Relationships among non-allophanic/allophanic indicators in six Japanese forest Andosol profiles; Implications for soil classification and genesis

Alam, M. M.*; Yamakita, Eri*; Tamanna, S.*; Thae, E. P.*; Koarashi, Jun   ; Atarashi-Andoh, Mariko  ; Abe, Yukiko; Nakayama, Masataka  ; Mori, Yuki*; Hiradate, Shuntaro*

Andic Andosols, prevalent in Japan, have been classified as Allophanic or Non-allophanic, based on indicators: oxalate-extractable silicon (Sio), the ratio of pyrophosphate- to acid-oxalate-extractable aluminum (Alp/Alo), and exchangeable acidity (y1), in the Fifth Committee for Soil Classification and Nomenclature 2017 (FCSCN 2017). This study investigated chemical and mineralogical properties in six forested Andosol profiles to assess the consistency of these indicators and their link to soil formation. While FCSCN 2017 classified two profiles as Allophanic and four as Non-allophanic, inconsistencies were found among the indicators. Sio content is proposed as a more reliable indicator of allophanic material richness than the Alp/Alo ratio, which is influenced by organic matter content. Sio and y1 are suggested as informative parameters for diagnosing allophanic content and soil acidity, respectively. The findings contribute to refining Andosol classification and enhancing our understanding of Andosol formation under forests.