Effect of crop residues on grain yield response of sorghum (t Sorghum bicolor) (L.) to application of N and P fertilizer

A field experiment was conducted on two soil types for seven years (1988–1994) to investigate the effect of the presence of crop residue on grain yield response of sorghum to NP fertilizer applied every year or once only at the start of the experiment. Grain yield was increased by the NP fertilizer alone, but was not further significantly increased by application of both residues and NP fertilizer. During the study period yields decreased abruptly with decreasing rainfall after the first year particularly on the Typic Pellustert. Thus there was a difference according to soil type.