Quantitative Relationship Between Soil Macropore Properties and Preferential Flow and Transport Using Computed Tomography.

The elusive relationship between preferential flow dynamics and soil structure is a main factor prohibiting accurate estimation of flow and transport in structured soils using current simulation models. Therefore, it is essential to develop quantitative relationships between soil structure (especially macropore network) and soil hydraulic properties. Two types of soils (Hagerstown and Morrison series) with contrasting soil structure/texture and land use (crop and pasture) were selected for this study. Five soil columns (10-cm in diameter and 30-cm in length) were taken for each land use-soil type combination. The soil columns were scanned using

X-ray CT

to obtain soil structural parameters such as macroporosity, volumetric pore size distribution, pore length density, pore hydraulic radius, pore continuity, pore connectivity, fractal dimension, and lacunarity. The flow and solute experiments were conducted with each soil column and the parameters related to preferential flow and transport (such as saturated hydraulic conductivity, dispersion coefficient, mass transfer coefficient, and the fraction of mobile volume) were reversely estimated using non-equilibrium models. The resultant two types of the parameters were analyzed to establish the quantitative relationship between soil structure and preferential flow and transport. In addition, basic soil properties such as bulk density, particle size distribution, organic matter content, and soil profile description data were used to develop pedotransfer functions for estimating soil hydraulic properties. The relationships established in this study will enhance the quantification and prediction of preferential flow and transport in structured soils.