Some microbes act as very good biofertiliser. Explain with the help of three suitable examples

Bio-fertilisers are living organisms which help in increasing the fertility of soil.It helps in improving plant growth through the supply of plant nutrients.These are introduced to seeds, roots or soil to mobile the availability of nutrients by their biological activity. The main sources of bio-fertilisers are bacteria, fungi and cyanobacteria.

Rhizobium is a symbiotic bacteria found in the root nodules of leguminous plant, they have the ability to fix free atmospheric nitrogen into organic forms, which is used by the plant as nutrient.

Other bacteria can fix atmospheric nitrogen while free-living in the soil, e.g: Azotobacter and Azospirillum, thus enriching the nitrogen content in soil.

Fungi is also known to form symbiotic association with plants (Mycorrhiza). the fungal symbiont in these association absorbs phosphorus from soil and passes it to the plant.It also shows other benefits such as resistance to root-borne pathogens, tolerance to salinity and drought.

Cyanobacteria are autotrophic microbes, many of which can fix atmospheric nitrogen. Eg: Anabaena, Nostoc, Oscillatoria,etc…..In paddy fields, cyanobacteria serve as an important biofertiliser.