Spatial Variability of Humification Degree in Tropical Peat of Oil Palm Plantations and Forests

Abstract

The productivity of crops largely depends on the peat’s degree of humification and the amount of fertilizer applied. Significant variability in oil palm growth within plantations suggests potential heterogeneity in peat humification at the local scale. However, the spatial variability of peat humification has not been previously demonstrated. This study aimed to compare the degree of peat humification between oil palm plantations and forests in East and West Malaysia, and to map its spatial distribution across the two ecosystems. The research was conducted in one-hectare plots divided into 20 m × 20 m subplots at Sebungan Oil Palm Plantation and Sabaju Secondary Forest in East Malaysia, and Amanah Saham Pahang Oil Palm Plantation and Pekan Forest Reserve in West Malaysia. The findings revealed that forest peat had a significantly lower C/N ratio than plantation peat, suggesting higher nitrogen accumulation relative to carbon. However, the C/N ratio did not correlate with spectroscopic humification indices, which indicated a higher degree of humification in plantation peat. This suggests that direct comparison of C/N ratios between forest and plantation peat may be inappropriate due to differences in nitrogen cycling. Mapping of the humification degree demonstrated some degree of spatial variability. The weak correlation between humification degree and soil moisture indicates that other factors, particularly those related to plantation management, may also influence peat humification.