Nitrogen fertilisation, although a cornerstone of modern agricultural production, negatively impacts the environment through gaseous losses of nitrous oxide (N2O), a potent greenhouse gas (GHG), and ...ammonia (NH3), a known air pollutant. The aim of this work was to assess the feasibility of urea treated with urease inhibitors to reduce gaseous N losses in temperate grassland, while maintaining or improving productivity compared to conventional fertiliser formulations. Urease inhibitors were N-(n-butyl)-thiophosphoric triamide (NBPT) (urea + NBPT) and N-(n-propyl)-thiophosphoric triamide (NPPT) (urea+ NBPT + NPPT), while conventional fertilisers were urea and calcium ammonium nitrate (CAN). N2O emission factors were 0.06%, 0.07%, 0.09% and 0.58% from urea + NBPT, urea, urea + NBPT + NPPT and CAN, respectively, with CAN significantly higher than all the urea formulations, which were not significantly different from each other. Ammonia loss measured over one fertiliser application was significantly larger from urea, at 43%, compared with other formulations at 13.9%, 13.8% and 5.2% from urea + NBPT, urea + NBPT + NPPT and CAN, respectively. Changing fertiliser formulation had no significant impact on grass yield or N uptake in four out of five harvests. In the last harvest urea + NBPT significantly out-yielded urea, but not CAN or urea + NBPT + NPPT. Overall, urea treated with either one or both urease inhibitors significantly reduced emissions of N2O and NH3, while preserving yield quantity and quality. Therefore, changing fertiliser formulation to these products should be encouraged as a strategy to reduce GHG and air pollution from agricultural practices in temperate climate.
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•N fertilisation is a large source of N2O and NH3 in agriculture.•Fertiliser formulations largely impact gaseous N losses in agricultural systems.•Urea with urease inhibitors reduced N2O to level comparable to unfertilised control.•Addition of urease inhibitors reduced NH3 by nearly 70%.•Fertiliser formulation had no effect on yield quantity and quality.
To comply with the United Nations Framework Convention on Climate Change (UNFCCC) greenhouse gas (GHG) emissions reporting requirements, the Intergovernmental Panel on Climate Change (IPCC) developed ...guidelines for calculating national GHG inventories in a consistent and standard framework. Although appropriate for national level accounting purposes, IPCC methodologies lack the farm level resolution and holistic approach required for whole farm systems analysis. Thus, whole farm systems modelling is widely used for farm level analysis. A review of 31 published whole farm modelling studies of GHG emissions from beef and dairy cattle production systems indicated a number of important outcomes. For example, improvements in animal productivity (i.e., liveweight gain milk production) and fertility (i.e., lower culling, lower replacement rates) can reduce GHG emissions/kg product. Additionally, intensification of production as output/ha can reduce emissions/kg product provided input requirements of feed and/or fertilizer are not excessive. Carbon sequestration into agricultural soils has the potential to offset emissions from pastoral based production systems. A product based metric is widely used and allows a wide range of objectives, including farm profitability and food security to be met. Variation in farm system parameters, and the inherent uncertainties associated with emission factors, can have substantial implications for reported agricultural emissions and thus, uncertainty or sensitivity analysis in any modelling approach is needed. Although there is considerable variation among studies in relation to quality of farm data, boundaries assumed, emission factors applied and co-product allocation approach, we suggest that whole farm systems models are an appropriate tool to develop and measure GHG mitigation strategies for livestock farms.
This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.
The accelerating use of synthetic nitrogen (N) fertilisers, to meet the world's growing food demand, is the primary driver for increased atmospheric concentrations of nitrous oxide (N2O). The IPCC ...default emission factor (EF) for N2O from soils is 1% of the N applied, irrespective of its form. However, N2O emissions tend to be higher from nitrate-containing fertilisers e.g. calcium ammonium nitrate (CAN) compared to urea, particularly in regions, which have mild, wet climates and high organic matter soils. Urea can be an inefficient N source due to NH3 volatilisation, but nitrogen stabilisers (urease and nitrification inhibitors) can improve its efficacy. This study evaluated the impact of switching fertiliser formulation from calcium ammonium nitrate (CAN) to urea-based products, as a potential mitigation strategy to reduce N2O emissions at six temperate grassland sites on the island of Ireland. The surface applied formulations included CAN, urea and urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and/or the nitrification inhibitor dicyandiamide (DCD). Results showed that N2O emissions were significantly affected by fertiliser formulation, soil type and climatic conditions. The direct N2O emission factor (EF) from CAN averaged 1.49% overall sites, but was highly variable, ranging from 0.58% to 3.81. Amending urea with NBPT, to reduce ammonia volatilisation, resulted in an average EF of 0.40% (ranging from 0.21 to 0.69%)-compared to an average EF of 0.25% for urea (ranging from 0.1 to 0.49%), with both fertilisers significantly lower and less variable than CAN. Cumulative N2O emissions from urea amended with both NBPT and DCD were not significantly different from background levels. Switching from CAN to stabilised urea formulations was found to be an effective strategy to reduce N2O emissions, particularly in wet, temperate grassland.
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•N2O emission factor for CAN was higher than the IPCC default and variable between sites and years.•Urea products decreased direct N2O emissions from CAN on average by 80%•Switching from CAN to urea products reduces both N2O emissions and fertiliser costs.
•Nitrous oxide (N2O) emissions from this temperate spring cereal system were substantially lower than the 1% IPCC default emission factor ascross all fertiliser types.•N2O emissions varied depending ...on fertiliser N formulation and N stabiliser.•Cropping system-specific emission factors are required to represent N2O emissions more accurately.
The application of nitrogen (N) fertilisers to agricultural soils is a major source of nitrous oxide (N2O) emissions. The Intergovernmental Panel on Climate Change (IPCC) has set a default emission factor of 1% (EF1) for N fertiliser applied to managed agricultural soils. This value does not differentiate between different N fertiliser formulations or rates of N application. The objective of this field study under spring barley was to determine N2O EF’s for different N fertiliser formulations including urea and urea stabilised with the nitrification inhibitor dicyandiamide (DCD) and/or the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and to evaluate their N2O loss abatement potential relative to calcium ammonium nitrate (CAN). The highest EF1 measured was 0.49% for CAN which was less than half the IPCC default value of 1%. While the urease inhibitor did not reduce emissions relative to CAN; the nitrification inhibitor significantly reduced emissions compared to CAN with EF1 as low as 0.00% for a typical spring barley site. There was no significant impact of CAN or urea application rate on EF1 but there was a significant negative relationship observed for urea in 2013. The study highlights the importance of generating higher Tier emission factors in terms of fertiliser type for use in national inventories.
Cattle excreta deposited on grazed grasslands are a major source of the greenhouse gas (GHG) nitrous oxide (N2O). Currently, many countries use the IPCC default emission factor (EF) of 2% to estimate ...excreta-derived N2O emissions. However, emissions can vary greatly depending on the type of excreta (dung or urine), soil type and timing of application. Therefore three experiments were conducted to quantify excreta-derived N2O emissions and their associated EFs, and to assess the effect of soil type, season of application and type of excreta on the magnitude of losses. Cattle dung, urine and artificial urine treatments were applied in spring, summer and autumn to three temperate grassland sites with varying soil and weather conditions. Nitrous oxide emissions were measured from the three experiments over 12months to generate annual N2O emission factors. The EFs from urine treated soil was greater (0.30–4.81% for real urine and 0.13–3.82% for synthetic urine) when compared with dung (−0.02–1.48%) treatments. Nitrous oxide emissions were driven by environmental conditions and could be predicted by rainfall and temperature before, and soil moisture deficit after application; highlighting the potential for a decision support tool to reduce N2O emissions by modifying grazing management based on these parameters. Emission factors varied seasonally with the highest EFs in autumn and were also dependent on soil type, with the lowest EFs observed from well-drained and the highest from imperfectly drained soil. The EFs averaged 0.31 and 1.18% for cattle dung and urine, respectively, both of which were considerably lower than the IPCC default value of 2%. These results support both lowering and disaggregating EFs by excreta type.
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•N2O emissions were measured from cattle excreta applied to pasture.•N2O was universally higher from urine compared with dung.•N2O was driven by rainfall, temperature and soil moisture deficit.•Emission factors were highest in autumn and from imperfectly-drained soil•N2O emission factors were lower than the 2% IPCC default value.
•Choice of slurry spreading techniques influence ammonia and greenhouse gas release.•Trailing shoe versus splash plate reduces ammonia but increases nitrous oxide emission.•Spring slurry application ...mitigates both ammonia and greenhouse gas emission.•Emission factor for N2O from slurry is lower than calcium ammonium nitrate.•Single use of emission factors for national inventories may not be suitable.
Agriculture contributes to 98% and 33% of ammonia and greenhouse gas (GHG) emissions in Ireland, respectively. Those emissions are mainly associated with livestock production. The Gothenburg Protocol and the EU National Emissions Ceilings Directive are policy drivers which set new and more demanding targets from 2020 to reduce these gaseous emissions. A field experiment was set up in Wexford (Ireland) between April 2009 and August 2010, on a grassland site established with a uniform ryegrass (Lolium perenne) sward for more than ten years. The objective was to investigate the impact of slurry dry matter (DM) content, application technique and timing of application on the overall GHG balance from cattle slurry applied to grassland soils. The treatments on plots were a control, calcium ammonium nitrate (CAN) and cattle slurry, either grass-based or maize-based and with varying DM contents, applied by mimicking trailing shoe and splash plate application. The dry matter contents were varied by mixing different ratios of faeces and urine. The results showed that, while ammonia (NH3) volatilisation losses were significantly increased on slurry spread plots, cumulative direct nitrous oxide emissions, and corresponding emission factors, were significantly higher when applying CAN. In terms of GHG field balance, the potential decrease in indirect nitrous oxide (N2O) emissions, calculated from a reduction of ammonia volatilisation losses using trailing shoe as opposed to splash plate, could be easily offset by an increase in direct N2O emissions and ecosystem respiration. Switching from summer to spring application was much more efficient for mitigation of both NH3 and GHG emissions, due to favourable soil and climatic factors which enhanced crop growth. Any potential trade-off between NH3 and N2O emissions was cancelled, leading to an overall positive effect on reactive nitrogen losses and offering agronomic benefits to farmers.
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•Intensification scenarios increased absolute N emissions compared to baseline.•Intensification scenarios may result in reduced N emission intensity.•Mitigation methods ameliorate ...increased emissions associated with intensification.•Mitigation methods may not offset absolute increase in N loss due to intensification.
Increased global demand for dairy produce and the abolition of EU milk quotas have resulted in expansion in dairy production across Europe and particularly in Ireland. Simultaneously, there is increasing pressure to reduce the impact of nitrogen (N) losses to air and groundwater on the environment. In order to develop grassland management strategies for grazing systems that meet environmental targets and are economically sustainable, it is imperative that individual mitigation measures for N efficiency are assessed at farm system level. To this end, we developed an excel-based N flow model simulating an Irish grass-based dairy farm, to evaluate the effect of farm management on N efficiency, N losses, production and economic performance. The model was applied to assess the effect of different strategies to achieve the increased production goals on N utilization, N loss pathways and economic performance at farm level. The three strategies investigated included increased milk production through increased grass production, through increased concentrate feeding and by applying a high profit grass-based system. Additionally, three mitigation measures; low ammonia emission slurry application, the use of urease and nitrification inhibitors and the combination of both were applied to the three strategies. Absolute N emissions were higher for all intensification scenarios (up to 124 kg N ha−1) compared to the baseline (80 kg N ha−1) due to increased animal numbers and higher feed and/or fertiliser inputs. However, some intensification strategies showed the potential to reduce the emissions per ton milk produced for some of the N-loss pathways. The model showed that the assessed mitigation measures can play an important role in ameliorating the increased emissions associated with intensification, but may not be adequate to entirely offset absolute increases. Further improvements in farm N use efficiency and alternatives to mineral fertilisers will be required to decouple production from reactive N emissions.
Management changes such as drainage, fertilisation, afforestation and harvesting (clearfelling) of forested peatlands influence watertable (WT) position and groundwater concentrations of nutrients. ...This study investigated the impact of clearfelling of a peatland forest on WT and nutrient concentrations. Three areas were examined: (1) a regenerated riparian peatland buffer (RB) clearfelled four years prior to the present study (2) a recently clearfelled coniferous forest (CF) and (3) a standing, mature coniferous forest (SF), on which no harvesting took place. The WT remained consistently below 0.3 m during the pre-clearfelling period. Results showed there was an almost immediate rise in the WT after clearfelling and a rise to 0.15 m below ground level (bgl) within 10 months of clearfelling. Clearfelling of the forest increased dissolved reactive phosphorus concentrations (from an average of 28–230 μg L−1) in the shallow groundwater, likely caused by leaching from degrading brash mats.
•An upland peat forest was studied before and after harvesting (clearfelling).•Watertable fluctuations and groundwater nutrient concentrations were studied.•Clearfelling of a forest on blanket peat raised the watertable.
Nitrous oxide (N2O) emissions associated with urine nitrogen (N) deposition during grazing are a major component of greenhouse gas emissions from domestic livestock. The present study investigated ...the relationship between urine N loading rate and the efficacy of a nitrification inhibitor, dicyandiamide (DCD), on cumulative N2O emissions from a grassland soil in Ireland over 80 and 360-day periods in 2009/10 and 2010/11. A diminishing curvilinear relationship between urine N rate and cumulative N2O emissions was observed in both years. Despite this increase in cumulative N2O emissions, the emission factor (EF3) for N2O decreased with increasing urine N rate from, on average, 0·24 to 0·10% (urine applied at 300 and 1000 kg N/ha, respectively), during an 80-day measurement period. This was probably the result of a factor other than N, such as carbon (C), limiting the production of N2O. The efficacy of DCD varied with urine N loading rate, and inter-annual variability in efficacy was also observed. Dicyandiamide was effective at reducing N2O production for 50–80 days after urine application, which accounted for the major period of elevated daily flux. However, DCD was ineffective at reducing N2O production after this period, which was likely a result of its removal from the soil via degradation and leaching.
Ruminant urine patches deposited onto pasture are a significant source of greenhouse gas nitrous oxide (N2O) from livestock agriculture. Increasing food demand is predicted to lead to a rise in ...ruminant numbers globally, which, in turn will result in elevated levels of urine-derived N2O. Therefore mitigation strategies are urgently needed. Urine contains hippuric acid and together with one of its breakdown products, benzoic acid, has previously been linked to mitigating N2O emissions from urine patches in laboratory studies. However, the sole field study to date found no effect of hippuric and benzoic acid concentration on N2O emissions. Therefore the aim of this study was to investigate the in situ effect of these urine constituents on N2O emissions under conditions conducive to denitrification losses. Unadulterated bovine urine (0mM of hippuric acid, U) was applied, as well as urine amended with either benzoic acid (96mM, U+BA) or varying rates of hippuric acid (8 and 82mM, U+HA1, U+HA2). Soil inorganic nitrogen (N) and N2O fluxes were monitored over a 66day period. Urine application resulted in elevated N2O flux for 44days. The largest N2O fluxes accounting for between 13% (U) and 26% (U+HA1) of total loss were observed on the day of urine application. Between 0.9 and 1.3% of urine-N was lost as N2O. Cumulative N2O loss from the control was 0.3kgN2O–Nha−1 compared with 11, 9, 12, and 10kgN2O–Nha−1 for the U, U+HA1, U+HA2, and U+BA treatments, respectively. Incremental increases in urine HA or increase in BA concentrations had no effect on N2O emissions. Although simulation of dietary manipulation to reduce N2O emissions through altering individual urine constituents appears to have no effect, there may be other manipulations such as reducing N content or inclusion of synthetic inhibitory products that warrant further investigation.
•N2O emissions on day of urine application ranged 13–26% of total N2O loss.•Hippuric and benzoic acids do not reduce N2O in situ under high WFPS conditions.•N2O urine emission factor ranged 0.9–1.3% over 66days.
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