Rehabilitation of a semiarid ecosystem in Senegal : 1. Experiments at the hillside scale

The groundnut cropping basin of Senegal suffers environmental degradation, with a negative impact on local agriculture, shown by intense soil erosion. Despite the existence of many extensive programmes, there are few results concerning actual effects, at the hillside scale, of rehabilitation practices. The objective of the study, carried out from 1983 to 1993, was to give evidence of the actual effects, in terms of hydrology and agronomy, of conservation measures set-up in a small cultivated watershed (60 ha). The measures included, on the basis of ecological features and human uses, live-hedges, stone bunds and improved cropping practices. The hydrological survey, based upon the paired watershed technique, gives evidence of land conservation, rather than land restoration, due to these developments. The efficiency of the hedges is mainly due to the favourable planting conditions. The proposed cropping practices were adopted by farmers to varying degrees, and field monitoring showed no actual effect on average crop production. To improve the cost/benefit ratio, the scientific staff should have emphasized, for the attention of the farmers, the necessary linkage between fertility restoration and runoff control. Despite this limitation, an increasing number of farmers and village communities are asking for technical assistance. (Résumé d'auteur