SOIL VARIABILITY AND EFFECTIVENESS OF SOIL AND WATER CONSERVATION IN THE SAHEL

Sahelian sylvopastoral lands often degrade into bare and crusted areas where regeneration of soil and vegetation is impossible in the short term unless soil and water conservation measures are implemented. Five combinations of tillage with and without mulch on three crust type/so il type combinations were evaluated. The texture and organic matter co ntent of the crusts are determined more by crust type than by soil typ e. Differences in crust characteristics are linked with the genesis of the crusts. Germination of Cassia tora L. was lower on runoff crusts than on erosion crusts. Combining soil tillage with mulching resulted in a higher average germination than soil tillage or mulching as singl e measures. We also monitored the mortality of C. tora seedlings 4 wee ks after germination. Seedling survival showed a similar, though less pronounced trend to germination. Average survival was slightly better on erosion crusts than on runoff crusts. Although tillage is necessary to trigger germination of herbaceous species, it may simultaneously i nhibit establishment of these species by bringing about severe soil cr usting. Soil tillage combined with mulching provided the best conditio ns for the ultimate establishment (the product of germination and surv ival) of C. tora. It appears that soil differences have less influence on germination and survival than do differences in surface conditions .