Urine patches and dung pats from grazing livestock create hotspots for production and emission of the greenhouse gas, nitrous oxide (N2O), and represent a large proportion of total N2O emissions in many national agricultural greenhouse gas inventories. As such, there is much interest in developing country specific N2O emission factors (EFs) for excretal nitrogen (EF3, pasture, range and paddock) deposited during gazing. The aims of this study were to generate separate N2O emissions data for cattle derived urine and dung, to provide an evidence base for the generation of a country specific EF for the UK from this nitrogen source. The experiments were also designed to determine the effects of site and timing of application on emissions, and the efficacy of the nitrification inhibitor, dicyandiamide (DCD) on N2O losses. This co-ordinated set of 15 plot-scale, year-long field experiments using static chambers was conducted at five grassland sites, typical of the soil and climatic zones of grazed grassland in the UK. We show that the average urine and dung N2O EFs were 0.69% and 0.19%, respectively, resulting in a combined excretal N2O EF (EF3), of 0.49%, which is <25% of the IPCC default EF3 for excretal returns from grazing cattle. Regression analysis suggests that urine N2O EFs were controlled more by composition than was the case for dung, whilst dung N2O EFs were more related to soil and environmental factors. The urine N2O EF was significantly greater from the site in SW England, and significantly greater from the early grazing season urine application than later applications. Dycandiamide reduced the N2O EF from urine patches by an average of 46%. The significantly lower excretal EF3 than the IPCC default has implications for the UK's national inventory and for subsequent carbon footprinting of UK ruminant livestock products.

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The global warming potential of nitrous oxide (N 2 O) and its long atmospheric lifetime mean its presence in the atmosphere is of major concern, and that methods are required to measure and reduce emissions. Large spatial and temporal variations means, however, that simple extrapolation of measured data is inappropriate, and that other methods of quantification are required. Although process-based models have been developed to simulate these emissions, they often require a large amount of input data that is not available at a regional scale, making regional and global emission estimates difficult to achieve. The spatial extent of organic soils means that quantification of emissions from these soil types is also required, but will not be achievable using a process-based model that has not been developed to simulate soil water contents above field capacity or organic soils. The ECOSSE model was developed to overcome these limitations, and with a requirement for only input data that is readily available at a regional scale, it can be used to quantify regional emissions and directly inform land-use change decisions. ECOSSE includes the major processes of nitrogen (N) turnover, with material being exchanged between pools of SOM at rates modified by temperature, soil moisture, soil pH and crop cover. Evaluation of its performance at sitescale is presented to demonstrate its ability to adequately simulate soil N contents and N 2 O emissions from cropland soils in Europe. Mitigation scenarios and sensitivity analyses are also presented to demonstrate how ECOSSE can be used to estimate the impact of future climate and land-use change on N 2 O emissions. C max A constant (set at 50 kg N ha -1 ) that adjusts the maximum rate of nitrification possible [this occurs at high levels of NH 4 ? and will be dependent on soil composition (Parton et al. 1996)] D p Potential denitrification rate (kg N ha -1 layer -1 day -1 ) k nitrif A rate constant for nitrification [set at 0.6 (Bradbury et al. (1993)] m b Biological activity rate modifier m NO 3 Modifies the amount of denitrification depending on soil NO 3 -content m pH A rate modifier due to soil pH m t A rate modifier due to soil temperature m w Soil water rate modifier for decomposition m w0 Soil water rate modifier for decomposition at permanent wilting point and saturation = 0.2 m 0 w Soil water rate modifier for denitrification N d The amount of N emitted from the soil during denitrification (kg N ha -1 layer -1 ) N d;N 2The amount of N 2 gas lost by denitrification (kg N ha -1 day -1 ) N d;N 2 O The amount of N 2 O gas lost by denitrification (kg N ha -1 day -1 ) N d50The soil nitrate content at which denitrification is 50% of its full potential (kg N ha -1 layer -1 ) N FERT N in NH 4 ? and urea in the added fertiliser (kg N ha -1 ) N n Nitrification rate (kg N ha -1 layer -1 ) N n;N 2 O The amount of N 2 O gas released during nitrification (kg N ha -1 day -1 ) N NH 4

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