Leonardo Daniel Rivera, Douglas R. Cobos and Gaylon S. Campbell, Decagon Devices, Inc., Pullman, WA
The measurement of water potential in unsaturated soils is essential in many areas of soil science like modeling hydraulic properties or analyzing shrink-swell characteristics from the soil water characteristic (SWC) curve. For many years, pressure plates, hanging water columns, and filter paper made the majority of the SWC curves, but these techniques are time consuming and have shown equilibration issues (Bittelli & Flury, 2009; Solone et al., 2012). The vapor pressure method overcomes these, but past instruments lacked the resolution in the critical -100 to -1000 kPa range. Recently, technological advances have made it possible to measure water potential up to -50 kPa. In addition, a new, automated method (Wind/Schindler) provides the wet end of the SWC curve. SWC curves were developed for a variety of soil types. Dry end (vapor pressure) and wet end (Wind /Schindler) SWC curves crossed over each other smoothly, demonstrating the ability to use the two techniques to generate exceptionally accurate full range SWC curves.