Biological inoculants for sustainable intensification of agriculture in sub-Saharan Africa smallholder farming systems

Abstract

Land degradation in the smallholder farming systems in sub-Saharan Africa is mainly related to insufficient adoption of sustainable agriculture technologies. This study was aimed at investigating the potential of biological inoculants to improve crop yields and control plant diseases in a profitable manner. Three rhizobia inoculants for soybean or common bean, 2 arbuscular mycorrhizae fungi (AMF) for sweet potato, and 2 Trichoderma products for tomato were applied to determine their effect on yields and tomato late blight disease. The study was conducted in Ghana, Kenya, Tanzania, and Uganda, but the treatments varied among the countries. The Rhizobia inoculants produced significant soybean or common bean yield increases in Ghana, Kenya, and Tanzania at p ≤ 0.05 when compared to the untreated control, and an economic analysis of the Ghanaian data found that Legumefix was profitable with a value–cost ratio of >3. There was significant spatial variability in crop yields (coefficients of variation: 37–64 %), indicating a need for further investigation to correct the limiting factors. The sweet potato response to AMF was variable across sites and seasons, and a significant response (p ≤ 0.05) was shown only under drought conditions in a soil with low organic matter content (1.2 %). The Trichoderma inoculants controlled late blight disease in tomatoes significantly better than Ridomil (p ≤ 0.05), a synthetic fungicide currently used by farmers in Kenya. Biological inoculants can therefore improve the productivity of the sub-Saharan Africa smallholder farming systems, and awareness of them should be created for relevant stakeholders to increase understanding and adoption of technologies for sustainable agricultural intensification.