This systematic review of 44 publications by SDSN member Ken Giller and colleagues shows that rotating grain legumes with cereals in Sub-Saharan Africa generally resulted in 41% higher yields than continuous cropping of cereal alone. All grain legume types significantly improved cereal yields, with larger improvements after soybean and groundnut than after cowpea. Consistent responses at multiple sites that differ in climatic conditions or soil fertility provide strong support that cereal yields are enhanced after grain legumes.

Future research on nitrogen fixation by grain legumes and residual N benefits should focus on explaining the wide variability observed among sites. There is a clear need for more detailed mechanistic studies to assess the occurrence and relevance of non-N effects of grain legumes, particularly in relation to common pests and diseases in cereals.