Nitrogen Cycle: Denitrification
Several biochemical steps involved in the nitrogen cycle are:
1. Proteolysis
2. Ammonification
3. Nitrification
4. Nitrate reduction and
5. Denitrification.
5. Denitrification:
This is the reverse process of nitrification. During denitrification nitrates are reduced to nitrites and then to nitrogen gas and ammonia. Thus, reduction of nitrates to gaseous nitrogen by microorganisms in a series of biochemical reactions is called “denitrification". The process is wasteful as available nitrogen in soil is lost to atmosphere. The overall process of denitrification is as follows:
NaR NiR NoR NoR
Nitrate —–> Nitrite —-> Nitric Oxide —-> Nitrous Oxide ——> Nitrogen gas
This process also called dissimilatory nitrate reduction as nitrate nitrogen is completely lost into atmospheric air. In the soils with high organic matter and anaerobic soil conditions (waterlogged or ill-drained) rate of denitrification is more. Thus, rice / paddy fields are more prone to denitrification.
The most important denitrifying bacteria are Thiobacillus denitrificans, Micrococcus denitrificans, and species of Pseudomonas, Bacillus, Achromobacter, Serrtatia paracoccus etc.
Denitrification leads to the loss of nitrogen (nitrate nitrogen) from the soil which results into the depletion of an essential nutrient for plant growth and therefore, it is an undesirable process / reaction from the soil fertility and agricultural productivity. Although, denitrification is an undesirable reaction from agricultural productivity, but it is of major ecological importance since, without denitrification the supply of nitrogen including N2 of the atmosphere, would have not got depleted and No3 (which are toxic) would have accumulated in the soil and water.