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

Certain microorganisms possess the unique ability to convert atmospheric nitrogen into forms usable by plants, aiding in the enrichment of soil fertility. These include:

1. Rhizobium: These bacteria form symbiotic relationships with leguminous plants, residing in root nodules. Rhizobium bacteria convert atmospheric nitrogen into ammonia, which plants utilize for growth, while the plants provide carbohydrates to the bacteria.

2. Azotobacter: Found freely in various soil types, Azotobacter bacteria are free-living nitrogen-fixers. They contribute to nitrogen availability by converting atmospheric nitrogen into forms accessible to plants.

3. Cyanobacteria: Certain species like Anabaena and Nostoc are nitrogen-fixing microorganisms. They inhabit soil, water bodies, or establish symbiotic associations with plants. Cyanobacteria use specialized cells known as heterocysts to convert atmospheric nitrogen into usable compounds.

These microorganisms are pivotal in the nitrogen cycle, converting inert atmospheric nitrogen gas into compounds like ammonia that plants can assimilate, thus playing a crucial role in enhancing soil fertility and supporting plant growth.