Examination of soil and slope factors as erosion controlling variables under varying climatic conditions

Abstract

Soil erosion is an environmental problem that has reached alarming proportions in many parts of South Africa. Understanding the complex interactions between climate, slope and soil factors is important to ensure that soil erosion is controlled and that soil resources are used sustainably. The objectives of the study were to (i) determine soil and slope variables controlling soil erosion in different climatic units and (ii) establish guidelines for the delineation of land with high potential for cropping. The degree of soil erosion was determined from field observation and existing erosion maps. The slope gradient and length were calculated from Digital Elevation Models. Numerical values of soil and slope factors were regressed against the degree of erosion using step-wise regressions. Soils in humid regions were found to be stable, irrespective of parent material, and their stability was controlled by oxides of iron and aluminium, and kaolinite. Dolerite derived soils were the most stable while mudstone and shale derived soils were vulnerable to erosion in arid, semi-arid and subhumid regions. Fine and very fine sand fractions were most important in controlling erosion of soil in arid and semi-arid climate while kaolinite and sesquioxides were more important in subhumid areas. Critical slope limits varied with soil type. Guidelines for the delineation of arable land were formulated which guided the identification of high priority land for crop development.