Hysteresis of Water Retention Curve of Saline Soil

The soil water retention curve of a soil is usually not unique. It depends on the soil water flow process. Fully primary curves for draining and wetting processes are necessary in soil water flow modeling. Usually, the primary draining curve can be produced from an experiment with a hanging column apparatus together with a pressure plate apparatus. However, the pressure plate cannot supply the necessary data for the wetting process; therefore only the scanning wetting curve can be derived from the hanging column. By using the primary draining curve and the wetting scanning curve as guides, the primary wetting curve can be constructed. Six saline soil samples from around Khon Kaen City in northeastern Thailand were used for testing. The hystereses of the soil water retention curves were found for all soil samples with varying degrees of hysteresis. The degree of hysteresis was found to vary with the percentage of silt portion of the soil sample.