Green Manuring — Free Nitrogen for Your Farm
Growing and incorporating green plant material to add nitrogen, organic matter, and microbial life to soil. The most cost-effective organic nitrogen strategy in India.
Green manuring is the practice of growing a crop — usually a legume — and incorporating it into the soil while still green. It adds organic matter, nitrogen, and feeds soil biology. Done correctly, it can replace 50-100 kg of urea per hectare — for free.
Why Green Manuring Works
When a legume crop is incorporated, three things happen simultaneously:
- Nitrogen release: The root nodules (Rhizobium) contain fixed nitrogen. When incorporated, this nitrogen releases over 4-6 weeks as the material decomposes.
- Organic matter addition: Green biomass adds carbon that feeds soil microbes.
- Root decomposition: Decomposing roots create channels for air and water, and release root exudates that stimulate soil biology.
A well-managed Dhaincha crop can fix 80-120 kg N/ha in 45-60 days — equivalent to 170-260 kg of urea at zero cost.
Best Green Manure Crops for India
| Crop | Botanical Name | N Fixed (kg/ha) | Season | Days | States |
|---|---|---|---|---|---|
| Dhaincha | Sesbania bispinosa | 80-120 | Kharif pre-season | 45-60 | Pan-India |
| Sunn Hemp | Crotalaria juncea | 80-120 | Any warm season | 45-60 | Pan-India |
| Sesbania rostrata | Sesbania rostrata | 150-200 | Pre-Kharif | 45 | Wet areas |
| Cowpea | Vigna unguiculata | 40-60 | Kharif | 45-60 | All India |
| Cluster bean (Guar) | Cyamopsis tetragonoloba | 40-80 | Kharif | 60 | North India |
| Pillipesara | Vigna aconitifolia | 30-50 | Rabi/Zaid | 50 | South India |
| Berseem (Egyptian clover) | Trifolium alexandrinum | 80-120 | Rabi | 60-80 | North India |
| Lucerne (Alfalfa) | Medicago sativa | 100-150 | Rabi perennial | — | Punjab, HP |
Dhaincha (Sesbania bispinosa) — The King of Green Manures
Dhaincha is the most widely used and highest-performing green manure crop in India. It is fast-growing, drought-tolerant, flood-tolerant, grows in poor soils, and can even be grown in saline soils where other crops fail.
- Grows 1.5 to 2.5 metres in 45-60 days
- Produces 15-25 tonnes of green biomass per hectare
- Fixes 80-120 kg N/ha via Rhizobium nodules
- Grows in waterlogged conditions — ideal for pre-paddy in wet fields
- Seed cost: Rs 40-60/kg, need 20-25 kg/ha
Sesbania rostrata — The N-fixing Champion
Sesbania rostrata has a unique ability to fix nitrogen not just in root nodules but also in stem nodules (orange nodules visible on the stem). This allows it to fix nitrogen even in waterlogged conditions where root nodules fail.
- Fixes 150-200 kg N/ha — the highest of any annual green manure
- Grows even in standing water — ideal for wet paddy preparation
- Available from ICAR and state KVKs
How to Do Green Manuring (Step by Step)
For Pre-Kharif Rice (Most Common Application)
Timeline: April to June, before Kharif rice transplanting in June-July.
- April 10-15: Prepare field with light tillage after Rabi harvest
- April 15-20: Broadcast Dhaincha seed at 20-25 kg/ha (mix with sand for even distribution)
- April 20: Light irrigation or wait for pre-monsoon shower
- April 20 to June 10: Dhaincha grows without care (water-saving)
- June 10-15: Dhaincha reaches 1-1.5m height with visible nodules on roots
- June 10-15: Incorporate by disc harrow or tractor rotavator — slice into soil
- June 15-25: Wait 10-15 days for decomposition before transplanting rice
- Late June: Transplant rice paddy into green-manure-enriched soil
What to look for at incorporation: Abundant orange/white nodules on roots = maximum nitrogen. No nodules = crop was stressed or Rhizobium absent.
Critical: Incorporate at 50% flowering — maximum biomass and nitrogen content. Do not wait until seeds form — N will be locked in seeds, not available to soil.
For Pre-Rabi Wheat
- Sow Cowpea or Sunn hemp after Kharif harvest (October)
- Grow for 45-60 days
- Incorporate in November before wheat sowing
- This replaces the entire basal nitrogen dose for wheat
As In-situ Mulch (No-Till Version)
Instead of incorporating, you can slash the green manure at the base and leave it as surface mulch. This works especially well in no-till or SRI paddy systems:
- Grow Dhaincha between rice rows (row spacing of 40-45 cm)
- At flowering, slash with sickle — leave on soil surface
- Decomposes in 3-4 weeks — releases N slowly
- Works as mulch — retains moisture while releasing N
Green Manure + Jeevamrutham Combination
Applying Jeevamrutham at green manure incorporation dramatically accelerates decomposition by inoculating the soil with decomposer bacteria. The combination produces results much faster than either alone:
- At incorporation, apply Jeevamrutham 200 L/acre as soil drench
- Decomposition time reduces from 2-3 weeks to 10-12 days
- More N becomes available faster before the next crop
Common Mistakes
Incorporating too late: Once seeds form, nitrogen is locked in seeds, not leaves and stems. Incorporate at 50% flowering.
Not waiting after incorporation: Decomposing green material temporarily immobilizes nitrogen as microbes consume it. Wait at least 10-15 days after incorporation before sowing.
Not inoculating with Rhizobium: Without Rhizobium, legumes cannot fix nitrogen — they just grow as regular crops and provide carbon only. Always inoculate seeds with crop-specific Rhizobium strain.
Drought stress: Dhaincha and Sunn hemp need moisture for at least the first 2 weeks of establishment. If there is no rain, give one light irrigation.
Economics
| Item | Cost |
|---|---|
| Dhaincha seed (25 kg/ha) | Rs 1,000-1,500 |
| Rhizobium inoculant | Rs 150-200 |
| Sowing labour | Rs 500-800 |
| Incorporation (tractor) | Rs 1,200-1,800 |
| Total cost/ha | Rs 2,850-4,300 |
| N fixed (100 kg N/ha) | Equivalent of 215 kg urea |
| Urea market price (215 kg) | Rs 4,730 |
| Net saving | Rs 430-1,880/ha (plus soil health benefits) |
The economics only improve over time as soil biology builds up and the same inoculation effort produces better results.