Agricultural Use of Cultivated Peatlands in Hokkaido, Northern Japan: Development History, Land Subsidence, Greenhouse Gas Emissions, and Sustainable Management

Draining peatlands for agricultural purposes accelerates land subsidence, greenhouse gas emissions, and the degradation of surrounding wetlands. To achieve sustainable peatland agriculture, land management must consider not only crop productivity but also the global environment. Peatlands account for approximately 1% of Japan’s land area, with about 61% of that 1% located in Hokkaido. This review summarizes the history of agricultural land use on peatlands in Japan and efforts to address land subsidence, greenhouse gas emissions, and the degradation of wetlands surrounding farmland, focusing primarily on case studies from Hokkaido. To allow peatlands to be used for agriculture, drainage, and mineral soil dressing have been carried out. The drying, shrinkage, consolidation, and decomposition of peat resulting from drainage cause land subsidence. Paddy rice cultivation and cyclic irrigation are land management methods that balance the mitigation of land subsidence with food production. Drainage from farmland degrades the vegetation of any surrounding wetlands. On forage-harvesting farmland, buffer zones are established between the farmland and any surrounding wetlands to mitigate the degradation of these wetlands. Lowering the groundwater level increases CO2 and N2O emissions, while raising it increases CH4 emissions. A global meta-analysis has reported that maintaining the groundwater level between −20 cm and −40 cm results in the lowest total greenhouse gas emissions. However, data on greenhouse gas emissions from peatlands used for agricultural purposes with mineral soil coverage in Japan and the reduction in such emissions are limited. In Hokkaido, the introduction of groundwater level control systems has recently been progressing; the challenge of verifying the effectiveness of subsidence control and peat decomposition control through subsurface irrigation on fields other than paddy fields remains.