Oil palm trunk recycling at replanting: why zero-burn is the right agronomic and environmental choice

At the end of a 25-year oil palm production cycle, each hectare contains approximately 143 mature palms. When these palms are felled for replanting, each trunk weighs between 300 and 600 kg, containing significant reserves of organic matter, potassium, nitrogen, and other nutrients accumulated over the crop's lifetime. The decision of what to do with this biomass at replanting has profound consequences for the next crop's soil environment: and for the long-term productivity trajectory of the estate.

For decades, burning was the default practice. A felled palm block was torched, reducing trunks and fronds to a thin layer of ash within hours. The ash supplied a brief flush of soluble minerals, but the vast majority of the organic matter and nitrogen in those trunks was sent into the atmosphere as smoke: contributing to haze, releasing greenhouse gases, and destroying the biological community within the trunks that was actively building soil. Zero-burn replanting, now mandated under Malaysian government policy and RSPO certification requirements, mandates chipping, stacking, or field-returning felled biomass rather than combustion.

What trunks contain: the organic capital being preserved or lost

A fully mature oil palm trunk contains approximately 150 to 200 kg of organic matter, 1.5 to 2.5 kg of nitrogen, 1.8 to 3.0 kg of potassium, and substantial quantities of calcium, magnesium, and phosphorus accumulated over 25 years. Multiplied by 143 palms per hectare, trunk biomass at replanting represents a nutrient capital equivalent to several years of fertiliser applications. Burning releases virtually all the nitrogen as volatile ammonia and nitrogen oxides, and converts most of the organic carbon to CO2. Only the inorganic minerals: K, Ca, Mg: remain in the ash.

Zero-burn retains this nitrogen and organic carbon in the field. As trunk material decomposes over 2 to 3 years following replanting, the organic nitrogen mineralises gradually into the root zone of the new young palms. Published data from MPOB-managed trials show that zero-burn replanting results in significantly greater soil organic carbon (SOC) in the 0 to 30 cm layer compared to burned replanting after 5 years, with measurable improvements in CEC, water holding capacity, and microbial biomass carbon.

The challenge: Ganoderma inoculum in trunk debris

Zero-burn's primary agronomic complication is that felled trunks from Ganoderma-infected blocks retain viable fungal inoculum. Leaving infected trunk material in the field maintains the pathogen's capacity to infect new palms as their roots grow into the debris zone during the first 2 to 5 years after replanting. This is the primary reason some growers historically preferred burning: it eliminated inoculum alongside the biomass.

Research-based solutions to this challenge exist. On infected blocks, complete removal of trunks and root balls from the field (chipping and transport off-site) is the most effective approach: it eliminates both the inoculum and the physical trunk material, preventing root-to-root contact transmission. On blocks with low or moderate BSR history, chipping trunks to small fragments and spreading them across the interrow accelerates decomposition by maximising surface area, reducing the moist, intact wood microhabitat that sustains Ganoderma, and increasing microbial access to organic matter.

Accelerating trunk decomposition with soil conditioners

Intact oil palm trunks have a high carbon-to-nitrogen ratio (C:N ratio of 50:1 to 80:1), which slows natural decomposition by starving the microbial community of nitrogen. Without supplemental nitrogen, trunk material can persist largely intact for 5 to 7 years: long enough to create a physical obstacle to planting operations and maintaining the high-C environment that favours fungal growth over the bacteria-driven mineralisation that builds available soil nutrients.

Adding nitrogen to chipped trunk material: either as urea solution applied to chip piles, as POME, or through biological soil conditioners: reduces the effective C:N ratio and dramatically accelerates decomposition. Trials applying organic soil conditioners to chipped trunk windrows in Sabah and Johor show that treated material reaches 60 to 70% decomposition within 18 months versus 36 to 48 months in untreated controls. SoilBoost EA applied to chip piles at establishment, and to the interrow during the first year of the new crop, stimulates the enzyme activity (cellulases, ligninases) that breaks down the fibrous trunk material and incorporates its carbon into stable humus rather than releasing it as CO2.

Cover crops during the immature phase

The first 3 years after replanting (the immature phase) are when ground cover management most directly shapes the soil environment the new crop will grow in for its entire 25-year productive lifespan. With no canopy, the soil surface is exposed to full tropical sun and intense rainfall. Establishing leguminous cover crops: Mucuna bracteata, Pueraria javanica: in the interrow between rows of decomposing trunk chips creates a protective and productive ground cover that suppresses weeds, fixes atmospheric nitrogen, and prevents erosion of the loose, freshly disturbed soil.

The combination of decomposing trunk biomass (organic matter and nutrient source), leguminous cover crops (nitrogen fixation and erosion protection), and biological stimulants for decomposition creates the foundation for a high-organic, biologically active soil profile that will sustain the new crop into peak production. This foundation cannot be retroactively applied once the young palms close canopy at 3 to 4 years: it must be built during the replanting window.

For estates committed to long-term soil health and RSPO compliance, zero-burn with trunk recycling and leguminous cover crop establishment is the most evidence-based approach to maintaining plantation productivity across replanting cycles. CSB Organico applied to young palms during the immature phase: alongside cover crops and trunk decomposition: completes the nutrient cycle, ensuring that the organic capital preserved at replanting flows effectively into the new crop system.