Nitrogen the living block of living cells is one of the core components of proteins. It plays an important role in the biochemical processes that take place in living beings. It limits the rate of production in ecosystems.

Nitrogen Fixation:

The atmosphere is the largest reservoir (78% approximately) of free nitrogen. The nitrogen in this form cannot be used by the living systems. It has to be converted into nitrates through a process known as nitrogen fixation and then it is available for use by plants.

Plants take nitrogen in the form of nitrates from the soil and animals obtain nitrogen by eating plants or animals which eat plants

The atmospheric nitrogen enters the soil in the following ways:

• Nitrogen and oxygen in the air combine to form nitric oxide. This nitric oxide is then converted into nitrogen dioxide by the oxygen of the atmosphere.
• Nitrogen oxide along with oxygen dissolves in rainwater forming nitric acid.
• Nitric acid is washed down by rainwater into the soil. In the soil, this nitric acid reacts with minerals like calcium carbonate to form calcium nitrate and is absorbed by the roots of the plants.
• Nitrogen-fixing bacteria like Azobacter, Rhizobiurn, etc. convert the atmospheric nitrogen into nitrates, that are soluble in water. This process is called nitrogen fixation. Nitrogen thus assimilated, is used by the plants to form nitrogenous compounds, mainly proteins that enter the food chain.
• Nitrogen is returned to the soil through manure. excreta and earthly remains of plants and animals, and micro-organisms. Nitrogen in organic form is insoluble and cannot be used by plants. Therefore the organic matter of plant and animal origin is decomposed to ammonia and amino acids by micro-organisms in the soil through the process of ammonification and nitrification respectively.

 

Ammonification:

Ammonification is the process of ammonia formation carried out by all organisms. The ammonia may escape to the atmosphere or be retained in the soil and is sometimes oxidised to nitrates.

Nitrification:

Nitrification is the process of conversion of ammonia to nitrates by the bacteria, (Nitrosomonas in soil and Nitrosococcus in marine systems).

Denitrification:

Denitrification is the process by which some other bacteria (decomposers) reduce nitrates back to nitrogen or to ammonia or to some other oxides. Free nitrogen returns to atmospheric pool and oxides are taken up by plants.