X-ray microtomography analysis of soil structure deformation caused by centrifugation

Abstract

Abstract. Centrifugation provides a fast method to measure soil water retention curves over a wide moisture range. However, deformation of soil structure may occur at high angular velocities in the centrifuge. The objective of this study was to capture these changes in soil structure with X-ray microtomography and to measure local deformations via digital volume correlation. Two samples were investigated that differ in texture and rock content. A detailed analysis of the pore space reveals an interplay between shrinkage due to drying and soil compaction due to compression. Macroporosity increases at moderate angular velocity because of crack formation due to moisture release. At higher angular velocities, corresponding to capillary pressure of ψ < −100 kPa, macroporosity decreases again because of structure deformation due to compression. While volume changes due to swelling clay minerals are immanent in any drying process, the compaction of soil is a specific drawback of the centrifugation method. A new protocol for digital volume correlation was developed to analyze the spatial heterogeneity of deformation. In both samples the displacement of soil constituents is highest in the top part of the sample and exhibits high lateral variability explained by the spatial distribution of macropores in the sample. Centrifugation should therefore only be applied after the completion of all other hydraulic or thermal experiments, or any other analysis that depends on the integrity of soil structure.

Effects of the long‐term fertilization on pore and physicochemical characteristics of loess soil in Northwest China

“…Procedures for image processing and subsequent analysis were identical for the ROI of soil cores. The 3‐D soil core was volume rendered and visualized with the ImageJ 3‐D Viewer Plug‐in (Schmid et al., 2010); examples are shown in Figure 1d. Pore were divided into four sizes according to the equivalent diameter and the resolution of the CT scanning is <50, 50–100, 100–1000, and >1000 μm, respectively.…”

“…This technique has been applied in analyzing the distribution, number, shape, length and connectivity of soil pores on a different scale (Schlüter et al., 2018; Zhao et al., 2017). Properties of pore network measured with X‐ray CT and image analysis have been used to explain a range of soil properties like water and solute transport (Larsbo, Koestel, & Jarvis, 2014; Paradelo et al., 2016), soil structure turnover (Schlüter, Leuther, Vogler, & Vogel, 2016) and soil friability (Munkholm, Heck, & Deen, 2012).…”

Denitrification in soil as a function of oxygen availability at the microscale

“…2b), (2) average air distance derived from the histogram of the Euclidean distances between all nonair voxels and their closest connected-air voxel (Fig. 2c, d) (Schlüter et al, 2019), and (3) the ansvf which corresponds to the volume fraction of air distance larger than a certain threshold. Therefore, in a sensitivity test, air distance thresholds of 0.6, 1.3, 2.5, 3.8, and 5.0 mm were used to estimate the ansvf and to find the best correlation between ansvf and N 2 O as well as (N 2 O + N 2 ) fluxes.…”

“…The dependence of denitrification on diffusion constraints was demonstrated by several models that were developed to predict the formation of anoxic centres within soil aggregates (Greenwood, 1961;Arah and Smith, 1989;Arah and Vinten, 1995;Kremen et al, 2005). The distance threshold for anoxic conditions to emerge was set on an ad hoc basis at 5 mm from connected air at the end of incubation but is likely to vary with O 2 demand by local microbial activity (CO 2 release represented by the green fringe area, item 2) during the incubation (Kremen et al, 2005;Rabot et al, 2015;Ebrahimi and Or, 2018;Keiluweit et al, 2018;Kravchenko et al, 2018;Schlüter et al, 2019). Because we could only conduct X-ray CT scans at the end of incubation, redistribution of water during the incubation time cannot be ruled out.…”

Emergent Properties of Microbial Activity in Heterogeneous Soil Microenvironments: Different Research Approaches Are Slowly Converging, Yet Major Challenges Remain

“…Yet, as far as soils are concerned, forays along these lines have been timid. At the mesoscale, very interesting work, starting already 25 years ago, describing how earthworm burrow systems evolve over time ( Joschko et al, 1991 ; Capowiez et al, 1998 ), how the geometry of macropores in paddy soils evolves during soil shrinkage ( Bottinelli et al, 2016 ), or how loamy soils are compacted during centrifugation ( Schlüter et al, 2016 ). Also, various researchers have used MRI systems to monitor the infiltration of water in clay and coarse sandy loam columns ( Amin et al, 1994 , 1996 ; Preston et al, 2001 ; Votrubová et al, 2003 ), γ-ray CT equipment to quantify the swelling of vertisols over time ( Biassusi et al, 1999 ), or neutron CT systems to investigate the dynamics of water flows in soil, especially in the rhizosphere ( Badorreck et al, 2010 ; Perfect et al, 2014 ; Tötzke et al, 2017 ).…”