METHANE PRODUCTION AND ITS FATE IN PADDY FIELDS .3. EFFECTS OF PERCOLATION ON METHANE FLUX DISTRIBUTION TO THE ATMOSPHERE AND THE SUBSOIL

Special attention is being paid to methane fluxes from paddy fields in relation to the greenhouse effect. However, the flux to the atmosphere is not the sole flux direction of methane produced in paddy soils. A pot experiment where rice plants were grown was conducted to analyze the effects of the percolation rate and rice straw application on the methane fluxes both to the atmosphere and subsoil. The amount of methane carbon percolated to the subsoil was evaluated in comparison with other forms of organic carbon in the leachate. The increase of the percolation rate accelerated the methane fluxes to the subsoil, while it did not affect the methane fluxes to the atmosphere. Application of rice straw increased the methane fluxes in both directions until the panicle initiation stage of rice plants. The total amount of methane flux to the subsoil accounted for 8.6% of the sum of the amount of emitted and leached methane under 15 mm/d percolation condition. The amount of methane carbon in the leachate was larger than that of the total dissolved organic carbon after the panicle initiation stage.