|Way, Thomas - Tom|
Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2003
Publication Date: 10/15/2003
Citation: Horn, R., Way, T.R., Rostek, J. 2003. Effect of repeated tractor wheeling on stress/strain properties and consequences on physical properties in structured arable soils. International Journal of Soil and Tillage Research. 73:101-106. Interpretive Summary: Tractors and other equipment traffic the soil during production of agricultural crops. This traffic causes the soil to compact and deform as the soil aggregates and particles move relative to one another. A clay soil was trafficked by 10 passes of both a front and a rear tire of a tractor and the resulting shear and displacement occurring in the soil were found to be capable of causing a highly compacted soil layer. This research emphasizes the detrimental effect that traffic from tractors and other vehicles can have on soil.
Technical Abstract: The discussion about the effect of repeated short duration tire passes on long-term changes in soil structure and pore functioning reveals a great uncertainty. On the one hand, it is said that soil structure elements are rigid and do not undergo intense changes in pore functions as a consequence of the short loading duration during each pass of a tire. On the other hand, the complete deterioration of the structure elements and pore functions is assumed to occur, and this results in changes in the shrinkage pattern and soil strength, including even strength regain. Consequently, the effect of tire passes on soil deformation and the distribution of stress and strain was investigated in a soil bin containing Hiwassee clay. If the soil is very strong due to aggregation, plow pan formation or dryness, soil stresses applied by repeated tire passes cause increased soil particle displacement, primarily in the vertical direction. During repeated tire passes, up to 10 passes of both a front and rear tire of a tractor, a more pronounced displacement linked with a more intense movement of particles occurs. With increasing numbers of tire passes, new platy or again coherent structure elements are formed, and these create a very different pore system. At a given pore water pressure value, as the intensity of tire passes increases, the saturated hydraulic conductivity decreases and unsaturated hydraulic conductivity increases. As the rearrangement of the still-existing aggregates into new units like plates becomes more complete, such changes become more pronounced. Shear in soil and the three-dimensional soil displacement, even when the soil is dry, can cause the aggregates to be re-disturbed and a coherent but very compacted soil horizon can be formed. Under conditions like these, the soil bulk density can be even greater than the Proctor density.