Impact of agricultural land use on soil organic carbon sequestration at sub-catchment scale

Soil organic carbon (SOC) pool determines the potential of soil to perform ecosystem services and maintain climatic stability. Land use plays a significant role in determining the carbon (C) sequestration in soil. This study aimed to determine the impact of long-term agricultural land uses on SOC and other physico-chemical properties and to determine interrelationships between SOC stock and topographic variables at sub-catchment scale in upcountry of Sri Lanka. Soil samples were collected from surface (0-30 cm) and subsurface (30-60 cm) at 109 locations from vegetable (n = 42), tea (n = 44) and forest (n = 23) land uses in a sub-catchment (360 ha) in Nuwara Eliya. Average SOC in different land uses were compared by analysis of variance followed by Tukey post-hoc mean comparison. The largest surface SOC stock was observed in forested area (71.8 Mg/ha) followed by vegetable lands (61.8 Mg/ha) and it was significantly lesser in tea lands (50.7 Mg/ha). The forest soils showed the largest subsurface SOC stock (67.1 t/ha) as well, followed by tea (64.8 Mg/ha) and vegetable (57.9 Mg/ha) land uses. No significant relationship was observed between SOC stock and topographic variables, namely elevation, slope, wetness index and stream power index. This study concludes that the land use is a key determinant of the spatial heterogeneity of SOC and forest have the greater ability of sequestering C compared to vegetable and tea land uses in the studied sub-catchment area.