Team Organic Mandya ·
PSB and Azospirillum: Biofertilisers for Organic Farms
PSB (Phosphate Solubilising Bacteria) and Azospirillum are two of the most cost-effective biofertilisers available to organic farmers — PSB converts locked-up soil phosphorus into plant-available form, while Azospirillum fixes atmospheric nitrogen directly in the root zone, supplying a portion of the crop’s nitrogen requirement from the air. Together, they address two of the three primary soil nutrient requirements (N and P) through biological means. At ₹50–100 per kg of commercial product and application rates of 2–2.5 kg/acre for soil treatment, a season’s biofertiliser programme costs ₹200–500/acre vs ₹2,000–5,000/acre for equivalent NPK chemical inputs. The catch: these are living organisms, and effectiveness depends entirely on proper application — correct timing, compatible soil conditions, and not mixing with fungicides.
20–30 kg N/acre
Nitrogen fixed by Azospirillum annually in active soil — equivalent to 40–60 kg urea savings in supportive conditions
PSB unlocks 30–50%
Of soil phosphorus that was previously locked in insoluble forms — reducing need for added phosphate inputs
5 g/kg seed
Standard seed treatment rate for both PSB and Azospirillum — coat moist seeds before sowing
Do not mix with copper
Both PSB and Azospirillum are killed by copper fungicides and chemical pesticides — apply separately
What Is PSB and How Does It Work?
Phosphate Solubilising Bacteria (primarily Bacillus megaterium, Pseudomonas striata, and related species) secrete organic acids — gluconic acid, citric acid — that dissolve insoluble tricalcium phosphate, iron phosphate, and aluminium phosphate compounds in the soil, converting them to plant-available orthophosphate. In most Indian soils, 70–80% of applied phosphorus becomes locked in insoluble forms within days of application. PSB essentially unlocks this phosphorus bank.
Where phosphorus locking is most severe:
- Red laterite soils (common in Karnataka, Tamil Nadu) — high iron content locks phosphorus as iron phosphate
- Acid soils (pH below 6.0) — aluminium and iron phosphate precipitation
- Alkaline black soils — calcium phosphate precipitation
PSB effectiveness is highest when:
- Organic matter is above 1% (microbes need carbon to metabolise)
- Soil pH is 6.5–7.5 (extreme pH reduces bacterial activity)
- Soil moisture is adequate (40–60% field capacity)
- Used in combination with organic matter additions (vermicompost, jeevamrutha)
What Is Azospirillum and How Does It Work?
Azospirillum (Azospirillum brasilense, A. lipoferum) is a free-living nitrogen-fixing bacterium that colonises the root zone and rhizosphere of cereal crops, vegetables, and grasses, fixing atmospheric nitrogen (N₂) into ammonium (NH₄⁺) that plants absorb. Unlike Rhizobium (which fixes nitrogen only in legume root nodules), Azospirillum works on virtually all crops without forming nodules — it lives freely near roots and fixes nitrogen in the root zone.
Additional benefits beyond N fixation:
- Produces plant growth hormones (IAA — indole acetic acid), increasing root length and root hair density
- Increased root surface area improves water and nutrient absorption even beyond nitrogen
- Produces siderophores that chelate iron and make it available to plants in iron-deficient soils
Crops that respond best to Azospirillum:
- Cereals (paddy, maize, wheat, sorghum, finger millet) — 15–30% of nitrogen requirement covered
- Vegetables (all types) — root growth stimulation; 10–20% N savings
- Sugarcane — widely used in Karnataka; documented 10–25% yield increase
Get organic seeds, bio-inputs & farm supplies from our shop — trusted by 12,000+ farmers.
Visit Our Shop →How Do You Apply PSB and Azospirillum?
| Application Method | Rate | Timing | Notes |
|---|---|---|---|
| Seed treatment | 5 g per kg of seed for each product | Just before sowing; treat seeds within 24 hours of application | Moisten seeds lightly; sprinkle PSB and Azospirillum powders; mix to coat; dry in shade 30 minutes; sow immediately |
| Seedling root dip | 250 g each in 10 litres water; dip roots for 30 minutes | At transplanting — before placing seedling in transplant hole | For transplanted crops (tomato, brinjal, capsicum, chilli); combined with Trichoderma root dip is excellent |
| Soil application (broadcast) | 2–2.5 kg each per acre mixed with 100 kg vermicompost or FYM | At last ploughing or bed preparation; incorporate into top 15 cm | Most effective if mixed with vermicompost; vermicompost provides carbon and protects microbes during soil application |
| Drip fertigation | 1 kg dissolved in 10 litres water; inject at 1:50 dilution | Monthly during crop season; early morning application | Filter through fine cloth before injection; flush drip system after; do not use within 7 days of any copper spray |
Can you apply PSB and Azospirillum together? Yes — they are fully compatible and recommended together. Apply both in the same seed treatment or soil application.
What Is the Difference Between PSB, Azospirillum, and Rhizobium?
| Biofertiliser | Mechanism | Crops | Notes |
|---|---|---|---|
| PSB (Phosphate Solubilising Bacteria) | Solubilises locked soil phosphorus | All crops | No crop specificity; works universally; most impactful in red laterite and acid soils |
| Azospirillum | Free-living N fixation in root zone; root growth stimulation | All crops — most effective on cereals and vegetables | Does not form nodules; works on all crops; 15–30% N savings documented |
| Rhizobium | Symbiotic N fixation inside root nodules | Legumes only (bean, groundnut, soybean, cowpea, guar) | Fixes 50–200 kg N/acre in legumes; completely ineffective on non-legumes; highly crop-specific strains |
| Mycorrhizae (AMF) | Hyphal network extends root reach; phosphorus and water uptake | All non-brassica crops | Not a N or P producer — extends access to existing soil P and water; synergistic with PSB |
| Trichoderma | Biological fungicide; root zone disease suppression | All crops | Not a nutrient fixer — pathogen control only; compatible with all biofertilisers |
How Do You Store and Handle Biofertiliser Products?
PSB and Azospirillum are perishable living products — storage conditions determine effectiveness:
- Ideal storage: 4–10°C (refrigerator is adequate); never freeze
- Shelf life: 6–12 months from manufacture date; check the expiry date on every packet
- Never store in direct sunlight or in a vehicle in summer — 30 minutes at 45°C can kill 80% of viable cells
- After opening, seal tightly and use within 1 month
- Quality check: good PSB smells earthy; Azospirillum product has a slight musty fermented smell; if it smells putrid (rotten egg / strong ammonia), the product is dead
Mix Biofertilisers with Jeevamrutha for a Complete Soil Drench — One Application, Multiple Benefits
A powerful soil drench combines Jeevamrutha (microbial inoculant, growth factors) with PSB and Azospirillum dissolved in it: prepare 200 litres Jeevamrutha as usual; add 500 grams each of PSB and Azospirillum powder; mix and apply as soil drench at 200 litres per acre. This single application delivers native soil microbes (from Jeevamrutha), phosphorus-solubilising bacteria, and nitrogen-fixing bacteria simultaneously. The Jeevamrutha provides the carbon, moisture, and microbial community that supports all three. In Karnataka’s laterite soil conditions — where phosphorus locking is acute — this combination addresses two major soil deficiencies in one step. Cost for the combined treatment: ₹300–500 per acre vs ₹3,000–6,000 for chemical NPK equivalents.
Ready to start your organic farming journey?
Get everything you need from our store — seeds, bio-inputs, and farm tools.
Shop Organic Mandya →Last updated: March 2026
Organic Mandya Training
Earn ₹1 Lakh/Month on 1 Acre — Live Online Workshop
Related Guides
Last updated: March 2026