Soil Displacement and Soil Bulk Density Changes as Affected by Tire Size
The selection of the appropriate tire size and inflation pressure for a particular load and soil condition is a critical consideration to ensure that the effects of vehicle traffic on soil compaction are minimized and that agricultural soils are managed in a sustainable manner. This study investigated the changes in soil bulk density from soil displacement data produced by a range of combine harvester tires (680/85R32, 800/65R32, and 900/60R32) with vertical load of 10.5 t and inflation pressures in the range of 0.19 to 0.25 MPa to provide a valuable indicator for tire selection. The study was conducted in a soil bin facility using a sandy loam soil (Cottenham series) maintained at 10% (w w-1) moisture content. Results showed that the initial density (γ) was the main factor influencing soil displacement and soil bulk density changes beneath the tires. Increased tire size and low inflation pressure reduced soil displacement and the resultant increase in soil bulk density. After a single pass of the tires over the soil, these increases were approximately 26% for a low (γ = 1.20 g cm-3), 17% for a medium (γ = 1.40 g cm-3), and 4% for a high (γ = 1.60 g cm-3) initial bulk density soil, respectively. The advantages of increasing tire size and lowering inflation pressure were also reflected in the results obtained from the cone penetrometer resistance data. The tire with the highest inflation pressure (0.25 MPa) produced a significantly (p < 0.05) higher increase in soil cone index (0 to 700 mm depth range) compared with the tires with lower inflation pressures (0.19 and 0.22 MPa, respectively), particularly at the centerline of the wheeling. Linear relationships (R2 ≥ 0.98) between drop cone penetration and rut depth were established; these data were subsequently related to the calculated increase in soil bulk density determined from soil displacement data. The increase in soil bulk density resulting from a single pass of a tire over the soil can be determined for a range of tire configurations and initial soil conditions with the data produced by this study.