Soils, their formation, properties, composition, and relations to climate and plant growth in the humid and arid regions

by Eugene W. Hilgard

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].