Effects of conservation tillage on sheet erosion from sandy soils at two experimental sites in Zimbabwe

Abstract

Soil erosion from low-fertility sandy soils in Zimbabwe's Communal Areas is a major problem. The main factors causing soil degradation are inappropriate livestock management and poor cropping technology. The latter is due to insufficient knowledge concerning appropriate permanent cultivation techniques under tropical rainfall and soil conditions. The existing tillage method is characterized by clean cultivation, which begins with inversion tillage, followed by clean weeding through hoeing ( badza). These practices encourage water erosion under the prevailing rainfall pattern. Therefore, one pressing research need in Zimbabwe is to reduce soil erosion in the Communal Areas through improved tillage systems. Consequently, a project was initiated in 1988 to test the sustainability of several ox-drawn tillage systems considered potentially suitable to dryland farming conditions in the Communal Areas. Of the systems tested, a method known as no-till tied ridging showed the greatest potential. With one exception, experimental soil losses were always lower than 0.5t ha −1yr −1, whereas up to 9.5t ha −1yr −1 was typical under the conventional system of mouldboard ploughing. Similarly, ripping into crop residues revealed a distinct downward trend in sheet erosion rates over the seasons, with losses of only 0.6t ha −1yr −1 during the 1990–1991 season at both research sites in the current programme. The remaining methods under investigation—ripping into bare ground and hand hoeing—showed sheet erosion rates similar to conventional tillage.