Dynamics of methane emission,active soil organic carbon and their relationships in wetland integrated rice-duck systems in Southern China

A randomized field experiment with three replicates was conducted in the subtropical region of China to investigate the effects of integrated rice-duck system (RD) on methane (CH₄) emission, active soil organic carbon fractions and their relationships in 2007 and 2008, compared with conventional rice system (CK). Methane emissions were measured at 7–9 days intervals using a closed static chamber technique, and two fractions of active soil organic carbon, namely, dissolved organic carbon (DOC) and microbial biomass carbon (MBC), were analyzed simultaneously. Soil DOC and MBC in RD and CK had similarly distinct seasonal variation patterns within the 2 years. During this time DOC and MBC concentrations were low at the early growth stage, increased during panicle differentiation and heading period, and dropped during grain filling period of rice. CH₄ emission fluxes from RD and CK followed a similar seasonal variation pattern both in 2007 and 2008. Two peaks of CH₄ emission were observed, the first at the tillering stage, second at panicle differentiation and heading stage. The CH₄ cumulative emission was reduced in RD by 19.3 and 19.6% in 2007 and 2008, respectively, compared with CK. Seasonal variation pattern of CH₄ emission was regulated by soil DOC, MBC and soil temperature, all of which were significantly positively correlated with methane emissions. Improvement in soil redox status was the predominant reason for significant reduction of CH₄ emission in RD. These results clearly indicate that integrated rice-duck system could be an effective mode of rice farming for decrease in methane emission in southern China.