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Abstract
Extract
Inland valleys (IVs) are distributed throughout most parts of West Africa and are used in the cultivation of most crops, rice especially. The total area of IVs is estimated to be 20– 50 million ha in West Africa (Windmeijer and Andriesse, 1993). According to the estimation by Wakatsuki et al. (1994), the potential area for irrigated rice in whole sub-Sahara Africa is 20 million ha, of which more than 80% are distributed in West Africa. However, West Africa has presently only about 300 thousand ha of irrigated rice. Large quantities of rice are imported annually to compensate for the less than adequate annual production (WARDA 1986). In our previous paper, general fertility parameters of soils of inland valleys in four agro-ecological zones of West Africa were presented (Issaka et al. 1994). In this paper, the geographical distribution of some selected soil fertility parameters and the possible effect of geological factors are analyzed.