Clay Minerals and Iron Oxides of Selected Red and Yellow Soils in Northeast Plateau and Southeast Coast, Thailand

Abstract

A study on clay minerals and iron oxides was conducted on five selected red and yellow soils in the Northeast Plateau and the Southeast Coast mailand, using x-ray diffraction analysis and differential thermal analysis methods. The results reveal that the red and yellow soils have kaolinite as the dominant clay mineral. Vermiculite, smectite and illite are also present in minor quantities in the soils. The iron oxide content of these soils varies according to their parent materials. The iron oxide minerals found include hematite, goethite and magnetite. The clay minerals and iron oxides in these soils account for their poor fertility status and care should be taken on soil system for fertilizer application. The soils belong to Ultisols and Oxisols and can be correlated well with established soil series in Thailand.