Abstract

<p>Andosols, volcanic ash-derived soils, play a vital role in upland farming in Japan, with distinct categorization into allophanic and non-allophanic types. Allophanic Andosols, constituting 69.9% of the total Andosol land area in Japan, are prevalent in regions with significant Holocene tephra deposition. In contrast, non-allophanic Andosols, accounting for 30.1% of the total Andosol area, occur in areas with minor tephra deposition. Both categories exhibit distinctive characteristics such as a thick black A-horizon, high phosphate fixation, superior water retention, and low bulk density. Despite similarities in morphology, chemistry, and physical attributes, non-allophanic Andosols possess unique features due to the presence of 2:1 mineral. Notably, non-allophanic Andosols, characterized by substantial exchangeable aluminum (represented by exchangeable acidity y1), pose a significant challenge by inducing severe aluminum toxicity in common agricultural crops. Hence, distinguishing between allophanic and nonallophanic Andosols is crucial for effective agricultural management.</p>