Major classes of agricultural biofertilizers
- Nitrogen-fixing biofertilizers: Symbiotic Rhizobium for pulses and legumes; free-living Azotobacter for cereals; associative Azospirillum for millets and grasses.
- Phosphate-solubilizing biofertilizers (PSB): Fungi and bacteria that secrete organic acids to release fixed phosphorus into plant-available orthophosphate.
- Potassium and Zinc-mobilizing biofertilizers: Microbes that dissolve soil silicate minerals, mobilizing potassium and zinc into plant-available ionic forms.
- Vesicular Arbuscular Mycorrhiza (VAM): Fungal symbionts that extend hyphal networks deep into the soil to absorb phosphorus, zinc, and water for host roots.
Microbial mechanisms of action in the rhizosphere
- Biological Nitrogen Fixation (BNF): Converts inert atmospheric nitrogen gas into plant-absorbable ammonium via the nitrogenase enzyme complex.
- Organic acid secretion: Produces citric, gluconic, and lactic acids that lower micro-site pH and chelate bound calcium, iron, and aluminum phosphates.
- Plant growth promoting substances: Secretes natural phytohormones (auxins, gibberellins, cytokinins) that stimulate root branching and elongation.
Quality standards, carrier vs liquid forms and application
Biofertilizers are available in peat/lignite carrier powders or advanced liquid formulations offering longer shelf life. Seed treatment (slurry coating with jaggery sticker), seedling root dip, and soil broadcasting mixed with vermicompost are standard application methods. Maintain carrier biofertilizers away from direct sunlight and never mix directly with chemical pesticides or acidic chemical fertilizers.
Official source
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National Centre of Organic & Natural Farming (NCONF) ↗Related on KisanPe
Common questions
What is the definition of a biofertilizer?
A biofertilizer is a substance containing live microorganisms that colonizes the rhizosphere and promotes plant growth by increasing the supply of primary nutrients.
Can biofertilizers completely replace chemical fertilizers?
In organic farming, they form the core nutrient supply; in integrated farming, biofertilizers typically replace 20 to 25 percent of synthetic nitrogen and phosphorus inputs while improving soil health.
How should biofertilizers be applied to pulse crops?
Treat legume seeds with Rhizobium culture mixed in a cooled jaggery water solution, dry in the shade for 30 minutes, and sow within 24 hours in moist soil.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
More Fertilizers & Crop Nutrition guides
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