Biological Nitrogen Fixation - Status, Potential and Prospects in Supplementing Nitrogen Needs of the Crops

摘要

Out of the projected 45 million tonnes (Mt) of the plant nutrients (N + P2O5 + K2O) needed to produce 301 Mt of food grains to feed 1.4 billion population in the country by 2025, 35 will be supplemented through chemical fertilisers and the remaining 10 Mt will have to be added through the organic sources including organic manures, biofertilisers, crop residues etc. At least 5 to 6 Mt N will have to be supplemented through organics. Biological nitrogen fixation (BNF) is a proven time-tested, sustainable microbiological process in the biosphere, which can convert inert atmospheric di-nitrogen (N=N or N2) to reactive NH4-N through enzyme nitrogenase mediated by prokaryotic micro-organisms including bacteria "Rhizobium". This process is constrained by genetic and environmental factors. Genetic approach includes developing transgenic inoculants, N-independent cereals and endophytic-N fixation. Similarly development of effective and competitive rhizobial strains tolerant to high temperature, drought, soil acidity, alkalinity/sodicity and capable of working efficiently on marginal soils, deficient in plant nutrients and organic matter etc. poses a daunting challenge. To overcome these constraints it is a must to create better growing environment for both host crops and the bio-inoculum. Biologically fixed nitrogen can supplement 25-60% of N requirement of different crops grown under diverse environments. As a green strategy, optimisation of the BNF process is prerequisite.