Organic carbon sequestration at gambier (Uncaria gambier L.) cultivation in sloping area under wet tropical region

Abstract

Organic carbon (OC) is an important factor for soil and the environment. This research aimed to identify OC sequestration under different age of gambier crops in central Gambier, Pesisir Selatan, West Sumatra. Soil samples were taken from different crop ages ( 2, 5, and 10 years old), and then under secondary forest nearby as a comparison at 0-30 cm soil depth. The results showed that, in general, soil OC content was considered low to very low either under Gambier crops (<2%), or under forest land use (2.11%). Then, the OC stock increased by increasing crop age from 2 to 10 years old. The OC stock at ten years old Gambier reached 90% of that at the forest on the top 30 cm soil depths. Rate of OC sequestration was approximately 1.03 Mg ha-1 y-1 and 4.88 Mg ha-1 y-1, respectively, for crop age between 2 and 5 as well as between 5 and10 years old. This low soil organic carbon (SOC) content combined with fine soil particles caused the soil had medium-high soil BD, low-medium total soil porosity, rather slow-medium hydraulic conductivity rate, and unstable-rather stable soil aggregate stability. The study concludes that SOC sequestration under Gambier plantation in the sloping area was quite slow, especially during the first five years due to new crop establishment and the leaves harvested.