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Denitrification


Denitrification biochemical reduction of nitrate or nitrite to gaseous nitrogen, either as molecular nitrogen or as an oxide of nitrogen. Organisms involved in the process of denitrification are facultative anaerobes. Most common heterotrophic organisms responsible for denitrification belong to the genera of Pseudomonas, Micrococcus, Bacillus and Alcaligenes. The autotrophic denitrifier Thiobacillus denitrificans can reduce nitrate during oxidation of sulphur.

Denitrification is a common phenomenon in Submerged Soils of Bangladesh. The floodplain soils, namely non-calcareous alluvium, calcareous alluvium, non-calcareous floodplain, calcareous grey floodplain, grey piedmont, non-calcareous dark grey floodplain, calcareous dark grey floodplain, non-calcareous brown floodplain, calcareous brown floodplain, acid basin clays and black terai soils comprise 65% of the total agricultural land. These soils are seasonally flooded and are extensively used for lowland rice cultivation. An appropriate portion of terrace soils namely deep red brown, shallow red brown, brown mottled, deep grey, shallow grey terrace soils, and grey valley soils, either irrigated or flooded seasonally during monsoon, also support production of lowland rice.

Nitrogen is the most limiting plant nutrient element in Bangladesh and invariably urea is applied broadcast for nitrogen in all the soils of Bangladesh. The ammonia existing in the oxidised layer of rice soils originated either by hydrolysis of applied urea or by decomposition of nitrogen containing organic compounds soon will be oxidised to nitrite and nitrate. Since these two forms of nitrogen are not susceptible to soil adsorption, they want to migrate downward either by diffusion or with percolating water. As soon as they pass through the boundary of two layers, they are denitrified microbiologically and a small portion by chemical process to gaseous nitrogen. It has been found that the extent of loss of added nitrate through denitrification during six weeks of incubation under waterlogged condition varied between 84 and 90% for three soils of Bangladesh. Thus a great majority of the added nitrogen is lost through the process of denitrification into the atmosphere. [Rameswar Mondal]