Soil fertility management and cowpea production in the semiarid tropics uri icon


  • Cowpea (Vigna unguiculata (L.) Walp.) is an important grain legume in the semiaridzone of West Africa as it is a major source of dietary protein for the people. Itis usually grown as an intercrop with the major cereals, namely millet and sorghum.Despite its importance, its yields are very low due to several constraints includingpoor soil, insect pests, and drought. The soils in semiarid West Africa are inherentlylow in nitrogen and phosphorus. Soil, water, and nutrient management practicesare inadequate to sustain food production and to meet the food requirements of thefast growing population. Research results show that proper management of organicamendments such as crop residues and manure, which are essential complementsto mineral phosphorus fertilizers, can increase yields of cowpea and associatedcereals more than three fold. Direct application of indigenous phosphate rocks canbe an economical alternative to the use of imported, more expensive soluble phosphorusfertilizers for cowpea production in the region. The agronomic effectivenessof indigenous phosphate rock is about 50% compared to the imported single superphosphate.Furthermore, when the unreactive phosphate rocks are partially acidulatedat 50%, their agronomic effectiveness can increase to more than 70%. Studieson cereal?cowpea rotation revealed that yields of cereals succeeding cowpeacould, in some cases, double compared to continuous cereal cultivation. Witheffi cient soil fertility management, cowpea can fi x up to 88 kg N/ha and this resultsin an increase of nitrogen use effi ciency on the succeeding cereal crop from 20%in the continuous cereal monoculture to 28% when cereals are in rotation withcowpea. Furthermore, the use of soil nitrogen increased from 39 kg N/ha in thecontinuous cereal monoculture to 62 kg N/ha in the rotation systems. Futureresearch needs to focus on understanding the factors affecting phosphorus uptakefrom different sources of natural rock phosphate. There is also a need to quantifythe below-ground nitrogen fi xed by different cowpea cultivars. The increase ofcowpea productivity in the cropping systems in this region will improve the nutritionof people, increase the feed quantity and quality for livestock, and contributeto soil fertility maintenance. This should contribute to reduction in poverty andenvironmental degradation

publication date

  • 2003