Effects of soil wetness and tyre pressure on soil physical quality and maize growth by a slurry spreader system

Slurry spreaders are among the heaviest machines used for farming operations. The effects of soil wetness and tyre pressure on physical soil properties were evaluated by using a ˜5 Mg wheel load slurry spreader mounted on a tractor. The impacts were also compared with Terranimo® model predictions and X-ray micro-computed tomography (X-ray micro-CT) parameters. In the consecutive maize growing season, soil physical properties, total mineral nitrogen content and maize above biomass were evaluated additionally between in and out track positions. Immediately after traffic, penetration resistance (PR) was significantly higher (P < 0.05) under moist conditions and at in-track positions compared with dry conditions and out-track positions for the top 10 cm. Tyre pressure did not affect PR at in- or out-track position. At 10 cm depth, bulk density and macro-porosity (d> 30 μm) of soil trafficked under moist conditions was different (P ≤ 0.10) from those under dry conditions. Macro-porosity showed a clear response (P < 0.10) to tyre pressure and all the trafficked treatments. Deeper in the profile, there were no significant differences in these soil physical quality indicators. X-ray micro-CT results agreed well with the soil physical quality indicators, and detected slight changes in degree of compaction more precisely. Terranimo® well predicted the contact area and mean ground pressure (RMSE=0.06 m²). It indicated considerable compaction risk from the tractor's rear wheels, which seemed to contradict with the relatively minor changes in soil physical properties observed. In the maize growing season, soil physical properties and nitrogen content showed no significant differences (P > 0.05) between in- and out-track positions while above ground dry biomass of maize reduced with ˜7% at in-track positions.