Assessment of nitrous oxide emission factors for arable and grassland ecosystems

Abstract

We quantified seasonal nitrous oxide (N 2 O) emissions and the associated emission factors (EFs) from: (i) winter oilseed rape (WOSR) cultivated under conventional tillage (CT) and strip tillage (ST) at four fertilizer rates (0, 160, 240 and 320 kg N ha −1) in 2014/ 2015, and (ii) grassland plots receiving no fertilizer (0 kg N ha −1), or mineral nitrogen (67 kg N ha −1), and either cattle or pig slurry (50, 100 and 200 m 3 ha −1). Greater fluxes were observed at higher soil temperatures and a higher water filled pore space, suggesting that denitrification was the main source of N 2 ON from the applied fertilizer/slurry. For WOSR, the N 2 O EFs ranged from 0.03 to 1.20% with no effect of the cultivation practice on EFs for equal rates of nitrogen fertilizer. Lower EF values were linked to differences in plant growth at individual sites rather than a specific management effect. For the grassland, the N 2 O EFs were highly variable, ranging from −0.70 to 0.49%, but were generally the highest in treatments receiving the highest concentrations of slurry. The EF values for WOSR illustrates that the Tier 1 approach for calculating EFs may be inadequate and the identification of site-specific effects can aid in refining N 2 O EF inventories. For the grassland plots all the EFs were significantly lower than the IPCC default values. Although the reason(s) for the low EFs with slurry amendments on grassland is not known, ammonia volatilization could decrease the pool of inorganic N that is available to nitrifying bacteria thereby lowering N 2 O fluxes.

Greenhouse Gas Emissions and Crop Yields From Winter Oilseed Rape Cropping Systems are Unaffected by Management Practices

“…Tillage management had little impact on N 2 O emissions in this study (Table 2 and Table 3) in line with earlier work examining CT and RT systems (Abdalla et al, 2010;Liu et al, 2016). Peak N 2 O emissions that were found in the MT and ST but not in the CT treatments coincided with a higher WFPS (>70%) and higher temperatures (>10°C) as noted in previous studies (Adviento-Borbe et al, 2007;Abdalla et al, 2010;Žurovec et al, 2017;O'Neill et al, 2020). This indicates that denitrification is the main source of N 2 O production and the N 2 O emissions are largely dependent on the extent of soil anaerobiosis.…”

“…Emissions of N 2 O and CH 4 were measured using the manual closed chamber method (Chadwick et al, 2014). Accumulation of N 2 O within the chamber headspace, measured at four time points over 1 hour (T 0 , T 20 , T 40 , T 60 ), was determined to be linear on 84% of occasions (O'Neill et al, 2020). The unvented chambers (above) were sealed onto the collars for an enclosure period of 40 min (T 40 ) and sampling carried out between 9.00 and 13.00 h (Barton et al, 2015).…”

“…The rate of N 2 O production is controlled by factors that are affected by tillage intensity, such as the soil waterfilled pore space (WFPS), soil organic C availability and temperature (Butterbach-Bahl et al, 2013). The reported effects of RT operations on N 2 O emissions are equivocal, showing either increases (Ball et al, 1999;Shakoor et al, 2021), decreases (Kessavalou et al, 1998;Chatskikh and Olesen, 2007;Ussiri et al, 2009) or similar N 2 O emissions (Abdalla et al, 2010;O'Neill et al, 2020).…”

Effect of slurry application techniques on nitrous oxide emission from temperate grassland under varying soil and climatic conditions

“…The low N 2 O‐N EFs observed in this study are not uncommon, as previous studies on temperate grasslands have reported low N 2 O EFs (<0.5%) for organic N inputs (Reinsch et al, 2020; Voglmeier et al, 2019). For example, Irish grasslands receiving 160–640 kg N ha −1 year −1 cattle slurry emitted only −0.20% to 0.43% of the applied N (O'Neill et al, 2020).…”

Non-CO2 greenhouse gases: the underrepresented, complex side of the climate challenge

“…This Special Issue contains a selection of contributions to the symposium. It consists of this overview and seven topical papers as illustrative examples of the scientific results presented at the symposium (Wilson and Scholes 2020;O'neill et al 2020;Godwin and Ferenchiak 2020;Howarth 2020;Laban et al 2020;Verchot et al 2020;Zou and Osborne 2020). In the following section, we give an impression of the seven contributions.…”