Fig. (1) A conceptual diagram highlighting the diverse set of microsites that can support N₂ fixation by NS N₂-fixing bacteria and its role in the soil N cycle. (1) A diverse array of bacterial genera have been found in the rhizosphere and endophytic environment of a variety of cereals and other crop plants; the amount of N₂ fixation in the field environment is yet to be properly quantified, (2) A significant amount of N₂ fixation has been shown to occur in the below- and above-ground plant environments with sugarcane, (3) fresh decomposing residues, especially with wide C:N ratios, provide optimal conditions for N₂ fixation, (4) stable aggregates not only provide protective sites for free-living, N₂-fixing bacteria but also provide the required low oxygen conditions for nitrogenase activity, and (5) a diverse group of microflora in termite guts and nests possess nifH genes that show potential for N₂ fixation in natural environments mainly in semi-arid and arid ecosystems.