Q.Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.

Microbes offer a powerful way to reduce our dependence on chemical fertilisers and pesticides by working as biofertilisers and biopesticides.

As biofertilisers, certain bacteria, fungi, and cyanobacteria enrich the soil with nutrients naturally. For example, Rhizobium bacteria live in root nodules of legumes and fix atmospheric nitrogen into a form the plant can use. Free-living bacteria like Azospirillum and Azotobacter also fix nitrogen. Fungi like Glomus form mycorrhizal associations with plant roots, helping them absorb phosphorus and other minerals from the soil. Cyanobacteria like Anabaena and Nostoc also fix nitrogen, especially in waterlogged fields like paddy. By using these, farmers can cut down on synthetic nitrogen and phosphorus fertilisers. …

The overuse of chemical fertilisers and pesticides in modern agriculture has created serious problems: soil degradation, water pollution, and the development of resistant pests. Microbes offer a natural, sustainable alternative. Instead of feeding plants directly with synthetic salts, we can enlist living organisms to do the work — fixing nitrogen, solubilising phosphorus, or attacking insect larvae. This is the core idea behind biofertilisers and biopesticides.

Let’s start with biofertilisers. These are preparations containing live or latent cells of efficient nitrogen-fixing, phosphate-solubilising, or cellulolytic microorganisms. They are applied to seeds, plant surfaces, or soil, and they colonise the rhizosphere or the interior of the plant. The most well-known example is the symbiotic bacterium Rhizobium, which forms nodules on the roots of leguminous plants (peas, beans, groundnut). Inside these nodules, Rhizobium converts atmospheric nitrogen (N2) into ammonia, which the plant can use. The NCERT textbook emphasises that this relationship is mutually beneficial — the bacterium gets shelter and food from the plant, and the plant gets a steady supply of fixed nitrogen.

Another important group is the free-living nitrogen-fixing bacteria, such as Azospirillum and Azotobacter. Azospirillum lives in close association with the roots of cereal crops like wheat, maize, and rice, fixing nitrogen without forming nodules. Azotobacter is a free-living aerobe found in soil. Both are used as biofertilisers, especially for non-leguminous crops. The textbook also mentions cyanobacteria (blue-green algae) like Anabaena and Nostoc. These are photosynthetic, nitrogen-fixing organisms that are particularly valuable in paddy fields. They can be inoculated into the water of rice paddies, where they fix nitrogen and also add organic matter to the soil.

Beyond nitrogen fixation, some microbes help make other nutrients available. Phosphate-solubilising bacteria (like Pseudomonas and Bacillus) and fungi (like Aspergillus and Penicillium) convert insoluble phosphates in the soil into soluble forms that plants can absorb. This reduces the need for phosphate fertilisers.

Now, turning to biopesticides. These are living organisms (or their products) that control pests — insects, fungi, weeds, or nematodes — without the toxic residues of synthetic pesticides. The NCERT textbook gives several clear examples.

The most famous bacterial biopesticide is Bacillus thuringiensis (often called Bt). This bacterium produces a protein crystal (the Bt toxin) during sporulation. When an insect larva ingests these crystals, the alkaline pH of its gut dissolves the crystal, releasing the toxin. The toxin binds to the gut wall, creating pores, which stops the insect from feeding and eventually kills it. Importantly, the Bt toxin is specific to certain insect orders (like Lepidoptera, Coleoptera, Diptera) and is harmless to mammals, birds, and most beneficial insects. The gene for this toxin has also been inserted into crop plants (Bt cotton, Bt corn), but the question here is about using the microbe itself — Bt spores can be sprayed on crops as a biological insecticide.

Treat biofertilisers and biopesticides as solving two different problems with the same underlying idea (a living organism replacing a chemical input) -- biofertilisers replace the nutrient a plant needs (nitrogen, phosphorus), biopesticides replace the protection a plant n …