Two-Dimensional Modeling of Infiltration in Heterogeneous Soils: The Effects of Topsoil-Subsoil Interface and Wheel Track Compaction

Accurate prediction of infiltration into the soil is essential for a variety of applications, including irrigation planning, flood prediction, and pollutants transport. In this study, we applied a two-dimensional model for simulating infiltration in heterogeneous soils, focusing on the effects of topsoil-subsoil interface morphology with the presence of wheel tracks. The model is based on the Richards equation and includes different soil hydraulic properties (SHP) for three soil materials: topsoil, subsoil and wheel track. To examine the effects of the topsoil-subsoil interface and wheel track compaction on infiltration, we conducted field experiments on a 16 m2 plot with simulated rain with constant precipitation intensity. We collected soil moisture and soil water pressure data at different depths and used these data to optimize the SHPs. The topography of the soil surface and the morphology of topsoil-subsoil interface were also recorded using photogrammetric methods. The results of the model simulations show that the topsoil-subsoil interface and wheel track compaction have significant effects on infiltration. The topsoil-subsoil interface acts as an infiltration barrier. The morphology of the interface causes a large heterogeneity in the water flow field and completely diminishes the effect of the slope on the water flow. The wheel track caused an infiltration excess overland flow while the topsoil outside the wheel track exhibited saturation excess overland flow. Subsoil in the wheel track remained unsaturated throughout the rainfall simulation period, affecting water redistribution after the rainfall ended. This study demonstrates that even the small-scale heterogeneity in the shallow part of the soil profile strongly influences the water flow field. The disturbed flow field can affect the distribution of water and nutrients in the root zone and potentially cause the activation of preferential pathways due to the spatial variability of saturation at the topsoil-subsoil interface. The work presented above was supported by an EU TuDi project no. 101000224 and by State Environmental Fund of the Czech Republic project no. 085320/2022.