Agronomic management of cereal/cowpea cropping systems for major toposequence land types in the West African sacanna

In the local agriculture of the West African Sudanian and Sahelian savanna zones, the major cereal crops are grown in patterns closely linked to major toposequence land types. Moreover, crops are commonly grown in intercrop combinations of which cereal/cowpea is the most widespread. The present series of experiments investigates the impact of cereal density and of a cowpea intercrop on the grain yields of maize, sorghum, pearl millet, and several introduced sorghum genotypes. In all the studies, a spreading and photosensitive local cowpea cultivar was used. In some seasons, even a low cowpea intercrop density of 5000 plants/ha could significantly reduce sorghum and maize yields on moisture-stressed soils, whilst with adequate soil moisture cereal yields were increased. The competitive effects of the cowpea intercrop, particularly on drought sensitive lands, were enhanced by increasing cowpea density, by lowering cereal density, by sorghum cultivars with relatively open leaf canopies (e.g., the local Guiniensis types) and by a relatively high phosphate status of the soil. Because of the unpredictability of rainfall during the growth season and large local variations in soil fertility, high densities of cowpea and cereal would increase yield variation between locations and between years which is not beneficial for subsistence farmers. However, because of its positive effects on upland soil protection, and on cereal yields on moist lower slopes, a low cowpea intercrop density in the range of 2500 to 10000 plants/ha should have positive and stabilizing effects on cereal production in the long-term