Effects of cowpea, crotalaria and sorghum crops and phosphorus fertilizers on maize productivity in semi-arid West Africa

Cowpea and sorghum grain crops, fertilized with 26 kg of phosphorus (P) per ha from either a P-soluble (SP) or a slightly P-soluble fertilizer (Kodjari, a natural rock phosphate (RP) indigenous to Burkina Faso), and cowpea and crotalaria (Crotalaria retusa) green manure crops, either unfertilized or fertilized with 26 kg P/ha from RP; were studied for their effects as preceding crop treatments for maize. The experiment was conducted in semi-arid West Africa (SAWA) at Farako-Bâ in Burkina Faso in 1983–86. Nitrogen (N) and soluble P fertilized and unfertilized subtreatments, applied to maize the following year, allowed the effects of the preceding crop treatments in improving soil fertility and the direct effects of P and N fertilizers applied to the maize crop to be assessed. Maize productivity was increased both by P fertilization and by soil improvements following cowpea and crotalaria; N fertilization in excess of 60 kg N/ha was not beneficial. Cowpea grain crop treatments, especially when fertilized with a P-soluble source, maximized maize yields, whereas cowpea and crotalaria green manure treatments were either similar to the cowpea grain treatment fertilized with RP or were intermediate between the latter and the sorghum treatment fertilized with SP. Sorghum, regardless of the source of P-fertilizer used, appeared not to be a suitable preceding crop for maize in SAWA.