Nitrogen use efficiency and N 2 O and NH 3 losses attributed to three fertiliser types applied to an intensively managed silage crop

Abstract. Three different nitrogen fertilizer types, ammonium nitrate, urea and urea coated with a urease inhibitor (Agrotain ® ), were applied at standard rates (70 kg N ha −1 ) to experimental plots in a typical and intensively managed grassland area at Easter Bush Farm Estate (Scotland). The nitrogen use efficiency of the fertilisers was investigated as well as nitrogen losses in the form of nitrous oxide fluxes (N 2 O) and ammonia (NH 3 ) and during fertilisation events in the 2016 and 2017 growing seasons. Nitrous oxide was measured by the standard static chamber technique and analysed using Bayesian statistics. Ammonia was measured using passive samplers combined with the FIDES inverse dispersion model. On average, fertilisation with ammonium nitrate supported largest yields and had the highest nitrogen use efficiency, but as large spatial and seasonal variation persisted across the plots, yield differences between the three fertilizer types and zero N control were not consistent. Overall, ammonium nitrate treatment was found to increase yields significantly (p-value  2 O (0.76 % of applied Nr) and the urea was the largest emitter of NH 3 (16.5 % of applied Nr). The urea coated with a urease inhibitor did not significantly increase yields; however, ammonia emissions were substantially smaller (90 %) when compared to the uncoated urea and N 2 O emissions were also smaller (47 %) when compared with ammonium nitrate fertiliser. This study suggests that urea coated with a urease inhibitor is environmentally the best choice in regards to nitrogen pollution, but because of its larger cost and lack of agronomic benefits, it is not economically attractive when compared to ammonium nitrate.