Pedotranslocation in Planosols and its management implications in Kinangop area, Kenya

Abstract

In this study transfer of clay and other soil constituents was evaluated using soil samples from Kitiri Scheme in the Kinangop plateau. The total area covered by the study which is based on pedotranslocation in Planosols of the area is about 100 hectares. The approach used was basically physical and chemical laboratory analyses. Parameters used include CEC, exchangeable base, bulk density, pH, water retention, particle size analysis, mineralogical composition and geochemical composition. Depth of the slowly permeable layer and related management constraint was noted in the field so as to provide a scientific basis for the rational use of the soils. The area was divided into 3 transects based on position in slope before the Planosols were characterized. Samples were obtained from representative profiles of each transect and analyzed at the University's Soil Science laboratory jGeology Department and Ministry of Natural Resources. The parameters mentioned indicated the p o ss ib i 1 i ty of clay translocation in the soil sola of the entire area since there were significant differences '1 the values in adjacent horizons especially between Bt and E horizons. The silt/silt + clay ratios of adjacent horizons of th~ 3 transects especially between E and Bt horizons were significantly different indicating either clay accumulation or differences in parent material which would release clays at different rates resulting into the disparity obser?ed. However, despite the textural breaks observed in the pedons studied, mineralogical tests provided evidence of parent material uniformity hence differences in ratios reflect clay accumulation. Textural breaks observed in sand and silt fractions in E and B horizons is likely due to leaching of soil components which has resulted to the slowly permeable layer (Bt horizon). Th~ slowly permeable layer occurs at an average depth of 4: cm in the three transects. Imperfect drainage observed in the field is due to the compact Bt-horizon. The horizon allows shallow rooted crops to be grown but drainage conditions and low temperatures restrict crop choice to mainly potatoes and cabbages which are grown in relatively better drained sites. Otherwise much of the area is under grass for grazing, land use which is rational for the small scale farmers in the area