Enhancing the Evaporation Method for Accurately Determining Unsaturated Soil Properties in the Wet Range

Abstract

The evaporation (EV) method is a widely used experimental approach to determine unsaturated hydraulic conductivity (UHC) and soil water retention (SWR) functions. However, the EV method has some limitations in evaluating accurate UHC values near the wet range. This restricts the working range of the models that utilize these UHC values for predicting soil water content and water fluxes for problems involving wet conditions (e.g., infiltration under ponding conditions). Our experimental study shows that when using the EV method, tensiometer offset errors as low as 1 cm can cause problems with wet-range measurements. Current methods to overcome these errors are expensive, inefficient, or cumbersome. In this study, we developed an improved EV method that utilizes a simple experimental protocol for standardizing the soil saturation procedure and a robust calibration method to quantify tensiometer offset errors. The proposed approach utilizes existing EV method hardware without requiring additional specialized instrumentation. Experiments performed using a silt loam soil sample show that our approach can extend the working range of the EV method to the wet range. Therefore, reliable estimates of the UHC and SWR functions can now be obtained over the entire range of soil suction heads. Our study also contributes to a better understanding of the EV method and uses this knowledge for collecting reliable and reproducible SWR and UHC data. The improved EV method is simple, effective, and cost-efficient. This method has the potential to greatly improve soil water content predictions, leading to better-informed decisions for groundwater resources management, sustainable agriculture, and environmental protection.