature is largely dependent upon the control of the water-content of the same, which has been discussed in a former chapter. Even in the 301 302 SOILS. condition of moisture known to be most favorable to plants, viz., one-half of the maximum water capacity, the influence of the water-content upon the temperature will still be as great as that of the entire soil mass. This consideration emphasizes the importance of such control. Cold and Warm Rains.—lIt is not surprising then that the occurrence of cold or warm rains or the use of cold or warm irrigation water at critical periods, may largely determine the success or failure of the crop. It is well known that the oc- currence of a cold rain after vegetation has started actively in early spring, may not only destroy the season’s fruit crop by preventing the setting, or thereafter causing the dropping, of the fruit, but may even, if the suppression of vegetative action be continued for some length of time, result in serious injury to, or death of trees. Widely extended disastrous experience of the kind was had in California in February and March, 1887, resulting in the death of tens of thousands of fruit trees and vines during that and the following season. It is obvious that in such a case as this the rapid draining-off of the cold water through underdrains would have materially mitigated, if not wholly prevented, such injury. Solar Radiation.—Aside, however, from such overwhelming influences as the above, the soil temperatures are measurably controlled by the extent to which they receive and absorb the sun’s heat rays, whether directly or through the mediation of the air. The direct effect of the sun’s rays upon the surface is, upon the whole, the most generally potent, although warm winds may occasionally exert a very strong influence. The varying influence of the sun’s rays depends primarily upon the change of seasons, which themselves result from the vary- ing angles at which the sun’s rays strike the surface; as well as upon the duration of the day. The greater or less cloud- iness or fogginess of the sky, of course, exerts a decided effect in this connection. The Penetration of the Sun’s Heat into the Soil.—In the temperate regions of the earth the daily variations of temper- ature cease to be felt at depths ranging from two to three feet, according to the nature of the soil material and its more or less compacted condition. The monthly variations, of course, RELATIONS OF SOILS TO HEAT. 303 reach to greater depths; while the annual variations do not disappear in the temperate zone, e. g., at Paris, Ziirich and Brussels, at a less depth than seventy-five feet. At these depths of constant temperature we find approximately the same temperature as that which we can deduce from the ther- mometric observations as the annual mean. From similar causes the mean annual temperature of any place may be ap- proximately deduced from the observation of the water of wells and springs derived from moderate depths. For below the level of constant annual temperature the latter begins to ascend steadily as we progress downward, owing to the in- terior heat of the earth. Change of Temperature with Depth—The following table of observations made at Brussels illustrates the decrease of annual range of temperature with depth: At feet: Average temperature. Annual range. BeeG a nisits Sele on stemleae Ce Ge 10.5, C. BCIGH Chparsinlocs wiayesarsterar’ aus C. Ta OF BOG aah sara aieieisnt's 16:4, C: ie He Os HS One venience eet: 170: O07: It is interesting to compare with this record that of a well sunk by Ermann at Yakutzk, Siberia, where the mean annual temperature is—g.7 C. (14.6 F.). This temperature was found a few feet below the surface. At 50 feet the tempera- ture was—7.2 C. (19° F.); at 145 feet—5° Cent. (23° F.) at 350 feet—.9g° C. (30.8° F.) showing that the ground was be- low the temperature of freezing water for some distance far- ther down; so that the search for liquid water was abandoned. We thus see that in the Arctic regions, owing to the pres- ence of water in the form of ice, the melting of which impedes the access of solar heat, the level of no variation is found at the distance of a few feet below the surface, despite the great variations in temperature between the short but hot summer and the extremely cold winter. In the tropics, also, the annual temperature-variation disappears at a less depth than 2 feet, in consequence of the very slight difference between the two seasonal extremes of temperature. Surface—Conditions that influence Soil-Temperature. Among these color has already been mentioned, and to a cer- 304 SOILS. tain extent discussed. While it is true that, broadly speaking, dark-colored soils absorb more of the sun’s heat than light- colored ones, other things being equal, it must still be under- stood, that the nature of the color-giving substance exerts a very material influence upon the amount of heat absorbed. Thus charcoal is among all known substances the one absorb- ing and radiating the sun’s heat rays most powerfully, and all kinds alike; so much so, that its absorbent power is taken as 100. But other substances which to the eye appear equally black, have by no means the same absorbing power. The heat absorption by black humus is high, though not quite equal to that of charcoal; and many gray soils, though appearing to the eye of rather light tint, really absorb more heat than others which, to our perception, have the darker tint, but are colored by other substances. Gardeners and especially vine growers in the colder portions of Europe often take advantage of the powerful absorbing power of carbon by spreading charcoal or black slate powder over the surface of the soil where early maturity is specially desired; and slate powder is similarly used by the peasants at Chamouni to hasten the melting of the snow. Heat of High and Low Intensity.—It must also be kept in view that the surfaces, and especially the colors that favor ab- sorption of the intense rays of the sun, may comport them- selves quite differently toward heat rays of low intensity, such as those thrown back from the soil at night when it cools. Were this otherwise, a soil that absorbs much heat in the daytime would lose it with corresponding rapidity at night. But this is true only of charcoal; in the case of most other substances, there is a material difference in favor of the re- tention of the heat, of low intensity, by slower radiation into a “heat-trapping ’’ atmosphere. Reflection vs. Dispersion of Heat.—Theoretically, a smooth surface reflects more heat than a rough one, and warms much more slowly by absorption; as is strikingly shown by the use of polished metal screens placed on walls to prevent their being overheated by a flue near by. In the case of soils, also, the condition of the surface affects materially the absorption of heat, but not in accordance with the above rule so far as the RELATIONS OF SOILS TO HEAT. 305 result is concerned. For it is found that, other things being equal, a loose or cloddy surface disperses in many directions the heat it receives, and does not permit it to penetrate by conduction to so great extent as would a more compact soil, whose smooth surface would waste less of the heat received by radiation. King has called special attention to the difference of temperature existing between soils smoothed and compacted by a roller, and the unrolled soil having a loose surface. He found that the former at a depth of one and a half inches was as much as 5.5°C. (10°F.) warmer than the loose soil, and that even at a depth of three inches a difference as high as 3.5°C. (6.5°F.) existed between the two. He observed at the same time that the temperature of the air over the unrolled ground was considerably warmer than above the rolled, thus corroborating the differences observed in the soil itself. But at night the heat is given out more rapidly from the rolled than from the unrolled surface, the latter acting as a non-conductor and keeping the soil warmer than that of the more compact rolled land. King gives as the average difference observed between rolled and unrolled land on eight Wisconsin farms, 1.6°C. (3°F.) in favor of the rolled land between 1 and 4 p.m. It will thus be seen that the loose tilled layer, while im- peding the penetration of the sun’s heat into the deeper por- tions of the soil during the day, on the other hand serves to retain it at night better than a more compact soil. This ob- viously places it within the power of the farmer to exert con- siderable control over the soil-temperature at critical times; restraining or favoring the access of the sun’s heat in accord- ance with the requirements of the climate or season, as the case may be. Influence of a Covering of Vegetation, and of Mulches.—A cover of either living or dead vegetation depresses the tem- perature of the soil as compared with the bare land, as elabor- ately shown by Wollny and Ebermeyer. In the monthly aver- ages these differences rarely exceed .8° C. (1.5 degrees F.), and are mostly below .50° C. (1° F.), but during different parts of the day they may rise to 2.2 to 2.5° C. (4 to 4.5° F.), at 4 inches depth. In summer they are greater than at other seasons. Of course the density of the vegetation or the thick- ness of the mulch influences them materially. Forests exert 20 306 SOILS. the greatest cooling influence upon the soil, and next to these the dense herbaceous crops, such as clover, and the legumes generally. Influence of the Nature of the Soil-Material_—Aside from the surface condition, the nature of the material itself exerts a certain influence, not only upon the rate of introduction of heat, but also upon the amount taken up. Thus quartz sand having the highest density (greatest weight per cubic foot) and also the highest capacity for heat among the usual mineral soil-ingredients, will, mass for mass, experience a smaller rise of temperature than would clay or loam soil, of less density or volume-weight, and also of lower heat-capacity. While this holds good theoretically, differences corresponding to this consideration rarely occur in nature, for the reason that the much greater influence of the mechanical condition of the soil mostly overbalances these effects. Thus Wollny has shown that while quartz is a better heat-conductor than clay, quartz cobbles or gravel will materially increase the tem- perature of the soil in which they are imbedded. Yet com- pact clay is a better conductor of heat than loose sand; hence the latter, when exposed to the intense heat of the summer sun in the desert, becomes intensely hot on the surface, yet al- lows of the existence of abundant moisture at a depth of ten or twelve inches; while clay in the same region, being usually in a compacted condition, will show a lower surface-tempera- ture and will be warmer and drier at a depth at which sand will still retain abundant moisture, and be comparatively cool (See chap. 13, p. 257.) So much indeed depends upon the state of mechanical division and flocculation in which the sev- eral soils may happen to be, that a hard-and-fast statement in regard to their relations to heat cannot and should not be given, as it would only lead to disappointments and practical mistakes; the more as in all cases the moisture-condition ex- erts an influence predominating by far over that of the dry material itself, and this moisture-condition is subject to rapid changes, owing to intrinsic differences in the several classes of soils. Wollny states as the result of his experiments, that in summer sandy soils are warmest; then humous, lime and loam soils; while in winter humous soils are warmest, then loams; and sand coldest. RELATIONS OF SOILS TO HEAT. 307 Influence of Evaporation—lIn treating of the Consery- ation of Soil Moisture (chapter 13), the effects, conditions and control of evaporation from the soil have already been dis- cussed from several points of view; so that a summary review of the subject must suffice in this place. It has been stated above that in the case of an average loam soil saturated with water, the heat required to raise the tem- perature of the water one degree would be about twice that needed to so change the dry soil material itself. But if it is required to evaporate the same amount of water from the soil, nearly ten (9.667) times that amount of heat will be required ; or in the case assumed, twenty times as much as would suffice to raise the temperature of the dry soil through an equal in- terval of temperature. While in a few cases the cooling of the soil by evaporation is desirable, in the vast majority of cases it is injurious to the progress of vegetation, and should be restricted as much as possible by the means outlined in a former chapter. Formation of Dew.—There is, however, another aspect of evaporation from the soil which has been long misunder- stood, although the true state of the case was partially recog- nized long ago. Dew is in common parlance said to “ fall,” it being supposed that, like rain, it is derived from the atmos- phere. While this is partially true, inasmuch as from very moist, and notably from foggy air dew is frequently deposited on grass and foliage generally, as well as on wood and other strongly heat-radiating surfaces; yet as a matter of fact, in by far the majority of cases, as shown by H. E. Stockbridge * and confirmed by everyday observation, dew is formed from the vapor rising from the warmer soil into a colder atmos- phere, and condensed on the most strongly heat-radiating sur- faces near the ground, such as grass, leaves both green and dry, wood, and other objects first encountering the rising vapor. In manifest proof of this it will be noted that very heavy dews may be seen on the ground, when the roofs of houses as well as the higher shrubs and trees remain perfectly dry. In winter this may be most strikingly seen in the deposition of hoar-frost in and immediately around the cracks of plank sidewalks, whose surface remains dry. 1“ Rocks and Soils,” pp. 175-189. 308 SOILS. Dew rarely adds Moisture.—Candid observations will con- vince any one, therefore, that in most cases the supposed addi- tion to the moisture of the soil from dews is an illusion. Whatever dewdrops fall on the ground are in general simply the return to the soil of a part of what came from it; while the dew that evaporates from the bedewed leaves or other objects represents simply a delayed outgo of moisture from the soil, which for a time retards evaporation direct from the ~ soil, and thus effects a slight saving of moisture. But while this is measurably true of inland and especially of continental areas like the great plains of North and South America, it is also true that in deep moist valleys, and on the rainy and foggy coast regions of continents, dews are found to both fall and rise, not uncommonly to such an extent as to be equivalent to a not inconsiderable aggregate precipitation. Thus in the moist coast belt of Oregon and Washington lying west of the Cascade range of mountains, the morning dews of summer are frequently so copious that the water falls in showers from the lower trees and shrubs, so as to necessitate the use of water-proof clothing when traversing the woods in the morning, quite as much as though rain was actually falling. In hilly and more especially in mountainous regions the cold air descending from above and flowing down in the ravines will often cause a heavy condensation of dew in these, while the bordering ridges, which rise above the cold currents, remain free from dew. These descending currents as a rule not only bring no surplus moisture with them, but in their downward course become warmer by contraction and therefore relatively drier. In these cases also, therefore, the dew is purely moisture derived from the ground, which in rising encounters the cold air and is thus condensed. The fact that dew is most commonly derived from the soil could have been foreseen from the other fact, long ascertained and known, that during the night the soil is as a rule warmer than the air above it; as has been shown by the earlier ob- servers, as well as more specifically by Stockbridge. Dew within the Soil.—It is obvious that whenever dew is formed above the surface of the soil, the air within the latter must be at or near its point of saturation with vapor, as in fact is usually the case a few inches below the surface. It follows that when a depression of temperature occurs within RELATIONS OF SOILS TO HEAT. 309 the soil, e. g., at night, dew must be deposited within the soil down to the depth to which the nightly variation reaches, in- creasing at that depth as the vapor from the warmer soil be- low rises, to be in its turn condensed. There is thus formed at that level a zone of greater moisture, which may sometimes be noted in digging pits, by a deeper tint, without any cor- responding variation in the nature of the soil. The daily re- petition of this process, at varying depths, and its greater or less recurrence at or near the limit-levels of monthly and even annual variations, must exert a not inconsiderable influence upon the vertical distribution of moisture in the soil; which instead of being usually found in horizontal bands or zones of varying moisture-contents, is usually remarkably uniform for considerable depths, despite the fitfully recurrent additions from rains. It is at least probable that this process of dew- formation within the soil materially assists capillarity in effecting a measurably uniform vertical distribution of mois- ture. (See also page 207, chapter 11). Plant-development under different Temperature—Condi- tions.—In the arctic regions the ground, frozen in winter to unknown depths, may thaw to only three to five feet during the summer, notwithstanding the great length and continuous sunshine of the arctic day. The shallow-rooted arctic flora develops very rapidly under the influence of the continuous daylight and heat, in the course of from five to eight weeks. The seeds of these plants must, of course, be capable of ger- minating at very low temperatures; and as a matter of fact, we find that both in the arctic regions and in the higher mount- ains, certain plants are found growing and blooming on slopes flecked with snow; each plant surrounded by a small circle of bare ground, where the snow has been melted under the influence of the dark-tinted earth and leaves. It is clear that here germination has occurred, the foliage has been formed, and the roots have been exercising their vegetable functions, in ground soaked with water practically ice-cold. Germination of Seeds.—While wild plants of special adapta- tion may thrive in very low (or high) temperatures, it is also true that few of our cultivated plants will germinate, and still less grow thriftily, at such low temperatures. The limit be- 310 SOILS. low which most cultivated plants may be considered as remain- ing practically inactive lies between 4.4 and 7.2° C. (40 and 45° F.). Few tropical plants will germinate much below 23.8° (75° F.) and in some cases not below 35° Cent. (95° F.). Even maize and pumpkins, according to Haberlandt, germinate most rapidly between 35 and 38.3° C. (95 and ro1° F.), while for wheat, rye, oats and flax the best temperature for germination lies between 21.1 to 26.1 (70 to 79°). Un- der the most favorable conditions of temperature and moisture, some small seeds which readily absorb moisture will germinate in from twenty-four to forty-eight hours, while at a lower temperature they may require from three days to two weeks. Thus Haberlandt found that while oats would germinate in two days at a temperature of 17.2 to 17.5° C. (63° to 63.5°), it took a full week for germination when the temperature was only 5° C. (41° F.). It is obvious that seeds remaining inert in the soil for such lengths of time will be subject to a variety of vicissitudes that may injure or destroy their vitality. There are many bacteria and fungous parasites which at low tem- peratures are perfectly capable of attacking and destroying the water-soaked seed. There is thus for each plant, from the lowest to the highest, a certain temperature most favorable to development; and both above and below this, the vegetative activity is seriously interfered with or wholly checked. A knowledge of these limits is manifestly of the utmost practical importance. The influence of too high a temperature in preventing the germina- tion of cinchona seed from India, was curiously exemplified when it was subjected to a supposedly favorable steady temperature of 23.8°C. (75°F.) under otherwise most favorable conditions. Not a single one came up in the course of six weeks, and the box in which it had been sown was put away outside of the hothouse as a failure. Within two weeks a full stand of seedlings was obtained, at temperatures ranging between 12.7 and 15.5°C. (55° and 60°F.). The fact that the cinchona is a tree of the lower slopes of the Andes (three to five thousand feet) although at home strictly within the tropics, explains the apparent anomaly. ’ BARD IRD: CHEMISTRY OF SOILS. CHARTER Vie THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS IN RE- LATION TO CROP PRODUCTION. THE chemical constituents of soils have been incidentally mentioned and discussed above, both in connection with the processes of soil-formation, and with the minerals that mainly participate therein. The manner of their occurrence and their relations to plant life, so far as known, must now be consid- ered more in detail. HISTORICAL REVIEW OF SOIL INVESTIGATION. While the obvious importance of the physical soil-conditions has long ago rendered them subjects of close study by Schtb- ler 1 Boussingault and others, the chemistry of soils was very generally neglected for a considerable period, after the hopes at first entertained by Liebig that chemical analysis would furnish a direct indication and measure of soil fertility, had been sorely disappointed in respect to the only soils then in- vestigated, viz., the long-cultivated ones of Europe. The re- sults of chemical analysis sometimes agreed, but as often pointedly disagreed, with cultural experiences; so that after the middle of the nineteenth century, but few thought it worth while to occupy their time in chemical soil analysis. Popular Forecasts of Soil Values.—In newly-settled coun- tries, and still more in those yet to be settled, the questions of the immediate productive capacity, and the future durability of the virgin land are the burning ones, since they determine the future of thousands for weal or woe. This need has long ago led to approximate estimates made on the part of the settler, 1 The early work of Schiibler on soil physics, published at Leipzig in 1838 under the title of “Grundsatze der Agrikulturchemie ” and now almost inaccessible outside of old libraries, is remarkable as having anticipated very definitely much that has since been brought forward and elaborated anew. He is really the father of agricultural physics. 313 314 SOILS. by the observation of the native growth, especially the tree growth; and where this consists of familiar species, normally developed, such estimates on the part of experienced men, based on previous cultural experience, are generally very ac- curate; so much so that in many of the newer states they have been adopted in determining not only the market value, but also the tax rate upon such lands, their productiveness, and probable durability being a matter of common note. Thus in the long-leaf pine uplands of the Cotton States, the scattered settlements have fully demonstrated that after two or three years crop- ping with corn, ranging from as much as 25 bushels per acre the first year to ten and less the third, fertilization is absolutely necessary to farther paying cultivation. Should the short-leaved pine mingle with the long-leaved, production may hold out for from five to seven years. If oaks and hickory are superadded, as many as twelve years of good production without fertilization may be looked for by the farmer; and should the long-leaved pine disappear altogether, the mingled growth of oaks and short-leaved pine will encourage him to hope for from twelve to fifteen years of fair production without fertilization. Corresponding estimates based upon the tree growth and in part also upon minor vegetation, are current in the richer lands also. The “ black-oak and hickory uplands,” the “ post-oak flats,” “hickory bottoms,” “‘ gum bottoms,” “ hackberry ham- mocks,” “* post-oak prairie,’ “ red-cedar prairie,’ and scores of other similar designations, possess a very definite meaning in the minds of farmers and are constantly used as a trust- worthy basis for bargain and sale, and for crop estimates. Moreover, experienced men will even after many years’ cul- tivation be able to distinguish these various kinds of lands from one another. Cogency of Conclusions based upon Native Growth.—Since the native vegetation normally represents the results of secular or even millennial adaptation of plants to climatic and soil-conditions, this use of the native flora seems eminently rational. Moreover, it is obvious that if we were able to in- terpret correctly the meaning of such vegetation with respect not only to cultural conditions and crops, but also as regards the exact physical and chemical nature of the soil, so as to THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 315 recognize the causes of the observed vegetative preferences: we should be enabled to project that recognition into those cases where native vegetation is not present to serve as a guide; and we might thus render the physical and chemical examination of soils as useful practically, everywhere, as is, locally, the observation of the native growths. To a certain extent, such knowledge would be useful in determining the salient characters of cultivated soils, also; and would be the more useful and definite in its practical indications the more nearly the cultural history of the land is known, and the less the latter has been changed by fertilization. For, so soon as the first flush of production has passed, the question of how to fertilize most effectually and cheaply demands solution. It was from this standpoint, suggested by his early experi- ence in the Middle West and subsequently most impressively presented to him in the prosecution of the geological and agri- cultural survey of Mississippi, that the writer originally un- dertook, in 1857, the detailed study of the physical characters and chemical composition of soils. It seemed to him incred- ible that the well-defined and practically so important distinc- tions based on natural vegetation, everywhere recognized and continually acted upon by farmers and settlers, should not be traceable to definite physical and chemical differences in the respective lands, by competent, comprehensively-trained scien- tific observers, whose field of vision should be broad enough to embrace concurrently the several points of view—geological, physical, chemical and botanical—that must be conjointly con- sidered in forming one’s judgment of land. Such trained ob- servers should not merely do as well as the “ untutored farmer,” but a great deal better. “ Ecological” studies—Yet thus far we vainly seek in gen- eral agricultural literature for any systematic or consistent studies of these relations. We do find “ ecological ”’ lists of trees and other plants, or “ plant associations,” growing in cer- tain regions or land areas, described in some of the general terms which may refer equally well to lands of profuse pro- ductiveness, or to such as will hardly pay for taxes when cul- tivated. Or when the productive value is mentioned, the probable cause of such value is barely alluded to, even con- jecturally, unless it be in describing the “ plant formations ” 316 SOILS. as xerophytic, mesophytic or hydrophytic, upon the arbitrary assumption that moisture is the only governing factor; wholly ignoring such vitally important factors as the physical texture of the soil, its depth, the nature of the substrata, and the (oftentimes abundantly obvious) predominant chemical nature of the land. And on the other hand, we find even public sur- veys proceeding upon the basis of physical data alone, practic- ally ignoring the botanical and chemical point of view, and inferentially denying, or at least ignoring, their relevancy to the practical problems of the farm. * Early Soil Surveys of Kentucky, Arkansas and Misstssip pt. —Among the few who during the middle of the past century maintained their belief in the possibility of practically useful results from direct soil investigation, were Drs. David Dale Owen and Robert Peter, who prosecuted such work exten- sively in connection with the geological and agricultural sur- veys of Kentucky and Arkansas; and the writer, who carried out similar work in the states of Mississippi and Louisiana, with results in many respects so definite that he has ever since regarded this as a most fruitful study, and has later continued it in California and the Pacific Northwest. This was done in the face of almost uniform discouragement from agricultural chemists until within the last two decades; with occasional severe criticisms of this work as a waste of labor and of public funds. Investigation of Cultivated Soils—All this opposition was largely due to the prejudices engendered by the futile attempts to deduce practically useful results from the chemical analysis of soils long cultivated, without first studying the less complex phenomena of wirgin soils; and these prejudices persisted longest in the United States, even though in Europe the re- action against the hasty rejection of chemical soil work had begun some time before; as is evidenced by the methods em- ployed at the Rothamsted Experimental Farm in England, the Agricultural College of France, the Russian agronomic sur- veys, and at several points in Germany. In none of these cases, however, more than the purely chemical or physico- chemical standpoint was assumed; although in Russia at least, 1 Bull. 22, Bureau of Soils, U. S. Dept. of Agriculture. THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 317 virgin soils were easily obtainable and their native growth verifiable; and were actually in part made the subject of chemi- cal investigation. In the course of their work, Owen and Peter always care- fully recorded the native vegetation of the soils collected; but neither seems to have formulated definitely the idea that such vegetation might be made the basis of direct correlation of soil-composition with cultural experience. Owen repeatedly expressed to the writer his conviction that such a correlation could be definitely established by close study; but early death prevented his personal elaboration of the results of his work. Peter likewise stoutly maintained to the last his conviction that soil analysis was the key to the forecasting of cultural possi- bilities; but not being a botanist he did not see his way to put such forecasts into definite form. Change of Views. In the United States as well, the ancient prejudices have now gradually given way before the urgent call for more de- finite information than could otherwise possibly be given to farmers by the experiment stations, most of whose cultural experiments, made without any definite knowledge of the na- ture of the soil under trial, were found to be of little value outside of their own experimental fields. Even the multipli- cation of culture stations in several states, unaccompanied by soil research, is found to be a delusive repetition of the same inconclusive, random experimenting, since it takes into con- sideration only the climatic differences, but leaves out of con- sideration the potent factors of soil quality and soil variations. At most these were usually mentioned by them in such inde- finite terms as “a clay loam,” “a coarse sandy soil,” “ gray sediment land,” and the like; frequently not even with a state- ment of the depth and character of the subsoil and substrata, much less of their geological derivation or correlations. Thus any one not happening to be personally acquainted with the land in question would be wholly without definite data to cor- relate the results with his own case. It is quite obvious that even if only to make possible the identification of new lands with others that have already fallen under cultural experience, 318 SOMES: and can therefore afford useful indications to the new settler, a close physical and chemical characterization of lands should be made the special object of study by the experiment stations and public surveys, particularly in the newer states. Advantages for Soil Study offered by Virgin Lands.— Among the special advantages, then, offered by virgin soils for the study of the correlations of soils and crops, the usual exist- ence of a native flora, representing the results of secular adapt- ation, is of fundamental importance. As it is at this time still historically known of most lands west of the Alleghenies what was their original timber growth, it is clear that their original condition can still be ascertained by comparison with uncul- tivated lands of similar growth, usually not very far away; and as their cultural history also is largely within the memory of the living generation, the behavior of such lands under cul- tivation is known or verifiable. Foremost among the data thus ascertainable is the duration of satisfactory crop produc- tion, and its average amount. To ascertain these surviving data by inquiry among the farming population should be among the foremost duties of those connected with soil sur- veys; and persons temperamentally unable to enlist the farm- er’s sympathy and interest in such inquiries must be consid- ered seriously handicapped, no matter what their scientific qualifications may be. In no quest is it more literally true that there is no one from whom the earnest inquirer may not learn something worth knowing. Practical Utility of Chemical Soil-Analysis; Permanent Value vs. Immediate Productiveness—In many existing trea- tises so much emphasis is given to the alleged proofs of the in- utility of chemical soil examination in particular, that a special controversion of these arguments seems necessary, in connec- tion with a detailed statement of what can, and in part has been, done in that direction. Hence the often-repeated allusion, in the sequel, to points bearing on this question. Hence, also, the detailed discussion of many points which in most agricultural publications are given only passing notice. In all these discussions the difference between the ascertain- ment of the permanent-productive value of soils, as against that of their immediate producing capacity, must be strictly | THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 319 kept in view. The former interests vitally the permanent settler or farmer; the latter concerns the immediate outlook for crop production, the ‘ Dungerzustand”’ of the Germans. The methods for the ascertainment of these two factors are wholly distinct, even though the results and their causes are in most cases intimately correlated. The failure to observe this distinction accounts for a great deal of the obloquy and reproach that has in the past so often been heaped upon chem- ical soil-analysis and its advocates. PHYSICAL AND CHEMICAL CONDITIONS OF PLANT GROWTH. While it is true that plants cannot form their substance or develop healthy growth in the absence or scarcity of the chem- ical ingredients mentioned on page xxxi of this volume, it is also true that they cannot use these unless the physical condi- tions of normal vegetation are first fulfilled. Both sets of con- ditions are intrinsically equally important and exacting as to their fulfilment; and the farmers’ task is to bring about this concurrence to the utmost extent possible. The chemical in- gredients of plant-food can, however, be artificially supplied in the form of fertilizers, should they be deficient in the soil; but as has been shown in the preceding pages, it is not always possible to correct, within the limits of farm economy, phy- sical defects existing in the land. Hence, however important is the natural richness of the soil in plant-food, the first care should always be given to the ascertainment of the proper phy- sical conditions in the soil, subsoil and substrata. Without these, oftentimes, no amount of cultivation, fertilization and irrigation is effective in assuring profitable cultural results. Condition of the Plant-food Ingredients in the Soil.—But even the abundant presence of the plant-food ingredients, as shown by analysis, will not avail, unless at least an adequate portion of the same exists in a form or forms accessible to plants. Of course this condition would seem to be best ful- filled by the ingredients in question being in the water-soluble condition. But in the first place, plants are quite sensitive to an over-supply of soluble mineral salts, as is evidenced by the injurious effects produced by the latter in saline and alkali lands. Furthermore, substances in that form would be very 320 SOILS, liable to be washed or leached out of the soil by heavy rains or irrigation, and would be lost in the country drainage. It is therefore clearly desirable that only a relatively small pro- portion of the useful soil-ingredients should be in the water- soluble or physically absorbed condition, but that a larger sup- ply should be present in forms not so easily soluble, yet ac- cessible to the solvent action which the acids of the soil and of the roots of plants are capable of exercising. This virtually available supply we may designate as the reserve food-store. Finally, there is practically in all soils a certain proportion of the sotl-minerals in their original form, as they existed in the rock-materials from which the soil was formed. These minerals being usually in a more or less finely divided or pul- verulent condition, they are attacked much more rapidly by the chemically-acting “ weathering’ agencies, viz., water, oxygen, carbonic and humus acids, than when in solid masses; and thus, transformation of the inert rock-powder into the other two classes of mineral soil-ingredients progresses in naturally fertile soils with sufficient rapidity to produce, in a single season, sensible and practically important results, known as the effects of fallowing. The Reserve.—The nature of these processes has been dis- cussed in chapters I to 4; and it will be remembered that two of their most prominent results are the formation of clay, and of zeolitic-compounds, the latter being, as heretofore stated (pp. 36 ff) hydrous silicates of earths and alkalies, easily de- composable by acids, and also capable of exchanging part or the whole of such basic ingredients with solutions of others that may enter the soil. These zeolitic compounds therefore fulfil two important functions in the premises, viz.: a ready yielding-up of part of their ingredients to acid solvents, and a tendency to fix, by exchange, a portion or the whole of the soluble compounds that may be set free in, or brought upon the land. The first-mentioned property is of direct avail in that the soil-humus forms, and the roots of plants exude, acid solvents on their surface, and can thus draw upon the reserve store of food; the second tells in the direction of preventing the waste of water-soluble manurial ingredients supplied to, or formed in the soil. (See above, chapter 3, page 38). THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 321 The reserve food-store may then be placed under the fol- lowing heads: Hydrous or “ geolitic”’ silicates, from which dilute acids can take up the bases potash, soda, lime and magnesia. These silicates may be in either the gelatinous or powdery form; in the former case they may also occlude water-soluble sub- stances. Carbonates of lime and magnesia, which are readily dis- solved by carbonated water as well as by the vegetable acids. Phosphates of lime and magnesia, not very readily soluble in carbonated water, but more readily attacked by the acids of the soil and of plant roots; thus supplying phosphoric acid to plants. The more finely divided they are the more readily they are dissolved; some soils containing only crystalline needles of apatite (see chap. 5, p. 63) only are nevertheless poor in available phosphoric acid. The natural phosphates of iron and alumina are practically insoluble in all solvents at the disposal of vegetation and though present in considerable amounts in some soils, (see chapter 19, page 355), may be considered as being permanently inert, and therefore not to be counted among the soil resources for plant nutrition. As yet no artificial process by which their phosphoric acid can be made available within the soil, has been discovered. Water-soluble Ingredients——As regards these it has already been explained that they are largely retained in the condition of purely physical adsorption, as in the case of charcoal or quartz sand, through which sea water filters and is thereby partially deprived of its salts. But these can be gradually withdrawn by washing with pure water alone, and still more easily when stronger solvents are used. Since the soil-water is always more or less charged with carbonic acid, and the roots themselves secrete carbonic as well as stronger acids in their absorption of mineral plant-food, there is no difficulty about explaining the manner in which such physically con- densed ingredients are taken up.* 1 Whitney (Bull. 22, U. S. Bureau of Soils) claims on the basis of a large number of (three-minute) extractions of soils made with distilled water, that these solutions are essentially of the same composition in all soils; that all soils contain enough plant-food to produce crops indefinitely; and that the differences in production 21 ‘ 322 SOILS. Recognition of the Prominent Chemical Character of Soils. In a former chapter the soils formed from the several minerals and rocks have been discussed in a general manner. We can as a rule obtain some insight into the nature of any soil which we can trace to its parent rock or rocks, if we are acquainted with the composition of the latter. Similarly, but in a much more direct manner, we can ob- tain a strong presumption as to the nature of any soil by de- termining the undecomposed minerals present in it. In all ordinary cases the presumption must be that the decomposed portion of the soil has been derived from the minerals still found in it. Of course it may happen in the case of lands de- rived from widely distinct and distant regions that no such characteristic minerals can be found; this is very commonly true of the soils forming the deltas of large rivers, in which sometimes the only remaining recognizable mineral is quartz in its several forms, with occasional grains of such hardy minerals as tourmaline, garnet, etc. Apart from such cases, the hand lens or the microscope permits us to recognize in most soils the minerals that have mainly contributed to their formation, thus also gaining a clew to their prominent chem- ical nature. Such recognition sometimes involves, of course, a somewhat intimate knowledge of mineralogy; yet a little practice will enable almost any one to identify the more important soil- forming minerals, under the lens or microscope, according to the degree of abrasion or decomposition they may have un- dergone. The details of such researches lie outside of the limits of this treatise, but some general directions on the sub- ject are given farther on.* Acidity, Neutrality, Alkalinty.—A test never to be omitted are due wholly to differences in the moisture supply, which he claims is, aside from climate, the only governing factor in plant growth. The tables of analytical results given in Bull. 22 fail to sustain the first contention; the second is pointedly contradicted both by practical experience, and by thousands of cumulative culture experiments made by scientific observers ; the third fails with the second, except of course in so far as an adequate supply of moisture is known to be an absolute condition both of plant growth, and the utilization of plant-food. It is moreover well known that it is not water alone, but water impregnated more or less with humic and carbonic acids, that is the active solvent surrounding the plant root. 1 See Appendix B. THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 322 is that of the reaction of the soil on litmus or other test paper, to ascertain its acid, neutral or alkaline reaction. Should the latter occur quickly (by the prompt blueing of red litmus paper), “ black alkali’ would be indicated; but a blueing after 20 to 30 minutes means merely that a sufficiency of lime car- bonate is present. An acid reaction (the reddening of blue litmus paper) of course indicates a “‘ sour”’ soil (see chap. 8, page 122). Chemical Analysis of Soils—When the observations men- tioned above give no very decisive results or inferences as to the soil’s chemical character, the more elaborate processes of qualitative and quantitative chemical analysis may be called in. It would seem at first sight that these ought to yield very de- finite results to guide the cultivator; yet such is by no means always the case. Both the previous history of the land, and the method of anaylsis, influence materially the practical utility of the results of chemical soil analysis. The cause of this uncertainty becomes obvious when we consider the three groups of ingredients outlined above, viz., the insoluble or unavailable, wholly undecomposed rock mine- rals; the “ reserve,” consisting of compounds not soluble in water but soluble in or decomposable by weak acids; and the water-soluble portion, either actually dissolved in the water held by the soil, or held by the soil itself in (physical) absorp- tion. While the latter portion is directly and immediately available to plants, the amounts thus held are usually quite small, and (outside of alkali lands) would rarely suffice for the needs of a crop during a growing season.t This demand must be materially supplemented by what can be made avail- able from the soil minerals and the “ reserve’ by weathering, conjoined with the direct action of the acids secreted from the plant’s root-hairs upon the soil particles to which they are attached. It is obvious that the greater or less abundance of the plant-food in the soil-material upon which these processes 1 The investigations of King (On the Influence of Soil Management upon the Water Soluble Salts in Soils and the Yield of Crops, Madison, 1903) show that from some soils at least, a sufficiency of plant-food ingredients for a season’s crop may be dissolved by distilled water alone, if the soil be repeatedly leached and dried at 110°. Whether such a supply can be expected under field conditions, remains to be tested. 324 SOILS. may be brought to bear, must essentially influence the ade- quacy of the plant-food thus supplied. Moreover, the greater or less extent to which these sources may have been drawn upon previously in the course of cultivation, will similarly in- fluence that adequacy, on account of the diminution of the readily available supply. Water-soluble and Acid-soluble Portions most Important.— It thus seems that while the undecomposed rock minerals are indicative of the nature of the soil, but not directly concerned in plant nutrition, the most direct interest attaches to the water- soluble portion, and the acid-soluble reserve. Both of these can, of course, be withdrawn from the soil by treatment with acids of greater or less strength; and it would seem that if we knew just what is the kind and strength of the acid solvent employed by each plant, we could so imitate their action as to determine definitely whether or not the soil contains an adequate or deficient supply of actually available food for the coming crop. We Cannot Imitate Plant-root Action—lIn this, however, we encounter serious difficulties. The acids secreted by the plant roots are not the only solvents active in the dissolution of plant-food ; as yet we know the nature of only a few; and even these, instead of acting for a long time (season) on a relatively small number of soil particles touched by the root-hairs, can in our laboratories only be allowed to act for a short time on the entire soil-mass. Clearly, the results thus obtained can- not be a direct measure of the amount of plant-food which a plant may take up in a given time; we can only gain com- parative figures. These, however, can be utilized by com- parison with actual cultural experience obtained in similar cases. Cultural experience must, of course, be the final test in all these questions; and it is generally more fruitful to investi- gate the causes underlying such actual practical experience, than to attempt to supply, artificially, the supposed conditions of plant growth. The latter are so complex and so difficult of control, that the results obtained by synthetic, small-scale experiments are constantly liable to the suspicion that they THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 325 are partly or wholly due to other causes than those purposely supplied by the experimenter. Analysts of Cultivated Soils.—It is also clear that in view of the in- evitable complexity of the conditions governing vegetable growth, we should whenever feasible proceed from the more simple to the more complex. The failure to conform to this rule in soil investigation has been the cause of an enormous waste of energy and work bestowed, at the very outset, upon the most complex problem of all, viz., the investi- gation of soils long cultivated and manured ; lands which, having been subject perhaps for centuries to a great and wholly indefinite variety of crops and cultural practices, had thereby become so beset with artificial conditions that without a previous knowledge of what constitutes the normal régime in natural soils, the correlation of their chemical consti- tion, as ascertainable by our present methods, with their production under culture, became as complex a problem as that of motions of three mutually gravitating points in space. Neither can be solved by the ordinary processes of analysis, chemical or mathematical. Nevertheless, though it was at one time contended that the minute proportion of plant-food ingredients withdrawn from soils by cultivation could not be detected by quantitative analysis, numerous examples have shown that with our present more delicate methods this can in most cases be done, though not always after a single year’s crop. Methods of Soil Analysis.—The more or less incisive solvent agents used in extracting a soil for analysis will of course produce results widely at variance with each other. When fusion with carbonate of soda, or treatment with fluohydric acid is resorted to, we obtain for each soil-ingredient the sum of all the amounts contained in each of the three categories—the unchanged minerals, the zeolitic ‘‘ reserve,” and the water-soluble portion. It was early recognized that the results of such analyses bear no intelligible relation to the productive capacity of soils; for pulverized rocks of many kinds, or volcanic ashes freshly ejected and notoriously incapable of supporting plant growth, might be made to give exactly the same composition. The amounts of plant- food ingredients thus shown might be several hundreds or thousands of times greater than what one crop would take from the soil, and yet not an ear of grain could be produced on the material. The only case in which any useful information could be thus obtained would be that of the absence, or great scarcity, of one or more of the plant-food in- gredients. 326 SOILS. The next step was to use in soil analysis acids of such strength as to dissolve all the zeolitic (and water-soluble) portion, leaving the un- weathered soil minerals behind; it being assumed that the prolonged action of the roots and soil-solvents would in the end act similarly to the acids employed, such as chlorhydric or nitric acids. But here also the results of analysis very commonly failed to cor- respond to cultural experience in the case of cu/tvated soils; which frequently failed utterly to produce satisfactory crops even when the acid-analysis had shown an abundance of plant-food ingredients. Upon this evidence, this method of soil investigation was also condemned as being of little or no practical utility; and this has ever since been a widely prevalent view. The preferable investigation of cultivated soils was due to the fact that they are practically the only ones available in the countries where the study of agricultural science was then being prosecuted; and the paucity of useful results there achieved discouraged the undertaking of similar researches where, as in the United States, the materials for the investiga- tion of the simpler cases—those of unchanged, natural or virgin soils—were readily accessible. It was not apparent on the surface that the indefinitely varied conditions introduced by long culture would inevitably cause this lack of definite correlation between the immediate productive capacity of a soil and the composition of its acid-soluble portion, and that yet the same might not be true of natural, uncultivated soils, which have all been subjected, alike, only to the natural pro- cesses of weathering, and to the annual return of nearly the whole of the ingredients withdrawn by plant growth. Following the failure of the treatment with strong acids to yield with cultivated soils results definitely correlated with cultural experience, numerous attempts were made to gain better indications by the employment of weaker acid solvents. The pure arbitrariness of such diluted solvents was equaled by the total indefiniteness and irrelevance of the results with different soils. Only two rational alternatives seem to re- main, viz., either to push the extraction to the full extent be- yond which action becomes so slow as to clearly exclude any farther effective action of plant acids; or else to use the latter themselves at such strengths as by actual experiment is found THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 327 to exist in their root sap. The first alternative aims to ascer- tain the permanent productive values of soils; the latter to test their tmmediate productive capacity. Both alternatives are purely empirical, and derive their only claim to practical value from their accordance with practical experience (see chap- ter 19). THE SOLVENT ACTION OF WATER UPON SOILS. The almost universal solvent power of pure water has already been alluded to in chapter 2 (see p. 18), and illustrated by the analyses of drain and river waters. While these con- vey a general idea of the chief substances dissolved and car- ried off, the direct investigation of the solutions actually ob- tainable from the soil by longer treatment and with no more water than is compatible with the welfare of ordinary crops, necessarily gives somewhat different results. For when drains flow during or after heavy rains the water has not time to become saturated. The following data afford a clearer in- sight into the actual and possible solvent effects of water in the soil, and its possible adequacy to plant nutrition unaided by acid solvents. Extraction of Soils with Pure Water.—Eichhorn and Wun- der treated soils from Bonn, and from Chemnitz (Saxony) re- spectively for ten days and four weeks with about one-third of their weight of water; the solutions thus obtained contain in 1,000,000 parts: Bonn. Chemnitz. STUNGBhe o'o URC OOO EE BOBS Be OTC LOC Ene Steen 48.0 25.7 RacALCUS FAME (Ea (©) Fareye ctetspatcse icv er arove eleieera re: 8 sia sve avelovaleieterereres 115.4 75 ‘S162, (NEKO Ba arictiarce BEB OO CEE REC E GPA aC eEe 11.0 30.4 ILintns: (Cel) So een ee oc ere aoe OO DC COe eI eD Cen Cn are 128.0 $3.6 REREAD ONTO) liens! os siainc eitelslsia gale c's Sav e's wleie 38.4 37-4 Regoriel COLL lrOn. (PegOs)inr.osic vicis:e odes se souls vedas et Trace 11.7 uedlointings, (UMEOS) 2 bog GOBCOn CORE oe RICE One ete ? ? Phosphoric acid (P2Os)..........+ pecvahaovefaralatetnvete eich sue 31.0 Trace PATE GtA CIN (S,Oa) erg nasi siaelc co cersiaroieve ig e's orerbiors.e ecots.8 6 100.2 Chllorid of Sodium (NaCl).......-------seccc cece. 38.6 ‘47.6 328 SOLES. These figures differ widely in most respects from those given for drain and river waters. Potash especially is far more abundantly present in the Bonn soil solution than in the drain water, and so is phosphoric acid; while lime is not widely dif- ferent. Eichhorn therefore calculates that with a reasonably adequate supply of water, these ingredients would fully suffice for a full crop of wheat. The Chemnitz soil, on the other hand, does not yield enough plant-food for more than a very small crop upon the same assumptions. Continuous Solubility of Soil-ingredients——It seems to be impossible to exhaust a soil’s solubility by repeated or con- tinuous leaching with water. This was demonstrated in 1863 and 1864 by Ulbricht * and by Schultze;? their general con- clusions have quite lately been corroborated by King,® as the result of extended and very careful investigations. Schultze experimented on a rich soil from Mecklenburg, by continuous leaching with distilled water for six days, one liter passing every twenty-four hours, with the following results. RICH SOIL FROM MECKLENBURG (Schultze.) 1,000,000 PARTS OF EXTRACTS CONTAINED: . | ee ————————————— en | ; a < Total matter| Organic and I 4 Phosphoric dissolved. volatile. morgenic: acid. ; Hinstaexthactic cj-jsiccrsler- 535-0 340.0 195 5-6 ¥ SECONUAOs Bre. srisiersselere 120.0 57-0 63 8.2 Atavigel” "Glos Gdcacoaaoue 261.0 IOI.0 160 8.8 lUOWIAIN CES Goooocaoscc 203.0 83.0 120 7.5 ifthe dos Ueecrictetseere 260.0 82.0 178 6.9 SHoqd GS SéaGonobode 200.0 77.0 12 4.4 mo alllerercreisvevelororeraictel= 1,579.0 740.0 839 41.4 It thus appears that while the first extraction removed the main portion of the organic matter, the inorganic matters dis- solved were not greatly diminished in subsequent leachings; and that phosphoric acid continued to come off to the last. The rich soil used in this case gave results corresponding in 1 Vers. Stat. V. p. 207. 2 Tbid. VI. p. 411. 3 Proc. Ass’n Prom. Agr. Sci. 1904. ee a =—— THE, PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 329 general to these from the Bonn soil, in the previous table. From a poorer soil similarly treated by Ulbricht, described by him as a ferruginous sand from Dahme, the leaching of which was continued for thirty days in periods of three days each, with a total of forty times its weight of water, the results were as follows: SOIL OF LOW PRODUCTION FROM DAHME (Ulbricht). THE SEVERAL EXTRACTS CONTAINED IN 1,000,000 PARTS: First | Second | Third | Fourth | Fifth Sixth Extract.) Extract.| Extract.) Extract.) Extract.| Extract. Rotashysteociciak.. isc ee siete 7 6 7 3 SOdai sie creristeteesaie veltous 4I II 26 17 8 IUIMNEb ab cdbowasaocsaoeer 96 70 55 48 62 ia onESIateec aq. rcustetislen 14 10 9 7 8 Phosphoric acid..........| trace 2 trace I BOt al St risteteteretstsetseis ele 158 99 97 80 70 II It will be seen that there is a considerable difference both in the total amounts of matters dissolved and in the phosphoric acid taken out by the water, as compared with the rich soil treated by Schultze. The uniformity of the amounts of potash removed at the successive leachings is remarkable. King’s Results —The same general features are again strik- ingly illustrated by King’s results, as given in the following table. King’s first leachings were always made by shaking up the soil with ten times its dry weight of water for three minutes, then after subsidence filtering the solutions through a Chamberland (porcelain biscuit) filter, and then (without evaporation) determining the ingredients dissolved, by very delicate, mostly colorimetric methods. Subsequent leachings were made by packing the soil around the filters and washing with five times the weight of water, taking about fifteen minutes each time; but drying the soil at 120 degrees C. between successive leachings. 330 SOILS. WATER EXTRACTION OF SOILS OF LOW AND HIGH PRODUCTION, By F. H. KING. PARTS PER MILLION. 2 = = Ry . ao & C) fe) : > fe) 3 = 2 n 2 = > od a a ie Vil ec ee ieee 6S! || ei (BS ee ee Glaee ee #08) 2 le | so) eo aoe ae ° 42 = ec Ci Bc = A a er Ne A, a Oo a SOILS OF LOW PRODUCTION. Sassafras sandy § 1 extraction | 12.62] 74.39] 17.82 | 18.03 7.41] 53.84] 13.94] 1 5.60 soil. { 11 extractions] 218.25 | 135-35] 147-45 | 21.76] 64.16 | 203.96 | 221.33 | 2 170.20 Norfolk, al 1extraction | 21.17] 58.30] 22.91 | 30.64] 130.15] 42.82] 20.42] 1 8.24 Carolinasandysoil | 11 extractions} 166.08 | 162.98] 125.00| 27.11 | 80.34 | 172.42 | 148.52] 2 122.20 Average. 192.60] 149.20] 136.23 | 24.44] 72.25 | 126.13 | 184.93] 2.- | 146.20 SOILS OF HIGH PRODUCTION. Janesville, si rextraction | 25.35] 135.30] 51.72] 55.10] 16.96]125.43| 29.31] 2.67 | 40.28 Loam. 11 extractions |} 313.70 |1120.30| 500.60 | 51.42 | 418.85 | 592.75 | 472.95 | 0.00 | 414.50 Hagerst’wn, Pa textraction | 21.73] 165.25| 76.88] 25.72] 11.51 | 187.59] 97-09] 1.67 | 21.17 Clay loam. 11 extractions] 301.55 | 967.80] 463.15 | 96.04 | 136.21 | 502.82 | 620.00 | 0.00 | 283.80 Average. 307.60 |1044.05] 487.88 | 73.73 | 277-03 | 547-79 | 546.48 | 0.00 | 349.15 King’s observations show strikingly both the continuous solubility of the soil, and the differences between the solutions derived from soils of low and high productiveness; wholly negativing the contention of Whitney that the solutions from different soils are of practically the same composition.? King also calls attention to the fact, shown in other experi- ments made in the extraction of soils without intermediate dryings, that the amounts extracted were very much less in sub- sequent than in the first extraction; doubtless because the evap- oration from the soil particles had carried a large proportion of soluble matters to the surface, whence it was readily abstracted by the first touch of the solvent water. At each drying not only are the soluble waters again drawn to the surface, but heating a soil even to 100° renders additional amounts of soil ingredients soluble both in water and in acids. It can scarcely be doubted that the intense heating which desert soils undergo during the warm season is similarly effective; and thus the great productiveness of these soils under irrigation, and the marvelously rapid development of the native vegetation when 1 Bulletin No. 22, Bureau of Soils, U. S. D. A. THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 331 rains moisten the parched soil, is in part at least accounted for by this immediate availability of a large supply of plant-food. Composition of Janesville loam.—In connection with the above data given by King, it is interesting to note the compo- sition of the soil in the above table yielding the highest pro- portions of soluble matter, when analyzed according to the method practiced by the writer (see chap. 19, p. 343). This analysis was made under the supervision of Professor Jaffa in the laboratory of the California Experiment Station by Assistant Charles A. Triebel. Loam Soil from Janesville, Wisconsin ; sample sent by Prof. F. H. King, Madison, Wis. This soil is a light friable loam, resembling the northern Loess in color and texture ; it is highly productive. It is underlaid at 5 feet by the drift gravel of that region, enclosing much calcareous material, which evidently has had a large share in the formation of this soil, just as is the case in southern Michigan. The soil, when dried at 110° C., consisted of CHEMICAL ANALYSIS OF FINE EARTH. Insolublesmatte tec. or. cece 12) 101 sie) s)eteiciacielerics tisers ; SOlubleysilicakire syaicrsiarsteteterere aisrateVereisisiste actors seers oe Botashi(Kc@s)icacn. cos ancesiosoacte ers stnewie ae 59 Soda (iNas@) ives cera cloneeiie es cevsiutanelecsees 04 ILitins: (CAO) choi uedobes sogcaacosnconuss coved 83 Mapriesial (MgO). cic). uth c-< lciscielseelcte cia sycieores ack Br.jox, of Manganese \(Mns0))i..1-..2. 00-16-10 .08 Reroxidiofelrony (Hes Oar ertieierreliclotet toterelerelel= 3-60 Alumina (ATs Os) eee teraleye cava tercletclers cel siete oeteiote 5.26 Phosphone acid) (Ps@§)\se-p ewes sctelelelelelsisiseicre .06 Suilmive Evetel (QKO\saaa ae ooouedousooougndouode 10 Wiaterandroreanic matterorracisieierjieeirciictc cies 8.72 eo tallsecciayeisre| stops ohalstolsiaie oh ieetsiaetererste 100.03 It will be noted that in accordance with the interpretation of analyses of soils as given in the next chapter, this is a high-class soil in every respect, except that its content of phosphoric acid is only just above the lower limit of sufficiency. But as is also shown below, in presence of a large supply of lime even lower percentages of phosphoric acid are adequate for long-continued production (see chap. 19, pp. 354, 365)- by rendering the substance more freely available ; and that this is true in this case is shown by the result of King’s leachings, in which this soil yields a maximum of 419 parts per million as against 80 and 64 parts in the poor soils, which at the same time yield only one fourth as much of lime. Unfortunately we have no full analyses of these other 332 SOILS. < soils for comparison ; although they have served as a basis of comparison for years in the Washington Bureau of Soils. Solubility of Soil Phosphates in Water.—The solubility of the phosphate contents of soils has been elaborately investi- gated by Th. Schloesing fils.1 He found in the case of a num- ber of soils investigated by him that the amount of phosphoric acid P2O5 in the soil-solution ranged from less than one mil- lionth (or one milligram per liter of water) in a poor soil, to over three milligrams in a rich one. He also found that for one and the same soil the amount so found was constant, if about a week’s time were allowed for saturation. He calcu- lates that while in general the amount of phosphoric acid capa- ble of being supplied to the crop during a growing season of twenty-eight to thirty weeks would suffice for but few crops, the supply so afforded is in no case a negligible quantity, fre- quently amounting to more than half of the crop-requirements. Experiments with various crops prove that these dilute solu- tions are utilized by all of them, sometimes to the extent of completely consuming the content of the solution. The much smaller content of phosphoric acid in drain waters is accounted for by the lack of time for full saturation during the time that the flow lasts. Whitney, (Bureau of Soils, Bulletin 22) has extracted the soil-solution by means of the centrifuge from several soils; the contents of phosphoric acid thus found are in general of the same order as those shown in the preceding table by King, but much in excess of Schloesing’s figures ; notwith- standing the fact that Whitney’s soils had been in contact with water for only twenty-four hours. The cause of this wide dis- crepancy is not clear. Practical Conclusions from Water Extraction.—As regards the practically useful conclusions to be drawn from the ex- traction of soils with pure water, the data given above, and especially the results obtained by King, seem to prove that there is a more or less definite correlation between the immedi- ate productiveness of soils and the amount and kinds of in- gredients dissolved; especially in the case of phosphoric acid, the adequacy of the supply of which for immediate production 1 Ann. de la Sci. Agron., 2de serie tome 1, pp. 416-349; 1899. THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 333 is assumed to be thus demonstrable by many French chemists. Moreover, a number of King’s results, tabulated in curves, exhibit a remarkable general parallelism of the curves showing totals of plant-food extracted by water, and actual crop pro- duction. This is the more remarkable since it is known to be, not pure water, but such as is more or less impregnated with carbonic acid at least, that is actually active in soil-solution and plant-nutrition. The farther development of this method may, it would seem, lead to definite conclusions at least in re- spect to the immediate productive capacity of cultivated, and perhaps also of virgin soils. But it is not likely to give any definite clew as to the durability of such lands. ASCERTAINMENT OF THE IMMEDIATE PLANT-FOOD REQUIRE- MENTS OF CULTIVATED SOILS BY PHYSIOLOGICAL TESTS. PHYSIOLOGICAL SOIL-ANALYSIS. As has already been stated, the quantitative analysis of culti- vated soils by means of strong acids affords a presumptive in- sight into their immediate productiveness, and the kind of fertilizer needed to improve it, only in case of the extreme deficiency of one or several of the chiefly important plant- foods. The limits of deficiency of these in virgin soils have been discussed above; but since in cultivated soils amounts of soluble plant-food so small as to be beyond the limits of ordi- nary analytical determinations, when distributed through an acre-foot of soil may, when rightly applied, nevertheless pro- duce very decided effects, the indications thus obtainable are not absolute. Thus a dressing of 150 lbs. of Chile saltpeter, containing only about 24 lbs. of nitrogen, is capable of causing the production of a full crop of wheat where otherwise, even under favorable physical conditions, only a fraction of a crop would have been harvested; provided, that all the other re- quisite ingredients were present to a sufficient extent and in available form. Yet the amount of nitrogen thus added would amount, in one acre-foot of soil to only .0008%, say eight ten- thousandths of one percent; which, with the amounts of sub- stance usually employed in soil analysis, would be an unweigh- able quantity, and might easily be overlooked. Since the amounts of potash and phosphoric acid actually 334 SOILS. taken out of the soil by one crop are in general of the same order of magnitude as the above, what is taken out by one or two crops will usually fall within the limits of analytical errors, especially of those incurred in sampling the soil. Yet that the changes caused by a number of successive crops can be proved, even by the ordinary methods, has been abundantly verified. For it seems that the losses of soil ingredients in cultivated lands exceed considerably those calculated from the actual drain represented by the crops. Plot Tests ——There is, however, an obvious and apparently simple method by which every farmer might make his own fertilizer tests, on a small and inexpensive scale, the results of which may afterwards be put in effect on his entire land. It is to apply in proper proportions on plots (of say from one twentieth to one fortieth of an acre), the several plant-food ingredients usually supplied in fertilizers, singly as well as conjointly with each other, leaving check unfertilized plots around as well as among them. By comparison with these, the cultural results should at once determine which of the fertilizers can most advantageously be applied to the land. Such tests when carried out with all the proper precautions are often very decisive and practically successful. But they so frequently suffer from seasonal influences (such as scanty or excessive rainfall, cold or heat, etc.), inequality of soil condi- tions, failure to apply the fertilizers at the right time, or in the right way, the depredations of insects and birds, and other causes, that it generally takes several seasons’ trial to obtain any definite results. On level lands of uniform nature and depth, they are most likely to be successful; while on undu- lating or hill lands it is not only very difficult to secure uni- formity of soil and subsoil on areas of sufficient size, but also to prevent the washing of fertilized soil, or fertilizer in solu- tion, from one plot to the other by the influence of heavy rains or irrigation; thus wholly vitiating the experiments. In very many cases, especially in the arid region, the results of such trials have been practically mi, for the reason that physical de- fects of the soil, and not lack of plant-food, were the cause of unsatisfactory production. A full examination of physical conditions, as outlined in previous chapters, should in all cases precede the application of THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. N 12 N Chile Saltpeter. Superphosphate. Tankage. P+ N Blank. Superphosphate Blank. and Chile Saltpeter. 1S IN ae Ui Pee kK Superphosphate Blank, Superphosphate and sulfate of Chile Saltpeter and Potash. Sulfate of Potash. K+N Blank. Sulfate of Potash Blank. and Nitrogen. P K. IY Bone meal. Sulfate of Thomas Phosphate Potash. Slag. Scheme for Plot-tests of Fertilizers. 335 336 SOILS. fertilizers; such examination will at the same time serve to determine the greater or less uniformity of soil-conditions, which is of first importance to the cogency of fertilizer tests. As a matter of fact, few farmers possess the necessary qualifi- cations to carry out such tests successfully, since their execu- tion requires a certain familiarity not only with the principles and methods of experimentation, but also the faculty and practice of close and reasoning observation; which, unfortu- nately, is not as yet a part of instruction in our schools. The experience so often had in co-operative work between experi- ment stations and farmers is cogent on this point. Those desiring to do such work, however, can make use of something like the plan given above; it being understood that in the case of clay soils, the unplanted paths left between the plots should be at least two feet in width; in the case of sandy soils the distance should be not less than three feet, and more if the plots are located on a slope. The crop from each plot should if possible be weighed as a whole; but if the plot be large and the crop measurably uniform, an aliquot part, such as one fourth, may be weighed instead. In regular experi- mentation the crops are weighed both in the green (freshly cut) condition, and after drying. Since the dry matter is the real basis of value in the case of most field crops, its weight is the most important; as the water-content of green crops may vary considerably. But in the case of vegetables as well as fruit crops, not only must the weight of the fresh crop be determined, but it should be sorted into the ‘‘ marketable’ and “unmarketable”’ sizes and qualities. Failure to do this may vitiate the entire experiment for practical purposes. Pot Culture Tests —The uncertainty attending plot culture tests on account of the difficulty of controlling seasonal and other external conditions, has resulted in the extended adoption of indoor culture tests, usually conducted in zine or “ gal- vanized ” cylinders of a size sufficient to contain from twelve to twenty or more pounds of soil. These are kept in a green- house whose temperature and moisture-condition can be regu- lated at will, and where the soil-moisture is wholly under con- trol, For investigations of the effects of various kinds of plant- food upon vegetable development, this method has served most satisfactorily and effectually, and striking photographs of re- THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 337 sults thus obtained are seen on all hands: for which reason, to save space, they have not been introduced into this volume. It seems at first sight that the same method should serve admi- rably to determine the manure-requirements of soils under con- trolled conditions. It must, however, be remembered that the field conditions as regards subsoil, evaporation, ascent of moisture from below, penetration and spread of roots, etc., in other words, all the physical conditions so vitally concerned in crop production, except the temperature and moisture-condition of the soil, are wholly left out of consideration in this method. Hence the application of the results so obtained to actual field conditions can only be made with great caution, and are often widely dis- crepant with actual experience. The method has of late been carried to an extreme by the U. S. Bureau of Soils in the proposition to supplant the large soil-pots here- tofore used by small paraffined wire-cloth baskets, 3 X 3 inches in size, in which the soil to be tested is sown with seeds which are allowed to develop only for three to five weeks; it being claimed that the devel- opment occurring during that time is quite sufficient to indicate what will be the ultimate outcome in crop production. But practical ex- perience has long ago demonstrated that these early stages of growth cannot be relied upon to show the crop results to be expected. Yet if this minute scale of pot-culture should, on further test, prove to give truthful forecasts even in a mere majority of cases, the facility with which it may be carried out will entitle it to favorable consideration. A great deal more proof is needed on this point than the confident claims of the Bureau indicate. CHEMICAL TESTS OF IMMEDIATE PRODUCTIVENESS. Testing chemical soil-character by crop analysis.—Another method for the determination of immediate soil requirements has been elaborated by E. Godlewski.1 The principle upon which this method rests is that plants growing in a soil defi- cient in available plant-food of any one kind will in their ash show a corresponding deficiency, or at least a minimum pro- portion of the same; and that in many cases, the nature of the 1 Zeitschr. Landw. Vers. Oesterr., 190. 22 338 SOILS: deficiency manifests itself in the form or development of the plant, so clearly as to render chemical analysis unnecessary (see below, chapter 22). To a certain extent the latter idea has been and is constantly being utilized in practice. It is essentially involved in the habit of judging of land by its natural vegetation; and by agri- cultural chemists and intelligent farmers, when they check ex- cessive growth of stems and leaf (indicating excess of nitro- gen) by the use of lime or phosphates; or prescribe the use of nitrogenous manures when a superabundance of small, un- marketable fruit is produced. From the coincidence of such indications with the results of the analyses of soils and ashes, very definite and permanently valuable indications as to the proper fertilization and other treatment of the land may be deduced. Godlewski insists strongly, and with a good deal of plausibility, upon the importance of making such trials in the open field and not merely in pots. While this is true, it is also true that such field experiments suffer from the same liability to imperfection as the “ plot fertilizer- test’? plan just described ; viz., that the season may exert a much more powerful influence than the fertilization, and the tests may lead to wholly erroneous conclusions unless the experiments are continued for a number of years, and under skilled supervision. But when once the normal ratio between the ash ingredients for a particular soil and climatic region have been ascertained, the data will be of lasting benefit to agriculture there, and perhaps, other things being equal, to the world at large. H. Vanderyst has discussed the entire subject of physio- logical soil analysis elaborately in the Revue Génerale Agro- nomique of Louvain, 1902-3 (Exp’t St. Record, April 1904, Vol. 8, page 757) and shows in detail the conditions under which it may be successful. Among these he reckons as full a knowledge of the chemical characteristics of a soil as can be obtained by chemical analysis. Chemical Tests of Immediately Available Plant-food.—It is scarcely doubtful that plants differ considerably in the energy of their action upon the “ reserve’’ soil ingredients; hence no one solvent used by the analyst could represent correctly the THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS, 339 action of plant-roots in general upon the soil, even if we could give that action the same time (a growing season) and op- portunity afforded them in nature by the root-surface. We are forced to proceed empirically; and among the numerous solvents suggested for the purpose of soil extraction, that of Dyer, already mentioned, viz., a one per cent solution of citric acid, making allowance for such neutralization as may occur in the soil, has seemed to the writer to give results most largely in agreement with cultural experience. | Walter Maxwell has recommended aspartic acid in lieu of citric, as approaching nearer to practical results, at least with sugar cane. According to the investigations of Dyer, on Rothamstead soils of known productiveness or manurial condition, it ap- pears that when the citric-acid extraction yields as much as .005 % of potash and .o10% of phosphoric acid, the supply is adequate for normal crop production, so that the use of the above substances as fertilizers would be, if not ineffective, at least not a profitable investment. These figures refer to the ordinary field crops of England and to soils originally fertile and well supplied with lime. It can readily be foreseen that under other climatic and soil conditions, different figures may have to be established. So far as the writer’s experience goes, however, the above figures are very nearly valid for the arid climates as well; only the figures obtained for arid soils are usually far in excess of the above minimum postulates. Fig- ures for lime and nitrogen are given in chapters 8 and 19. But the results obtained with the highly ferruginous soils of Hawaii show that under such conditions, figures far exceeding the minimum ones established by Dyer nevertheless coexist with need of phosphate fertilization, CHAPTER XS THE ANALYSIS OF VIRGIN SOILS BY EXTRACTION WITH STRONG ACIDS. As stated already, the analysis of soils by extraction with strong acids is intended to enlighten us, not in- regard to their immediate productiveness (the “ Dtngerzustand ” of German agricultural chemists), but as to their permanent value or pro- ductive capacity. As has been seen in the preceding chapter, the efforts to unite investigators upon a generally applicable and acceptable method for the testing of immediate produc- tiveness have not been very successful, and the number of methods employed in different countries and by different chemists within the same country are widely at variance, with no immediate prospect of agreement. Moreover, in most cases the effort is to combine both problems—temporary and permanent productive capacity—in one method or operation; which still farther confuses the issue. Convinced that the only way to unification lies in the direc- tion of falling back upon a method that is based upon a natural limitation about which there can be no difference of opinion, the writer has, in following the lead of Owen and Robert Peter, endeavored to settle definitely the natural limit of the action of a suitable acid upon soils, and the time and strength of acid producing the maximum effect. Loughridge’s Investigation—Systematic work on_ these points was undertaken, at his suggestion, by Dr. R. H. Lough- ridge in 1871 and 1872. ‘The results of this work were pub- lished in the succeeding year in the Amer. Journal of Science, and in the proceedings of the A. A. A. S. for 1873. They seem to be of sufficient general interest to be reproduced here. The soil selected for this purpose was a very generalized one, representing large areas in the states of Kentucky, Tennessee, Mississippi and Louisiana, bordering on the east the immediate 340 THE ANALYSIS OF VIRGIN SOILS. 341 valley of the Mississippi river, and known locally as the “ Table lands; ”’ a noted cotton-producing upland region. The brown or yellow, moderately clayey loam is of great uni- formity throughout its region of occurrence, and is evidently derived from such widely-spread sources that it represents no special rock or complex of rocks. Its natural growth is a mix- ture of oaks and hickories, strong and well-developed trees, such as any land-seeker would at once approve for settlement. Its cotton product when fresh was a 400-pound bale of cotton lint per acre. It may therefore well be considered a typical generalized soil of the humid upland of the Mississippi valley. Its physical analysis is given in chapter 6, it being No. 219 of the table on p. 98. Strength of Acid used.—Three different strengths of acid were simultaneously employed, viz., chlorhydric of 1.10, I.115 and 1.160 density. With these the soil was digested at steam heat in porcelain beakers covered with watch glasses for five days each, then evaporated and analyzed as usual. The results were as follows: ANALYSIS WITH ACID OF DIFFERENT STRENGTHS. Ingredients. Sp. G. of Acid. 1.10 I.II5 1.160 insoluble residues -)c).-0.-- + -6)-2'« -\s1-15)- 71.88 70.53 74.15 Solve Gi saat ee ansocspaa ose ore 11.38 12.30 9.42 LACUS) \ Gort Son aa SCOP RO ECO EEO RIESE .60 63 48 SO ettetencrevere yal ouel ns stat ans iarelcinversueleves to,se) alate ot} 09 35 HEC REN ete afelgshis,c:< oles sare clase oan ee Sie a2 7, 27 23 WWIAOTEST Als Lins ccc vers! jve'c evaie' at baielys iisiares 45 45 45 IBiOXsR AN GANIESE aicie cers ale alos nereie vfere's .06 .06 .06 He TTC MO NIG sreper tok iaiclate vsiefele clalelel ciel eye's 5.15 5.11 5.04 PMINMETEUTL Ae age yoll fai ste/siaieysvol s, -42 44 47 45 44 Br. Ox. Manganese.... ... 04 .06 .06 .06 .06 1aenate OhsClFs Gea doccoodosr 4.77 5.01 5-43 5-11 4.85 ANNIE, congbhodooando0er 5.15 7.38 7.07 7.88 7.16 Phosphoric acid aiesesieiclelsi- <2 ol .21 pI 12Y Sulburielacidiyacsrrte sie .02 .02 .02 .02 02 Wotatiletmatter--\-meeie 3-14 3.14 3.14 3.14 3.14 POtall iecisieyelsavelelene es 99.63 100.68 100.55 100.69 99.80 Amount of soluble matter.. 19.67 24.88 25.57 27.02 24.87 Amount of soluble bases... 11.05 13.68 13.91 14.49 13.68 While these results pointed clearly to the five-day period as being sufficiently effective so far as the plant-food ingredients are concerned, it was not easy to understand why a ten-day digestion should be less incisive than a five-day one. Instead of repeating the ten-day experiment, it was thought preferable to re-treat the residue from the five-day digestion for five days more. The result was that only more silica and alumina went into solution—in other words, additional clay was alone being decomposed. This being of no interest in the matter of plant nutrition, the five-day period was definitely adopted by the THE ANALYSIS OF VIRGIN SOILS. 343 writer for his work; and it, together with the acid of 1.115 density, is the basis of all the results given in this volume, ex- cept where otherwise stated. There appeared to him to be no good reason for the acceptance of the arbitrary method of soil-extraction suggested by Kedzie and since adopted by the Association of Official Agricultural Chemists; the more as to do so would throw out of comparison all the previous work done by Owen, Peter, and himself and his pupils, which had already been definitely correlated with the natural conditions and with cultural experience.* Virgin Soils with High Plant-food Percentages are Always Productive.—In strong contrast to the contradictory evidence deduced from the analysis, by any method, of cultivated soils when compared with cultural experience, it seems to be gener- ally true that virgin soils showing high percentages of plant- food as ascertained by extraction with strong acids (such as hydrochloric, nitric, etc.), variably prove highly productive: provided only that extreme physical characters do not interfere with normal plant growth, as is sometimes the case with heavy clays, or very coarse sandy lands.—To this rule no exception has thus far been found. The composition of some represen- tative soils falling within this category is given in the annexed table, which at the same time conveys some idea of the propor- tion of acid-soluble ingredients usually found in the best class of natural soils. Discussion of Table.—It will be noted in this table that while the total of the matters soluble in acids (inclusive of silica) ranges from a little below 50 to over 77 per cent, the total of directly important mineral plant-food ingredients (potash, lime, magnesia and phosphoric acid), constitute in moderately calcareous soils only from about 2.5 to somewhat over four per cent of the whole. Yet if all these were in available form, the supply would be abundant for many hundreds and even 1 While regretting to thus “secede” from the fellowship of his colleagues, the writer cannot but regret equally their voluntary decision to do over again, or lightly reject, all that had been done before in correlating soil-composition and plant-growth. He still thinks that it is idle to expect any unification, national or international, of methods of soil analysis based upon purely arbitrary prescriptions, unless previously shown to be definitely correlated with natural and cultural con- ditions ; as is measurably the case with Dyer’s method. SOILS. 344 fre seeeee-ssusejod a[qeIeAy tre ss ***proe ‘soyd ajquireay olor rr eee ee ee i AOD AEA a re! sceuaseXofeteteie) seleiaielereeeeereitie Jee DOC LOSE *ainysto fy d1do0oso1SA Fy L9° ed i . Cs i ee *[lOS Ul UesOININN lolol 44 Pe Stee ewe eee eee eee ee seeeeeesssnuMny Ul UasOIUINT go't Ce DO Pen A COTTA TCE 8G a) of zl‘66 +L:66 $z‘oo1 gl‘oor 6g'001 zz‘oo1 1O'1Or (Sexe) ORDO ODO OTOMOO GUO IBOOLOOUDOOOGO i Xap £9°9 zl tS-z 6c'¥ PEE é Flor (Ah \|\O0 seeeeesss19}7RUI 1URSIO PUR I3]E MA zit aierele/otuieleiaierele||ieisieleteluteleisiatate gi zl 166 a \ble/bie)aieiejsia v1 ei]ieiejeie.ejeie’e ejeleiel|lelclelaie.eyuiersiejsle: [lve atelstelera ++++(8Q5) prow o1uoqies Zz ZI" £o° 10° or: to: cz gr zo’ seeee sisioxe/sieleis.sinzoleieie) (18 (6) poe INNS rl: re ol’ Se: £1 ou Sr- LY ot seis ey treseseses(SO6q) prov s110ydsoyg ot:Z gi'6 99'S gles ot'g 11°6 SeSr aya Sor woisinveisnsiereicvermusle ereree.eisiicietstainetae (18 Gy Urea) eulUIn,y fz 10's 98°9 39'°9 bry bob orl LLY ZQssi w|i sroseeceess(BQC37) UOLT JO pIxoleg 9°" Ir go" So- fo" Lo ¥r10 zr zr *--(%O&uy) ssauesuryy jo xo ig gue 677 Ig'r 60°% L6:z £S'1 83" 16" Zo;1 | sjeieie leyeleieioie)elcl9i"/(@) a TAT) MEISOU SETA IVz LL 93°! ore 19° fbr zL torr Seer : Hoa) (OED) eau gr ZI° zS° gr’ gr zz €r- tz €or fhe eierebeisiere;cievessleressfeceleleis:s\eleisieiershersite.s/(@) OB NR) REPOS Lg° £6" oz'l zber gr io41 for o6: ol'l . POOC OO TIO ID SCO OROOIOODUGNSG/ (1dr) ysej0g ; { 00°61 i Lo't 09'9 oS'S ‘ €Ee°S : gz lr r gloz ) orb A ol‘oz rs GRECO OA AN IG alqn[os tbeel 7) fb es fete} re { £f-L9 gozL Stir o06"£9 L5°3S of £5 {Poot $z'9S grse ob $6:69 ZL eos Dre eevee eeecerececeerseses1933RUT a[qn[OSUT ‘HLUVY ANIQ AO SISAIVNY TVOINAHD 190% orl 6S11 z6o1 gos LE oFz gst o6€ ‘ajduieg jo Jaquinny “meOT ye PAGEAOUE *yUSUIIPaS *(wre0'T) *(Av[gQ Aavayzyz) ‘ATTIVA |'wWleOT xed |wvo'y sutelg TOSSP GES WIS *yUSUIPIS “ysiued apuriy “ARTIC A ‘uoyeig |, SPOPPPUN | moog Apueg j;auuoqasay,| ‘Ayun09 “w0}}0g : ofouy yeing yuawedx ay ASTRA ed ope10jo) “woyOg ‘eumnoy ulyUey ooze "0D odstqQ | ‘oD ourjog | ‘0D aEny, | aes 0D apurly ony | “yuaWIpes outed [LOS siny ues PI ra oZ91q] ueS Aureo'T rq yoysyong *VINMOAITVD) ‘SVXHJ, |‘ WNVISINOT “Id dISSISSIJL ‘STIOS NI ADVINAOUAd GOOA-LNVTId HOIH ONIAAITANAXA ATAVL | DHE ANALYSI5; OF VIRGIN: SOILS. 345 thousands of crop years. For, one-tenth of one per cent in the case of the clayey soils of the preceding table would amount to about 3500 pounds per acre-foot, and to 4000 in the case of the sandy ones. Hence the amount of phosphoric acid ine. g., the Mississippi delta soil from Houma would suffice for the production of about 440 crops of wheat grain (at 20 bushels per acre) if only one foot depth were drawn upon; but as the roots of grain easily penetrate to twice and half and three times that depth even in the humid region, the number might be tripled. As a matter of fact, however, that soil has pro- duced full crops for from forty to fifty years only; yet this is considered an exceptionally long duration of profitable pro- duction without fertilization. The first and last soils in the above list represent probably the highest types of productiveness known. ‘The Yazoo bottom soil has produced up to one thousand pounds of cotton lint per acre when fresh, and is still producing from four to five hundred pounds after thirty years’ culture. The Arroyo Grande soil of California with its extraordinary percentages of phosphoric acid and nitrogen, as well as exceptionally high proportion of available phosphoric acid and potash, has made such a record of productiveness, and high quality of the seeds produced, that it has for a number of years been excluded from competition for prizes offered by seed-producers elsewhere, in order to give other sections a chance. Both these soils are rather heavy clays, but readily tillable in consequence of their abundant lime-content. The remarkably high content of acid-soluble silica, indicating the presence of much easily available zeolitic matter, is doubtless connected with the exceptional productiveness. Experience, then, proves that lands showing such high plant-food percentages will yield profitable harvests for a long time without fertilization, or with only such partial returns as are afforded by the offal of crops. Also that when fertiliza- tion comes to be required, instead of supplying all the ingre- dients usually constituting fertilizers, only one or two of these will as a rule be actually needed, and even these in smaller 1The Rio Grande and Colorado bottom soils contain amounts of lime carbonate largely in excess of reqnirements, 2 to 3°, of that compound being all that is needed to insure all the advantageous effects of lime in any soil (see this chapter, page 367). 346 SOILS. ‘ amounts than in “ poor” lands; thus materially reducing the expense of fertilization. The high production and durability of such lands therefore amply justify their higher pecuniary valuation; for which there would be no rational permanent ground if they required fertilization to the same extent as poor lands. In other words, if the entire amount of soil-in- gredients removed by crops had had to be currently replaced equally in all cases (as is implied in the hypothesis, advanced by some, that the chemical composition of soils is of no prac- tical consequence), the high prices which from time imme- morial have been paid for black prairie and rich alluvial lands as against meagre uplands and barrens, would have been so much money wasted. The explanation of these advantages evidently lies largely in the larger amounts of soil ingredients annually rendered available in rich soils by the fallowing effect of the atmospheric agencies, because of the generous totals present. The actual amounts of soil ingredients thus rendered accessible to plants, other things being equal, are evidently more or less directly proportional to the totals of acid-soluble plant-food ingredients present. And 1f this is true in cultivated lands, the inevitable conclusion is that the same must be true of virgin lands; whose productive capacity and duration can therefore be forecast by such analyses. It will be observed that the above data, which could be indefinitely increased by corroborative analyses, seem to establish the fact that about one per cent of acid-soluble potash, one of lime, the same, or less, of magnesia, and .15% of phosphoric acid, are thus shown to be “ high” percentages of these ingredients in virgin soils. It is not easy to see how the above conclusions can be suc- cessfully controverted; they are, moreover, thoroughly in ac- cordance with cultural experience. Difficulties of interpreta- tion arise mainly in the case of medium soils, which show neither very high nor very low percentages of plant-food; and which raise the question of what amount or percentage con- stitutes ‘‘ adequacy ” of each of the several substances. Low Percentages.—On the other hand, whenever in virgin soils acid-analysis shows the presence of but a very small pro- portion of one or several of the essential ingredients, we have ~ it 9 ‘1 ae ev Sis, THE ANALYSIS OF VIRGIN SOILS. 347 a valuable indication as to the one of these that will first be required to be added when production slackens. What are “ Adequate” Percentages of Potash, Lime, Phos- phoric Acid and Nitrogen?—It is evident that a very critical discussion of cultural experience can alone answer this ques- tion; and at first sight such experience often appears very con- tradictory when compared with the results of analysis. One of the chief causes of such apparent discrepancies is readily in- telligible when we consider the differences in root-development of the same plant in different soils. In “light” or sandy lands the roots may penetrate to several times the depth attained by them in heavy clay soils. Having thus within their reach a soil-mass several times larger, and aérated to a much greater depth, it is but reasonable to expect that in deep, sandy lands plants would do equally well with correspondingly smaller percentages of plant-food than would suffice in clay soils, in which the root-range is very much more restricted. The well-known fact that the production of heavy clay lands may be increased by their intermixture with mere sand, adding nothing to their store of plant- food, emphasizes this expectation and elevates it into a maxim. On this ground alone, therefore, it is evident that the mere consideration of plant-food fercentages found, can be a true measure of productive- ness only in the case of virgin soils with Azgh percentages. Soil Dilution Experiments.—The extent to which dilution with mere “ lightening’”’ materials can be carried without im- pairing production, can of course be determined for concrete cases only; but the following experiment made at the Cali- fornia Station is a case in point: One kilogram of the heavy but highly productive black clay soil of the experimental grounds of the University of Cali- fornia was used in each of five experimental cultures, each made in duplicate, in cylindrical vessels of zinc-covered (“ gal- vanized’’) sheet iron, all proportioned alike in height and diameter, but containing respectively one, two, four, five and six volumes of total soil. In the smallest was placed one kilo- gram of the undiluted, original soil, in the others successively the same amount of the soil thoroughly mixed with one, three, four, and five volumes of a dune sand fully extracted with chlorhydric acid, and washed with distilled water. The water- 348 SOILS. capacity of each of the mixtures was determined and the earth in the pots kept at the point of half-saturation generally ad- mitted to be the optimum (best condition) for plant growth. Each pot was sown with ten seeds of white mustard, subse- ~ quently reduced to five plants selected for their vigor. The (“ galvanized”) vegetation pots were made as nearly as possible of similar proportions in depth and width for each dilution, so as to give opportunity for the proportional develop- ment of the root systems. The photographs show the latter as nearly as practicable in their natural form, restored after washing off the adherent soil. It was of course extremely dif- Fic. 53.—Natural Adobe Clay Soil. Fic. 54.—Adobe Soil diluted with Sand, 1 to 1. — SS Fic. 55.—Same, diluted 1 to 3. DEVELOPMENT OF ROOTS OF WHITE MUSTARD IN CLAY SOIL, DILUTED WITH — VARIOUS PROPORTIONS OF PURE SAND. BES ANALYSIS Ob VIRGIN SOILS. 349 ficult to preserve intact the extreme circumferential rootlets and hairs; yet the general development is correctly shown. oe < Fic, 57.—Adobe Soil diluted 1 to 5. Fic. 56,—Adobe Soil diluted 1 to 4. 350 SOILS, Fic. 58.—Soil-dilution Experiment: Photograph showing Mature Plants. The following table shows the percentage composition of the original as well as the diluted soils, while the photographs show the development of the plants in their successive stages, COMPOSITION OF BLACK ADOBE AND SAND DILUTIONS. Original DILUTIONS. Chemical analysis of fine earth. soil. it 8) I Bait TS A Bra 1 5 AinSoluibleimaiteracessnse+ eaceoeesessee 54.50 77-25 88.62 go.00 Q2. 42 SKONMONKS HUNCH Ie se cedbesocubseconsccsca cic 66050 19.00 9,50 4.75 3.80 3.07; Potash (Kg @) eas csceecocscntest este ceeeees 7B 36 18 15 510) SYOGEY (ONG) eosSancepdohocossaqucsedsnbuceccd : .20 51) .05 .04 .03 Temes (CAO) | vel necnsseco-seeeoaseasecceseese : UES) 57 2 .22 HO) Masiesiay Mic ©) eins -s.ncsoscesmee-eeeeeee 1.08 54 27 .22 18 Br. ox. of Manganese (Mn3Q,)........ fo toy .O1 OT .O1 Rercoxicdtotelronm (Mer Og \sessscaceesse 8.43 | 22 2.11 1.68 1.40 AN Kanon’ (UNIKO}) ps icsoteceosone Goducoooacoo yO Pa es 10.0) 1.98 1.58 BP IPin@syainvarme Zvoial (IBXO)\\s5sscscdenconsc0n0" 19 10 05 04 .03 SHEMba UTES: BUCH) (SQ aJl6 ocpacosq0accenessco00s 04 .02 OL .O1 .O1 @arbonicacmE(GOs) pee eeceeseece wddee. | 0.55™™...... 2.00 2.50 4.00 3-00 5.00 IVs: WeyP Goo > 50 dcend0oonsabE 98.00 97-50 96.00 97.00 95-00 CHEMICAL ANALYSIS OF FINE EARTH. Insolublepmatterne..s-clelsehei i 15-34 14.49 26.99 28.66 21.07 Solublegsilicassersnserrcee src 14.07 30.37 10.26 7.35 2.68 Poa (IK-O\ooesbeassoccoccac “45 .26 .40 61 44 Siok GNELONSgsangosoosesocoan 14 .08 26 .17 25 Wuimle! (CAO) erseieisteleve stecsieksl saree .26 1.04 52 638 28 Marsiesian (Mig ©) erernctrsetrie ater 65 80 96 1.04 .60 Br. ox. of Manganese (Mng3QOs).. 05 03 ra .20 .O7 Peroxid of Iron (Fe2Os)....,....] 39.05 19.63 19.10 18.23 30.10 Alumina (Als ©) eee else eee 14.61 18.29 21.41 20.18 14.38 Phosphoric acid (P,O,)........ 19 aya 64 70 .97 Sulfuric acidl((S@s) senescence 03 .09 32 .21 2 (Caroorme cous (COR os assoncore Sager aan wee sealants a Qersts Water and organic matter...... 14.18 14.59 18.60 21.65 28.60 UGiMleodo osdco0uncsodocd 99.52 100.04 99.67 99.61 99-73 lal SacogganosoegounaoDobece 3-35 3-24 4.84 5-43 9.95 Gi ASMNsscoooobebo ade yepeKoreters Ba12 2.22 2.76 3.50 6.70 ‘¢ Nitrogen, p. c. in Humus.. 3.30 9.500 2.800 3-100 vei ss ss 5 De Ca int Coils co oe ati 314 134 168 17 Phosph. acid inhumusash...... 110 166 580 sete) |! sococ Soluble in 2 °/, Citric acid.... .004 .020 035 .037 .025 in Nitric acid, 1.20 sp. g..... .190 .320 .640 .700 .970 in Chlorhydric acid 1.115 sp. g .430 -350 1.600 1.280 20950 Hygroscopic moisture 15°C..... 18.50 21.2 23.07 23.14 23.81 Unavatlability of Ferric Phosphate.—\t will be noted that in the soils from Oahu with an overwhelming amount of ferric oxid (mostly in the form of hydrate or rust) the citric acid has taken up only an insigni- ficant amount of phosphoric acid ; nitric acid took up 40 to 50 times as much, and chlorhydric doubled even this. In the much less ferruginous Hawaiian soils, though containing more alumina, the citric acid ex- tracted nearly ten times as much; proving that it is chiefly ferric oxid, and not the alumina as has been supposed, that causes the insolubility 3 . THE ANAEYsIS OF VIRGIN SOILS. 357 of phosphoric acid in soils and doubtless also in fertilizers. The very unusually high content of phosphoric acid in the Hawaiian soils, ex- ceeding all others on record, so far as known to the writer, emphasize the effects of ferric hydrate upon soluble phosphates ; while the fact that these very soils are greatly benefited by the use of phosphate fer- tilizers, proves that the Dyer (citric acid) method for the determination of available phosphoric acid which in soils Nos. 21 to 26 yielded results largely in excess of the established limit in European soils, cannot be successfully applied to these highly ferruginous soils. It should also be noted that the amounts of phosphoric acid found in the humus extracted by the Grandeau method is in the first two Hawaiian soils over ten times the amount extracted by citric acid, but that while they rise and fall together, no definite quantitative ratio exists between the two. It is obvious that in such soils, fertilization with water-solu- ble phosphates would be likely to result in the quick partial withdrawal of the same from useful action, and that any ex- cess not promptly taken up by the crop, is likely to become inert and useless. It will evidently be desirable to use the phosphates in the form of bone-meal or basic slag (Thomas Phosphate), which because of their difficult solubility will be acted upon but very slowly, if at all, by the ferric and aluminic hydrates. Nitrogen.—In determining the nitrogen-content of the soil, a great variety of methods has been followed. Some include all that can be obtained by the combustion of the organic mat- ters of soil and from the nitrates present in the same; while others, the writer among the number, believe that the mainly important source of nitrogen to the plant being the nitrifica- tion of the humus-nitrogen, the determination of the humus by the method of Grandeau, and of the nitrogen contained in it, should be the standard; the unhumified vegetable matter being of no definitely ascertainable value, and the nitrates varying from day to day and being liable to be lost by leach- ing at any time; therefore forming no permanent feature of the soil. Considering the variety of methods, the unanimity with which about one-tenth of one per cent (.10) has been assumed as the ordinarily adequate percentage is remarkable. In view of the extremely variable amount of nitrogen in the humus (ranging from 1.7 to nearly 22%), the amount of the latter 358 SOILS. cannot, of course, afford even an approximation to the nitro- gen-content ; except that as in the humid region, the nitrogen- percentage is not known to exceed about 5 or 5.5%, an ap- proximate estimate can be made on that basis. In the arid region, according to location, the nitrogen-percentage may be from three to six times greater for a similar amount of humus. (See chap. 8, p. 135). In the writer's experience, a nitro- gen-percentage of 1% in the arid region is a very satisfactory figure, indicating that the need of nitrogen-fertilization is not likely to arise for a number of years. Nitrification of the Organic Matter of the Soil.—n order to test the question whether or not the nitrogen of the unhumified debris existing in surface soils is directly nitrifiable, the writer selected a soil which in its natural condition sustains intense nitrification, so that at some points it contains as much as 1200 pounds of sodic nitrate per acre. The composition of this soil, representing the land of the ‘ten-acre tract” of the southern California sub-station, is as follows : , SOIL FROM “ TEN-ACRE TRACT,’ SOUTHERN CALIFORNIA SUB-STATION, NO. 1284. (Coase WAEIINIS 2 OBR oa ococgos sasnobosasooacous 1.00 Hime mB anthingetercrecaccyeraeesp ates oko Pele -evensionel seeaickenneets yates 99.00 100.00 CHEMICAL ANALYSIS OF FINE EARTH. ImSolublemmattera-rirerpees cote erlekieier mele cr ree ttrarete =. 62020) ee Soluble ssilicass |< aos seteian ae ee ee torae a3 8.30\\ epee Potash is @ recs ae ienvnecenoerettinn blows eee OO eee 95 stocky (INGO oedoacvascacbb0 ods dooavdDOd G00 s090 000% .50 Herve) (Gai) wersrstiemctevateinis ol ove braieiee eee onsets i eee 5.07 Matonesia (Mic.©))-tsatericacieisiiie se le citi iste corsets ters 384 Bie OLS NEnEmMETE: (MIMIOA)e cascopsoococcosbancsdse .06 Peroxidi of Tiron (He2Os)\aciac ce srsote citer eer ieteveroeie er 6.43 ANitiramiaiey (UNEOW) aos eonob coco es weopoRboaucnenoDaacc . 3.88 Phosphoric acide (22O5) treet tscscieiteme eect eee 21 Sulftunrckacid! (SiO ss) =o sheca sles) ciete cas eerie cetera eh omer .06 Carbomictacid'(C Oo) achraectsrersiciel stetsreiois's evsleieveroe see disse 3.66 Water andiorganie matter yy ameter -/letetslencoteier-leneleisteneteisle 6.02 Aoi stan Oma BECentCGaD DUG caemcabcoas. 99.70 Wratersolubleimattersper Cent.) eiereeietlmeetieeeiont U3, OCHS MITZI, Se Celia oagcanod coon sdb OS ooNSCbO CO SE .020 ETUATATUS | yepep ters eich acer sotclisysrerchate orale puresteomererer era ere Ears 1.99 s ASIN e505 Doo Gn 6U OOS oOC dS BHT OGDODDODDedOOC OORT ligt 3} ¥ INCOM, PIE Coats ww lalwieNTs ss o6s050 cacacanuer 10.30 < Ue 5 DIETCEM TN Soils Sescogadsooccssouesc -208 AMGhirlll INjiieoyeten, iin GOWlsco5 asnposo cs eooucabrocousnunNS: -330 « s io WuminUpeowbolerel jeMNNHSIG = A Gaga oqacasaooOkC 127 AvailablesPotashmene ce. ol) clinic: a Available Phosphoric acid ] method Geine apm oe SS 03 Ely or OScopiceMOISEUNE re evolayeqetespereles atelel-lareereltelsetlsteist=is 5.81 ADS OND edalte res sapere tetaiors sicher ene ekeieke ctererierere ube (Gs TEE ANSE Y Sis) Ob VIRGIN SOILS: 359 It will be noticed that this is a rather strongly calcareous soil, (nearly 9% of calcic carbonate), slightly impregnated with alkali, of which about one-ninth is saltpeter. One portion of this soil was thoroughly leached with distilled water until not a trace of nitrates could be detected in the leachings. Another portion was treated for the removal of humus according to the Grandeau method (see chapter 8, page 132); the ex- tracted soil showed under the microscope an abundance of vegetable debris, some slightly browned as from incipient humification. The calcic and magnesic carbonates withdrawn in the humus-extrac- tion were then restored to the soil in the form of finely divided pre- cipitates and thoroughly mixed in, first in the dry and then in the wet condition ; the extracted soil being repeatedly wetted with turbid water from the leached soil, in order to replace and reinfect it with the nitri- fying bacteria. Both soils were then spread out in flat glass dishes and placed in a wooden box containing also a similar flat dish with distilled water, upon which played the draught from the inlet pipe opening into the outer air, with outlet-holes in the cover at the opposite end; thus keeping the air within fairly moist. In addition, the soils themselves were moistened with distilled water every three days and restored to a loose condition by stirring. The whole was placed so as to maintain, during the greater part of the 24 hours, a temperature of from 30 to 35 degrees C. At intervals the samples of both soils were leached and color-titrated for their nitrate content by the picric-acid test. The results, calculated as sodic nitrate, during two years were as follows: Nitrate formedudurning eee ..-|Four months. |Twelve months. |Two years. Weachedinaturalisoilbmesaaecsenteee O12 .0420 06 Batra ctedusoill: ii crispere ciel tpevelete sus ok None. .0030 0042 It will be noted that in the course of four months, nitrification had not sensibly set in in the extracted soil; while in the leached natural soil the nitrate-content had reached to three-fifths the amount originally present, and in the course of a year the nitrate-content of the latter was more than double that of the original (unleached) soil; while that in the extracted soil had only reached one-seventh of the same. At the end of two years we find a still farther increase of nitric nitrogen in both, the ratio between the two remaining about the same (1:14). At the same time the ratio of increase attained at first had materially diminished in the water-leached soil, probably on account of. the accumu- lation of the niter itself. 360 SOILS, It thus appears that although the nitrogen of the unhumified organic matter constituted about 40% of the total in the origi- nal soil, it would during the entire year have contributed only to an insignificant extent to the available nitrate-supply ; while the fully humified “ matiere noire’ contributed fourteen times as much. During the ordinary growing-season of four or five months the unhumified organic matter would have yielded practically nothing to the crop. Functions of the unhumified Vegetable Matter—The chief utility of the unhumified matter in the soil consists of course in its gradual conversion into true humus, in the course of which it evolves carbonic gas to act on the soil minerals; while at the same time it helps to render the soil more porous and thus facilitates the action of the aerobic bacteria, for which it serves as food. Hence the addition of vegetable matter to soils not already too “light” is always advantageous, so long as it does not introduce injurious, non-humifiable ingredients, like turpentine in the sawdust of resinous pines. But it is al- ways advisable to first use such matter as litter for stock, in order to better prepare it for the processes of humification, under the influence of ammonical fermentation, such as occurs in the decay of green plants or animal matter. A portion of the ash ingredients also is quickly utilized by solution in the soil-water. Matiére Noire the Only Guide.—According to these results it is clear that in order to gain any tangible indications with re- spect to crop-bearing, it is the nitrogen in the humus proper, the matiére noire only, that should serve as the basis; and that as a current source of nitrogen to the plant, the unhumified matter is hardly entitled to more consideration than the “ in- soluble silicates.” For, the favorable conditions for nitrifica- tion under which the above experiment was conducted, will very rarely be even approached under field conditions. What are the Adequate Nitrogen Percentages in the Humus? The nitrification of the matiére noire being, apparently, the main source of plant-nutrition with that element under ordin- ary conditions, the question naturally arises as to what may be considered an adequate nitrogen-content of that substance, so as to permit a full supply of nitrates to the crop. THE ANALYSIS: GF VIRGIN SOILS. 301 The data extant on this subject are rather scanty, and thus far have all been obtained at the California Experiment Sta- tion. But they seem to be very cogent in proving that the growth of crops removed from the soil causes a rapid deple- tion of the nitrogen in the humus-substance, and that so soon as the nitrogen-percentage in the same falls below a certain point, the soil becomes “ nitrogen-hungry;” so that the applica- tion of nitrogenous fertilizers is needed and is very effective. The data in the table below, as well as the figure of a culture experiment (No. 52 below), illustrate this point. ADEQUACY AND INADEQUACY OF NITROGEN CONTENTS OF HUMUsS. Collec- Per cent. | Per cent. | Per cent. tion Kind of Locality. Num- Soil. Humus in| Nitrogen} Nitrogen ber. Soil. jin Humus.} in Soil. 6 Black Adobe.|Near Stockton, San Joaquin Gos, Cally rea cre tee 1.05 18.66 .196 1679 do Virgin Soil, University Grounds, Berkeley, Beyaiciat 1.20 18.58 203 1842 do Ramie plot, Univ. Grounds, 10 years cultivated. . 1.80 4.17 075 1841 do Grass plot, Univ. Grounds, IO years Cultivated....... 1.65 3-40 056 29 | Dark loam. |Sugar-cane land, Maui, H. Bee i rayersuniciariors seek reroeta 10.90 ill : 27 | Dark loam. |Guava-land hills, near Hilo, Z Sr sacl Jala aun MAS ao eo oo sca 9.95 1.71 170 Nos. 6 and 1679 show the usual humus- and nitrogen-percentages in the “black adobe” or “ prairie” soils of California. Nos. 1842 and 1841 represent the same soil as 1679, upon which, however, ramie and ray grass had respectively been growing, without fertilization, for about ten years ; showing that while the Aumus-content of the soil has increased, the nitrogen-content of the humus has decreased in the case of ramie by 72.78%, in that of the grass by 76.78% ; reducing the land to figures commonly found in the humid region. In the case of the ramie, the partial return through the leaves has resulted in a higher humus-content, 1 The Supply of Soil Nitrogen, Rep. Cal. Expt. Station, 1892-93, page 68 ; ibid., 1894-95, page 28; Zhe Recognition of Nitrogen Hungrinessin Soils, in Bull. 47, Div. of Chemistry, U.S. Department of Agriculture, 1895 ; Landw. Presse, No. 53, July 1885. See also for detailed data chapter 8, page 135. 2 Calculated upon the true humus substance (matiére noire), zo¢ by determining total (incl. unhumified) nitrogen in the soil. 362 SOILS: together with higher nitrogen-percentage, than in the case of the grass, which in the several cuttings annually made, caused a greater depletion in nitrogen and a smaller accession of humus. The grass was very weak in its growth and partially dying out. No. 29, the sugar-cane land from Maui, was still in fair production, but beginning to weaken as against its first production. No. 27, the guava land from Hawaii, originally bore a luxuriant cover of wild guava, but after bearing one fair crop of seed-cane and one of ratoons, the cane planted on it ‘“spindled up”’ and died so soon as the seed-cane planted was exhausted. Both the island soils, originally derived from the weathering of the black basaltic lavas of the region, were well supplied with mineral plant-food (see above, page 356), and the humus-content in both was exceptionally high ; and neither was in an acid condition. The difference in their nitrogen-content, both in the totals and in the humus itself, suggested that notwithstanding the relatively high total of nitrogen in No. 27, it might be nitrogen-hungry, in view of the low percentage of the nitrogen in the humus. Confirmatory Experiment.—A pot-culture with wheat, the results of which are shown in the figure below, fully confirm Unmanured a eee Sos pee a oe a a - bs Saltpete r, 2g: ae Fic. 59.—Growth of Wheat on Guava Soil from Hawaii Island. this suspicion. One kilogram of soil was used in each of two pots, one being fertilized with half a gram of Chile saltpeter. THE ANALYSIS<*‘OF) VIRGIN SOILS. 363 The experiment could not be carried to full completion on ac- count of the overwhelming invasion of mildew; but the figures speak for themselves. Moreover, a field trial made on the island with saltpeter, in pursuance of the writer’s recommen- dation, resulted in a luxuriant growth of the cane. Data for Nitrogen-adequacy.—It appears from the facts shown above, that for the growth of grasses a nitrogen-per- centage in the humus of 1.7 is wholly inadequate, no matter how much humus may be present. A percentage of 3.15 in the Maui soil, No. 29, containing nearly 11% of humus, gave only a fair crop of sugar-cane; on the Berkeley grass plot, with 3.40% and only 1.65 of total humus, the ray grass was barely maintaining life. The ramie, with 4.17% of nitrogen in the soil-humus, was still doing fairly well. It is doubtless impossible to give one and the same absolute figure for nitrogen-deficiency for all plants and soils. Where the conditions of nitrification are favorable, as in the presence of much of the earth carbonates, a smaller percentage may suffice for the same plants that elsewhere suffer ; and it is highly probable that different minima will be found for plants of dif- ferent relationship and root-habits. But there is every reason to believe that in the nitrogen-percentage of soil-humus, con- sidered in connection with other chemical and physical €ondi- tions and soil derivations, we have a means of ascertaining the needs of plants with respect to nitrogen-fertilization, if proper study be given to the subject. Broadly speaking, it appears to be necessary to keep the nitrogen-percentage of soil-humus near 4% to insure satisfactory production. It having been suggested that the frequent and disastrous crop failures on the noted tchernozem or black-earth soils of Russia might be due in part at least to nitrogen-depletion of the humus, the writer obtained through the courtesy of Prof. P. Kossovitch of St. Petersburg soil samples from the center of the Black-earth region, both cultivated and unculti- vated. These samples are in appearance exactly like some of the dark alluvial soils of Louisiana and California, and ap- proach therh very nearly in the essentials of composition, as will be seen from the table below : 364 SOILS. ANALYSES OF BLACK SOILS, Tchernozem Alluvial (Russia.) Black clay lands. Louisiana. California. No. 240. | No. 1167. Back-land | Black-land Houma. Tulare. CHEMICAL ANALYSIS OF FINE EARTH. (No coarse material in soils.) Insolubl evmattencis\scjs'eireio\ere vases oles -i= 48.38 55.09 35-48 62.43 Solublegsilicanaprkeeceias seciioieeieiraiers 13.21 12.28 20.76 16.99 Rotash (gO) pesca eee peoddasoDOe Ve 52 1.03 1.09 SKoks (INGWHOoscocaacsdoo conobUOO0CK -20 oils’ 13 oi) Wimre (CaO) ke erteloreutoveletstersiorcrernere -keless « 1.51 1.31 Gite 1.46 Magnesian((Mip ©) tae sist lelerisclielieieieiele 73 75 88 1.44 Br. ox. of Manganese (Mn,Q,)........ .05 03 .O1 .06 Peroxid of Tron’ ((He;Os)icls). + isre'-)-)21- 7.12 4.80 7.10 4.98 Alumina: (Als @=)heetnyaciste cleliteieicier= 5.22 4.73 15-45 6.87 Phosphoric acid (PAO) aeussicisiesisleleleler 14 13 15 Bie SulfuriclacidG(S Os )\eccemieeicieele 5006 .07 .08 25 .02 Carbonic sacidi(C Os) Rass setys -eereiere 2 Bes eee pee Shia Water and organic matter............ 22.78 19.94 18.52 MOP ec occonccobopadossonds 100.13 99.79 100.48 100.59 Jah CGY bso soocods ood aoosenoDS ue 5-11 5-54 5.07 1.33 se IMNosconsoce ooo cnecoacaoWnat 1.80 1.40 QI 30 se Nitrogen, per cent.in Humus.. 4.63 4.22 fh s per cent. in soil.. .. 527 24 Available Potash....... citric acid -O14 O10 Bare oe Available Phosph. acid method OI .008 .08 .O1 Ely STOSCOpIc MOIStuTe deterrent 56,0¢ 12.07 18.82 5-38 FXO AE scooby sabocncoont wooo Fie a gitC 15°C It will be seen that the Russian soil is of high fertility ac- cording to the standards given above, and that the nitrogen- content of the abundant humus is amply within the limits of adequacy suggested by the experience in California and Ha- wali. The humus-content of the arid California soils is char- acteristically low as compared with the Russian tchernozem as well as with the Houma back-land of humid Louisiana; but its nitrogen-content is doubtless at least three times that of the latter, as is that of the humus of similar lands in which it has been determined. THE ANALYSIS OF VIRGIN SOILS. 365 INFLUENCE OF LIME UPON SOIL FERTILITY. Assuming as substantially correct the numerical data given above in respect to the three leading ingredients of plant-food —phosphoric acid, potash and nitrogen,—the dominant role of lime in soil fertility, already mentioned, requires some farther illustration and discussion. “A Lime Country is a Rich Country.”—The instant change of vegetation when we pass from a non-calcareous region to one having calcareous soils, has already been alluded to. (See this chapter, p. 354). But it is not necessary to be a botanist to see the change in the prosperity of the farming population as one enters a lime district. The single log-cabin with, prob- ably, a wooden barrel terminating the mud-plastered chimney, is replaced, first by double log-houses, then by frame, and far- ther on by brick buildings, with the other unmistakable evi- dences of prosperity. Thus this is seen in passing from the mountain region of Kentucky into the “bluegrass” country, which is throughout underlaid by calcareous formations; and thus, likewise, in crossing the strike of the formations of Ala- bama, Mississippi and Louisiana, or any other region where un- derlying calcareous formations have contributed to the for- mation of the soils, as compared with some adjacent district where this is not the case. The calcareous loess areas border- ing on the Mississippi river and some of its chief tributaries, are conspicuous cases in point, as are also the prairies of Illi- nois and Indiana. Effects of High Lime-content in Soils—The table below il- lustrates the fact that in the presence of high lime-percentages. relatively low percentages of phosphoric acid and potash may nevertheless prove adequate; while the same, or even higher amounts, in the absence of satisfactory lime-percentages prove insufficient for good production." 1 This statement appears contradictory of the observations of Schloesing fils upon the solubility of phosphoric acid in presence of lime carbonate (Am. Sci. Agron., tome 1, 1899), but the natural conditions seem to justify fully the above conclusion. 306 o ‘£1 o ‘Lr (0) Gs (oh Of o Si o -Sr Sines Lg SoS 99°F og'r rZS og’ + II'gr $z'oo1 zg‘oor ol 66 46:66 Zz‘OO1 61'0o1 6z'oo1 £9°S Lot 60'b 00'z £9°9 $f Lek zo" 10° So: 10° zo" zo° zr° (Ae to: So: £o" So: tor So- bzo1 gr'3 Loy LP's 1f"z1 8z'9 gf'11 66'9 49°9 1Z'1 6o'r zS'11 19'S zS"b zr* 10° us zo" So: zo" Sr° £e°€ ot: Lo: a zz ob tL: Tle or go" Lo: 09° zo'r ob'r gc" to go" Lo: 1 £b- to: go" eran oS: 61° 60° grr Sz oes ; 06'9 : oh 5 gf'r ; 96h og’ OLr'iz tz es SE-S9 gt 08 | aol 6£°63 ; go v6 | z9°£6 z6 991 EOF 6L-gL 6z a “(THOS 3eIS) Loz oss gh tg1 £111 66+ 1Lr *Ayunod “Ayunod “Ayuno0d *Ayunod *Ayunod *Ayunod *Ayunod dproquin PyseYS youread MPSEIIYD lopewy eqny uoula A “RIULOJI[ED “iddisstsstjy “BIULOJI[RD *RUPISINO'T ‘AWIT MOT ‘HWI'T HOI *Ayunod) roduiay ‘tddisstssty(l ‘ADVLINAONAd GIOV DINOHdSOHd MOT DNIMOHS STIOS Io BOBHN OOS an SEO CUSUOUb IT) jer Lalita sloreiehelsisce/sieteisielel=ievmeicci@ ITA SLOTAL aidoosoish yy elosesnielelels)cletstereieieieleveleialeloleieiT ey Oly To eseeeesess19y RUT OIURSIO pue 13}B A, sVefeloivro(aletate Bo 0=0/(l ay) ploe o1uoqies5 yecepopBopcne 5009 (Eyays\) proe ouingqns staleledstolerels (Sy EE) proe s0ydsoyg 5 teeeeeeseeees (EQ Sry) eurunypy Byateberetevere **(8Q%a,q) WoL] Jo pIxo19g seeees(POSuyy) asouvsuryy jO "xo “1g pheveded hol leseialsLersisTehhetsry((¢ay'ch TAH) vISsUSe PL SoREGOOSSENADGNGGOAG GOO ((G}Iy) aulr’'y eecccccce sensecce ***(Q%eN) Repos weet eee cccccces 2% (O}2>30)) ysej}og "* BOIS BTGNTOS cieserereltecgslelerentololelselrs typ y a[qnyposuy ‘HLUVY HNIQ AO SISATVNY TVOINAHD ‘ajdwies jo raquinyy THE ANALYSIS OF VIRGIN SOILS. 367 Nos. 139 and 171 are heavy black prairie soils of high productive capa- city, whose production had, at the time of sampling, lasted almost un- diminished for over twenty years. Nearly the same is true of the two California soils, Nos. 499 and 1113; which, however, are ferruginous loams of only moderate clay-content. In all, the percentage of phos- phoric acid shown by the analysis is at or below the recognized limit of deficiency, while the lime-content of all is as high as is required for the welfare of any soil, however constituted. The potash-percentage also is low in all except the “red foothill soil,’ No. 1113. Passing to the soils of low lime-content, we find the two Mississippi soils, poor in both potash, lime and phosphoric acid, so low in produc- tion as to be wholly unprofitable in cultivation without previous ferti- lization; No. 559, from California, produced two fair crops of barley and then no more. No. 207, is the soil of Eel river bottom, California ; profusely productive at first, by virtue of its high content of both potash and phosphoric acid; but “giving out’ under a few years’ culture of clover or alfalfa (which draw heavily upon lime), and quickly restored to productiveness under the influence of dressings of quicklime. In this case the soil had become acid, a condition which always militates against the success of culture plants, and more especially against those of the leguminous relationship. What are Adequate Lime Percentages?—We have in the presence or absence of the natural vegetation peculiar to cal- careous soils (“‘calciphile’”’) an excellent index of the pres- ence or absence of such amounts of lime carbonate as fulfil the conditions of its beneficial effects. Lists of such plants for the United States are given farther on; they agree almost through- out with such plants as are everywhere recognized by Ameri- can farmers as indicating productive soils. All soils bearing such vegetation show with red litmus paper, when wetted, a neutral reaction at first, which after the lapse of twenty or thirty minutes turns to a blue alkaline one; such as is given under the same conditions by the carbonates of lime and magnesia. But the reverse is not necessarily true; for we occasionally find soils containing considerable amounts of lime carbonate that yet fail to bear lime vegetation. This is the case of ex- tremely heavy clay soils, as exemplified in the table below in the case of the last three soils; while the first, No. 220, ex- 368 SOILS. emplifies a case where, although potash is exceptionally high, only scrubby oak growth is produced in presence of an amount of lime that in sandy lands would show profuse lime growth. TABLE ILLUSTRATING THE NEED OF HIGH LIME-PERCENTAGES IN HEAVY CLAY SOILS. Mississippi. California. Flatwoods,| Hog-wal- Ridge Yellow Pontotoc jlow, Jasper| Prairie, | ridge, Ala- Co. Co. Smith Co. | meda Co. a ff INO MS amp let remrrteciciolieieetrel- vette 230 242 203 4 CHEMICAL ANALYSIS OF FINE EARTH. Insoluble smiatterteaierreretece ereleverstell eis iexeticrchepetoncl|faloiste sperenetatel | stererettotenciciare| le sfote siete Megs Soluble#silicatr sae eretebeissecriciets 77:85 76.76 51-75 86.00 Botashig (KG ©) metaststacteleiarelerclelereaer apis 53 53 19 Soda (Na,O)....... SG Odd 0D0b08C sti 19 .22 15 ISTE (CHONG otal podessuanloosoc 18 .42 .48 48 Macnesialic@ kre riences 83 .67 1.01 45 Br. ox. of Manganese (MnsQ,)... 17 .56 .10 04 Peroxid of Iron (FeaOs)......... 5-90 4.12 23-79 4.01 Alumina (AlzOs)................ 10.30 10.06 10.85 5-53 Phosphoric acid (P2Os).......... 05 .06 AS .06 Sulfuric acid(S.Os) ici ceri clve seer 03 .06 02 -02 Garbonteiacteli (COs) 5h ciotereteictell rst ocoincrsta uorell ototeesyexcitetorssel||chelioveucte ctoveiate| lecerater eieramettens Water and organic matter....... 3-69 5-73 11.39 4.05 Motalvateiesvsuieisieoityomekerats 99.86 99.17 100.29 100.99 Hygroscopic Moisture........... 9-3 6.8 TO37) > 4iloisteieeietetsiekels absorbediat auaceserseiects AG 22.0 air-dry 17 OW il clstaeccretemn All of the soils in this table are heavy clays, very difficult to till; in all, the lime-percentage falls below .5%; and none bear any lime vegetation, the Mississippi soils having a stunted growth of black jack and post oaks, such as is universally known to indicate soils too poor for profitable cultivation. The California soil bears stunted live oak (Q. agrifolia) ; but not being as heavy as its brethren from Mississippi, though un- thrifty, is more readily improved. Comparison with the two first sandy soils in the table on p. 352 shows, that with plant-food percentages equal to, or even much below those here shown, not only was vigorous lime growth present, but crop-pro- duction was good and even high. “ e THE ANALYSIS OF: VIRGIN SOILS. 369 We are thus led to the conclusion that the greater the clay percentage in a soil, the more lime carbonate it must contain in order to possess the advantages of a calcareous soil; and that while in sandy lands lime growth may follow the presence of only .10% of lime, in heavy clay soils not less than about .6% should be present to bring about the same result. This is apparent to the eye in that the dark-tinted humus characteris- tic of truly calcareous lands, does not appear in clay soils until the lime-percentages rise to nearly 1% ; while in sandy lands a much smaller amount (say .2% ) will produce this effect. European Standards.—It is of interest to consider, in connection with preceding discussions, the estimates given by Maercker of Halle, of the practical value of soils corresponding to chemical composition as ascertained by analysis with strong acids, substantially in accordance with the methods adopted by the writer. PRACTICAL RATING OF SOILS BY PLANT-FOOD PERCENTAGES ACCORDING TO PROF, MAERCKER, HALLE STATION, GERMANY. <-_ FOr WW ODPOOWOOn">7~DDDDmRDeEOEOEOENENENNNeeeueeemeomemeoeeeeeeooooooooooooeoeooooooooooooooeNN_ ee | Ss Lime. é Phosphoric Total Humus Grade of Soil. Potash. : — ‘ : Acid. F a Nit : b i Clay Soil. | Sandy Soil. BE OR SHS cee POOF, «<0. <0 000 cccer ere Below 0.05 | Below 0.05 | Below .10| Below .os | Below .os MWediumiesc-|e2o =e Boe ee) Bt eS ee | | oe eee | ope ia cineca fF A. 8 Fy BE & & = 2 2 ey}: ® wp ere) Pi iy lee _ : a.” gt 69 og'tZ orl 82°99 LLL gs'bg oLLL 98'9£ bE-SZ g6'o0L vo'SZ th-9g o9'gL 6S'1g Lr'tg zg'tg “aNpIsayy a[qnjosuy : r612 Pewee ER eREITe OPAC £ZS 601 £ zgz zz oz gt gI £z “Zr 6S gli FE br oS Or oF of oz “pazfjeue Jaquin "*** UOISayY puy 1oj soseisay “ts*sapeose) | UO}SUIYSE AL jo ysey | uos2109) Pet teres eeteeee eee eprmogEs °** LepRAONT Pett ete eee ee esse ee eee pHOZUy Peete eee e ee eeeeeeeeeees UT Fieeeeseeees oppiojos PPR SOOGCI ODOT OUT crs fOUICE COM AI \ Peres ete eeeeeeeteeeeeee* QURDT Pt esrereeeeeeeeeeees -paRUOW “NOIDHY CIUNV treeeeeeeesoZa1 10} AVIA 7 (PHE tdreS — x EIOAEC YON “++ pluiny-1uIagG—,,B}OSIuUI Ay “NOIDHY NOILISNVUL sissies Sa 3B 1 STAC iy “uo1say pluinyzy Joy VBe1DAW **7**(SapeoSED JO “A\) UOSIIO Wet eee eee ee eeeeeeee ees OIG See eee eet wne trees i SOILS: OF THE-ARTD AND HUMID REGIONS. 415 cribes, in part, the long duration of fertility in the regur lands. The regur also contains fragments of calcareous hardpan (here called guvarayi), just as in the Great Valley of California. The eighteen analyses of regur given by Leather agree so nearly in their essential points that it is admissible to average them; two other examples are however also given in the table. It will be noted that while the contents of lime, magnesia and alumina are uniformly high, the content of potash has a wide range; it rises very high (1.14%) in the maximum, while the average is fair. One conspicuous defect of these soils is their extremely low content of nitrogen, in view of which their lasting productive- ness is difficult to understand; unless it be that, as in California, their high lime-content causes a copious crop of leguminous weeds, constantly replacing the nitrogen supply.t Unfor- tunately we have no determinations of humus or of its nitrogen- content. Leather attributes the black color of the regur to some mineral substance rather than to humus; but his argu- ments are not quite convincing, so long as the Grandeau test has not been made. In view of the low rainfall and the close- ness of the texture of regur, it is probable that little if any nitrates are currently washed out of the black cotton lands. The regur soil-sheet seems to be underlaid over the greater part of its area by a basaltic eruptive sheet (not by meta- morphic rocks, as stated by Leather), and it is not easy to con- ceive how such a soil stratum can have been formed from such rocks as a sedentary formation. Elsewhere such soils are usually rather light and porous, as is the case in the Hawaiian and Samoan islands; and very high in iron-content. The regur has the character of an alluvial backwater or lake de- posit; but how such a formation can have occurred on the Deccan plateau, is a question not easily answered. Red Soils of the Madras Region.—Interspersed with and to seaward of the regur lands there are in the Madras presidency considerable bodies of “red” lands, which appear to be sedentary soils formed from underlying dark-colored, mostly eruptive rocks. Some of these are very rich in lime and pot- ash, others very poor, and it seems impossible to classify them 1 See Voelcker, Report on the Improvement of Indian Agriculture, 1892, p. 46, par. 60. 416 SOMES: under any definite category either from the chemical or physical point of view, except as to their red tint. Even this tint, how- ever, is not always found associated with exceptionally high contents of iron oxid, but due rather to its fine diffusion in the soil mass. As compared with the regur, with which the “red ”’ areas are interspersed, these soils contain, on the aver- age, less lime, potash and ferric oxid; and phosphoric acid is uniformly low. The alluvial (brown and black) soils from the same region, exemplified in the table, are doubtless derived partly from the regur, and their color and composition varies accordingly. “ Laterite Soils.” —These are defined by Wohltmann ( Trop- ische Agricultur, 1892) as being “ the characteristic sedentary soils (Verwitterungsboden) of the tropics, formed under the influence of heavy precipitation, high temperatures and drought.” This definition does not indicate their derivation from any particular rock, such as laterite is supposed to be; but its definition puzzles even geologists, and so, as Leather ob- serves, the definition of laterite soils will naturally puzzle agricultural chemists. Accordingly it is difficult to deduce from the analyses given any definite common characters. Leather describes those analyzed by him as red or reddish, sandy and gravelly, the gravel or cobbles often incrusted with a dark-smooth crust of limonite, which to the uninitiated looks as though the rock itself had been fused and vitrified. The samples from Lohardaga and Singhbhum show the effects of these limonite crusts upon the composition of the soils, which resembles that of the Hawaiian soils mentioned above; but in the latter the iron oxid is wholly pulverulent. But it is prob- able that, as in the case of the latter, the high content of phosphoric acid shown in the statement (.64 for the Lohardaga soil) is tightly locked up in the insoluble form of ferric phos- phate. Wohltmann’s definition of laterite soils seems best rep- resented by the “terra roxa” of Brazil, which as he states has .02 to .0o8% of potash, .o2 to .10% of lime, and .045 10 10% of phosphoric acid. Humus and nitrogen are very de- ficient in all these soils. While most prominent in the coast region of Bengal, they also occur not only near Madras (Saidapet) but also in the SOILS OF THE ARID AND HUMID REGIONS. 417 belt of high rainfall on the Malabar (western) coast of the Indian peninsula. The productiveness of the laterite soils seems throughout to be only moderate, yet much higher than would be expected of soils of similar composition in the temperate zones, where the rate of soil-formation is so much slower than in the tropics. From the analyses of “ coffee soils’? from Yarcand in the Sheveroy hills, north of Madras, we learn that coffee does well with a fairly liberal supply of lime (.30 to .44%) and phos- phoric acid, but is satisfied with a much smaller amount of potash than is found in the tea soils of Assam. A farther systematic investigation of the soils of India, with simultaneous accurate observations on their depth, subsoil, geological derivation, topographical location and relations to rainfall, could not fail to yield very important practical results. The examination of samples collected and sent in by persons unfamiliar with the proper mode of taking soil specimens, and the information which should accompany them, always 1n- volves a great deal of uncertainty and waste of labor, and in- definiteness of results. INFLUENCE OF ARIDITY UPON CIVILIZATION. In connection with the facts given and discussed above, as to the relative productive capacity of lands of the humid and arid regions, it becomes of interest to consider what influence, if any, these differences may have had in determining the choice of the majority of the ancient civilizations in favor of countries where nature imposes upon the husbandman, who supplies the prime necessaries of life, the onerous condition of artificial irrigation. Preference of Ancient Civilizations for Arid Countries.—A brief review suffices to establish the fact of such choice. Aside from Egypt, the permanent fertility of which is ascribed to the inundations of the Nile, we find to westward the oases of the Libyan and Sahara deserts, the high fertility of which has become proverbial and has caused them to be cultivated from ancient times to the present. Similarly, on both sides of the 1 Verhandlungen der Deutschen Physiologischen Gesellschaft in Berlin, Decem. ber, 1892; North American Review, September, 1902. 27 418 SOILS. Mediterranean Sea, we find that, instead of the humid forest country, it was in the arid but irrigable coast countries, such as the vegas of Valencia, Alicante, Granada, Malaga, and the even more arid domain of which Carthage was the metropolis; and farther east, in the Graeco-Syrian archipelago and the ad- jacent coasts, that noted centers of civilization were developed and maintained. Thence the arid belt requiring irrigation extends from Egypt and Arabia to Palestine, Syria, Assyria, Mesopotamia and Persia, and across the Indus through the anciently recognized regions of Indian civilization—Sindh, the Panjab, Rajputana and the Northwestern provinces—to the Ganges, embracing such well-known centers as Lahore, Delhi, Meerut, Agra, etc., inhabited by much more hardy and progressive races than the humid and highly productive tropical portions of the Indian peninsula. Throughout the extensive and important portion of northern India, irrigation is neces- sary to maintain regular production; and in default of it, periodic famines ravage the country. Thousands of years ago, millions upon millions of treasure were expended there upon irrigation works, as has again been done in modern times; yet in the rainy, forested districts we still find large areas prac- tically tenanted by wild beasts. In Asia Minor, as well as in Central Asia, the remains of ancient cities once surrounded by richly productive irrigated fields, are found where at present only the herds of nomads pasture. The Khanates of southern Turkestan with their historic cities, illustrate the same obsti- nate bias in favor of arid climates. Similarly, in the New World, it was not in the moist and exuberantly fertile forest lands of the Orinoco and Amazon, but on the arid western slopes of the Andes, that the civilization of the Incas was de- veloped. In Mexico, also, it was the high central, arid plateau, not the bountifully productive tierra caliente, over which the Aztecs chose to establish the main centers of their empire. Even to northward, the inhabitants of the high, dry plains of Arizona and New Mexico were, as their descendants of the Pueblos are to-day, superior in social development to their forest-dwelling neighbors of the Algonquin race. From time immemorial they have practiced irrigation in connection with cultivation, maintaining a comparatively dense population on very limited areas. SOILS OF THE ARID AND HUMID REGIONS. 419 It might be thought that the desire to avoid the labor of clearing the forest ground was the motive which guided the choice of the ancient nations toward the cheerless-looking, tree- less regions. But 1f we consider the cost and labor of establishing and maintaining irrigation ditches, it certainly seems that a stronger motive, based on the intrinsic nature of the case, must have influenced their selection. Neither can we with any degree of plausibility ascribe the preference for the arid open country to the fear of enemies lurking in the forest, since war was in early times practically the normal condition of man- kind, and was waged with little hesitation wherever booty was in sight. It has also been asked how the ancients could have known of the high productive capacity of arid lands; but no one who has ever seen the springing-up of luxuriant vegeta- tion after the periodic overflows of the arid-region streams, or the same surrounding the springs in the deserts, would ask that question. Irrigation necessitates Co-operation.—lItrigation enterprises can be accomplished in a very limited degree only by individ- uals or even families. Its permanently successful execution re- quires the co-operation of at least several social groups, ulti- mately of communities and states, if it is not to give rise to acrimonious contentions or actual warfare; witness the ‘ shot- gun policy’ resorted to in the arid West in times not very remote. Irrigation, in other words, compels co-operative social organization quite different and far in advance of that neces- sary in humid countries. And such organization is mani- festly conducive to the preservation and development of the arts of peace, which means civilization. The most ancient systematic code of Jaws known to us is that of Hammurabi, the king of arid Assyria. The high and permanent productiveness of arid soils induces permanence of civil organization.—In humid countries, as 1s well known, cultivation can only in exceptional cases be con- tinued profitably for many years without fertilization. But fertilization requires a somewhat protracted development of agriculture to be rationally and successfully applied in the humid regions, and the Germanic tribes, like the North-Ameri- can Indians, seem to have shifted their culture grounds fre- 420 SOMES: quently in their migrations. No such need was felt by the inhabitants of the arid regions for centuries, for the native fertility of their soils, coupled with the fertilizing effects of irrigation water bringing plant-food from afar, relieved them of the need of continuous fertilization; while in the humid regions, the fertility of the land is currently carried into the sea by the drainage waters, through the streams and rivers, causing a chronic depletion which has to be made up for by artificial and costly means. What with the greater intrinsic fertility and the great depth of soil available for plant growth, much smaller units of land will suffice for the maintenance of a family in arid countries; a fact which is even now being il- lustrated in the irrigated region of the United States, where ten acres of irrigated land instead of 40 or 160, as in the East, form the unit. The arid regions were, therefore, specially conducive to the establishment of the highly complex polities and high culture, of which the vestiges are now being unearthed in what we are in the habit of calling “deserts;” the very sands of which usually need only the lifegiving effects of water to transform them into fruitful fields and gardens. It is also quite natural that the wealthy and prosperous communities so formed should in the course of time have excited the cupidity of the “barbarous” forest-inhabiting races, and as history records, have been over and again overwhelmed by them—a similar fate often afterwards overtaking the con- querors in their turn, after the Capuan ease of their existence had weakened their warlike prowess. At the present time, the arid regions of the old world are still largely suffering from having been overrun by the nomadic Turanians, whose original habitat—Mongolia and Turkestan—while also arid, does not permit of the ready realization of the advantages above outlined, on account of the rigorous climate brought about by altitude. Mahometanism first expelled, and has since repelled, occidental civilization from the arid regions of the Old World, remaining to-day as an obstacle to its prog- ress. The peaceful aggression of railroads and telegraphs now seems likely to gradually overcome this repulsion; and when Constantinople and Bagdad shall be linked together by the steel bands, the desert will lose its terrors, and Mesopotamia re SOLES Ob Tees Ak De ND er OMI REGIONS: 421 and Babylonia will again become garden lands, as of old, under the abundant waters of the Euphrates and Tigris. Until the water-supplies of the arid countries shall have been more definitely gauged, it is impossible to foretell to what ex- tent food-production may be increased by their cultivation under irrigation, after the relief from political misrule shall have rendered such undertakings safe. But it can even now be foreseen that with improved modern methods of cultivation, the productive area of the world can be vastly increased by the utilization of the countries where, as the Turcomans say, “ the salt is the life of the land.” CHAPTER Oe ALKALI SOILS. Alkali Lands and Sea-shore Lands.—Alkali lands proper, as already stated, are wholly distinct in their nature and origin from the salty lands of sea-coast marshes, past or present. The latter derive their salts from sea-water that occasionally overflows them, or from that which has evaporated in segre- gated basins or estuaries; and the salts impregnating them are essentially “‘ sea salts,’ that is, common salt, together with bittern (magnesium chlorid), Epsom salt (magnesium sulfate ) gypsum, etc. (see chapter 2, p. 26). Very little of what would be useful to vegetation or desirable as a fertilizer is contained in the salts impregnating such soils; and they are by no means always intrinsically rich in plant-food, but vary greatly in this respect. While sea-shore lands are by no means always of high fer- tility even when freed from their salts, especially when very sandy, it is otherwise when they occur near the mouths of streams or rivers, whose finest sediments they then receive. From such lands are formed the profusely productive Polders of Holland and northern Germany, and the equally noted *colmates ” of France and Italy. These, so soon as imeem from salt, may be considered as possessing the same advantages as “delta” alluvial lands, and from the same causes; notably the accumulation of the finest sediments derived from the rivers’ drainage basins. Origin.—Alkali lands proper bear no definite relation to the present sea; they are mostly remote from it or from any other sea bed, so that they have sometimes been designated as “terrestrial salt lands.” Their existence is in the majority of cases definitely traceable to climatic conditions alone. They are the natural result of a light rainfall, insufficient to leach out of the land the salts that always form in it by progressive weathering of the rock powder of which all soils largely con- 22 ALKALI SOILS. 423 sist. Where the rainfall is abundant, that portion of the salts corresponding to “sea salts” is leached out into the bottom water, and with this passes through springs and rivulets into the country drainage, to be finally carried to the ocean.) An- other portion of the salts formed by weathering, however, is partially or wholly retained by the soil; it is that portion chiefly useful as plant food. It follows that when, in consequence of insufficient rainfall, all or most of the salts are retained in the soil, they will contain not only the ingredients of sea-water, but also those useful to plants. In rainy climates a large portion even of the latter is leached out and carried away. In extremely arid climates, on the contrary, the entire mass of the salts remains in the soils; and, being largely soluble in water, evaporation during the dry season brings them to the surface, where they may accumulate to such an extent as to render ordinary useful vegetation impossible; as is seen in “ alkali spots,” and some- times in extensive tracts of ‘ alkali desert.” Three compounds, viz. the sulfate, chlorid and carbonate of sodium, usually form the main mass of these saline efflorescences. Magnesium sul- fate (Epsom salt) is in many cases a very abundant ingredient ; some calcium sulfate is nearly always present, and calcium chlorid is not infrequently found. In some cases the above salts are in part at least derived from the leaching of adjacent or subjacent geological deposits impregnated with them at the time of their formation. Such is the case in portions of Wyoming, Colorado and New Mexico, in the Colorado river delta, and in the Hungarian Plain; and it is in these cases especially that the chlorids of calcium and magnesium also form part of the saline mixture. Geographical Distribution of Alkali Lands.—In looking over a rainfall map of the globe* we see that a very considerable portion of the earth’s surface, forming two belts to poleward of the two tropics, has deficient rainfall; the latter term being commonly meant to imply any annual average less than 20 inches (500 millimeters). The arid region thus defined in- cludes, in North America, most of the country lying west of the one hundredth meridian up to the Cascade Mountains, and 1 See Chapter 2, p. 26. 2 See above, chapter 16, p. 294. 424 SOILS. northward beyond the line of the United States; southward, it reaches far into Mexico, including especially the Mexican plateau. In South America it includes most of the Pacific Slope (Peru and Chile) south to Araucania; and eastward of the Andes, the greater portion of the plains of western Brazil and Argentina. In Europe only a small portion of the Mediterranean border 1s included; but the entire African coast- belt opposite, with the Saharan and Libyan deserts, Egypt and Arabia, are included therein, as well as, south of the Equator, a considerable portion of South Africa (Kalahari desert). In Asia, Asia Minor, Syria (with Palestine), Mesopotamia, Persia, and northwestern India up to the Ganges, and north- ward, the great plains or steppes of central Asia eastward to Mongolia and western China, fall into the same category; as does also a large portion of the Australian continent. Utilization of World-wide Importance.—Over these vast areas alkali lands occur to a greater or less extent, the excep- tions being the mountain regions and adjacent lands on the side exposed to the prevailing winds. It will therefore be seen that the problem of the utilization of alkali lands for agricul- ture is not of local interest only, but is of world-wide import- ance. It will also be noted that many of the countries referred to are those in which the most ancient civilizations have ex- isted in the past, but which at present, with few exceptions, are occupied by semicivilized people only. It is doubtless from this cause that the nature of alkali lands has until lately been so little understood, that even their essential distinctness from the sea-border lands has been but recently recognized in full. Moreover, the great intrinsic fertility of these lands when freed from the noxious salts, has been very little appreciated; their repellent aspect causing them to be generally considered as permanently waste lands. Repellent aspect—This aspect is essentially due to their natural vegetation being in most cases confined to plants useless to man, com- monly designated as “saline vegetation,” ' of which but little is usually relished by cattle. Notable exceptions to this rule occur in North and South America, Australia, and Africa, where the “saltbushes’’ of the former and the “ karroo”’ vegetation of the latter form valuable pasture 1See Chapter 23. SOILS, ALI ALK: “euros Te) ‘Aa][ BA UINbvof uvg ut Spuey ley], y—'o9 ‘og 426 SOILS. and browsing grounds. Apart from these, however, all efforts to find culture plants for these lands generally acceptabie, or at least profitable, in their natural condition, have not been very successful. Figure 60 illustrates the usual aspect of alkali lands in the San Joaquin valley of California. It will be noted that the alkali-covered surface is only in spots, with clumps of vegetation between, so that cattle can find both pasture and browsing on a portion of such lands, even though the plants so growing are not usually of the most desirable kind. We find in all arid regions, however, considerable areas either wholly destitute of vegetation, or bearing only such saline growth as is rejected by all kinds of domestic animals. Effects of Alkali upon culture plants.—In land very strongly impregnated with alkali salts, most culture plants, if their seed germinates at all, will show a sickly growth for a short time, “spindle up”’ and then die without fruiting. In soils less heavily charged the plants may simply become dwarfed, and fruit scantily. The effect on grown trees around which alkali has come up, is first, scanty leafage and short growth of shoots, themselves but sparsely clothed with leaves. This state of things is well shown in figures 61 and 62, which represent apricot trees growing but a short distance apart, but one com- ing within range of an expanding alkali spot. The characteris- tic sparseness of the foliage of the “ alkalied ” tree as compared with the adjacent one is well shown. Nature of the injury to plants from Alkali—When we examine plants that have been injured by alkali, we will mostly find that the visible damage has been done near the base of the trunk, or root crown; rarely at any considerable depth in the soil itself. In the case of green herbaceous stems, the bark 1s found to have been turned to a brownish tinge for half an inch or more, so as to be soft and easily peeled off. In the case of trees, the rough bark is found to be of a dark, almost black, tint, and the green layer underneath has, as in the case of herbaceous stems, been turned brown to a greater or less extent. In either case the plant has been practically “ girdled,” the effect being aggravated by the diseased sap poisoning more or less the whole stem and roots. The plant may not die, but it will be quite certain to become unprofitable to the grower. It is mainly in the case of land very heavily charged with i> a KALI SOILS AL “MPALV 03 Surplarx— z9 ‘org ‘dNNOWOS ITVNTV NO SH4aYL LOOMdvV “papayeug—'rg ‘org 428 SOILS. common salt, as in the marshes bordering the sea, or salt lakes, that injury arises from the direct effects of the salty soil-water upon the feeding roots themselves. In a few cases the grad- ual rise of salt water from below in consequence of defective drainage, has seriously injured, and even destroyed, old orange orchards. The natural occupancy of the ground by certain native plants may be held to indicate that the soil is too heavily charged with saline ingredients to permit healthy root growth or nutrition until the excess of salts is removed. (See below, chapters 23 and 26). The fact that in cultivated land the injury is usually found to occur near the surface of the soil, concurrently with the well-known fact that the maximum accumulation of salts at the surface is always found near the end of the dry season, indicates clearly that this accumulation is due to evaporation at the surface. The latter is often found covered with a crust consisting of earth cemented by the crystallized salts, and later in the season with a layer of whitish dust resulting from the drying-out of the crust first formed. It is this dust which becomes so annoying to the inhabitants and travelers in alkali regions, when high winds prevail, irritating the eyes and nostrils and parching the lips. Effects of Irrigation —One of the most annoying and dis- couraging features of the cultivation of lands in alkali regions is that, although in their natural condition they may show but little alkali on their surface, and that mostly in limited spots, these spots are found to enlarge rapidly as irrigation 1s practiced. Yet since alkali salts are the symptoms and result of insufficient rainfall, irrigation is a necessary condition of agriculture wherever they prevail. Under irrigation, neigh- boring spots will oftentimes merge together into one large one, and at times the entire area, once highly productive and perhaps covered with valuable plantations of trees or vines, will become incapable of supporting useful growth. This annoying phenomenon is popularly known as “ the rise of the alkali” in the western United States, but is equally well known in India and other irrigation regions. The soil being impregnated with a solution of the alkali salts, and acting like a wick, the salts naturally remain behind on the surface as the water evaporates, the process only stop- 2 iM ALKALI SOILS. 429 ping when the moisture in the soil is exhausted. We thus not infrequently find that after an unusually heavy rainfall there follows a heavier accumulation of alkali salts at the surface, while a light shower produces no perceptible permanent effect. We are thus taught that, within certain limits, the more water evaporates during the season the heavier will be the rise of the alkali; provided that the water is not so abundant as to leach the salts through the soil and subsoil into the subdrainage. Leaky Irrigation ditches—Worst of all, however, is the effect of irrigation ditches laid in sandy lands (such as are naturally predominant in arid regions), without proper pro- vision against seepage. The ditch water then gradually fills up the entire substrata so far as they are permeable, and the water-table rises from below until it reaches nearly to the ditch level; shallowing the subsoil, drowning out the deep roots of all vegetation, and bringing close to the surface the entire mass of alkali salts previously diffused through many feet of sub- strata. Surface and Substrata of Alkali Lands.—Aside from the desert proper, in the greater portion of the alkali country “alkali spots,” 7. e. ground covered with saline efflorescences and showing little or no vegetation, are interspersed with larger areas apparently free from salts and covered with the ordinary vegetation of the region. A view of such country is given in a plate on a previous page. The alkali spots are usually some- what depressed below the surrounding lands, and after rains remain covered with water for some time; the water frequently assuming a brown or blackish tint after standing. When a pointed steel probe is pushed down within such an alkali spot, it will usually be found that, although the soil may appear quite sandy, it is penetrated with some difficulty ; while outside of the spots, the probe does not encounter serious re- sistance until it reaches the depth of two or three feet, when it frequently becomes impossible to penetrate farther without the aid of a hammer. On the margin of the spots, the transi- tion from utter barrenness to a luxuriant vegetation of native weeds is mostly quite sudden; as is shown in the figure, p. 425. Vertical Distribution of the Salts in Alkali Land.—The re- sults of a comparative examination of such land before and 430 SOILS, after irrigation,! are shown in the annexed diagrams; in which the kind and amount of salts is shown for every three inches of vertical depth, down to four feet, by curves whose extension from left to right indicate the several percentages, while the outer curved line gives the total of salts for each of the several depths. Fig. 63 represents the condition of the salts in an “ alkali spot” as found at the end of the dry season at the Tulare substation, California. The soil was sampled to the depth of two feet at intervals of three inches each. It is easy to see that at this time the bulk of the salts was accumulated within the first six inches from the surface, while lower down the soil contained so little that few culture plants would be hurt by them. How Native Plants Live.-—Fig. 64 represents similarly the state of things in a natural soil alongside of the alkali spot, but in which the native vegetation of brilliant flowers develops annually without any hindrance from alkali. Samples were taken from this spot in March, near the end of the wet, and in September, near the end of the dry season, and each series fully analyzed. There was scarcely a noticeable difference in the results obtained. It is seen in the figure that down to the depth of 15 inches there was practically no alkali found (0.035%), and it was within these 15 inches of soil that the native plants mostly had their roots and developed their annual growth. But from that level downward the alkali rapidly increased, and reached a maximum f (0.529%), at about 33 inches; decreasing rapidly thence until, at the end of the fourth foot in depth, there was not more alkali than within the first foot from the surface. In other words, the bulk of the salts had accumulated at the greatest depth to which the annual rainfall (7 inches) ever reaches, forming there a sheet of tough, intractable clay- hardpan. The shallow-rooted native plants germinated their seeds freely on the alkali-free surface ; their roots kept above the strongly-charged subsoil, and through them and the stems and foliage all the soil mois- ture was evaporated by the time the plants died. Thus no alkali was brought up from below by evaporation. ‘The seeds shed would remain uninjured, and would again germinate the coming season. 1 Hilgard and Loughridge, Bulletin No. 128, California Experiment Station; Re port California Experiment Station, 1894-95, p. 37; Bulletin No. 30, Office of Experiment Stations; Wollny’s Forsch. Geb. Agr. Phys., 1896. ai J) vICAME SOMES, *b6gr ‘raquiajdag *RIUIOJLD “uorej}s-qns uauadxy aren, uayey, “Mord jou pynom Aapr1eq YOIyM Uo “[Los 1peyye ur sidap snore yw s}es ITeyYLe Jo uorsoduroy puv syunoure Sapmoys werseyq —'f9 -r T ae 802 #02 O02 I6T (030N/LNOD) SLNNOWY i ea 26/ 887 967 a ee CS EEE] == . = (aa Ba SS Ea SS Pe italia Ppgee-e (ee a faaqondensfendee eye pagan aps ~_+> 7 y 7 / aE v8 08 9. + 80/ 20/7 0074 Ie oO #8/ O81 9L1 2L1 891 b9/ O91 98L--257 °F eeI__ORL--SE7 267 Bei PZT OT (@39NILNOD) SLNIOWY = — | pe Sees —cospudehs spurt 17), Wen Seen wpe ee Ya cL BF bo 09 IF CS 8 ye Pa Oe, 98) 2 82" inns OG mie O) Lae I “W109 SO OOL Ni SLNFIOFZHIN{ JO SLNNOWY SOILS. 432 *RIMIOJI[ED “UONeIS-qns jusuedx| s1v[n J, S6gr ‘yore UOxV], ‘“UOTe}OSIA VATJEU YIM pas9Aod ‘pury Yyeyxye yoeyq ur syidap snowwa jv s}yes I[ex[e JO UoTTsoduro9 pur s}unowy Sutmoys weiseiq —b9 ‘org >—> 400 F nae " —— eden 68 = epost << c 9990 & ———E—EEE EE [_— ee a <—| wedppep-nesty+—> = — 0€ = tron _=——_S L2FPOg S}y[vg Sie | I Tes = aoe | tresry sect ot 909, 2 Tqnjog Bape. 1 a ae 1% ha ane Nera yoy at ee or Ie 4oog T 3 ¢__ Tos jo yydaq LINGO LS FNM OF SULT FUNCT Dill OF NNEGS NCO GUNNIL YS DuNEGG NUL OS cau GCUMNNNCO SUN TC NLC Sunn OGUNINEES CoNNO Lou LUNE C LN O LGN OO COON FORINT CO NTO) [Log Jo OOT UT SJUAIpaIBuUT Jo SyUNOIUY ALKALI SOLES. 433 It is thus that the luxuriant vegetation of the San Joaquin plains, dotted with occasional alkali spots, is maintained; the spots themselves being almost always depressions in which the rain water may gather, and where, in consequence of the in- creased evaporation, the noxious salts have risen to the surface and render impossible all but the most resistant saline growth; particularly when, in consequence of maceration and fermenta- _ tion in the soil, the formation of carbonate of soda has caused the surface to sink and become almost water-tight. Upward Translocation from Irrigation.—Fig. 65 shows the corresponding profile of the same soil after several years’ irri- gation. The upward movement of the salts is clearly seen by comparison with the previous figure; and the surface soil has become so charged with salts that the seeds of culture plants refuse to germinate. Ten feet from this bare alkali ground, on which barley had refused to grow, a crop of barley four feet high was harvested the same year, without irrigation. Investigation proved that here the condition of the soil was intermediate between the two preceding diagrams. The irrigation water had dissolved the alkali of the subsoil, and the more abundant evaporation had brought it nearer the surface; but the shading by the barley crop and the evaporation of the moisture through its roots and leaves had prevented the salts from reaching the surface in such amounts as to injure the crop, although the tendency to rise was clearly shown. By the use of gypsum, moreover, the injuriousness of the alkali had been somewhat diminished. The same season, grain crops were almost a failure on alkali- free land in the same region; and in connection with this result it should be noted as a general fact that alkali lands always re- tain a certain amount of moisture perceptible to the hand dur- ing the dry season, and that this moisture can be utilized by crops; so that at times when crops fail on non-alkaline land, good ones are obtained where a slight taint of alkali exists in the soil. Actual determinations showed that while a sample of alkali soil containing .54% of salts absorbed 12.3% of moisture from moist air, the same soil when leached absorbed only 2.5 % —a figure corresponding to that of sandy upland loams. | Alkali in Sandy Lands.—In very sandy lands, and particu- larly when the alkali is “ white” only, the tendency to accumu- 28 434 *RIULOJTTLD “uoNEsqns Jusuitiadx | aren y, *p6g1 ‘daquiajdag uayey, ‘poyeSiwir {Mois you pjnom Aopivq stay ‘pur| 1[ex[e eeq Ul syjdap snoiva ye sj[¥s 1[By] JO UOT}IsSOdWMIOD puk SyuNOUIY SuUIMOYS WIeASLIq]—'S9 “D1 er Lp Seeen ee 640 faa Tt e OF OF GF BF GF OF BF PY BW OF GF GE HS 2 OF B2 Sz be we OF B! ST H 2 OF 80 H WO WO "109 40 OO[ NM! SLNFI0I¥9N] 40 SLNNOWY ALKALI SOILS. A35 lation near the surface is much less, even under irrigation. In the natural condition the salts are in such cases often found quite evenly distributed through soil columns of four feet, and even more. This is an additional cause of the lesser injurious- Ome e2 704) 06" 08 Ee lle Ste Ou aoe Le eae ae SS / / ot! O/ cay \Z Le ue = a egret | iN aoe Ne ~ SQ \ aw an Pile F ness of “ white alkali.” An illustration of the distribution of the salts in very sandy lands, from the Tulare substation, is given in Fig. 66. Here we see that the maximum is not at, but some distance below the surface, the entire saline mass is Fic. 66.— Distribution of Alkali Salts in Sandy Lands. 436 SOILS. lower down than in the more clayey loam of the same locality, and is more widely distributed in depth. Distribution of Alkali Salts in Heavy Lands.—The mode of distribution of alkali salts in the heavier, close-grained soil of the Chino experimental tract in southern California, is illus- trated in Fig. 67. This land is permanently moist, from a water-table ranging from five to seven feet below the surface in ordinary years. There is therefore no opportunity for the formation of “alkali hardpan”’ as in the case of the Tulare soil; the salts always remain rather near the surface, viz. with- in twelve to fifteen inches. But being in much smaller average amounts than at Tulare (an average of about 5300 lbs. per acre), quite a copious natural vegetation of grasses, sunflowers, and * yerba mansa ” covered the whole surface, save in a few low spots. A similar mode of distribution of the salts is found in the still more clayey “ black adobe” lands of the Great Valley of California. The scanty rains cannot penetrate these soils to any great depth, so that evaporation will soon bring the salts carried by them back to within a short distance of the surface. Their accumulation there is frequently indicated by the entire absence of any but the most resistant alkali weeds, even though the total of salts in the land may not be very great. Salton Basin.—A peculiar state of things is illustrated in the Salton Basin, which represents what was at one time the head of the Gulf of California, and at the lowest point of which, 268 feet below sea level, there now lies a large deposit of rock salt. It has been cut off from the present Gulf by the delta deposits of the Colorado river, which now, however, overflows into the Basin at times of extreme high water. Although appearing level to the eye, the general slope of the country is to the lowest point of the former sea-bottom. The region, now in progress of settlement by means of irrigation water brought from the river near Yuma, was investigated with respect to its alkali conditions in 1900 (Bulletin No. 140, Calif. Agric. Expt. Sta). The annexed diagram 68 shows the distribution of the salts to a depth of 21 feet. It will be noted that here also the alkali content becomes insignificant at 4 feet depth, but increases again to a second maximum at about 15 feet, below which there is a second decrease ; : 437 ALKALI SOILS, *S6gr qudy ut yoo ysvy uayry SuoNES juoutiadxy eruszo0st[e5 UWIIYIMOS IYI Fe JvA} 919¥-U9} BY} UL sjulod puv syydap snotea qe sy[es TTeyxle jo worjtsoduwio9 pur syunouy—Z 9 ‘O1Y a= Lice oe UI) Se) ie 7 ON | CO) Ga nT 7 0 80° 90° 0° 20° 0 OT PLS aE OL 802) 008) ar D nD: <— [10§ JO 00T Ut syuatparsuy Jo syunowy . 5) a) iF 3 8 +5 I) * s +] I, 3 | 4] |e al ll + al || 4 + df i|* bee] 6 101d a . ¢ [| #3 fs 2101 sag | £ 7 (ie he ta) & Ii ai S iS | & iS +) |g uw» oO ANI +1] & [s} ’ 4a = ‘ cal f rs ey| 4\]2 Q Ra SH N+ AME med & Xx u a Se & ‘ {\- & es SS £ Srl, 1 ys o, | B aro ta Z ain in Sue 12 ! | & i Al re | 1 |> & ay) Ty) Ie] A zi | Sie |X Po wales = | & / aS 9 i] FI g ‘3 en CH to lel 8 wt [> ox son ‘ =o /°)4 ai Net FALE eteyit - ey lial = [ay lel Pay \e I, ico * H sl 9) , G9) | \ Ko) * fl al | y * Depth of Soil Column ——> Lf g Eee [es a | BREBESEE Cee eH ERESESIo | ne [| a a | a | | BeBe EeiAL fn ef Ta | HEEEEE EEE BREESE eea oo | et | fo a a | | (a {ttt E3 fa] ea fc cf tan (a | aa a a fa fa ef ff RN ff a a | | 3 | | a | a eo | ESIRRBTee EaEBe Bel EERE RERREeeSRoes | {8 || eli [ray | | ea sf tL LL. | EoEe oes (a a [| a | a | ma a a a | ea TE | Is fe | 1 a a | a | EERE RRR sa fa | | ep Is feet [ak ia 8 a a | w]e a fs esi it tt 5 EERE EECEEEE EEC E REE EC EEE 3 iia | in| | Ce | at] a | a (UR eas (| Bees = ECE eee EEEEEEEEEE EEE EEE EEE EEE oc Looe Eee SoS Sec SeeeSeeeoe BeSeceeooe q EREREERERoae ea a a a ee | | & Ht HJ 3 S0500e50085050000065500000800 0000505 .. SEER ee Saf BESSRSEESSeeeeseaseesanea! TORSETTaSreTecEreee } EEE EE H +--+ ---Hs. n | HEH EEE EHR E EEE aes BEN (ini) SERERSESEERSeEeath BS BEERSYENER - REMMMAREEeeeas a LE EET ERE ttt oe HEH = JENS eoe LEB eeeoSI hy RRR MiGeeee Sa FA LY a a | | (| PEER ERE c RII ERS Esaee SHER ES Sel iS eSeSeeeaee Jp eels g IMMERSE awes [Pen a [met he Feat Ts FTA a a a at Aa Sah | AA a | | BRERA RAED 0) PRE ERRERe eS 5 FO es] | = i] ft ee PE EEE 2 Me 4H Hs 8 9° . (8 i as HEE EEE HH ELBA RERERREAALS sf SEEERE REESE Ge! EREEREERRIL ARGU z 125 SBOE aRae ERESESEeSheaoa EERBEEERERIIRERaS: Ce > HH EP tt | BOHRA [Rel | = SHEA ea a a EREEBERERICECEDS | HH HH i ia a | i | a || EREEEERR AES ac Hiinn RSE sesSEe EREBEERER Bao |: a ane a CAPLAN a a (at Fe a | BSBA BG se PTA Roe | [Pa a a | RSE R eRe a CPAP tol [| a | || a [| | Rtf BEEEEOREZOL 5 aeons BEES Ea Nana BEES BRe REDO: TEENIE af tf ERRTCMRAES 6 EIR VELRSaRS [| [| AV Vat | Lig [tls © Tit \ | EREBETAVHNEEw (TH fof TT 3 xl] \\ Ge ad V {| \\ | BUMESEEaR | $NA | | PT A \\_! (a aa Q ; SEE WEDS HEBEREEE | YE IIMB Bene’, he aa HH pas HE! oA {EBaSeo 4 IGP EReo Wa , {7 | ABBBMH 7 |_| |_| (BERERERO Npereeaeey tector [_| u HH | \\ /\\s | 1 s a cea eeeeeceeeeeeet cette st ta At ol ne] a a i fe 0 [a [SS | fo | [| ERR se Rese eaeN FEIT HS ee ae ce a ee Oa ee Els S92 eat mo) ||| ia si en eS 7 oe ahi jRQnRuCoTnBeBSC SReenreTNSBeeeL Ole fete j sa pebenhsseeet sess nh nes SUSUSLOGOMEUE ASSESS Er) : q ~ \ a5 8 Ding NN SINININT Hid IL AIGA Ss Ones: 439 below this, at 20 feet, there isa final very heavy increase, not only of the totai salts but especially of common salt, which evidently represents the drainage toward the salt deposit. Above this level there is a very remarkable predominance of Glauber’s salt (sodium sulfate), also observ- able elsewhere, ¢. g. near White Plains, Nev., whose name is derived from the copious surface accumuiation of the sulfate. It seems as though this must have been formed in some way from the common salt. Horizontal Distribution of Alkali Salts in Arid Lands.—The constant occurrence of “alkali spots”’ in arid lands shows at once the great inequality of horizontal distribution of alkali impregnation. This is as prominent in level lands as on slopes, and in extremely arid regions it is mostly not possible to recog- nize even very considerable differences without close examina- tion. Thus in lands appearing exactly alike on the surface, on the edge of the Salton basin in California, on the same forty acre 1.4% (56,000 pounds per acre) was found in the surface four feet at one point, and a hundred yards away, 12.5% (500,000 pounds). The mapping of alkali lands is therefore somewhat precarious unless carried into great detail. More- over, it has been found that the location of the salts changes from year to year, especially in irrigated land, as might be ex- pected. Those cultivating alkali lands have therefore to exer- cise constant watchfulness, unless the salts have been defi- nitively eliminated by underdrainage over a considerable area; as merely local operations may be rendered ineffectual by the migration of the salts from neighboring tracts not reclaimed. Alkali in Hill Lands.—As a rule, hill lands themselves are remarkably free from alkali, even in the arid regions; except when water is gathered in depressions, where strongly saline waters may be found in Washington, Montana and elsewhere. But on level plateau lands, where drainage is slow or imperfect, alkali appears as freely as it does in the same regions in the stream bottoms. In the latter the leachings and seepage of the uplands naturally causes a concentration of the salts, and thus we find alkali salts incrusting the surface in the valleys of the streams, as ¢. g., that of the Yellowstone, Musselshell, Judith, Yakima and others in the north, and of Green river, Platte, Pecos, and Rio Grande farther south; as well as in numerous valleys of central and southern California. 440 SOILS. Usar Lands of India.—These lands have been investigated first by the “ Reh Commission ”’ appointed to investigate the causes of the deterioration of lands in the Aligarh district (south of Delhi, between the Ganges and Jumna rivers), in 1876. The occasion of this appointment was the appearance of “‘reh” (alkali salts) in a region which had previously been free from them.! Subsequently, a more elaborate investigation of the subject was made by Dr. J. W. Leather, Agricultural Chemist to the Government of India.2_ From these documents it appears that “usar lands” exist largely not only in the Northwestern Provinces and Oudh, but also in the Panjab, especially on the lands bordering the Chenab river; likewise to a slight extent in the Bombay presidency. Leather’s investi- gation shows that not all the lands designated by the natives as usar contain soluble salts in injurious amounts, some being simply lands having very hard, clayey soils difficult to till with the imperfect methods employed. Yet the general phenomena of the true “ reh”’ lands are practically identical with those of the American alkali lands, including also the calcareous hard- pan, there called kankar. Owing probably to the long culti- vation of the Indian lands (mostly under irrigation), the salts are there at their maximum in the first foot, decreasing as depth increases. It is noteworthy also that in the majority of cases the predominant salt is carbonate of soda or black alkali, which there as in California renders the lands impervious to water until treated with gypsum. This fact accounts for the popular use of the same name for non-saline impervious clay soils, and the alkali or reh lands proper. We have an entirely analogous case in the “ Szek”’ lands of the Hungarian plain, some of which are simply poor refractory soils containing a trace of soluble salts; while lower down in the valley of the Theiss we find genuine alkali lands, both black and white, which have long furnished carbonate of soda for local use and commerce. In this case, however, the alkali salts seen to come largely, in some cases wholly, from under- lying saline clays whose salts in coming to the surface suffer 1 An abstract of the report of this commission is given in the Report of the California Experiment Station for 1890. 2 See Agricultural Ledger, 1897, No. 13; ibid. 1901, No. 13. ALKALI SOILS. 441 precisely the same transformations experienced in California and India, in presence of calcic carbonate (see below, p. 450 ff). The accounts given by v. Middendorff of the nature and oc- currence of alkali lands in Turkestan (Ferghana) agree en- tirely with those given above for California and India; as do also the investigations made by other Russian observers on the saline lands of the steppes of European Russia. COMPOSITION AND QUANTITY OF ALKALI SALTS. Black and White AlkaliimBroadly speaking, the world over alkali salts consist mainly of three chief ingredients, already mentioned, namely, common salt, Glauber’s salt (sulfate of soda), and salsoda or carbonate! of soda. The latter causes what is popularly known as “black alkali,” from the black spots of puddles seen on the surface of lands tainted with it, owing to the dissolution of the soil humus;? while the other salts, often together with Epsom salt and bittern (Magnesium chlorid), constitute “ white alkali,” which is known to be very much milder in its effect on plants than the black. In most cases all three are present, and all may be considered as prac- tically valueless, or noxious, to plant growth. Nutritive Salts in Alkali—With them, however, there are almost always associated, in varying amounts, sulfate of pot- 1 Jn this designation are included, in this volume, both the normal (mono-) car- bonate and the two other compounds, the bi- or hydrocarbonate and the inter- mediate (so-called sesqui-) compound or trona; all of which are commonly present simultaneously, but in utterly indefinite relative proportions, varying from day to day and from inch to inch of depth, inasmuch as their continued existence depends upon the greater or less formation of carbonic acid in the soil, and the access of air. Hence their separate quantitative determination at any one time is of little practical interest. All naturally occurring carbonate of soda contains, and ae sometimes consists of, these ‘‘super-carbonates,” according to the greater or less exposure to air and solar heat. They are much milder in their action on plants than the mono-carbonate, which unfortunately, in the nature of the case, always predominates near the surface, and thus injures the root-crown. ? A wholly different kind of “ black alkali” exists in some regions, especially in the delta lands of the Colorado of the West and in the Pecos and Rio Grande country in New Mexico. 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The potash salt is usually present to the extent of from 5 to 20 per cent of the total salts; phosphate, from a fraction of one to as much as 4 percent; the nitrate from a fraction of one to as much as 20 percent. In black alkali the nitrate is usually low, the phosphate high; in the white, the re- verse is true. Both relations are readily intelligible from a chemical and bacteriological point of view. Estimation of Total Alkali in Land.—The investigations detailed above having shown that in California at least, out- side of the axes of valleys no practically important amount of alkali salts is usually found at a depth exceeding four feet, it became possible to determine approximately the amounts of salts that would have to be dealt with when irrigation and evaporation should bring the entire amount to or near the sur- face; a necessary prerequisite to the determination of possible cultures. While, as already shown, the salts occur lower down in very sandy lands, yet the diagram on p. 435 shows that even then, an estimate on this basis would not be very wide of the truth. It is at least probable that the same is measurably true of level alkali lands elsewhere, when not underlaid by geologi- cal deposits impregnated with salts. The total amount of these salts ordinarily found in alkali lands (2. e. in such as in the dry season show saline efflores- cences on the surface) is from about one tenth of one per cent to as much as three per cent of the weight of the soil, taken to the depth of four feet. The percentage of salts having been determined in samples representing a tract, it becomes easy to calculate, approximately, the total amounts of each salt present per acre, on the basis of the weight of the soil per acre foot. For the soils of the arid region, such weight will usually range from three million five hundred thousand to four million pounds per acre-foot ; the latter being the most usual figure, of which it may be conveniently remembered, that forty thousand pounds represent I per cent. We are thus enabled to esti- mate e. g. the amount of gypsum required to neutralize the carbonate of soda in the salts, or the amounts of valuable nutri- a ALKALI SOILS. 44% tive ingredients—potash, phosphoric acid and nitrates—present in the land in the water-soluble form. As has been shown in the preceding discussion, the analysis at the surface foot alone, which has frequently been alone made, gives no definite clew whatever to the total amounts of salts to be controlled. A full estimate is of special importance in enabling us to forecast what culture plants are likely to suc- ceed on a given tract, by reference to the table of “ tolerances ” given below (chapter 23, page 467). Composition of Alkali Soils as a Whole-—As may be im- agined, the presence of the alkali salts finds expression in the analytical statement of their composition, although not to the extent usually anticipated from their superficial aspect. The table annexed gives the composition of fourteen alkali soils, taken to the depth of one foot, at times when there was no visi- ble accumulation of salts on the surface. The averages of the several ingredients determined are given in the fifteenth col- umn, and a comparison of its figures with those of the general table on page 377 of chapter 20 will show some marked characteristics. We find the average potash-content to be but little less than twice as great as in the general average for the state of California ; in the case of lime the ratio is nearly as one to three, in the case of magnesia nearly one to two; in that of phosphoric acid, one to two and a half, of which in the presence of carbonate of soda an unusually large proportion is in a readily soluble, often in the water-soluble, condition (see preceding table). The usual proportion of soda, of one-fourth to one-half of the amount of potash, is changed to one-half or three-fourths; in the case of the strongest alkali lands soda may equal or even exceed the potash content. As the latter, however, is in- variably high to very high, it does not happen as frequently as might be supposed that the soda content exceeds that of potash as shown by the usual method of soil-extraction with water. 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In most cases the potash-percentage exceeds .75 %, and rises as high as 2.0% ; as is shown in the table. This table exhibits also another standing characteristic of alkali soils, which is to be anticipated from the conditions of their formation; viz, high lime-content, which sometimes rises to the extent of marliness. In phosphates, also, alkali soils are almost always high; and an unusually large proportion is found to be readily soluble. In presence of much carbonate of soda, nitrates are usually scarce or altogether absent; while owing to the action of the alkaline solution upon the humus, ammonia salts, or even free (or carbonated and therefore readily dissociated and assimi- lated) ammonia may be present, so as to be perceptible to the senses by its odor in hot sunshine. But in the case of “ white alkali,” more especially of the sulphate in moderate amounts, nitrification is exceedingly active and nitrates may sometimes rise to as much as 20% of the soluble salts. As alkali spots are usually low in the central portion and therefore more moist than around the edges, we sometimes find ammonia salts in the middle of a spot, while nitrates are abundant along the mar- gin of the same. These differences, first demonstrated by an investigation made by Colmore,! illustrate some of the reac- tions that are essentially concerned in the agricultural avail- ability of alkali lands. A summary of Colmore’s results is given in the table below. Cross Section of an Alkali Spot.—The spot examined lies outside of Tulare, California, substation; it being late in the season, when the bulk of the salts is found near the surface, the samples were taken to the depth of one foot only, at points four feet apart, from the center out. 1 Report of the California Exp’t St’n for 1892-94, p. 141. ALKALI SOILS. 449 AMOUNT AND COMPOSITION OF SALTS IN ALKALI SPOT FROM CENTER TO CIRCUMFERENCE, 4 FEET APART, I FT. DEPTH. 2 3 4 5 Mineral Salts. Center | Four Eight | Twelve | Outer of spot. feet. feet. feet. margin. Rotassiumysulfateectecie eels 6.70 9:55 11.92 19.26 13.95 Sodiumisulfatemerrr i191 19.84 12.85 23-72 23.97 16.96 Magnesium sulfate............. 3.07 .07 95 2.05 8.29 Sa@diumpchloricdteriry iste: 13.80 23.73 24.12 24.23 29.69 Nodiumuigcarbonatersysleceeraiciciels 50.72 50.96 37°55 35-49 20.94 Sodium'phosphate apy.) 5-57 2.88 o7 ? 1.04 SOGMMPM ETA Chrayers seloyeyellealetel= 30 ? .87 ? ag LONG dbo acbonbobooNs oe bo 100.00 | 100.00 | 100.00 | 100.00 ! 100.00 Organicimattereccsieercitretelets ale 30.00 24.80 19.48 23.36 20.31 otalisolubletinsoiliice ss sneee oe 78 54 70 “By/ 34 Mineraljsaltsneon eine sonics sicies .38 .40 54 25 23 While the table shows an obvious irregularity in some of the data at the eight-foot point, arising doubtless from an irregularity of surface or of texture overlooked in taking the samples, we find a very remarkable regularity of progression in the cases of potassium sulfate, sodium chlorid, sodium carbonate and sodium phosphate in the other four samples. The maxima of the “black alkali” and the soluble organic matter (humus) coincide, as does that of the phosphate; the total mineral salts at the outer margin are only a little over half of what is found at the center. This is natural, as owing to the deflocculating effect of the black alkali, the center is nearly a foot lower than the margin. The lowering of the nitrate-content at the outer margin is obviously due to the luxuriant vegetation growing adjacent. Reactions between the Carbonates, Chlorids and Sulfates of Alkalies and Earths. That a soluble earth-salt, such as the sulfate or chlorid of calcium, will react upon an alkaline carbonate solution so as to form an alkali sulfate, and e.g. lime carbonate, is well known; the neutralization of the sodic carbonate in the soil by means of gypsum, above referred to, is based upon this reaction.. It is not so well known that the latter may be reversed, partly or wholly, by the presence of carbonic acid in the solution of the soil. Although observed as early as 1824 by Brandes, and again in 1859 by A. Miiller, this reaction is not mentioned in text- books and attracted no attention as a source of naturally occurring alkali carbonates which in the past have formed the basis of extensive commerce from the Orient, until in 1888, the writer together with Weber 29 450 SOs: and later with Jaffa, investigated it quantitatively... It was found that up to.75 grms. per liter, the entire amount of sodic sulfate present in solution is transformed into carbonate in presence of calcic carbonate, by a current of carbonic dioxid ; but the amount so transformed does not continue to increase beyond about 4 grams per liter. A correspond- ing amount of calcic sulfate is formed. In the case of potassic sulfate, the transformation also occurs, proportionally to the molecular weight. This relation is shown in the subjoined diagram, which also shows in the curves on the left, the residual alkalinity left after evapora- tion and drying the residue at 100° C. Grams‘per Liter KHCO 3 6%) 18) 069) 10) Th 1) 184 1b) 16 17) 1819) 80S (230232425 is 8 3 fi fA als Te oS SSRs ID AT ASS a ee _ ra Aan a A Me Dt eT 2804 oa Grams per Liter K. ou ses Free nw ~ 2 Cle? SSa.FSaw Fic. 69.—Progressive Transformation of Alkali Sulfates into Carbonates. (The figures along upper line represent tenths of one per cent.) The corresponding reaction occurs also, of course, between sodium chlorid and calcium carbonate, but not to the same extent, because unlike the difficultly soluble gypsum, the reac- tion product is the very soluble calcium chlorid, the presence of which in the solution limits the reaction much sooner than when most of the decomposition product is thrown down in 1 Proc. Am. Soc. Agr. Sci., 1888; ibid., 1890; Rep. Cal. Expt. Sta., 1890, p. 100; Ber. Berlin, Chem. Ges., 1893; Am. Jour. Sci., August 1896. ALKALI SOILS, 451 the solid state. The calcium chlorid not uncommonly found in some alkali regions is undoubtedly the product of the above re- action. As the saline solutions in the soil are mostly quite dilute, and calcic carbonate is always present, it follows that whenever under the influences which favor the oxidation of organic mat- ter in the soil, and the activity of the plant roots, carbonic gas is formed somewhat copiously, alkali sulfates and chlorids present may be partially or wholly transformed into carbonates within the soil. As a matter of fact, it is found that this trans- formation occurs most readily in the moister portions of the soil and subsoil, and invariably so when an alkali soil is “ swamped” by excessive irrigation or rise of bottom water; while the reaction is again reversed whenever free access of air reduces the carbonic dioxid below a certain point. It thus be- comes intelligible why in the diagrams showing the distribu- tion of the salts (this chapter pp. 431 and 432), we always find the sodic carbonate relatively decreasing as the surface is approached. Thus, also, is explained the fact that sodium carbonate is formed more abundantly toward the center of the root system of alkali plants, such as the greasewood, beneath which the soil is always more abundantly charged with “ black alkali” than is the surrounding earth. Good aération of the soil mass, then, is essential in main- taining the neutralization of the “ black alkali” soils brought about by the use of gypsum (land plaster). Inverse Ratios of Alkali Carbonates and Sulfates.—Ac- cording to the above considerations, it is not surprising that we should often find an apparent inverse ratio between the alkali sulfates and carbonates in soils so closely adjacent that their salts must be presumed to be similar in composition. A striking example is shown in fig. 70, in which this inverse ratio becomes apparent four times in succession in one and the same soil profile. While this inference is plain on the face of the diagram, it is not quite easy to explain in detail how this alter- nation came about from the condition observed two months previously. Most probably it was caused by corresponding alternations of weather, in which short, warm spring showers alternated with similarly brief periods of drying north winds; ‘BIUIOSED ‘uoEIsqns yuauTedxy| sen], “puey yexALy peunerses Apjsed ur syydap snorea ye s}eS YeYLY JO uortsoduioy pur syunowmy—'oZ ‘1,7 StH 1903 F Lope TBsUreyy your 6:10ITV gest AvIT( 4) vn = 5 {row n 008 oy w av? = na —+— qnoar® A =. gs. lye) es" 06°) 88° 9s" Fs°> BS" 0s? eK or 452 or’ 4 Wale Fo 8 UST 4993 g Aopreg ) (S), 96st Worerg (2) I Iele E [SI 5 bl » fo} fe} a= Als a ° a] 3 ad (71 : HAN SUNTAN EK UBEK é PRCT DPE EL Ess 0" Br | Pel CUTTA TTT ope 2 Lue LLU LEB SU Err . or 9 FB" ; : 90° #0" ~—7— [198 J0 GOT UT sustpoaduy Jos o #yUNOUTY ALKALI SOILS: 453 the latter causing a reversal of the formation of sodic carbonate that had been induced by the former. Exceptional Conditions.—While the phenomena of alkali lands as outlined above probably represent the vastly predomi- nant conditions on level lands, yet there are exceptions due to surface conformation, and the local existence of sources of alkali salts outside of the soil itself. Such is the case where salts ooze out of strata cropping out on hillsides, as at some points in the San Joaquin Valley in California, and in parts of New Mexico, Colorado and Wyoming; also where, as in the Hungarian plain, saline clays underlie within reach of surface evaporation. Again, it not infrequently happens that in sloping valleys or basins, where the central (lowest) portion receives the salts leached out of the soils of the adjacent slopes, we find belts of greater or less width in which the alkali impregnation may reach to the depth of ten or twelve feet, usually within more or less definite layers of calcareous hardpan, likewise the outcome of the leaching of the valley slopes. Such areas, however, are usually quite limited, and are at present scarcely reclaimable without excessive expenditure; the more as they are often un- derlaid by saline bottom water. In these cases the predominant saline ingredient is usually common salt, as might be expected and as is exemplified in the Great Salt Lake of Utah, in the Antelope and Perris Valleys, and in Salton basin in California ; in the Yellowstone valley near Billings, Mont.' in the Aralo- Caspian desert, and at many other points. Conclusions.—Summing up the conclusions from the fore- going facts and considerations, we find that— (1) The amount of soluble salts in alkali lands is usually limited ; they are not ordinarily supplied in indefinite quantities from the bottom-water below. These salts have mostly been formed by weathering in the soil-layer itself. (2) The salts move up and down within the upper four or five feet of the soil and subsoil, following the movement of the moisture; descending in the rainy season to the limit of the annual moistening as a maximum, and then reascending or not, according as surface evaporation may demand. At the end of 1 Farmer’s Bull. No. 88, U. S. Dept. Agr., 1899. 454 SOILS. the dry season, in untilled irrigated land, practically the entire mass of salts may be within six or eight inches of the surface. (3) The direct injury to vegetation’ is caused largely, within a few inches of the surface, by the corrosion of the bark, usually near the root crown. This corrosion is strongest when carbonate of soda (salsoda) forms a large proportion of the salts; the soda then also dissolves the vegetable mold and causes blackish spots in the soil, popularly known as black alkali. (4) The injury caused by carbonate of soda is aggravated by its action in puddling the soil so as to cause it to lose its crumbly or flaky condition, rendering it almost or quite un- tillable and impervious. It also tends to form in the depths of the soil-layer a tough, impervious hardpan, which yields neither to plow, pick, nor crowbar. Its presence is easily ascertained by means of a pointed steel sounding-rod. (5) While alkali lands share with other soils of the arid region the advantage of unusually high percentages of plant- food in the insoluble form, they also contain, alongside of the noxious salts, considerable amounts of water-soluble plant- food. When, therefore, the action of the noxious salts is done away with, they should be profusely and lastingly productive; particularly as they are always naturally somewhat moist in consequence of the attraction of moisture by the salts, and are therefore less liable to injury from drought than the same soils when free from alkali. 1 For a general statement and discussion of the physiological effects of saline solutions on plants, see chapter 26. —— CHAPTER air. UTILIZATION AND RECLAMATION OF ALKALI LANDS. Alkali-Resistant Crops.——The most obvious mode of utiliz- ing alkali lands is to occupy them with crops not affected by the noxious salts. Unfortunately but few such crops of general utility have as yet been found for the stronger class of alkali lands. The question is always one of degree, which frequently cannot be decided without an actual determination of the amount and kind of salts to be dealt with, to which the crops can then be adapted in accordance with the greater or less sensi- tiveness of the several plants, as indicated in the table of toler- ances given farther on. But aside from this, there are certain general measures and precautions which in any case will serve to mitigate the effect of the alkali salts. Foremost among these, and applicable everywhere, is the prevention of evapora- tion to the utmost extent possible. Counteracting Evaporation.—Since evaporation of the soil- moisture at the surface is what brings the alkali to the level where the main injury to plants occurs, it is obvious that evapo- ration should be prevented as much as possible. This is the more important, as the saving of soil-moisture, and therefore of irrigation water, is attainable by the same means. Three methods for this purpose are usually practiced, viz., shading, mulching, and the maintenance of loose tilth in the surface soil to such depth as may be required by the climatic conditions. As to mulching, it is already well recognized in the alkali regions of California as an effective remedy in light cases. Fruit trees are frequently thus protected, particularly while young, after which their shade alone may (as in the case of low-trained orange trees) suffice to prevent injury. The same often happens in the case of low-trained vines, small-fruit, and vegetables. Sanding of the surface to the depth of several inches was among the first attempts in this direction; but the 455 456 SOILS. necessity of cultivation, involving the renewal of the sand each season, renders this a costly method. Straw, leaves, and ma- nure have been more successfully used; but even these, unless employed for the purpose of fertilization, involve more ex- pense and trouble than the simple maintenance of very loose tilth of the surface soil throughout the dry season; a remedy which, of course, is equally applicable to hoed field crops, and is in the case of some of these—e. g., cotton—a necessary con- dition of cultural success everywhere. The wide prevalence of “light” soils in the arid regions, from causes inherent in the climate itself, renders this condition relatively easy of ful- filment. Turning-under of Surface Alkali—Aside, however, from the mere prevention of -surface evaporation, another favorable condition is realized by this procedure, namely the comming- ling of the heavily salt-charged surface-layers with the rela- tively non-alkaline subsoil. Since in the arid regions the roots of all plants retire farther from the surface because of the deadly drought and heat of summer, it is usually possible to cultivate deeper than could safely be done with growing crops in humid climates. Yet even there, the maxim of “ deep prep- aration and shallow cultivation” is put.into practice with ad- vantage, only changing the measurements of depth to corre- spond with the altered climatic conditions. Thus while in the humid States, three to four inches is the accepted standard of depth for summer cultivation to preserve moisture without injury to the roots, that depth must in the arid region fre- quently be doubled in order to be effective; and will even then scarcely touch a living root in orchards and vineyards, particu- larly in unmanured and unirrigated land. A glance at fig. 63, chapt. 22, p. 431), will show the great advantage of extra-deep preparation in commingling the alkali salts accumulated near the surface with the lower soil-layers, diffusing the salts, say through twelve instead of six inches of soil mass. This will in very many cases suffice to render the growth of ordinary crops possible if, by subsequent frequent and thorough cultivation, surface evaporation, and with it the re-ascent of the salts to the surface, is prevented. A striking example of the efficiency of this mode of proced- ure was observed at the Tulare substation, California, where a UTILIZATION AND RECLAMATION OF ALKALI LANDS. 457 portion of a very bad alkali spot was trenched to the depth of two feet, throwing the surface soil to the bottom. The spot thus treated produced excellent wheat crops for two years—the time it took the.alkali salts to reascend to the surface. It should therefore be kept in mind that whatever else is done toward reclamation, deep preparation and thorough culti- vation must be regarded as prime factors for the maintenance of production on alkali lands. The Efficacy of Shading, already referred to, is strikingly illustrated in the case of some field crops which, when once established, will thrive on fairly strong alkali soil, provided that a good thick “stand” has once been obtained. This is notably true of the great forage crop of the arid region, alfalfa or lucern. Its seed is extremely sensitive to “ black” alkali, and will decay in the ground unless protected against it by the use of gypsum in sowing. But when once a full stand has been obtained, the field may endure for many years without a sign of injury. Here two effects combine, viz., the shading, and the evaporation through the deep roots and abundant foliage, which alone prevents, in a large measure, the ascent of the moisture and salts to the surface. The case is then precisely parallel to that of the natural soil (see p. 432, chapter 22), ex- cept that, as irrigation is practiced in order to stimulate produc- tion, the sheet of alkali hardpan will be dissolved and its salts spread through the soil more evenly. The result is that so soon as the alfalfa is taken off the ground and the cultivation of other crops is attempted, an altogether unexpectedly large amount of alkali comes to the surface and greatly impedes, if it does not altogether prevent, the immediate planting of other crops. Shallow-rooted annual crops that give but little shade, like the cereals, while measurably impeding the rise of the salts during their growth (see fig. 70, page 452) frequently allow of enough rise after harvest to prevent reseeding the following season. “ Neutralizing’ Black Alkali—Since so little carbonate of soda as one-tenth of one per cent. may suffice to render some soils uncultivable, it frequently happens that its mere trans- formation into the sulfate is sufficient to remove all stress from alkali. Gypsum (land plaster) is the cheap and effective agent to bring about this transformation, provided water be also 458 SOILS. present. The amount required per acre will, of course, vary with the amount of salts in the soil, all the way from a few hundred pounds to several tons in the case of strong alkali spots; but it is not usually necessary to add the entire quantity at once, provided that sufficient be used to neutralize the sodic carbonate near the surface, and enough time be allowed for the action to take place. In very wet soil, and when much gypsum is used, this may occur within a few days; in merely damp soils in the course of months; but usually the effect increases for years, as the salts rise from below. The effect of gypsum on black-alkali land is often very strik- ing, even tothe eye. The blackish puddles and spots disappear, because the gypsum renders the dissolved humus insoluble and thus restores it to the soil. The latter soon loses its hard, puddled condition and crumbles and bulges into a loose mass, into which water now soaks freely, bringing up the previously depressed spots to the general level of the land. On the sur- face thus changed, seeds now germinate and grow without hin- drance; and as the injury from alkali occurs at or near the sur- face, it is usually best to simply harrow in the plaster, leaving the water to carry it down in solution. Soluble phosphates present are decomposed so as to retain finely divided, but less soluble earth phosphates in the soil. It must not be forgotten that this beneficial change may go backward if the land thus treated is permitted to be swamped by irrigation water or otherwise. Under the same conditions naturally white alkali may turn black (see above, chapter 22, p. 451). Of course, gypsum is of no benefit whatever on soils containing no “ black” alkali, but only (‘‘ white’’) Glauber’s and common salt. Removing the Salts from the Soil.—In case the amount of salts in the soil should be so great that even the change worked by gypsum is insufficient to render it available for useful crops, the only remedy left is to remove the salts, partially or wholly, at least from the surface of the land. Three chief methods are available for this purpose. One is to remove the salts, with more or less earth, from the surface at the end of the dry season, either by sweeping or by means of a horse scraper set so as to carry off a certain depth of soil. Thus sometimes in a single season one-third or one-half of the total salts may be got UTILIZATION AND RECLAMATION OF ALKALI LANDS. 459 rid of, the loss of a few inches of surface soil being of little moment in the deep soils of the arid region. Another method affording partial relief is to flood the land for a sufficient length of time to carry the alkali three or more feet below the surface, then carefully preventing its reascent by suppressing evaporation (see this chapter, p. 455) as much as possible. The best of all, the final and universally efficient remedy, is to leach the alkali salt out of the soil into the country drainage; supplementing by irrigation water what is left undone by the deficient rainfall. It is not practicable, as many suppose, to wash the salts off the surface by a rush of water, as they instantly soak into the ground at the first touch. Nor is there any certain relief from allowing the water to stand on the land and then drawing it off; in this case also the salts soak down ahead of the water, and the water standing on the surface remains almost unchanged. In very pervious soils and in the case of white alkali, the washing-out can often be accomplished without special provis- ion for underdrainage, by leaving the water on the land suffi- ciently long. But the laying of regular underdrains greatly accelerates the work, and renders success certain. Leaching-Down.—In advance of underdrainage, it is quite generally feasible, where the land has been leveled and diked for irrigation by surface flooding, to leach the salts out of the first three or four feet by continued flooding, thus taking them out of reach of the crop roots, or at all events giving the seed an opportunity to escape injury from alkali. This plan is es- pecially effective in the case of alfalfa, the young seedlings of which are very sensitive, while the grown plant is rather re- sistant. In order to obtain this relief so as to know what is being accomplished, the farmer should ascertain beforehand how fast water will soak down in his ground;? for in heavy clay soils, and especially in those containing black alkali, the soak- age is sometimes so slow that the upward diffusion of the salts keeps pace with the downward soakage; in which case nothing is accomplished by flooding, and underdrainage is the only remedy. But in most soils of the arid region flooding from three days to a week will remove the alkali beyond reach of the roots of ordinary crops. If subsequently irrigation is done 1 See p. 242, Chap. 13. 460 SOILS. by means of deep furrows, the alkali salts may be either kept at a low level continuously, or if the land be at all pervious, the alkali may ultimately be permanently leached out into the sub- drainage by farther flooding. When the alkali has not accumu- lated near the surface to any great extent, irrigation by deep furrows may, alone, afford all the relief needed. In the case illustrated by figures 71 and 72, irrigation by shallow furrows with water too strongly charged with salts had so far added to the natural alkali-content of the land that Fic. 71.—Lemon Orchard Affected by Alkali; Before Deep Irrigation. the lemon trees were being defoliated. Upon the advice of the California Station the deep-furrow system was adopted, and within two years the results were as shown in figure 72, the salts having been carried down and diluted so as to be- come harmless. Underdrainage the Final and Universal Remedy for Alkali. —When we underdrain an alkali soil, we adopt the very means by which the existence of alkali lands in the humid regions is wholly prevented; the leaching-out of the soluble salts formed in soil-weathering as fast as they are formed. The long and abundant experience had with underdrainage in reclaiming UTILIZATION AND RECLAMATION OF ALKALI LANDS. 461 saline sea-coast lands, applies directly and cogently to alkali lands. It is the universal remedy for all the evils of alkali, and its only drawback is the first expense, and the necessity for obtaining an outlet for the drain waters, which cannot always be had on the owner’s land. Hence it requires co-operation or legislation to render the great improvement of underdrainage feasible. Such legislation 1s well established in the old world, and has been enacted in several states even of the humid region. Where irrigation is practiced as a matter of necessity, Fic. 72.--The Above Orchard after Alkali was Driven Down by Deep Irrigation, followed by Cultivation. underdrainage is a correlative necessity, both to avoid the evils of over-irrigation and to relieve the land of noxious alkali salts. The drainage law now existing in California does not go farther than to authorize the formation of drainage districts, within which the necessary taxes may be levied; and there is some difficulty in securing popular action. But bitter experi- ence will doubtless in time compel unanimity, such as now ex- ists, e. g., in Illinois, where drainage is not nearly so urgently needed as it is in the irrigation States. 462 SOLLS: Possible Injury to Land by Excessive Leaching.—It should not be forgotten, however, that excessive leaching of under- drained land by flooding is lable to injure the soil in two ways: first, by the removal of valuable soluble plant-food ; and further, by rendering the land less retentive of moisture, such retention being favored by the presence of small amounts of alkali salts, not sufficient to injure crops. After the salts have been carried down to a sufficient depth to prevent injury to annual crops, and with proper subsequent attention to the pre- vention of surface evaporation, the flooding will not need to be repeated for several years. Thus in many soils excellent crops may be grown even in strong alkali land, pending the establishment of permanent drainage systems. The importance of thoroughly washing the alkali deeply into the soil before the seed is planted, and keeping it there by proper means until the foliage of the plant shades the soil sufficiently to prevent the rise of moisture and alkali, is well illustrated in fields in the region of Bakersfield, Cal., where alfalfa is now growing in soils once heavily charged with alkali. From one of these fields samples of soil were taken where the alkali was supposed to be strongest beneath the alfalfa, and also from an adjoining untreated alkali spot, which was said to represent conditions before alfalfa was planted. ‘The results.are given in pounds per acre in four feet depth. Sulfate. Car- Common] _ Total bonate. Salt. Alkali. Alkali spot before alfalfa was planted.| 60,120 720 175,840 | 236,680 Alfalfa field; alkali washed down.... 14,400 ee 1,040 18,640 Here the surface foot of the natural soil contained nearly 140,000 pounds of common salt, a prohibitory amount. Similar experience has been had near Yuma, Arizona. Dificulty in Draining “ Black” Alkali Lands.—An import- ant exception to the efficacy of draining, however, occurs in the case of black alkali in most lands. In this case either the impervious hardpan or (in the case of actual alkali spots) the 1 Bull. 133, Cal. Expt. Sta., by R. H. Loughridge. UTILIZATION AND RECLAMATION OF ALKALI LANDS. 463 impenetrability of the surface soil itself will render even under- drains ineffective unless the salsoda and its effects on the soil are first destroyed by the use of gypsum, as above detailed. This is not only necessary in order to render drainage and leaching possible, but is also advisable in order to prevent the leaching-out of the valuable humus and soluble phosphates, which are rendered insoluble (but not unavailable to plants) by the action of the gypsum. Wherever black alkali is found in lands not very sandy, the application of gypsum should precede any other efforts toward reclamation. Trees and vines already planted may be temporarily protected from the worst effects of the black alkali by surrounding the trunks with gypsum or with earth abundantly mixed with it. Seeds may be similarly protected in sowing, and young plants in planting. Swamping of Alkali Lands.—It should, however, be remem- bered that the swamping of alkali lands, whether of the white or black kind, is fatal not only to their present productiveness, but also, on account of the strong chemical action thus induced, greatly jeopardizes their future usefulness. Many costly in- vestments in orchards and vineyards have thus been rendered unproductive, or have even become a total loss. Reduction of Alkali by Cropping.—Another method for diminishing the amount of alkali in the soil is the cropping with plants that take up considerable amounts of salts. In taking them into cultivation, it is advisable to remove en- tirely from the land the salt growth that may naturally cover it, notably the greasewoods (Sarcobatus, Allenrolfea), with their heavy percentage of alkaline ash (12 to 20 per cent). Crop plants adapted to the same object are mentioned farther on. Such crops should also, of course, be wholly removed from the land. Total Amounts of Salts Compatible with Ordinary Crops; Tolerance of Culture Plants——Since the amount of alkali that reaches the surface layer is largely dependent upon the varying conditions of rainfall or irrigation, and surface evaporation, it is difficult to foresee to what extent that accumulation may go, unless we know the total amount of salts present that may be called into action. This, as already explained, can ordinarily be ascertained by the examination of one sample representing the average of a soil column of four feet. By calculating the figures so obtained to an acre of ground, we can at least ap- proximate the limits within or beyond which crops will suc- ceed or perish. Applying this procedure to the cases repre- sented in the diagrams (pp. 434, 452, chapter 22) and estimat- ing the weight of the soil per acre-foot at 4,000,000 pounds, we find in the land on which barley refused to grow the figures 32,470 and 43,660 pounds of total salts per acre, respectively corresponding to 0.203 per cent. for the first figure (the second, representing only the two surface feet, is not strictly compar- able). For the land on which barley gave a full crop, we find for the May sample 25,550 pounds, equivalent to 0.159 per cent. for the whole soil column of four feet. It thus appears that for barley the limits of tolerance lie between the above two figures. It should be noted that in this case a full crop of barley was grown even when the alkali consisted of fully one-half of the noxious carbonate of soda; proving that it is not necessary in every case to neutralize the entire amount of that salt by means of gypsum, which in the present case would have required about 9% tons of gypsum per acre—a prohibitory expenditure. Relative Injuriousness of the Several Salts—Of the three sodium salts that usually constitute the bulk of “ alkali,” only the carbonate of soda is susceptible of being materially changed by any agent that can practically be applied to land. So far as we know, the salt of sodium least injurious to ordinary vege- tation is the sulfate, commonly called Glauber’s salt, which ordinarily forms the chief ingredient of ‘“ white” alkali. Thus barley 1s capable of resisting about five times more of the sulfate than of the carbonate, and quite twice as much as of common salt. Since the maximum percentage that can be re- sisted by plants varies materially with the kind of soil, it is difficult to give exact figures save with respect to particular cases. For the sandy loam of the Tulare substation, Cali- fornia, for instance, the maximum for cereals may be approxi- mately: stated to be one-tenth of I per cent. for salsoda; a fourth of 1 per cent. for common salt; and from forty-five to fifty one-hundredths of one per cent of Glauber’s salt. For clay soils the tolerance is in general markedly less, especially as re- gards the salsoda ; since in their case the injurious effect on the UTILIZATION AND RECLAMATION OF ALKALI LANDS. 405 tilling qualities of the soil, already referred to, is superadded to the corrosive action of that salt upon the plant. Liffect of Differences in Composition of Alkal Salts on Beets.—The marked differences which may occur as the result of even slight variations in the proportions of the several salts is well illustrated in the subjoined diagram of observations made by Dr. G. W. Shaw, of the Cal. Expt. station, upon beet fields in the neighborhood of Oxnard, Cal. The f 4 b CeEr eines aoc PN guekat | Ael aahad ad ae i NS SEC Nh ERBBGBEE hice 280 AC See S ak Sam 1 * = Fic. 74.—Beets from corresponding positions in the above field. lands lie not far from the sea-shore, and saline water underruns them for considerable distance inland. The soil and subsoil are quite sandy, so that it takes irrigation water only about seven hours to penetrate 30 406 SOILS. from the surface to bottom water at seven feet depth. The land on which these observations were made are apparently level to the eye, though probably the alkali belts on which the sugar beets were ‘ poor ”’ are slightly depressed swales. It will be noted that here the beets were “ good” where the sulfate (Glauber’s salt) ranged up to .8%, with .10 to .20 of common salt; but that so soon as the latter rose above .20, the beets were poor despite the low percentage of Glauber’s salt; then became “ good” again so soon as the common salt fell below .20%, although the Glauber’s salt increased. TOLERANCE OF VARIOUS CROP PLANTS. The following table, compiled by Dr. R. H. Loughridge mainly from his own observations,’ gives the details of the tolerance for various culture plants as ascertained at the several experiment substations in California, as well as at other points in that State and in Arizona where critical cases could be found. It is thought preferable to investigate analytically such cases in the field, rather than to attempt to obtain results from small-scale experiments artificially arranged, in which sources of error arising from evaporation and other causes are most difficult to avoid. The table is so arranged as to show the maximum tolerance thus far observed for each of the three single ingredients, as well as the maximum of total salts found compatible with good growth. In view of the ex- tremely variable proportions between the three chief ingredients found in nature, this seems to be the only manner in which the observations made can be intelligibly presented, until perhaps a great number of such data shall enable us to evolve mathematical formule expressing the tolerance for the possible mixtures for each plant. For it is certain that the tolerance-figures will be quite different in presence of other salts, from those that would be obtained for each salt separately ; or for the calculated mean of such separate determinations, proportionally pro-rated. It must also be remembered that in all alkali soils, lime carbonate is abundantly present, as is, nearly always, a greater or less amount of the sulfate (gypsum). As already stated, according to the in- vestigations of Cameron not only these compounds, but also calcium chlorid, exert a protective influence against the injury to plant growth from compounds of sodiumand potassium. The figures here given can 1 Bulletins Nos. 128, 133 and 140, Calif. Expt. Station. UTILIZATION AND RECLAMATION OF ALKALI LANDS, 467 therefore be regarded only as approximations, subject to correction by farther observation. They are arranged from the highest tolerances downward, for each of the three ingredients, as well as for the totals. The latter are not, of course, the sums of the figures given in the pre- ceding columns, but independent data. HIGHEST AMOUNT OF ALKALI IN WHICH FRUIT TREES WERE FOUND UNAFFECTED.! Arranged from highest to lowest. Pounds per acre in four feet depth. Sulfates (Glauber’s Salt). Grapeseed 40,800 Olives'yascccuets 30,640 IDERBnggooonogeec 24,480 Almonds ...... 22,720 Oranges: 2.10. 18,600 IDEATSpeieiereiicict 17,800 Apples...... -. 14,240] Reaches see =e 9,600 IPOS Syeroctelst- l= 9,240 Apricots....... 8,640 Iemons....... - 4,480 Mulberry...... 3,360 KGlreuteria.... 51,040 Eucal. am 34,720 Or. Sycamore... 19,240 Wash. Palm.... 13,040 Date Palm 5,500 Camph. Tree... 5,280 Saliturshieeieres. 125,640. 102,480) Alfalfa, old ... Alfalfa, young.. 11,120 Hairy Vetch.... 63,720 Sorghum. ....... 61,840 Sugar Beet..... 52.640 Sunflower...... 52,640 Radish......... 51,880 Artichoke...... 38,720 Carrotecicesisiersie'- 24.880 Gluten Wheat. . 20,960 Wihleatcrc/(e.-1- 1-0 x55120 arleyarerce|-t + 12,020 Goat s Rue.... 10,880 RV Erie steissclarefelers g,800 Cafiaigre....... 9,160 Ray Grass...... 6,920 Modiola........ 6,800 Bur Clover.... 5,700 bay tth eeaeeoooo 55440 White Melilot... 4,920 Weleny- 11-110! 4,080 Saltgrass... .. 44,000 1 The several co Carbonate Chlorid P (Salsoda). (Common Salt). Total Alkali. Grates occiscveces 755 50| GLADES mielelelelel=itel=1= 9,640|Grapes........... 45,700 Oranges... 33840) Olives) eve -ie1e ele1=1= 6:640 Olives tosses 40,160 HOMIWES serteterenectorats 2,880] Oranges........-- 3,360/Almonds......... 25,560 WREATS crete Seonets 1,760] Almonds......... 25400 HAGSieios oe see aii ZO OO |Almonds......... 1,440|Mulberry........ 2,240/Oranges.......... 21,840 IANS S) GAguedade HSOIEEENS eocooosaade 1300) |Pearseninisiin see 20,920 Hig -soferieivlel oreo cis rr20|/AippleSase-esiesiet 13240) Apples. -)-e/srr 16,120 Peaches 68o|(Bronesmerreneienr T200)|/PHINES erect eestor 11,800 Apples 640| Peaches......... . 1,000] Peaches vole Tk; 280 Apricots 480] Apricots.......... 960|Apricots.......... 10,080 ILO cocoa abOS 480|Lemons..........- 800|l.emons..........- 5,760 Mulberry......... rise] [Senaszconoo eae 800|Mulberry......... 5,760 OTHER TREES. KGlreuteria...... 9,920|Or. Sycamore.... 20,320|KGlreuteria...... 73,600 Or. Sycamore..... 3,200] Kélreuteria...... 12,640|Or. Sycamore.... 42,760 Date Palme 2,800] Eucal. am......- 2.900) Piicals, ame. sacee 40,400 Encal, am......... 2,720|Camph. Tree..... 1,420)Wash. Palm...... 15,200 |Wash. Palm....... 1,200| Wash. Palm...... 1,040]Date FPalm....... 8,328 Camph: Tree:./<..- 320 Camph. Tree..... 7,020 SMALL CULTURES. Naltboshtrrerecrtsr 18,560] Modiola posioanone 40,860)Saltbush......... 156,720 Barleyaspeeee oet2 scl Saltyushy se. sei X25520|'Altalta olden 110,320 Bur Cloveran ler 11,300|Sorghum......... 9,680) Alfalfa, young... 13,120 |Sorghum......... Q:S40\Gelenyace clei seins g,600|Sorghum......... 81,360 [Wwadis hirer jester 8,720/Onions........... 5,810] Hairy Vetch..... 69,360 i Miodiolaciercyeiysne 4,760| Potatoes.........: Brendel PRECKSIN se sboqngas 62,840 Sugar Beet....... 4,000] Sunflower........ 5,440|/Sunflower... ... 59,840 Gluten Wheat.... 3,000/Sugar Beet?...... 10,240|Sugar Beet....... 59,840 Artichoke......... 25700 BALL EY 2 -i ‘ANIT AO savak yyS Aq ‘sqy cor 0} SZ 0} YO Surrey ‘rwak ysay u0}309 ‘sq, ooz *sivad of ul sq] 00% 0} Zualsvaisep uty uojzj09 ‘sq, oot ‘ANDY UAg Nomonaoug *ysnd0] Asuoy ‘un3 yor[q pur joams YnuyeM ‘AroxI1Y “TRO *]euls ‘yeo ystueds pur jsod ‘yap1v9g *ysnooy Asuoy pure o[dde qvio ‘1epoo pel ‘yeo ysod pue yovl-yor;q Apanis Ayurey Tes yoouue Py 1e4S BGS MOpRay Devel THOS WPSSE eset LOS) OYsyong ,, [IOS ssoo'T 10 0g aos) PUL Sea uMOolg ‘weoT purjdy surg REEeIEO ‘TI0S OSpPrey pel orpgq Wes poomyey Aavay ‘THOS eBpry 90}0}U0g ‘weOT 93pry MOTPPA IPd ‘TOS ae g pela “NOILVLH9HA TIVANLVN ‘SANV1I IddISSISSIN NI ‘HSVLOd GNV GIOV OINOHdSOHd ‘aNVN 498 SOILS, DIFFERENCES IN THE FORM AND DEVELOPMENT OF TREES.? It will be noted that in the above table, as well as in the dis- cussion preceding it, identical species of trees are ascribed to vegetative areas of widely different productive capacity. Per- haps the most striking example is that the cretaceous prairies and the adjoining flatwoods belt, standing respectively highest and lowest in the scale of productiveness, are yet bearing specifically identical tree-growth, to-wit, the post oak (Quercus minor) and the black-jack oak (Q. marylandica). While to the field botanist ? there can be no question as to the absolute specific identity of the two trees as growing on the respective areas, yet the mode of development of both is so different in the two cases, that, as before remarked they are popularly sup- posed to be different ‘ kinds.” Forms of the Post Oak.—The post oak of the prairie lands is a tree 50 to 70 feet high, with a stout, excurrent, rather conical trunk, often somewhat curved to one side above, and densely clothed from within 12 or 15 feet of the ground with com- paratively short, sturdy branches set squarely to the trunk, much crooked (geniculate), often reflexed downward; alto- gether forming a dense head, beneath whose thick foliage, a bird or squirrel is quite secure from the hunter’s aim.—In the flatwoods, on the contrary, the post oak has a thin, rather short trunk, divided up at 15 or 20 feet height into long, rod-like branches, spreading broom-fashion, and scantily clothed with 1 It is a matter of regret to the writer that owing to the long distance intervening and the difficulty of securing competent and sympathetic observers for such work, it has not been possible for him to secure photographs of the tree-forms here dis- cussed. At the time his own observations were made, photography was prac- tically unavailable as yet, and the figures given are therefore based upon sketches made at the time, and partly upon recollection. They represent types rather than definite individuals, which were however described when fresh in mind, in the Report on the Agriculture and Geology of Mississippi, 1860, pages 254 et seq. 2 It has been already, and doubtless will be again and increasingly, attempted to make distinct “species” of these widely different forms of trees. But this is simply begging the question. Mere external diagnostic marks will not avail here; it would have to be shown that the seed of these different forms do not produce the other forms under changed conditions. Until this has been done, the number- less transition forms which he that runs may observe in the field, throw upon the species-makers the onus of proof of differences of specific value—if it be possible to define such value. RECOGNITION OF CHARACTER OF SOILS. 499 short twigs bearing tufts of leaves; thus forming an open head, in which no creature can hide effectually. On the brown-loam table-lands, again, the post oak has a straight, rather slender, excurrent trunk with long and more or less crooked limbs pro- jecting at a large angle, sometimes even drooping, and freely divided up into lateral, leafy branches; the trees attain from 40 to 55 feet in height. Again, on the high sandy ridges which are interspersed in the eastern portion of the brown loam area, we find, generally associated with a similarly depauper- ated form of the black-jack oak, and with the Upland Wil- low oak (Q. cinerea), a form of the post oak intermediate be- tween that of the Flatwoods and the Table lands; twelve to fifteen feet high, with thin trunk, “ sprangling”’ long, crooked branches, clothed with sparse tufts of leaves. These four strikingly distinct types are shown schematically, in their ex- treme development, in the subjoined figures. It is hardly necessary to say that between these extreme forms there are many degrees of transition, corresponding to the transitions between the several soil-classes respectively rep- resented by them; or they may be developed into depauperated types. Thus, for example, the forms of the post and black-jack oak found on the sandy ridges of the yellow loam region, hardly need experience in the observer to interpret them as characterizing a wretchedly poor soil. Forms of the Black-jack Oak.—Not less striking are the characteristics of the forms of the black-jack oak as developed upon these several kinds of land. The black-jack of the prai- ries is a low tree with a dense rounded head, often somewhat flattened above, and a low, thick-set trunk divided up into square-set branches, so densely clad with foliage that no light penetrates into the interior, and birds can safely hide and nest within it. The height rarely exceeds 35 feet, the’head being 20 to 30 feet across. The Flatwoods form, on the contrary, rarely exceeds 15 feet in height, with a very rough bark and a small, rather dense, rounded top, giving the whole the appearance of a small apple tree. Practically the same form is seen on poor, clay ridges of “ hogwallow ” land. On the brown-loam lands the black-jack, like the post oak, has a rather slender, often somewhat crooked, but excurrent ‘ a piente . NO Pe EE APR Ge PR ry SPE 9 “(USI 2907252790 “YSAv]y 40UiML SHIAINC)) YLO YSOd JO SWAY awaayxq-—62 org : *‘spoomyr| ‘sosplry Apues = *purjdg weroT A Pe 2 A ee Bh Me ‘auteld YORI SOILS. SEES Ne is ii Gn kt la ate O 50 RECOGNITION OF CHARACTER OF SOILS. 501 trunk 35 to 50 feet high, with more or less crooked limbs of moderate length, well provided with leafy branches, but form- ing altogether a rather open crown. ) o6'f z6'9 €6°br $g° zS'h ooze 06'S £6'r tgz piotelnxelen sl suse sceneneleuses sieeslessiea (08 (¢) Ci) pre oNj[Ng og‘or 00°S Tree Lr: Scr £3" 09'S 1S‘ 0g'z DOB OOUCIOUDOUDO OOD ROD (EK YA pj ohiahtepeoio(aheso ts oo'S’é 29'S PO'11 1g" 6L:99 £L°9L oo'F IQ II bz9g1 Sig gchetiels haetaiae Wier areinnes oles ie ekeiens ate slerereisseie ee LeOPOTT TS : : : ; ' ; ; : See te cece ee csceee sie cee eecce (SET) runny y S6:z 69'S 611 6£:z zzz pep jou gol fee t sete seecseeeeeeeseees(8Q%8Q 7) UOIT JO pIxolog 1S" Sz or zz teeeeeereeeerers(POSu asouvSuLyy Jo “xo “Ag o9'f£ gSz £9'91 oLgz Si'¥ Sé'z 6o'r 60"! €ze aYs{erasejelerazoivloleralala\slslsiereiatelerelstole (@qy'sh TATn) PISOUSE IAT £3°6 1S'0z L6°Sz 99°S9 So'g ozs ol'g gf'r SLs SisheZeiesjeiase) sxe olelereiersietencieeve\oies einehxeleel (iG) Bay) sully oLz gtr €z'9 glz SxS giz gs ze Sr 6£ 6E:SE we eetr noes sole) sicletoseseiointesscesetersssisse}((@)\YNTp) epos 0g'gz zltr LZr'Sz 19't gis ofe 1rof €S-gr Zeir axe olereieiese, clei eie) eleisiehinlcisvekeseleieieirie.eo521((() Sisto) ysej}og S19 S96 Sees. gubz 66:2 Ig'Il 1g'fr forz1 Le-61 °°), Sued poupare ‘ysy SSS Se ee SS eS SS SSS Sea jer] e ‘J ar) 2G) oe a cS n i=} i=] o 4 an 8>5 2 Ob: we ERAS a2 GES | spor re Be Ba. eee ees epee eenioe gig | soe oz 2) Nau} rea 02 aiew oof Eos Fae) ete “= B gee Baw go BES Beg Bes | SP ee = po a 8 GB ae & & B a8 = "5 5 spe ee S a aoe OS eae ee ee ee eee Se a ‘SdOU4O ADVAOA AO | ‘SLNVI1d ITVH1V ONY ANITVS 40 SHHSV AO SHUSATVNV — SALINE AND ALKALI LANDS. 531 always moist to the touch, containing ordinarily over 15% of moisture. It is therefore much liked by stock when fed intermixed with other hay, and thus supplies all the salt needed by cattle. The greasewood is much less liked by stock, and bushy samphire is wholly rejected by them. Comparing with these fleshy plants the ash of the two grasses, the first a world-wide ‘salt grass,” the other a common grass of the American arid region, we note that not only do they contain much less soluble ash than the saltbushes, but especially much smaller amounts of sodium salts; proving that even when growing in company with the saltbushes on strongly impreg- nated land, they can repel from absorption these to them use- less or injurious salts. But in the case of the “shad scale,” also a “saltbush” of the Great Basin, the ash-content is remarkably low—only about one-fifth of that of its Australian relative—and it differs widely from the latter in having but a very low proportion of soda, and a very high one of lime and potash, approaching in these respects to our usual forage crops; and being also fairly rich in nitrogen, it forms accept- able browsing when other pasture plants are scarce. It there- fore does not exert the laxative action produced by the exclu- sive feeding on the more saline herbages. The exceptionally high ash-content of the cactus or prickly pear, also given in the table, arises, it will be noted, not from the soluble salts but from the absorption of extraordinarily high proportions of lime and magnesia. Owing probably to the latter substance, and also the oxalate form in which lime is usually found in the cactus tribe, this plant when used as forage is also somewhat laxative. Altogether, this table offers remarkable examples of wide differences in the kind and amount of ash ingredients ab- sorbed by plants growing upon similar soils and under identi- cal climatic conditions; indicating a selective power which no merely physical theory of soil-action in plant growth can ex- plain. Injury to Plants from the Various Salts—The early ob- servers, especially Contejean, were predisposed from _ their observations of lime on vegetation to ascribe the action of salt upon marine vegetation to the sodium component. But the wide differences in the effects of different sodium compounds, 532 SOILS. notably of common salt and Glaubers salt, led some to the con- clusion that the acidic ingredients are the chief determin- ing factors. Moreover, it was soon found that a single salt is more injurious than a mixture of several, such as sea water. This also led to the inference that the varying degree _of dissociation of these salts essentially influences the effects. Kearney and Cameron have investigated these relations,’ and have by artificial cultures in solutions of varying concentration and com- position studied the behavior of plant roots and the limits of their endurance. ‘They found for the several salts occurring in alkali soils, taken separately, the following figures, in 100,000 parts of water: Magnesium sulfate? 2620 sus eva tecrenenene aeeete i ae ehlorid sain he Pa ee nee ae 12 Sodium carbonate..... SHENG ev Svetarcoan wa hatene tenes 26 i Sulfate Acc seutveus mo oes cease tee seta te & CHIOEIG acu. eee ere cis er ocaeeee Ciera i tO es bicarbOmate cia... cers 2c aes sone hovers 167 Calcium ~“chionds4..5- ire aie ened cueee eee Loy It will be noted that in many respects the results given in this table stand in marked contrast to the facts observed in alkali lands every- where ; and therefore while interesting physiologically, are not directly applicable to practice. Magnesium sulfate, which according to this table is the most injurious of all, is a common ingredient of alkali lands from Wyoming to New Mexico, as also is sodium sulfate ; yet there, as well as in the Musselshell valley in Montana, and at many other points, it shows no specially deleterious action either upon native or cultivated plants, and in Europe as well as in New England the mineral kieserite is freely used as a fertilizer at many points. ‘That sodium sulfate should be twice as harmful as sodium chlorid or common salt, and half as harmful as the carbonate or black alkali, is again wholly contrary to actual experience, which as shown elsewhere in this chapter, indicates that the majority of plants will tolerate between three and four times as much of sodium sulfate as of common salt ; while the ratio of tolerance as against the carbonate seems sometimes to rise as high as ten to one. It is clearly evident, however, that it is the metallic or basic ingre- dient that in the main determines the toxicity of these salts. The universal presence of lime in some form in all alkali lands doubtless 1 Report No. 71, U. S. Dep’t of Agriculture, 1902. SALINE AND ALKALI LANDS. 533 explains the discrepancies mentioned, since lime is especially potent in counteracting the injurious effects ; thus throwing additional light upon the importance of the lime-content of alkali soils proper, and also upon the causes of the narrow limitations of the littoral (marine saline) flora ; inasmuch as, unlike alkali soils, marine alluvial lands are by no means always calcareous. Cameron goes so far as to attribute the favorable effects of gypsum upon black alkali not so much to the conversion of the latter into neutral sulfate, as to the effect of gypsum solution in counteracting the saline effects. This interpretation, however, seems rather far-fetched, since there can be no question about the double decomposition of gypsum with carbonate of soda ; or the intense injur- iousness of carbonate of soda in the actual corrosion of vegetable tissues. The corresponding protective influence of various salts, more especially of those of lime, against the injurious effects of pure common salt on marine animals, has already been mentioned (chapter 20, page 380), and later investigations by Osterhout on marine algae, show the same relation to hold true for them also. Reclamation of Marine Saline Lands for Culture.—The reclamation of sea-coast lands and marshes for agricultural use is based in general upon the same methods as those al- ready outlined for alkali lands in chapter 20; except that in this case no chemical neutralization is possible, since common salt cannot be changed by any practically feasible means. It must be removed by leaching, and this, in the humid countries in which such reclamations have chiefly been made, is usually done by the agency of rains, aided by ditching. The “ polder ”’ lands thus reclaimed along the shores of the North Sea, from Belgium to Prussia, are especially esteemed for their productiveness, doubtless owing to the alluvium of the numerous rivers tributary to that sea, which is distributed along its shores and in the numerous inlets and bays. The tides are of course excluded by dikes provided with gates opening outward, so as to permit of the outflow of rain- or irrigation-water used for leaching purposes. Out of reach of stream alluvium no exceptional fertility is to be expected of sea-shore lands, which then commonly assume the form of sand dunes or bars, incapable of nourishing any cultural vegetation. Of the latter, the groups listed below as tolerant of alkali salts, may also be considered with reference to reclaimed sea-shore lands; the first cereal to succeed being usually barley, the first root crop, beets. Asparagus is also available while salt is being leached out. THE VEGETATION OF ALKALI LANDS. The general character of alkali-land vegetation is not unlike that of saline sea-shore lands; some species of plants are com- mon to both, but the alkali lands harbor a much greater variety of plants, owing to the differences in climates and soils as well as to the nature of the impregnating salts. Moreover, owing to the very causes which underlie the presence of these salts, viz, aridity, the xerophile or dry-land character of the alkali-land flora is much more pronounced than that of the saline sea-shore vegetation. In view of the very complex conditions, the discussion of the alkali-flora is of necessity much more complex than that of the marine group; and the data for its full elucidation with respect to the nature of the soils and salts are as yet very incomplete. RECLAIMABLE AND IRRECLAIMABLE ALKALI LANDS AS DIS- TINGUISHED BY THEIR NATURAL VEGETATION. While, as shown above (chapter 20), the adaptation or non-adaptation of particular alkali lands to certain cultures may be determined by sampling the soil and subjecting the leachings to chemical analysis, it is obviously desirable that some other means, if possible available to the farmer himself, should be found to determine the reclaimability and adapta- tion of such lands for general or special cultures. In alkali lands, as in others, the natural plant-growth affords such means, both as regards the quality and quantity of the saline ingredients. The most superficial observation shows that certain plants indicate extremely strong alkali lands where they occupy the ground alone; others indicate pre- eminently the presence of common salt; the presence or ab- sence of still others form definite or probable indications of reclaimability or non-reclaimability. Many such characteris- tic plants are well known to and readily recognized by the farmers of the alkali districts. “ Alkali weeds” are com= SALINE AND ALKALI LANDS. 535 monly spoken of almost everywhere; but the meaning of this term—1. ¢., the kind of plant designated thereby—varies ma- terially from place to place, according to climate as well as the quality of the soil. It is obvious that if these characteristic plants were definitely observed, described and named, while also ascertaining the amount and kind of alkali they indicate as existing in the land, lists could be formed for the several regions, which would indicate, in a manner intelligible to the farmer himself, the kind and degree of impregnation with which he would have to deal in the reclamation work; thus enabling him to go to work on the basis of his own judgment, without previous chemical examination. A study of the lands of California having this purpose in view, was undertaken in the years 1898 and 1899 by the Cali- fornia Station; but lack of funds prevented its prosecution beyond the ascertainment of those plants the abundant oc- currence of which prove the land to be irreclaimable without the use of the universal remedy, viz, underdrainage, which on the large scale is usually beyond the means of the land-seeker. The botanical field work and collection of soil samples was carried out by Mr. Jos. Burtt Davy; the chemical work, as heretofore, being done by Dr. R. H. Loughridge. The re- sults here reported are therefore essentially their joint work. It is hoped that in the future, a more comprehensive study and close comparison of the native vegetation with the chemical determination of the quality and kind of alkali corresponding to certain plants, or groups of plants, naturally occurring on the land, may enable us to come to a sufficiently close estimate of the nature and capabilities of the latter from the native vegetation alone, or with the aid of test plants purposely grown, for the farmers’ purposes. Plants Indicating Irreclaimable Lands.—The plants herein- after mentioned and figured are, then, to be understood as indicating, whenever they occupy the ground as an abundant and luxuriant growth, that such land is irreclaimable for ordi- nary crops, unless underdrained for the purpose of washing out surplus salts. The occurrence merely of scattered, more or less stunted individuals of these plants, while a sure indi- cation of the presence of alkali salts, does not necessarily show that the land is irreclaimable. 5 36 SOILS. The plants which may best serve as such indicators in California are the following: Tussock-grass (Sporobolus airoides Torr.), Fig. 82. Bushy Samphire (Allenrolfea occidentalis (Wats.) Ktze.), Rie 1O3 Dwarf Samphire (Salicornia subterminalis Parish, and other species), Fig. 84. Saltwort (Swaeda torreyana Wats., and S. suffrutescens, Wats. ), Fig. 85. Greasewood (Sarcobatus vermiculatus (Hook.) Torr.), Fig. 86. Alkali-heath (Frankenia grandifolia campestris Gray), Bic. 37: Cressa (Cressa truxillensis Choisy), Fig. 88, perhaps identical with C. cretica auct. Salt-grass (Distichlis spicata), Fig. 89. Tussock Grass (Sporobolus airoides, Torr.) ; Fig. 82. (“ Buneh grass” of New Mexico). The three sets of Tussock-grass soil which have been analyzed show that the total amount of all salts present is in no case less than 49,000 pounds per acre, to a depth of four feet; and that it sometimes reaches the extraordinarily high figure of 499,000 pounds. Of these amounts the neutral salts (Glauber’s salt and common salt) are usually in the heaviest proportion (Glauber’s salt, 19,600 to 323,000 pounds per acre; common salt, 3,500 to 172,800) ; the corrosive sal- soda varying from 3,000 to 44,000 pounds.—Tussock-grass apparently cannot persist in ground which 1is_ periodically flooded. It is of special importance because it 1s an acceptable forage for stock. Tussock-grass 1s a prevalent alkali-indicator in the hot, arid portions of the interior, from the upper San Joaquin Valley, the Mojave desert, and southward; also through southern Nevada and Utah as far east as Kansas and Ne- braska. In the San Joaquin Valley it has not been found far- ther north than the Tulare plains, although east of Reno it occurs near Reno. Coville observes that in the Death Valley region “‘it is confined principally to altitudes below 1,000 meters’ (3,280 feet). Hillman, however, reports it from “eee Cw deen WL eee ee ~~. i: | 537 SALINE AND ALKALI LANDS. ™_ ee Se a ~ ao Qs Fic. 82 —Tussock Grass--Sporobolus airoides Torr. 538 SOMES: near Reno, Nevada, at an altitude which cannot be much less than 4,500 feet. The tussocks formed by this grass, which are unfortunately not shown in the figure, sometimes appear as veritable little grass trees, and when denuded by the browsing of cattle seem like trunks 18 and 20 inches high. It is therefore very easily recognized; but it should be noted that in view of the extra- ordinary range of its tolerance, shown above, its scattered occurrence does not necesarily indicate irreclaimable land. BusHy SAMPHIRE. (Allenrolfea occidentalis (Wats.) Kitze:)) Pigs 83: This plant is locally called greasewood, but as this name is much more commonly used for Sarcobatus vermiculatus, it seems best to call Allenrolfea ‘‘ bushy samphire,” as it closely. resembles the true samphire (Salicornia). Bushy Samphire usually grows in low sinks, in clay soil which in winter is excessively wet, and in summer becomes 2 “dry bog.’ Wherever the plant grows luxuriantly the salt content is invariably high, the total salts varying from 327,- 000 pounds per acre, to a depth of three feet, to 494,520 pounds in four feet. The salts consist mainly of Glauber’s and common salts (a maximum of about 275,000 pounds each) ; salsoda varies from 2,360 to 4,800 pounds per acre. The percentage of common salt and total salts is higher than for any other plant investigated, and the content of Glauber’s salt is also excessive. The areas over which this plant grows must therefore be considered among the most hopeless of alkali lands, for although its salts are ‘‘ white,” submergence during winter precludes the growth of Australian saltbushes. Full underdrainage alone could reclaim the soil-areas it occu- pies. Bushy Samphire is common on low-lying alkali lands in the upper San Joaquin Valley, California, and extends northward along the eastern slopes of the Coast Range to Suisun Bay. It is also abundant in the Death Valley region, apparently overlapping the southward range of the Sarco- batus, the greasewood properly so-called. DwArRF SAMPHIRE (Salicornia subterminalis, Parish, and other species of the interior) ; Fig. 84. The three or four species of Dwarf Samphire which grow Ss “i eh rade Saw Gea aie oo we Ge 8 - aa SALINE AND ALKALI LANDS. Be Tat is aan a Ktze Wats.) G. Fic. 83.— Bushy Samphire--A Vlenrolfea occidentalis (S. 540 SOILS. in the interior valleys of the State are not usually very abund- ant, save locally. Wherever the species do occur, however, they may be considered as indicating excessively saline soils. ee te OO OE Eo O) 4 Q) g y L Y i 4 0s ve iS <5 R Uw he U) os i b \ iA ; | We le 5 are Cs ,, Vite, eo gd ff : ‘Je . Sy 0 4 \ s ? we fe is E ve ly - BK 1) hf 4 y o\f ‘ MU ip Va I\AWY Jf . NV, // : : A / f Y // 7 iL | ZZ i ( ng : | \\ 1A j = | ii 3 al iB 2 hy K Se q \ i NIA y Y/ - B 4 i) é ps | Fic. 84.--2alicornia subterminalis. Alkali samphire. “* A. Much-branched form. i B. Slender form. . C. Flower with the perianth removed showing the simple pistil and the two stamens. A D. Portion of flowering spike, showing two joints. The flowers are impressed in the joints in opposite clusters of three. In each cluster the middle flower stands slightly above the two laterals } as shown in the lower joint. Dwarf Samphire soil has shown a total salt content of 441,- ; . > 880 pounds per acre in a depth of four feet. The neutral Glauber’s salt amounts to 314,000 pounds, almost as much as in Tussock-grass soil; common salt up to 125,640 pounds . . > a rd SALINE AND ALKALI LANDS. 541 while the salsoda varies from 2,200 to 12,000. We may con- sider the plant as indicative of almost the highest percentage of common salt, Glauber’s salt and total salts. Like the preceding species it indicates land strongly charged with salts, more especially common salt, and susceptible to cultivation only after reclamation by under-drainage. Salicornia subterminalis, S. herbacea (L.), S. mucronata, and another species, all occurring inland, differ materially in habit and botanical characters from the one so conspicuous 1n submerged salt marshes along the seashore; but all alike indi- cate strongly saline soils, reclaimable only by thorough drain- age. SALTwort (Suaeda torreyana, Wats., S. suffrutescens, Wats., and perhaps one other species) ; Fig. 85. Samples of saltwort soil from Bakersfield and Byron Springs, California, taken to a depth of one foot and three feet respectively, show that this plant grows luxuriantly in a soil containing 130,000 pounds of total salts per acre in the first foot, and with 10,480 pounds of the noxious salsoda, and 39,760 pounds of common salt in three feet; while only a sparse growth is found on soils containing only 3,700 pounds of salts in three feet. It thus appears to indicate a lower percentage of salsoda than does Greasewood, but a higher percentage than Bushy Samphire. Further investigation 1s necessary to determine the exact relation of the different salts to the growth of the plant, and as to whether carbonates occur in large quantity ; but enough data have been gathered to show that a luxuriant growth of Suaeda torreyana indicates a soil reclaimable only by thorough-drainage. Suaeda torrevana occurs on low alkali lands throughout the State of California, from San Bernardino to Honey Lake, in the desert sinks, and in the Great Valley, in appropriate locations. Sometimes it is replaced by S. suffrutescens and perhaps other species, but all the saltworts appear to grow in similar habitats, and it is probable that the soil-conditions are practically the same for all these species. They indicate land too heavily impregnated for the growth of ordinary crops, but which will perhaps allow the Australian saltbush to suc- ceed. 542 SOILS. Fic. 85.—Saltwort—Swaeda Torreyana, Wats. GREASEWooD (Sarcobatus vermiculatus (Hook. Torr.) ; Fig. 86. This, the true Greasewood of the desert region east of the Sierra Nevada, and not either of the plants known under that name in the San Joaquin Valley and in Southern California, invariably indicates a heavy impregnation of the land with black alkali or carbonate of soda. Since, as before stated, black alkali is most likely to occur in low ground, we fre- quently find the true greasewood forming bright green patches in the swales, and on the benches of periodic streams, as well as on the borders of alkali ponds or lakes. Stock un- accustomed to it will frequently go to these patches on a run, -o~ewe SALINE AND ALKALI LANDS. 543 only to turn away badly disappointed after taking a few bites, the plant being both bitter and salty. Fic. 86.--Greasewood (proper)—Sarcobatus vermiculatus (Hook) Torr. Appearance of a branch when not in blossom. Spiny-branchlet from the same. Branchlet bearing cones of male flowers. . Cone of male flowers, enlarged. . Branch bearing fruits. . Cluster of fruits, enlarged. . Vertical section through a fruit, showing the seed with its curved embryo, (enlarged). Onno Oe > Where a luxuriant growth of this plant is found, the soil may contain from 38,000 to 117,000 pounds of total salts per | acre, of which sometimes nearly half is carbonate of soda; the content of common salt is usually low, and Glauber’s salt 544 SOILS: or sulfate of soda, sometimes with considerable proportion of epsom salt, forms a variable proportion of the total. Greasewood is distinctly a plant of the Great Basin, only reaching California in the adjacent counties of Lassen, Alpine, Mono, and northern Inyo. It 1s very abundant on the lower levels of Honey Lake valley, Cal. The Sarcobatus is chiefly found on silty or sandy soils of good native fertility (see page 445, chapter 22), so that when its excess of salsoda is neutralized by means of gypsum, the land becomes very productive. Unfortunately the cost of the amount of gypsum required to render such soils adapted to the tolerance of most culture plants is often prohibitive; but where the correction of only small spots is called for, the “white alkali”’ resulting from the gypsum treatment would be tolerated by many culture plants. ALKALI-HEATH (Frankenia grandifolia campestris Gray) ; Pig. 67. Fic. 87.—Alkali-Heath--Frankenia grandifolia campestris A Gray. Alkali-heath is perhaps the most widely distributed of any of the California alkali plants. Its perennial, deep-rooting | el A Ee Miner tere nike rad = dl | tee endo = + thease eos ——— SALINE AND ALKALI LANDS. 545 habit of growth, and flexible, somewhat wiry rootstock, which enables it to persist even in cultivated ground, render it a valuable plant as an alkali indicator. The salt-content where Alkali-heath grows luxuriantly is invariably high, ranging from 64,000 to 282,000 pounds per acre; salsoda varies from 680 to 19,590 pounds; common salt ranges from 5,000 to 10,000 pounds. Such soils would not be benefited by the application of gypsum, as the salts are already largely in the neutral state. Of useful plants only Saltbushes and Tus- sock-grass are likely to flourish in such lands, when not too wet. While Alkali-heath is thus one of the most alkali-tolerant plants, it is at the same time capable of growth with a mini- mum of salts (total salts 3,700 pounds, salsoda 680 pounds). Where only a sparse growth of this plant occurs, therefore, the land should not be condemned until a chemical examination of the soil has been made. Alkali-heath is found on soils of very varying physical tex- ture and degrees of moisture; while on soils of uniform texture and moisture-conditions, but differing in chemical composition, it varies with the varying salt-content. It has been found that Australian saltbush (Atriplex semi- baccata) can be successfully grown on the “ goose-lands,” of the Sacramento Valley, on soil producing a medium crop of Alkali-heath; it remains to be shown whether it will do equally well on soils producing a dense and luxuriant growth of the same. Alkali-heath is widely distributed throughout the interior valleys of California; a closely related form grows in the salt- marshes of the sea-coast. Cressa (Cressa cretica truxillensis Choisy) ; Fig. 88. Cressa soils show a low percentage of the noxious salsoda, but comparatively heavy total salts (161,000 to 282,000 pounds per acre.) Common salt varies from 5,760 to 20,840 pounds per acre in four feet. The maximum 1s lower than in the case of Alkali-heath, but Cressa seems to be much more closely restricted to strong alkali than does the former species. Cressa appears to be as widely distributed through the in- terior valleys of California as Alkali-heath. The Cressa is a oo 546 SOILS. cosmopolitan plant, occurring, as its name indicates, on the Ionian Islands, as well as in North Africa, Syria, and other arid countries of the world. Satt-cRass, Distichlis spicata—This grass is of world- wide distribution, and always indicates a sensible content of soluble salts, without apparently any special preference for either of the three most commonly occurring ones. Its maxt- mum tolerance, as will be seen by the preceding table, is very high, yet at the same time it will grow luxuriantly on lands containing so little that other saline plants like the samphires, saltwort or greasewood will refuse to grow. On the shores of ba 44 (i ©, WZ YZ ~_ Se LBS Fic. 88,--Cressa--Cressa cretica truxillensis, Choisy. Honey Lake, California, it may often be seen incrusted with the salts of the water concentrated by a long season of drought, yet maintaining life, though somewhat stunted. On lands lightly impregnated, stock will often eat it quite freely, so that it has been mistaken for Bermuda grass, to which its habit and foliage bears some resemblance. But Bermuda grass, while not as sensitive to alkali as most forage grasses, will probably not bear much over 12,000 pounds per acre. The mere presence of the salt grass cannot therefore be taken as a definite indication of anything more than that there is an unusual amount of salts in the soil; whether or not there ee —— SALINE AND ALKALI LANDS. Tepe Madea Sad Ee a chbias aianebene ivan, Atncele: Lie » S — COR aay SceRs Sa Sen % pe China da PRenmandiyne nos. o oaene 6 Ovhebad [Pe Rena ete) 547 Fic. 89.--Salt-Grass—Dzstichlis spicata (L.) Greede. 548 SOILS. is more than will be tolerated by the ordinary culture-plants, must be judged either from the accompanying plants, or by experiment or analysis. Relative Tolerance of the Ditferent Species—The follow- ing table shows in systematic order the tolerance of the several plants discussed above, for the different salts, so far as the data available permit. The column marked optimum shows under what proportions of salts the plants grew in about equal luxuriance, therefore under, apparently, the most favorable conditions. Both above and below the proportions mentioned in that column, the luxuriance (size) and (usually) the abundance of the plants was less; showing that while excess- ive amounts of salts depressed their welfare, yet they also suffered when the proportions dropped below a certain point. Whether this was partly or wholly the result of competition with other plants, is an unsettled question. ose ome ie —————<<« Se SALINE AND: ALKALI LANDS. 549 TABLE SHOWING MAXIMUM, OPTIMUM, AND MINIMUM OF SALTS TOLERATED BY EACH OF THE SEVERAL ALKALI PLANTS. Pounds Per Acre in feet. Optimum. | Maximum. Minimum. Total Salts. BUshygoamMphiner-rrcieieicirelciorielscieleieversisictelelele soadodooDdddcr 494,320 494,520 135,060 Dwarf Samphires............... 960006 lctovelereicteleleleisiereitcrels 441,880 441,880 441,880 . 81,960 PAM alisheathlcterelateis\elciajallvetaielololersietevelalelevateintelelelsleisiercialeie/aiatalelare ; Seen 499,040 3,720 Gressabyejicetiele erastete\eVavelcloistersterctetei teletapalstelslerskeleroiareteieivereteletsioiy 281,960 281,960 161,160 SALTON ES aisserorayoleleinioicicis\exelsisisteyereisiead eleveversiciclevsteree Metetecteteteveel= 130,000 153,020 3,720 GTEASE WOO Ieriseiielsleloisvelsiel cheisicinieyoleretererielelereleleleyere sOODoDBOGD 58,560 58,560 2,400 Tussock-grass ......... spndodacnogdonboods podedooacedc0s 49,000 499,040 49,000 Carbonate (Salsoda). BEISSOCKoOTASS eielslelefetoreielsleies-ieieteleleieieysie\s) seloselela lier Ga0c00b 23,000 44,460 3,040 ETUPEAES: eine ee er One toate fo Msi5ge } 19,590 680 Greasewood .............+. mtevaretclefefelelelctotalsieleletere) iototelotataterete 18,720 18,720 1,280 Dwarf Samphires....... 5 6a ododdound sdandoddengcooeae 12,120 12,120 2,200 Salt wortS iar cinierarcre oaieicveveiere ciasevelele/aie etwave aitelatatotcleistaticlelcicieicisre 10,480 12,120 1,120 @ressa:.... ve ec e etree eee eens pieleleetetsteteeivaietersisieveletenetsteiare 5.440 5,440 680 Bushy Sama phineecrciaieteieelctslelel-selalolleievelelersietetela 3000 95 sagon6 4,800 4,800 1,500 Chloride (Common Salt). Bushyssamphineseerisiisiac crcieioselelesicreleleieies Sponcoose0.65os 212,080 275,160 56,800 Dwarf Samphires...... SGgg0ng 000 -codabbOO0 adbouKDDadaOD 125,640 125,640 125,640 RS APE WOT ES ot clerk ols lee ntelsia te e)d-ere\si0io 6\e/arevaealorevacovals\aieceisvahiuersiere ao 39,760 52,900 1,040 (GreSsaryeteterileteie severe eet slelteteielstotey efeleleleNetetetetste/a'e Ganpaboda noo 20,840 20,840 5,760 : 80) Alkalistiea thins: ialepasticiverevsisielcrecetstaisiels mereieoueretsievere sie shite } me 212,080 1,040 PEMISSOG Ke hl SSteteteretetmtelelorslaleistoynialaterciciaisicieromsieieveleieteisiexeloietaiale > 6,200 172,800 3,530 GreasewGod sec... cc ccc cece Hocus cosbctboonTo0ddnnNd dose 3,680 3,680 160 Sulphates (Glauber’s salt). Dwarf Samphires......... Cosco cence sfetovareiocisleraictere alerererereste 314,040 314,040 314,040 Bushy OAM pire oa(eieiclsicielniclelelelsleisteleele/s leleteishetsiele soGoDone 56 277,640 277,640 50,080 Gressacceemercse winter ojejsisictel cjetalenstarsiatereeieieis elevates neveretarsierste 275,520 275,520 134,880 Alkali-heath....... waceanneee ayausn acre bondcddndGdane cadens ; en t 323,200 1,560 Rall LOO Steteretetcieinisiosioteleivicieieicinieietelelsistsietersiotsieisicisl= Syoretetaterceteters 44,160 104,040 1,560 Grease wots cleteisiereis cin felejereisieielsloterereinis Sialeralcte Moleleiaiets 36,160 36,160 960 PIISSOGICNGTASSeseferevsto's ohare a: cisic w/ sisleiais icra iotasleietetevonerenievertoeee 19,640 323,200 19,640 * This plant grows with equal luxuriance in soils containing only 680 pounds of carbonates. _ APPENDICES. APPENDIX A: DIRECTIONS FOR TAKING SOIL SAMPLES. ISSUED BY THE CALIFORNIA EXPERIMENT STATION. In taking soil specimens for examination by the Agricultural Ex- periment Station, the following directions should be carefully observed ; always bearing in mind that the examination, and especially the analysis, of a soil is a long and tedious operation, which cannot be indefinitely repeated. first.—Do not take samples at random from any points on the land, but consider what are the two or three chief varieties of soil which, with their intermixtures, make up the cultivable area, and carefully sample these, each separately ; then, if necessary, sample your particular soil, noting its relation to these typical ones. Second.—As a rule, and whenever possible, take specimens from spots that have not been cultivated, nor are otherwise likely to have been changed from their original condition of “virgin soils ?—e.g., not from ground frequently trodden over, such as roadsides, cattle-paths, or small pastures, squirrel holes, stumps, or even the foot of trees, or spots that have been washed by rains or streams, so as to have experienced a notable change, and not be a fair representative of their kind. Third.—Observe and record carefully the normal vegetation, trees, herbs, grass, etc., of the average virgin land; avoid spots showing unusual growth, whether in kind or in quality, as such are likely to have received some animal manure, or other outside addition. Fourth.—Always take specimens from more than one spot judged to be a fair representative of the soil intended to be examined, as an additional guarantee of a fair average, and mix thoroughly the earth taken from the same depths. Fifth.—After selecting a proper spot, pull up the plants growing on it, and sweep off the surface with a broom or brush to remove half- decayed vegetable matter not forming part of the soil as yet. Dig or bore a vertical hole, like a posthole, and note at what depth a change of tint occurs. In the humid region, or in humid lowlands of the arid, 553 554 APPENDIX A, this will usually happen at from six to nine inches from the surface, and a sample taken / that depth will constitute the “soil.” In California and the arid region generally, very commonly no change of tint occurs within the first foot, sometimes not for several feet ; hence, especially in sandy lands, the “ soil’’ sample will usually be taken to that depth, so as to represent the average of the first foot from the surface down. Samples taken merely from the surface, or from the bottom of a hole, have no definite meaning, and will not be examined or reported upon. Place the “soil”? sample upon a cloth (jute bagging should not be used for the purpose, as its fibres, dust, etc., become intermixed with the soil) or paper, break it up, mix thoroughly, and put a¢ asta quart of it in a sack or package properly labeled, for examination. This specimen will, ordinarily, constitute the “soil.” Should the change of color occur at a less depth than six inches, the fact should be noted, but the specimen taken to that depth nevertheless, since it is the least to which rational culture can be supposed to reach. In the same way take a sample of each foot separately to a depth of at least three feet ; preferably four or five, especially in the case of alkali soils, or suspected hardpan. Szxth.—Whatever lies beneath the line of change, or below the min- imum depth of six inches, will constitute the ‘subsoil.”” But should the change of color occur ata greater depth than twelve inches, the “soil”? specimen should nevertheless be taken to the depth of twelve inches only, which is the limit of ordinary tillage ; then another speci- men from that depth down to the line of change, and then the “ sub- soil’? specimens beneath that line. The depth down to which the last should be taken will depend on circumstances. It is always necessary to know what constitutes the foundation of a soil, down to the depth of three feet a¢ /eas/, since the question of drainage, resistance to drought, root-penetration, etc., will depend essentially upon the nature of the substratum. In the arid region, where roots frequently penetrate to depths of ten or twelve feet or even more, it is frequently necessary to at least prode the land to that depth or deeper. The specimens should be taken in other respects precisely like that of the surface soil, each to represent the average of not more than twelve inches, ‘Those of the materials lying below the third foot from the surface may sometimes be taken at some ditch or other easily accessible point, and if possible should not be broken up like the other specimens. A aN ee ne nies ae eee Camara ay © eos APPENDIX A. Bins If there is hardpan or heavy clay present, an unbroken lump of it should be sent, for much depends on its character. Seventh.—When in the case of cultivated lands, it is desired to ascertain the cause of differences in the behavior or success of a crop on different portions of the same field or soil area, do not send only the soil which bears unsatisfactory growth, but also the one bearing normal, good growth, for comparison. In all such cases, try to ascertain by your own observations whether or not the fault is simply in the sub- soil or substrata; in which case a sample of surface soil sent for exam- ination would be of little use. In such examinations the soil probe will be of great service, and save much digging or boring. Lighth.—Specimens of alkali or salty soils should preferably be taken towards the end of the dry season, when the surface layers will contain the largest amount of salts. A special sample of the first six inches should in that case be taken separately by means of a post-hole auger, and then, in a different spot close by, a hole four feet deep should be bored, and “he earth from the entire four-foot column intimately mixed before the usual quart sample is taken. Samples of the plants growing on the land should in all cases be included in the package, as they in- dicate very closely the agricultural character of the land. All samples taken while the land ts wet should be air-dried before sending ; tn the case of alkali soils this ts absolutely essential. Linth.—All peculiarities of the soil and subsoil, their behavior under tillage and cultivation in various crops, in wet and dry seasons, their location, position, ‘“lay,’’ every circumstance, in fact, that can throw any light on their agricultural qualities or peculiarities, should be care- fully noted, and she notes sent by mail. Without such notes, specimens cannot ordinarily be considered as justifying the amountof labor involved in their examinaton. Any fault found with the behavior of the land in cultivation or crop-bearing should be specially mentioned and de- scribed. The conditions governing crop—production are so complex that even with the fullest information and the most careful work, cases are found in which as yet the best experts will be at fault. APPENDIX B. SUMMARY DIRECTIONS FOR SOIL—EXAMINATION IN THE FIELD OR ON THE FARM. WuiLeE the general principles upon which the cultural value and adap- tations of lands should be judged, have been given in the text of this volume, it seems advisable to summarize their practical application to land examination here, for convenient reference. The directions given in Appendix I for the sampling of soils having been carried out, the samples so taken may be subjected to farther examination by any intelligent farmer to good purpose, and often with great saving of time and expense. Spread the samples from the several depths in regular order upon a table or bench, and note the differences in color and texture apparent to the eye or touch, and whether they will or will not crush readily between the fingers, wetand dry. Whatever the fingers can do, can similarly be done by the harrow, cultivator, clod crusher or roller. The tilling qualities of the surface soil and immediate subsoil are the first and most important matter to be ascertained ; including especially their behavior to water. Place some airdried lumps in a shallow dish with a little water; observe whether they take up the water quickly or slowly, and whether in so doing the lumps fall to pieces or retain their form. Slow penetration, and maintenance of form, will at once indicate a soil somewhat refractory and difficult to till ; while if the water is taken up easily and the lump falls to pieces, the land is easily cultivated and will absorb the rainfall and irrigation water readily. ‘The darkening of the tint on wetting will also give an approximate idea of its humus- content. Then take a wetted lump and work it between the fingers and on the palm of the hand, until its “ stickiness’ or adhesiveness ceases to increase. This “hand test” is of first importance and in skilful hands will largely supersede the need of elaborate mechanicai analysis. It will at once enable the operator to classify the soil as a light or heavy loam, clay loam or clay soil ; it will show directly what will be the result of plowing the land when wet, the liability to the formation of a plow- 556 APPENDIX B. 557 sole, and whether a single or a double team will generally be needed to cultivate it properly. Also whether stock can be allowed to pasture the land soon after rain. Comparison with the known land of neighbors will also thus become easy, and in a measure the crops best adapted to the physical qualities of the soil, subsoil and substrata, taking into account their respective depths, will at once be at least approximately determined. The presence of coarse and fine sand in greater or less amounts will also be thus readily ascertained, allowing estimates of the percolative properties; the latter can, of course, be more practically tested in the field, in the manner described in chapter 13, page 242. A more definite estimate of the amount and kind of sand present in the soil materials can be obtained by washing the kveaded sample into a tumbler, and allowing a thin stream of water to flow into it from a faucet while gently stirring the turbid water. The clay, together with the finest silts, will thus be carried off over the rim of the glass, and sand of any desired degree of fineness, according to the strength of the stream of water used, will be left behind. The kind and amount of these sandy materials can then be estimated, or definitely ascertained by weighing or measuring. This will, generally speaking, be as far as the uninstructed farmer can readily go; but these simple operations will give him an insight into the nature of his soil and subsoil that will enable him to avoid a great many costly mistakes. RECOGNITION AND MEANING OF THE SEVERAL SOIL MINERALS.? Those somewhat familiar with scientific methods and operations, and supplied witn pocket lens or microscope, can profitably go much farther towards the definite ascertainment of the permanent cultural value of the land, by the study of the minerals of which the sand is composed, and which as a rule represent those from which the entire soil has been formed ; therefore indicate in a general manner its chemical compo- sition. Such examinations are specially feasible and important when soils are not far removed from their parent rocks, as in most of the arid region, and in the states north of the Ohio. In the Southwestern states, in the coastal plain of the Gulf of Mexico, the original soil minerals have usually been too far decomposed to admit of definite identification. Sand is there as a rule made up of quartz grains of many varieties, with only an occasional tourmaline and pyroxene. Among the prominent soil minerals, quartz is almost always recogniz- 1 For more details see chapters 3 and 4. 558 APPENDIX B. able by its glassy lusterand the irregular fracture—absence of definite planes or facets of cleavage, causing the grains to be abraded or rounded nearly alike in all directions. The /e/dspars, on the contrary, always show atendency to cleave into fragments having definite, obviously oblique angles, which are perceptible even when the grains are somewhat worn ; because of the difference in the ease with which wear takes place in the several directions. Potash feldspar, moreover, which is the most im- portant to be recognized because it indicates a relatively large supply of potash in the natural soil, is but rarely glassy in luster, but mostly dull white, or reddish-white.—-The “me and Uime-soda feldspars rarely show as definite forms, because of their tendency to form complex crystalline aggregates (twins) : and their definite recognition requires somewhat complex (polarizing) appliances in connection with the mi- croscope. Insuch cases, however, the accompanying minerals (horn- blende, pyroxene, mica and others) often afford valuable indications, because of their known association with soda-lime feldspars in certain rocks. An abundant occurrence of hornblende fragments, characterized by their flat, tabular form, and bottle-green or black tint, indicate, almost always a fairly good supply of lime in the soil, but leaves the potash- supply in doubt. Pyroxene (distinguished by its smooth, polished sur- face from the angularly-weathering, usually rusty hornblende fragments) rarely occurs with potash feldspar; and soils strongly charged with it are mostly poor in potash. Mica occurs in so many rocks and is of so little consequence as a soil--ingredient from the chemical point of view, because of its difficult decomposition, that its presence can mostly only serve to corroborate or contradict conclusions as to the derivation of a soil from some par- ticular rock or region. But mica’serves a good purpose in improving the tilling qualities of soils. Its thin scales must not be mistaken for the tabular fragments of hornblende. Calcite in its several forms is mostly easily recognized both by its form under the microscope, and by the effervescence its granules show when touched with an acid. This effervescence can generally be ob- served on touching the wetted soil with chlorhydric acid, so soon as the content exceeds two per cent; but something depends upon the size of the grains, as when these are very small, the giving-off of gas is less readily noted. ‘To facilitate it, the wetted soil may be warmed before touch- ing it with the acid. The recognition of the presence of lime carbon- ate in soils is so important as to justify considerable trouble in render- ing it definite. When the aid of a chemist cannot be commanded, APPENDIX B. 559 fairly definite conclusions may be drawn from the character of the native vegetation ; regarding which, detailed information may be found in Parts III and IV of this volume. But where, as in the arid region, this criterion is not available, since the controlling factor there is the mois- ture supply, a presumption may be gained by the application of a slip of moistened red litmus paper to the zwe/¢fed soil. Should the red paper be turned blue within one or two minutes it would indicate the presence of carbonate of soda (“black alkali’’) as well as of lime car- bonates : but if blued only after twenty minutes or more, it would indicate the presence of the carbonates of lime and magnesia. If not changed at all, the conclusion would be that either lime carbonate is in very small supply, or that the soil is in an acid condition. (See chapter 8, p- 122). Saline and Alkali Soils—The presence of an unusual or injurious amount of soluble salts, as in the case of seacoast and alkali soils, is commonly easily ascertained in the field; where, if the surface soil is at all seriously contaminated with soluble salts of any kind, these may be seen on the surface during a dry season, forming a whitish efflores- cence, which in most cases is definitely crystalline. In doubtful cases a tablespoonful of the surface soil may be leached with water, and the first ten or fifteen drops caught in a clean, bright silver spoon and evaporated. Or the soil may be stirred up with about twice its bulk of water and the mixture be allowed to clear by settling, then evaporating. A slight whitish film will almost always remain in the spoon ; but if the ~ amount be somewhat considerable, the presence of soluble salts is very readily recognized by pouring a few drops of clear water on one side of the spot, and then allowing it to flow gently over the spot to another place, where it is again slowly evaporated. Any considerable amount of salts present will be shown both in the diminution of the original spot, and in the soluble residue accumulated where the water was last evaporated. Should common salt be present to any considerable extent, the residue in the silver spoon will, if the last drops be allowed to evaporate slowly, show square or cubical crystals to the naked eye, and certainly to a common pocket lens. The residue may also be tested with red litmus paper for carbonate of soda, which would quickly turn it blue. More detailed examination requires chemical reagents and experience, but the above tests should be sufficient to prevent the mistaking of mere white spots, whose humus has been destroyed by fermentation caused by bad drainage, with true alkali caused by excess of soluble salts ; a mistake not uncommon in both the arid and humid regions. APPENDIX C. SHORT APPROXIMATE METHODS OF SOIL EXAMINATION USED AT THE CALIFORNIA EXPERIMENT STATION. BY R. H. LOUGHRIDGE. Tue California Experiment Station has for many years given the farmers of the State the privilege of having their soils examined to as- certain any physical defects, deficiency in plant-food, or the presence of alkali salts. ‘They have quite generally taken advantage of this, and the number of samples of soil sent in each year has been very large. A complete analysis of a soil-sample requires fully 15 days; hence the necessity of adopting some quick methods for the determination of the main elements of fertility, viz., humus, lime, potash, and phosphoric acid, that would at the same time give results sufficiently accurate for practical purposes. Similarly for alkali salts in the soil; the leach- ing-out and analysis of which often occupies more than a week. The following methods have been adopted, which shorten the time of examination for the plant-food of a soil to about one hour, except for potash, which requires a much longer time. For alkali salts the time is reduced to two days, and less if a pressure filter be used. FHlumus.—The Grandeau method of ammonia extraction requires the removal of the lime and magnesia with weak hydrochloric acid, wash- ing out of the acid and then digestion with weak ammonia ; all of which, with a soil rich in humus, may require many days, though a number of samples may be put through at the same time. The method adopted to determine adequacy or inadequacy of the humus (for this is all that is intended in this examination) is completed in less than half an hour. It is based on the color of the humus-extract and avoids the necessity of removal of the lime from the soil. The soil is pulverized in a mortar with a rubber pestle, and passed through a half-millimeter sieve. Seven grams of the fine earth is placed in a test tube with 15 or 20 cc. of a ten percent solution of caustic potash and boiled for ten or fifteen seconds, then allowed to settle. The humus is dissolved and the density of the color of the solution is an indication of adequacy or inadequacy. A dense black, non-trans- 560 * APPENDIX C. 561 lucent solution shows the presence of at least one per cent of humus in the soil; a deep brown translucent color indicates about one-half of one percent ; while a light brown color clearly shows a deficiency in the soil, and a need of a good green-manure crop. Lime.—Two grams of fine earth is treated with a little hydrochloric acid, boiled for a few seconds, and ammonia is added to precipitate the iron and alumina ; the whole, with the soil-residue, is quickly thrown on a filter to separate the mass from the lime solution, and washed. After adding ammonium chlorid the lime is precipitated with oxalate of ammonia, and its adequacy for soil-fertility judged of by the turbid- ity of the solution, or the bulk of the precipitate. Or the latter may be filtered off, dried and weighed. We thus obtain a measure of the carbonate and humate of lime present, by comparing it with the pre- cipitate obtained from a soil whose percentage of lime has been cor- rectly ascertained. Potash.—The determination of potash in the soils requires more time than either of the other ingredients, and is more rarely made by us. Our knowledge of the soils of the State of California obtained through myny analyses, gives us a clue to those localities where potash would probably be deficient, as well as to those whose soils are generally ex- tremely rich in potash ; the percentages reaching usually from .5 to as much as 1.5 per cent and more. For the determination, two grams of the fine earth is digested in hydrochloric acid over a steam bath for two days, the insoluble residue filtered off, the filtrate evaporated to dryness to render the silica in- soluble, again filtered and the iron, alumina and lime removed by pre- cipitation with ammonia and oxalate of ammonia and filtration. The filtrate is then evaporated to dryness, the ammonia salts destroyed with aqua regia or driven off by heat, and the alkalies changed to chlorids. Any residue is then filtered off and platin-chlorid added to precipitate the potash, which is separated and determined in the usual way, either by reduction of the platinum by ignition, or by measurement in a Plattner’s potash tube. Phosphoric Actd.—The determination of phosphoric acid is based on the volume of the phospho-molybdate precipitate in a tube made like a Plattner’s potash tube, but having a wider interior diameter for the smaller portion (not greater than 3 millimeters), and a length of 50 mm. With this diameter, one mm. in height of the precipitate obtained by our short method indicates one one-hundredth of one per cent of phosphoric acid in the soil. The unit of measure must be obtained for 36 562 APPENDIX C. each tube, unless of uniform diameter, and is ascertained by taking a soil whose phosphoric-acid percentage has been determined gravimet- rically and giving it the following quick treatment; which must, of course, be closely followed in each soil to be examined : Two grams of the fine earth is ignited in a platinum dish to destroy the organic matter, transferred to a test-tube containing 5 cc. of nitric acid and made to boil for only a couple of seconds, thus preventing the solution of silicates to any material extent. It is not allowed to stand, but a little water is immediately added and it is quickly thrown on a small filter and washed with a little water. The phosphoric acid is then precipitated with molybdic acid at the proper temperature ; allowing it to settle, the liquid is drawn off and the precipitate transferred to the measuring-tube. It settles into the small part in a short time if the latter is not too narrow, and is then measured with a millimeter scale. This represents the percentage as found in the soil by the gravimetric method, and serves as a guide for other examinations, whose agreement with gravimetric determinations is generally quite close, and quite suf- ficient for practical purposes. ‘The rapidity with which the solution is made and separated from the soil is a matter of special importance for comparative results, or determination of percentages; for if the acid solution be allowed to stand for some time before filtration from the soil, silica passes into solution also, and the volume of the molybdate precipitate is increased by it; thus vitiating the results and adding to the time required for the method. By this short method the practically important phosphoric acid in the soil may be approximately deter- mined within half an hour. SHORT METHOD FOR ALKALI SALTS. The old method of obtaining solutions of the salts by leaching the soil on a filter until all of the alkali had been washed out has been replaced by the following short one. 50 or 100 grams of the well- mixed soil is placed in a bottle containing 200 cc. of water, shaken up occasionally during 12 hours and allowed to settle. The solution may then be passed through a common filter (or preferably a pressure filter) and an aliquot part (usually 50 cc.) of the filtrate evaporated to dry- ness in a platinum basin and ignited at a temperature just below redness to destroy any organic matter that may be present. The basin and contents are weighed and the soluble salts are dissolved in a very little water and separated by filtration through a small filter into a 50 cc. cylinder and the alkali carbonates and chlorids determined by titration, being calculated as sodium compounds. wee ne eS ee tee aoe a ea ae ~~ <= APPENDIX C, 563 The material remaining on the filter and in the basin, consisting of insoluble earth, carbonates and calcium sulfate, is gently ignited in the basin and weighed; the difference between this and the first weight gives approximately the ‘ofa/ soluble salts, which should substantially correspond to the titrations made. The sulfates are determined by differences between these and the total alkalies. The solution may contain some sulfate of magnesia, or calcium and magnesium chlorids, and these are determined gravime- trically. Nitrates, which may have been destroyed in the first ignition, are determined in the original solution by the picric method. Any mag- nesia rendered insoluble by the ignition may usually be accounted for as chlorid, unless much nitrate is present which is rarely the case in carbonated alkali. If much nitric acid was found, it should be first assigned to magnesia. INDEX A. PAGE Absorption and movements of water in. soils: 0.0 .cJe. cslselele olds oats este 221 ofisolids:fromisolutions? 12868 Silanes saree ale atel ere 207 of gasesiby.Soilss'ts stead dao vee ties eee ere mmensioes . 272, 275 Acacias stoleranceyofsalali: saci camten ie ee ie oe oe eee 480 WWecessory muineralsis 28 iGascseeang eden eeeeds SA hae else tractoae toes aun areretoone 50 Weide strength used invsoil analysis. «< 7.:ia ds eae oe ee eee eels e eae 341 Acidic and basic eruptive and metamorphic rocks ...............000005 49 Weidity, neutrality, alkalinity ‘of soils.4,6s2.4.). S0.'d.boka ones acne se B22 Acids of different strengths, analysis with ; nie rue te Mitten eevee cictoels 326, 341 Action of plants in soil formation, giechanical and chemiical.......... sn LO Aeration and reduction as influencing nitrification............. ..-.++- 147 effectsiofinsuiicient any soll swans saeerrene eee scien 280 EXCESSIVE, 1NJUTY di atid TEGIOUSH. cl. tf soiseeiaia ciclets ema een here 280 Aatopicwandeanerobic bacteria susan oe eeeeeienee LR raaetaen oer 144 AAT MERU E HONS 111) SOLS. o\5 2). cresereicts aver ohede lolavel eo wlotots oie. olauetare oetelelee eieleisiele 279 MN OLISOUS COM POSIELOM OF 3)L42\sreyeiteravelobaraya tans iovalge ot oleteterete cena nlnlete eioreyee oer 280 PES PA COe1TA OMS 50 1 SUITE har crc orat shits) oe (a1o10s ool laye/e)eleleps = ofeleletefoieisboteiel ale! sieieere 108 Miabama> veretation aid soil-charactersy ./.5).).,.-0ajsiesics)sscisioseee serie ce 511 Alaskarcurrent,, effects.on, California:climate. .)./...)..h)ss000 ees see setae 296 PAM IATES irerepajetelctece teh evereitns’etclavate é Dare ater peters AN oar peepee J pcdogouddeNOUdoO 149 Alkali carbonates and sulfates, inverse ratio.................+s.-<- 451, 452 carbonates .ellectsomiGlayintia aa cvatotvaclectemtevorelete sive einen cater leks 62 effects.on culture’ plantsiy figure tye. 2)cie's\ce siamese aeonae 426, 427 Alkali-heath, range, tolerance of alkali, figure..................... 544, 545 Maikalilands, crops for stroney at asciclodaints ofl «ccs Male ey eale elem ee atte slirspsrctercrsteneions Selassie Aes lois ese DS HUTICHIONS) OF: 111 SOUS Es CAN Ais aye se ted ORS chopetonyorerelerolaic locale aerere 59 Pb HoIEAHHOKS rqehoa o) Hone oaugnogunce codosdcouddotd coc 110 Glaysyclaystones, clay shales: i.janj'slate oe eieiei miele useless 16 Decolorizing action, of soils, charcoal.........--... cee eee ee eee ee eee 267 Deep-rooting of native plantsin arid region. .............-- ee eee eee 174 WEetorestation memects Ole ser mete etal ilaieiels lols srieloleleeier elles ele iteias iad 219 Weltas MOonmatlonyote/euiaepvetecyelerctotetneraervtetoetserokietlsheked xh hoelcenelalatalelts U | Denitrifying bacteriasi:.). jewels syste) Maleiareic.n) ja ale mi nlatpiniaie »-/ea'= yalotolg\e) ofaintats 148 Deserts, effects Of Witds Un. o.oo e wielejre sisters telecon bicin/wisipios wislaaue 8 Desert sands, only lack water to become productive...............+++- 420 Dew, horimatwon vOlie s/s eiseiseeisier crs 0! eres © “ieyaley a= Pepe Palele: Shere peaclalnaaede ial sii 307 rarely adds moisture to soilS...........-s0e sees ee ee ees FOCIG oS oto 308 VPtelsvoal WD Jordin, ooo ped sodounseqaoddooogoU Sones. cloosesodooDo0e a5 1308 Differentiation of soil and sub-soil, causes Of...........00ss cece ee eeeee 121 Distance between furrows and ditches... -..-- 1.6. 6.05 oe ee ce ese mn oe ale 241 ADYelLovark tye REL OM el N LT EN Hs Ben are Baa Soa heo AiSIEN NO GId Ais Gad Gata. c 42 INDEX. 571 PAGE Drainage rights-of-way fobs. e's else sie eiiera wivie avi aleteetsiea che sagccnes aces 461 Drainacewatersuse Lor itl SAtLOMe a) ora) ataletalsiteeielei cicero ciel eiereusroleiatoiere 250 Mraingwaters. analiysesOLetablersyacrlsreureterveteestereicieertetselelenteietewors cre ieros 22 leachins efectsrol ieee a tesnel ante trevor poter ay sce 271 DVR al, AAAI HAVS OP shal Gio! Sole sassdasnadtocneuccovcbondgonucte Gos 167 IOUISH SOUS Vaart OL wae soapy aire elton sua oko sc Feleeuey Poel cke eS ase etl errs rete 104 slow penetration of water in........... labbmotce et oacln tan Sc 105 TD THSHASLOLMAS HN scehirenee tcl oe cic: arevetotctotacve layer a/airalay ct eA penera eet sv ener eek eee ates sodoo Oe 9 Dynamite, used tor shatterine dense!substratat.. a. ec niece clceeice nee e) LSE anehngsrerusie know ipthieknessa acter bet eee rereie iain iene Xxix HarthwOornns actonvor imesoll-tormationanseen eee ce eietiitcceen eee 158 FCORO TI Call SEUSS: 545.5, 10) ia eae sig, Sev le eines: exer S\arai SS rode alonapofeteein ale oene eee 314 EV Day otk DEMS ICS HO Rees, slay cise Sater evn cava n siaie avers ayaa ae eter hapa aba 2 Elements constituting earth’s crust, table of...................0.0-- Eip.e:0b:< important to agriculture, list of........... 2. atehatirs Sathana xxxi Blutnatonmeilsardes stone! acs selene lace reciniicieain eee ener 9I i PSOMlte epsoun Salt, tr SOM wc. it, /aaie cis ie wisi Srelatyy ease cee ekereee ete Pope thal PE RETITA CATISIS NS ti. loievare ae ai voesh epi lcih Aero eete arses aabeeelebovel oh MerooTele mt akeue er Gees 129 FE FOSIO MET ATI Cy LEOTOMS Nia) wi eiheres aie (chea cisiseenas aM epevcaystopaeeastaieiara theater sieneieratahe 219 AMMMASSISSIppl tablenlamas eo HOUKes:. 2 cere: eto steele eevee iciow alee 218 Lowerino (Or lan ds By te ise ci dic cbs ctins chaielaccle/siane Sagehty sash ays aoeys cone Sate 15 Oltocks Dyscandiy) HEUTE oe eae eee ele ateheiti ahold ave tercReush eee ane 10 EMUPEVE TOCKS, | MASIC AMG! ACIMIC! sachs 050 were, eens sa) sialekel dm wud. Sea athe ee 49 KOCKS SOM SCO Misc iia vse slats ey avei st ray aban hone once EaV SRE Ral ee: Nees 52 Mucalyptuss toleramce Gt valor oiic clots s xis «1c rgio ar olavoatee Slazss a4) aalabeueroaae 480 European observations on plant distribution.................. ....... 519 standards of plant-food adequacy—Maercker’s table.......... 369 Europe, predominance of calcareous formations in.................05. 525 Hyaporation and crop yields; calemlated .. . 1... 305 «2 = eye mala determina ele 193 anid crop) yields; observed (Hortier)\j 2a tac sande sees aerate 194 andi p lant oro witlar, vaguest ace siete Soasatsioanchce sa Preece nee 193 counteractinopanpalii RR aA eae" Sie 2 Wek ott Wee 255 1bXoysul TRESS HOnUaS chatal GUNES, suooodouccoone coowacaDooneKde 257 FLOM WALEL SHIPACES: 51/13 eid Ay, ls atl a ater ee 254 WE 2nd MOISE SONS. Gace s ws oes evoyeotaeinate tice ere 254 MAR ehenUCltnTatese. oe vos o.2 5556 dais aisle eee aidrg aoe 192, 256 Am ditterent localities. Californias sce ssie sive secicioie eee 255 restrained by loose 'scurlac layers ./s524 5, Bicistainpaibiaraiertelciciae 255 through roots and leaves, amount of.................. 262, 263 Bxpansion Dy Oxidation... 350.6 se eels og ob woe e's Bae OAS Saesteteeeee 5) atts: F, EMEC AO: SEALE THMATIINES, SY! srercs «5,5: set diss sive diet s-< als a alee cisions) oretesaetatets 72 eld snaks, weatheritig Obs /o.\savses = scoiaiaahoy enieleminaiale satel bicvevatekesstSestelerateners 31 PLOGIICES; OLN irale, sonnet oine ois lonsiateraiciorayciciar shah cists oteteiaiete 32 Bye INDEX. PAGE Ferchana alkali lands:in'.\k is neice ascmiaesecir eenmaence sabhaleleteloretenAA DL Kerric Hydrate) emects Of ss. ). he cihs srs ioicts stovolelata esialoraiets ae elses caine eee 100 functionsof Muni sols ass eee ae nen aor eee a 285 highsabsorptive power Of! awa. cae eee eee Oe eee 277 in Hawaiian soils ; table......... SAE AMPS Ania Aah OS c 356 more diffused in humid than in arid soils.............. 392 Kerrie phosphatesinnavyailabilitysofanse eae ieee eee eee eee 356 Ferroso-termichhydrateandloxidheeee nee n aan Eee nee he eee 18, 45 IN OETOUS IORI Ae ee Cul oc! RUA S EAT SENN NUE ar gn re) ApS DBI aera ot Lat serait 18 Ferruginous lands, injury from swanmipingiof)....2/50.1..:. ee ween eee 233 Rertilizers;mineralle.s 9 Wi sa Ha sce Dats INR Res en Char AeA es a ae ee 2 63 waste of Dy leaching sss ieee s lia hams bin ia itlat ins ae kareena 269 Plocewlation and\floceules! 2 ihn ce eis ka ee Lee ie Ue noe Wee Eee alo anes gI Elocculated) structure’; cements maintaining... c5.+ cee ee ees 110, III Plood- plains (Ob rivers iirc ele alcoateterte erecta etatets Bites SAE otus Foe 14, 15 OOR S (SOLAN NRHN IN MIM hha CTH nN A UUlEal dag Pel te eet ro dra eta ge aie 75 Force exertediby ‘roots isis es Shi es Gee Sede toe Me eae oe eae 19 Forecasts, general, of ‘soil'quality in forest lands. ................0c00% 507 of soil values; popularii: iin ehirai suas sete en cieten ies ate 313 Forestiitrees, formsion is eice CCH ae ee arava crete etalon aaah Reval 499 to 502 of Atlantic states on alkali lands....... shelels, ecw lols etote areeseteke 481 Form and development of trees, differences in. .........-...eeeeeeeees 498 Hormslofleavesstvariati opines as ae sauna ee sare iete ere eretefoielerereraiohe 502 lack jackal y Ni A OMN CALE G Meh eek A) oles eT see «+++ 499, 501 POStMoai Cay RNs He da hd SON SETS SAS erat pean toe aac aN et Subic 499, 500 trees; ;deciduons: ini atid wregiom sje each sa ceniniwscleieeiieleniee 516 willow, scarlet, black and Spanish oaks.... .... A colersuateeueeenerer 502 Bree7ing water, efrectsiof: Fine eke a Ay ec Se cetete yee tahoe eee 3 Frost eiect Of Soilsse dec ch Ae een nee ele idee awe oie eee serene 118 Pruiting, favored iby lime am soils )y- iyo e avian aie ccrencescdorse sales avila nebo 503 Bunpd-and molds actiom sof --\.)0i.\.(tec a awv.tchosayerstn otcheonnyore ate rsnete oreo ea levoiatekersted 123 Functions in) Humus-formationeeecseceee eae 157 G. Gases, absorption of, by'soils.ii 4) )5 ule cels 8s PON ea Paha Sy, Seeehe er 272, 275 Partial pressurarOh sec ne eC ilen Ae Lyd maha a lactis Ralayeate ner tate 276 Germination ofiscedsevisse heen Meine miertate ticle salem le eee etonie miete iteletotnet 309 Glacier four, fineness andufertility Of... 2 a ie einalts oon ee eee elec aaene 5 playsical antalysisiOk ssn 0's o gore eistecoe siereie oronels eves feaencvote inanataee 5 Glaciers, srindingaud!abrasion "by = /ASure 2) a). hee ee) ae ncale clarehelel = oleate 3 Glauberis Salty ncn nid iach le etsteleteo) oe,ors! ojatohstotovetieteke tere fovenoul eae micnoteterele eouerens Wi Glauconite, anycalcareousisatidstomesy he. sie smieicienircisnateieiel ietetetets 56 Geiss Sots eM aE crt ciestaiay Von Safe ra}-s| oletcnnlece evel Saree sAcTeene aie a tatehenNenetelers Sk Gobi desert miletationior lakesyy. jar afesyoie eisna tele ateyeic ots ite cya ele ane slo eiteters 9 Comeback of orchard sess acme cn eters inieesieie isis tle ciey ste felere rete ale te ele 182 Grain-sizes) effect on percolation): Cable Crile sii imicieieieeree scree elem 224 bay shuts cgay ory To Uides-quovqs, sy and caobopoooooncesan > savepelelenenete 100 ee a et We ee Rey ee ~wabdiga ow tS bie ey INDEX. 573 PAGE Grandeau method of humus estimation........... elelotsialeieinsietsicloveicte ere 132 Granite soils, potash and phosphoric acid in...... ...... sooosanbcsand Re Granitic rocks, weathering of........ .... a aiahe Mal eclatete cick: SielavarcVatafevattvacos 47 sand @tormation mn andechimatesaansaneees ees adedatmicrctsts 2 Grano-diorite soils sof olerra Neva danse ee eee eotee eet 51 Granular sediments, influence upon tilling qualities......... Sjonde dé 102 Crape-vine, alkali toleranceyofsi/nn); cralscisiresmisioncle siistorlarrahs Valsaers 475 Grasses, cultivated, sensitive to alkali... jcc csctcscceocccece a neistete A471 Greasewood, range, tolerance of alkali; figure............... stlete, 542543 Greenstonesy. soils fromis ccc ccc ceive ects eerie evaporate Slate laista ‘el soere,'sesis 51 Ground water, depth most’ favorables to;eropsi.|.:citsejn «1 vale eietola niet atetnesalste 228 VWarlation Of SULLACE: Of 5(5..)/..4.0 crercee vane arene: afsisvecore mie) raleroneis teal 228 Gulf-stream's 534.2500. Wahoreve yaratalalevonsushanMonsuslara/aeranarsyesstaleMcnsraturaavevenatatmsshetel saevers 295 Gypsum or selenite, formation from sea-water evaporation........ Feuao, We how recognized...... Seon aoe Goscounts pelcreveleent cttw Az H. CINE Pete Actaneievcleyols oers cache elejeteiate stein sia caamraierorate BAGO O DDE Ss GE aUBOLIOS aGOMc 76 Hardpans, causes, formation and cements of....... a faseiole lari stererels)efsiaceyels 185 Hardpan, physical, analysis Of. 6. .5..c.j% cesses ees Riekoteisteclehefoteielopncisisceicte 103 PLONV SOLS His) oie Sosaiceas & aiate ey ahateeess iaiaieiy te neverehauaieteare eee s000000C 241 Hawaiian Islands, humid and arid sides of...............6 Aeron oc 297 SOllSvanalySesOlasniiee enone eeee sioner aiahedateratel Seetehe 356 raya PACULWS 's OUTS. a delete © grasa «at loisioi aint seyelafe lager ebesivgannsivend sereises 149, 150 Eleatrvand cold effectsvoniroclesiia i.) ycrlers Meg cto areralora Seer eran nee I oihish andlow intensity: 4. ieee stasis ici saiicccieiuctenaienate iach 304 FeHection and dispersionitroul Soll Surtaces.. 50 s..6 1s see ae cei 304 relations to soils and plant growth........... MOSacaCoUGS DSA oC 301 LEAP PIS OL SUMS = wajehichi ness avsusis sesretaus yest ane louse eieieie seeitersiouteneteny cele 288 imeayiest clay soils, physical analysis Ofs. 4... ssceu seuarsea dove neemete 115 lea e-Otlts Of OLA ene leiar-ie elekelseieusiaveiciciel eee Satalesejeiovoraishoverest erste secret 119 JB STS ORD eRe erecae aA biG aeIG SHIGRKES MEAG OO OI GOnEG Become os boo c 44 Herbaceous: plants as soil ima@icatorss cc) cwlels(s ss sgracisleisia esis teres vesenre 517 IBIOee WANG ignn ponarooraroo oc soho on Soat badboonsnulgonnoChohanobos ons 114 Te toraalolkesnl-eyeral jeyypron. Wolhltmanni i225. al. cis see oer tees 403, physico-chemical investigation: Of 12) sc)205 1). Sin ies os sie wie oe ore 313 (see Table of Contents) Solarmradiationwintluencerolmeimsmcn ie dente cser ete cio ce eee ase ue aera 302 Solubility, continuous, of soils in water........ USE Ratan ater nee eeteeins 328 King’s table, rich and poor soils..............- 330 Schultze%sitablesrichesoileae yee cies rel cede selenide 328 Ulbricht!s tablesipoorisoile ns savsege ne ea cies 329 Solyentyaction of water upon/soilsy sis o- ined vc oc ce sensi crea si eieleijete whale 327 POWGCEIOL WALEE orctessp seep toparietieite/ sie) steel rons eet slate ur efare s aiaielicr= teisisiate Pip 3 / Solubility, increased with nitrogen-content. ...........05.scccceescscocs I4I SOUWiPr RIIESESS [S545 5005 Guu odoo cuoguU OLDS ObOb aobUEodedD SOURS Ee du0bdS 123 MMMS WATItisepLiCs PLO PELtles) OL. ae