Revisiting laboratory methods for measuring soil water retention curves

Abstract

Traditional laboratory methods for measuring soil water retention curves (SWRCs) typically consist of suction tables, pressure cells, and pressure plate apparatus (i.e., traditional methods). However, technological advancement has resulted in newer methods based on precision mini-tensiometers and dew point water potential meters (i.e., modern methods). This study investigated the discrepancy between SWRCs measured using traditional and modern methods in three soil textures. Our results showed that SWRCs from both traditional and modern methods were similar at the wet end (i.e., matric potentials 0 to −10 kPa) and at the dry end (−500 to −1,500 kPa) of the SWRC, with an average mean absolute difference (MAD) across all three soils of 0.033 and 0.017 cm³ cm⁻³, respectively. The largest discrepancy between methods was consistently observed at moderate tensions of −33 and −70 kPa for the three soils, with an average MAD of 0.059 cm³ cm⁻³ for −33 kPa and a MAD of 0.083 cm³ cm⁻³ for −70 kPa. Plant available water capacity differed by up to 20% between the traditional and modern methods in a clay loam soil. While previous studies have mostly focused on the dry end of the SWRC, our study suggests that additional research comparing traditional and modern methods is required at moderate (−70 and −500 kPa) tension levels.