Abstract. Three different nitrogen (N) fertiliser 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 the 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 (N2O) and ammonia
(NH3) 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 Flux Interpretation by Dispersion and Exchange over Short Range (FIDES) inverse dispersion model. On average,
fertilisation with ammonium nitrate supported the 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 fertiliser
types and zero N control were not consistent. Overall, ammonium nitrate
treatment was found to increase yields significantly
(p value < 0.05) when compared to the urea fertilisers used in this study. Ammonium
nitrate was the largest emitter of N2O (0.76 % of applied N), and the urea was the largest emitter of NH3 (16.5 % of applied N). Urea
coated with a urease inhibitor did not significantly increase yields when
compared to uncoated urea; however, ammonia emissions were only 10 % of
the magnitude measured for the uncoated urea, and N2O emissions were
only 47 % of the magnitude of those measured for 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.