Micromorphological Properties of Thai Paddy Soils

Abstract

Micromorphological properties of fourteen widely distributed paddy soils from North, Northeast, Central Plain and Eastern part of Thailand were studied. Properties differ between soils, especially texture and macro porosity. The macro porosity of topsoils of coarser-textured soils is less than in subsoils because of puddling. However, the macro porosity of topsoils of the finer-textured soils is greater in the subsoil because of cracking. The pedofeatures of these soils include clay coatings, carbonate and iron oxide concretions and nodules depending on parent material and cyclic wetting and drying. The chemical composition of the clay coatings and mottles is quite similar to that of the matrix, whereas the chemical composition of nodules is quite different indicating that they did not form in situ. The Si to Al ratio of these transported nodules is as the same as of kaolin whereas the clay matrix has a composition reflecting the smectite or illite-rich composition.