SUSTAINABLE AGRICULTURE IN THE SEMIARID TROPICS THROUGH BIOLOGICAL NITROGEN-FIXATION IN GRAIN LEGUMES

Sustainable agriculture relies greatly on renewable resources like bio logically fixed nitrogen. Biological nitrogen fixation plays an import ant role in maintaining soil fertility. However, as BNF is dependent u pon physical, environmental, nutritional and biological factors, mere inclusion of any N-2-fixing plant system does not guarantee increased contributions to the soil N pool. In the SAT where plant stover is als o removed to feed animals, most legumes might be expected to deplete s oil N. Yet beneficial legume effects in terms of increased yields in s ucceeding cereal crops have been reported. Such benefits are partly du e to N contribution from legumes through BNF and soil N saving effect, In addition, other non-N rotational benefits, for example, improved n utrient availability, improved soil structure, reduced pests and disea ses, hormonal effects are also responsible. In this paper we have revi ewed the research on the contribution of grain legumes in cropping sys tems and the factors affecting BNF. Based on the information available , we have suggested ways for exploiting BNF for developing sustainable agriculture in the semi-arid tropics (SAT). A holistic approach invol ving host-plant, bacteria, environment and proper management practices including need based inoculation for enhancing BNF in the cropping sy stems in the SAT is suggested.