Enhancing biological nitrogen fixation: An appraisal of current and alternative technologies for N input into plants

Biological nitrogen fixation (BNF) involves a highly specialized and intricately evolved interactions between soil microorganisms and higher plants for harnessing the atmospheric elemental nitrogen (N). This process has been researched for almost a century for efficient N input into plants. The basic mechanism and biochemical steps involved in BNF have been unraveled. It has become abundantly clear that the host plant (legumes) dominates in regulating the BNF process. Environmental factors as well influence this process. Perturbation or any manipulation of the interactions between the bacteria and the legumes seems to offset the critical balance, usually to the detriment of N fixation efficiency. Not much success has been obtained in either enhancing BNF in legumes or transferring important BNF traits to non-nitrogen fixing organisms. An appraisal is given for the lack of success in making the BNF process a popular and efficient agronomic practice. Alternative physiological approaches are presented for improving mobilization, redistribution and utilization of stored N reserves within the host plant.