Visualization and Quantification of 3-D Soil Macropore Networks with Different Soil Type-Land Use Combination Using Computed Tomography.

The importance of soil macropores as preferential pathways of water, air and chemicals has been widely recognized. The objectives of this study are to 1) visualize and quantify 3-D macropore networks in different soils, and 2) investigate the effects of soil type and land use on soil macropore properties. Two soil series (Hagerstown and Morrison) 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 computed tomography (CT). After image segmentation, macropore networks were quantified by macroporosity along depth, macropore numbers, volumetric pore size distribution, pore hydraulic radius, total surface area, fractal dimension, and lacunarity. After skeletonization (thinning algorithm), pore length density, pore tortuosity, and pore connectivity were also calculated. Macropore features were apparently different with different soil type-land use combinations. Within the same soil type, the soils with pasture land use had higher macroporosity, pore length density and pore connectivity, especially in the subsurface soil, because of higher organic matter content and more soil biota activity. Within the same land use, the sandy soils (Morrison) had less macropores and weaker structure than the silt loam to clay soils (Hagerstown). These results provide essential information for quantifying macropore networks and predicting preferential flow and transport at the pore to soil column scales.