Now showing 1 - 7 of 7
  • Publication
    Analysis of N2O emissions and isotopomers to understand nitrogen cycling associated with multispecies grassland swards at a lysimeter scale
    Nitrous oxide (N2O) is a potent greenhouse gas associated with nitrogen fertiliser inputs to agricultural production systems. Minimising N2O emissions is important to improving the efficiency and sustainability of grassland agriculture. Multispecies grassland swards composed of plants from different functional groups (grasses, legumes, herbs) have been considered as a management strategy to achieve this goal.
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  • Publication
    Sward composition and soil moisture conditions affect nitrous oxide emissions and soil nitrogen dynamics following urea-nitrogen application
    Increased emissions of N2O, a potent greenhouse gas (GHG), from agricultural soils is a major concern for the sustainability of grassland agriculture. Emissions of N2O are closely associated with the rates and forms of N fertilisers applied as well as prevailing weather and soil conditions. Evidence suggests that multispecies swards require less fertiliser N input, and may cycle N differently, thus reducing N loss to the environment. This study used a restricted simplex-centroid experimental design to investigate N2O emissions and soil N cycling following application of urea-N (40 kg N ha−1) to eight experimental swards (7.8 m2) with differing proportions of three plant functional groups (grass, legume, herb) represented by perennial ryegrass (PRG, Lolium perenne), white clover (WC, Trifolium repens) and ribwort plantain (PLAN, Plantago lanceolata), respectively. Swards were maintained under two contrasting soil moisture conditions to examine the balance between nitrification and denitrification. Two N2O peaks coincided with fertiliser application and heavy rainfall events; 13.4 and 17.7 g N2O-N ha−1 day−1 (ambient soil moisture) and 39.8 and 86.9 g N2O-N ha−1 day−1 (wet soil moisture). Overall, cumulative N2O emissions post-fertiliser application were higher under wet soil conditions. Increasing legume (WC) proportions from 0% to 60% in multispecies swards resulted in model predicted N2O emissions increasing from 22.3 to 96.2 g N2O-N ha−1 (ambient soil conditions) and from 59.0 to 219.3 g N2O-N ha−1 (wet soil conditions), after a uniform N application rate. Soil N dynamics support denitrification as the dominant source of N2O especially under wet soil conditions. Significant interactions of PRG or WC with PLAN on soil mineral N concentrations indicated that multispecies swards containing PLAN potentially inhibit nitrification and could be a useful mitigation strategy for N loss to the environment from grassland agriculture.
    Scopus© Citations 26  300
  • Publication
    Assessment of nitrous oxide emission factors for arable and grassland ecosystems
    We quantified seasonal nitrous oxide (N2O) 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 m3 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 N2O-N from the applied fertilizer/slurry. For WOSR, the N2O 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 N2O 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 N2O 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 N2O fluxes.
      216Scopus© Citations 7
  • Publication
    Source partitioning using N2O isotopomers and soil WFPS to establish dominant N2O production pathways from different pasture sward compositions
    Nitrous oxide (N2O) is a potent greenhouse gas (GHG) emitted from agricultural soils and is influenced by nitrogen (N) fertiliser management and weather and soil conditions. Source partitioning N2O emissions related to management practices and soil conditions could suggest effective mitigation strategies. Multispecies swards can maintain herbage yields at reduced N fertiliser rates compared to grass monocultures and may reduce N losses to the wider environment. A restricted-simplex centroid experiment was used to measure daily N2O fluxes and associated isotopomers from eight experimental plots (7.8 m2) post a urea-N fertiliser application (40 kg N ha−1). Experimental pastures consisted of differing proportions of grass, legume and forage herb represented by perennial ryegrass (Lolium perenne), white clover (Trifolium repens) and ribwort plantain (Plantago lanceolata), respectively. N2O isotopomers were measured using a cavity ring down spectroscopy (CRDS) instrument adapted with a small sample isotope module (SSIM) for the analysis of gas samples ≤20 mL. Site preference (SP = δ15Nα – δ15Nβ) and δ15Nbulk ((δ15Nα + δ15Nβ) / 2) values were used to attribute N2O production to nitrification, denitrification or a mixture of both nitrification and denitrification over a range of soil WFPS (%). Daily N2O fluxes ranged from 8.26 to 86.86 g N2O-N ha−1 d−1. Overall, 34.2% of daily N2O fluxes were attributed to nitrification, 29.0% to denitrification and 36.8% to a mixture of both. A significant diversity effect of white clover and ribwort plantain on predicted SP and δ15Nbulk indicated that the inclusion of ribwort plantain may decrease N2O emission through biological nitrification inhibition under drier soil conditions (31%–75% WFPS). Likewise, a sharp decline in predicted SP indicates that increased white clover content could increase N2O emissions associated with denitrification under elevated soil moisture conditions (43%–77% WFPS). Biological nitrification inhibition from ribwort plantain inclusion in grassland swards and management of N fertiliser source and application timing to match soil moisture conditions could be useful N2O mitigation strategies.
      352Scopus© Citations 15
  • Publication
    Optimising soil P levels reduces N2O emissions in grazing systems under different N fertilisation
    The effect of long-term soil phosphorus (P) on in situ nitrous oxide (N2O) emissions from temperate grassland soil ecosystems is not well understood. Grasslands typically receive large nitrogen (N) inputs both from animal deposition and fertiliser application, with a large proportion of this N being lost to the environment. Understanding optimum nutrient stoichiometry by applying N fertilisers in a relative balance with P will help to reduce N losses by enabling maximum N-uptake by plants and microbes. This study investigates the N2O response from soils of long-term high and low P management receiving three forms of applied N at two different rates: a nitrate-based fertiliser (KNO3) and an ammonium-based fertiliser ([NH4]2SO4) (both at 40 Kg N ha−1), and a synthetic urine (750 Kg N ha−1). Low soil P significantly increased N2O emissions from KNO3 and (NH4)2SO4 fertilisers by over 50% and numerically increased N2O from urine by over 20%, which is suggested to be representative of the lack of significant effect of N fertilisation on N-uptake observed in the low P soils. There was a significant positive effect of soil P on grass N-uptake observed in the synthetic urine and KNO3 treatments, but not in the (NH4)2SO4 treatment. Low P soils had a significantly lower pH than high P soilss and responded differently to applied synthetic urine. There was also a significant effect of P level on potential nitrification which was nearly three times that of low P, but no significant difference between potential denitrification and P level. The results from this study highlight the importance of synergy between relative nutrient applications as a deficiency of one nutrient, such as P in this case, could be detrimental to the system as a whole. Optimising soil P can result in greater N uptake (over 12, 23 and 66% in (NH4)2SO4, KNO3 and synthetic urine treatments, respectively) and in reduced emissions by up to 50% representing a win-win scenario for farmers.
      138Scopus© Citations 2
  • Publication
    Greenhouse Gas Emissions and Crop Yields From Winter Oilseed Rape Cropping Systems are Unaffected by Management Practices
    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.
      82Scopus© Citations 8