Biofertilisers
உயிரி உரங்கள்
Chemical fertilisers are a slow poison to the soil microbiome. If you think crop yield is only about NPK, you are failing the ecology section of your NEET paper. Biofertilisers are the only sustainable biological solution to restore soil fertility.
The idea
Biofertilisers are organisms that enrich soil nutrient quality. Bacteria like Rhizobium fix atmospheric nitrogen in leguminous plants, while Azospirillum and Azotobacter fix nitrogen in free-living conditions. Fungi like Glomus form mycorrhizal associations to absorb phosphorus from soil. Cyanobacteria, such as Anabaena and Nostoc, serve as critical biofertilisers in paddy fields.
Why it matters
They exist to provide a sustainable, eco-friendly way to replenish soil nutrients, thereby promoting organic farming and reducing environmental pollution.
NEET lens
NEET focuses on the specific roles of microbes: Rhizobium (symbiotic), Azospirillum (free-living), and Glomus (mycorrhiza). Memorise the table of organisms and their specific functions. Expect match-the-following questions. Do not confuse free-living nitrogen fixers with symbiotic ones.
Clinical significance
Excessive chemical fertiliser runoff leads to eutrophication in water bodies, causing algal blooms and oxygen depletion. This disrupts the aquatic ecosystem, eventually impacting human health through contaminated water supplies and bioaccumulation of toxic heavy metals in the food chain.
Introduction
Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources are bacteria, fungi and cyanobacteria.
Core concept
Examples (NCERT): Rhizobium — nodules on roots of leguminous plants, fixes atmospheric nitrogen into organic forms usable by the plant; Azospirillum and Azotobacter — free-living bacteria in soil that fix atmospheric nitrogen; Glomus — mycorrhizal fungi that absorb phosphorus from soil and pass it to the plant; cyanobacteria (autotrophic microbes) such as Anabaena, Nostoc and Oscillatoria fix atmospheric nitrogen — important biofertilisers in paddy fields, which also add organic matter to the soil and increase its fertility. In India, a number of biofertilisers are available commercially, and farmers use them regularly to replenish soil nutrients and reduce dependence on chemical fertilisers.
Go deeper
Chemical fertilisers pollute soil and water; biofertilisers supply nutrients naturally and are part of organic farming.
From Class 10
Some bacteria and fungi naturally add nutrients like nitrogen to the soil — farmers can use them instead of chemical fertilisers.