Biological Nitrogen Fixation

Nitrogen is the most common amongst al1 soil nutrients required by the plants in larger quantity. But the di-nitrogen gas (N2), i.e., the atmospheric nitrogen is not available directly to them in any usable form. It is due to the stability of the N º N triple bond in N2 that makes N2 extremely inert and its activation is a very energy demanding process.

However, there are only two pathways to make nitrogen available to the plants (i) through the formation of industrial fertilizers, and (ii) nitrogen fixation by microbes, i.e., the biological nitrogen fixation. Nitrogen, therefore, chiefly comes naturally from microbial fixation characteristically by some prokaryotes (eukaryotes completely lack this ability); the prokaryotic microbes reduce atmospheric nitrogen to ammonia which acts as the source of cell nitrogen.

Therefore, the utilization of atmospheric di-nitrogen gas (N2) as a source of cell nitrogen by way of its reduction to ammonia is called biological nitrogen fixation The general equation of N2-fixation is: