This study concerns the results of four long-term experiments conducted in sub-Saharan Africa in which plots with and without organic manure applications were compared. The aim was to monitor crop yields along with concomitant changes in soil C levels on the basis of data collected in each experiment and using an identical experimental design in all trials. Organic manure application was found to have a minor impact on soil C levels, and the noted increases in crop yield generated by these inputs were explained by mineral effects.