Clay Mineral Composition of Paddy Soils in Northern Thailand

Abstract

Using X-ray diffraction (XRD), kaolinite was established as the dominant clay mineral of paddy soils in the Northern Region of Thailand with a sharp peak at the 7 A reflection. Mica was the second dominant clay mineral, corresponding with the 10 A layer silicates. The 14 A clay minerals comprised mainly vermiculite and some montmorillonite, however, the content of both was very low with onlytraces of chlorites is reflected in the high potasium and low magnesium content of these soil groups.
The clay contents of the Low Humic Gley Soils and fresh Water Alluvial Soils of the Chiang Mai, Phreae and Nan valleys of North Thailand were similar to those of the Non-Calcic Brown (Hydroorphic) soils in the Central Plains Region, which generally have more mica than kaolinite; the later also contain vermiculite and small quantities of chlorite. The similarities between the soil groups in the Northern and Central Regions reflects a similar weathering history.