Nitrogen is introduced into terrestrial and aquatic ecosystems by biological and chemical nitrogen fixation and removed again by denitrification. This article presents a scientific overview of the process of ammonification. Ammonification refers to chemical reactions in which amino groups (NH2) associated with organic forms of nitrogen are converted into ammonia (NH3) or ammonium (NH4+). Ammonium is then available for use in plants as a nutrient, or as a substrate for the nitrification processes. In crop and livestock production systems, nitrogen assimilated by plants and animals is converted into cellular tissue. Nitrogen is reintroduced into the soil system in the form of crop residues and animal manure. In the absence of ammonification, these organic forms of nitrogen would accumulate in large quantities. Ammonification of organic nitrogen is an important processes in water because biological assimilation of ammonium by bacteria, biofilms, and aquatic plants is preferred to nitrate assimilation. In sediment, dissimilatory nitrate reduction (nitrate ammonification) results in microbial excretion of ammonium into the environment where it is available for use as a plant nutrient or as a substrate for nitrification. In saturated soil and sediment, under anaerobic conditions, nitrogen can undergo respiratory denitrification resulting in the reintroduction of nitrogen into the atmosphere.
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- Nitrogen cycle