CONTRIBUTION OF LEGUME-N BY NODULATED GROUNDNUT FOR GROWTH OF MAIZE ON AN ACID SOIL

A series of glasshouse and field experiments was undertaken to test the hypothesis that intensive cropping of a selected groundnut cultivar inoculated with a compatible and highly effective strain of Bradyrhizobium could contribute substantial amounts of N to the succeeding cereal crops. In the glasshouse experiment, the Bradyrhizobium(strain CB756)-groundnut cultivar (V13) combination produced maximum pod yield and N concentration in the haulm on unlimed and limed soil. An equivalent of 77 kg N ha(-1) without lime and 105 kg N ha(-1) when limed was estimated to be returned to the soil as legume-N through the groundnut residue. This symbiotic combination was used in a limed (4 t ground magnesium limestone ha(-1)) crop rotation field experiment to estimate the amount of N contributed by groundnut residue as measured by the yield of maize. After 1-3 successive legume crops, an estimated 20-56 kg N ha(-1) were contributed to the subsequent maize crops. This accounted for 31 and 37% recovery of the respective total legume-N.