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.

Winter oilseed rape is traditionally established via plough-based soil cultivation and conventional sowing methods. Whilst there is potential to adopt lower cost, and less intensive establishment systems, the impact of these on greenhouse gas emissions have not been evaluated. To address this, field experiments were conducted in 2014/2015 and 2015/2016 to investigate the effects of 1) crop establishment method and 2) sowing method on soil greenhouse gas emissions from a winter oilseed rape crop grown in Ireland. Soil carbon dioxide, nitrous oxide and methane emission measurements were carried out using the static chamber method. Yield (t seed ha−1) and the yield-scaled global warming potential (kg CO2-eq. kg−1 seed) were also determined for each management practice. During crop establishment, conventional tillage induced an initially rapid loss of carbon dioxide (2.34 g C m−2 hr−1) compared to strip tillage (0.94 g C m−2 hr−1) or minimum tillage (0.16 g C m−2 hr−1) (p < 0.05), although this decreased to background values within a few hours. In the crop establishment trial, the cumulative greenhouse gas emissions were, apart from methane, unaffected by tillage management when sown at a conventional (125 mm) or wide (600 mm) row spacing. In the sowing method trial, cumulative carbon dioxide emissions were also 21% higher when plants were sown at 10 seeds m−2 compared to 60 seeds m−2 (p < 0.05). Row spacing width (125 and 750 mm) and variety (conventional and semi-dwarf) were found to have little effect on greenhouse gas emissions and differences in seed yield between the sowing treatments were small. Overall, management practices had no consistent effect on soil greenhouse gas emissions and modifications in seed yield per plant countered differences in planting density.

N-(n-butyl) thiophosphoric triamide (NBPT) is a urease inhibitor utilised in urea-based fertilizers. In Ireland, fertilizer treated with NBPT is applied to pasture to mitigate both ammonia and nitrous oxide emissions, but concerns arise as to the potential for residues in milk products. A quick ultrafiltration extraction and ultra-high performance liquid chromatography coupled with mass spectrometry triple quadrupole (UHPLC-MS/MS) quantitation method was developed and validated in this study. The method was applied in the analysis of samples collected from a field study investigating potential transfer of NBPT residues into milk. NBPT and NBPTo residues, were extracted from fortified milk samples and analysed on a UHPLC-MS/MS with recoveries ranging from 74 to 114%. Validation of the UHPLC-MS/MS method at low (0.0020 mg kg−1) and high (0.0250 mg kg−1) concentration levels in line with SANTE/12682/2019 showed overall trueness in the range of 99 to 104% and precision between 1 and 10%, RSD for both compounds. The limit of quantitation (LOQ) was 0.0020 mg kg−1 and other tested parameters (linearity, sensitivity, specificity, matrix effect, robustness, etc.) satisfied acceptance criteria. Stability assessment using spiked samples revealed the compounds were stable in raw and pasteurised milk for 4 weeks at –80 °C storage temperature. Maintaining samples at pH 8.5–9.0 further improved stability. Analysis of 516 milk samples from the field study found that NBPT and NBPTo concentrations were below the LOQ of 0.0020 mg kg−1, thus suggesting very low risk of residues occurring in the milk. The method developed is quick, robust, and sensitive. The method is deemed fit-for-purpose for the simultaneous determination of NBPT and NBPTo in milk.

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