Generating accurate soil water characteristic curves over the full range of soil suction by combining the Wind-Schindler and dewpoint hygrometer techniques

Abstract

The Soil Water Characteristic Curve (SWCC) is of fundamental importance for understanding the characteristics and behavior of unsaturated soil. For many years, filter paper and axis translation (pressure plate extractors) have been used to make the bulk of the suction measurements necessary to generate the SWCC, but these techniques are time consuming and inaccurate. The dew point potentiometer Vapor Pressure Method (VPM) has many advantages over other suction measurement methods, including simple setup, fast measurement times and good accuracy. Recently, technological advances in the VPM have made it possible to measure soil suction accurately to around 2.7 pF (50 kPa). In addition, a new adaptation of the Wind/Schindler Method (WSM) makes it possible to generate unattended, high resolution SWCCs for suctions less than 2.9 pF (80 kPa), thus filling in the wet end of the SWCC where the VPM is limited. Our results showed that in most cases the SWCCs from the two techniques meshed nicely over the full range of soil textures. However, in fine textured soils, the effect of sample disturbance is important and should be considered when collecting samples for the VPM measurements. Additionally, significant differences were found in SMCCs that were generated along the two legs of the hysteresis loop with the DH method, with SMCCs generated on the desorption leg matching WSM most closely.