Q.Why are blue green algae not popular as biofertilisers?
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Start your 14-day free trial to unlock the full solution →Blue-green algae (cyanobacteria) are not widely used as biofertilisers because they are slow-acting, require specific waterlogged conditions, and are less effective for most dryland crops compared to other biofertilisers like Rhizobium or Azotobacter.
To understand why blue-green algae (BGA) — also called cyanobacteria — are not the first choice for farmers, we need to look at what a biofertiliser is supposed to do. A biofertiliser is a living microbe that enriches the soil with nutrients, especially nitrogen. The most popular ones, like Rhizobium (for legumes) and Azotobacter (for many cereals), work fast, fix nitrogen efficiently, and can be used on a wide range of crops. Blue-green algae, on the other hand, have a very different set of strengths and weaknesses.
The main strength of BGA is that they are photosynthetic — they make their own food using sunlight and carbon dioxide. This means they can survive in waterlogged, sunlit fields like rice paddies. In fact, the NCERT textbook specifically mentions that BGA are used as biofertilisers in rice fields, where they fix atmospheric nitrogen and also add organic matter to the soil. But this very strength becomes a limitation outside such environments.
The biggest reason BGA are not popular is that they are slow and site-specific. Unlike Rhizobium, which forms root nodules and starts fixing nitrogen within days, BGA grow as a surface mat on water or moist soil. They need standing water and bright sunlight to thrive. For dryland crops like wheat, maize, or sugarcane, these conditions simply don't exist. A farmer growing wheat cannot flood the field just to make BGA work — that would ruin the crop. So BGA are essentially restricted to wetland rice cultivation.
Another practical problem is handling and storage. BGA are living, photosynthetic organisms. They need to be kept moist and exposed to light, which makes them difficult to package, transport, and store for long periods. Compare this to Rhizobium or Azotobacter, which can be mixed with a carrier like peat or charcoal and stored as a dry powder for months. Farmers prefer products that are easy to buy, carry, and apply. BGA cultures often come as a wet slurry or need to be grown on site, which is inconvenient.
The NCERT textbook does mention that BGA like Anabaena and Nostoc are used in rice fields, but it does not claim they are popular for other crops. The textbook is silent on exact market share or yield data, so we stick to the biological and practical reasons given.
There is also the issue of competition with other microbes. In a typical agricultural soil, BGA have to compete with faster-growing bacteria and fungi. They are not aggressive colonisers. Even in a rice field, the BGA mat can be patchy and may not cover the entire area uniformly. This means the nitrogen fixed per hectare is often lower than what you get from a good Rhizobium inoculation or from chemical fertilisers. …
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