Crust formation on sandy soils in the Sahel. II. Tillage and its effect on the water balance

The water balance for millet fields and for permanently crusted natural pastures is described, with special emphasis on the role of the crust in governing infiltration and runoff. Tillage destroys the crust and increases the surface storage for rainwater. The crust-breaking effect will last for only a few rainshowers, but the increase of surface storage is more permanent. The effect of a tillage system on the water balance of a millet crop is calculated. Tied ridges, giving a surface storage of 20–30 mm, could prevent runoff (which is about 50% under the conventional system) completely. It is expected that this would allow earlier sowing and thus prolong the vegetative growth by as much as 20 days, which might increase the average millet yield (500 kg ha−1) by 40%