Nitrogen is primary nutrient important for survival of all living organisms. It is an essential component of proteins, DNA and chlorophyll. Atmosphere is a rich source of nitrogen and contains about 78% nitrogen. Plants and animals cannot utilize atmospheric nitrogen. They can use it only if it is in the form of ammonia, amino acids or nitrates.
Processes involved in nitrogen cycle are:
- Nitrogen fixation: Nitrogen fixation is the conversion of atmospheric nitrogen, which is inert, into reactive compounds available to living organisms. This conversion is done by a number of bacteria and blue green algae (Cyanobacteria).
- Nitrogen assimilation: Plants absorb nitrate ions and use them for making organic matter like proteins and nucleic acids.
- Ammonification: The process of decomposition of nitrogenous waste by putrefying bacteria and fungi into ammonium compounds is called ammonification
- Nitrification: The ammonium compounds formed by ammonification process are oxidised to soluble nitrates. This process of nitrate formation is known as nitrification. The bacteria responsible for nitrification are called as nitrifying bacteria.
- Denitrification: Free-living soil bacteria such as Pseudomonas sp. reduce nitrate ions of soil into gaseous nitrogen which enters the atmosphere.