Influence of no-tillage on soil conservation, carbon sequestration and yield of intensive rotation maize-cotton : research on sandy Alfisols of Cameroon and Mali

To compare conventional tillage to various direct drilling systems (no-tillage or tooth tillage reduced to the sowing line), two sets of runoff plots (lOO m-) (57 in Cameroon and 17 in Mali) were built on fragile sandy Alfisols under Sudanese savannah areas. After 3 to 4 years with 900 to 1500 mm of annual rainfall, it was clear that the litter/legumes/weeds cover on no-till reduced the runoff (-20%) and erosion risks (to 1/3) compared to the conventional tillage system. Although mineral fertilizers were applied intensively, the highest yields were observed from the plowed fields (30 to 50% more of maize grain and + or 10% for cotton). It seems that cotton is less sensitive to well drained soils and nitrogen leaching than maize during the first 2 months of growth. Carbon sequestration by the direct drilling system was not systematic on very sandy soils but more important if the clay content is over 25%. The direct drilling system with glyphosate herbicide was quickly adopted by small farmers as a labor-saving system during the sowing and weeding period, but the soil surface was not well covered with mulch because of the traditional African habits of free grazing and bushfire incidence during the dry season.