Abstract
We have reported the existence of Cumulic Non-allophanic Kuroboku soils in Kuju Plateau, Oita Prefecture, Japan (Kubotera et al 2009). In order to elucidate the distribution and lateral continuity of horizons sequence of this soil, we investigated horizons sequence and chemical properties, and conducted soil classification in 10 profiles around Mt. Kuju. Black surface horizons were observed from the surface to the depth of 34 to 100+ cm above brownish black to brown subsoil horizons in all investigated profiles. Weathered gravels that probably corresponded to the Danbaru scoria (ca. 4.8 cal. ka BP) were observed in lower part of the black surface horizons or brownish black to brown subsoils in 8 profiles. Upper part of the black surface horizons met the requirements of chemical properties of non-allophanic Kuroboku horizons, i.e., y_1 ≥ 6 or Si_o < 6g kg^<-1> or Al_p/Al_o ≥ 0.5, in all investigated profiles except for one profile in eastern area of Kuju Plateau. These non-allophanic horizons showed acidity and carbon contents remarkably larger than those of the allophanic horizons, and the horizons with larger carbon contents showed higher acidity. The profiles that were classified into Non-allophanic Kuroboku Soils in the Unified Soil Classifications System of Japan, with non-allophanic horizons of 25 cm or thicker, were distributed in the north side of the Old Oguni Road in the southern foothill of Mt. Kuju.
