Introduction: What Are Nitrogen-Fixing Trees?
Nitrogen-fixing trees (NFTs) are special trees that can convert nitrogen gas from the air into a form that plants can use. This process is called nitrogen fixation, and it is done with the help of Rhizobia bacteria or actinomycetes in the tree’s root system.
Benefits of Nitrogen-Fixing Trees in Plantations
| Benefit | Explanation |
|---|---|
| Improves Soil Fertility | Adds nitrogen to the soil naturally, reducing the need for synthetic fertilizers |
| Supports Tree Health | Strengthens surrounding crops or trees by sharing nutrients through roots |
| Boosts Organic Matter | Leaf litter and biomass improve soil structure and moisture retention |
| Enhances Biodiversity | Provides shelter and food for beneficial insects and animals |
| Increases Yield | Healthier trees and better soil conditions support higher productivity |
Common Nitrogen-Fixing Trees in the Philippines
| Tree Species | Fixation Type | Notes |
|---|---|---|
| Gliricidia sepium | Rhizobial | Excellent hedgerow or shade tree; fast-growing |
| Leucaena leucocephala | Rhizobial | Good for fodder, alley cropping, and erosion control |
| Sesbania grandiflora | Rhizobial | Useful as windbreak and fast decomposer |
| Calliandra calothyrsus | Rhizobial | Provides nitrogen and high biomass for mulch |
| Pterocarpus indicus (Narra) | Rhizobial | Native NFT and national tree of the Philippines |
| Intsia bijuga (Ipil) | Rhizobial | Nitrogen-fixer and high-value timber tree |
| Moringa concanensis | Rhizobial | Reported to show signs of nitrogen fixation, good for agroforestry |
| Caesalpinia pulcherrima | Rhizobial (when inoculated) | Ornamental and potential nitrogen-fixer with Rhizobia inoculation |
What is Inoculation?
Inoculation means adding beneficial Rhizobia bacteria to the roots of nitrogen-fixing trees to ensure successful nitrogen fixation.
Benefits of Inoculating NFTs:
- Improves early growth
- Ensures nodule formation
- Increases nitrogen input to the soil
Tip: Inoculate tree seedlings in the nursery using commercial Rhizobia powders or slurries before field planting.
Planting NFTs in Agroforestry Systems
Suggested Spacing:
- Gliricidia/Leucaena: 1.5 to 2 meters apart
- Large NFTs (Narra/Ipil): 4 to 6 meters apart
Interplanting:
- Combine NFTs with main crops like Aquilaria (agarwood), coffee, cacao, or fruit trees
- Plant NFTs on borders or in alleys for maximum soil benefit
Visual Guide to NFT Benefits
✅ Nitrogen Fixation
✅ Soil Enrichment
✅ Mulching & Green Manure
✅ Support for Main Tree Crops
[Insert infographic with illustrations of root nodules, intercropping layout, and benefits]
Management & Maintenance
- Prune regularly to avoid shading of main crops
- Use pruned branches as mulch or compost
- Monitor for pests (especially in young seedlings)
- Replenish inoculants if trees are stunted
Tools & Supplies
- Inoculated seedlings or Rhizobia packs
- Trowel or spade
- Watering can
- Organic mulch
Sustainability Impact
NFTs help reduce reliance on chemical fertilizers, protect watersheds, and increase resilience of farming systems.
Field Application Tip:
Alternate every 2–3 rows of agarwood with a row of NFTs to maximize long-term soil fertility and tree health.