Contour ploughing is a well-established agronomic measure that contributes to soil and water conservation (Krüger et al. 1997) (see figure 1). The soil is ploughed along the contour instead of up- and downward (see figure 1). This decreases the velocity of runoff and thus soil erosion by concentrating water in the downward furrows (Tidemann1996) (see figure 2). Contour ploughing on the other hand purposely builds a barrier against rainwater runoff which is collected in the furrows. Infiltration rates increase and more water is kept in place. Contour ploughing is especially important at the beginning of the rainy season when biological conservation effects are poor (Krüger et al. 1997). The effectiveness of contour ploughing decreases with increase in slope gradient and length, rainfall intensity and erodibility of the soil (Lal 1995).
Contour ploughing in the Gina River catchment
In the Gina River catchment contour ploughing is also practised to reduce soil erosion (see figure 2). However, it could only once be monitored due to the period of field investigation and thus was not considered in the assessment of soil erosion risk in the drainage basin.
Besides these measures, it is also important to consider some socio-economic, institutional and political aspects of soil and water conservation.