Oil palm empty-fruit bunch application effects on the earthworm population and phenol contents under field conditions
The amounts of polyphenols at several stages of oil palm empty-fruit bunch (EFB) composting, the types of phenol compounds in several types of EFB composting processes and the effects of phenol compounds on EFB composting in an earthworm population were evaluated under field conditions. The amount of extractable phenols from decomposed EFB increased at the early stage of decomposition and decreased with increasing age of the EFB compost. The phenol content in soil with added EFB did not differ from that in the control soil. Under an open system and in the presence of soil, the phenol released from EFB easily degraded. The empty fruit bunches released phenol into their surroundings and no harmful effects were found on the earthworm population under the natural system. Using gas chromatograph-mass spectrometry (GC-MS), 2,4-bis(1,1-dimethylethyl) was identified in fresh EFB which was similar to the type of phenol compound in composted and field-decomposed EFB; 2,6- bis(1,1-dimethylethyl). In contrast, no phenolic compounds were detected in the vermicomposted EFB. This means that the vermicomposting process can be used to degrade toxic compounds such as phenol. Compared to normal compost, vermicompost contains fewer toxic compounds, which might be related to its advanced decomposition stages.
Key words: Earthworm population, oil palm waste, EFB composting, phenolic compounds