Chemical properties and sulfur-oxidizing bacteria flora of the paddy soil dressed with the soil dug from agricultural waterway and the dug soil

In area on the right bank of the Kokufu River, Sado Island, Niigata, paddy rice was damaged in the paddy field dressed with the soil dug from agricultural waterway. The surface soils of the paddy field and the dug soil by depth (O-1, 1-2, 2-3m) were collected and examined about chemical properties and sulfur-oxidizing bacteria and iron-oxidizing bacteria. As for the chemical properties of the paddy soil, soil pH (H2O) of the strongly damaged point in the paddy field was lower than that of the little damaged point and the contents of water-soluble SO42- and Fe3+ of the strongly damaged point were higher than those of little damaged point. Soil pH (H2O) of both points had dropped under 4.0 and both soils developed into acid sulfate soil in aerobic condition during fall and winter. In addition, we found that dug soil contained much reduced sulfur compounds such as pyrite. So it was proved that the origin of the paddy field acidification is the accumulation of SO42-, which is oxidative product of reduced sulfur compounds derived from the dug soil. As for the dug soil itself, soil pH (H2O) was lower and contents of water-soluble SO42- and Fe3+. was higher in topsoil compared with subsoil. Although the number of sulfur-oxidizing bacteria of all soil samples was almost same regardless of soil depth and pH in liquid culture medium, the number of iron-oxidizing bacteria of topsoil was more than that of subsoil. Although the number of iron-oxidizing bacteria of the strongly damaged point in paddy field was more than that of the little damaged point, the number of sulfur-oxidizing bacteria of both points was almost same. These results suggested that iron-oxidizing bacteria take more important part in formation of acid sulfate soil than sulfur-oxidizing bacteria. We tried isolating sulfur-oxidizing bacteria from the dug soil and 11 species of (facultative) autotrophic bacteria that has sulfur-oxidation activity were isolated.