Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma Estimation of vineyard soil structure and preferential fow using dye tracer, X-ray tomography, and numerical simulations Vilim Filipović a, ⁎ , Jasmina Defterdarović a , Jiří Šimůnek b , Lana Filipović a , Gabrijel Ondrašek a , Davor Romić a , Igor Bogunović c , Ivan Mustać a , Josip Ćurić d , Radka Kodešová e a University of Zagreb Faculty of Agriculture, Department of Soil Amelioration, Zagreb, Croatia b Department of Environmental Sciences, University of California Riverside, Riverside, CA, USA c University of Zagreb, Faculty of Agriculture, Department of General Agronomy, Zagreb, Croatia d University of Zagreb, School of Medicine Clinical Hospital Dubrava, Department of Diagnostic and Interventional Radiology, Croatia e University of Life Sciences Prague, Faculty of Agrobiology, Food and Natural Resources, Department of Soil Science and Soil Protection, Prague, Czech Republic ARTICLE INFO Handling Editor: Yvan Capowiez Keywords: Arable soil structure Dye staining Nonequilibrium fow X-ray imaging Numerical modeling HYDRUS ABSTRACT The appearance and distribution of soil pores have a signifcant infuence on water fow and solute transport in the soil vadose zone. The pore system is highly variable in arable soils where crop rotation, tillage, trafcking, soil amendments, and various management practices are commonly implemented. The aim of this study was to assess the porous system and preferential fow pathways in a vineyard soil using undisturbed soil columns, and by combining laboratory and numerical methods with dye staining and X-ray imaging. It was hypothesized that the integration of various methods could reveal more information about soil structure, and fow and transport behavior of structured arable soil. Soil water retention and hydraulic conductivity curves were obtained using the evaporation method, while water fow was assessed using intermittent leaching experiments. Water fow and the transport of Brilliant Blue were simulated using HYDRUS-1D. A single-porosity model of soil hydraulic properties provided a good description of data collected during the evaporation experiments. Data collected during leaching experiments did not provide enough experimental evidence for the occurrence of none- quilibrium fow patterns and the diferentiation between the single- and dual-permeability models of soil hy- draulic properties. However, dye staining and X-ray imaging revealed a complex pore-architecture network with large vertical and horizontal biopores. The staining patterns (Brilliant Blue FCF) within the vertical column sections documented the extent of preferential fow. The study showed that the bi-modal character of pore structure could often be hidden when a limited number or non-adequate methods are applied for its quantif- cation from water fow behavior. The impact of preferential pathways on dye transport can be investigated with observations and simulations. A combination of various methods enabled us to adequately assess vineyard soil structure and fne-tune the description and extent of preferential water fow. 1. Introduction Most pronounced soil heterogeneity in terms of structural changes is present in the topsoil layer of arable soils, which are heavily modifed during each crop growing season by tillage and trafcking (Jirků et al., 2013; Strudley et al., 2008). Changes in climate, biological activity, and soil management practices may have a strong infuence on soil structure (Fér et al., 2016, 2019; Kodešová et al., 2011). Pagliai et al. (2004) demonstrated deterioration of the soil structure in arable soils due to enhanced oxidation of organic matter by aeration, mechanical disper- sion because of moist soil compression, or disaggregation of bare soil by rainfall. A newly developed pore system (e.g., after the tillage) in arable soils, even with a well-connected network of larger pores, is often un- stable and changes rapidly. As reported by Horn (2004), the temporal variability of soil structure and its evolution is infuenced by various biotic and abiotic factors, and it is often challenging to properly esti- mate its infuence on subsurface fow and transport properties. In the Mediterranean, vineyards are one of such agricultural systems with enhanced soil structure degradation due to topography, climatic con- ditions, intensive management, and trafcking practices (Bogunović et al., 2020; Galati et al., 2015; Prosdocimi et al., 2016a, 2016b). Vi- ticulture areas register some of the highest rates of soil and water losses in Europe as a result of employing unsustainable practices and man- agement (e.g., large interrow widths, low leaf cover, steep slopes, and https://doi.org/10.1016/j.geoderma.2020.114699 Received 27 April 2020; Received in revised form 26 August 2020; Accepted 29 August 2020 ⁎ Corresponding author. E-mail address: vflipovic@agr.hr (V. Filipović). Geoderma 380 (2020) 114699 0016-7061/ © 2020 Elsevier B.V. All rights reserved. T