Five main processes cycle nitrogen through the biosphere, atmosphere, and geosphere. Nitrogen uptake organism growth, nitrogen mineralization through decay, nitrification and denitrification.
Nitrogen Fixation- where N2 is converted to ammonium or NH4. This is the only way that organisms can attain nitrogen directly from the atmosphere.
Nitrogen Uptake- when the ammonium is quickly taken up by a host plant or another soil organism and incorporated into proteins and other organic nitrogen compounds like DNA. NH4+→ Organic N
Nitrogen Mineralization- after nitrogen is incorporated into organic matter, it is often converted back into inorganic nitrogen by this process. Organic N → NH4+
Nitrification- when some of the ammonium produced by decomposition is converted to nitrate (NO3-). NH4+→NO3-
Denitrification- Anaerobic process that is carried out by denitrifying bacteria, which converted nitrate to dinitrogen in the following sequence: NO3- → NO2- → NO → N2O → N2