EROSION SUSCEPTIBILITY AND SOIL LOSS ON GRAZING LANDS IN SOME SEMIARID AND SUBHUMID LOCATIONS OF EASTERN KENYA

Modified Gerlach-type sediment and runoff traps were installed in an open arrangement on 16 grazed areas to assess soil loss as related to erosion susceptibility. Erosion susceptibility was defined as a function of soil erodibility, slope characteristics, and average vegetative cover during the rainy season. To account for variations in rainfall between the different study sites, soil loss meas red was expressed in terms of unit soil loss per unit rainfall (g of soil . m-2 x mm rain-1). Results show that the apparent erosion susceptibility is significantly linked to average degree of grass cover as a result of grazing intensity of the areas. In the upper range of average grass cover(i.e. between 40 percent and 100 percent) the effect of cover reduction because of overgrazing bad little effect on soil loss. In the lower range of average grass cover, however, (i.e. below 40 percent) slight reductions in cover bad serious effects on soil loss. The study showed that under the conditions of the area, average degrees of grass cover as low as 40 percent do not influence soil loss dynamics significantly. The 40 percent cover level seems to be the critical cover level below which soil loss becomes serious.