SOIL DISPLACEMENT BENEATH AN AGRICULTURAL TRACTOR DRIVE TIRE

Authors: Way, Thomas - Tom; Erbach, Donald; BAILEY, ALVIN - RETIRED ARS EMPLOYEE; BURT, EDDIE - RETIRED ARS EMPLOYEE; JOHNSON, CLARENCE - RETIRED AUBURN UNIVERSITY

Submitted to: Soil Dynamics International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/19/2004
Publication Date: 1/3/2005
Citation: Way, T.R., Erbach, D.C., Bailey, A.C., Burt, E.C., Johnson, C.E. 2005. Soil displacement beneath an agricultural tractor drive tire. Soil Dynamics International Conference Proceedings. 42(1):35-46.

Interpretive Summary: To produce agricultural crops, tractors and other equipment must traffic the soil. This traffic causes soil compaction and other environmental concerns, including increased runoff and soil erosion, soil degradation, and crop production problems. Soil beneath a tractor drive tire undergoes strain, meaning it is compressed and elongated. Strain in a sandy loam soil beneath a radial-ply tractor drive tire was measured using transducers inserted in the soil. Results indicate that soil bulk density, which has often been used by researchers, does not always indicate soil displacement that occurs during traffic. This finding emphasizes the fact that soil strain typically occurs during traffic so connectivity of soil pores may be disrupted, thereby reducing water infiltration and water holding capacity, and increasing runoff and soil erosion, while initial and final soil bulk density information alone may not reflect this strain.

Technical Abstract: Soil strain transducers were used to determine strain in an initially loose sandy loam soil in a soil bin beneath the centerline of an 18.4R38 radial-ply tractor drive tire operating at 10% travel reduction. The initial depth of the midpoints of the strain transducers beneath the undisturbed soil surface was 220 mm. Strain was determined in the vertical, longitudinal, and lateral directions. Initial lengths of strain transducers were approximately 118 mm for the longitudinal and lateral transducers and 136 mm for the vertical transducer. The tire dynamic load was 25 kN and the inflation pressure was 110 kPa, which was the recommended pressure corresponding to the load. In each of four replications, as the tire approached and passed over the strain transducers, the soil first compressed in the longitudinal direction, then expanded, and then compressed again. The soil compressed in the vertical direction and the soil expanded in the lateral direction. Mean natural strains of the soil following the tire pass were -0.2000 in the vertical direction, +0.1274 in the lateral direction, and -0.0265 in the longitudinal direction. The mean final volumetric natural strain from the strain transducer data was -0.0991, which was only 35% of the mean change in natural volumetric strain calculated from soil core samples, - 0.2861. The strain transducer data indicated the occurrence of plastic flow in the soil during one of the four replications. These results indicate the complex nature of soil movement beneath a tire during traffic and emphasize a shortcoming of soil bulk density data because soil deformation can occur during plastic flow while soil bulk density remains constant.