A TOPOSEQUENCE OF FINE-TEXTURED SOILS IN THE HILLY AREA OF THE NORTHERNMOST PART OF HOKKAIDO .3. IMPORTANCE OF CHELATING LOW-MOLECULAR ORGANIC-ACIDS IN THE MIGRATION PROCESS OF ALUMINUM AND IRON

Dilute solution (10-3M) of low molecular organic acids was used for the leaching experiments to analyze the migration process of aluminum and iron in the “fine-textured” Spodosols. Among the acids used, oxalic and citric acids showed a strong effect on the dissolution of aluminum and iron through the formation of chelate complexes. The concept of chemical equilibria was applied to analyze the mobility of aluminum and iron within the profile. Based on the stability diagram, monovalent citric and oxalic complexes with aluminum and iron were considered to be dominant. To migrate within the fine-textured soils rich in active 2: 1 clay minerals, it is necessary for the aluminum and iron complexes not only to be in a low molecular weight form but also to have a low electric charge. The complexes predicted from the stability diagrams satisfied both conditions. Consequently, it was concluded that the formation of chelating low molecular organic acids was significant in the migration process of aluminum and iron. © 1990 Taylor & Francis Group, LLC.