Date of this Version
An increasing realization of the importance of preventing or controlling soil erosion has resulted in numerous scientific investigations. Some of these are concerned with soil characteristics which promote or retard erosivity (Middleton, '30; Middleton et al., '34; Lutz, '34; and Bouyoucos, '35). Many have to do with engineering methods of reducing soil wastage (Bates and Zeasman, '30; Ramser, '30; Roe, '33; and Bartel, '35). But perhaps most were planned to discover the effects of plants in protecting and binding the soil, reducing runoff, and consequent loss of soil and subsoil (Sampson and Weyl, '18; Duley and Miller, '23; Lowdermilk, '30; Forsling, '31; Miller and Krusekopf, '32; Bennett, '34; and Uhland, '35). Since a plant cover, either natural or cultural, is the main single controllable factor in erosion, an exact understanding of its effects is of extreme importance.
So far as the writers are aware, no attempt has been made to ascertain the rate of erosion of soil protected by both tops and roots of plants, or by underground plant parts alone, as compared with similar soil free from living plants.
Aside from the purely scientific aspects of the problem, immediate practical applications are found in crop growing, range and pasture management, orcharding, and most industries where production of crops is concerned.
In agricultural practice the tops of alfalfa, clover, and other mowed crops are removed close to the ground one or more times each growing season. Wheat and other small cereals may be headed and the straw left standing; the straw may be burned to the ground, or bound and removed in harvesting and accumulated in threshing into a single pile. Pastures and ranges may be so well managed that a covering of 15 to 25 per cent of the forage remains to protect the soil even at the end of the growing season, or so closely grazed and trampled as to leave the soil almost bare. Cover crops mayor may not be used in orchards. Soil of gardens may be protected by dead plant remains, straw mulch, etc., or left bare and at the mercy of wind and water.
After a consideration of the problem of further analyzing the effects of plants, and the development of a successful method of attack (Weaver and Harmon, '35), the spring, summer, and fall of 1935 were devoted to this study.