Name the microorganisms which can fix atmospheric nitrogen in the soil.

AcademicBiologyNCERTClass 8

Microorganisms that fix atmospheric nitrogen into the soil are nitrogen-fixing bacteria.


Nitrogen-fixing bacteria absorb atmospheric nitrogen and convert it into its compound.

Nitrogen Cycle is a biogeochemical process in which nitrogen is converted into multiple forms. In this cycle nitrogen consecutively passes from the atmosphere to the soil to organism and back into the atmosphere. It involves important processes such as nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.

Nitrogen fixation: It is the initial step of the nitrogen cycle in which Atmospheric nitrogen (N2) is converted into ammonia. During Nitrogen fixation, the inert nitrogen gas gets deposited into soils from the atmosphere through precipitation. Then the two nitrogen atoms get separated and combine with hydrogen to form ammonia (NH4+).

Nitrification: In this process, the ammonia is converted into nitrate by the oxidation of Ammonia with the help of Nitrosomonas bacterium species. Then the nitrites get converted into nitrates by Nitrobacter. The reaction involved in the process of Nitrification is as follows:

2NH4+ + 3O2 ------->  2NO2 + 4H+ + 2H2O

2NO2 + O2 -------->  2NO3

Assimilation: Plants take in the nitrogen compounds available in the form of ammonia, nitrite ions, nitrate ions, or ammonium ions from the soil. These are used in the formation of plant and animal proteins.

Ammonification: When plants or animal die the nitrogen present in the organic matter get released into the soil. Then decomposers such as bacteria or fungi convert the organic matter back into ammonium.

Denitrification: Denitrification is the process in which the nitrogen goes back into the atmosphere.  Denitrification is carried out by the denitrifying bacterial species Clostridium and Pseudomonas which convert nitrate (NO3-) into gaseous nitrogen (N).

Updated on 10-Oct-2022 12:46:41