15. Conservation tillage systems.
Adv. Agron., 33, 1981, pp. 58
Conservation tillage systems are systems of managing crop residue on the soil surface with minimum or no tillage. Other names are stubble mulching, ecofallow, limited/reduced/minimum tillage, no-tillage and direct drill. Leaving crop residues serves water and wind erosion control, conservation of soil and water and reduction of energy use. The review is limited to the salient points that have been researched over the last twenty years and is limited to the United States. For our purposes general remarks in the sections on seed bed preparation and crop seedling, control of wind erosion, control of water erosion, weed control with tillage and the three sections on soil temperature and the same number on soil structure and other physical properties are of most importance. On wind erosion, after a general introduction the wind erosion equation is dealth with. Tillage has a direct bearing on the factors I, soil erodibility; K, soil surface roughness and V, equivalent quantity of vegetative cover. Surface residue influences V, tillage proper influences mainly I and K. partial (de)coverage of a field would influence L, equivalent width of field (maximum unsheltered distance across the field along the prevailing wind erosion direction). Kind, amount, texture, height and orientation of surface residue all influence wind erosion. Tillage operations that minimize soil pulverization and smoothing are effective for maintaining K and keeping clodiness for maintaining I. Examples are given from the USA. A comparable approach is followed in the chapter on water erosion, using the influence of residue and tillage effects on the Universal Soil Loss Equation. The section on soil temperature deals with the effects of surface residue: changing the radiation balance accompanied with an insulation effect, and with residue factors involved in these effects: residue age (decoloration; decomposition), color, geometry, distribution and amount. Again some examples. Finally its biological effects on crops are dealt with. After dealing with soil aggregation, porosity and density as affected by tillage, other soil physical factors dealt with as influenced by tillage operations are soil texture, crusting, hydraulic conductivity and water storage capacity. Tillage reduction in the USA can't be considered without the rapid technological advances in the use of herbicides. It is estimated to serve from 5 to 15 cm of additional water to rain-fed agriculture. Only more interdisciplinary knowledge will advance this field of soil science.
1268 92 - 13/66
Erosion and desertification control
Asia, Indonesia, highlands, study, water runoff, erosion control practices, small plots, steep slopes
SIEBERT, S.F. and J.P. LASSOIE
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