Justidy the role of microbes as a bio-fertilizer.

Explanation

(i) Bio - fertilizers are formulation of living microoganisms that enrich the nutrient quality of the soil. They increase physico- chemical properties of soils such as soil structure, texture, water holding capacity, cation exchange capacity and pH by providing several nutrients and sufficient organic matter.
(ii) The main sources of bio-fertilisers are bacteria, fungi and cyanobacteria. Rhizobium is a example for symbiotic nitrogen fixing bacteria. This bacterium infects the root nodules of leguminous plants and fixes atmospheric nitrogen into organic forms. Azospirillum and Azotobacter are free living bacteria that fix atmospheric nitrogen and enrich the nitrogen content of soil.
(iii) A symbiotic association between a fungus and the roots of the plants is called mycorrhiza. The fungal symbiont in these associations absorbs the phosphorus from soil and transfers to the plant. Plants having such association show other benefits such as resistance to salinity, drought, enhances plant growth and development. For example, genus Glomus form mycorrhiza.
(iv) Cyanobacteria (or) blue green algae (BGA) are prokaryotic free-living organisms which can fix nitrogen. Oscillatoria, Nostoc, Anabaena, Tolypothrix are well knwon nitrogen fixing cyanobacteria. In waterlogged paddy fields Cyanobacteria multiply and fix molecular nitrogen. Cyanobacteria secrete growth promoting substances like indole-3-acetic acid. indole-3-butyric acid, naphthalene acetic acid, amino acids, proteins, vitamins which promotes plants growth and production.
(v) Biofertilisers are commonly used in organic farming methods.
(vi) This process involves the use of biological material, avioding synthetic substances to maintain soil fertility and ecological balance thereby minimizing pollution and wastage.