This refers to the biogeochemical cycle of nitrogen which describes the succession of changes which the different forms of nitrogen go through (gaseous nitrogen, nitrate, nitrite, ammonia, organic nitrogen (proteins)).  This cycle consists of six processes:

• the fixation of gaseous nitrogen (N2); enzymatic reduction of N2 (molecular nitrogen) to nitrogen-ammonia or ammoniac (NH3) by free-living or symbiotic bacteria;

• assimilation/immobilisation; conversion of inorganic nitrogen into organic forms; 

• Anammox biomass (anaerobic ammonium oxidation) – in the absence of oxygen, conversion of ammonium and nitrites into nitrates.

• “Ammonification” is the production of ammonium or ammonia as a result of a biological activity, the decomposition of an organic matter.

• “Nitrification” is the transformation of ammonium/ammoniac ions into nitrites and then into nitrates by what are called nitrificating bacteria.

• “De-nitrification” is the reduction of nitrates into nitrous oxide then into gaseous nitrogen due to what are called denitrifying bacteria.