Pueraria for Philippine rubber interrows: nitrogen to the trees

Pueraria javanica is the classic interrow cover for rubber: a vigorous nitrogen-fixing legume that blankets the ground between young trees, suppresses weeds, protects the soil, and moves fixed nitrogen toward the rubber. Research using nitrogen tracing has confirmed that nitrogen fixed by Pueraria transfers to Hevea (rubber) trees rather than staying locked in the cover. For Philippine rubber growers in Zamboanga, Basilan, and beyond, that nitrogen transfer is the reason this cover has been a standard for generations.

A naming note before anything else: Pueraria javanica is a managed tropical legume, not the invasive kudzu (Pueraria montana). They are different plants. The legume we plant in rubber interrows is the managed, agronomically valued cover species used across Southeast Asian plantations.

Does Pueraria really feed nitrogen to rubber trees?

Yes, and it has been measured. Work on nitrogen transfer from Pueraria to Hevea, using isotope tracing, shows that nitrogen fixed by the legume cover moves into the rubber trees. The cover is not just fixing nitrogen for itself; a portion ends up benefiting the crop you are actually growing. For a young rubber stand, that is supplementary nitrogen reaching the trees during the years when establishment matters most. The route is mainly indirect: a pot study found no significant direct transfer through shared mycorrhizal links, and the transfer most likely runs through root exudates and the breakdown of legume residues (Ikram et al. 1994).

For a measured figure: in one trial under young rubber in northeast Thailand, a well-established Pueraria stand accumulated about 250 kg N/ha/yr in above-ground biomass, 85 to 93% of it from the air, and 39 to 46% of the rubber leaf nitrogen came from the legume (Clermont-Dauphin et al. 2016). That is one trial's figure, not a guaranteed number: the amount depends on site, soil and stand. In the same trial, on the shallow soil with low water storage at the top of the slope, the cover improved tree growth but reduced the young trees' ability to survive intense drought (Clermont-Dauphin et al. 2016), so plan cover management with dry-season risk in mind.

What else does a Pueraria cover do in rubber?

Beyond nitrogen, the cover does the standard interrow jobs, and does them well because of its vigour:

• Smothers weeds across the interrow, cutting herbicide and slashing costs during the immature years.
• Protects the soil surface from raindrop impact and runoff, which matters on the sloping rubber land common in Mindanao.
• Holds soil moisture by shading the surface through dry spells.
• Builds soil organic matter as the cover cycles leaf and stem material back to the ground.

Like any vigorous legume, Pueraria needs to be kept off the young trees. Train and trim the cover so it does not climb the saplings, especially in the first couple of years.

How should I establish Pueraria in rubber interrows?

Establishment is about clean ground, the right seeding rate, and good timing:

• Sow onto prepared, reasonably weed-free interrow ground at the start of reliable rains.
• Recommended seeding rate for Pueraria sown alone: 10 kg/ha (our recommendation), drilled or planted in holes. For a mix with other cover legumes, the quantity of each species is set on the quotation for your stand.
• Ensure the right rhizobia are present so nitrogen fixation actually starts; on new ground, appropriate inoculation supports establishment.
• Keep the cover trimmed back from the young rubber stems through the vulnerable early years.

In a designed mix, Pueraria pairs well with shade-tolerant legumes that persist as the canopy closes, so the interrow keeps a living nitrogen source through the cycle.

Where does Pueraria fit in Philippine rubber?

It fits the immature and establishing phase of rubber most strongly, when interrows are open, weed pressure is high, and the young trees benefit most from supplementary nitrogen and erosion control. As the canopy closes, plan a transition to shade-tolerant companions so the ground does not go bare. For estates and smallholders alike, Pueraria is a widely used interrow legume for the establishment years.

FAQ

Is Pueraria javanica the same as invasive kudzu?

No. Pueraria javanica is a managed tropical legume, not the invasive kudzu (Pueraria montana). The interrow cover used in rubber and oil palm is the agronomically valued, managed legume species, not the aggressive temperate kudzu that causes problems elsewhere.

How much nitrogen does Pueraria fix, and does it reach the trees?

The one sourced figure is about 250 kg N/ha/yr accumulated in above-ground biomass, from a single trial under young rubber in northeast Thailand, and it varies by site. In the same trial, isotope measurements showed that 39 to 46% of the rubber leaf nitrogen came from the Pueraria, so the cover genuinely supplements the crop, not just itself. Legume cover contributes nitrogen; adjust your fertiliser programme only after soil and leaf analysis shows what the cover supplies on your block.

What seeding rate should I use in rubber interrows?

Our recommended seeding rate for Pueraria sown alone is 10 kg/ha, drilled or planted in holes. For a mix with other cover legumes, the quantity of each species is set on the quotation for your stand.

Get a Pueraria interrow plan for your rubber

We can match Pueraria javanica (PJ) and its companion legumes to your rubber stand, slope, and stage so the cover protects the ground and feeds nitrogen to the trees. To plan a mix and seeding rate, request a quote or message us on WhatsApp at +60 17-237 4058.

Sources

• Clermont-Dauphin, C., Suvannang, N., Pongwichian, P., Cheylan, V., Hammecker, C. & Harmand, J.-M. (2016). Dinitrogen fixation by the legume cover crop Pueraria phaseoloides and transfer of fixed N to Hevea brasiliensis: impact on tree growth and vulnerability to drought. Agriculture, Ecosystems and Environment 217: 79-88. https://doi.org/10.1016/j.agee.2015.11.002
• Ikram, A., Jensen, E.S. & Jakobsen, I. (1994). No significant transfer of N and P from Pueraria phaseoloides to Hevea brasiliensis via hyphal links of arbuscular mycorrhiza. Soil Biology and Biochemistry 26(11): 1541-1547. https://doi.org/10.1016/0038-0717(94)90096-5