Aluminum mobilization characteristics in four typical soils from different climate zones during their acidification

To identify the main factors affecting Al mobilization in soils from different climate zones.

XRD and ²⁷Al NMR were used to analyse clay minerals and the relative contents of four- and six-coordination Al. Soil acidification and Al mobilization were studied by constant pH automatic potentiometric titrator.

The relative content of tetrahedral Al (Al^IV) in the soils increased gradually from low to high latitude, and an opposite trend was observed for soil octahedral Al (Al^VI). The larger organic carbon (OC) content in surface soils (0–20 cm) effectively inhibited both soil acidification and Al mobilization compared with subsurface soils (20–40 cm). The content of mobilized Al followed the order: Inceptisol > Alfisol > Mollisol > Ultisol in both surface and subsurface soils, which determined by soil CEC, the contents of OC and clay and relative contents of Al^IV and Al^VI. After removal of OC from soil colloids, the amounts of mobilized Al were consistent with the relative contents of Al^IV in soil colloids and followed Mollisol > Inceptisol > Alfisol > Ultisol, suggesting that the solid Al in the soils from temperate and north subtropical regions was readily mobilized during soil acidification.

Al mobilization in different soils mainly depended on the CEC, the contents of OC and clay, and the coordination nature of Al in the soils. A larger CEC, a lower OC content, a greater clay content, and a higher content of Al^IV led to a greater amount of mobilized Al during soil acidification.