Temperature Dependence of Soil Water Retention Curves

Effects of entrapped air volume and surface tension of soil solution are often regarded as the primary cause of temperature effects on the water retention curve. A procedure was developed to determine simultaneously the water characteristic curves and the volume of entrapped air for a glass beads medium and a Norfolk sandy loam (Typic Paleudults) at two temperatures. The volume change of entrapped air was determined from the change in volume of the free gas phase and the volume of water outflow from or inflow into a pressure cell. The results indicate a decrease in entrapped air volume with increasing temperature and suction. Surface tension values, calculated from capillary height measurements, showed the temperature coefficient of surface tension of soil solution to be smaller in magnitude than that of pure water. It was concluded that neither changes in entrapped air volume nor the temperature coefficient of surface tension of soil solution could account for the temperature effect on experimentally determined water characteristic curves of the two porous media.