Response of selected soil physical properties to various traffic loads at three field landscape positions

Abstract

Machinery‐induced compaction and landscape position both influence soil physical properties that regulate water movement, gas exchange, and pore continuity. Despite their importance, the combined effects of compaction and topography on soil physical functions remain underexplored. The objective of this study was to quantify the responses of bulk density ( ρ _b ), air permeability ( K _a ), saturated hydraulic conductivity ( K _sat ), macropore volume (MPV), and soil water retention to four wheel‐traffic loads applied at summit (ST), backslope (BS), and toeslope (TS) landscape positions located on a Des Moines Lobe field in Iowa. Traffic loads included control (C = 0 Mg), planter (P = 11 Mg), grain cart (GC = 28 Mg), and grain cart plus planter (GC + P = 28 + 11 Mg). Soil physical properties varied significantly ( p  < 0.0001) by landscape position. TS had the smallest values for ρ _b (1.33 g cm ^{− 3} ), K _a (0.58 µm ² ), K _sat (0.18 cm h ⁻¹ ), and MPV (0.051 cm ³ cm ^{− 3} ), while retaining the greatest volumetric water content across matric potentials from 0 to −500 cm H ₂ O. Increasing wheel traffic load significantly affected ρ _b and MPV. K _a and K _sat varied by compaction treatments, but effects were not statistically significant. Across landscape positions, heavier loads (i.e., GC and GC + P) increased ρ _b by 4% relative to C. MPV declined progressively with compaction, showing a 16% reduction in the P treatment (MPV = 0.07 cm ³ cm ^{− 3} ) and losses exceeding 36% in the GC+P (MPV = 0.053 cm ³ cm ^{− 3} ) compared to C (MPV = 0.084 cm ³ cm ^{− 3} ). Wheel load had a minor effect on θ _v at saturation, but at drier matric potentials (below −25 cm H ₂ O), compacted treatments retained 4%–7% more water than the control, with responses varying by landscape position. These results indicate the combined effects of topography and compaction on soil properties, emphasizing the need to consider both factors in sustainable field traffic and compaction management strategies.