Characterising and linking X-ray CT derived macroporosity parameters to infiltration in soils with contrasting structures

• Published in: Geoderma 2018-03, Vol.313, p.82-91
• Main Authors: Müller, Karin, Katuwal, Sheela, Young, Iain, McLeod, Malcolm, Moldrup, Per, de Jonge, Lis Wollesen, Clothier, Brent
• Format: Article
• Language: English
• Subjects: Environment and Society; Environmental Sciences; Hydraulic parameters; Image analysis; Pore network; Soil structure; Tension disc infiltrometry
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2017.10.020

Soils deliver the regulating ecosystem services of water infiltration and distribution, which can be controlled by macropores. Parameterizing macropore hydraulic properties is challenging due to the lack of direct measurement methods. With tension-disc infiltrometry hydraulic properties near saturation can be measured. Differentiating between hydrologically active and non-active pores, at a given water potential, indirectly assesses macropore continuity. Water flow through macropores is controlled by macropore size distribution, tortuosity, and connectivity, which can be directly derived by X-ray computed tomography (CT). Our objective was to parameterize macropore hydraulic properties based on the imaged macropore network of three horizons of an Andosol and a Gleysol. Hydraulic conductivity Kunsat was derived from infiltration measurements. Soil cores from the infiltration areas were scanned with X-ray CT. Kunsat was significantly higher in the Andosol than in the Gleysol at all water potentials, and decreased significantly with depth in both soils. The in situ measurements guided the definition of new macroporosity parameters from the X-ray CT reconstructions. For the Andosol, Kunsat was best predicted using the imaged-limited macroporosity. A low total macroporosity, coupled with a high macropore density, indicated the abundance of smaller macropores, leading to homogeneous matrix flux. Imaged macropores were not well connected. In contrast, the Gleysol had a bi-modal macropore system with few very large, but well-connected macropores. Kunsat was best predicted using the imaged macroporosity consisting only of macropores with diameters between 0.75 and 3mm. Our research demonstrates that linking traditional soil physical measurements with soil-visualization techniques has a huge potential to improve parameterizing macropore hydraulic properties. The relevance of the relationships found in this study for larger scales and other soil types still needs to be tested, for example by a multi-scale investigation including a much wider range of different soils. •Tension infiltrometry guided defining macroporosity parameters from X-ray CT images.•Imaged macroporosity (pores: 0.38–1.5mm radius) predicted Kunsat well for Gleysol.•Imaged limited-macroporosity predicted Kunsat well for Andosol.•Linking measurement with visualization improved parameterizing macropore properties.