Distribution of Ultisols and Oxisols in the serpentine areas of East Kalimantan, Indonesia

抄録

In Southeast Asia, Ultisols are commonly distributed on sedimentary rocks and Oxisols on ultramafic rocks. To investigate the importance of parent material on the formation and distribution of Ultisols and Oxisols, the effects of parent material on soil physico-chemical and mineralogical properties were analyzed using soils derived from serpentine and sedimentary rocks in East Kalimantan. The pH and concentrations of bases and Fe oxides in soils decreased in the order serpentine>mudstone>sandstone. Oxisols are rapidly formed through loss of Si and relative accumulation of Fe oxides on the easily-weatherable serpentine and the richness of bases and Fe limits lessivage and maintains a high base saturation. On Fe-rich mudstone, Ultisols are formed through lessivage and acidification. On base and Fe-poor sandstone, clay destruction by acidification and lessivage is responsible for clay enrichment of the subsoil. In East Kalimantan, the major pedogenetic processes are lessivage and acidification. Ferralitization is not a common process. The leaching condition and the lower concentrations of bases and Fe in sedimentary rocks than in serpentine could account for the dominance of Ultisols in East Kalimantan. Because serpentine is easily weathered to oxic materials, parent material is also a primary factor responsible for the distribution of Oxisols in this area.