How are microbes useful in biofertilisers?

(A) Environmental pollution is a major cause of concern. The use of chemical fertilisers to meet the ever-increasing demand for agricultural produce has contributed significantly to this pollution.
There are problems associated with the overuse of chemical fertilisers,and there is significant pressure to switch to organic farming.
Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria,fungi,and cyanobacteria.
$1$. Bacteria: The nodules on the roots of leguminous plants are formed by the symbiotic association of $Rhizobium$. These bacteria fix atmospheric nitrogen into organic forms,which are used by the plant as nutrients. Other bacteria,such as $Azospirillum$ and $Azotobacter$,can fix atmospheric nitrogen while living freely in the soil,thus enriching the nitrogen content.
$2$. Fungi: Many fungi form symbiotic associations with plants known as mycorrhiza (e.g.,genus $Glomus$). The fungal symbiont absorbs phosphorus from the soil and passes it to the plant. These associations also provide resistance to root-borne pathogens,tolerance to salinity and drought,and promote overall plant growth and development.
$3$. Cyanobacteria: These are autotrophic microbes that fix atmospheric nitrogen (e.g.,$Anabaena$,$Nostoc$,$Oscillatoria$). In paddy fields,they serve as important biofertilisers,adding organic matter to the soil and increasing its fertility.
Currently,many biofertilisers are available commercially,helping farmers reduce their dependence on chemical fertilisers.