Soil carbon sequestration potential under different land use systems in tropical highlands

Abstract:

How much carbon can tropical highland soils hold, and does the type of land use determine the answer? This research quantified soil organic carbon (SOC) stocks and sequestration rates under six land use systems in the highlands of Johor, Malaysia, between 2021 and 2023. Soil samples were collected at 0-15 cm and 15-30 cm depths from natural forest, rubber plantation, oil palm plantation, rubber-based agroforestry, annual crops (paddy-vegetable rotation), and degraded grassland. Natural forest held the highest carbon stock at 86.2 Mg C/ha in the top 30 cm, followed by agroforestry at 67.8 Mg/ha. Degraded grassland stored the least at 26.8 Mg/ha. Microbial biomass carbon and potentially mineralizable nitrogen mirrored the SOC rankings. Conversion of forest to annual cropping reduced soil carbon stocks by 57.8%, while agroforestry retained 78.6% of the forest carbon. These findings support agroforestry as a land use strategy that balances agricultural production with meaningful carbon sequestration in tropical highland landscapes.