Sustainable agriculture in the semi-arid tropics through biological nitrogen fixation in grain legumes

As biological nitrogen fixation (BNF) is dependent upon physical, environmental, nutritional and biological factors, mere inclusion of any N2-fixing plant system does not guarantee increased contributions to the soil N pool. In the semiarid tropics (SAT) where plant stover is also removed to feed animals, most legumes might be expected to deplete soil N. Yet beneficial legume effects in terms of increased yields in succeeding cereal crops have been reported. Such benefits are partly due to N contribution from legumes through BNF and soil N saving effect. In addition, other non-N rotational benefits, for example, improved nutrient availability, improved soil structure, reduced pests and diseases, hormonal effects are also responsible. Research on the contribution of grain legumes in cropping systems and the factors affecting BNF is reviewed. Ways are suggested for exploiting BNF for developing sustainable agriculture in SAT. A holistic approach involving host-plant, bacteria, environment and appropriate management practices including need based inoculation for enhancing BNF in the cropping systems in SAT is suggeste