Sustainable intensification and diversification options with grain legumes for smallholder farming systems in the Guinea savanna of Ghana

Food security is a critical issue in the Guinea savanna of Ghana where about 60% of the rural population, mostly smallholder farmers are food insecure. Food insecurity results from poor crop yields due to low soil fertility compounded by erratic unimodal rainfall and the inability of households to purchase required supplemental food. Rapid population growth means that the numbers of food insecure people are likely to increase, necessitating sustainable intensification and diversification to increase crop production per unit area of land. This thesis focused on testing spatial and temporal intensification and diversification options suitable for the variable biophysical and socio-economic conditions of smallholder farming systems in the Guinea savanna to increase productivity, mitigate the risk of crop failure, and thus to increase food self-sufficiency. One site in the southern Guinea savanna and one in the northern Guinea savanna were selected which differed in biophysical and socio-economic resources. In each site, field experiments were conducted on three fields differing in soil fertility (fertile, medium fertile, poorly fertile) to quantify: N2-fixation and N contribution to soil fertility by grain legumes in sole and intercropping; impact of replacement intercropping on increasing resource use efficiency and crop productivity; and productivity of relay (additive) intercropping and rotation of grain legumes with maize. Scenario analysis was performed with data from the N2Africa Ghana project supplemented with data from the on-farm experiments and literature to test the impacts of intensification and diversification options on household food self-sufficiency. Sole legumes fixed larger amounts of N2 than under intercropping. The soil N balance was generally positive and similar between intercrops and sole crops suggesting that both systems could be sustainable intensification and diversification options. Poor fields stimulated grain legumes to rely on atmospheric