SOILS

THEIR FORMATION, PROPERTIES, COMPOSITION,
AND RELATIONS TO CLIMATE AND PLANT GROWTH
IN THE HUMID AND ARID REGIONS

BY
E. W. HILGARD, Ph.D., LL.D.,

PROFESSOR OF AGRICULTURE IN THE
UNIVERSITY OF CALIFORNIA, AND DIRECTOR
OF THE CALIFORNIA AGRICULTURAL EXPERIMENT STATION

New York
THE MACMILLAN COMPANY
LONDON: MACMILLAN & CO., Ltd.
1921

Copyright, 1906,
By THE MACMILLAN COMPANY.

Set up and electrotyped. Published July, 1906.

Norwood Press: Berwick & Smith Co.,
Norwood, Mass., U.S.A.

SUMMARY OF CHAPTERS.

1.Origin and Formation of Soils.
Introduction.
ChapterI.Physical Processes of Soil Formation.
“II.Chemical Processes of Soil Formation.
“III.Chief Soil-forming Minerals.
“IV.The Various Rocks as Soil-Formers.
“V.Minor Mineral Ingredients of Soils. Mineral
Fertilizers. Minerals Injurious to Agriculture.
2.Physics of Soils.
ChapterVI.Physical Composition of Soils.
“VII.Density, Pore Space, and Volume-Weight of Soils.
“VIII.Soil and Subsoil; Causes and Processes of
Differentiation; Humus.
“IX.Soil and Subsoil; Organisms Influencing
Soil-Conditions. Bacteria.
“X.Soil and Subsoil in their Relations to Vegetation.
“XI.Water of Soils; Hygroscopic and Capillary Moisture.
“XII.Water of Soils; Surface, Hydrostatic, and Ground
water; Percolation.
“XIII.Water of Soils; Conservation and Regulation of
Soil Moisture. Irrigation.
“XIV.Absorption by Soils of Solids from Solutions.
Absorption of Gases. The Air of Soils.
“XV.Colors of Soils.
“XVI.Climate.
“XVII.Relations of Soils and Plant-Growth to Heat.
3.Chemistry of Soils.
ChapterXVIII.Physico-Chemical Investigation of Soils in
Relation to Crop Production.
“XIX.Analysis of Virgin Soils by Extraction with
Strong Acids, and its Interpretation.
“XX.Soils of Arid and Humid Regions.
“XXI.Soils of Arid and Humid Regions continued.
“XXII.Alkali Soils, their Nature and Composition.
“XXIII.Utilization and Reclamation of Alkali Lands.
4.Soils and Native Vegetation.
Chapter XXIV.Recognition of the Character of Soils from their
Native Vegetation. Mississippi.
“XXV.Recognition of the Character of Soils from their
Native Vegetation. United States at large, Europe.
“XXVI.Vegetation of Saline and Alkali Lands.

TABLE OF CONTENTS.

Preface [xvii]

Introduction, [xxiii].—Definition of Soils, [xxiii].—Elements Constituting the Earth’s Crust, [xxiii].—Average Quantitative Composition of the Earth’s Crust, [xxiii].—Clarke’s Table, [xxiv].—Oxids Constitute Earth’s Crust, [xxiv].—Elements Important to Agriculture; Table, [xxv].—The Volatile Part of Plants, [xxvi].

CHAPTER I.

Agencies of Soil Formation, [1].—[1]. Physical Agencies, [1].—Effects of Heat and Cold on Rocks, [1].—Unequal Expansion of Crystals, [2].—Cleavage 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 Corrasion 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].—Lowering of the Land Surface by Soil Formation, [15].

CHAPTER II.

Chemical Processes of Soil Formation, [16].—[2]. Chemical Disintegrations 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].—B. Chemical; Action of Root Secretions, [19].—Bacterial Action, [20].—Humification, [20].—Causes Influencing Chemical Action and Decomposition, [21].—Heat and Moisture, [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 Landlocked Lakes, [25].—Results of Insufficient Rainfall; Alkali Lands, [28].

CHAPTER III.

Rock-and Soil-Forming Minerals, [29].—Quartz, quartzite, jasper, hornstone, 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; Limestones, 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].—Natural 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].—Minerals used as Fertilizers, [63].—Apatite; Phosphorites of the U. S., Antilles, Africa, Europe, [63].—Phosphatic Iron Ores, “Thomas Slag,” [64].—Animal Bones; Composition and Agricultural Use, [64].—Vivianite, Dufrenite, [65].—Chile Saltpeter, [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 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].—Application of Stable Manure in Humid and Arid Climates, [74].—Minerals Unessential or Injurious to Soils, [75].—Iron Pyrite, 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; Carbonate 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].—Schöne’s Instrument, [90].—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 Designations 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, [100].—Other Substances, [101].—Aluminic Hydrate, [101].—Influence of Granular Sediments upon the Tilling Qualities of Soils, [102].—“Physical” 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-space and Volume-weight of Soils, [107].—Density of Soil Minerals, [107].—No Great Variation, [107].—Volume-weight most Important, [107].—Weight per Acre-foot, [107].—Air-space in Dry Natural Soils. Figure, [108].—May be Filled with Water, [108].—Effects of Tillage. Figures, [109].—Crumb or Flocculated Structure; Cements, [109].—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].—Crumbling of Calcareous Clay Soils on Drying, [116].—Yazoo Bottom, Port Hudson Bluff, [116].—Loamy and Sandy Soils, [117].—Formation of Surface Crusts, Physical Analyses, [117].—Effects of Frost on the Soil; Heaving; Ice-flowers, [118].

CHAPTER VIII.

Soil and Subsoil; Causes and Processes of Differentiation Humus, [120].—Soil and Subsoil ill-defined, [120].—The Organic and Organized Constituents of Soils, [120].—Humus in the Surface Soil, [120].—Soil and Subsoil; Causes of their Differentiation, [121].—Ulmin Substances 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 Humification, [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, “Matière 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 IX.

Soil and Subsoil (continued), [142].—Organisms Influencing Soil-Conditions. Bacteria, [142].—Micro-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].—Multiplication of the Bacteria, [144].—Aerobic and Anaerobic Bacteria, [144].—Food Materials required, [145].—Functions of the Bacteria, [145].—Nitrifying 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, Functions in Soils, [148].—Denitrifying Bacteria. Figures, [148].—Ammonia-forming Bacteria. 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].—Table 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 Humid Climates, [162].—Subsoils in the Arid Region, [163].—Deep Plowing 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 (Wisconsin) Fruit Tree, [168].—Comparison of Root Development in the Arid and Humid Regions, [169].—Prune on Peach Root, [169].—Adaptation of Humid Species to Arid Conditions, [169].—Grapes, [170].—Kentucky and California Maize, [175], [176].—Hops, [172].—Deep-Rooting in the Arid Region, [174].—Goose Foot and Figwort, [174].—Importance of Proper Substrata in the Arid Region, [173].—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, Moorbedpan 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, [188].—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, [190]. 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].—Ascent in Uniform Sediments. Figure, [204].—Maximum and 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 Requirements 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 in the 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 Variety of Grain-sizes, [224].—Table of King’s Experiments, [224].—Percolation in Natural Soils. Figure, [225].—Ground or Bottom Water, [227].—Lysimeters, Surface of Ground Water; Variations, [227].—Depth of 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 XIII.

Water of Soils; The Regulation and Conservation of Soil, Moisture; 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 Penetration, [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 Irrigation Waters, [246].—Saline Waters; Figures of Effects on Orange Trees, [246].—Limits of Salinity, [246].—Mode of Using Saline Irrigation Waters; Apparent Paradox, [249].—Use of Drainage Waters for Irrigation, [250].—“Black Alkali” Waters, [250].—Variations in the Salinity of Deep and Shallow Wells, [250].—Muddy Waters, [251].—The Duty of Irrigation Waters, [251].—Causes of Losses, [252].—Loss by Percolation. Figure, [252].—Evaporation, [253].—Tables Showing same at California Stations, [255].—Evaporation in Different Climates; Table, [255].—Evaporation 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].—Absorption of Solids, [267].—Desalination, [267].—Decolorization, [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].—Composition of Gases Absorbed by Various Bodies from the Air. Table, [275].—Discussion of Table, [277].—The Air of Soils, [279].—Empty Space in Dry Soils, [279].—Functions of Air in Soils, [279].—Insufficient and Excessive Aeration, [280].—Composition of the Free Air of Soils, [280].—Carbonic Dioxid vs. Oxygen, [281].—Relation to Bacterial and Fungous Activity, [281].—Putrefactive Processes, [282].

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 Conditions, [287].—Ascertainment and Presentation of Temperature Conditions, [288].—Annual Mean not a Good Criterion, [289].—Extremes of Temperature are most Important, [289].—Seasonal and Monthly Means, [289].—Daily Variations, [290].—The 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 Conditions 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].—Germination 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 Production, [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, [322].—Chemical Analysis, [323].—Water-Soluble and Acid-Soluble Portions 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].—The 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 Requirements 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].—Discussion of Table, [343].—Low Plant-food Percentages not always Indication 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 Soils, [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; Matière 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].—Influence of Lime upon Soil Fertility, [365].—“A Lime Country is a Rich Country,” [365].—Effects of High Lime-Content in Soils, [365].—Table of Soils showing Low Phosphoric Acid with High and Low Lime-Content, [366].—What are Adequate Lime-percentages? 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 Humid 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 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].—Lime; Summary of Physical and Chemical Effects of Lime Carbonate in Soils, [378].— Discussion of Summary, [379].—Magnesia: Its role in Plant Nutrition, [381].—Manganese: Its Stimulant Action, [383].—The “Insoluble Residue” 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].—Ferric Hydrate, [392].—Phosphoric Acid, [392].—Sulfuric Acid, [394].—Potash and Soda, Retained more in Arid Soils, [394].—Arid Soils Rich in Potash, [395].—Humus, Low in Arid Soils, but Rich in Nitrogen, [396].—The Transition Region, [397].

CHAPTER XXI.

Soils of Arid and Humid Regions Continued, [398].—Soils of the Tropics, [398].—Humus in Tropical Soils, [399].—Investigations of Tropical Soils, [401].—Soils of Samoa and Kamerun, [402].—Soils of the Samoan Islands, [403].—Soils of Kamerun, [404].—Soils of Madagascar, [405].—Soils of India, [410].—The Indo-Gangetic Plain, [411].—The Brahmaputra Alluvium in Assam, [413].—Black Soils of Deccan, [414].—Red Soils of the Madras Region, [415].—Laterite Soils, [416].—Influence of Aridity upon Civilization, [417].—Preference of Ancient Civilizations for Arid Countries, [417].—Irrigation Necessitates Co-operation, [419].—High and Permanent 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].—Predominant 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 Alkali 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 Alkali Soils as a whole. Tables, [445].—Presence of much Carbonate of Soda, [448].—Cross Section of an Alkali Spot. Table, [448].—Reactions between the Carbonates and Sulfates of Earths and Alkalies. Figure of Curve, [449].—Inverse Ratios of Alkali Sulfates and Carbonates. Diagrams, [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 Surface 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 Alkali 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].—Sunflower Family, [473].—Root Crops, [474].—Stem Crops, [475].—Textile Plants, [475].—Shrubs and Trees, [475].—Vine, Olive, Date, Citrus Trees. Deciduous 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 Vegetation the Basis of Land Values in the United States, [488].—Investigation of Causes Governing Distribution of Native Vegetation, [488].—Investigations 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].—Characteristic 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].

CHAPTER XXV.

Recognition of the Character of Soils from their Native Vegetation. 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].—Absorption of the Salts. Table, [529].—Injury from the Various Salts, [531].—Reclamation of Marine Saline Lands for Culture, [533].—The 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].