Estimation of soil organic carbon turnover using natural 13C abundance in Asian tropics:: A case study in the Philippines

The organic carbon (C) content and natural C-13 abundance (delta(13)C) of two series of forest and sugarcane soils from Central Luzon and Negros Island in the Philippines were analyzed to determine the origin and turnover of soil organic C in the Asian tropics. The organic C contents and delta(13)C values were investigated after a long period (years) of sugarcane cultivation following forest clearing. Conversion of forest areas to field for sugarcane cultivation had been associated with a rapid decrease of the soil organic C content and increase of the soil delta(13)C values. The easily mineralisable compartment accounted for 95 and 98.5% of forest-derived C and the half-lives were 1.2 and 1.8 years in Central Luzon and on Negros Island, respectively. On the other hand, sugarcane-derived C accumulation accounted for 25 and 22% of the soil organic C content of natural forests.