Many coconut plantations in the Philippines are kept bare: bare between palms, bare under palms, bare along inter-row paths. The reason is simple: coconut roots are shallow and fibrous, and managers fear competition. But bare soil under strong sun loses moisture to evaporation, loses nitrogen, and is quickly colonised by hagonoy (Chromolaena odorata) and cogon (Imperata cylindrica). Slash-and-burn or manual weeding is labour-intensive, especially where cogon is well established.
A legume cover crop (pueraria (PJ), Mucuna bracteata (MB), or Calopogonium mucunoides (CM)), kept managed, competes little with coconut. It fixes atmospheric nitrogen and suppresses weeds through shading. Once established, it needs only mowing or soft slashing, not digging. Benefits can show in the first season and build year after year.
Why Nitrogen Matters Under Coconut
Nitrogen is often one of the nutrients that limits coconut yield (copra, oil, or dried kernel mass) on Philippine soils, and every harvest removes some of it. Where residue is burned or removed and soil organic matter is low, nitrogen mineralised from organic matter cannot replace what the crop takes, and the soil is progressively depleted. Soil and leaf analysis shows how far your own block has run down.
Applied fertiliser closes some of the gap, but it is a recurring expense, and it is easy to fall behind what the crop removes. A legume cover adds nitrogen from the air for the cost of seed and labour, and the fixed nitrogen returns to the soil in leaf litter and residue, where it also builds organic matter. Legume cover contributes nitrogen; adjust your fertiliser programme only after soil and leaf analysis shows what the cover supplies on your block.
The N-fixing capacity depends on legume species, rainfall, and soil P availability. The only sourced PJ figure comes from one trial under young rubber in northeast Thailand, where PJ accumulated up to 250 kg of nitrogen per hectare per year in above-ground biomass (Clermont-Dauphin et al. 2016); under a closing canopy or on dry ground, expect less. MB derived 67-84% of its nitrogen from fixation in a 15N study under three-year-old oil palm on Jawa Series soil in Malaysia (Cheah et al. 2010); that is a share, not a quantity, and no annual rate is asserted for it. MB forms a dense, high-biomass cover, though it is slower to establish. CM has no verified annual fixation rate; it establishes quickly but is less suitable for under-palm use. PJ is a common choice under coconut.
Pueraria and Mucuna bracteata Suppress Weeds
Hagonoy and cogon germinate in bare soil gaps, especially in the months after the monsoon when soil is moist and air is warm. A dense legume cover blocks light at the soil surface and so limits weed germination. In an oil palm trial on mineral soil in Malaysia, weed dry weight under the cover crop treatments was 97.3 to 99.9% lower, and weed density 94.77 to 99.73% lower, than in unweeded plots 9 to 24 months after planting (Samedani et al., 2015); coconut blocks have not been measured the same way, so count your own weeding rounds. Mucuna bracteata establishes more slowly than PJ but forms a dense, persistent cover once established. With the cover kept up by light mowing, you should need fewer manual weeding rounds; record them on your trial block.
Suppression mechanisms are both mechanical (shading) and chemical (some legumes release allelopathic compounds from leaves and roots). The net effect is that hagonoy and cogon seedlings cannot compete, and existing plants regenerate less. If hagonoy and cogon are already present at high density, slash before sowing legume, allow a short period of resprouting so you can identify what is there, then establish cover crop. Subsequent mowing of the legume (which now contains dormant weed seed) prevents weed completion of seed maturation.
Over the following years, a cover crop replaces repeated manual weeding cycles with a single establishment and occasional light mowing. Record the labour saved on your trial block to judge the return on your own farm.
Soil Moisture and Litter Effect
Bare coconut soil under intense sun dries quickly. A legume canopy and the mulch of its dead leaves shade the surface, which reduces evaporation and keeps the soil cooler; measure soil moisture on your trial block and on a bare block to see the difference on your own ground. This matters in dry spells between the northeast and southwest monsoons, when water stress in coconut limits nut set and kernel development.
The litter layer of dried legume leaves improves soil structure and feeds microbial activity. Over several seasons, a maintained cover adds organic matter to the topsoil; a soil test before and after on your trial block shows how much. Higher organic matter means more water-holding capacity, more nutrient-holding capacity, and more food for the microbes that mineralise nutrients for the palm.
Pueraria and Mucuna bracteata: Establishment Guide
Pueraria (PJ): Recommended seeding rate (sown alone): 10 kg/ha (our recommendation). For a mixture, the quantity of each species is set on the quotation for your block. Drill or plant in holes on bare soil after slash, or between crop rows if soil is accessible, when the soil is moist; broadcasting does not guarantee good germination, especially where the soil dries out easily. Mow when growth gets dense, to keep overgrowth in check and limit seed drop. Where PJ has not been grown before, ask us about inoculation with the right rhizobia. N fixation: no per-season figure is verified; the one sourced figure is the Thai rubber trial above, so expect less under mature palms. Mowed regularly, a PJ cover can persist for several years; re-sow where it thins.
Mucuna bracteata (MB): MB is not broadcast. Recommended seeding rate: 1 kg/ha sown alone, drilled or planted in holes. MB can also be raised in a nursery and transplanted; in MPOB's trial on deep peat, 320 seedlings/ha, two per palm point, were raised from about 500 seeds (75 g) (MPOB TT No. 501). It is slower to establish than PJ: ground cover reached about 100% at 6 months on mineral soil at 680 seedlings per hectare (Samedani et al., 2015), but 31% at 6 months and 58% at 12 months on deep peat at 320 seedlings per hectare (MPOB TT No. 501). Once established, it forms a dense, persistent ground cover. It is grown for ground cover and green manure, not harvested for grain. It derived 67-84% of its nitrogen from fixation in a 15N study under three-year-old oil palm in Malaysia (Cheah et al. 2010).
Calopogonium mucunoides (CM): Recommended seeding rate (sown alone): 10 kg/ha, drilled or planted in holes. No verified annual fixation rate. It establishes quickly: PROSEA notes it can cover the soil 3 to 6 months after sowing, but the plants are short-lived and are the first to be shaded out in a mixed cover (Chen Chin Peng & Aminah, 1997). Use it for fast early cover in the inter-row, alongside a persistent species.
Start With One Block
Do not replant the entire hacienda in one season. Pick a 1-2 hectare recently replanted block or a block with high weed pressure. If possible, pick a block where you have baseline weed data (hours of labor, number of weeding operations, weed density). Sow PJ seed, drilled or planted in holes, at 10 kg/ha sown alone or the rate on the quotation (or sow Mucuna bracteata the same way at 1 kg/ha, or transplant MB nursery seedlings) in April-May. Monitor every 2 weeks. Mow PJ if growth gets dense, to keep overgrowth in check and avoid a thick mat that could reduce air circulation. Assess soil and weed suppression in October, comparing the trial block to an adjacent untreated block.
If results are good, expand to the next block the following season. Document the cost savings and yield (if you weigh nuts) or nut count in the trial block. This data justifies the investment to neighboring farmers and your own farm management.
A cover crop can deliver savings in foregone weeding plus the value of the nitrogen it fixes, and improved soil structure and coconut health in year two and beyond; results vary by site. The compounding benefits come from improved soil structure and a reduced weed seed bank.
Coconut is a long-rotation crop. A small investment in soil biology and ground cover now can compound into better nut yield and lower labour cost over the productive life of the plantation; results vary by site.
References
Chen Chin Peng & Aminah, A. (1997). Calopogonium mucunoides Desv. In: Faridah Hanum, I. & van der Maesen, L.J.G. (eds). Plant Resources of South-East Asia No. 11: Auxiliary plants. Backhuys, Leiden.
Cheah, S.S., Zaharah, A.R. & Aminuddin, H. (2010). Biological nitrogen fixation by Mucuna bracteata under oil palm field environments. Oil Palm Bulletin 60: 22-27. Malaysian Palm Oil Board. https://palmoilis.mpob.gov.my/publications/OPB/opb60-Cheah.pdf
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
Hasnol Othman, Farawahida Mohamad Darus and Zulkifli Hashim (2012). Best management practices for oil palm cultivation on peat: Mucuna bracteata as ground cover crop. MPOB TT No. 501 (MPOB Information Series 588, June 2012). Malaysian Palm Oil Board. https://tot.mpob.gov.my/files/2020/02/TT-501.pdf
Samedani, B., Juraimi, A.S., Rafii, M.Y., Sheikh Awadz, S., Anwar, M. and Anuar, A.R. (2015). Effect of cover crops on weed suppression in oil palm plantation. International Journal of Agriculture and Biology 17(2): 251-260.
Tropical Forages: an interactive selection tool (2020 edition, CIAT and ILRI). Species fact sheet: Neustanthus phaseoloides (Pueraria javanica). tropicalforages.info