Nitrogen is the most important essential element needed for the metabolism, growth, development and reproduction of all living organisms. Animals and human being obtain their nitrogen requirements from the plants. The nitrogenous compounds then again reach the soil by way of death and excretion in the form of animal and plant residues. The organic matter in the soil undergoes microbial decomposition by the process of ammonification into ammonia and by nitrification into nitrates. These compounds are again absorbed by the plants or converted into nitrogen gas by the process of denitrification. Thus, there exists a bio geochemical cycle, called nitrogen cycle.