• denitrification
  • 1) The loss of nitrogen from soil by biological or chemical means. It is a gaseous loss, unrelated to loss by physical processes such as through leachates. 2) The breakdown of nitrates by soil bacteria, resulting in the release of free nitrogen. This process takes place under anaerobic conditions, such as are found in water-logged soil, and it reduces soil fertility.
Abstract from DBPedia
    Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitrification as a type of respiration that reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter. The preferred nitrogen electron acceptors in order of most to least thermodynamically favorable include nitrate (NO3−), nitrite (NO2−), nitric oxide (NO), nitrous oxide (N2O) finally resulting in the production of dinitrogen (N2) completing the nitrogen cycle. Denitrifying microbes require a very low oxygen concentration of less than 10%, as well as organic C for energy. Since denitrification can remove NO3−, reducing its leaching to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content. Denitrification can leak N2O, which is an ozone-depleting substance and a greenhouse gas that can have a considerable influence on global warming. The process is performed primarily by heterotrophic bacteria (such as Paracoccus denitrificans and various pseudomonads), although autotrophic denitrifiers have also been identified (e.g., Thiobacillus denitrificans). Denitrifiers are represented in all main phylogenetic groups. Generally several species of bacteria are involved in the complete reduction of nitrate to N2, and more than one enzymatic pathway has been identified in the reduction process. The denitrification process does not only provide energy to the organism performing nitrate reduction to dinitrogen gas, but also some anaerobic ciliates can use denitrifying endosymbionts to gain energy similar to the use of mitochondria in oxygen respiring organisms. Direct reduction from nitrate to ammonium, a process known as dissimilatory nitrate reduction to ammonium or DNRA, is also possible for organisms that have the nrf-gene. This is less common than denitrification in most ecosystems as a means of nitrate reduction. Other genes known in microorganisms which denitrify include nir (nitrite reductase) and nos (nitrous oxide reductase) among others; organisms identified as having these genes include Alcaligenes faecalis, Alcaligenes xylosoxidans, many in the genus Pseudomonas, Bradyrhizobium japonicum, and Blastobacter denitrificans.

    脱窒(だっちつ)とは、窒素化合物を分子状窒素として大気中へ放散させられる作用または工程を指す。窒素循環の最終段階であり、主に微生物によって行われる。 無機窒素塩類を化学肥料として多用する近代農業のもとでは、作物の同化作用へ吸収されず残留したそれら塩類が地下水へ侵入・汚染することを制限する役割を果たしている。 * 硝酸は陰イオンであり、土壌(粘土鉱物、腐食質)もマイナスコロイドである。このため降雨により地下浸透しやすい。 * 施用された硝酸塩の大部分が土壌・地下水へ浸透し上水汚染につながることは、1960年代にアメリカのイリノイ州デカトール市で同位体比法(窒素の同位体15Nが植物へ吸収されにくい現象を利用する)により、初めて立証された。 * 日本の硝酸性窒素及び亜硝酸性窒素への規制は水質汚濁防止法により行われる。 大気汚染源としての窒素酸化物も、降水・降下で土壌や水系へ移行後にこの作用で還元される。