Problem hydromorphic soils in north-east Thailand. 1. Environment and soil morphology.

Abstract

The Roi Et soil, a Gleyic Acrisol (FAO, 1974) is one of the main soils on the extensive seasonally wet, low terrace in north-east Thailand. The soil looks poor and produces traditionally low yields of one paddy rice crop/year. With fertilizers and dry-season irrigation, problems of water-logging, surface salinity and acidity caused poor germination and low yields of both rice and dry-season dryland crops. X-ray stereo radiographs, and macro- and micromorphological data indicate that the processes that have taken place in this soil include perforation and homogenization by roots and soil fauna; iron mobilization and redistribution; clay translocation; alteration of clay and formation of secondary silica; and surface slaking alternated with ploughing. The clay translocated appears to be fossil clay. Two stages of iron mobilization under (seasonally) wet conditions are indicated, the later one, with clay alteration, continuing at present. The soil has considerable macroporosity, due to worms and termites, mainly in the subsoil. The ploughpan and the deep subsoil have low porosity. (Abstract retrieved from CAB Abstracts by CABI’s permission)