Soil degradation in parts of the upper Migori river catchment

Abstract

The rate of soil erosion in parts of the Upper Migori River Catchment in Kenya was studied using three relevant land qualities and characteristics and soil conservation measures are recommended. The area has steep Leptosol slopes and gentler Greyzem slopes, both of which have been eroded. Sheet and rill erosion occurs extensively in the recently settled uplands where Leptosols, Cambisols and Phaeozems have been degraded and on the Oloololo Plateau where Plinthsols have been adversely affected by vegetation burning, cultivation and overgrazing. The qualities used were: susceptibility to erosion by water (rated using slope parameters and vegetation cover type), soil resistance to erosion (rated using the percentage of organic carbon, silt:clay ratio and bulk density), and vegetation generation possibility (rated using CEC, base saturation and percentage of organic carbon). The soils that are highly susceptible to erosion were generally found on the hilly parts, they also suffer from gully erosion. It is suggested that physical conservation measures such as bench terraces would aid soil conservation. Since the plateau/bottomland soils were characterized by moderate resistance to erosion and poor drainage on gentle slopes it is suggested that they may require gabions and biological methods (including tree planting, alley cropping and maintenance of good cover) to control gully erosion. The river valley soils were moderately susceptible to erosion since existing cover provides good resistance, the valleys are forested and lower down. It is recommended that these forests should be conserved to avoid soil erosion on steeper slopes. In conclusion, susceptibility to erosion gave a good reflection of the current soil erosion status.