Potential aerobic C mineralization of a red earth paddy soil and its temperature dependence under long-term fertilizer treatments

Topsoil samples from a long-term fertilizer trial on a red earth rice paddy from Jiangxi Province, China, were used to investigate soil organic carbon (SOC) mineralization using aerobic incubation for 58 days at 20 degrees C and 25 degrees C. SOC mineralization rates varied between 0.62 and 0.76 mg C/g SOC/h at 20 degrees C, and between 0.65 and 0.97 mg C/g SOC/h at 25 degrees C. There was no significant correlation between the mineralization potential and SOC content in treated soil samples. However, a close correlation was found between total C mineralization and the carbon stability index. This suggests that the potential C release from the soil is controlled by C lability rather than by total SOC. The calculated Q10 quotient was negatively correlated with dithionate-citrate-bicarbonate-extracted Fe. It is suggested that the free Fe-oxyhydrates that are prevalent in red earth paddy soils provide physico-chemical protection and control biological decomposition rates under warming and these are modified in the long-term fertilizer treatments. The enhancement of physico-chemical protection of labile SOC by free Fe-oxyhydrates is a potential mechanism for soil C stabilization under warming conditions. The interaction with fertilizers in the red earth-derived paddies of South China deserves further study.