How are microbes useful in biofertilisers ?

Explanation

Environmental pollution is a major cause of concern. The use of chemical fertilisers to meet the ever increasing demand of agricultural produce has contributed significantly to this pollution There are problems associated with the overuse of chemical fertilisers and there is a large pressure to switch to organic farming. Biofertilisers are organisms that enrich nutrient quality of the soil. The main source of biofertilisers are bacteria, fungi and cyanobacteria. The nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic farms. Which is used by the plant as nutrient. Other bacteria can fix atmospheric nitrogen while free living in the soil (example Azospirillum and Azotobacter) thus enriching the nitrogen content of the soil. Fungi are also known to form symbiotic associations with plants (mycorrhiza). Many members of the genus Glomus form mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant. Plants having such associations show other benefits also, such as resistance to root borne pathogens, tolerance to salinity and drought and an overall increase in plant growth and development. Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria etc. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility. Currently in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.