Nitrification

nitrification [‚nī·trə·fə′kā·shən]

(microbiology)

Formation of nitrous and nitric acids or salts by oxidation of the nitrogen in ammonia; specifically, oxidation of ammonium salts to nitrites and oxidation of nitrites to nitrates by certain bacteria.

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Nitrification 

the microbiological conversion of ammonium salts to nitrates, the main form of nutrient nitrogen for plants. Nitrification takes place in the soil and in bodies of water. It is the final stage of the mineralization of organic nitrogen compounds, which begins with ammonification, and it is an index of soil fertility. The process is caused by chemosynthesizing nitrifying bacteria.

Nitrification proceeds in two stages. An ammonium ion is oxidized to a nitrite ion by bacteria of the first stage, and then the nitrite ion is oxidized to a nitrate ion by bacteria of the second stage. Nitrification takes place at a soil pH of 5–9 and is carried out by aerobic organisms. An insufficiency of air in the soil leads to cessation of nitrification. Proper soil management improves aeration, thus intensifying nitrification.

As a result of the increasing combustion of fuel in industrial plants and internal-combustion engines, nitrogen oxides are formed in the atmosphere and are deposited in large amounts in the soil and in the water of reservoirs with rainfall. They are then converted to nitrates by the action of nitrifying bacteria. The excess concentration of nitrates in water makes it unsuitable for drinking. To prevent large-scale formation of nitrates in water, chemical preparations that prevent nitrification in the soil are sometimes used.

G. A. ZAVARZIN