Effects of soil management on changes of soil carbon content in alluvial paddy soil in Niigata

Effects of soil management on carbon content in alluvial paddy were investigated using past soil survey data of Niigata prefecture, Japan. The changes of soil management were as follows; (1) slight decrease in nitrogen and phosphate fertilizer application rates, (2) decrease to half in the application of soil amendments, like calcium silicate, (3) decrease in compost application and increase in rice straw application, (4) increase in pipe drainage. In spite of these changes, negligible change of carbon content in the plow-layer of alluvial paddy soils had been observed for past twenty-five years. However, without rice straw application and paddy-upland rotations, the soil carbon content had been decreased. Carbon content of alluvial paddy soils classified into Gley Lowland soil (Fluvisol or Gleysol) at the depth of 0-30 cm was calculated about 49-103 g/kg and gross carbon sequestration was calculated 7.68 Mt in the paddy field soils in Niigata prefecture.