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Various steps involved in nitrogen cycle are as below -

Nitrogen fixation: The conversion of atmospheric nitrogen into usable compounds of
nitrogen such as, nitrites and nitrates is called nitrogen fixation.

It occurs by two methods -

1. By lightning

2. Symbiotic bacteria like Rhizobium found in root nodules of leguminous plants and
free-living bacteria, like, blue-green algae,convert atmospheric nitrogen into usable
compounds of nitrogen.

Nitrogen assimilation: Plants take Nitrates from soil and produce proteins. Plants and
their products are eaten by animals and, thus, nitrogen is incorporated into living
organisms’ body.

Ammonification: Animals excrete ammonia and ammonia is released from dead
bodies of plants and animals. it is done by fungi and bacteria.

Nitrification: Conversion of ammonia to nitrates is called nitrification. It is done by
bacteria(Nitrosomonas and Nitrobacter).

Denitrification: Some amount of Nitrates produced is used by the plants and some
amount is converted into gaseous form of nitrogen. The conversion of nitrates into
atmospheric nitrogen is called denitrificaton. It is done by bacteria like pseudomonas.