Primary Classes of Agricultural Biofertilizers
Biofertilizers are categorized based on the specific plant nutrient they assimilate or mobilize in the rhizosphere.
Major functional categories:
- Nitrogen-fixing biofertilizers (Symbiotic): Rhizobium strains that form root nodules on leguminous crops (chickpea, soybean, groundnut) to fix atmospheric nitrogen directly.
- Nitrogen-fixing biofertilizers (Free-living & Associative): Azotobacter (for non-legume cereals like wheat, mustard, and maize) and Azospirillum (for paddy, sugarcane, and millets).
- Phosphorus-solubilizing biofertilizers (PSB): Beneficial bacterial and fungal cultures (such as Bacillus, Pseudomonas, and Aspergillus) that produce organic acids to convert insoluble soil phosphates into plant-available orthophosphate ions.
- Mycorrhizal fungi (VAM): Vesicular Arbuscular Mycorrhizae (Glomus spp.) that form extensive fungal hyphal networks, extending root reach to absorb phosphorus, zinc, and water from deep soil layers.
Potassium, Zinc and Bio-Composting Mobilizers
Modern biological inoculants also target essential secondary nutrients and organic matter decomposition.
Advanced microbial inoculants:
- Potash-mobilizing bacteria (KMB): Strains like Frateuria aurantia that solubilize fixed potassium trapped in soil clay lattices.
- Zinc-solubilizing bacteria (ZSB): Inoculants that release insoluble zinc compounds, preventing zinc chlorosis in paddy and maize.
- Waste decomposer cultures: Consortium of cellulolytic and lignolytic fungi that accelerate the in-situ decomposition of crop stubble into rich compost.
Application Methods and Inoculation Precautions
Proper inoculation technique ensures high living bacterial counts when seeds germinate.
Recommended application methods:
- Seed treatment: Mix biofertilizer powder or liquid formulation with cooled jaggery solution, coat certified seeds uniformly, and dry in shade for 30 minutes before sowing.
- Seedling root dip: Dissolve biofertilizers in a bucket of clean water and submerge transplant seedlings for 20 to 30 minutes before planting.
- Storage caution: Store biofertilizer packets in cool, shaded spaces away from direct sunlight and never mix directly with synthetic chemical pesticides or fungicides.
Official source
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Common questions
Which biofertilizer is specifically recommended for pulse crops?
Rhizobium is the specific symbiotic biofertilizer recommended for leguminous pulses, groundnut, and soybean.
What is the function of Phosphorus Solubilizing Bacteria (PSB)?
PSB secrete organic acids that dissolve fixed, insoluble soil phosphates into soluble forms that plant roots can readily absorb.
Can biofertilizers be mixed directly with chemical fungicides?
No, chemical fungicides can kill beneficial live microbial cultures; always maintain an interval or apply biofertilizers after chemical seed treatment.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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