COMPARATIVE SOIL ASSESSMENT OF ALLOPHANIC AND NON-ALLOPHANIC LAYERS IN VOLCANIC ASH SOIL: KYUSHU, JAPAN

Abstract

Andosols, characterized as soils formed from volcanic ash, constitute the cornerstone for upland agriculture in Japan. These soils are further categorized into allophanic and non-allophanic types. Allophanic Andosols, covering 4.51 million ha or 69.9% of the total Andosol area, are primarily located in regions with substantial Holocene tephra deposits. Conversely, non-allophanic Andosols, accounting for 1.95 million ha or 30.1% of the total Andosol area, predominate in areas with minor tephra deposition (Saigusa and Matsuyama, 1998). While both types share core properties such as a thick black A-horizon, high phosphate fixation, excellent water retention, and low bulk density, non-allophanic Andosols exhibit distinct characteristics due to the presence of 2:1 minerals (Saigusa et al., 1991). Notably, owing to substantial exchangeable Al, non-allophanic Andosols often pose a risk of severe Al toxicity to common agricultural crops. Consequently, from an agricultural management standpoint, the division between allophanic and non-allophanic Andosols is of critical importance.