Properties of paddy soils on lower Chi basin: III. Clay mineral components

Study was conducted to identify clay mineral components of paddy soil profile which field morphology, particle size distribution and sand size distribution had previously analyzed. Hypothesis of this study is that the difference in profile development and landform may result in different types of clay minerals. The clay slides of each horizon were prepared for X-ray diffraction analysis. The results revealed that soils from floodplain with low profile development, in most cases, contained the 2:1 type clay, while kaolinite was observed only at the upper parts of profiles. For the 2:1 type clay, vermiculite was noticed throughout the depth of Profile No. 1 vermiculite dominated in Profile No. 2 down to the depth of 210 cm where as montmorillonite was found in the greater depths. Drainage condition of both, less developed profiles on the floodplain was very poor. Thus, parent materials still have very much effects on clay mineral types. The high content of 2:1 type clay confirmed this idea. The kaolinite on the upper parts of profiles illustrated the transformation of 2:1 type clay to kaolinite because oxidation-reduction processes in this part of profile are stronger than the greater depths. For the profiles from low terrace, they contained more kaolinite than those from floodplain. The upper 140 and 80 cm of Profile No. 4 and 5 had kaolinite more than the other depths which the kaolinite decreased while the 2:1 type clay-the montmorillonite increased. The 2:1 type clay of Profile No. 3 and 6, in most cases, is vermiculite. The Profile No. 7 and 8 on the upper part of low terrace, the kaolinite dominated throughout the depth. It can be concluded that the results of study confirmed the hypothesis. The difference in landform and development of soil profile affected clay mineral types. In this study, the less development profile-the more 2:1 type clay dominated. Kaolinite content increased at the upper part of the more developed profile. But for the greater depths, reduction still going on and degree of soil forming processes still show 2:1 type clay was noticed and increased with depth. Because the sites of Profile No. 7 and 8 are higher than the others of low terrace and oxidation-reduction could be processed well, thus the more resistant clay mineral-the kaolinite, dominanted through the profiles.