Assessing the farm-scale impacts of cover crops and non-inversion tillage regimes on nutrient losses from an arable catchment

The impact of cover crops and non-inversion tillage regimes on soil and riverine nutrient concentrations is assessed at the farm-scale. [Display omitted] •A three-year farm-scale cover crop and non-inversion tillage trial was conducted.•Oilseed radish cover crop reduced soil water nitrate concentrations by 75–97%.•Corresponding reductions in riverine nitrate concentrations were not observed.•Non-inversion tillage alone was ineffective at reducing nutrient leaching losses.•Mitigation trial profit margins were comparable with conventional farm practice. The efficacy of cover crops and non-inversion tillage regimes at minimising farm-scale nutrient losses were assessed across a large, commercial arable farm in Norfolk, UK. The trial area, covering 143ha, was split into three blocks: winter fallow with mouldboard ploughing (BlockJ); shallow non-inversion tillage with a winter oilseed radish (Raphanus sativus) cover crop (Block P); and direct drilling with a winter oilseed radish cover crop (Block L). Soil, water and vegetation chemistry across the trial area were monitored over the 2012/13 (pre-trial), 2013/14 (cover crops and non-inversion tillage) and 2014/15 (non-inversion tillage only) farm years. Results revealed oilseed radish reduced nitrate (NO3-N) leaching losses in soil water by 75–97% relative to the fallow block, but had no impact upon phosphorus (P) losses. Corresponding reductions in riverine NO3-N concentrations were not observed, despite the trial area covering 20% of the catchment. Mean soil NO3-N concentrations were reduced by ∼77% at 60–90cm depth beneath the cover crop, highlighting the ability of deep rooting oilseed radish to scavenge nutrients from deep within the soil profile. Alone, direct drilling and shallow non-inversion tillage were ineffective at reducing soil water NO3-N and P concentrations relative to conventional ploughing. Applying starter fertiliser to the cover crop increased radish biomass and nitrogen (N) uptake, but resulted in net N accumulation within the soil. There was negligible difference between the gross margins of direct drilling (£731ha−1) and shallow non-inversion tillage (£758ha−1) with a cover crop and conventional ploughing with fallow (£745ha−1), demonstrating farm productivity can be maintained whilst mitigating diffuse pollution. The results presented here support the wider adoption of winter oilseed radish cover crops to reduce NO3-N leaching losses in arable systems, but caution that it may take severa