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3. Greenhouse gas and ammonia emission mitigation priorities for UK policy targets

Author

Buckingham, Sarah, Topp, Cairistiona F.E., Smith, Pete, Eory, Vera, Chadwick, David R., Baxter, Christina K., Cloy, Joanna M., Connolly, Shaun, Cooledge, Emily C., Cowan, Nicholas J., Drewer, Julia, Duffy, Colm, Fox, Naomi J., Jebari, Asma, Jenkins, Becky, Krol, Dominika J., Marsden, Karina A., Mcauliffe, Graham A., Morrison, Steven J., O'Flaherty, Vincent, Ramsey, Rachael, Richards, Karl G., Roehe, Rainer, Smith, Jo, Smith, Kate, Takahashi, Taro, Thorman, Rachel E., Williams, John, Wiltshire, Jeremy, and Rees, Robert M.

Subjects
Agriculture and Soil Science, Atmospheric Sciences
Abstract

Agriculture is essential for providing food and maintaining food security while concurrently delivering multiple other ecosystem services. However, agricultural systems are generally a net source of greenhouse gases and ammonia. They, therefore, need to substantively contribute to climate change mitigation and net zero ambitions. It is widely acknowledged that there is a need to further reduce and mitigate emissions across sectors, including agriculture to address the climate emergency and emissions gap. This discussion paper outlines a collation of opinions from a range of experts within agricultural research and advisory roles following a greenhouse gas and ammonia emission mitigation workshop held in the UK in March 2022. The meeting identified the top mitigation priorities within the UK’s agricultural sector to achieve reductions in greenhouse gases and ammonia that are compatible with policy targets. In addition, experts provided an overview of what they believe are the key knowledge gaps, future opportunities and co-benefits to mitigation practices as well as indicating the potential barriers to uptake for mitigation scenarios discussed.

Published
2023

6. Nitrous oxide emission factors from an intensively grazed temperate grassland: a comparison of cumulative emissions determined by eddy covariance and static chamber methods

Author

Murphy, Rachael M., Saunders, Matthew, Richards, Karl G., Krol, Dominika J., Gebremichael, Amanuel W., Rambaud, James, Cowan, Nicholas, Lanigan, Gary J., Murphy, Rachael M., Saunders, Matthew, Richards, Karl G., Krol, Dominika J., Gebremichael, Amanuel W., Rambaud, James, Cowan, Nicholas, and Lanigan, Gary J.

Abstract

Quantifying nitrous oxide (N2O) emissions from grazed pastures can be problematic due to the presence of hotspots and hot moments of N2O from animal excreta and synthetic fertilisers. In this study, we quantified field scale N2O emissions from a temperate grassland under a rotational grazing management using eddy covariance (EC) and static chamber techniques. Measurements of N2O by static chambers were made for four out of nine grazing events for a control, calcium ammonium nitrate (CAN), synthetic urine (SU) + CAN and dung + CAN treatments. Static chamber N2O flux measurements were upscaled to the field scale (FCH FIELD) using site specific emission factors (EF) for CAN, SU+CAN and dung + CAN. Mean N2O EFs were greatest from the CAN treatment while dung + CAN and SU + CAN emitted similar N2O-N emissions. Cumulative N2O-N emissions over the study period measured by FCH FIELD measurements were lower than gap-filled EC measurements. Emission factors of N2O from grazing calculated by FCH FIELD and gap-filled were 0.72% and 0.96%, respectively. N2O-N emissions were derived mainly from animal excreta (dung and urine) contributing 50% while N2O-N losses from CAN and background accounted for 36% and 14%, respectively. The study highlights the advantage of using both the EC and static chamber techniques in tandem to better quantify both total N2O-N losses from grazed pastures while also constraining the contribution of individual N sources. The EC technique was most accurate in quantifying N2O emissions, showing a range of uncertainty that was seven times lower relative to that attributed to static chamber measurements, due to the small chamber sample size per treatment and highly variable N2O flux measurements over space and time.

Published
2022

9. Beneficial effects of multi-species mixtures on N2O emissions from intensively managed grassland swards

Author

Cummins, Saoirse, Finn, John A., Richards, Karl G., Lanigan, Gary J., Grange, Guylain, Brophy, Caroline, Cardenas, Laura M., Misselbrook, Tom H., Reynolds, Christopher K., and Krol, Dominika J.

Abstract

In a field experiment, annual nitrous oxide (N2O) emissions and grassland yield were measured across different plant communities, comprising systematically varying combinations of monocultures and mixtures of three functional groups (FG): grasses (Lolium perenne, Phleum pratense), legumes (Trifolium pratense, Trifolium repens) and herbs (Cichorium intybus, Plantago lanceolata). Plots received 150 kg ha−1 year−1 nitrogen (N) (150 N), except L. perenne monocultures which received two N levels: 150 N and 300 N. The effect of plant diversity on N2O emissions was derived from linear combinations of species performances' in monoculture (species identity) and not from strong interactions between species in mixtures. Increasing from 150 N to 300 N in L. perenne resulted in a highly significant increase in cumulative N2O emissions from 1.39 to 3.18 kg N2O-N ha−1 year−1. Higher N2O emissions were also associated with the legume FG. Emissions intensities (yield-scaled N2O emissions) from multi-species mixture communities around the equi-proportional mixture were lowered due to interactions among species. For N2O emissions scaled by nitrogen yield in forage, the 6-species mixture was significantly lower than L. perenne at both 300 N and 150 N. In comparison to 300 N L. perenne, the same N yield or DM yield could have been produced with the equi-proportional 6-species mixture (150 N) while reducing N2O losses by 63% and 58% respectively. Compared to 150 N L. perenne, the same N yield or DM yield could have been produced with the 6-species mixture while reducing N2O losses by 41% and 24% respectively. Overall, this study found that multi-species grasslands can potentially reduce both N2O emissions and emissions intensities, contributing to the sustainability of grassland production.

Published
2021

11. Source partitioning using N2O isotopomers and soil WFPS to establish dominant N2O production pathways from different pasture sward compositions

Author

Bracken, Conor J., primary, Lanigan, Gary J., additional, Richards, Karl G., additional, Müller, Christoph, additional, Tracy, Saoirse R., additional, Grant, James, additional, Krol, Dominika J., additional, Sheridan, Helen, additional, Lynch, Mary Bridget, additional, Grace, Cornelia, additional, Fritch, Rochelle, additional, and Murphy, Paul N.C., additional

Published
2021
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12. Ammonia and nitrous oxide emission factors for excreta deposited by livestock and land‐applied manure

Author

van der Weerden, Tony J., primary, Noble, Alasdair, additional, de Klein, Cecile A. M., additional, Hutchings, Nicholas, additional, Thorman, Rachel E., additional, Alfaro, Marta A., additional, Amon, Barbara, additional, Beltran, Ignacio, additional, Grace, Peter, additional, Hassouna, Mélynda, additional, Krol, Dominika J., additional, Leytem, April B., additional, Salazar, Francisco, additional, and Velthof, Gerard L., additional

Published
2021
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14. DATAMAN : A global database of nitrous oxide and ammonia emission factors for excreta deposited by livestock and land-applied manure

Author

Beltran, Ignacio, van der Weerden, Tony J., Alfaro, Marta A., Amon, Barbara, de Klein, Cecile A.M., Grace, Peter, Hafner, Sasha, Hassouna, Mélynda, Hutchings, Nicholas, Krol, Dominika J., Leytem, April B., Noble, Alasdair, Salazar, Francisco, Thorman, Rachel E., Velthof, Gerard L., Beltran, Ignacio, van der Weerden, Tony J., Alfaro, Marta A., Amon, Barbara, de Klein, Cecile A.M., Grace, Peter, Hafner, Sasha, Hassouna, Mélynda, Hutchings, Nicholas, Krol, Dominika J., Leytem, April B., Noble, Alasdair, Salazar, Francisco, Thorman, Rachel E., and Velthof, Gerard L.

Abstract

Nitrous oxide (N2O), ammonia (NH3), and methane (CH4) emissions from the manure management chain of livestock production systems are important contributors to greenhouse gases (GHGs) and NH3 emitted by human activities. Several studies have evaluated manure-related emissions and associated key variables at regional, national, or continental scales. However, there have been few studies focusing on the drivers of these emissions using a global dataset. An international project was created (DATAMAN) to develop a global database on GHG and NH3 emissions from the manure management chain (housing, storage, and field) to identify key variables influencing emissions and ultimately to refine emission factors (EFs) for future national GHG inventories and NH3 emission reporting. This paper describes the “field” database that focuses on N2O and NH3 EFs from land-applied manure and excreta deposited by grazing livestock. We collated relevant information (EFs, manure characteristics, soil properties, and climatic conditions) from published peer-reviewed research, conference papers, and existing databases. The database, containing 5,632 observations compiled from 184 studies, was relatively evenly split between N2O and NH3 (56 and 44% of the EF values, respectively). The N2O data were derived from studies conducted in 21 countries on five continents, with New Zealand, the United Kingdom, Kenya, and Brazil representing 86% of the data. The NH3 data originated from studies conducted in 17 countries on four continents, with the United Kingdom, Denmark, Canada, and The Netherlands representing 79% of the data. Wet temperate climates represented 90% of the total database. The DATAMAN field database is available at http://www.dataman.co.nz.

Published
2021

15. Ammonia and nitrous oxide emission factors for excreta deposited by livestock and land-applied manure

Author

van der Weerden, Tony J., Noble, Alasdair, de Klein, Cecile A.M., Hutchings, Nicholas, Thorman, Rachel E., Alfaro, Marta A., Amon, Barbara, Beltran, Ignacio, Grace, Peter, Hassouna, Mélynda, Krol, Dominika J., Leytem, April B., Salazar, Francisco, Velthof, Gerard L., van der Weerden, Tony J., Noble, Alasdair, de Klein, Cecile A.M., Hutchings, Nicholas, Thorman, Rachel E., Alfaro, Marta A., Amon, Barbara, Beltran, Ignacio, Grace, Peter, Hassouna, Mélynda, Krol, Dominika J., Leytem, April B., Salazar, Francisco, and Velthof, Gerard L.

Abstract

Manure application to land and deposition of urine and dung by grazing animals are major sources of ammonia (NH3) and nitrous oxide (N2O) emissions. Using data on NH3 and N2O emissions following land-applied manures and excreta deposited during grazing, emission factors (EFs) disaggregated by climate zone were developed, and the effects of mitigation strategies were evaluated. The NH3 data represent emissions from cattle and swine manures in temperate wet climates, and the N2O data include cattle, sheep, and swine manure emissions in temperate wet/dry and tropical wet/dry climates. The NH3 EFs for broadcast cattle solid manure and slurry were 0.03 and 0.24 kg NH3–N kg–1 total N (TN), respectively, whereas the NH3 EF of broadcast swine slurry was 0.29. Emissions from both cattle and swine slurry were reduced between 46 and 62% with low-emissions application methods. Land application of cattle and swine manure in wet climates had EFs of 0.005 and 0.011 kg N2O–N kg–1 TN, respectively, whereas in dry climates the EF for cattle manure was 0.0031. The N2O EFs for cattle urine and dung in wet climates were 0.0095 and 0.002 kg N2O–N kg–1 TN, respectively, which were three times greater than for dry climates. The N2O EFs for sheep urine and dung in wet climates were 0.0043 and 0.0005, respectively. The use of nitrification inhibitors reduced emissions in swine manure, cattle urine/dung, and sheep urine by 45–63%. These enhanced EFs can improve national inventories; however, more data from poorly represented regions (e.g., Asia, Africa, South America) are needed.

Published
2021

16. DATAMAN: A global database of nitrous oxide and ammonia emission factors for excreta deposited by livestock and land‐applied manure

Author

Beltran, Ignacio, primary, van der Weerden, Tony J., additional, Alfaro, Marta A., additional, Amon, Barbara, additional, de Klein, Cecile A. M., additional, Grace, Peter, additional, Hafner, Sasha, additional, Hassouna, Mélynda, additional, Hutchings, Nicholas, additional, Krol, Dominika J., additional, Leytem, April B., additional, Noble, Alasdair, additional, Salazar, Francisco, additional, Thorman, Rachel E., additional, and Velthof, Gerard L., additional

Published
2021
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17. Sward composition and soil moisture conditions affect nitrous oxide emissions and soil nitrogen dynamics following urea-nitrogen application

Author

Bracken, Conor J., primary, Lanigan, Gary J., additional, Richards, Karl G., additional, Müller, Christoph, additional, Tracy, Saoirse R., additional, Grant, James, additional, Krol, Dominika J., additional, Sheridan, Helen, additional, Lynch, Mary Bridget, additional, Grace, Cornelia, additional, Fritch, Rochelle, additional, and Murphy, Paul N.C., additional

Published
2020
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18. Ammonia and nitrous oxide emission factors for excreta deposited by livestock and land‐applied manure

Author

Weerden, Tony J., Noble, Alasdair, Klein, Cecile A. M., Hutchings, Nicholas, Thorman, Rachel E., Alfaro, Marta A., Amon, Barbara, Beltran, Ignacio, Grace, Peter, Hassouna, Mélynda, Krol, Dominika J., Leytem, April B., Salazar, Francisco, and Velthof, Gerard L.

Abstract

Manure application to land and deposition of urine and dung by grazing animals are major sources of ammonia (NH3) and nitrous oxide (N2O) emissions. Using data on NH3and N2O emissions following land‐applied manures and excreta deposited during grazing, emission factors (EFs) disaggregated by climate zone were developed, and the effects of mitigation strategies were evaluated. The NH3data represent emissions from cattle and swine manures in temperate wet climates, and the N2O data include cattle, sheep, and swine manure emissions in temperate wet/dry and tropical wet/dry climates. The NH3EFs for broadcast cattle solid manure and slurry were 0.03 and 0.24 kg NH3–N kg–1total N (TN), respectively, whereas the NH3EF of broadcast swine slurry was 0.29. Emissions from both cattle and swine slurry were reduced between 46 and 62% with low‐emissions application methods. Land application of cattle and swine manure in wet climates had EFs of 0.005 and 0.011 kg N2O–N kg–1TN, respectively, whereas in dry climates the EF for cattle manure was 0.0031. The N2O EFs for cattle urine and dung in wet climates were 0.0095 and 0.002 kg N2O–N kg–1TN, respectively, which were three times greater than for dry climates. The N2O EFs for sheep urine and dung in wet climates were 0.0043 and 0.0005, respectively. The use of nitrification inhibitors reduced emissions in swine manure, cattle urine/dung, and sheep urine by 45–63%. These enhanced EFs can improve national inventories; however, more data from poorly represented regions (e.g., Asia, Africa, South America) are needed.

Published
2021
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19. Effects of urease and nitrification inhibitors on yields and emissions in grassland and spring barley

Author

Forrestal, Patrick J., Wall, David, Carolan, Rachael, Harty, Mary A., Roche, Leanne, Krol, Dominika J., Watson, C. J., Lanigan, Gary, Richards, Karl G., Department of Agriculture, Food and the Marine, Ireland, Agricultural Greenhouse Gas Research Initiative for Ireland, Department of Agriculture, Environment and Rural Affairs, Northern Ireland, Teagasc Walsh Fellowship Programme, 11/S/138, and 10/RD/SC/716

Subjects
Fertiliser nitrogen, nitrous oxide, efficiency, nitrification inhibitor, grassland, urease inhibitor, yield, ammonia, spring barley
Abstract

We thank the Department of Agriculture, Food and the Marine (Grant No. 11/S/138), the Agricultural Greenhouse Gas Research Initiative for Ireland (Grant No. 10/RD/SC/716), Department of Agriculture, Environment and Rural Affairs, Northern Ireland and the Walsh Fellowship Scheme for the funding provide to Ms Mary Harty and Ms Leanne Roche. Conference paper presented to the International Fertiliser Society at a Conference in Cambridge, United Kingdom, on 9th December 2016. In trials conducted in the temperate maritime climate of Ireland on a range of acidic soils, calcium ammonium nitrate (CAN) and urea gave comparable yield performance. There was little evidence of reduced yields by using urea for grassland or spring barley. Our finding that urea produced annual yields that were not significantly different from CAN differs from previous studies which found that yields from urea were lower than those from ammonium nitrate or nitrate based fertiliser in the UK. However, there are also published results from trials conducted in temperate Irish grassland showing equal yield performance of CAN and urea in the 1970s. Based on yield performance and the cost of fertiliser there is scope to dramatically increase the level of urea usage in straight and blended fertilisers in the temperate maritime climate of Ireland in both grassland and spring barley. Such an increase will bring substantial benefits in terms of reducing direct nitrous oxide (N2O) emissions from fertiliser applied to soil, particularly in poorly draining soils subject to high levels of precipitation. Nitrogen recovery by plants tends to be more sensitive to differences in fertiliser efficiency than is yield. Although yields did not differ between urea and CAN; urea had a lower nitrogen recovery indicating that urea usage will also result in a reduced level of fertiliser use efficiency. Reduced efficiency is less tangible to farmers who tend to be primarily concerned with dependable yield results. Reduced efficiency is a problem nonetheless, particularly as it is closely linked to NH3 emissions in urea usage. European countries including Ireland have committed to reduce national NH3 emissions to comply with the revised National Emission Ceilings Directive (2001/81/EC) in Europe. Increased urea usage, which looks attractive from a yield, cost and direct N2O perspective in Ireland, runs counter to meeting these commitments. Additionally, NH3 is a source of indirect N2O emissions that will negate some of the N2O savings from urea. Due to the issues of yield dependability, fertiliser efficiency, N2O and NH3 emissions the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) is a particularly attractive option for making urea use more efficient by addressing its key weakness in the area of variable NH3 loss and efficiency. The urease inhibitor NBPT along with the nitrification inhibitor dicyandiamide (DCD) were tested with urea in comparison with calcium ammonium nitrate (CAN). The nitrification inhibitor DCD was very effective in reducing fertiliser N associated N2O emissions. Indeed, its usage allowed N2O levels to be reduced to levels comparable to where no application of N fertiliser was made at some site-years. However, at the DCD incorporation rate tested, DCD contributed to variability in NH3 loss from urea and suppressed both yield response and fertiliser efficiency. Use of the urease inhibitor NBPT in addition to DCD went a substantial way to resolving these shortcomings. Continuing work is needed to tailor the rate of existing and new urease and nitrification inhibitors to optimise the balance between suppression of gaseous N emissions, agronomic performance and economic considerations. We thank the Department of Agriculture, Food and the Marine (Grant No. 11/S/138), the Agricultural Greenhouse Gas Research Initiative for Ireland (Grant No. 10/RD/SC/716), Department of Agriculture, Environment and Rural Affairs, Northern Ireland and the Walsh Fellowship Scheme for the funding provide to Ms Mary Harty and Ms Leanne Roche.

Published
2016

21. Mitigation of ammonia and methane emissions with manure amendments during storage of cattle slurry.

Author

Owusu-Twum MY, Kelleghan D, Gleasure G, Connolly S, Forrestal P, Lanigan GJ, Richards KG, and Krol DJ

Abstract

This study aimed at assessing the efficacy of manure amendments in abating ammonia (NH 3 ) and methane (CH 4 ) emissions during storage. Two experiments were carried out. Experiment 1 was conducted using 20 L of slurry for 98 days. Treatments were: aluminium sulphate (alum), lactogypsum, zeolite, actiglene, ammonium thiosulphate, biochar, dairy processing waste, Digest-IT and control (without amendment). Experiment 2 was conducted using 660 L of slurry in underground storage tanks for 77 days. Treatments were: sulphuric acid, gypsum, biochar and control (without amendment). NH 3 measurements for experiment 1 and experiment 2 were conducted using the photoacoustic gas monitor and dynamic chamber techniques, respectively. CH 4 was measured using the static chamber technique in both experiments. The effect of amendments on slurry composition was determined at the end of the experiments. Experiment 1 showed a significant reduction in NH 3 emissions in the alum (82%), lactogypsum (46%) and zeolite (32%) treatments relative to the control (100.3% total ammoniacal nitrogen (TAN)). CH 4 was reduced significantly in the alum (87%), ammonium thiosulphate (64%) and lactogypsum (67%) relative to the control (291.9 g m -2 ). Experiment 2 showed a significant reduction (32%) in NH 3 emissions in the sulphuric acid relative to the control (4.4% TAN). CH 4 was reduced significantly in the sulphuric acid (46%), gypsum (39%) and biochar (15%) treatments relative to the control (291.9 g m -2 ). In general, amendments altered slurry composition such as dry matter, volatile solids, carbon and nitrogen contents at the end of storage. Lactogypsum, alum and sulphuric acid were effective in abating both NH 3 and CH 4 emissions and can contribute to improving air quality., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Published
2024
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22. Low N 2 O emissions associated with sheep excreta deposition in temperate managed lowland grassland and extensively grazed hill pasture.

Author

Mancia A, Chadwick DR, Waters SM, and Krol DJ

Subjects
Ammonia analysis, Animals, Cattle, Grassland, Nitrogen, Sheep, Soil, Greenhouse Gases, Nitrous Oxide analysis
Abstract

Nitrous oxide (N 2 O) is a potent greenhouse gas (GHG) whose emission from soil can be enhanced by ruminant excretal returns in grasslands. The default (Tier 1) emission factors (EF 3PRP ; i.e. proportion of deposited nitrogen emitted as N 2 O) for ruminant excreta deposition are associated with a wide range of uncertainties and the development of country-specific (Tier 2) EF 3PRP is encouraged. In Ireland, a Tier 2 EF 3PRP has been developed for cattle excreta but no data are available for sheep. The aim of this study was to generate data to contribute to the derivation of a Tier 2 EF 3PRP for sheep excreta, while assessing the effect of excreta type, grassland type and season of deposition on N 2 O emissions. An experiment was carried out on two sites in the west of Ireland: a managed lowland grassland (LOW) and an extensively grazed hill pasture (HILL), characterised by mineral and acid peat soils, respectively. For each season, four treatments were applied to the soil in a fully randomized block design: control (C), sheep urine (U), sheep dung (D), and artificial urine (AU). Nitrous oxide fluxes were assessed over a full year following each application of treatments, using a static chambers methodology. Results showed a brief initial peak following each application of U/AU in LOW but not in HILL. Cumulative N 2 O emissions were significantly higher from the lowland site. Average EF 3PRP for combined excreta was negligible on both sites, thus lower than the IPCC Tier 1 EF 3PRP . Causes of low emissions are likely to depend on site characteristics (e.g. soil acidity in HILL) and season of application (i.e. ammonia volatilisation in summer). This study showed very low N 2 O emissions from sheep excretal returns in Irish grasslands and highlighted the importance of developing Tier 2, animal-specific EF 3PRP . More experimental grasslands should be assessed to confirm these results., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Published
2022
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23. Beneficial effects of multi-species mixtures on N 2 O emissions from intensively managed grassland swards.

Author

Cummins S, Finn JA, Richards KG, Lanigan GJ, Grange G, Brophy C, Cardenas LM, Misselbrook TH, Reynolds CK, and Krol DJ

Subjects
Fertilizers analysis, Nitrogen, Nitrous Oxide analysis, Poaceae, Grassland, Soil
Abstract

In a field experiment, annual nitrous oxide (N 2 O) emissions and grassland yield were measured across different plant communities, comprising systematically varying combinations of monocultures and mixtures of three functional groups (FG): grasses (Lolium perenne, Phleum pratense), legumes (Trifolium pratense, Trifolium repens) and herbs (Cichorium intybus, Plantago lanceolata). Plots received 150 kg ha -1 year -1 nitrogen (N) (150 N), except L. perenne monocultures which received two N levels: 150 N and 300 N. The effect of plant diversity on N 2 O emissions was derived from linear combinations of species performances' in monoculture (species identity) and not from strong interactions between species in mixtures. Increasing from 150 N to 300 N in L. perenne resulted in a highly significant increase in cumulative N 2 O emissions from 1.39 to 3.18 kg N 2 O-N ha -1 year -1 . Higher N 2 O emissions were also associated with the legume FG. Emissions intensities (yield-scaled N 2 O emissions) from multi-species mixture communities around the equi-proportional mixture were lowered due to interactions among species. For N 2 O emissions scaled by nitrogen yield in forage, the 6-species mixture was significantly lower than L. perenne at both 300 N and 150 N. In comparison to 300 N L. perenne, the same N yield or DM yield could have been produced with the equi-proportional 6-species mixture (150 N) while reducing N 2 O losses by 63% and 58% respectively. Compared to 150 N L. perenne, the same N yield or DM yield could have been produced with the 6-species mixture while reducing N 2 O losses by 41% and 24% respectively. Overall, this study found that multi-species grasslands can potentially reduce both N 2 O emissions and emissions intensities, contributing to the sustainability of grassland production., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Published
2021
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24. Source partitioning using N 2 O isotopomers and soil WFPS to establish dominant N 2 O production pathways from different pasture sward compositions.

Author

Bracken CJ, Lanigan GJ, Richards KG, Müller C, Tracy SR, Grant J, Krol DJ, Sheridan H, Lynch MB, Grace C, Fritch R, and Murphy PNC

Abstract

Nitrous oxide (N 2 O) 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 N 2 O 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 N 2 O fluxes and associated isotopomers from eight experimental plots (7.8 m 2 ) 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. N 2 O 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 = δ 15 N α - δ 15 N β ) and δ 15 N bulk ((δ 15 N α + δ 15 N β ) / 2) values were used to attribute N 2 O production to nitrification, denitrification or a mixture of both nitrification and denitrification over a range of soil WFPS (%). Daily N 2 O fluxes ranged from 8.26 to 86.86 g N 2 O-N ha -1 d -1 . Overall, 34.2% of daily N 2 O 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 δ 15 N bulk indicated that the inclusion of ribwort plantain may decrease N 2 O 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 N 2 O 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 N 2 O mitigation strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Published
2021
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