Distribution of Allophanic Andosols and Nonallophanic Andosols in Japan based on the Data of Soil Survey Reports on Reclaimed Land

Abstract

Distributions of allophanic Andosols and nonallophanic Andosols in Japan were approximately determined using the data of exchange acidity y_1 which appeared in the soil survey reports on reclaimed land. The soils having more than 15 g P_2O_5 kg^<-1> of phosphate absorption coefficient were separated as Andolols, and soil profiles of 4165 Andosols were divided into two groups by exchange acidity y_1: allophanic Andosols (y_1<6) and nonallophanic Andosols (y_1≧6). Allophanic Andosols occupied 52% of total Andosols and distributed in the regions having Holocene tephra deposits. The regions dominated by allophanic Andosols were also characterized by low rainfall, or basaltic or pumicious parent materials. On the other hand, nonallophanic Andosols occupied 48% of total Andosols and were widespread in the regions showing high rainfall or poor deposition of Holocene tephra. Compared to the ratio of nonallophanic Andosols to total Andosols in Tohoku district determined in this paper with that determined in detail by selective dissolution analysis in a previous paper, we concluded that the results obtained here reflect approximately the distribution of allophanic Andosols and nonallophanic Andosols in Japan.