Rapid Increase and Long-Term Slow Decrease in Soil C stock Due to Agricultural Development in Hokkaido Tokachi District

Soil properties and functions are dramatically altered by changes in agricultural land use. However, little is known about how ecosystem C stock and its partitioning change with deforestation for agricultural land use, especially in cold humid areas. In this study, we investigated how agricultural development influences temporal changes in soil C pools in upland crop fields using a paired-plot approach. Ten pairs of control forest and agricultural development plots (2 to more than 80 years) were selected with the same crop rotation under humid temperate climate in Northeast Japan. We detected a net gain in soil C during the first 2 years of agricultural land development under the flat field condition. This gain in soil C was caused by an increase in the light fraction soil C, which represents plant residue derived-C due to agricultural development. Agricultural development resulted in the loss of soil C in fields without manure application. There was no difference in the ecosystem C stock among soil types or with the amount of manure applied. Agricultural development resulted in a slow decrease in soil C storage, indicating a slow rate of C decomposition under cool climate conditions