9Agriculture is a major source of nitrous oxide (N2O) emissions, a potent greenhouse gas. Whilst direct 10 N2O emissions from soils have been widely investigated, indirect N2O emissions from nitrogen (N) 11 enriched surface water and groundwater bodies are poorly understood. In this contribution, indirect 12 N2O emissions from subsurface agricultural field drains and headwater streams were monitored over a 13 two-year period (2013)(2014)(2015) in an intensive arable catchment in eastern England. Indirect N2O 14 emission factors for groundwater (EF5g) and surface runoff (EF5r) were calculated for both field drain

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 ~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 ha-1) and shallow non-inversion tillage (£758 ha-1) with a cover crop and conventional ploughing with fallow (£745 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

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