Abstract
This study aims to clarify the fluctuation of concentrations of gas component : oxygen, carbon dioxide, in the subsoil of open system percolation at a stratified paddy field using a large lysimeter (length 15 m) for two years. Soil air extracted at 37 cm depth was selected from the exposed edge of the large lysimeter to the opposite edge of the lysimeter (2.5 m, 5.0 m,10.0 m,15.0 m horizontally from the edge), rhe stratified paddy field kept inundation for two years and air penetration occurred horizontally. The first year, the field was barren but the second year, rice was planted. Oxygen concentrations in the layer of the open system percolation decreased in summer but increased in winter. Carbon dioxide concentrations increased in summer but decreased in winter. It was thought that these annual changes depended upon soil temperature. The oxygen concentration lowered with the horizontal distance from the exposed edge, whereas the carbon dioxide concentration heightened with distance. Formation of carbon dioxide was only equal to oxygen consumption at 2.5 m from the exposed edge. The redox potential at 10.0 m and 15.0 m lowered when the oxygen concentration became lower than 2%. Then at 15.0 m elements of iron and manganese were detected in the downward water in the subsoil.
