[Effects of long-term fertilization on paddy soil organic carbon mineralization]

An incubation test was conducted with the paddy soil samples collected from three national long-term experiment stations in Hunan Province to study the characteristics of organic carbon mineralization under different fertilization treatments and its relationships with organic carbon fractions, i.e., total organic carbon (TOC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC). The results showed that in all fertilization treatments, the cumulative amounts of CO2 and CH4 ranged from 448.64 to 1516.77 microg x g(-1) and from 15.60 to 33.34 microg x g(-1), respectively. In the 58 days of incubation, the mineralized carbon accounted for 3.59%-5.57% of TOC. The CO2 production rate was higher in the early phase of incubation, decreased rapidly then, and tended to stable afterwards; while the CH4 production rate had a slow increase first and declined rapidly then. A combined application of chemical fertilizers and manure or straw increased the cumulative amounts of CO2 and CH4 significantly. In all fertilization treatments, the cumulative mineralized C had significant correlations with TOC, MBC and WSOC, but less correlation with its percentage in TOC.