Sandy soils of the Sahel area in West Africa, mainly cropped to millet (Pennisetum typhoides) are very sensitive to crust formation. Crusts strongly reduce infiltration capacity. In this area most fields are gently sloping (1–3%) and hence runoff is a widespread phenomenon; on the average 25% of the rain (mainly in the form of a few large storms during the rainy season) is lost by runoff. The causes of crust formation and its effect on the infiltration rate are discussed. On untilled soils the presence of a crust is a permanent feature. Rainfall characteristics play a key role in crust formation. Major rainfall characteristics of the Sahel differ significantly from those of other semi-arid areas.
- sandy soils