The effects of forest conversion to oil palm plantation on soil quality in the Kaos sub-watershed, Indonesia

Several countries have experienced widespread forest conversion, including Indonesia where Jambi Province is the most affected region. The majority of forests in the province have been converted to oil palm plantations. Between 1995–2018, 7,846 hectares of secondary forest in the Kaos sub-watershed were converted to oil palm plantations. Land conversion causes soil degradation that, in turn, impacts soil quality. Therefore, the aim of this study was to determine the potential change in soil quality (and the main factors that affect soil quality) as land undergoes conversion from secondary forest to oil palm plantations. Soil samples were taken from six locations in a secondary forest, a cleared forest area, and oil palm plantations of four different age classes, and a soil quality index (SQI) was calculated for each land use. Principal Component Analysis (PCA) was used to evaluate the soil data. SQI values in the Kaos sub-watershed ranged from 0.45–0.53, which indicates that the soils are of medium quality. The greatest SQI value (0.53) was associated with the secondary forest site, while the lowest SQI value (0.45) was found on oil palm plantation #1 (age class: 0–5 years). Furthermore, the factors that affected SQI in our study were found to be base saturation, organic carbon content, and bulk density. In conclusion, the conversion of secondary forest to oil palm plantations in the Kaos sub-watershed causes a decrease in the SQI values.