Soil carbon stock in typical grasslands in Japan
To evaluate the carbon (C) sequestration function of grassland soils in Japan, soil C stocks were measured in 24 grasslands (3–43-year-old pastures) across 14 livestock farms nationwide. Soil C stocks varied among soil types, and the values in the upper 25 and 50 cm were higher in Andosols (mean, 12.4 and 19.3 kg m−2, respectively) than in Brown Forest soils (7.5 and 13.7 kg m−2) and other soil types (5.5 and 7.5 kg m−2). At the same time, C stocks varied among pastures within each soil type. Compared to data from the published work on the C content shortly after pasture establishment, aged pastures had decreasing C concentrations as the soil depth increased, suggesting substantial C accumulation in the top soil layers during pasture aging. This C accumulation caused grassland soils to store as much C as adjacent forest soils. Although the C stocks in the grassland soils were not statistically different from those in the adjacent native forest soils, some grassland areas stored greater amounts of C than the forests, indicating a possibility of increasing soil C stocks through improved grassland management.