Define Nitrogen cycle briefly

Nitrogen cycle :a continuous series of natural processes by which nitrogen passes successively from air to soil to organisms and back to air or soil involving principally nitrogen fixation, nitrification, decay, and denitrification.

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.

Nitrification: Plants receive the components of the "fixed" nitorgen using nitrates in the soil to provide the nutrients they need. Bacteria such as Nitrosomonas, Nitrococcus, and Nitrobacter participate.

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.

Assimilation: Plant roots assimilate Nitrogen mainly in the form of nitrates while animals assimilate their nitrogen by eating the plants.

Ammonification: 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.