Final Report: Defra PE0206 Field Testing of Mitigation Options

1. Executive summary The Mitigation Options for Phosphorus and Sediment (MOPS) project aimed to investigate the efficacy and cost-effectiveness of different in-field mitigation options which could be used to control diffuse pollution losses in surface runoff from arable fields under combinable crops. In order to achieve this, a literature review, field experimentation, and economic analysis were undertaken. A review of the literature highlighted the large toolbox of mitigation measures available to land managers, but also demonstrated that there are few studies determining the effectiveness of these measures for controlling diffuse pollution across a range of soils in the UK. In particular, little reference could be found in the literature addressing the control of diffuse pollution from tractor wheelings. Field studies of mitigation options were carried out over three years at three sites in the UK with contrasting soil types: clay soils at Loddington (Leicestershire), silty-clay-loam soils at Rosemaund (Herefordshire) and sandy soils at Old Hattons (Staffordshire). All sites had similar long-term annual rainfalls (range 650-700 mm) and similar slope gradients (4-5°). Over the nine site-years, a total of 19 treatment options were trialled. These included conventional cultivation measures (as controls) and a range of mitigation measures (tramline disruption, residue incorporation, minimum tillage, contour cultivation, and vegetative barriers), which were considered both separately and in combinations. Losses of runoff, suspended sediment (SS) and phosphorus (P) were monitored from 52 hillslope lengths (68-270 m) giving a total of 156 plot-years of data collected. Table E1 summarises the effectiveness of each of the treatments at controlling losses of runoff, SS and P from arable fields under winter-sown combinable crops, and shows the results of the economic analysis of mitigation options, which was undertaken at the farm scale using standard farm rotations for the three years of the project. The results of this work demonstrate that: • Compacted, unvegetated tractor wheelings (tramlines) were important sources and pathways for pollutant transport at all sites. At Rosemaund, on silty soils, runoff from tramlines was around 20 to 40 times greater, and losses of SS and total P (TP) were up to 300 times greater from tramlines than losses from vegetated areas without tramlines. At Old Hattons on coarser sandy soils, losses of runoff, SS and TP were between five and 30 times greater from tramline areas, and at Loddington, on heavy clay soils in year 3, losses from tramline areas were between two and six times …