Assessment of soil structure using X-ray computed tomography

Abstract

Assessment of soil structure, characterized by complex morphological and functional properties, is difficult because most conventional soil physical investigations are destructive and variable in spatial resolution. The use of X-ray computed tomography, as a non-destructive technique, presents significant progress. It can be used to study soil structure at the millimetre scale, e.g. with a resolution of 0.25 mm in the horizontal direction and 1 mm in the vertical direction for the reported study. The measured Hounsfield Unit (HU) values characterize X-ray attenuation for each volume element of the soil core samples. From HU values, soil physical properties of soil cores or their subunits can be derived. They enable: (i) visual assessment of the soil structural condition through inspection of the X-ray CT images; (ii) 3D visualization of air-filled macropores; and (iii) calculation of the mean dry bulk density and standard deviation of voxel-related HU values for successive slices of soil cores. The degradation of structure of loamy and silty soils by tillage could be assessed by CT through quantification of decreased air-filled porosity, destroyed macropore connectivity, increased dry bulk density and decreased standard deviation of HU values in horizontal slices. Small-scale compactions near earthworm burrows could also be detected.

Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils

“…Voxel intensities were defined based on the Hounsfield scale commonly used in X-ray CT analyses to measure the radiodensity of materials (Rogasik et al, 2003). To have more intuitive results, the voxel intensity values initially ranging from −1948 to + 2148 (4096 possible gray level values) were normalized between 0 and 100.…”

“…Studying peat soil structure and various types of loamy and silty soils respectively, Turberg et al (2014) and Rogasik et al (2003) have shown the potential to observe changes in soil bulk density based on variations in voxel intensity. Based on the visual identification of different soil units from the previously drawn profiles and from the X-ray CT cross sections the direct correlation between the voxel intensity and the frozen wet soil bulk density has also been demonstrated in the present analysis.…”

“…The process of CT image acquisition is described in detail in Ketcham and Carlson (2001). CT scans provide a 3D intensity map of the soil where gray level variations are essentially related to changes in material density (Rogasik et al, 2003;Sander et al, 2008;Turberg et al, 2014). In the following text, the term radiodensity, as a commonly-used term to measure the transparency of a material to X-rays, will be used to refer to the soil bulk density imaged by X-ray data and expressed by changes in gray level values.…”

Applications of X-Ray Computed Tomography for Examining Soil Structure: A Review

“…In their studies, Rogasik et al (2003) assessed macropore length, size and connectivity of pores under different agricultural practices at the spatial scale of 0.25×0.25×1 mm.…”

Modellezett vízelöntés talajszerkezetre gyakorolt hatásának komputertomográfiás vizsgálata

“…A skála pozitív végpontja (3000 HU) a teljes sugárelnyelésnek felel meg. A skála közbenső értékei a leképezendő közeg sugárgyengülési együtthatóinak lineáris összesítéséből származtathatók (ROGASIK et al, 2003;GYARMATI, 2013).…”