Biofertilisers are formulation of living microorganisms that enrich the nutrient wuality of the soil . They increase physico - chemical properties of soils such as soil structure , texture , water holding capacity , cation exchage capacity and pH by providing several nutrients and sufficient organic matter . The main sources of biofertilisers are bacteria , fungi and cyanobacteria. Rhizobium is a classical example for symbiotic nitrogen fixing bacteria . This bacterium infects the root nodules of lenguminous 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.
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 shown other benefits such as resistance to rootborne pathogens , tolerance to salinity , drought enhances plant growth and developments . For example , many members of the genus Glomus form mycorrhiza . Cyanobacteria (or) blue gree algae (BGA) are prokaryotic free living organisms which can fix nitrogen . Oscillatoria , Nostoc , Anabaena, Tolypothrix are well known nitrogen fixing cyanobacteria . Their importance is realzed in the water logged paddy fields where Cyanobacteria multiply and fix molecular nitrogen. Cyanobacteria secrete growth promoting substance like indole -3- acetic acis indole -3- butyric acis , naphthalene acetic acid , amino acisds , proteins , vitamins which promotes plant growth and production. Biofertilisers are commonly used in organic farming methods Organic farming is a technique, which involves cultivation of plants and rearing of animals in natural ways . This process involves the use of biological materials , avoiding synthetic substances to maintain soil fertility and ecological balance thereby minimizing pollution wastage.
Key features of organic farming
Protecting soil quality using organic materials and encouraging biological activity.
Indirect provision of crop nutrients using soil microorganisms.
Nitrogen fixation in soils using legumes.
Weed and pest control based on methods like crop rotation , biological diversity , natural predators , organic manures and suitable chamical , thermal and biological interventions.
