Nitrification

Nitrification is an aerobic microbial process by which specialized bacteria oxidize ammonium to nitrite and then to nitrate. Nitrification is a very important part of the nitrogen cycle, because for most plants nitrate is the preferred chemical form of nitrogen uptake from soil or water.

Nitrification is a two-step process. The first stage is the oxidation of ammonium (NH₄⁺) to nitrite (NO₂^-), a function carried out by bacteria in the genus Nitrosomonas. The nitrite formed is rapidly oxidized to nitrate (NO₃^-) by bacteria in the genus Nitrobacter. Because nitrate and nitrite are much more mobile in soils than ammonium, nitrification can be viewed as a process that mobilizes nitrogen, making it more available for plant uptake but potentially allowing it to leach from the ecosystem. The latter is an undesirable attribute of nitrification because fixed nitrogen is an important component of the nutrient capital of ecosystems. In addition, large concentrations of nitrate or nitrite can pollute groundwater and surface waters.