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

Abstract

<p><strong>Abstract.</strong> Three different nitrogen fertilizer types, ammonium nitrate, urea and urea coated with a urease inhibitor (Agrotain<sup>®</sup>), were applied at standard rates (70 kg N ha<sup>−1</sup>) 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<sub>2</sub>O) and ammonia (NH<sub>3</sub>) 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 < 0.05) when compared to the urea fertilisers. Ammonium nitrate was the largest emitter of N<sub>2</sub>O (0.76 % of applied Nr) and the urea was the largest emitter of NH<sub>3</sub> (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<sub>2</sub>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.</p>

Nitrogen fertilisers with urease inhibitors reduce nitrous oxide and ammonia losses, while retaining yield in temperate grassland

“…However, inclusion of urease inhibitors significantly reduced NH 3 losses from 43% to below 14% from urea + NBPT and urea + NBPT + NPPT. This amounts to a 68% reduction in NH 3 compared to an average reduction of 78.5% reported by , 77% by Chambers and Dampney (2009) and approximately 90% by Cowan et al (2019), albeit at lower NH 3 loss levels. The reduction in NH 3 also represents savings in indirect N 2 O associated with emissions of volatilised and re-deposited N. Performance of urea with one or a combination of two urease inhibitors was not significantly different, which is unlike findings of Pasda et al (2016), where the combination of NBPT + NPPT outperformed NBPT in experiments carried out in cropland soils.…”

Enhanced foliar 15N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

“…The decrease in the NH 4 + :NO 3 − ratios with increasing N addition rates in the subsurface soil indicated enhanced nitrification rates and a significant positive relationship between leaf δ 15 N of plants and nitrification rates, which was consistent with previous studies on forest ecosystems (Bai et al, 2009; Gurmesa, Wang, et al, 2022; Pardo et al, 2006). Other studies also demonstrated that N addition significantly enhanced N 2 O emissions and NH 3 volatilization, thereby significantly enriching the available soil N pools with 15 N under exogenous N input (Cowan et al, 2019; Kahmen et al, 2008; Xu et al, 2010). However, some studies have reported a decrease in foliar δ 15 N with N addition (Sheng et al, 2019; Wang et al, 2021).…”

“…However, atmospherically deposited N includes various forms of N compounds (Cornell, 2011; Jia et al, 2016; Violaki et al, 2010), including the reduced and oxidized forms of inorganic N, such as ammonium bicarbonate (NH 4 HCO 3 ), NH 4 NO 3 , and ammonium sulfate ((NH 4 ) 2 SO 4 ) (Stevens & Gowing, 2014; Stevens et al, 2011), along with organic N compounds, such as urea (CO(NH 2 ) 2 ), free amino acids, and other methylated amines (Neff et al, 2002). Different N compounds can result in different soil N transformation processes, and consequently, different soil N dynamics and statuses (Cheng et al, 2019; Cowan et al, 2019; Du et al, 2021). They can also induce different extents of soil acidification (Hao et al, 2020; Liu et al, 2021; Schroder et al, 2011).…”