Application of Evaporation Method Using Two Tensiometers for Determining Unsaturated Hydraulic Conductivity beyond Tensiometric Range

Accurate determination of unsaturated hydraulic conductivity in low pressure head range is critical for predicting evaporation rate under localized irrigation or root water uptake under drought stress conditions. We proposed a relatively low cost and fast laboratory method to simultaneously determine water retention and hydraulic conductivity functions across a wide range of pressure heads. The method is quite similar to conventional evaporation method using two tensiometers. In addition to tensiometer readings, the proposed method uses water content profile at the end and cumulative evaporation. Experimental results for three soils with different textures showed that inversely optimized hydraulic conductivity functions agreed with K-data measured with the steady state evaporation method, indicating the reliability of the proposed method. The hydraulic conductivity functions fitted for K-data obtained by tensiometer readings with Campbell’s K(θ) function also agreed well with the reference K-data for two of the three soils, but largely deviated from those for the third soil. This indicates the importance of actual measurement of K(θ) in low pressure head range.