Effects of Tied Ridges, Terraces and Grass Leys on a Lateritic Soil in Kenya

Summary

In a study of soil and water conservation systems for high-altitude Kenya farming, control of accelerated erosion in two arable crops per year for six years was achieved by contour-ploughing and tied-ridging. The Kikuyu red loam latosol lay on 10 per cent and 12 per cent slopes under rainfall of intensities often exceeding 2 inches per hour. Soil structure measurements showed progressive reduction in the acceptance rate of rainfall, but gulley erosion occurred only in the absence of ties. Six years of intensive arable cultivations were compared with rotations having two, three or four years of perennial grass ley, with and without protection by Nichols terraces. Runoff, measured through Parshall flumes, was heaviest from well-established grass immediately after intensive grazing. Productivity was highest under grass. With a basal dressing of one hundred weight of double supers, 10 acres of Cynodon dactylon carried 20 Zebu steers for seven months without supplementation and showed a liveweight gain of 1·1 lb per steer per day. Grazing was reduced by failures in establishment of short legs. The grass depleted soil moisture to wilting point to a depth of ten feet within six months of planting and annually thereafter. Water use was approximately the same as total rainfall. Results, applicable locally, indicate a limit of four years duration for arable and a minimum of five years duration for pastures. Terraces can only be replaced by a high standard of management and skilled cultivation.