Contrasting Soil Properties of Allophanic and Non-Allophanic Horizons of Volcanic Ash Soils in Hokkaido District, Japan

This study examined the contrasting physical and chemical properties of allophanic and non-allophanic soil horizons in volcanic ash soils from the Hokkaido district described in the Soil Survey Data Book before Land Reclamation. A total of 741 investigation points and 2620 soil horizons were divided into two groups based on exchange acidity y1: allophanic horizons y1 < 6 and non-allophanic horizons y1 > 6. The soils were overall characterized as dark, weakly adherent, soft, dry, humic, and rich in active-Al. Soil acidity of the two horizons displayed significantly different pH, exchange acidity y1, and exchangeable Ca2+. Mean (±SD) humus contents of Layers Ⅰ (topsoil), Ⅱ (subsoil), and Ⅲ (deeper subsoil) were 8.9±4.6, 7.2±5.2, and 6.5±5.3%, respectively, for allophanic horizons, and 9.9±7.1, 8.1±7.9, and 5.8±7.7%, respectively, for non- allophanic horizons. Humus content of non-allophanic horizons was relatively higher compared to allophanic horizons in the Hokkaido district.