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

Abstract

The advanced classification of brown forest soils (BFS) is based on the specific properties of these soils, including the acid ammonium oxalate extractable aluminum (Alox) 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-Alox-NGv BFS, (2) H-Alox-Gv BFS, (3) M-Alox BFS, (4) L-Alox BFS. H-Alox-NGv BFS is derived from volcanic ash characterized by a high Alox content and no lithic fragment, whereas L-Alox BFS is derived from weathered bedrock and has a low Alox content. H-Alox-Gv BFS and M-Alox BFS are derived from mixtures of volcanic ash and weathered bedrock. H-Alox-Gv BFS is characterized by high Alox content and many lithic fragments, whereas M-Alox BFS has moderate Alox content. H-Alox-NGv BFS and black soils (BLS) develop from accumulated volcanic ash, as indicated by declining Alox 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.