Reduction of Nitrates
Reduction of Nitrates (Denitrification):-
1. Denitrification:-
> Denitrification is the process during which the nitrogen compound is released back into the atmosphere by converting nitrate (NO3-) into gaseous nitrogen (N).
> The process of denitrification is carried out during the absence of oxygen by Thiobacillus species and Pseudomonas bacteria present in the soil. In this process, the genus of Gram-negative bacteria degrades nitrate compounds present in the soil and aquatic systems into nitrous oxide (N2O)and nitrogen gas, which are eventually released into the atmosphere.
> In this process, a large range of microorganisms is involved; therefore, it is also called the microbial process.
> This biogeochemical process is one of the main responses to changes in the oxygen (O2) concentration in the environment. Denitrification is a universal process for both terrestrial and aquatic ecosystems, which occurs naturally under the extreme concentrations in managed ecosystems – marine and freshwater environments, tropical and temperate soils, wastewater treatment plants, aquifers, manure stores, etc.
2. Mechanism of Denitrification:-
> Denitrification is the last step in the nitrogen cycle. It is a naturally occurring, microbially mediated process, where nitrate is used as a form of energy for denitrifiers.
> In this process, soil bacteria convert plant-available soil nitrate (NO3–) into nitrogen (N) gases that are lost from the soil. Denitrification produces several gases: nitric oxide (NO), nitrous oxide (N2O) and dinitrogen (N2).
> The flowchart of the denitrification process is:
Nitrite → Nitric Oxide → Nitrous oxide → Nitrogen gas
3. Sit of Denitrification:-
> Denitrification is a microbial process of removing valuable nitrogen from the soil and releasing the greenhouse gas nitrous oxide (N2O), and the tropospheric pollutant nitric oxide (NO).
> The biological cycle of denitrification involves a cascade of different enzymes, which reduces nitrate to dinitrogen.
4. Reason of Denitrification:-
> When the oxygen (O2) supply in the soil becomes limited, a variety of bacteria use the oxygen instead of nitrate for respiration. Denitrification most commonly occurs in wet, moist or the soil flooded with water where the supply of oxygen for respiration is reduced or limited. Some fungi can denitrify, but they are not considered significant.
5. Time of Denitrification:-
> Denitrification is more active in the regions where water-filled pore space in the soil exceeds 60 per cent. The end-product gas depends on the soil conditions and the microbial community. As the deficiency of oxygen increases, microbes perform their functions by converting more of the nitrate to dinitrogen (N2) gas. For the purposes of nutrient management, denitrification results in a loss of valuable nitrogen (N), but the impact on the atmosphere will vary.
6. Factors Affecting the Denitrification Process:- The complete process of denitrification is influenced by the following factors:
The main factor which influences the process of denitrification is the organic content in the soil. The organic matter available within the soil is the only source of nutrition for the bacteria. Therefore, the soil bacteria require a source of readily available organic matter, either from the plants, from the soil or from other additional sources.
Other factors include:-
i. Soil pH
ii. Soil texture
iii. Temperature
iv. Oxygen content in the soil
v. Moisture content in the soil
vi. The concentrate of nitrate in the soil