Lesson 10 of 11 · 6 min
Biofertilisers
NCERT §8.6
Sunday: the last diary entry. Uncle's paddy field shines green, and he tells Ananya he has cut his chemical fertiliser bill. The secret, he says, is under the water and the soil.
The lesson in notes
In short
Overuse of chemical fertilisers has added to pollution, pushing farmers towards organic farming with biofertilisers: organisms that improve the nutrient quality of soil.
Biofertilisers come mainly from three groups: bacteria, fungi and cyanobacteria.
Rhizobium lives symbiotically in the root nodules of leguminous plants and fixes atmospheric nitrogen into organic forms the plant uses.
Azospirillum and Azotobacter fix atmospheric nitrogen while living freely in the soil, raising its nitrogen content.
Fungi form symbiotic associations with plant roots called mycorrhiza; many members of the genus Glomus do so. The fungus absorbs phosphorus from the soil and passes it to the plant.
Plants with mycorrhiza also resist root-borne pathogens, tolerate salinity and drought, and grow and develop better overall.
Cyanobacteria are autotrophic microbes found in water and on land; many fix atmospheric nitrogen, for example Anabaena, Nostoc and Oscillatoria. They are an important biofertiliser in paddy fields, where blue-green algae also enrich the soil with organic matter.
Several biofertilisers are now sold commercially in India, and farmers use them to replenish soil nutrients and depend less on chemical fertilisers.