Organic carbon mineralization in various size aggregates of paddy soil under aerobic and submerged conditions.

With incubation tests in laboratory, the mineralization of organic carbon in various size aggregates of paddy soil was investigated under aerobic and submerged conditions. The results showed that the organic carbon mineralization in various size aggregates decreased quickly at the beginning of the incubation, but remained stable during the late period of incubation. The mineralization rate varied significantly with the size of the aggregates. Through the incubation time, the organic carbon in 1-2 mm aggregates had the highest mineralization rate, while that in < 0.053 mm aggregates had the lowest one. Statistic analyses indicated that the mineralization rate of organic carbon in various size aggregates was significantly and linearly correlated with the contents of organic carbon and microbial biomass carbon in the aggregates. 0.25-1 mm aggregates had the highest contribution to the cumulative mineralization of soil organic carbon, accounting for 41.77% under aerobic condition and 34.11% under submerged condition, while < 0.053 mm and 1-2 mm aggregates had the lowest contribution under aerobic and submerged conditions, accounting for 7.8% and 6.6%, respectively. [ABSTRACT FROM AUTHOR]