Detection of negative consequences of traffic on subsoil properties depends on measurement type and scale: The case of a Calcaric Chernozem

Larger, heavier agricultural machinery compacts subsoil, degrading structure, impairing hydraulic properties, and increasing greenhouse gas (GHG) emissions. The impacts of traffic-induced compaction can be assessed in the laboratory or the field, though results from these methods often differ. This study aimed to quantify changes in subsoil properties caused by field traffic using lab and field methods, compare traffic-induced pore structure alterations at two sample size scales, and explore links between pore structure and greenhouse gas emissions. A compaction experiment was conducted on a Calcaric Chernozem loam soil, comparing a trafficked treatment (TF) with a 3 Mg wheel load to a non-trafficked (NT) reference. Six months later, we evaluated the impact of the traffic event on the subsoil (30–35 cm depth) by conducting field measurements [saturated hydraulic conductivity ( K s ), visual evaluation of subsoil structure (SubVESS), and penetration resistance (PR)]. Different laboratory measurements conducted on intact soil cores (100 cm 3 and 580 cm 3 ) included soil water retention curve (SWC), air-filled porosity (ε a ), Darcy air permeability (k a-Darcy ), gas diffusivity (D p /D 0 ), and bulk density (BD), X-ray computed tomography (CT) analysis of soil pore structure, and potential N 2 O and CO 2 emissions. Both field and laboratory measurements indicated negative impacts of traffic. In the field, traffic reduced K s by 31 % (p = 0.45), increased PR by 22 % (p = 0.2), and lowered SubVESS structural quality (p = 0.001). Laboratory measurements showed that traffic significantly (p < 0.05) increased BD by 4 %, and at pF 2, it decreased ε a , k a-Darcy , and D p /D 0 by 23 %, 71 %, and 48 %, respectively, alongside a decrease (p > 0.05) in CT-derived macroporosity volume. Potential greenhouse gas emissions were higher in the trafficked (TF) treatment. The effect of compaction on BD, ε a , and k a-Darcy was similar regardless of sample size, though, for a given treatment, the 100 cm 3 samples were denser and had lower ε a , and slower airflow (k a-Darcy ) compared to 580 cm 3 samples. The effect of traffic on soil properties, relative to established thresholds indicating harmful deterioration of soil functions, varied depending on whether the variable was measured in the field or laboratory, and whether small or large rings were used. Further research is needed to establish critical limits for soil properties and functions using different sample scales. • Impact of 3 Mg wheel load on loam subsoil was assessed by field and lab methods using two sample sizes (100 and 528 cm 3 ). • Traffic negatively impacted penetration resistance, fluid flow, and pore structure. • Traffic effects were consistent for the two sizes, but larger samples had lower density and faster airflow. • Lab-based measures showed stronger traffic impacts than field-based ones. • Traffic increased potential greenhouse gas emissions.