Relationship between clay mineralogy and exchangeable Al in red and yellow soils from the Islands of Okinawa and Java

Abstract

Red and yellow soils from tropical regions are generally more mature than their subtropical counterparts. Most of these soils contain kaolin as the dominant clay mineral. Exchangeable aluminium (Al) generally balances permanent negative charges and occupies strongly acidic exchange sites of the soil clay. The objective of this study was to identify those clay minerals that are most highly implicated in contributing exchangeable Al to red and yellow soils collected from the Islands of Okinawa and Java.

All soils exhibited an acid reaction but varied in their exchangeable Al content and clay mineralogy. Clay content was high in all Javan soils but varied in those from Okinawa. Javan soils were dominated by kaolinite, and Okinawan soils by an association of illite and halloysite. However, 2 : 1-2 : 1 : 1 intergrades were significant components in both the Oku red soils (Okinawa Island) and the Pamagersari red soils (Java Island). Javan soils were characterised by a more mature (advanced) state of weathering than those from Okinawa. The source of exchangeable Al was halloysite in Okinawan soils and 2 : 1-2 : 1 : 1 intergrades in Javan soils.