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.