Biofertilizers: What's Actually in the Packet

Almost every crop protocol on this site tells you to "apply PSB + Azotobacter" or "use Rhizobium seed treatment" — but what are these products, what do they actually do, and how do you know if the packet you bought is still alive? This article fills that gap.

What a Biofertilizer Is

A biofertilizer is a carrier material (usually lignite powder, charcoal, or peat) loaded with a single living microbial species, packaged to deliver a known population of that organism to your seed or soil. Unlike Jeevamrutham or Panchagavya (which are farm-made, multi-species, broad-spectrum), biofertilizers are single-strain, lab-cultured, and commercially manufactured — sold at agri-input shops, KVKs, and state seed corporations.

They are not a replacement for Jeevamrutham-style inputs — they're a complementary, targeted tool. Most serious organic farms use both.

The Five Major Biofertilizers

1. Rhizobium — Nitrogen Fixation for Legumes

What it does: Colonizes legume root hairs, forms root nodules, fixes atmospheric N₂ into ammonium the plant can use directly.

Critical fact: Rhizobium is host-specific. A strain cultured for chickpea will not nodulate cowpea or soybean. Always buy the species-specific product:

Crop	Rhizobium Species
Chickpea (Chana)	Mesorhizobium ciceri
Pigeonpea (Tur)	Bradyrhizobium sp. (cowpea-type)
Soybean	Bradyrhizobium japonicum
Groundnut	Bradyrhizobium sp. (arachis-type)
Cowpea, Moong, Urad	Bradyrhizobium sp. (cowpea-type)
Lentil, Pea	Rhizobium leguminosarum

Application: Mix packet with jaggery-water slurry (10% jaggery solution), coat seeds, dry in shade 30 minutes, sow same day.

2. Azotobacter — Free-Living Nitrogen Fixer (Non-Legumes)

What it does: Fixes atmospheric nitrogen without needing a host root nodule — works in the rhizosphere of cereals, vegetables, and any non-legume crop. Also produces growth-promoting hormones (IAA, gibberellins).

Best for: Wheat, rice, maize, cotton, vegetables — any crop where Rhizobium doesn't apply.

Typical N contribution: 15–20 kg N/ha under good conditions — meaningfully supplements but does not replace full nitrogen needs on its own.

3. Azospirillum — Nitrogen Fixation + Root Growth (Cereals)

What it does: Similar free-living N fixation to Azotobacter, but specifically associates with cereal root systems (rice, wheat, sorghum, millets, sugarcane) more effectively. Also stimulates root hair proliferation, increasing nutrient and water uptake surface area.

Best for: All cereals and grasses — often the first-choice biofertilizer for rice and wheat nurseries.

4. PSB (Phosphate Solubilizing Bacteria) — Unlocking Bound Phosphorus

What it does: Most Indian soil already contains substantial phosphorus — but 65–80% of it is chemically locked (bound to calcium in alkaline soil, or iron/aluminum in acid soil) and unavailable to plants. PSB (commonly Bacillus megaterium or Pseudomonas striata) secretes organic acids that dissolve these bound forms, releasing plant-available phosphate.

Best for: Every crop, every soil type — phosphorus deficiency is near-universal in Indian agriculture, making PSB one of the most consistently valuable biofertilizers.

Pairs well with: Rock phosphate (PSB accelerates its very slow natural release) — see Mineral Organic Fertilizers.

5. VAM / Mycorrhiza — Already Covered in Depth

See the dedicated article: Mycorrhizal Fungi — The Wood Wide Web. Sold as VAM powder, applied at sowing/transplanting.

Carrier Types — What You're Actually Buying

Carrier Type	Shelf Life	Notes
Lignite/charcoal powder	6 months from manufacture date	Most common, cheapest, India-standard
Liquid formulation	12–18 months	Higher cost, longer shelf life, increasingly available
Peat-based	6–9 months	Common for imported products, less common in India

Always check the manufacture date, not just an expiry date — biofertilizer viability declines continuously from the day of culturing, regardless of what the label says. A 5-month-old "6-month shelf life" packet has far fewer live organisms than a 1-month-old one.

How to Verify a Packet Is Still Viable

Check minimum cell count on label — legitimate manufacturers state CFU (colony forming units) per gram; look for at least 10⁷–10⁸ CFU/g
Smell test — fresh biofertilizer carrier has a mild earthy smell; sour or foul smell indicates contamination
Simple germination/nodulation check (Rhizobium specifically): treat a small batch of seed, grow in a pot, uproot at 25–30 days, check for pink-interior nodules (see Pulses guide for full diagnostic)
Buy from certified sources: State Agricultural Universities, KVKs, and National Biofertilizer Development Centre (NBDC) licensed manufacturers carry quality-controlled stock

Mixing Order When Combining Multiple Biofertilizers

A common mistake is mixing several biofertilizer powders dry together before adding liquid — this can cause one species to dominate or cross-contaminate culturing conditions in the packet before application. Correct sequence for seed treatment:

Prepare jaggery-water slurry (10% solution) fresh
Add Rhizobium (if legume) first, mix seeds thoroughly, let sit 10 minutes
Add PSB second, mix again
Add Azotobacter/Azospirillum last if using (only for non-legume intercrop seed in mixed sowing)
Spread seeds in shade to dry for 20–30 minutes — never direct sun
Sow within 24 hours

Never treat seed with biofertilizers and chemical fungicide simultaneously — most seed-coating fungicides kill the very bacteria you're trying to introduce. If fungicide-treated seed is unavoidable, biofertilizer benefit is largely lost for that batch.

Storage

Keep all biofertilizer packets in a cool, shaded place — never direct sun, never near chemical fertilizer storage (residual chemical contamination)
Ideal storage temperature: below 30°C
Use within shelf life window — there is no "still mostly fine" stretch period; expired biofertilizer should be treated as compost input, not seed treatment

Biofertilizers: Rhizobium, Azotobacter, PSB, Azospirillum, and Mycorrhiza Explained