STUDIES ON SALINE SOILS IN KHON-KAEN REGION, NORTHEAST THAILAND .2. SEASONAL-CHANGES OF PHYSICAL AND CHEMICAL-PROPERTIES

The dynamics of salt movement and the seasonal changes of the physical and chemical properties, especially pH and clay dispersion, of the saline soils in the Khon Kaen Region, Northeast Thailand, were investigated to obtain basic information for the improvement of saline soils. The results obtained are as follows. Not only the salt but also the clay moved upward with the capillary movement of the soil solution, and downward with the percolation of rain water. The soil pH was very low (less than 4) in the dry season and very high (nearly 9) in the rainy season, based on the following reactions: H-clay + NaCl →Na-clay + HCl (dry season); Na-clay + H2O → H-clay + NaOH (rainy season). The soil contained large amounts of dispersible clay in the rainy season, but a small amount in the early dry season. FeS dissolved in the groundwater was considered to be another acidification agent, as it became oxidized to ferric hydroxide (precipitation) and sulfuric acid when it reached the soil surface by capillary movement. © 1990 Taylor & Francis Group, LLC.