SOIL-EROSION EFFECTS ON SOIL PROPERTIES IN A HIGHLAND AREA OF CENTRALKENYA

One of the most important features that is neglected in many soil eros ion studies in Africa is the monitoring of changes to the soil during the progress of the experiment. Objectives of this study were therefor e to monitor runoff, soil loss, and enrichments of eroded soil materia l and to assess the effect of cumulative soil loss on soil chemical pr operties of an Alfisol in one of the high-potential areas of Central K enya highlands. Runoff, soil loss, and enrichments of eroded sediments were measured on newly opened ground from 1991 to 1992. Annual rainfa ll was 948 and 1125 mm for 1991 and 1992, respectively. Soil loss rang ed from 0.8 to 247.3 t ha(-1), and runoff ranged from 1 to 89 mm. No s ignificant correlations were observed between enrichment ratios (ER) a nd soil loss. The ER were greater than or equal to 1 and sediments wer e mostly enriched with P and Na. The P and Na concentrations were 4 to 10 and 2 to 3 times the source material, respectively. Sediment from the plots was 247 to 936% richer in P than the soil from which it orig inated. Changes in soil pH, percentage organic C, and percentage total N following erosion were significantly correlated with cumulative soi l loss (r values of 0.77, 0.59, and 0.71, respectively, n = 20). The d ata indicated that nutrient loss due to erosion is one of the major ca uses of soil fertility depletion of Kenyan soils.