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 meth ane emission which is enhancing global warming. To estimate decomposit ion processes of organic carbon in paddy soil quantitatively, firstly, kinetics of anaerobic decomposition of soil organic carbon (C) were i nvestigated in laboratory experiments with or without organic amendmen ts at 5, 20, 30 and 40 degrees C for 84 days of incubation. Produced C H4, CO2 and accumulated fatty acids were measured periodically, and fi rst-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 paramete rs included in the model with those of adjacent upland soil, paddy soi l contained smaller but faster components of decomposable organic matt er. Secondly, methane emission from paddy soil was examined in paddy s oil microcosms to find the possible mitigation options for reduction o f the emission. Ammonium sulfate and potassium sulfate (S) were applie d to compare with ammonium chloride and potassium chloride(C). Additio nally ferrous oxide (F) was also applied to half sets of each treatmen t to make totally four treatments. Methane emission rate was significa ntly reduced by addition of S, much more effective than addition of F. Gas formation in the soil corresponded with the amendments, and the r atio of produced CH4 to CO2 decreased by addition of S at peak time of methane emission. (C) 1997 IAWQ. Published by Elsevier Science Ltd.