The New Student's Reference Work/Soils
Soils, the different forms of earth on the surface of the rocks, formed by the breaking down or weathering of rocks. The soils will vary with the minerals in the rocks, the principal ones being quartz, felspar, clays, mica and limestone. When the soil is made from the rocks in their original position, they are called sedimentary; but if formed from rocks above them and carried to them, they are known as transported soils. When the soil is carried by glaciers, it forms drift soils; when carried by running water, it is known as alluvial soil. They are also known as clays, loams etc. Plants also make soil by their decay. So do animals, especially earthworms (q. v.). A mixed soil or loam is usually better than a clay or a sandy soil. The plants grown in the soil take from it from 200 to 600 pounds per acre yearly of the minerals found in it, and the passage of water through it also carries away other quantities, so that, where crops are removed, the soil would gradually lose its power of supporting plant life, were it not enriched. This is done naturally by the gradual decomposition of the minerals composing the soil, and also by the artificial process of applying manures and other fertilizers. Another mode of overcoming the difficulty to some extent is by changing the crops grown, as different kinds of crops take up the ingredients of the soil in different proportions. Agricultural scientists are constantly studying soils. See Agriculture, Fertilizers, Manure and Nitrogen-Gathering Crops. Consult the Department of Agriculture Experiment-Station’s Bulletin 106; the Soil-Bureau's Publications; the Weather Bureau’s Bulletins 3, 4 and 5; Fream: Soils; King: The Soil; Roberts: Fertility of Land; and Shaler: Origin of Soils (in U. S. Geological Survey’s 12th Annual Report, 1890–1, Vol. One, pp. 213–45).