Anaerobic decomposition of organic carbon in paddy soil in relation to methane emission to the atmosphere

Paddy fields are regarded as one of the most important sources of methane emission which is enhancing global warming. To estimate decomposition processes of organic carbon in paddy soil quantitatively, firstly, kinetics of anaerobic decomposition of soil organic carbon (C) were investigated in laboratory experiments with or without organic amendments at 5, 20, 30 and 40 °C for 84 days of incubation. Produced CH4, CO2 and accumulated fatty acids were measured periodically, and first-order kinetics models were applied to the amount of decomposed C. Two components' model fitted decomposition pattern for unamended soil, but not for glucose or alanine-amended soils. To compare the parameters included in the model with those of adjacent upland soil, paddy soil contained smaller but faster components of decomposable organic matter. Secondly, methane emission from paddy soil was examined in paddy soil microcosms to find the possible mitigation options for reduction of the emission. Ammonium sulfate and potassium sulfate (S) were applied to compare with ammonium chloride and potassium chloride (C). Additionally ferrous oxide (F) was also applied to half sets of each treatment to make totally four treatments. Methane emission rate was significantly reduced by addition of S, much more effective than addition of F. Gas formation in the soil corresponded with the amendments, and the ratio of produced CH4 to CO2 decreased by addition of S at peak time of methane emission.