Methane production and its fate in paddy fields

The effects of the application level of rice straw and percolation rate on the leaching amounts of methane, total water soluble organic carbon (TOC), hexose, Fe2+, and Mn2+ with percolating water were investigated in a soil column experiment. The amount of methane in the leachate was larger as the application level of rice straw (0.3–1.0 × 10-2 kg kg-1) increased. The methane concentration in the leachate reached a saturation level around the 18th day after incubation in the 0.6 and 1.0 × 10-2 kg kg-1 rice straw treatments, and remained at the same level afterwards. In the treatments with percolation rates of 0.26, 0.52, and 1.0 cm/d, the methane concentration in the leachate did not change. The total amounts of methane percolated during a 30 d period corresponded to ca. 3, 7, and 15% of the estimated methane production from rice straw in a whole crop season, respectively. The amounts of percolated TOC, hexose, Fe2+, and Mn2+ also increased with the increase of the application level of rice straw and the percolation rate. The maximum amount was reached on the 6–15th days, and it subsequently decreased in contrast to the increase of the methane level.