SOIL-EROSION - ITS MEASUREMENT, EFFECTS AND PREDICTION - CASE-STUDY FROM THE SOUTHERN LESOTHO LOWLANDS

Soil and nutrient losses, under different management options and scale s, for cropland and rangeland were investigated in Lesotho, Southern A frica. An approximation of soil formation was estimated with a simple weathering experiment. The replacement cost of lost soil nutrients was calculated and the concept of soil life applied to the results. The v arious approaches and scenarios included in the calculations result in predicted crop yield losses of between 1% and 5% per year. The two mo st common erosion prediction equations in Southern Africa, USLE and SL EMSA, were tested on the results. The ease of validation inherent to t he SLEMSA equation is the most remarkable fact from these tests. Once the erodibility factor is established, SLEMSA fairly accurately predic ts soil loss from a variety of land uses and management options, both over entire seasons and from single storms. However, the USLE equation proved to be the best tool for single-storm, unvalidated prediction.