*Nitrogen Fixation.is an anaerobic (without oxygen) process in which atmospheric nitrogen (N2)is reduced to NH3. Bacteria are responsible for this process. Bacteria in terrestrial and aquatic(water) environments participate in this process. These organisms must have a special enzyme known as dinitogenase to be able to to this.
Plants cannot use the nitrogen in our atmosphere without the assistance of nitrogen-fixing bacteria.
*Nitrification involves two steps. First, the ammonium ion (NH4+) is oxidized into NO2-. Then, this compound is further oxidized into NO3-. Again, bacteria in the soil participate in both processes.
Plant roots assimilate Nitrogen mainly in the form of nitrates while animals assimilate their nitrogen by eating the plants.
Ammonification Denitrification. Ammonia is formed in the soil by the decompostion of plants and animals and by the release of animal waste.
*Denitrification. This is the reduction of nitrates to gaseous nitrogen. Denitrifying bacteria perform almost the reverse of the nitorgen fixing bacteria. this is the process.