How do biofertilisers enrich the fertility of the soil?

(N/A) Bio-fertilizers are living organisms that help in increasing the fertility of the soil.
They involve the selection of beneficial microorganisms that improve plant growth by supplying essential nutrients.
These organisms are introduced to seeds,roots,or soil to mobilize nutrient availability through their biological activity.
They enrich the soil with organic nutrients,making them highly beneficial.
Many species of bacteria and cyanobacteria have the ability to fix free atmospheric nitrogen.
$Rhizobium$ is a symbiotic bacterium found in the root nodules of leguminous plants.
$Azospirillum$ and $Azotobacter$ are free-living nitrogen-fixing bacteria,whereas $Anabaena$,$Nostoc$,and $Oscillatoria$ are examples of nitrogen-fixing cyanobacteria.
Bio-fertilizers are cost-effective and eco-friendly alternatives to chemical fertilizers.