Authored by: James I. Prosser

Handbook of Soil Sciences Properties and Processes

Print publication date:  November  2011
Online publication date:  November  2011

Print ISBN: 9781439803059
eBook ISBN: 9781439803066
Adobe ISBN:


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Nitrification is the microbial oxidation of reduced forms of nitrogen to nitrate. Most nitrification in soil is carried out by autotrophic ammonia and nitrite oxidizers, sequentially converting ammonia to nitrite and nitrate. Heterotrophic nitrifiers oxidize organic forms of reduced nitrogen, for example, amines to nitrate. The major sources of soil ammonia are mineralization of organic matter, animal excreta, and two anthropogenic sources of increasing importance: nitrogen fertilizers and atmospheric nitrogen deposition, supplying 100 and 25 Tg N year−1, respectively (Gruber and Galloway, 2008). Whereas NH4 + is held within the soil, due to the predominance of negatively charged particulate material, NO3 is readily leached from the soil. Nitrification is therefore important in controlling the levels of ammonium and nitrate available for plant growth and losses of fertilizer nitrogen, which can lead to polluting levels of nitrate in groundwaters. Within the soil, nitrate is also lost through denitrification to nitrogen and the greenhouse gas nitrous oxide, which is generated by both nitrifiers and denitrifiers.

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