Compaction of an Eutric Cambisol under heavy wheel traffic in Switzerland — field data and modelling

Heavy agricultural machinery can cause structural degradation in agricultural subsoils. Severe structural degradation impedes plant growth. Therefore, compaction must be limited to layers that can be structurally reclaimed and remoulded with reasonable effort by tillage. The purpose of this study was to investigate the impact of a single pass with a sugar beet harvester on the soil properties of an unploughed Eutric Cambisol. Field measurements and laboratory testing were carried out in Frauenfeld, Switzerland. In addition 2D calculations of strain, stress and subsequent compaction were conducted using a three-phase (soil skeleton, pore water, and air) model for unsaturated soil incorporating a recently developed constitutive law. Model data were compared to the field measurements. Due to the pass of the machinery, the soil was compacted down to a depth of at least 0.15 m and at most 0.25 m. This compaction was indicated by an increase in soil bulk density and pre-consolidation pressure as well as by a decrease in total porosity and macroporosity. The surface displacement measured in the field was consistent with the calculated model data. The calculated and measured stresses at depths of 0.35 and 0.55 m stand in good accordance with each other, whereas at a depth of 0.15 m the pressure measured in the field exceeded the calculated pressure. In this study, we show the degree of compaction due to heavy wheel traffic and the suitability of a model approach to describe compaction processes.