Assessment on the rates and potentials of soil organic carbon sequestration in agricultural lands in Japan using a process-based model and spatially explicit land-use change inventories – Part 1: Historical trend and validation based on nation-wide soil monitoring

[摘要] In order to estimate a country-scale soil organic carbon (SOC) stock changein agricultural lands in Japan, while taking into account the effect of land-usechanges, climate, different agricultural activities and the nature of soils, aspatially explicit model simulation system was developed using RothamstedCarbon Model (RothC) with an integration of spatial and temporalinventories. Simulation was run from 1970 to 2008 with historicalinventories. Simulated SOC stock was compared with observations in anation-wide stationary monitoring program conducted during 1979–1998.

Historical land-use change, characterized by a large decline in the areaof paddy fields as well as a small but continuous decline in the area oforchards, occurred along with a relatively large increase in upland cropfields, unmanaged grasslands, and settlements (i.e. conversion ofagricultural fields due to urbanization or abandoning). Results of thesimulation on SOC stock change under varying land-use change indicated thatland-use conversion from agricultural fields to settlements or other lands,as well as that from paddy fields to croplands have likely been an increasingsource of CO₂ emission, due to the reduction of organic carbon input tosoils and the enhancement of SOC decomposition through transition of soil environmentfrom anaerobic to aerobic conditions.

The area-weighted mean concentrations of the simulated SOC stocks calculatedfor major soil groups under paddy fields and upland crop fields werecomparable to those observed in the monitoring. Whereas in orchards, thesimulated SOC stocks were underestimated. As the results of simulationindicated that SOC stock change under managed grasslands and settlements hasbeen likely a major sink and source of CO₂ emission at country-scale,respectively, validation of SOC stock change under these land-use types,which could not have been accomplished due to limited availability or a lackof measurement, remains a forthcoming challenge.

[学科分类] 地球化学与岩石