8.6. Microbes as Biofertilisers

With our present day life styles environmental pollution is a major cause of concern. The use of the chemical fertilisers to meet the ever-increasing demand of agricultural produce has contributed significantly to this pollution. Of course, we have now realised that there are problems associated with the overuse of chemical fertilisers and there is a large pressure to switch to organic farming – the use of biofertilisers.

This chunk emphasizes the urgent need to address environmental pollution caused by chemical fertilizers, which are overused in modern agriculture. It highlights the rising concerns and pressures from both the public and experts to shift towards organic farming methods, particularly through the use of biofertilisers, which are natural alternatives that can enrich soil without contributing to pollution.

Consider a garden where you use a lot of chemical fertilizers. In the short term, your plants may grow quickly; however, you might notice that the soil becomes less fertile over time, requiring you to use even more chemicals. By switching to organic methods and using biofertilisers like compost or natural soil enhancers, you help restore soil health and contribute to a cleaner environment.

Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria.

Biofertilisers refer to live microorganisms that promote plant growth by increasing the supply of essential nutrients to the plant. These organisms can include bacteria, fungi, and cyanobacteria, which work together to enhance soil fertility sustainably.

Think of it like having a team of helpful friends who each offer different skills. Some friends (bacteria) can 'fix' nutrients from the air into a usable form for your plants, others (fungi) help with nutrient absorption, while some (cyanobacteria) can contribute additional nutrients from the water. Together, they create a supportive environment for your plants to thrive.

You have studied about the nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient. Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.

Nitrogen-fixing bacteria, such as Rhizobium, form beneficial partnerships with leguminous plants, creating nodules on their roots where they convert atmospheric nitrogen into a form that plants can use as a nutrient. Free-living bacteria like Azospirillum and Azotobacter also contribute to nitrogen fixation in the soil, improving its nutrient content.

Imagine if a friend could magically convert fresh air into food. That's what nitrogen-fixing bacteria do for plants – they take nitrogen from the air and turn it into a fertilizer that plants can 'eat,' making them healthier and stronger.

Fungi are also known to form symbiotic associations with plants (mycorrhiza). Many members of the genus Glomus form mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant. Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development.

Mycorrhiza is a type of symbiotic association between fungi and plant roots, where fungi help plants absorb phosphorus and other nutrients from the soil more efficiently. These associations also provide plants with additional benefits, such as improved resistance to diseases and environmental stresses.

Think of a partnership between a student and a tutor. The tutor helps the student understand complex subjects (nutrient absorption) better. Additionally, the student learns strategies to overcome challenges (disease resistance), becoming more resilient and successful in school.

Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility.

Cyanobacteria, also known as blue-green algae, are key players in enhancing soil fertility, especially in paddy fields where they fix nitrogen. These organisms can convert atmospheric nitrogen into a usable form for plants and they also contribute organic matter, enriching the soil overall.

Consider cyanobacteria as nature’s gardeners. Just like gardeners who improve soil health by adding compost, cyanobacteria help make the soil richer and more productive by adding nutrients and improving its structure.

Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.

In many regions, biofertilisers are now commercially available, enabling farmers to use them to enhance soil nutrients and reduce reliance on harmful chemical fertilizers. This shift not only helps improve crop yield but also promotes ecological sustainability.

Think of shopping for groceries: instead of always buying processed food, you choose fresh fruits and vegetables to promote better health. Similarly, farmers are now 'shopping' for natural biofertilizers to keep their soil healthy and productive, resulting in better crops and a cleaner environment.

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