Comparison of Laboratory‐ and field‐determined soil water retention curves in a well‐aggregated tallgrass prairie soil

Soil water retention curves (SWRCs) are traditionally determined in the laboratory, but modern sensors enable their measurement under field conditions. This study compared SWRCs obtained from laboratory and field instrumentation within the same soil volume. A well‐aggregated tallgrass prairie soil was instrumented with co‐located sensors that measured volumetric water content and matric potential at 3.5‐cm depth inside collars that prevented root intrusion, minimized lateral flow, and ensured consistent sensor placement. The field experiment was conducted from June 1 to August 11, 2023, capturing multiple wetting and drying cycles. Afterward, the collars were excavated and analyzed in the laboratory using precision mini‐tensiometers and a dewpoint water potential meter. Laboratory‐derived SWRCs consistently showed greater water contents near saturation compared to field‐derived SWRCs, which were consistent across three drydown periods and collars. The two methods produced nonequivalent SWRCs, likely due to sensor responsiveness, air entrapment, and rapid macropore drainage that limited in situ measurement of near‐saturation conditions.