There is a little controversy about the relative importance of organisms in this cycle. Some believe that the role of organisms is minor compared to cycling that occurs in the abiotic reservoir. Nitrogen Cycle - another atmospheric cycle . The latter three are mostly dissolved in water. Favored by warm temperature and neutral pH. Wastes and decayed organic materials decomposed by another set of bacteria into ammonia - called ammonification.
Various microbes are responsible, favored by cool temperatures, all pH's.
Denitrification - closes the cycle. Returns nitrogen to the atmosphere. Note the heavy reliance on microbes for the function of this cycle. V. Phosphorus Cycle - a sedimentary cycle. Much slower than other cycles.