Oil palm peat ecosystem do not emit as much greenhouse gas (GHG) as what has been previously postulated. When plantations are established on peat, it is postulated that 86t/ha/yr of CO₂ emission will occur. The range of CO₂ emission is from 73 to 100 t/ha/yr⁽¹⁾. This postulation does not take into account the possible methane and nitrous oxide emissions.

Carbon dioxide, methane and nitrous oxide are the dominant GHG that are emitted when peatland is drained and cultivated. The fluxes of these three GHG were measured in an oil palm plantation planted on peat in Sarawak, Malaysia over a period of one year. Measurements were done with below canopy technique  by using the “closed chamber”. The oil palms were 4 years old and planted at a density of 160 palms/hectare. The water table in the field was kept at 50-70 cm from the soil surface.

CO₂ emission was found to be 1.5 kg C/m²/yr⁽²⁾. Nitrous oxide emission amounted to 3.3 kg N /ha /yr⁽³⁾. On the other hand, the oil palm ecosystem was found to be a methane sink with an uptake of 15.14 mg C /m²/yr⁽⁴⁾. This was so because the water table had been lowered for oil palm cultivation. This increased the thickness of the aerobic zone in the soil solum. In addition, drainage and compaction in the oil palm ecosystem also increased the soil bulk density by 33%. Such compaction also reduced the diffusion of methane upwards.

Table 1: Total emission of major GHG in oil palm plantation on peat

Notes: +  indicates source;  – indicates sink; global warming potential (GWP) of CH₄  is 23; GWP of N₂Ois 296

The emissions ofthese three GHG are converted into CO₂ equivalents based on theirglobal warming potentials (Table 1). The total GHG emission is 56 tonnes CO₂/ha /yr.

In reality, the GHG emission is expected to be evenlower if carbon sequestration by the growing oil palms is taken into account.The carbon stock value of oil palm plantations, excluding below ground biomass,but including litter, palm residues and dead wood accumulation in soil iscalculated to be 165 t  CO₂ /ha/yr⁽⁵⁾.Thus, the amount of CO₂ emitted from the peat surface would not beenough for the carbon requirement by the oil palm annually. Thus, the oil palmis a net carbon sink. This leaves behind the other two GHG viz.  N₂O and CH₄ ,which when combined,have a net GWP of only 1,111 kg CO₂ /ha/yr.

References used

1. Hooijer,A., Silvius,M., Wosten,H., Page,S.2006.PEAT-CO2, Assessment of CO2 emissions from drained peatlands in SE Asia. DelftHydraulics report Q3943).

2. Melling,L.,Hatano,R., Goh,K.J.2005. Soil CO₂ flux from three ecosystems intropical peatland of Sarawak, Malaysia. Tellus B, 57,1,1-11.

3. Melling,L.,Hatano,R., Goh,K.J. 2007. Nitrous oxide emissions from three ecosystems intropical peatland of Sarawak, Malaysia. Soil Science  & Plant Nutrition, 53, 792-805.

4. Melling,L., Hatano,R., Goh,K.J. 2005. Methane fluxes from three ecosystems in tropical peatland of Sarawak, Malaysia. SoilBiology  & Biochemistry, 37,1445-1453.

5.Wicke,B.,Dornburg,V., Junginger,M., Faaij,A. 2008. Different palm oil production systemsfor energy purposes and their greenhouse gas implications. Biomass andEnergy.32,1322-1337 IN MPOB’s “Concerns with the EPA Notice of DataAvailability (NODA) concerning renewable fuels produced from palm oil under theRFS Program”.

Article credit: Dr.Yew Foong Kheong