Sesbania Seeds for Green Manure: Complete Nitrogen-Fixing Cover Crop Guide
Sesbania green manure is one of the most effective biological nitrogen sources available to tropical and subtropical farmers. Capable of fixing 80 to 300 kg of nitrogen per hectare per year, sesbania species outperform most other green manure crops in speed, biomass output, and tolerance of difficult growing conditions. This guide covers everything you need to know about using green manure seeds tropical farmers rely on to build soil fertility, cut fertilizer costs, and boost crop yields.
What Is Green Manure?
Green manure is a crop grown specifically to be incorporated into the soil while still green and actively growing. Unlike harvested crops, green manure plants are plowed under to decompose in place, releasing nutrients—especially nitrogen—directly into the root zone of the subsequent crop. Leguminous green manures like sesbania are particularly valuable because they fix atmospheric nitrogen through symbiotic bacteria (Rhizobium and Azorhizobium) in their root and stem nodules, effectively converting free atmospheric N₂ into plant-available ammonium and nitrate.
Green manuring has been practiced for thousands of years across Asia, Africa, and Latin America. In modern sustainable agriculture, it serves multiple purposes: nitrogen supply, organic matter addition, weed suppression, erosion control, and soil structure improvement. Among all green manure crops, sesbania species stand out for their exceptional speed of growth and nitrogen-fixing capacity in tropical environments.
Why Sesbania Is the Best Green Manure Crop
Several characteristics make sesbania the preferred green manure crop for tropical and subtropical agriculture. No other green manure legume matches the combination of sesbania nitrogen fixation rates, rapid biomass production, and environmental tolerance that sesbania delivers.
Nitrogen Fixation by Sesbania Species
Not all sesbania species fix equal amounts of nitrogen. The table below summarizes sesbania nitrogen fixation data from published agronomic research, giving you the information you need to select the right species for your green manure program.
| Species | N Fixation (kg N/ha/year) | Biomass (t/ha fresh, 60 days) | Nodulation Type | Best Environment |
|---|---|---|---|---|
| S. rostrata | 150–300 | 20–30 | Root + Stem nodules | Flooded/lowland rice paddies |
| S. sesban | 100–200 | 15–25 | Root nodules | Semi-arid to sub-humid uplands |
| S. bispinosa (Dhaincha) | 80–120 | 15–20 | Root nodules | Waterlogged, saline, alkaline soils |
| S. grandiflora | 60–100 | 10–15 | Root nodules | Humid tropical lowlands |
| S. aculeata | 60–100 | 12–18 | Root nodules | Marginal and degraded soils |
S. rostrata is the standout performer. Its unique ability to form stem nodules (via Azorhizobium caulinodans) allows it to maintain nitrogen fixation under waterlogged conditions where root nodule activity would normally cease. This biological advantage translates directly into higher nitrogen contributions—up to 300 kg N/ha/year in favorable conditions, rivaling or exceeding the nitrogen supplied by heavy synthetic fertilizer applications.
How to Use Sesbania as Green Manure: Step by Step
Successfully using sesbania as a green manure crop requires attention to timing at each stage. Follow this field-proven protocol used by farmers across South and Southeast Asia.
- Field Preparation and Sowing Prepare the field with one light plowing or disking. Broadcast sesbania seeds at 30–50 kg/ha, or drill in rows 25–30 cm apart at 20–30 kg/ha. Sow at the onset of the rainy season or 60–75 days before the planned transplanting date of your main crop. No inoculation is typically needed in fields with prior sesbania or legume history, though Rhizobium or Azorhizobium inoculant can boost nodulation in new fields.
- Growth Period (45–60 Days) Allow sesbania to grow for 45–60 days. During this window, plants reach 1.5–3 meters in height, produce maximum biomass, and accumulate peak nitrogen in their tissues. Monitor for 50% flowering—this signals the ideal incorporation window. The crop requires minimal management; its vigorous growth suppresses weeds naturally.
- Incorporation Timing Incorporate the sesbania crop at 50% flowering stage, typically 45–60 days after sowing. Use a rotary tiller, disc plow, or moldboard plow to chop and turn the biomass into the top 15–20 cm of soil. In flooded rice systems, knock down the plants and flood the field simultaneously. Incorporation before flowering reduces total nitrogen; waiting past seed set diverts nitrogen from leaves to seeds.
- Decomposition Period (10–14 Days) Allow 10–14 days for the incorporated biomass to decompose before transplanting or sowing the next crop. Sesbania's low C:N ratio ensures rapid breakdown. Under warm, moist conditions, 60–70% of the nitrogen is mineralized within the first two weeks. In flooded paddies, decomposition proceeds faster due to anaerobic microbial activity.
- Planting the Next Crop Transplant or sow the subsequent crop (rice, vegetables, maize, or other cereals) 10–14 days after incorporation. The first flush of mineralized nitrogen is available immediately; a second release occurs 4–6 weeks later as more resistant plant tissues decompose. This two-phase nitrogen release pattern aligns well with the nutrient demand curve of most cereal crops.
Sesbania Green Manure in Rice Systems
Rice-sesbania integration is the most extensively researched and commercially practiced green manure system in the world. The International Rice Research Institute (IRRI) and national agricultural research systems across Asia have documented consistent yield improvements when sesbania green manure is incorporated before rice transplanting.
IRRI Research Findings
- Rice yield increase: 20–40% higher grain yield compared to unfertilized controls when S. rostrata green manure is incorporated before transplanting
- Nitrogen equivalence: 20–25 tonnes/ha of fresh sesbania biomass supplies 80–120 kg N/ha, equivalent to 175–260 kg urea
- Residual effect: 15–25% of the nitrogen from green manure carries over to benefit the second rice crop in double-cropping systems
- Soil organic carbon: Continuous green manuring for 3–5 years increases soil organic carbon by 0.2–0.4 percentage points, improving long-term soil fertility
Nitrogen Credit Calculations for Rice
When planning your fertilizer program, calculate the nitrogen credit from sesbania green manure using this framework:
Available N from green manure = Fresh biomass (kg/ha) x Dry matter fraction (0.15–0.20) x N content (0.025–0.035) x Mineralization efficiency (0.60–0.70)
Example: 20,000 kg fresh biomass x 0.18 (DM) x 0.030 (N%) x 0.65 (efficiency) = 70.2 kg available N/ha
This is equivalent to approximately 153 kg urea/ha (at 46% N content), representing a significant saving on synthetic fertilizer inputs.
Seed Rate Calculator
Sesbania Seed Rate Calculator
Need to calculate the exact seed quantity for your green manure program? Use our interactive seed rate calculator to determine the right amount based on your field area, sowing method, and target plant population.
Covers broadcast, drill, and row planting methods for all sesbania species
Cost-Benefit Analysis: Sesbania Green Manure vs. Synthetic Fertilizer
The economic case for sesbania green manure is compelling, especially in regions where fertilizer prices are high or supply is unreliable. The following analysis compares the cost of nitrogen from sesbania green manure against synthetic fertilizer sources.
| Parameter | Sesbania Green Manure | Synthetic Fertilizer (Urea) |
|---|---|---|
| Nitrogen supplied | 80–120 kg N/ha | 80–120 kg N/ha |
| Input cost | $25–45/ha (seed + sowing labor) | $55–120/ha (urea at $350–550/tonne) |
| NPK equivalent value | N: 80–120 kg + P: 15–25 kg + K: 40–80 kg | N only (urea provides no P or K) |
| Organic matter added | 3–5 tonnes dry matter/ha | None |
| Soil improvement | Improved structure, water retention, microbial activity | Potential acidification with repeated use |
| Environmental impact | Carbon-neutral; reduces N₂O emissions | Manufacturing CO₂ footprint; leaching risk |
| Total value (NPK equivalent) | $120–200/ha | $55–120/ha (N value only) |
When the full NPK value is considered—including the phosphorus (15–25 kg P/ha) and potassium (40–80 kg K/ha) released during biomass decomposition—sesbania green manure delivers 2 to 4 times the nutrient value of an equivalent urea application at comparable or lower cost. The organic matter contribution and soil health benefits compound over multiple seasons, making the return on investment even stronger in the medium to long term.
Best Sesbania Species for Green Manure by Climate and Soil
Choosing the right sesbania species for your green manure program depends on your soil type, water conditions, and climate. Use this selection guide to match species to your field conditions.
S. rostrata — The High-Performance Choice
Best for: Lowland rice paddies, flooded fields, waterlogged soils
Why: Stem nodulation enables nitrogen fixation under flooded conditions. Highest N fixation (150–300 kg/ha/year) and fastest biomass accumulation. Recommended wherever rice is the primary crop and fields are regularly flooded.
Learn more: Sesbania Species Comparison Guide
S. sesban — The Versatile All-Rounder
Best for: Semi-arid to sub-humid climates, rainfed uplands, agroforestry systems
Why: Tolerates a wide range of soil pH (5.0–8.5) and moisture conditions. Excellent for alley cropping and relay intercropping. Strong performance in East African and South Asian contexts. Fixes 100–200 kg N/ha/year.
Learn more: Sesbania Sesban Seeds
S. bispinosa (Dhaincha) — The Tough Survivor
Best for: Saline soils, alkaline soils, waterlogged conditions, marginal lands
Why: Exceptional tolerance of soil salinity (up to 8–10 dS/m) and alkalinity (pH up to 10). The most widely planted green manure species in the Indian subcontinent. Fixes 80–120 kg N/ha/year. Extremely low seed cost and high availability.
Learn more: Sesbania Bispinosa (Dhaincha) Seeds
S. grandiflora — The Multi-Purpose Tree
Best for: Humid tropical lowlands, home gardens, integrated farming systems
Why: Combines green manure with edible flowers, leaves, and pods. Lower N fixation (60–100 kg/ha/year) but offers food security co-benefits. Best used as a perennial hedgerow green manure with periodic pruning and incorporation.
Learn more: Sesbania Grandiflora Seeds
S. aculeata — The Degraded Soil Specialist
Best for: Degraded, nutrient-poor, and compacted soils; mine rehabilitation
Why: Deep taproots break through compacted layers. Establishes well on severely degraded soils where other legumes struggle. Fixes 60–100 kg N/ha/year and is often used as the first crop in soil rehabilitation sequences.
Ordering Green Manure Seeds from Kohenoor International
Kohenoor International has supplied premium sesbania seeds to farmers, agricultural programs, and NGOs across 70+ countries since 1957. Our green manure seed offering includes all five species covered in this guide, with the quality assurance and logistics expertise that large-scale agricultural programs require.
Order Details
- Minimum Order Quantity (MOQ): 1 metric tonne (1,000 kg) for export orders; smaller quantities available for trial programs on request
- Packaging: 25 kg or 50 kg polypropylene bags, double-stitched with lot number and species label; custom packaging available for branded programs
- Quality Standards: Germination rate 85%+, purity 98%+, moisture content below 10%; certificate of analysis provided with every shipment
- Shipping: FOB Karachi or CIF to any global port; 20 ft container holds 18–20 MT; lead time 2–3 weeks from order confirmation
- Documentation: Phytosanitary certificate, fumigation certificate, certificate of origin, and ISTA seed testing report included. See our export documentation guide for details.
For pricing inquiries and custom green manure seed programs, contact our sales team directly. We work with government procurement agencies, development organizations, and private-sector buyers to deliver sesbania seeds that meet international seed quality standards.
Frequently Asked Questions
How much nitrogen does sesbania green manure fix per hectare?
Sesbania nitrogen fixation ranges from 60 to 300 kg N/ha/year depending on the species. Sesbania rostrata is the highest performer at 150–300 kg N/ha/year, followed by S. sesban at 100–200 kg N/ha/year, S. bispinosa at 80–120 kg N/ha/year, and S. grandiflora and S. aculeata at 60–100 kg N/ha/year each.
When should I incorporate sesbania green manure into the soil?
Incorporate sesbania green manure at 45–60 days after sowing, ideally at 50% flowering stage. At this point, biomass nitrogen content is at its peak (2.5–3.5% N on a dry weight basis) and the carbon-to-nitrogen ratio is low enough (15:1 to 20:1) for rapid decomposition. Incorporation before flowering results in lower total N, while waiting until seed set causes nitrogen to be redirected from leaves to seeds.
Can sesbania green manure replace urea in rice production?
Yes, sesbania green manure can replace 50–100% of synthetic nitrogen fertilizer in rice systems. IRRI research shows that incorporating 20–25 tonnes/ha of fresh sesbania biomass provides 80–120 kg N/ha, equivalent to 175–260 kg of urea. Many farmers use a combined approach—sesbania green manure plus a reduced urea application—to achieve optimal yields while cutting fertilizer costs by 40–60%.
What is the best sesbania species for waterlogged soils?
Sesbania rostrata is the best species for waterlogged and flooded soils. Unlike most legumes, S. rostrata forms stem nodules (in addition to root nodules) that remain active even under flooded conditions. This makes it uniquely suited for lowland rice paddies and flood-prone fields where other green manure crops fail. Sesbania bispinosa (dhaincha) also tolerates waterlogging well and is widely used across South and Southeast Asia.
What is the recommended seed rate for sesbania green manure?
The recommended seed rate for sesbania green manure is 30–50 kg/ha when broadcast sown, or 20–30 kg/ha when drilled in rows spaced 25–30 cm apart. Higher seed rates (40–50 kg/ha) produce denser stands that suppress weeds more effectively and generate maximum biomass within the 45–60 day growing window. Use our seed rate calculator for precise recommendations based on your field conditions.
Order Premium Sesbania Green Manure Seeds
Kohenoor International has exported sesbania seeds to 70+ countries since 1957. Contact us for bulk pricing, species selection advice, and green manure program support.