In the nitrogen cycle [local], nitrogen moves in a large atmospheric cycle. Our atmosphere is about 78% gaseous nitrogen (N₂). Nitrogen atoms move through the ecosystem by nitrogen fixation, assimilation and biosyntheses, decomposition, ammonification, and nitrification.

Nitrogen fixation involves the conversion of N₂ to ammonia (actually soluble ammonium (NH₄⁺). Plants assimilate and use fixed nitrogen in the biosynthesis of amino acids, proteins, and nucleic acids. Plant tissues are the only source of nitrogen for animals. Microbial nitrogen fixation.

During decomposition and ammonification, fungi and bacteria break down wastes containing nitrogen. The decomposers use some of the released proteins and amino acids for their metabolism. The left over nitrogen is available for plants.

Ammonium, nitrite and nitrate are sensitive to leaching and runoff. Managing these soluble products is a large issue in agricultural production and waste management. Nitrogen and the Hydrologic Cycle [local].