ROLE OF MANURES AND CROP RESIDUE IN ALLEVIATING SOIL FERTILITY CONSTRAINTS TO CROP PRODUCTION - WITH SPECIAL REFERENCE TO THE SAHELIAN AND SUDANIAN ZONES OF WEST AFRICA

In the West African semi-arid tropics (WASAT), continous cultivation leads to drastically reduced levels of soil organic matter. Such reductions in the level of soil organic matter have resulted in decreased soil productivity. The addition of organic materials either in the form of manures or crop residue has beneficial effects on the soils' chemical and physical properties. For many of the countries in this region, the amounts of nutrients in crops and crop residue are often several orders of magnitude higher than the quantity of the same nutrients applied as fertilizers. The return of the crop residue for soil fertility improvement cannot be overstressed. It is essential that more information on the rates of organic matter decomposition as well as the many reactions between products of organic matter decomposition and the soil under WASAT conditions be made available.