ROTATION AND TILLAGE EFFECTS ON YIELD OF PEARL-MILLET (PENNISETUM-GLAUCUM) AND COWPEA (VIGNA-UNGUICULATA), AND ASPECTS OF CROP WATER-BALANCE AND SOIL FERTILITY IN A SEMIARID TROPICAL ENVIRONMENT

A 4-year field experiment was conducted from 1986 to 1989 in Niger to determine the effects of pre- and post-harvest tillage and rotation of pearl millet (Pennisetum glaucum (L). R. Br.) and cowpea (Vigna ungui culata (L.) Walp.) on crop yield, crop water use and soil fertility on a sandy soil. Pre-sowing tillage increased grain and crop residue yie lds over the traditional system of no tillage. Post-harvest tillage re sulted in lower yields than pre-sowing tillage during the last 2 years of the experiment. Millet-cowpea rotation increased yield and there w ere no important tillage x rotation interactions. Crop water use was s imilar for a dry and a wet year, but less water was held in the profil e after the harvest of cowpea. Compared to pre-sowing tillage and no t illage, post-harvest tillage increased the amount of water conserved u ntil the next season. In all treatment combinations, soil organic matt er and total N content both declined on average by 62%, and soil pH (K Cl) decreased from 4.6 to 4.3.