Biochar from oil palm biomass: how charcoal improves tropical acid soils and cuts emissions

Every year, the Malaysian palm oil industry generates large volumes of biomass: empty fruit bunches (EFB), mesocarp fibre, palm kernel shells, fronds, and trunks from replanting. Most of this material is left in the field to decompose, burned in mill boilers for energy or, in older operations, openly burned at disposal sites. Converting this biomass to biochar offers a different pathway: turning agricultural residues into a stable soil amendment that can improve acid tropical soils, reduce nutrient leaching and keep carbon in the soil for many years.

Biochar is widely studied as a way to keep carbon from crop residues in the soil instead of releasing it to the air, and estimates for Malaysian oil palm residues depend heavily on the feedstock, the pyrolysis process and how the biochar is used. For an industry navigating increasingly stringent RSPO sustainability requirements, biochar is both an agronomic option and a possible carbon accounting asset.

What biochar does to acid tropical soils

Biochar is produced by heating organic material with little or no oxygen: a process called pyrolysis. The resulting charcoal-like material has a highly porous microstructure, a large internal surface area, and a predominantly alkaline pH (how alkaline depends on production temperature and feedstock). These physical and chemical properties produce several simultaneous soil improvements when biochar is incorporated into Malaysian acid Ultisols and Oxisols.

pH buffering is the most immediate effect. EFB biochar is alkaline, so mixing it into acid soil raises soil pH; how far depends on the biochar, the rate applied and the soil's buffering capacity. Unlike lime, which reacts relatively quickly, biochar is resistant to microbial decomposition, so it stays in the soil for many years and part of its effect persists.

Cation exchange capacity (CEC) can increase after biochar addition. The large surface area of biochar particles, combined with negatively charged functional groups on their surfaces, provides new sites for holding K+, Ca2+, Mg2+, and NH4+ ions. Pot and field trials report CEC increases after biochar amendment, most clearly on low-CEC sandy soils: the same soils where potassium leaching is most severe. Where CEC rises, more of the applied nutrients can be held in the root zone instead of being lost to drainage.

Lower nitrogen leaching is one of the more frequently reported effects. Studies with biochar, including biochar made from EFB, have reported less ammonium-N leaching from amended soil than from unamended soil under heavy simulated rainfall. On sloping soils where nitrate and ammonium loss to drainage is a significant cost and environmental issue, biochar amendment may help improve the nitrogen use efficiency of applied urea and compound fertilisers.

Water retention in sandy and degraded soils

Biochar's porous microstructure holds water within its internal channels. This micro-reservoir can buffer soil moisture during the short dry spells that occur in El Nino years in Peninsular Malaysia and Sabah. On degraded sandy soils, biochar-amended plots can hold more moisture in the days after rain than unamended soil. For oil palm facing bunch abortion during heat stress and water deficit, this extra buffering may help reduce moisture stress during short dry spells.

Biochar and soil biology

The porous structure of biochar provides habitat for soil microorganisms. Bacteria and fungi colonise biochar pores, where they are protected from predation and desiccation. In the months and years after application, field studies have reported higher microbial biomass carbon, greater diversity of bacterial genera and higher enzyme activity (for example phosphatase and urease) in biochar-amended soils than in unamended controls, although results vary with soil and biochar type.

This biological activity can add to the chemical effects of biochar. Higher phosphatase activity releases phosphorus from organic sources, and higher urease activity speeds the conversion of urea to plant-available ammonium. Used alongside soil conditioners such as SoilBoost EA and organic inputs, biochar can be part of a programme to build a biologically richer root zone.

Application rates and practical considerations

EFB biochar is available from some Malaysian palm oil mills that have invested in pyrolysis units. Set the rate for an initial amendment of degraded or strongly acid soils, and for any follow-up applications, from a soil test and a small block trial, because published responses vary widely with soil, biochar quality and rate. Biochar usually costs more per tonne than lime; whether its longer persistence makes it competitive depends on local biochar prices and the response measured on your own soils.

Biochar is most effective when incorporated into the topsoil rather than surface applied, as incorporation maximises contact with the root zone. At replanting, biochar mixed into planting holes delivers concentrated soil improvement at the point where young palm roots first develop. In mature stands, biochar can be surface applied to the palm circle and worked into the soil during normal interrow management operations.

Combined with organic inputs such as CSB Organico, EFB mulch and leguminous cover crop biomass from Pueraria javanica, biochar can be one part of a soil programme for Malaysian acid plantation soils.