Characterization of Pore-Structural Parameters for Different Textured Soils by Using Microfocus X-Ray CT System

Abstract

Mass transport in soil is highly controlled by pore-structural parameters. In this study, we visualized soil-pore networks for different textured soils including sand, loam, and silty clay loam by using a microfocus X-ray CT system and analyzed pore-structural parameters such as effective pore radius (reff), pore coordination number (Nj, and pore tortuosity (Tzz). Correlations between the porestructural parameters and laboratory measured gas transport parameters including air permeability ka and soil gas diffusion coefficient DP were examined. Both sand and loam soils were packed at different densities, while intact silty clay loam soil cores were collected from different positions of an apple orchard. The histograms of reff were fitted well by log normal distribution curves and those forTi and Tzz were fitted well by normal distribution curves for all tested samples. With increasing reff values, measured ka values of the sand increased linearly. On the other hand, the ka values of the loam and silty clay loam did not correlate with reff. Except for the intact silty clay loam at field water content, measured Dpfe values decreased slightly with increasing Tzz and reff. Especially, those moist samples collected from the alley area of an apple orchard, the Dp/s values became lower than others. This might have been caused by disconnected pore space due to water blockage.