X-ray microtomography analysis of soil pore structure dynamics under wetting and drying cycles

Area of Science:

• Soil Science
• Environmental Science
• Geophysics

Background:

• Soil water retention is crucial for predicting plant available water, pore size distribution, and hydraulic conductivity.
• Standard measurement methods involve multiple wetting and drying (W-D) cycles, assuming stable soil structure.
• However, soil structure is dynamic and can change with repeated W-D cycles, affecting pore architecture.

Purpose of the Study:

• To investigate the impact of W-D cycles on soil pore architecture during water retention curve evaluation.
• To analyze changes in porosity, connectivity, tortuosity, and pore shape.
• To assess how these microstructural changes influence soil water retention measurements.

Main Methods:

• High-resolution X-ray Computed micro-Tomography was employed to visualize soil pore architecture.
• Two regions of interest were analyzed: the whole sample (ROI_W) and the region near the hydraulic contact (ROI_HC).
• Samples underwent 0, 6, and 12 W-D cycles.

Main Results:

• W-D cycles significantly altered soil porous architecture.
• Porosity increased in ROI_HC but remained unchanged in ROI_W.
• Pore connectivity improved in ROI_HC, while pore alignment (tortuosity) increased in both ROIs.
• Pore size and shape were significantly influenced by W-D cycles, especially in ROI_W.

Conclusions:

• Repeated W-D cycles during water retention curve measurements induce significant changes in soil pore architecture.
• These microstructural alterations, particularly in the sample region near the hydraulic contact, can affect the accuracy of water retention evaluations.
• Understanding these dynamic soil morphological changes is essential for reliable soil hydraulic property assessment.