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 semi-arid tropical environment

SUMMARY 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 unguiculata (L.) Walp.) on crop yield, crop water use and soil fertility on a sandy soil. Presowing tillage increased grain and crop residue yields over the traditional system of no tillage. Post-harvest tillage resulted in lower yields than pre-sowing tillage during the last 2 years of the experiment. Millet-cowpea rotation increased yield and there were no important tillage × rotation interactions. Crop water use was similar for a dry and a wet year, but less water was held in the profile after the harvest of cowpea. Compared to pre-sowing tillage and no tillage, post-harvest tillage increased the amount of water conserved until the next season. In all treatment combinations, soil organic matter and total N content both declined on average by 62%, and soil pH (KCI) decreased from 4·6 to 4·3.