Study about an application of Unified Soil Classification System of Japan aimed for the improvement of an estimation of forest soil carbon stook

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Soil organic carbon (SOC) plays an important role in the global C dynamics and in the fertility of agricultural and forest soils. This study was performed to investigate i) the relationship between the stocks of SOC and the stocks of various soil constituents derived from volcanic ash materials, such as Al and Fe constituents extracted by acid oxalate and/or pyrophosphate, the effects of locational condition, such as altitude, slope gradient, and vegetation management on the stocks of various soil constituents derived from volcanic ash materials, to apply to some soil classification systems (Fundamental Land Classification Survey, Forest soil classification system, Unified Soil Classification Systems of Japan, World Reference Base for Soil Resources) and iv) to evaluate each characteristic on the estimation of soil C stock in Okuchichibu mountain zone based on soil survey and soil chemical analyses. As a result, large area classified into Brown Forest Soils by Fundamental Land Classification Survey was proved to be affected by volcanic ash as a soil parent material. Furthermore, soil C stock was apparently significant with soil parent materials and particularly, with the amount of materials derived from volcanic ash. Distribution pattern of volcanic ash soils and soil C stock considerably varied in areas of Okuchichibu mountain zone. That is because of large variation of surface geological characteristics, topographical characteristics and vegetation. In mountain zone composed by steep topographical features, the use of soil classification system that gives priority to the parent materials and detailed understanding of accumulation status of volcanic ash soil are thought to be important to estimate soil C stock.