The use of oil palm empty fruit bunch, an agricultural waste from oil palm plantations, as a feeding material for earthworms during composting provides an alternative source of nutrients for plants. Information regarding the ability of earthworms in processing phosphorus-enriched empty oil palm fruit bunch and their effects on plants is still lacking. The objective of this study was to compare the effects of phosphorus-enriched empty oil palm fruit bunches applied as fresh, composted or vermicomposted media in supplying nutrients on a test crop, Setaria splendida L., grass planted on Bungor (Typic Kandiudult) soil. The soil treated with phosphorus-enriched vermicomposted empty oil palm fruit bunch increased the grass dry matter yield significantly higher compared to that treated with composted empty oil palm fruit bunch and control. The root volume of vermicomposted-and composted-empty oil palm fruit bunches treated soil was similar but significantly greater than the control. There was significant interaction between dosage and type of growing media on cumulative N, P, K, Ca, and Mg uptake. However, these factors did not show significant influence on total N, P, Ca and Mg in the soil amended with composted oil palm empty fruit bunch at the end of the experiment. In general, phosphorus-enriched vermicompostedand phosphorus-enriched composted-empty oil palm fruit bunches treated soil resulted in a greater positive effect on growth and nutrient uptake of S. splendida, and also on the total nutrient content in soil except for total K. Total soil K in the control treatment was 242.0 mg/kg and significantly higher compared to soil treated with composted-(173 mg/kg) and vermicomposted-empty oil palm fruit bunches (167 mg/kg). The vermicomposted empty oil palm fruit bunch resulted in better growth performance of the S. splendida in comparison to composted-and fresh-empty oil palm fruit bunches due to the readily available P and other nutrients being readily available to the plants.
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; 2,6bis(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.
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