CHAPTER VIII.. Soil and Subsoil; Causes and Processes of Differentiation

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.