Estimating the Wet‐End Section of Soil Water Retention Curve by using the Dry‐End Section

Direct determination of the wet‐end section of soil water retention curve (SWRC) (water potential ψ more than −15,000 cm) is time consuming and expensive. However, the dry‐end section of SWRC (ψ less than −15,000 cm) often shows a linear trend and can be relatively rapidly and easily acquired using a few measured data. The objective of this study is to provide a simple approach for deriving the wet‐end section of SWRC using the information of the dry‐end section of the same SWRC and soil bulk density. The new method is based on the assumption that the dry‐end section of SWRC is the tangent of the wet‐end section at the point of ψ equals −15,000 cm. A total of 21 soils with different textures (clay contents vary between 0 and 47%) were used for evaluating the method. Results showed that the root mean square errors and the mean errors generated by the proposed method were in the ranges of 0.009 to 0.113 and −0.098 to 0.002, respectively. These results were comparable with those from literature, suggesting that the proposed method may be used to predict the wet‐end section of SWRC. The prediction performances were obviously improved when residual water content was set to a nonzero small value such as a value at log 10 (−ψ) = 5 and for sandy soils the edge points were increased from −10 4.2 cm to −10 3.8 cm. In general, the measurement of the dry‐end section of SWRC is helpful to the prediction of the wet‐end section.