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

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 143 ha, was split into three blocks: winter fallow with mouldboard ploughing (Block J); 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 similar to 77% at 60-90 cm 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 (731 pound ha(-1)) and shallow non-inversion tillage (758 pound ha(-1)) with a cover crop and conventional ploughing with fallow (745 pound ha(-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 several years before catchment-scale impacts downstream are detected. (C) 2016 Elsevier B.V. All rights reserved.