Free oxides and short-range ordered mineral properties of brown forest soils developed from different parent materials in the submontane zone of the Kanto and Chubu districts, Japan

Abstract

The general chemical properties of Brown Forest Soils (BFS) differ according to the nature of their parent materials. The influence of volcanic ash as a soil parent material must be regarded as a factor producing differences in the submontane zone of the Kanto and Chubu districts in Japan. To determine the influence of volcanic ash, the free oxides and short-range ordered mineral compositions of these soils were examined. Brown Forest Soils, excluding the soils derived from volcanic ash in these regions, had crystalline iron oxide as the main fraction of the free oxides. Iron/aluminum–humus complexes were formed in these surface horizons. In BFS derived from volcanic ash, parameters such as the indexes of allophane and imogolite increased with depth, and became dominant at deeper horizons. Black Soils derived from volcanic ash had chiefly non-crystalline iron oxide and non-crystalline Al-hydrous oxide. Even most BFS derived from non-volcanic ash in the Kanto and Chubu districts had a little volcanic ash influence. Therefore, the possibility for these soils to be classified as Andisols was suggested, regardless of the surface geological features in the Kanto and Chubu districts.