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13. 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

19. 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

21. 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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25. Optimising soil P levels reduces N2O emissions in grazing systems under different N fertilisation.

Author

O'Neill, Rosie Mary, Gebremichael, Amanuel Woldeselassie, Lanigan, Gary J., Renou‐Wilson, Florence, Müller, Christoph, and Richards, Karl G.

Subjects
SOILS, GRASSLAND soils, GRAZING, DEFICIENCY diseases, NITROUS oxide, PHOSPHORUS in soils
Abstract

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. Highlights: P deficiency in grassland soils causes greater N2O emissions.Insufficent soil P inhibits N‐uptake, regardless of rate or form of N.Optimising soil P levels can reduce N2O emissions and improve overall NUE. [ABSTRACT FROM AUTHOR]

Published
2022
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28. 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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29. Hobson's Choice: Finding the right mix of agricultural and environmental policy for Irish agriculture

Author

Donnellan, Trevor M, Hanrahan, Kevin F, and Lanigan, Gary J

Subjects
climate change, Agricultural and Food Policy, agricultural production, greenhouse gas mitigation
Abstract

As part of its international obligations, Ireland faces emission reduction targets with respect to greenhouse gases (GHG). These reduction targets are to be achieved both in the short term and over the coming decades. Agriculture is a substantial source (33%) of Ireland’s GHG emissions. Whereas the economic welfare of farmers has been the dominant force in shaping agriculture policy for several decades, there has been a notable increase in environmental concerns and a gradual emergence of environmental policies which are relevant to agriculture, particularly in the last 10 years. The future evolution of the agri-food sector in Ireland must therefore be seen in the context of both the economic growth objectives of national agricultural policy, as well as national environmental policy objectives arising from international obligations. In light of the recent proposals with respect to the EU Common Agricultural Policy (CAP) post-2020 (EC, 2018), environmental objectives will become an increasingly important subset of the CAP objectives and the implementation of the CAP in Ireland. The EU Effort Sharing Decision (ESD) requires that Ireland reduce its non-ETS GHG emission by 20% by 2020 relative to the 2005 level. The reduction target for the non-ETS sector for 2030 is 30%, but incorporates so called flexibility mechanisms designed to make the achievement of this target less onerous. A partial equilibrium model of Irish agriculture is used to explore differing future outcomes in terms of the sector’s size and associated GHG emissions to 2030. The scenario analysis employed demonstrates the implications of different future pathways for bovine (dairy and beef) agriculture, the dominant sector in Irish agriculture and the principal source of its GHG emissions. Mitigation actions are then factored in to provide measures of future levels of emissions inclusive of this mitigation capacity. While technical mitigation actions are largely grounded in interventions that are based on science, the scenario analysis makes clear that the scale of the ultimate challenge in mitigating agricultural GHG emissions will be determined by the overall size of the agriculture sector and the intensity of production per hectare. The dairy and beef sectors in Ireland are noteworthy for their contrasting levels of profitability; dependence on support payments; and farm income. Now that the EU milk quota has been eliminated, from the perspective of economic development, an increase in the size of the dairy sector and entry into the dairy sector are desirable economic policy objectives. However, the paper demonstrates the strong contrast between dairy and beef farms, not just in terms of income but also in terms of intensity of production per hectare and the associated level of emissions produced. It follows that a transition from beef production to dairy production, while desirable from the point of view of farm income, could have adverse consequences for emissions.

Published
2019
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30. Long-term elevation of temperature affects organic N turnover and associated N2O emissions in a permanent grassland soil

Author

Jansen-Willems, Anne B., Lanigan, Gary J., Clough, Timothy J., Andresen, Louise C., and Müller, Christoph

Abstract

Over the last century an increase in mean soil surface temperature has been observed, and it is predicted to increase further in the future. In order to evaluate the legacy effects of increased temperature on both nitrogen (N) transformation rates in the soil and nitrous oxide (N2O) emissions, an incubation experiment and modelling approaches were combined. Based on previous observations that gross N transformations in soils are affected by long-term elevated-temperature treatments we hypothesized that any associated effects on gaseous N emissions (e.g. N2O) can be confirmed by a change in the relative emission rates from various pathways. Soils were taken from a long-term in situ warming experiment on temperate permanent grassland. In this experiment the soil temperature was elevated by 0 (control), 1, 2 or 3 °C (four replicates per treatment) using IR (infrared) lamps over a period of 6 years. The soil was subsequently incubated under common conditions (20 °C and 50 % humidity) and labelled as NO315NH4 Gly, 15NO3NH4 Gly or NO3NH4 15N-Gly. Soil extractions and N2O emissions were analysed using a 15N tracing model and source-partitioning model. Both total inorganic N (NO3− + NH4+) and NO3− contents were higher in soil subjected to the +2 and +3 °C temperature elevations (pre- and post-incubation). Analyses of N transformations using a 15N tracing model showed that, following incubation, gross organic (but not inorganic) N transformation rates decreased in response to the prior soil warming treatment. This was also reflected in reduced N2O emissions associated with organic N oxidation and denitrification. Furthermore, a newly developed source-partitioning model showed the importance of oxidation of organic N as a source of N2O. In conclusion, long-term soil warming can cause a legacy effect which diminishes organic N turnover and the release of N2O from organic N and denitrification.

Published
2018

31. Development and verification of a novel isotopic N2O measurement technique for discrete static chamber samples using cavity ring-down spectroscopy.

Author

Bracken, Conor J., Lanigan, Gary J., Richards, Karl G., Müller, Christoph, Tracy, Saoirse R., Well, Reinhard, Carolan, Rachael, and Murphy, Paul N. C.

Subjects
*CAVITY-ringdown spectroscopy, *MASS spectrometers, *EFFECT of human beings on climate change, *TRACE gases, *ISOMERISM, *MASS spectrometry
Abstract

Rationale: N2O isotopomers are a useful tool to study soil N cycling processes. The reliability of such measurements requires a consistent set of international N2O isotope reference materials to improve inter-laboratory and inter-instrument comparability and avoid reporting inaccurate results. All these are the more important given the role of N2O in anthropogenic climate change and the pressing need to develop our understanding of soil N cycling and N2O emission to mitigate such emissions. Cavity ring-down spectroscopy (CRDS) could potentially overcome resource requirements and technical challenges, making N2O isotopomer measurements more feasible and less expensive than previous approaches (e.g., gas chromatography [GC] and isotope ratio mass spectrometry [IRMS]). Methods: A combined laser spectrometer and small sample isotope module (CRDS & SSIM) method enabled N2O concentration, δ15Nbulk, δ15Nα, δ15Nβ and site preference (SP) measurements of sample volumes <20 mL, such as static chamber samples. Sample dilution and isotopic mixing as well as N2O concentration dependence were corrected numerically. A two-point calibration procedure normalised d values to the international isotope-ratio scales. The CRDS & SSIM repeatability was determined using a reference gas (Ref Gas). CRDS & SSIM concentration measurements were compared with those obtained by GC, and the isotope ratio measurements from two different mass spectrometers were compared. Results: The repeatability (mean ± 1s; n = 10) of the CRDS & SSIM measurements of the Ref Gas was 710.64 ppb (± 8.64), 2.82? (± 0.91), 5.41? (± 2.00), 0.23? (± 0.22) and 5.18? (± 2.18) for N2O concentration, δ15Nbulk, δ15Nα, δ15Nβ and SP, respectively. The CRDS & SSIM concentration measurements were strongly correlated with GC (r = 0.99), and they were more precise than those obtained using GC except when the N2O concentrations exceeded the specified operating range. Normalising CRDS & SSIM d values to the international isotope-ratio scales using isotopic N2O standards (AK1 and Mix1) produced accurate results when the samples were bracketed within the range of the d values of the standards. The CRDS & SSIM δ15Nbulk and SP precision was approximately one order of magnitude less than the typical IRMS precision. Conclusions: CRDS & SSIM is a promising approach that enables N2O concentrations and isotope ratios to be measured by CRDS for samples <20 mL. The CRDS & SSIM repeatability makes this approach suitable for N2O "isotopomer mapping" to distinguish dominant source pathways, such as nitrification and denitrification, and requires less extensive lab resources than the traditionally used GC/IRMS. Current study limitations highlighted potential improvements for future users of this approach to consider, such as automation and physical removal of interfering trace gases before sample analysis. [ABSTRACT FROM AUTHOR]

Published
2021
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32. Identifying urine patches on intensively managed grassland using aerial imagery captured from remotely piloted aircraft systems

Author

Maire, Juliette, Gibson-Poole, Simon, Cowan, Nicholas, Reay, Dave S., Richards, Karl G., Skiba, Ute, Rees, Robert M., Lanigan, Gary J., Maire, Juliette, Gibson-Poole, Simon, Cowan, Nicholas, Reay, Dave S., Richards, Karl G., Skiba, Ute, Rees, Robert M., and Lanigan, Gary J.

Abstract

The deposition of livestock urine and feces in grazed fields results in a sizable input of available nitrogen (N) in these soils; therefore significantly increasing potential nitrogen pollution from agricultural areas in the form of nitrous oxide (N2O), ammonia (NH3), and nitrate (NO3−). Livestock deposition events contributes to high spatial variability within the field and generate uncertainties when assessing the contribution that animal waste has on nitrogen pollution pathways. This study investigated an innovative technique for identifying the spatial coverage of urine deposition in grasslands without the need for manual soil measurements. A Remotely Piloted Aircraft System (RPAS) using a twin camera system was used to identify urine patches in a 5 ha field, which had been grazed by sheep 3 weeks previous to measurements. The imagery was processed using Agisoft Photoscan (Agisoft LLC) to produce true and false color orthomosaic imagery of the entire field. Imagery of five areas (225 m2) within the field were analyzed using a custom R script. For a total of 1,125 m2 of grassland, 12.2% of the area consisted of what was classified as urine patch. A simple up-scaling method was applied to these data to calculate N2O emissions for the entire field providing an estimate of 1.3–2.0 kg N2O-N ha−1 emissions from urine and fertilizer inputs.

Published
2018

35. Clay illuviation provides a longterm sink for C sequestration in subsoils

Author

Torres-Sallan, Gemma, Schulte, Rogier, P.O., Lanigan, Gary J., Byrne, Kenneth A., Reidy, Brian, Simo, Iolanda, Six, Johan, Creamer, Rachel E., Torres-Sallan, Gemma, Schulte, Rogier, P.O., Lanigan, Gary J., Byrne, Kenneth A., Reidy, Brian, Simo, Iolanda, Six, Johan, and Creamer, Rachel E.

Abstract

peer-reviewed, Soil plays a key role in the global carbon (C) cycle. Most current assessments of SOC stocks and the guidelines given by Intergovernmental Panel on Climate Change (IPCC) focus on the top 30 cm of soil. Our research shows that, when considering only total quantities, most of the SOC stocks are found in this top layer. However, not all forms of SOC are equally valuable as long-term stable stores of carbon: the majority of SOC is available for mineralisation and can potentially be re-emitted to the atmosphere. SOC associated with micro-aggregates and silt plus clay fractions is more stable and therefore represents a long-term carbon store. Our research shows that most of this stable carbon is located at depths below 30 cm (42% of subsoil SOC is located in micro-aggregates and silt and clay, compared to 16% in the topsoil), specifically in soils that are subject to clay illuviation. This has implications for land management decisions in temperate grassland regions, defining the trade-offs between primary productivity and C emissions in clay-illuviated soils, as a result of drainage. Therefore, climate smart land management should consider the balance between SOC stabilisation in topsoils for productivity versus sequestration in subsoils for climate mitigation., PUBLISHED, peer-reviewed

Published
2017

36. Clay illuviation provides a long-term sink for C sequestration in subsoils

Author

Torres-Sallan, Gemma, Schulte, Rogier P.O., Lanigan, Gary J., Byrne, Kenneth A., Reidy, Brian, Simó, Iolanda, Six, Johan, Creamer, Rachel E., Torres-Sallan, Gemma, Schulte, Rogier P.O., Lanigan, Gary J., Byrne, Kenneth A., Reidy, Brian, Simó, Iolanda, Six, Johan, and Creamer, Rachel E.

Abstract

Soil plays a key role in the global carbon (C) cycle. Most current assessments of SOC stocks and the guidelines given by Intergovernmental Panel on Climate Change (IPCC) focus on the top 30 cm of soil. Our research shows that, when considering only total quantities, most of the SOC stocks are found in this top layer. However, not all forms of SOC are equally valuable as long-term stable stores of carbon: the majority of SOC is available for mineralisation and can potentially be re-emitted to the atmosphere. SOC associated with micro-aggregates and silt plus clay fractions is more stable and therefore represents a long-term carbon store. Our research shows that most of this stable carbon is located at depths below 30 cm (42% of subsoil SOC is located in microaggregates and silt and clay, compared to 16% in the topsoil), specifically in soils that are subject to clay illuviation. This has implications for land management decisions in temperate grassland regions, defining the trade-offs between primary productivity and C emissions in clay-illuviated soils, as a result of drainage. Therefore, climate smart land management should consider the balance between SOC stabilisation in topsoils for productivity versus sequestration in subsoils for climate mitigation.

Published
2017

47. Confirmation of co-denitrification in grazed grassland

Author

Selbie, Diana R., primary, Lanigan, Gary J., additional, Laughlin, Ronald J., additional, Di, Hong J., additional, Moir, James L., additional, Cameron, Keith C., additional, Clough, Tim J., additional, Watson, Catherine J., additional, Grant, James, additional, Somers, Cathal, additional, and Richards, Karl G., additional

Published
2015
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50. High-Resolution Denitrification Kinetics in Pasture Soils Link N2O Emissions to pH, and Denitrification to C Mineralization.

Author

Samad, Md Sainur, Bakken, Lars R., Nadeem, Shahid, Clough, Timothy J., de Klein, Cecile A. M., Richards, Karl G., Lanigan, Gary J., and Morales, Sergio E.

Subjects
DENITRIFICATION kinetics, NITROUS oxide & the environment, MINERALIZATION, PH effect, NITROGEN in soils, SOIL microbiology
Abstract

Denitrification in pasture soils is mediated by microbial and physicochemical processes leading to nitrogen loss through the emission of N2O and N2. It is known that N2O reduction to N2 is impaired by low soil pH yet controversy remains as inconsistent use of soil pH measurement methods by researchers, and differences in analytical methods between studies, undermine direct comparison of results. In addition, the link between denitrification and N2O emissions in response to carbon (C) mineralization and pH in different pasture soils is still not well described. We hypothesized that potential denitrification rate and aerobic respiration rate would be positively associated with soils. This relationship was predicted to be more robust when a high resolution analysis is performed as opposed to a single time point comparison. We tested this by characterizing 13 different temperate pasture soils from northern and southern hemispheres sites (Ireland and New Zealand) using a fully automated-high-resolution GC detection system that allowed us to detect a wide range of gas emissions simultaneously. We also compared the impact of using different extractants for determining pH on our conclusions. In all pH measurements, soil pH was strongly and negatively associated with both N2O production index (IN2O) and N2O/(N2O+N2) product ratio. Furthermore, emission kinetics across all soils revealed that the denitrification rates under anoxic conditions (NO+N2O+N2 μmol N/h/vial) were significantly associated with C mineralization (CO2 μmol/h/vial) measured both under oxic (r2 = 0.62, p = 0.0015) and anoxic (r2 = 0.89, p<0.0001) conditions. [ABSTRACT FROM AUTHOR]

Published
2016
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