The contribution of tyre evolution to the reduction of soil compaction risks

The use of today’s heavy machinery in agriculture poses a great risk to soil in the form of compaction. Subsoil compaction has been found to persist for decades, thus reducing the risk is extremely important. The stress distribution in the contact area between the tyre and the soil is of primary importance for the propagation of stress in the soil. The characteristics of the tyre therefore affect soil stress. The objective of this study was to compare effects of five generations of tyres (introduced from before the 1970s to 2018) on soil stress and soil structure, including two standard narrow tyres and three larger low-aspect-ratio tyres. Wheel loads of 2900 and 4300 Mg were chosen for the front and rear axles respectively, and the load-rated inflation pressure ranged from 240 to 60 kPa. The contact stress distribution was estimated using the FRIDA model and was used as input for calculation of the vertical stress through the soil profile. Mean normal stress and physical properties were quantified in a field experiment on a clay soil in Clermont-Ferrand, France. The results show that for a given wheel load, the tyre-evolution reduced soil stress when the development included an increase in the tyre-soil contact area and an associated decrease in the tyre inflation pressure. FRIDA model calculations indicated a reduction in soil stress for newer tyres due to a more even contact stress distribution, and were confirmed by the mean normal stress measurements. Although the difference in soil stress between the various tyres decreased with depth, a significant reduction was measured even at 0.6m depth beneath the centreline of both front and rear tyres. We found only a very limited effect of the traffic on the dry bulk density and air permeability at 0.3m depth below the centre of the tyres.