Nitrogen use efficiency and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O and NH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; losses attributed to three fertiliser types applied to an intensively managed silage crop

Nicholas Cowan,Andrea Moring,Mark Sutton,Juliette Maire,Ute Skiba,Roseanne Mcdonald,Joana Marinheiro,Polina Voylokov,Connie Mcneill,Ling Song,Ivan Simmons,Jocelyn Brichet,Amy Stephens,Colin Bache,Peter Levy,Benjamin Loubet,Amy Pickard

doi:10.5194/bg-16-4731-2019

Abstract

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.

Highlights

IntroductionDue to a large and rapidly expanding global population, modern-day agriculture requires regular inputs of industrially produced reactive nitrogen fertilisers (Nr) (i.e. nitrogen compounds that plant life can consume through root systems such as ammonium nitrate and urea) in order to keep up with increasing food demand (Lassaletta et al, 2014)
Due to a large and rapidly expanding global population, modern-day agriculture requires regular inputs of industrially produced reactive nitrogen fertilisers (Nr) in order to keep up with increasing food demand (Lassaletta et al, 2014)
Large variations in crop yield measurements show that none of the fertiliser types used in this study consistently outperforms the others in terms of nitrogen use efficiency (NUE)

Summary

Introduction

Due to a large and rapidly expanding global population, modern-day agriculture requires regular inputs of industrially produced reactive nitrogen fertilisers (Nr) (i.e. nitrogen compounds that plant life can consume through root systems such as ammonium nitrate and urea) in order to keep up with increasing food demand (Lassaletta et al, 2014). This widescale intensive application of Nr has resulted in significant anthropogenic alterations of virtually every process in the natural global nitrogen cycle (Fowler et al, 2013; Vitousek et al, 1997). Cumulative flux Std. error in cumulative Flux minus background flux (kg N ha−1)

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