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Integrating X-ray CT data into models

X-ray Computed Tomography (X-ray CT) offers important 4-D (i.e., 3-D scanning over time) structural information of the soil architecture. This imaging tool provides access to the 3-D morphological properties of the soil pore space such as the 3-D connectivity of pores that are essential to the understanding of water, solute, and gas transport processes. Other morphological properties such as pore-size distribution, specific surface area, or spatial heterogeneity of soil can be obtained from the X-ray CT images. Many studies have used this technique to better understand the evolution of macroscopic soil physical properties such as structural stability and relate it to spatial descriptors of soil pore space morphology when the soil undergoes wetting/drying cycles (e.g., Diel et al., 2019) or when it is subjected to different agricultural practices (e.g., Papadopoulos et al., 2009; Dal Ferro et al., 2013; Caplan et al., 2017). Non-equilibrium transfer processes, such as preferential transport, have also been related to the quantification of macropores in X-ray CT images (e.g., Larsbo et al., 2014; Katuwal et al., 2015; Soto-Gómez et al., 2018). In addition, X-ray CT data have proved particularly useful for reconstructing the skeletons of biopore networks, such as those burrowed by earthworms (Capowiez et al., 1998), and for monitoring their temporal dynamics (Joschko et al., 1993) (see Chap. 10). The role of air-filled soil pores and in particular their connectivity in 3-D in the transport of microbial-generated gaseous products (N2O, CO2) have been hypothesized (Rabot et al., 2015; Porre et al., 2016). X-ray CT data have also provided new knowledge about the 3-D architecture of root systems (e.g., Helliwell et al., 2013) and their impact on the 3-D soil architecture (see Chap. 9). For instance, root hairs were shown to modify the pore-size distribution and connectivity in the rhizosphere (e.g., Keyes et al., 2013; Koebernick et al., 2017, 2019). X-ray CT measurements have also allowed imaging aerenchymatous roots and the gas bubbles entrapped in the soil of rice paddies to explain transport of CO2 and O2 between roots and the atmosphere (Kirk et al., 2019). The dynamics of the spatial dispersion of soil microorganisms could be related to the 3-D description of the pore space obtained by X-ray CT (Juyal et al., 2020). The role of some pore-size classes could also be linked with soil carbon storage (Kravchenko et al., 2020) (see Chap. 10).