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

Cooper, Richard J., Hama-Aziz, Zanist, Hiscock, Kevin M., Lovett, Andrew A., Dugdale, Steve J., Sünnenberg, Gisela, Noble, Lister, Beamish, James, Hovesen, Poul
Agriculture, ecosystems & environment 2017 v.237 pp. 181-193
Raphanus sativus, biomass, cover crops, direct seeding, fallow, farms, leaching, nitrate nitrogen, nitrates, nitrogen, nonpoint source pollution, nutrients, oilseeds, phosphorus, plowing, profits and margins, radishes, rooting, soil profiles, soil water, starter fertilizers, vegetation, watersheds, United Kingdom
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 several years before catchment-scale impacts downstream are detected.