Relating Water Retention to Transient Soil Bulk Density

Tuesday, 25 July 2017: 3:00 PM
Paul Brest West (Munger Conference Center)
Zhengchao Tian and Joshua L Heitman, North Carolina State University Raleigh, Raleigh, NC, United States
Soil bulk density (ρb) changes over time due to tillage, root growth, rainfall, freeze-thaw cycles and a range of other processes and disturbances. In turn, transient ρb influences many surface soil hydraulic properties, such as the water retention curve, but associated changes are usually ignored by vadose zone and soil-water simulation models. In this study, we introduce an approach to relate the van Genuchten water retention model and transient ρb. The four parameters used in the van Genuchten model are expressed by ρb-related empirical equations. To determine the empirical expressions of the four parameters, we applied a curve fitting procedure to measured water retention curves with two different ρb. These fitted equations were next used to predict the water retention curve of the soils under various ρb conditions. Six soils with a range of textures were used to evaluate the accuracy of the proposed approach. The predicted water retention curves agree well with measured data. The coefficient of determination varied from 0.967 to 0.999 and RMSE varied from 0.005 to 0.025 m3 m-3 between predicted and measured water retention curves. Therefore, the proposed approach could accurately predict soil water retention curves with transient ρb and has the potential to be used in soil-water simulation models to account for dynamic soil surface properties.