Impact on soil compaction of driving agricultural machinery over ground frozen near the surface

The compaction of arable soils caused by driving over them with agricultural machinery poses a serious problem in numerous agricultural regions across temperate climate zones. The risk of compaction is particularly high in early spring or late autumn when soils are wet. This is why driving over soils frozen near the surface is recommended in some cases in temperate climate zones to prevent soil compaction. However, no findings have been available about the thickness of frozen soil required to effectively prevent compaction when the soil is driven over. In one experiment, soil physical measurements were carried out on the topsoil after a single pass with a tractor (4100 kg wheel load, 80 kPa inflation pressure) over an unfrozen variant, a variant with 2–3 cm frost covering and a variant with 5–7 cm frost covering, with comparisons made with a control variant that had not been driven over. Driving over the unfrozen variant led to a significant compaction of the whole of the topsoil. By contrast, the frozen surfaces were able to significantly buffer the compaction. No appreciable differences were detected between the two depths of frost penetration. A depth of frost penetration of as little as 2–3 cm was therefore sufficient to reduce the risk of compaction with a wheel load of approximately 4000 kg and appropriately adjusted inflation pressure.