Nitrogen is an essential element for plants and is found in abundance as atmospheric nitrogen. But most plants are unable to use it. Why is it so and in what form do plants utilise nitrogen ?

Explanation

Most plants cannot utilise the atmospheric nitrogen as it is almost inert in nature. Nitrogen combines with oxygen by atmospheric activities and is brought down by rain to the soil. Highly specialised organisms called nitrogen fixers, occur in the soil and they convert nitrogen gas into anionic forms such as nitrates or nitrites of a reduced cationic form like ammonium. These compounds enter the plants as nutrients in the form of dissolved nitrites and nitrates through the root and are assimilated as organic nitrogen