Subsoil compaction caused by heavy sugarbeet harvesters in southern Sweden: I. Soil physical properties and crop yield in six field experiments

The introduction of six-row sugarbeet harvesters, with total loads of approximately 35 Mg on two axles, caused major concern among Swedish sugarbeet (Beta vulgaris L.) growers regarding the risk for subsoil compaction. A project was started in 1995, which included six long-term field experiments in southern Sweden. The objective was to study effects of heavy axle load traffic during harvest of sugarbeets on penetration resistance, saturated hydraulic conductivity, bulk density and crop yield. Three of the field sites were loams (Eutric Cambisols), two were sandy loams (Eutric Cambisols) and one was sand (Haplic Arenosol). The treatments were: no traffic, four passes by a three-row harvester towed by a tractor (approximately 18 Mg total load on four axles, tyre inflation pressure of tractors 100–150, and 200–250 kPa for the harvester) and one and four passes by a self-propelled six-row harvester (approximately 35 Mg total load on two axles, tyre inflation pressure 200–240 kPa). Traffic was applied late in the autumn at a soil moisture content close to field capacity, but the treatment with four passes with a six-row harvester was also carried out under drier conditions earlier in the autumn. spring after traffic, no significant changes in penetration resistance were found. When measured 2–4 years after traffic, significant changes between treatments were found to 0.5 m depth on three sites. Differences between years are possibly an effect of age-hardening. ted hydraulic conductivity at 0.3 and 0.5 m depth, measured on cores sampled in the spring after traffic, was in several cases reduced by about 90% after four passes with a six-row harvester. As an average for all sites, this traffic significantly reduced saturated hydraulic conductivity and increased bulk density at 0.5 m depth. At two sites, measurements were repeated 4 years after traffic and differences in saturated hydraulic conductivity between treatments were approximately the same as on the first sampling occasion. Despite the great effects on soil physical properties, differences in yield between treatments were mainly small and insignificant. ta concerning saturated hydraulic conductivity may be useful for modelling the effects of subsoil compaction, for example on erosion and denitrification, since little such data is available in the literature. The results clearly demonstrate to farmers that heavy traffic during harvest of sugarbeet implies a major risk for compaction of the subsoil, which can be seen as a long-term threat to soil productivity.