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Nitrification is important in agricultural systems, where fertilizer is often applied as ammonia. Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble than ammonia. Nitrification also plays an important role in the removal of nitrogen from municipal wastewater.
The nitrogen cycle is an important process in the ocean as well. While the overall cycle is similar, there are different players [40] and modes of transfer for nitrogen in the ocean. Nitrogen enters the water through the precipitation, runoff, or as N 2 from the atmosphere. Nitrogen cannot be utilized by phytoplankton as N
[12] [13] Complete nitrification, the conversion of ammonia to nitrate in a single step known as comammox, has an energy yield (∆G°′) of −349 kJ mol −1 NH 3, while the energy yields for the ammonia-oxidation and nitrite-oxidation steps of the observed two-step reaction are −275 kJ mol −1 NH 3, and −74 kJ mol −1 NO 2 − ...
Usable nitrogen may be lost from soils when it is in the form of nitrate, as it is easily leached, contrary to ammonium which is easily fixed. [69] Further losses of nitrogen occur by denitrification, the process whereby soil bacteria convert nitrate (NO 3 −) to nitrogen gas, N 2 or N 2 O.
The most common denitrification process is outlined below, with the nitrogen oxides being converted back to gaseous nitrogen: 2 NO 3 − + 10 e − + 12 H + → N 2 + 6 H 2 O. The result is one molecule of nitrogen and six molecules of water. Denitrifying bacteria are a part of the N cycle, and consists of sending the N back into the atmosphere.
Since denitrification can remove NO 3 −, reducing its leaching to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content. Denitrification can leak N 2 O, which is an ozone-depleting substance and a greenhouse gas that can have a considerable influence on global warming.
If the C:N ratio of the decomposing plant material is above about 30:1 the soil microbial population may take nitrogen in mineral form (e.g. nitrate). This mineral nitrogen is said to be immobilized. Microorganisms out-compete plants for NH4+ and NO3- during immobilization, and therefore plants can easily become nitrogen deficient.
NO 2 + O 3 → NO 3 + O 2. During the daytime, NO 3 is quickly photolyzed back to NO 2, but at night it can react with a second NO 2 to form dinitrogen pentoxide. NO 2 + NO 3 (+M) → N 2 O 5 (+M). N 2 O 5 reacts rapidly with liquid water (in aerosol particles or cloud drops, but not in the gas phase) to form HNO 3, N 2 O 5 + H 2 O (liq) → 2 ...