A Conceptual Framework for Assessing Soil Structural Attributes Across Contrasting Land-Use Types

Abstract

Soil structure governs ecosystem functioning across scales, but its complexity requires integrative approaches that capture geometric and functional properties. This study proposes a methodological framework that integrates field-based visual evaluation of soil structure (VESS), X-ray computed tomography (CT) and soil hydraulic property (SHP) assessment to quantify structural attributes for contrasting land-use types (arable land, grassland, forest). This approach assesses soil structure from three perspectives: aggregate architecture, macropore connectivity and hydraulic function. As a conceptual framework to isolate structural and texture effects and quantify differences related to land use, we chose three sites in Switzerland with similar topsoil texture and close proximity (~1 km). Undisturbed topsoil samples were collected for CT and SHP measurements (250 mL, 5–10 cm depth) while VESS was performed in situ (5–10 cm and 0–30 cm depth). Assessment of SHP included measuring the soil water retention curve and the saturated and unsaturated hydraulic conductivity. CT imaging (91 μm pixel size) quantified macropore volume and connectivity metrics (Euler-Poincaré characteristic EPC and gamma indicator). Saturated hydraulic conductivity data aligned closely with CT metrics, especially macroporosity and the EPC, highlighting their utility in bridging structural observations with functional implications. Despite smaller total porosity, soils at the arable site showed a better VESS score and greater macroporosity and saturated hydraulic conductivity than soils at the grassland site, underscoring the importance of combining different metrics in structural interpretation. The combined methods capture complementary aspects of soil structure, ranging from aggregate-scale features to pore connectivity and hydraulic function, and improve structural interpretation for soil health assessment. Following upon this methodological framework with a small sample size (11 samples) and results related to site specific conditions, future research should validate whether relationships between field-based VESS scores and laboratory metrics hold across broader pedological conditions, to potentially make VESS a quantitative predictor of soil structural functionality for large-scale monitoring.