Water retention curve correction using changes in bulk density during data collection

Soil shrinkage commonly occurs during centrifugation for soil water retention curve (SWRC) measurement. This phenomenon increases bulk density and results in a deviation of the SWRC from the true curve, reducing the accuracy of soil water movement simulations. This study considers the change in bulk density during SWRC measurement and corrects for it. Five soils, classified as either loam or sandy loam, were selected as experimental samples from Liaoning, Yunnan, Xinjiang, Shandong, and Shaanxi Provinces of China. Corrected and uncorrected SWRCs were employed in cumulative infiltration simulations to determine whether such a correction is necessary. Results showed that the sample heights decreased as the linear shrinkage ratios increased during dehydration; bulk densities increased relative to the designated values and altered the SWRC. The values of soil moisture for the corrected SWRC were always higher than those for uncorrected SWRC, with an average increment of 6%-18%. SWMS_2D simulations predicted the observed cumulative infiltration values more accurately when using the corrected SWRC than when using the uncorrected SWRC according to the smaller percent bias, root mean square error, and mean absolute percentage error. The results suggested that a correction of the SWRC for changes in bulk density is necessary.