What are biofertilisers ? Describe their role in agriculture. Why are they preferred over chemical fertilisers ?

Explanation

Biofertilisers are the living organisms that promote the growth of plants by replenishing the nutrients in the soil. These include bacteria, fungi and cyanobacteria.
Role of biofertilisers in agriculture Some biofertilisers such as Rhizobium bacteria live in symbiotic association with plants. They live within the root nodules of leguminous plants. These bacteria fix atmospheric nitrogen and enrich the nitrogen content of soil.
Fungi, such as Glomus forms symbiotic association with plants (mycorrhiza) by absorbing phosphorus and passing it to plants.
Cyanobacteria such as Nostoc and Anabaena fix atmospheric nitrogen and act as biofertilisers especially in paddy fields.
Biofertilisers are preferred over chemical fertilisers,
(a) Chemical fertilisers significantly increase the soil pollution and reduce quality of soil, also cause water pollution, when it drains into nearby water bodies, after rain.
(b) Overuse of chemical fertiliser makes the soil infertile and causes different diseases in humans such as cancer.