Methane Oxidation in Subsoil Leached from Plow Layer of Paddy Field

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Retention and oxidation in subsoil of ferrous iron percolated from plow layer were well known in paddy fields. This finding suggested the possibility of methane oxidation in subsoil percolated from the plow layer. The followings are the first results of methane oxidation in subsoil of paddy fields.1.The amounts of methane percolated to subsoil increased proportionally with the increase of amounts of percolating water. The growth of rice plant decreased the amounts of methane percolation to subsoil due to accelerating the methane fluxes to the atmosphere. The percolated methane to subsoil was more than 10% of the amounts of methane to the atmosphere.2.Large portion of methane dissolved in percolating water was oxidized in subsoil. But the remained methane was considered to be carried to the lower parts of subsoil without oxidation. This was because the anaerobic oxidation of methane requires organic substrates by methane oxidizing microorganisms, and the substrates in percolating water were not enough for complete oxidation of methane.3.Subsoil decomposed and/or retained the organic materials percolated from plow layer with percolating water. The subsoil of Fukushima soil both decomposed and retained methane, while that of Anjo soil mainly retained methane without its appreciable oxidation.4.The amounts of methane oxidation in subsoil were also different between soils; Fukushima soil oxidized methane significantly while Anjo soil did it only in small amounts.