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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]

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]

The nitrogen (N) cycle represents one of the most well-studied systems, yet the taxonomic diversity of the organisms that contribute to it is mostly unknown, or linked to poorly characterized microbial groups. While new information has allowed functional groups to be refined, they still rely on a priori knowledge of enzymes involved and the assumption of functional conservation, with little connection to the role the transformations, plays for specific organisms. Here, we use soil microcosms to test the impact of N deposition on prokaryotic communities. By combining chemical, genomic and transcriptomic analysis, we are able to identify and link changes in community structure to specific organisms catalysing given chemical reactions. Urea deposition led to a decrease in prokaryotic richness, and a shift in community composition. This was driven by replacement of stable native populations, which utilize energy from N-linked redox reactions for physiological maintenance, with fast responding populations that use this energy for growth. This model can be used to predict response to N disturbances and allows us to identify putative life strategies of different functional and taxonomic groups, thus providing insights into how they persist in ecosystems by niche differentiation. [ABSTRACT FROM AUTHOR]

In temperate grasslands, N source influences greenhouse gas emissions. Nitrification and urea hydrolysis inhibitors can reduce these losses. The objective of this study was to evaluate the impact of N source, urease inhibitors, and nitrification inhibitors on temperate grassland yields and N uptake. Experiments were conducted at three locations over 2 years (6 site-years) on the island of Ireland, covering a range of soils and climatic conditions. Results showed that calcium ammonium nitrate (CAN), urea+N-(n-butyl) thiophosphoric triamide (NBPT), urea+NBPT+dicyandiamide (DCD), and urea had equal annual dry matter yield. Urea+DCD had lower dry matter yield than CAN for 3 site-years. Calcium ammonium nitrate and urea+NBPT consistently had the same N uptake, urea+DCD had lower N uptake than CAN in 4 of 6 site-years, urea had lower N uptake than CAN in 2 site-years, and urea+NBPT+DCD had lower N uptake than CAN in 1 site-year. Urea+NBPT is a cost-effective alternative to CAN, which is consistently equal in terms of yield and N uptake in temperate grassland. [ABSTRACT FROM AUTHOR]

An increase in mean soil surface temperature has been observed over the last century, and it is predicted to further increase in the future. The effect of increased temperature on ecosystem carbon fluxes in a permanent temperate grassland was studied in a long-term (6 years) field experiment, using multiple temperature increments induced by IR lamps. Ecosystem respiration (R-eco) and net ecosystem exchange ( NEE) were measured and modeled by a modified Lloyd and Taylor model including a soil moisture component for R-eco (average R2 of 0.78) and inclusion of a photosynthetic component based on temperature and radiation for NEE ( R2 = 0.65). Modeled NEE values ranged between 2.3 and 5.3 kg CO2 m−2 year−1, depending on treatment. An increase of 2 or 3°C led to increased carbon losses, lowering the carbon storage potential by around 4 tonnes of C ha−1 year−1. The majority of significant NEE differences were found during night-time compared to daytime. This suggests that during daytime the increased respiration could be offset by an increase in photosynthetic uptake. This was also supported by differences in δ13C and δ18O, indicating prolonged increased photosynthetic activity associated with the higher temperature treatments. However, this increase in photosynthesis was insufficient to counteract the 24 h increase in respiration, explaining the higher CO2 emissions due to elevated temperature. [ABSTRACT FROM AUTHOR]

Denitrifying bioreactors convert nitrate-nitrogen (NO3-N) to dinitrogen and protect water quality. Herein, the performance of a pilot-scale bioreactor (10 m long, 5 m wide, 2 m deep) containing seven alternating cells filled with either sandy loam soil or lodgepole pine woodchip and with a novel "zig-zag" flow pattern was investigated. The influent water had an average NO3-N concentration of 25 mg L-1. The performance of the bioreactor was evaluated in two scenarios. In Scenario 1, only NO3-N removal was evaluated; in Scenario 2, NO3-N removal, ammonium-N (NH4-N), and dissolved reactive phosphorus (DRP) generation was considered. These data were used to generate a sustainability index (SI), which evaluated the overall performance taking these parameters into account. In Scenario 1, the bioreactor was a net reducer of contaminants, but it transformed into a net producer of contaminants in Scenario 2. Inquisition of the data using these scenarios meant that an optimum bioreactor design could be identified. This would involve reduction to two cells: a single sandy loam soil cell followed by a woodchip cell, which would remove NO3-N and reduce greenhouse gas (GHG) emissions and DRP losses. An additional post-bed chamber containing media to eliminate NH4-N and surface capping to reduce GHG emissions further is advised. Scenario modeling, such as that proposed in this paper, should ideally include GHG in the SI, but because different countries have different emission targets, future work should concentrate on the development of geographically appropriate weightings to facilitate the incorporation of GHG into a SI. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions are subject to intra- and interannual variation due to changes in weather and management. This creates significant uncertainties when quantifying estimates of annual N2O emissions from grazed grasslands. Despite these uncertainties, the majority of studies are short-term in nature (<1 year) and as a consequence, there is a lack of data on interannual variation in N2O emissions. The objectives of this study were to (i) quantify annual N2O emissions and (ii) assess the causes of interannual variation in emissions from grazed perennial ryegrass/white clover grassland. Nitrous oxide emissions were measured from fertilized and grazed perennial ryegrass/white clover grassland (WC) and from perennial ryegrass plots that were not grazed and did not receive N input (GB), over 4 years from 2008 to 2012 in Ireland (52°51'N, 08°21'W). The annual N2O-N emissions (kg ha-1; mean ± SE) ranged from 4.4 ± 0.2 to 34.4 ± 5.5 from WC and from 1.7 ± 0.8 to 6.3 ± 1.2 from GB. Interannual variation in N2O emissions was attributed to differences in annual rainfall, monthly (December) soil temperatures and variation in N input. Such substantial interannual variation in N2O emissions highlights the need for long-term studies of emissions from managed pastoral systems. [ABSTRACT FROM AUTHOR]

Bioenergy from crops is expected to make a considerable contribution to climate change mitigation. However, bioenergy is not necessarily carbon neutral because emissions of CO2, N2O and CH4 during crop production may reduce or completely counterbalance CO2 savings of the substituted fossil fuels. These greenhouse gases ( GHGs) need to be included into the carbon footprint calculation of different bioenergy crops under a range of soil conditions and management practices. This review compiles existing knowledge on agronomic and environmental constraints and GHG balances of the major European bioenergy crops, although it focuses on dedicated perennial crops such as M iscanthus and short rotation coppice species. Such second-generation crops account for only 3% of the current European bioenergy production, but field data suggest they emit 40% to >99% less N2O than conventional annual crops. This is a result of lower fertilizer requirements as well as a higher N-use efficiency, due to effective N-recycling. Perennial energy crops have the potential to sequester additional carbon in soil biomass if established on former cropland (0.44 Mg soil C ha−1 yr−1 for poplar and willow and 0.66 Mg soil C ha−1 yr−1 for M iscanthus). However, there was no positive or even negative effects on the C balance if energy crops are established on former grassland. Increased bioenergy production may also result in direct and indirect land-use changes with potential high C losses when native vegetation is converted to annual crops. Although dedicated perennial energy crops have a high potential to improve the GHG balance of bioenergy production, several agronomic and economic constraints still have to be overcome. [ABSTRACT FROM AUTHOR]