Biofertilizers in India

Biofertilizers are substances which contain living microorganisms which, when applied to seed, plant surfaces, or soil, colonize the interior of the plant and promote growth by increasing the supply or availability of primary nutrients to the host plant.

Biofertilizers add nutrients through the natural processes of nitrogen fixation, solubilizing phosphorus, and stimulating plant growth through the synthesis of growth-promoting substances. They can be seen as an important component of integrated nutrient management and play a key role in organic farming systems.

Types of Biofertilizers

There are five main types of biofertilizers which have been incorporated into India’s Fertilizer Control Order (FCO), 1985:

• Rhizobium
• Azotobacter
• Azospirillum
• Phosphate Solubilizing Bacteria
• Mycorrhiza

These biofertilizers have traditionally been used in India to improve soil fertility and crop yields through natural processes.

Rhizobium

Rhizobium is a soil bacteria which forms symbiotic relationships with leguminous plants such as pulses. The bacteria forms nodules on the roots of host plants and fixes atmospheric nitrogen, making it available for plant growth. The use of Rhizobium inoculants is well-established for pulses and can increase yields by 25-30%. Commonly used strains include Rhizobium leguminosarum, Rhizobium phaseoli, Rhizobium meliloti, and Rhizobium japonicum.

Azotobacter

Azotobacter species are free-living soil microbes which fix atmospheric nitrogen non-symbiotically. Azotobacter inoculants have been used with success in a wide variety of crops including wheat, maize, mustard, cotton, potato and other vegetables. Popular species include Acetobacter chroococcum and Azotobacter vinelandii. Azotobacter is easy to grow and apply and sustains nitrogen availability over long time periods.

Azospirillum

Azospirillum inoculants have also emerged as an efficient supplement to chemical fertilizers, especially for cereals like wheat, sorghum, pearl millet, and maize. Species like Azospirillum lipoferum and Azospirillum brasilense can fix up to 20kg nitrogen per hectare when applied as seed or soil inoculants. They also produce plant hormones which encourage root growth and nutrient uptake.

Phosphate Solubilizing Bacteria

Phosphate solubilizing bacteria have the ability to convert insoluble phosphates in soil into forms usable by plants such as orthophosphates. Common phosphate solubilizers used as inoculants include species of Pseudomonas, Bacillus, Rhizobium, Burkholderia, Achromobacter, Agrobacterium, Microccocus, Aereobacter, Flavobacterium and Erwinia. Two efficient strains are Pantoea agglomerans strain P5 and Pseudomonas putida strain P13.

Mycorrhiza

Mycorrhiza are symbiotic associations between soil fungi and plant roots. The extensive hyphal network of mycorrhizal fungi effectively extends the root system and absorbs nutrients from larger volumes of soil. Mycorrhizae also improve soil structure and enhance resistance to root pathogens. Common mycorrhizal inoculants include species of Glomus, Gigaspora, Acaulospora and Sclerocystis.