Seasonal changes in fluxes of methane and volatile sulfur compounds from rice paddies and their concentrations in soil water.

摘要

Fluxes of methane and dimethyl sulfide (DMS), and the concentrations of methane, DMS and several other volatile sulfur compounds in soil water and flood water were measured in four lysimeter rice paddies (2.5 X 4 m, depth 2.0 m) once a week throughout the entire cultivation period in 1995 in Tsukuba, Japan. The incorporation of rice straw into paddy soil was also examined for its influence on methane or DMS emissions. The annual methane emission from plots with rice straw (37.7 g m-2) was approximately 8 times higher than that from those without (4.8 g m-2). Application of rice straw had little influence on DMS fluxes. Significant diurnal and seasonal changes in DMS fluxes were observed. Peak DMS fluxes occurred around noon. DMS was emitted from the flood water in the early growth stage of rice and began to be emitted from rice plants during the middle stage. DMS fluxes increased with the growth of rice plants and the highest flux, 15.1 鎔 m-2 h-1, was recorded before heading. DMS in the soil water was negligible during the entire cultivation period. These facts indicate that the DMS emitted from rice paddies is produced by metabolic processes in rice plants. The total amount of DMS emitted from rice paddies over the cultivation period was estimated to be approximately 5-6 mg m-2. CH3SH was emitted only from flood water during the first month after flooding.