How dobiofertilisers enrich the fertility of the soil?

Bio-fertilizersare living organisms which help in increasing the fertility of soil.It involves the selection of beneficial micro-organisms that help inimproving plant growth through the supply of plant nutrients. Theseare introduced to seeds, roots, or soil to mobilize the availabilityof nutrients by their biological activity. Thus, they are extremelybeneficial in enriching the soil with organic nutrients. Manyspecies of bacteria and cyanobacteria have the ability to fix freeatmospheric nitrogen. Rhizobium is a symbiotic bacteria foundin the root nodules of leguminous plants. Azospirilliumand Azotobocter are free living nitrogen-fixing bacteria,whereas Anabena, Nostoc, and Oscillitoria are examplesof nitrogen-fixing cyanobacteria. Bio-fertilizers are cost effectiveand eco-friendly.