Proposal for advanced classification of brown forest soils in Japan with reference to the degree of volcanic ash additions(Soil Genesis)

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The advanced classification of brown forest soils (BFS) is based on the specific properties of these soils, including the acid ammonium oxalate extractable aluminum (Al_<OX>) and lithic fragment contents, as well as their vertical distributions in the soil profile. In the present study, these properties were used to classify BFS, resulting in four types: (1) H-Al_<OX>-NGv BFS, (2) H-Al_<OX>-Gv BFS, (3) M-Al_<OX> BFS, (4) L-Al_<OX> BFS. H-Al_<OX>-NGv BFS is derived from volcanic ash characterized by a high Al_<OX> content and no lithic fragment, whereas L-Al_<OX> BFS is derived from weathered bedrock and has a low Al_<OX> content. H-Al_<OX>-Gv BFS and M-Al_<OX> BFS are derived from mixtures of volcanic ash and weathered bedrock. H-Al_<OX>-Gv BFS is characterized by high Al_<OX> content and many lithic fragments, whereas M-Al_<OX> BFS has moderate Al_<OX> content. H-Al_<OX>-NGv BFS and black soils (BLS) develop from accumulated volcanic ash, as indicated by declining Al_<OX> and clay content with decreasing depth in the surface horizons, as a result of successive additions of less-weathered volcanic ash to the soil surface.