One option for ground drive systems with large harvesting equipment is to use rubber belted tracks; however, little is known about the performance of these relative to appropriately sized pneumatic tyres. We aimed to study the effect of self propelled wheels and a track with high axle loads (9-24t) on soil compaction. This was assessed by embedding talcum powder lines as tracer into the soil during preparation to measure soil displacement and soil density changes. Additionally, soil dry bulk density and penetrometer resistance were measured. The track with loads of both 10.5 and 12 t compacts the soil less than wheels at 10.5 t load in both weak uniform and stratified soil. Towed implement wheels with 4.5 t load caused similar soil displacement to the track with a load of 12 t. Inflation pressure had a significant influence on soil parameters and a larger overall diameter is more beneficial than a wider tyre. The study emphasises the importance of contact pressure and its distribution with respect to soil density changes. Total axle loads are less important than how these are distributed on the ground.

This paper reports on a study of the effect of the passage of multi-axle harvesting machines on the soil physical properties. In particular, to determine the effect of the rear tyre of a combine harvester on the amount of soil compaction subsequent to the passage of the front tyre/track. The work was conducted in controlled laboratory conditions to determine the effect of a simulated self propelled combine harvester with a total machine weight of 30-33 t. This was assessed by embedding talcum powder lines as a tracer in the soil to measure soil displacement and soil density changes. Additionally, dry bulk density and penetrometer resistance were measured. The results showed that the benefit of the rubber track found by Ansorge and Godwin (2007, a) was maintained after the additional passage of the rear tyre. After the passage of a track the effect of rear tyre size was insignificant, but the rear tyre size had a significant influence on soil density when following a leading tyre. This was due to a higher strength layer at the soil surface created by the track which was able to withstand the load of the subsequent passes and protect the soil below from further compaction. Results similar to those found for a tracked machine were also achieved by three passes of a 900 mm section width tyre at 5 t load and 0.5 bar inflation pressure. The track results for the 33 t machine were very similar to those of a smaller combine harvester with a total load of 11 t and similar rut width. The study corroborated the benefit of tracks with regard to soil compaction and emphasised the fact that total axle loads and machine weights are less important than how the loads are distributed on the soil.

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Abstract.