Temporal and Vertical Variability of Post-Tillage Topsoil Hydraulic Properties at a Local Scale

• Post-tillage topsoil shows strong temporal and vertical hydraulic variability. • Depth explains ∼ 50% of hydraulic variance, seasonality ∼ 30–40%. • SWRC parameters and full curves reveal complementary variability patterns. • Assuming uniform topsoil layer hydraulics risks major model bias. • Ignoring effect sizes or single-parameter summaries misrepresents soil hydraulics. Soils exhibit considerable variability in their physical and hydraulic properties, which can change both spatially and temporally. However, studies capturing short-term temporal and internal vertical variability within tilled topsoil remain limited. In this one-year study (May 2023–2024), we investigated seasonal changes in the physical and hydraulic properties of the bare topsoil after tillage in a humid continental climate in Czechia. Monthly sampling was conducted on a 16 m 2 plot, targeting the upper 12 cm of soil, divided into 0 to 5 cm and 7 to 12 cm layers. A total of 28 disturbed and 107 undisturbed samples were collected, and 40 soil water retention curves (SWRCs) were measured and fitted with the van Genuchten–Mualem model to derive hydraulic parameters ( α, n, θ r , θ s , K s ). Robust statistical analyses (permutation tests, Kruskal–Wallis, Dunn’s test, LOWESS, and MANOVA) were used to evaluate vertical and temporal variability. The results revealed significant changes in the hydraulic properties of the fitted devices. The depth explained approximately half of the total multivariate variance (η 2 ≈ 0.5), while time accounted for roughly one-third (η 2 ≈ 0.3–0.4). The upper layer exhibited greater heterogeneity in the n parameter (1.404 ± 0.126) compared to the deeper layer (1.254 ± 0.103), while α showed comparable variability (0.060 ± 0.019 vs. 0.075 ± 0.024). These moderate-to-large effect sizes indicate that, even within the first 12 cm, hydraulic behavior is neither uniform nor static. The contrasting patterns between the fitted full SWRCs and their derived parameters highlight the importance of evaluating both datasets jointly. Relying solely on parameter statistics or individual retention curve risks overlooking meaningful temporal and vertical dynamics. Our findings demonstrate that post-tillage topsoil evolves structurally and hydraulically even in the absence of vegetation or management, emphasizing the need for depth- and time-resolved parameterization in hydrological and soil-process modeling.