By Kudzuseeds Agronomy Team

Most coconut plantations in the Philippines are bare. Soil is 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 30°C sun and Luzon humidity loses moisture to evaporation, loses nitrogen to volatilization, and fills with hagonoy (Chromolaena odorata) and cogon (Imperata cylindrica) within one season (Tan & Zaharah 2015). Slash-and-burn weeding is labour-intensive. In older plantations with deep cogon establishment, one manual weeding campaign takes 15-20 labor days per hectare.

A legume cover crop—pueraria (PJ), Mucuna bracteata (MB), or Calopogonium mucunoides (CM)—does not compete for water or nutrients with coconut. It fixes atmospheric nitrogen, suppresses weeds through shading, and costs less than one round of manual weeding. Once established, it requires only mowing or soft slashing, not digging. The return is visible in the first season and compounds year after year.

Why Nitrogen Matters Under Coconut

Coconut yield (copra, oil, or dried kernel mass) is nitrogen-limited on most Philippine soils. A palm producing 80-100 nuts/year removes 40-60 kg N/hectare annually. If soil organic matter is below 2%—common on old coconut soils where residue is burned or removed—mineralized N from organic matter cannot replace this loss. Instead, the soil becomes progressively depleted. Yield plateaus around 50 nuts/palm, well below the 80-100 potential under good nutrition (Tan & Zaharah 2015).

Applied urea closes some of the gap, but it is a recurring expense, so farmers often apply only one application per year (20-30 kg N/hectare), leaving a deficit of 10-30 kg N/hectare that compounds over years. A legume cover fixing 50-80 kg N/hectare per season requires only seed and labour, and no further input. It also does not volatilize like applied urea; fixed N is stable and builds organic matter as well.

The N-fixing capacity depends on legume species, rainfall, and soil P availability. Under good conditions (adequate P, moist soil), PJ fixes 60-90 kg/hectare/season. MB is a strong fixer (deriving 67-84% of its nitrogen from fixation) and the highest-biomass of these species, though slower to establish. CM fixes 80-120 kg/hectare but is slower to establish and less suitable for under-palm use. PJ is the standard choice for mature coconut.

Pueraria and Mucuna bracteata Suppress Weeds

Hagonoy and cogon germinates in bare soil gaps, especially during the months after the monsoon when soil is moist and air is warm. Pueraria establishes a dense ground layer (80% cover by week 12) that blocks light and prevents germination of competing weeds. Mucuna bracteata establishes more slowly but forms a dense, persistent, high-biomass cover (60-70%) that can be managed with a single mid-season mow (Chong 2019). Both systems reduce manual weeding from 2-3 operations per year to 1, or eliminate it entirely if the cover is maintained through light mowing.

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 do not regenerate. If hagonoy and cogon are already present at high density, slash before sowing legume, allow 10 days 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 three years, a cover crop replaces repeated manual weeding cycles with a single establishment and occasional light mowing. The labour saved alone justifies the investment.

Soil Moisture and Litter Effect

Bare coconut soil under intense sun loses 2-4 mm of moisture per day through evaporation (Chong 2019). Legume canopy and mulch (leaves of dead PJ or MB) reduce surface evaporation by 30-50% and cool the soil by 2-4°C. Soil moisture at 15 cm depth on legume-covered plots was 18% compared to 12% on bare plots in Quezon trials. This matters in dry spells between northeast and southwest monsoon, when coconut water stress limits nut set and kernel development.

The litter layer (2-4 cm of dried legume leaves) improves soil structure and feeds microbial activity. Organic matter content of the top 10 cm increased from 1.8% to 2.4% after two seasons of PJ cover in a Laguna trial. This is not trivial: 0.6% OM gain over 24 months is substantial in tropical soils where decomposition is fast. Higher OM means more water-holding capacity, more nutrient-holding capacity, and more food for microbes that mineralize nutrients for the palm.

Pueraria and Mucuna bracteata: Establishment Guide

Pueraria (PJ): Seed rate 4-6 kg/hectare. Broadcast on bare soil after slash, or between crop rows if soil is accessible. Germinates in 7-10 days if soil is moist. Establishes vines in 8-12 weeks. Mowing at week 16 and week 28 controls overgrowth and prevents seed drop. Rhizobia are present in most Philippine soils; inoculation is rarely needed, though it does not hurt. N fixation: 60-90 kg/hectare/season. Can persist 2-3 years if mowed regularly, or replanted each year.

Mucuna bracteata (MB): Established by nursery transplant at about 320 seedlings/hectare (about 85-100 g seed/hectare), not broadcast by the kilogram. Slower to establish than fast-broadcast PJ, but once established it forms a dense, persistent, long-lasting ground cover. Mow at physiological maturity for green manure incorporation; it is grown for ground cover and green manure, not harvested for grain. A vigorous perennial and the highest-biomass of these legume cover crops, it is a strong nitrogen fixer (deriving 67-84% of its nitrogen from fixation).

Calopogonium mucunoides (CM): Seed rate 4-6 kg/hectare. Most vigorous fixer (80-120 kg/hectare/season) but slowest to establish (14-18 weeks to full canopy). Best for blocks with severe cogon infestation. Allelopathic effects are strong. Not suitable under-palm where vigorous vines can shade the crown. Better for inter-row use.

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). Broadcast 4-6 kg PJ seed (or transplant Mucuna bracteata nursery seedlings at about 320 seedlings/hectare) in April-May for June-August cover. Monitor every 2 weeks. Mow PJ at week 16 if growth is dense; this controls overgrowth and prevents 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—and they will be—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 delivers savings in foregone weeding plus the value of nitrogen fixed (50-80 kg/hectare), with a net financial benefit in year one, plus improved soil structure and coconut health in year two and beyond. 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 compounds into higher nut yield and lower labor cost over the next 10-15 years of plant and ratoon cycles.

References

Tan & Zaharah (2015) Legume cover crops and nutrient cycling in coconut-based agroforestry systems. Journal of Tropical Agriculture 53(2):112–120.

Chong (2019) Soil moisture and microbial community under legume intercrops in tropical coconut plantations. Malaysian Agricultural Journal 12(1):45–53.

Eroy (2019) Humic acid application and soil chemical properties in acid soils. PCA-Davao Field Trial, FPA Registry.