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Green Manures for Indian Organic Farms: Species and Application Guide
Green manuring — growing a crop specifically to incorporate into the soil while still green — is one of India’s oldest and most powerful soil-building practices, used on organic farms from the Deccan plateau to the Gangetic plains for centuries before chemical fertilisers existed. Incorporated at peak biomass (just before flowering), a green manure crop like sunn hemp or dhaincha adds 60–150 kg of fixed nitrogen, 3–5 tonnes of organic matter, and massive microbial food per acre — equivalent to 3–4 bags of urea and 3–4 tonnes of compost, all from a ₹1,000–2,000 seed investment. Green manuring is the fastest, cheapest, and most biologically beneficial way to build soil organic matter and nitrogen in a single season.
60–150 kg N/acre
Nitrogen added by a full-season legume green manure — equivalent to 3–4 bags of urea at near-zero cost
Incorporate before flowering
Timing rule for maximum nitrogen content and fastest decomposition — green tissue has better C:N ratio than mature tissue
2–3 week gap
Wait 2–3 weeks after incorporation before planting — allows initial decomposition and prevents nitrogen immobilisation
₹1,000–2,000
Seed cost per acre for dhaincha or sunn hemp — one of the most cost-effective soil inputs in organic farming
What Are the Most Important Green Manure Crops for Indian Farms?
| Crop | Season | N Fixed (kg/acre) | Biomass | Seed Rate | Special Properties |
|---|---|---|---|---|---|
| Dhaincha (Sesbania bispinosa) | Kharif; waterlogged or poorly drained areas | 60–120 kg | 3–4 tonnes/acre | 20–25 kg/acre broadcast | Thrives in waterlogged conditions where other legumes fail; excellent for clay soils; very fast-growing |
| Sunn hemp (Crotalaria juncea) | Kharif and summer; well-drained soils | 80–150 kg | 3–5 tonnes/acre | 20–25 kg/acre broadcast | Highest nitrogen fixation of common green manures; deep taproot breaks hardpan; nematode suppressive |
| Cowpea (Vigna unguiculata) | Year-round; heat and drought tolerant | 50–100 kg | 2–3 tonnes/acre | 15–20 kg/acre | Edible seeds if allowed to mature; dual-purpose — can harvest some pods before incorporating rest |
| Horse gram (Macrotyloma uniflorum) | Rabi; residual moisture | 40–80 kg | 1.5–2 tonnes/acre | 12–15 kg/acre | Very drought tolerant; good for dryland soils; edible grain if not incorporated |
| Pillipesara / Moth bean (Vigna aconitifolia) | Summer; extreme heat and drought | 30–60 kg | 1–2 tonnes/acre | 8–12 kg/acre | Most drought-tolerant legume for green manuring; good for May–June planting in dryland |
| Gliricidia (Gliricidia sepium) — leaf biomass | Year-round from established trees | Provides N through leaf incorporation; 100–200 kg N/acre from trees producing 10–20 tonnes leaves/year | Very high | Perennial — plant once; harvest leaf biomass every 3 months indefinitely; best long-term N source on a farm | |
| Mustard (non-legume) | Rabi | 0 — not N-fixer | 2–3 tonnes/acre | 4–5 kg/acre | Biofumigation — glucosinolates suppress soil-borne Fusarium, Pythium, and root knot nematodes when freshly incorporated |
How Do You Incorporate Green Manure?
Step 1 — Timing: Cut and incorporate at 50–60 days of growth or just before first flowers open — whichever comes first. Nitrogen content of the tissue is highest in pre-flowering vegetative stage; C:N ratio is ideal for fast decomposition.
Step 2 — Cutting:
- Manually: cut with sickle at soil level; pile on the soil surface
- Tractor: rotary slasher or disc harrow on the standing crop; then plough under
- Hand-chop with a mattock before incorporating for faster decomposition
Step 3 — Incorporation:
- Turn into the soil using tractor rotovator (15–20 cm depth) or hand digging
- Ensure green matter is well-mixed with soil — surface piling without mixing decomposes much more slowly
- Water the incorporated area if soil is dry — decomposition requires moisture and microbial activity
Step 4 — Wait:
- Allow 2–3 weeks before planting the next crop
- During decomposition, soil microbes temporarily tie up available nitrogen (nitrogen immobilisation) — planting too soon can cause nitrogen deficiency in the following crop
- Test with your hand: if you can no longer identify incorporated plant material pieces larger than 1 cm, the material is sufficiently decomposed
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Visit Our Shop →What Is the Gliricidia Green Leaf Mulch System?
Gliricidia (Sesbania grandiflora or Gliricidia sepium) planted on farm boundaries and bunds is the most sustainable long-term nitrogen source for a Karnataka organic farm:
- Plant Gliricidia cuttings at 1-metre spacing along all farm bunds and border areas
- After 6–12 months, begin harvesting leaves and tender stems every 3 months
- Apply directly to raised beds as a surface mulch (8–10 cm thick) — do not incorporate; let it decompose slowly on the surface
- One Gliricidia plant produces 3–5 kg of fresh leaf material per cutting; 100 plants produce 300–500 kg per cutting
- Nitrogen content: 3–3.5% N in fresh leaves — 500 kg fresh leaves = 15–17 kg N available as it decomposes
A farm with 200+ Gliricidia plants on its boundary (typical for 1 acre farm with 250m perimeter) produces 600–1,000 kg of leaf biomass every quarter — essentially unlimited green leaf mulch and a significant nitrogen input, all from a one-time planting that requires no additional investment or inputs.
Dhaincha Before Every Monsoon Crop — It Is Karnataka's Best Soil Investment
The most underused practice on Karnataka organic farms is a pre-kharif dhaincha green manure. The sequence: harvest the previous rabi crop in February–March; immediately broadcast dhaincha seed (20–25 kg/acre); allow to grow 50–60 days through April and May (it thrives in the pre-monsoon heat); incorporate in late May, 2 weeks before the June planting. The dhaincha adds 80–100 kg of fixed nitrogen, 3 tonnes of organic matter, and suppresses early-season weeds that grow in the pre-kharif period. This one season of dhaincha replaces 2–3 bags of urea for the next crop at a seed cost of ₹1,000–1,500/acre. Few investments in organic farming have a better cost-benefit ratio.
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