Heavy Traffic with Repeated Wheeling Induced Deep Soil Compaction and Impeded Root Growth.

Soil compaction is considered a major threat to soil quality and crop productivity. The objective of this contribution was to evaluate the effect of heavy traffic on subsoil structure and root growth. Measurements were carried out in an experiment initiated 2010 on a Danish sandy loam. Six levels of compaction were applied prior to sowing with spring barley. In this study, we used the non-compacted reference, a moderate (3 Mg wheel load) and two heavy traffic treatments, i.e. 8 Mg wheel load at high inflation pressures and 12 Mg wheel load at moderate inflation pressures. The treatments were applied early spring in 2010-2013 using a tractor with a slurry trailer (3 and 8 Mg) or a 3 wheel self-propelled slurry tanker with (12 Mg) to create wheel tracks covering the entire plot. In May 2015 the profiles were visually evaluated, penetration resistance measured at 0-90 cm depth and soil cores sampled at 30, 50, 70 and 90 cm depth. Early June 2015, soil cores were taken in reference, 3 Mg and 8 Mg for root growth measurement. The 8 Mg multiple-wheel pass treatment had visually assessed poorest subsoil structure (25-80 cm depth) and highest penetration resistance down to 60 cm depth. The 12 Mg one-wheel pass treatment slightly reduced subsoil structure quality in the upper subsoil (i.e. 25-45 cm) as compared with the reference treatment. The difference between the heavy traffic treatments was ascribed to lower inflation pressure and fewer wheel passes for 12 Mg than 8 Mg. The 8 Mg treatment impeded subsoil root growth as compared with the other treatments. In conclusion, this study showed marked negative impact of heavy multi-wheel pass traffic on subsoil structure and root growth. The results also confirmed the applicability of using visual methods to assess subsoil compaction damages.