What is the Nitrogen Cycle?


Pooja Jain
Academic Counsellor

78% of the Earth’s atmosphere is made up of nitrogen – a colorless, odorless, and tasteless gas. Nitrogen is also a component of several important biomolecules such as DNA, proteins, and chlorophyll. Despite its abundance in the atmosphere, it is not accessible by primary producers in its molecular form (N2 gas).

There exists a biogeochemical cycle through which the conversion of nitrogen into different chemical forms takes place. This cycle is commonly referred to as the nitrogen cycle. The nitrogen cycle process can be broken down into the following individual processes:

Nitrogen Fixation

The nitrogen fixation process involves the conversion of atmospheric nitrogen gas (N2 gas) into nitrates (compounds containing the NO3 ion) and nitrites (compounds containing the NO2 ion). Diazotrophs (a type of bacteria) are responsible for the majority of nitrogen fixation.


In this process, the nitrates and ammonium ions are absorbed by plants through their roots. The plants then proceed to reduce the nitrates into ammonium ions and then incorporate these ions into chlorophyll, amino acids, and nucleic acids.


Ammonification refers to the conversion of organic nitrogen (compounds containing carbon and nitrogen) into inorganic ammonium. Organic nitrogen is found in animal waste and plant/animal remains.


Some bacteria that exist in the soil convert ammonium into nitrites and eventually nitrates. This process is known as nitrification. Nitrosomonas bacteria oxidize ammonium into nitrites. These nitrites are further oxidized into nitrates by Nitrobacter.


The final process that completes the nitrogen cycle is known as denitrification. It involves the conversion of nitrates into nitrogen gas. This is primarily accomplished by Pseudomonas and Paracoccus bacteria.

To conclude, Nitrogen is a very important element which is an integral part of all living things. Even some lipids contain nitrogen. The nitrogen cycle is a very important process that is responsible for the conversion of nitrogen into different chemical forms. Inert atmospheric nitrogen is made available to plant life via this process. The ammonification process also involves the decomposition of plant and animal bodies, which helps clean up the environment. Since nitrogen is an integral part of cells, the nitrogen cycle is essential for the survival of many life forms on the planet. To learn more about the nitrogen cycle and other related topics such as the carbon cycle, subscribe to the BYJU’S Youtube channel and enable notifications.