Meaning
Bio-fertilizers are living or biologically active microbial inoculants consisting of bacteria, algae, or fungi which enhance soil fertility by fixing atmospheric nitrogen, solubilising phosphorus, decomposing organic matter, or mobilising nutrients in the soil. Unlike chemical fertilizers, bio-fertilizers are renewable, eco-friendly, and improve long-term soil health without causing environmental pollution.
They play a critical role in sustainable agriculture, as they reduce dependence on synthetic fertilizers, improve nutrient availability, and maintain soil biological balance.
Why Bio-Fertilizers are Important
- Reduce chemical fertilizer requirement
- Improve soil fertility and structure
- Enhance crop yield and quality
- Promote microbial activity in soil
- Lower environmental pollution
- Energy-efficient and cost-effective in the long run
Mechanism of Action
Bio-fertilizers act through one or more of the following mechanisms:
- Biological nitrogen fixation (conversion of atmospheric N₂ into plant-usable forms)
- Solubilisation of insoluble phosphorus
- Production of plant growth-promoting substances (auxins, gibberellins, vitamins)
- Improved root surface area and nutrient absorption
- Enhanced soil microbial diversity
Major Types of Bio-Fertilizers
1. Rhizobium
- A symbiotic nitrogen-fixing bacterium forming root nodules in leguminous plants.
- Nodules act as mini nitrogen factories.
- Fixes more nitrogen than required by the host plant; surplus nitrogen enriches the soil.
- More efficient than free-living nitrogen fixers.
Use: Pulses, legumes (pea, gram, lentil, soybean)
2. Azotobacter
- Free-living, aerobic nitrogen-fixing bacteria.
- Lives in the rhizosphere (soil around roots).
- Fixes nitrogen non-symbiotically and benefits cereals.
- Produces growth-promoting hormones.
Use: Wheat, maize, barley, rice (non-legumes)
3. Azospirillum
- Associative symbiotic nitrogen fixer.
- Lives on root surfaces but does not form nodules.
- Enhances root development and nutrient uptake.
- Supplies vitamins and growth hormones.
Use: Cereals and grasses
4. Blue-Green Algae (Cyanobacteria)
- Free-living, photosynthetic nitrogen-fixing organisms.
- Common genera include Nostoc and Anabaena.
- Particularly effective in flooded rice fields.
5. Azolla–Anabaena Bio-fertilizer
- Azolla is an aquatic fern hosting nitrogen-fixing Anabaena.
- Contains 2–3% nitrogen (wet weight).
- Adds organic matter to soil.
- Widely used in paddy cultivation.
Limitation: Requires standing water; growth constrained in summer.
6. Phosphorus Solubilising Microorganisms (PSM)
- Certain bacteria and fungi solubilise immobilised phosphorus in soil.
- Phosphorus is essential for:
- Root growth
- Energy transfer (ATP)
- Nodulation in legumes
7. Mycorrhizal Fungi
- Symbiotic association between fungi and plant roots.
- Increase absorptive surface area of roots.
- Enhance uptake of phosphorus and micronutrients.
- Provide resistance to:
- Drought
- Salinity
- Extreme pH
- Heavy metal toxicity
- Plant diseases
Compost Tea (Liquid Bio-fertilizer)
- An aerobic liquid extract of compost rich in beneficial microbes.
- Prepared by oxygenating water to promote beneficial bacteria and fungi.
- Sprayed directly on leaves or soil.
- Occupies infection sites and suppresses pathogens.
Bio-fertilizers vs Chemical Fertilizers
| Aspect | Bio-fertilizers | Chemical Fertilizers |
| Nature | Living organisms | Synthetic chemicals |
| Soil health | Improves | Degrades (long term) |
| Pollution | Minimal | High |
| Sustainability | High | Low |
| Cost (long term) | Low | High |
Limitations of Bio-Fertilizers
- Crop-specific effectiveness
- Sensitive to temperature, moisture, and soil conditions
- Slower action compared to chemicals
- Require proper storage and handling
- Initial adoption requires farmer awareness
