Mitigation measures designed to reduce soil compaction decrease the surface runoff, soil erosion and phosphorus losses from tramlines in agricultural fields

The use of tramlines or wheelings to carry out agricultural operations, such as spraying and fertilizer applications, is common across the world. They are often orientated up and down the slope and the soil that is driven on becomes compacted because of machinery weight transferring stress through the soil profile. This compaction leads to tramlines becoming conduits for water moving over the soil surface. Like water, sediment and phosphorus are also detached and transported. Reducing surface runoff and diffuse pollution losses from surface runoff associated with wheelings has received some research attention, but results are often difficult to interpret. This is because of the low number of replicates that are possible in agricultural landscapes, if the research is to be conducted at meaningful scales and to remain feasible. To address this, we utilize effect sizes and confidence intervals to analyse surface runoff and diffuse pollution data from a series of studies at five arable field sites, in the UK where surface runoff, sediment and phosphorus was collected from hillslope scale tramline plots utilizing the same methodology. In addition, we tested the impact of very flexible tyres, rotary harrows and a surface profiler roller on surface runoff and diffuse pollution loses. Although the monitoring period did not encompass widespread flood inducing storms, we demonstrate that the magnitude of the sediment and total phosphorus (TP) losses from the tramline plots across the study sites are significant in the UK context. Annual sediment losses from the study plots are in the order of 0.5-4.5 Mg ha-1 yr.-1 and consistent with the magnitudes of soil erosion in the UK. TP fluxes observed at the study plots, ranged between 0.8 and 3.9 kg ha-1 yr.-1, are consistent with the TP losses reported for surface runoff from arable plots in the UK. By utilizing effect size analysis, we demonstrate the significant impact of tramline mitigation on surface runoff and diffuse pollution losses. The rotary harrow performed best overall, and the combination of the rotary harrow and the very flexible tyre was superior to all other methods. This was the case for all treatments apart from some, where the surface profiler performed well in reducing sediment fluxes. Our work supports the need for incorporating tramline management measures into soil management strategies for arable landscapes and provides evidence for policymakers developing measures for agri-environmental schemes.