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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.)

Drained, lowland agricultural peatlands are greenhouse gas (GHG) emission hotspots and a large but vulnerable store of irrecoverable carbon. They exhibit soil loss rates of ~2.0 cm yr -1 and are estimated to account for 32% of global cropland emissions while producing only 1.1% of crop kilocalories. Carbon dioxide emissions account for >80% of their terrestrial GHG emissions and are largely controlled by water table depth. Reducing drainage depths is, therefore, essential for responsible peatland management. Peatland restoration can substantially reduce emissions. However, this may conflict with societal needs to maintain productive use, to protect food security and livelihoods. Wetland agriculture strategies will, therefore, be required to adapt agriculture to the wetland character of peatlands, and balance GHG mitigation against productivity, where halting emissions is not immediately possible. Paludiculture may substantially reduce GHG emissions but will not always be viable in the current economic landscape. Reduced drainage intensity systems may deliver partial reductions in the rate of emissions, with smaller modifications to existing systems. These compromise systems may face fewer hurdles to adoption and minimize environmental harm until societal conditions favour strategies that can halt emissions. Wetland agriculture will face agronomic, socio-economic and water management challenges, and careful implementation will be required. Diversity of values and priorities among stakeholders creates the potential for conflict. Successful implementation will require participatory research approaches and co-creation of workable solutions. Policymakers, private sector funders and researchers have key roles to play but adoption risks would fall predominantly on land managers. Development of a robust wetland agriculture paradigm is essential to deliver resilient production systems and wider environmental benefits. The challenge of responsible use presents an opportunity to rethink peatland management and create thriving, innovative and green wetland landscapes for everyone's future benefit, while making a vital contribution to global climate change mitigation., (© 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Excreta deposition onto pasture, range and paddocks (PRP) by grazing ruminant constitute a source of nitrous oxide (N 2 O), a potent greenhouse gas (GHG). These emissions must be reported in national GHG inventories, and their estimation is based on the application of an emission factor, EF 3PRP (proportion of nitrogen (N) deposited to the soil through ruminant excreta, which is emitted as N 2 O) . Depending on local data available, countries use various EF 3PRP s and approaches to estimate N 2 O emissions from grazing ruminant excreta. Based on ten case study countries, this review aims to highlight the uncertainties around the methods used to account for these emissions in their national GHG inventories, and to discuss the efforts undertaken for considering factors of variation in the calculation of emissions. Without any local experimental data, 2006 the IPCC default (Tier 1) EF 3PRP s are still widely applied although the default values were revised in 2019. Some countries have developed country-specific (Tier 2) EF 3PRP based on local field studies. The accuracy of estimation can be improved through the disaggregation of EF 3PRP or the application of models; two approaches including factors of variation. While a disaggregation of EF 3PRP by excreta type is already well adopted, a disaggregation by other factors such as season of excreta deposition is more difficult to implement. Empirical models are a potential method of considering factors of variation in the establishment of EF 3PRP . Disaggregation and modelling requires availability of sufficient experimental and activity data, hence why only few countries have currently adopted such approaches. Replication of field studies under various conditions, combined with meta-analysis of experimental data, can help in the exploration of influencing factors, as long as appropriate metadata is recorded. Overall, despite standard IPCC methodologies for calculating GHG emissions, large uncertainties and differences between individual countries' accounting remain to be addressed., 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.)

Grasslands (natural, semi-natural and improved) occupy approximately one-third of the terrestrial biosphere and are key for global ecosystem service provision, storing up to 30% of soil organic carbon (SOC). To date, most research on soil carbon (C) sequestration has focused on croplands where the levels of native soil organic matter (SOM) are typically low and significant potential exists to replenish SOM stocks. However, with the renewed push to achieve "net zero" C emissions by 2050, grasslands may offer an additional C store, utilising tools such as biochar. Here, we critically evaluate the potential for biochar as a technology for increasing grassland C stocks, identifying a number of practical, economic, social and legislative challenges that need to be addressed before the widescale adoption of biochar may be achieved. We critically assess the current knowledge within the field of grassland biochar research in the context of ecosystem service provision and provide opinions on the applicability of biochar as an amendment to different types of grassland (improved, semi-improved and unimproved) and the potential effect on ecosystem provision using a range of application techniques in the topsoil and subsoil. We concluded that the key question remains, is it possible for managed grasslands to store more C, without causing a loss in additional ecosystem services? To address this question future research must take a more multidisciplinary and holistic approach when evaluating the potential role of biochar at sequestering C in grasslands to mitigate climate change. Highlights: Carbon (C) rich grassland soils may offer an additional C store, utilising tools such as biochar Identification of practical, economic, social and legislative challenges for scaled adoption of biochar in grasslands Key question: will enhanced C storage in grasslands soils cause a loss in additional ecosystem services? [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Drainage and cultivation of peat soils almost always result in rapid soil degradation and a loss of soil organic matter (SOM). Winter cover crop cultivation and subsequent incorporation and watertable elevation have been considered as potential strategies to improve soil quality and decrease nutrient loss in drained and cultivated peatlands. However, the combined effect of residue incorporation and watertable management on greenhouse gas (GHG) emissions in these highly productive fen peat soils remains unknown. In the present study, two winter cover crops with contrasting carbon/nitrogen ratios (vetch [Vicia sativa], 45–60; rye [Secale cereale], 13–14) were incorporated into peat soils as green manure (without extra synthetic/organic N addition) at two watertable depths (−50 and −30 cm). Our results showed that fast mineralization of incorporated residues can cause a large pulse of GHG release under favourable environmental conditions. Both vetch and rye incorporation increased CO2 emissions compared with the bare soil treatments due to labile C addition and removal of N constraints. However, the two cover crops had strongly contrasting effects on N2O emissions. Incorporation of low C/N ratio vetch stimulated N2O emissions (average 21.8 ± 7.3 mg N m−2 hr−1) compared with the bare soil treatments, whereas high C/N ratio rye decreased N2O emissions (average 0.09 ± 0.03 mg N m−2 hr−1). Raising the watertable slightly reduced CO2 emissions from an average of 1.3 ± 0.4 (the bare soils) to 0.9 ± 0.3 g C m−2 hr−1 by inhibiting SOM mineralization but significantly increased N2O emissions in the vetch treatments by stimulating denitrification. CH4 fluxes were not affected by watertable depth, and their contribution to total global warming potential was negligible. Therefore, we conclude that high C/N ratio cover crops (e.g., rye) in combination with a raised watertable may represent a viable management option to mitigate GHG fluxes in fen peat soils. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Challenges identified to implementing GHG mitigation measures in livestock systems. • Practical, knowledge and cognitive limitations interact with interests. • Cognitive limitations and critical perspectives of change highlighted. • Conceptual model for policymakers links main types of challenge. Abstract Livestock agriculture is a significant global emitter of greenhouse gases (GHG) and the sector is under pressure to reduce its environmental footprint. Dairy, sheep and beef production are major contributors to emissions. Here, a study of the barriers to implementing GHG mitigation measures on sheep, beef and dairy farms in Wales provides insights into challenges for these sectors globally. Data were gathered from 18 stakeholder organisations and farmers using semi-structured interviews and facilitated workshops. Participants were asked about the challenges to implementing measures associated with different parts of the farming system. Data were analysed using a grounded theory approach. Identified themes covered the range of challenges to the implementation of climate-friendly agricultural practice described in a global review. A conceptual model linking categories of challenge (Practical limitations, Knowledge limitations, Cognitive limitations and Interests) was developed from the data. Comparing the findings with existing work on behavioural change revealed two major differences: i) The concept of Cognitive limitations highlighted the importance of cognitive processes recognised in social psychology to the implementation of change in livestock agriculture. It differentiated specific cognitive biases incorporated in behavioural models from constraints affecting the thought processes in which these biases develop and which they affect, ii) Critical elements such as power relationships and conflicting stakeholder interests were highlighted as important factors outside the scope of behavioural change models. The conceptual model developed can support policymakers in understanding and tackling challenges to change in livestock agricultural systems. [ABSTRACT FROM AUTHOR]

Growing evidence suggests that tropospheric ozone has widespread effects on vegetation, which can contribute to alter ecosystem carbon (C) dynamics and belowground processes. In this study, we used intact soil mesocosms from a semi-improved grassland and investigated the effects of elevated ozone, alone and in combination with nitrogen (N) fertilization on soil-borne greenhouse gas emissions and ecosystem C fluxes. Ozone exposure under fully open-air field conditions was occurred during the growing season. Across a one-year period, soil methane (CH 4) and nitrous oxide (N 2 O) emissions did not differ between treatments, but elevated ozone significantly depressed soil CH 4 uptake by 14% during the growing season irrespective of N fertilization. Elevated ozone resulted in a 15% reduction of net ecosystem exchange of carbon dioxide, while N fertilization significantly increased ecosystem respiration during the growing season. Aboveground biomass was unaffected by elevated ozone during the growing season but significantly decreased by 17% during the non-growing season. At the end of the experiment, soil mineral N content, net N mineralization and extracellular enzyme activities (i.e., cellobiohydrolase and leucine aminopeptidase) were higher under elevated ozone than ambient ozone. The short-term effect of single application of N fertilizer was primarily responsible for the lack of the interaction between elevated ozone and N fertilization. Therefore, results of our short-term study suggest that ozone exposure may have negative impacts on soil CH 4 uptake and C sequestration and contribute to accelerated rates of soil N-cycling. • Temperate grassland mesocosms were exposed to ozone with or without N fertilizer. • Elevated ozone had negative effects on soil CH 4 uptake and net ecosystem CO 2 exchange. • Aboveground biomass was reduced during the non-growing but not the growing season. • A positive feedback of soil N-cycling to ozone exposure was detected. [ABSTRACT FROM AUTHOR]

Dairy cattle housing is a significant source of NH3 and GHG emissions to atmosphere. However, the climate, temperature in particular, and the characteristics of the excreta of the housed cattle, may have a strong influence on the magnitude of such emissions. The objectives were to assess the effects of temperature and excreta characteristics of heifers, dry cows and lactating cows on potential NH3, N2O, CO2 and CH4 emissions. The experiment was conducted using laboratory chambers where constant amounts of urine and faeces were applied to a concrete floor. Potential NH3 and GHG emissions were measured over 120-h following application at 5, 15, 25 and 35 °C. Increasing temperature promoted a significant increase in NH3 emissions. At temperatures ≥15 °C, total NH3 emissions accounted for more than 100% of the urea–N content of the urine for the three dairy cattle types, indicating that other organic N compounds of urine and faeces are an important source of NH3. The cumulative amount of N2O released did not vary significantly with temperature and ranged from 1 to 2% of total N deposited. Cumulative CO2 emissions were ca. 14–58% of total C deposited and the cumulative CH4 emissions were significantly higher at 25 °C than at all other temperatures. It was concluded that increasing temperature from 5 to 35 °C significantly increased potential NH3, CO2 and CH4 emissions but did not significantly influence N2O emissions. Also, the diet supplied to lactating cows led to significantly higher NH3, N2O and CO2 emissions relative to heifers and dry cows. [Copyright &y& Elsevier]

Abstract The return of agricultural crop residues are vital to maintain or even enhance soil fertility. However, the influence of application rate of crop residues on denitrification and its related gaseous N emissions is not fully understood. We conducted a fully robotized continuous flow incubation experiment using a Helium/Oxygen atmosphere over 30 days to examine the effect of maize straw application rate on: i) the rate of denitrification, ii) denitrification product stoichiometry N 2 O/(N 2 O+N 2), and iii) the contribution of fungal denitrification to N 2 O fluxes. Five treatments were established using sieved, repacked sandy textured soil; i) non-amended control, ii) nitrate only, iii) low rate of straw + nitrate, iv) medium rate of straw + nitrate, and iv) high rate of straw + nitrate (n = 3). We simultaneously measured NO, N 2 O as well as direct N 2 emissions and used the N 2 O 15N site preference signatures of soil-emitted N 2 O to distinguish N 2 O production from fungal and bacterial denitrification. Uniquely, soil NO 3 − measurements were also made throughout the incubation. Emissions of N 2 O during the initial phase of the experiment (0–13 days) increased almost linearly with increasing rate of straw incorporation and with (almost) no N 2 production. However, the rate of straw amendment was negatively correlated with N 2 O, but positively correlated with N 2 fluxes later in the experimental period (13–30 days). Soil NO 3 − content, in all treatments, was identified as the main factor responsible for the shift from N 2 O production to N 2 O reduction. Straw amendment immediately lowered the proportion of N 2 O from bacterial denitrification, thus implying that more of the N 2 O emitted was derived from fungi (18 ± 0.7% in control and up to 40 ± 3.0% in high straw treatments during the first 13 days). However, after day 15 when soil NO 3 − content decreased to <40 mg NO 3 −-N kg−1 soil, the N 2 O 15N site preference values of the N 2 O produced in the medium straw rate treatment showed a sharp declining trend 15 days after onset of experiment thereby indicating a clear shift towards a more dominant bacterial source of N 2 O. Our study singularly highlights the complex interrelationship between soil NO 3 − kinetics, crop residue incorporation, fungal denitrification and N 2 O/(N 2 O + N 2) ratio. Overall we found that the effect of crop residue applications on soil N 2 O and N 2 emissions depends mainly on soil NO 3 − content, as NO 3 − was the primary regulator of the N 2 O/(N 2 O + N 2) product ratio of denitrification. Furthermore, the application of straw residue enhanced fungal denitrification, but only when the soil NO 3 − content was sufficient to supply enough electron acceptors to the denitrifiers. Highlights • Straw application rate does not directly affect N 2 O/(N 2 O+N 2) ratio. • N 2 O emission following straw application is controlled by soil NO 3 − content. • Straw addition increases fungal N 2 O. [ABSTRACT FROM AUTHOR]

This chapter reviews contributions made to agricultural and environmental science and practice from research on temperate grassland carried out from 1982 to present at Rothamsted Research's North Wyke Research Station, Devon, UK. It describes the evolution of the research program and demonstrates the importance of sustained, interdisciplinary, and collaborative research. North Wyke has maintained a clear research focus, alongside an ability to adapt to changing grassland and environmental research needs and funding sources, and despite having changed affiliations on several occasions. The substantial contribution to agricultural and environmental science arising from the research station has influenced and continues to influence farm practice, research, and policy nationally and internationally. Some key topics have included nutrient cycling, farm waste management, gaseous emissions, biodiversity, grazing management, animal production (meat and milk), and forage quality. Currently, North Wyke Research Station is leading the way on taking increasingly holistic approaches to researching more efficient, sustainable approaches to grazing-livestock agricultural production. This involves the use of world-leading, facilities such as the North Wyke Farm Platform, comprising three farmlets, designed to test the productivity and environmental sustainability of contrasting temperate grassland beef and sheep systems. Future perspectives highlight key challenges facing the agricultural industry including climate change mitigation and adaptation, and the growing world population. Opportunities exist to tackle these challenges through technological advances, but also through increased integration of agricultural, environmental, economic and social research. North Wyke Research Station provides an example of a research facility where such challenges can be addressed. [ABSTRACT FROM AUTHOR]

Livestock emissions account for 74% of nitrous oxide contributions to greenhouse gases in the UK. However, it remains uncertain how much is directly attributable to localised sheep urination events, which could generate nitrous oxide emission ‘hot spots’. Currently, IPCC emission factors are mainly extrapolated from lowland grazing systems and do not incorporate temporal or spatial factors related to sheep behaviour and movement. Being able to gather data that reliably measures when, where, and how much sheep urinate is necessary for accurate calculations and, to inform best management practices for reducing greenhouse gas emissions and minimizing emission-based climate change. Animal-attached movement sensors have been shown to be effective in classifying different behaviours, albeit with varying classification accuracy depending on behaviour types. Previous studies have used accelerometers on cattle and sheep to assess active and non-active behaviours to help with grazing management, although no study has yet attempted to identify sheep urination events using this method. We attached tri-axial accelerometer sensor tags to thirty Welsh Mountain ewes for thirty days to assess if we could identify urination events. We used random forest models using different sliding mean windows to classify behaviours. Urination had a distinctive pattern and could be identified from accelerometer data, with a 5 s window providing the best recall and a 10 s window giving the best precision. ‘State’ behaviours considered (foraging, walking, running, standing and lying down) were also identified with high recall and precision. This demonstrates the extent to which the identification of discrete ‘event’ behaviours may be sensitive to the window size used to calculate the summary statistics. The method shows promise for identifying urination in sheep and other livestock, being minimally invasive compared to other methods, and has clear potential to inform agricultural management practices and policies. [ABSTRACT FROM AUTHOR]

• We measured soil profile CO 2 , CH 4 and N 2 O across multiple crop rotations. • Only the CO 2 concentration profile differed with crop type due to diffusivity. • The concentration gradient method underestimated CO 2 fluxes in a drought year. • We provide evidence of depth dependent CH 4 and N 2 O consumption. • CO 2 was biologically consumed in deep soil incubation. Agricultural soil emissions are a balance between sinks and sources of greenhouse gases (GHGs). The fluxes of GHGs from soils are complex and spatially and temporally heterogenous. While the soil surface is the exchange site with the atmosphere and is commonly where GHG fluxes are measured, it is important to consider processes occurring throughout the soil profile. To reduce emissions and improve agricultural sustainability we need to better understand the drivers and dynamics (production, consumption, diffusion) of these gases within the soil profile. Due to the heterogeneous nature of GHG processes at small to large scales, it is important to test how these processes differ with depth in different systems. In this study, we measured in situ CO 2 , N 2 O and CH 4 concentration gradients as a function of soil depth over subsequent maize and wheat growing seasons with active gas samplers inserted into an arable field at 10, 20, 30 and 50 cm depths. We found N 2 O and CH 4 concentrations increased with depth, but only CO 2 concentrations differed with depth between growing seasons due likely to differences in soil diffusivity driven by soil conditions. Using the concentration gradient method (GM), the CO 2 fluxes at each depth and their contribution to the surface flux were calculated and validated against a chamber method (CM) measured surface flux. We found the GM estimated surface CO 2 flux was only 6 % different in the wheat, but 28 % lower than the surface measured flux in the maize growing season, due to drought conditions reducing the accuracy of the GM. Finally, we measured fluxes of CO 2 , N 2 O and CH 4 in ambient and highly concentrated headspaces in laboratory mesocosms over a 72 h incubation period. We provide evidence of depth dependent CH 4 oxidation and N 2 O consumption and possibly CO 2 fixation. In conclusion, our study provides valuable information on the applicability of the GM and further evidence of the GHG production, consumption and diffusion mechanisms that occur deeper in the soil in a temperate arable context. [ABSTRACT FROM AUTHOR]

Dairy cattle are usually housed in naturally ventilated houses where removal of excreta is periodically performed. The aim of this controlled study was to compare the effect of two floor designs and three air temperatures (5, 15 and 25 °C) on NH3, N2O, CH4 and CO2 emissions arising from cattle excreta deposition to the floor. Two scale models were built to simulate a level solid floor without urine drainage, and a slatted concrete floor. Following application of a mixture of urine and faeces, these two floor type models were subjected to a constant airflow rate (12.5 exchanges h−1) and gaseous emissions were measured over a 72-h period. Emissions of NH3, N2O, CO2 and CH4 increased significantly with air temperature with both floor type models and emissions of NH3, N2O and CO2 were significantly greater from the solid floor relative to the slatted floor at all temperatures considered. The cumulative NH3 (27–66% of total N applied) and CO2 (<19% of total C applied) emissions were greater from the solid floor than from the slatted floor (by 36% and 44%, respectively). The cumulative N2O (<0.1% of total N applied) and CH4 (<0.4% of total C applied) emissions were relatively low and CH4 values did not differ significantly between treatments. Cumulative greenhouse gas emissions (as CO2-equivalents) increased significantly with temperature but did not differ between the floor types. [ABSTRACT FROM AUTHOR]

• Statistical relationships of pasture N 2 O, CO 2 & CH 4 fluxes & environmental data. • Extensive site N 2 O flux predictors consistent with controls & literature. • Use of a spatial regression changed predictors for Intensive site N 2 O fluxes. • Significant predictors of GHG fluxes are site- & GHG-specific. • Missing predictors or more complex (e.g. non-stationary) relationships. Greenhouse gas (GHG) fluxes from livestock grazed pasture soils are highly variable in both space and time but the quantitative importance of the factors regulating this variation remain poorly understood. Our aim was to explore this variability on contrasting extensively (low input) and intensively managed sheep-grazed 'case-study' pastures. We quantified (through standard and spatially-informed regressions) the statistical relationships between GHG fluxes (nitrous oxide (N 2 O), carbon dioxide (CO 2) and methane (CH 4)) and a range of soil, field and management characteristics. Fluxes of these three GHGs at two study sites were highly variable, but spatial structure (i.e. autocorrelation) was only observed in the variability of N 2 O fluxes across the intensive site and CO 2 fluxes across the extensive site. The regression analyses identified significant GHG predictor variables for the extensive site as: NO 3 − (p < 0.001) and vegetation-type (p < 0.01) for N 2 O (R 2 = 0.57; p = 0.000); NH 4 + (p < 0.05), slope (p < 0.05) and elevation (p < 0.01) for CO 2 (R 2 = 0.34; p = 0.000); and NO 3 − (p < 0.01), NH 4 + (p < 0.05) and soil moisture (p < 0.05) for CH 4 (R 2 = 0.25; p = 0.005). Significant GHG predictor variables for the intensive site were soil moisture (p < 0.01) and bulk density (p < 0.01) for N 2 O (R 2 = 0.27; p = 0.005); soil moisture (p < 0.001) for CO 2 (R 2 = 0.31; p = 0.001); while none were found for CH 4 (R 2 = 0.10; p = 0.655). Key factors driving GHG variation were both site- and GHG-specific, with fluxes controlled by local conditions leading to differences in limiting factors (possibly even at the within-site scale). Our statistical analyses suggest a larger range of driving variables (e.g. air and soil temperature or other soil chemical properties such as total extractable N) may be required to more fully capture the observed variability in the GHG processes considered here, and that it may also be fruitful for future analyses to consider non-linear, non-stationary and interacting relationships across space- and time-scales. Adequacies of each site's sample design also played a key interpretive role in the GHG processes, requiring further evaluation through additional sampling campaigns. [ABSTRACT FROM AUTHOR]

Fen peatlands represent a globally important carbon (C) store, while also providing highly productive agricultural land. Drainage of these organic soils is required to create conditions suitable for crop growth, but this results in substantial greenhouse gas (GHG) emissions. One potential GHG mitigation option is to raise the groundwater table to reduce the duration and volume of peat exposure to aerobic conditions. However, the trade-off between maintaining food production and securing ecosystem function under a high water table (WT) presents a serious challenge for both land managers and policy makers. Therefore, we conducted a controlled mesocosm experiment to investigate the effects of WT elevation (from −50 cm to −30 cm) under three contrasting scenarios: (i) WT raised throughout the year, (ii) WT raised in the winter only, and (iii) WT raised in the growing season only. We measured GHG emissions, nitrate, ammonium and dissolved organic C concentrations in soil solution, alongside the yield of a commercially important crop (lettuce). Raising the WT throughout the year reduced lettuce yields by 37% and reduced CO 2 emissions by 36% without changing the loss rates of N 2 O or CH 4. Raising the WT only in the winter did not significantly reduce crop yield, but still suppressed CO 2 emissions during the fallow period (by 30%). Raising the WT only in the growing season reduced root growth and CO 2 emissions (by 27%), but had no major effect on lettuce yield. In conclusion, the present study shows that raising the groundwater table in the non-growing season reduced GHG emissions without negatively affecting lettuce yields, and may therefore represent a viable GHG mitigation option for agricultural peatlands. Image 1 • We tested the impact of water table (WT) depth on lettuce yields and GHG emissions. • Annual high WT management reduced lettuce yields by 37% and CO 2 emissions by 36%. • Raising the WT only in winter did not affect crop yield but reduced GHG emissions. • Raising the WT in non-growing season may represent a viable GHG mitigation option. [ABSTRACT FROM AUTHOR]