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SOIL PHYSICS

Three-Dimensional Quantification of Intra-Aggregate Pore-Space Features using Synchrotron-Radiation-Based Microtomography

Dep. of Plant Nutrition and Soil Science Christian-Albrechts-Univ. Kiel Germany

^* Corresponding author (s.peth{at}soils.uni-kiel.de).

Pore network geometries of intra-aggregate pore spaces are of great importance for water and ion flux rates controlling C sequestration and bioremediation. Advances in non-invasive three-dimensional imaging techniques such as synchrotron-radiation-based x-ray microtomography (SR-µCT), offer excellent opportunities to study the interrelationships between pore network geometry and physical processes at spatial resolutions of a few micrometers. In this paper we present quantitative three-dimensional pore-space geometry analyses of small scale (5 mm across) soil aggregates from different soil management systems (conventionally tilled vs. grassland). Reconstructed three-dimensional microtomography images at approximate isotropic voxel resolutions between 3.2 and 5.4 µm were analyzed for pore-space morphologies using a suite of image processing algorithms associated with the software published by Lindquist et al. Among the features quantified were pore-size distributions (PSDs), throat-area distributions, effective throat/pore radii ratios as well as frequency distributions of pore channel lengths, widths, and flow path tortuosities. We observed differences in storage and transport relevant pore-space morphological features between the two aggregates. Nodal pore volumes and throat surface areas were significantly smaller for the conventionally tilled (Conv.T.) aggregate (mode 7.9 x 10^–7 mm³/ 63 µm²) than for the grassland aggregate (mode 5.0 x 10^–6 mm³/ 400 µm²), respectively. Path lengths were shorter for the Conv.T. aggregate (maximum lengths < 200 µm) compared with the grassland aggregate (maximum lengths > 600 µm). In summary, the soil aggregate from the Conv.T site showed more gas and water transport limiting micromorphological features compared with the aggregate from the grassland management system.

Abbreviations: Conv.T., conventional tillage • DU, down to upward flow • IK, indicator kriging • LR, left to right flow • PSD, pore-size distribution • SOC, soil organic carbon • SR-µCT, synchrotron radiation microtomography • TSD, throat-size distribution