The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into various chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems. Important processes in the nitrogen cycle include nitrogen fixation, assimilation of soluble nitrates, ammonification, nitrification, and denitrification.
Nitrogen Fixation- The process of the conversion of free atmospheric nitrogen into its compounds is called nitrogen fixation. Plants cannot absorb nitrogen directly as such. The conversion of nitrogen into its compounds takes place as follows. Plants that have nodules on their roots are called leguminous plants, for example, peas, grams, beans, etc. The nodules of these plants contain nitrogen fixing bacteria called rhizobium which absorbs nitrogen directly from the air and converts them into nitrates. These nitrates are converted into proteins.
Assimilation of soluble Nitrates: The process by which plants and animals incorporate nitrogen and ammonia formed through nitrogen fixation and nitrification.
Ammonification: When plants and animals die, bacteria break down nitrogen nutrients (proteins) to release ammonium salts and ammonia. The conversion process is called ammonification.
Nitrification: The process in which Nitrosomonas bacteria convert nitrogen into nitrite and then Nitrobacter converts nitrite to nitrate is called nitrification.
Denitrification: The reduction of nitrates into gaseous nitrogen for any anaerobic bacteria like pseudomonas.
