Biofertilisers

Biofertilisers are formulations of living microorganisms that enrich soil nutrient status and improve its physico-chemical properties — structure, texture, water-holding capacity, cation-exchange capacity and pH — by supplying nutrients and sufficient organic matter; their main sources are bacteria, fungi and cyanobacteria. Rhizobium is the classic example of a symbiotic nitrogen-fixing bacterium, infecting the root nodules of leguminous plants and fixing atmospheric nitrogen into organic forms the plant can use, while Azospirillum and Azotobacter are free-living bacteria that fix atmospheric nitrogen and enrich the nitrogen content of soil without needing a host plant. A symbiotic association between a fungus and the roots of plants is called mycorrhiza; the fungal symbiont (many members of the genus Glomus form such associations) absorbs phosphorus from the soil and transfers it to the plant, and mycorrhizal plants also gain other benefits such as resistance to root-borne pathogens, tolerance to salinity and drought, and enhanced growth and development. Cyanobacteria (blue-green algae, BGA) such as Oscillatoria, Nostoc, Anabaena and Tolypothrix are prokaryotic, free-living, nitrogen-fixing organisms that are especially important in water-logged paddy fields, where they multiply and fix molecular nitrogen while also secreting plant-growth-promoting substances such as indole-3-acetic acid, indole-3-butyric acid, naphthalene acetic acid, amino acids, proteins and vitamins. Biofertilisers are commonly used in organic farming, a technique that cultivates plants and rears animals in natural ways, using biological materials and avoiding synthetic substances to maintain soil fertility and ecological balance while minimising pollution and wastage. Its key features include protecting soil quality using organic mater …