Assessing soil compaction risk: identifying the optimal measure of effective load in multi-pass conditions

Soil compaction is a major challenge in modern agriculture. Multiple wheel passes with varying wheel types, sizes and loads are common, and the resulting impact on compaction remains unclear. This study aims to develop and evaluate a simple method to aggregate total wheel loads from multiple wheel passes to quantify their effect on soil compaction, disregarding other factors such as wheel size or type. From 2016 to 2021, 20 field trials were conducted on a silty loam site in northwest Germany, involving 1 to 8 wheel passes. For each wheel pass, static mass and vertical soil displacement at three depths were determined. Different aggregation schemes to calculate one effective load ( L e f f ) for all wheels were analyzed. A linear statistical model was applied to link vertical soil displacement to L e f f , soil depth, initial bulk density and water content. The best-performing scheme for L e f f closely matched the simple cumulative wheel loads (RMSE: 0.147 cm; r 2 : 0.59), while variants resembling maximum wheel load performed poorly (RMSE: 0.174 cm; r 2 : 0.43). All other variants lay between these two special cases. Our results suggest that for multiple wheel passes, the simple cumulative load is a reliable predictor for use in the assessment of soil compaction.