Cattle excreta deposited on grazed grasslands are a major source of the greenhouse gas (GHG) nitrous oxide (N2O). Currently, many countries use the IPCC default emission factor (EF) of 2% to estimate excreta-derived N2O emissions. However, emissions can vary greatly depending on the type of excreta (dung or urine), soil type and timing of application. Therefore three experiments were conducted to quantify excreta-derived N2O emissions and their associated EFs, and to assess the effect of soil type, season of application and type of excreta on the magnitude of losses. Cattle dung, urine and artificial urine treatments were applied in spring, summer and autumn to three temperate grassland sites with varying soil and weather conditions. Nitrous oxide emissions were measured from the three experiments over 12months to generate annual N2O emission factors. The EFs from urine treated soil was greater (0.30-4.81% for real urine and 0.13-3.82% for synthetic urine) when compared with dung (-0.02-1.48%) treatments. Nitrous oxide emissions were driven by environmental conditions and could be predicted by rainfall and temperature before, and soil moisture deficit after application; highlighting the potential for a decision support tool to reduce N2O emissions by modifying grazing management based on these parameters. Emission factors varied seasonally with the highest EFs in autumn and were also dependent on soil type, with the lowest EFs observed from well-drained and the highest from imperfectly drained soil. The EFs averaged 0.31 and 1.18% for cattle dung and urine, respectively, both of which were considerably lower than the IPCC default value of 2%. These results support both lowering and disaggregating EFs by excreta type.

Important biochemical reactions in soils are catalyzed by extracellular enzymes, which are synthesized by microbes and plant roots. Although enzyme activities can significantly affect the decomposition of soil organic matter and thus influence the storage and cycling of carbon (C) and nitrogen (N), it is not clear how enzyme activities relate to changes in the C and N content of different grassland soils. Here we address whether the activity of C-acquiring (b-1,4-glucosidase, BG) and N-acquiring (L-leucine aminopeptidase (LAP) and b-1,4-N-acetyl-glucosaminidase (NAG)) enzymes is linked to changes in the C and N content of a variety of human-managed grassland soils. We selected soils which have a well-documented management history going back at least 19 years in relation to changes in land use (grazing, mowing, ploughing), nutrient fertilization and lime (CaCO 3) applications. Overall we found a positive relationship between BG activity and soil C content as well as between LAP þ NAG activity and soil N. These positive relationships occurred across grasslands with very different soil pH and management history but not in intensively managed grasslands where increases in soil bulk density (i.e. high soil compaction) negatively affected enzyme activity. We also found evidence that chronic nutrient fertilization contributed to increases in soil C content and this was associated with a significant increase in BG activity when compared to unfertilized soils. Our study suggests that while the activities of C-and N-acquiring soil enzymes are positively related to soil C and N content, these activities respond significantly to changes in management (i.e. soil compaction and nutrient fertilization). In particular, the link between BG activity and the C content of long-term fertilized soils deserves further investigation if we wish to improve our understanding of the C sequestration potential of human-managed grassland soils.

*Corresponding authors karl.richards@teagasc.ieHighlights  The N 2 O emission factor for CAN was substantially higher than the IPCC default and highly variable between sites and across years. Urea products decreased direct N 2 O emissions from CAN on average by 80%  Switching from CAN to urea products reduces both N 2 O emissions and fertiliser costs. 3 AbstractThe accelerating use of synthetic nitrogen (N) fertilisers, to meet the world's growing food demand, is the primary driver for increased atmospheric concentrations of nitrous oxide (N 2 O). The IPCC default emission factor (EF) for N 2 O from soils is 1% of the N applied, irrespective of its form. However, N 2 O emissions tend to be higher from nitrate-containing fertilisers e.g. calcium ammonium nitrate (CAN) compared to urea, particularly in regions, which have mild, wet climates and high organic matter soils. Urea can be an inefficient N source due to NH 3 volatilisation, but nitrogen stabilisers (urease and nitrification inhibitors) can improve its efficacy. This study evaluated the impact of switching fertiliser formulation from calcium ammonium nitrate (CAN) to urea-based products, as a potential mitigation strategy to reduce N 2 O emissions at six temperate grassland sites on the island of Ireland. The surface applied formulations included CAN, urea and urea with the urease inhibitor N-(nbutyl) thiophosphoric triamide (NBPT) and/or the nitrification inhibitor dicyandiamide (DCD). Results showed that N 2 O emissions were significantly affected by fertiliser formulation, soil type and climatic conditions. The direct N 2 O emission factor (EF) from CAN averaged 1.49% overall sites, but was highly variable, ranging from 0.58% to 3.81.Amending urea with NBPT, to reduce ammonia volatilisation, resulted in an average EF of 0.40% (ranging from 0.21 to 0.69%)-compared to an average EF of 0.25% for urea (ranging from 0.1 to 0.49%), with both fertilisers significantly lower and less variable than CAN.Cumulative N 2 O emissions from urea amended with both NBPT and DCD were not significantly different from background levels. Switching from CAN to stabilised urea formulations was found to be an effective strategy to reduce N 2 O emissions, particularly in wet, temperate grassland. 4Key words nitrous oxide mitigation; emission factor; calcium ammonium nitrate; stabilised urea; nitrification inhibitor Dicyandiamide (DCD); urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT).5

Fertiliser nitrogen (N) contributes to ammonia (NH 3 ) emissions, which European Union member states have committed to reduce. This study evaluated NH 3 -N loss from a suite of N fertilisers over multiple applications, and on gaining insights into the temporal and seasonal patterns of NH 3 -N loss from urea in Irish temperate grassland using wind tunnels. The fertilisers evaluated were: calcium ammonium nitrate (CAN), urea, and urea with the N stabilisers N-(n-butyl) thiophosphoric triamide (NBPT), dicyandiamide (DCD), DCD+NBPT, and a maleic and itaconic acid polymer (MIP). 200 (and 400 for urea only) kg N/ha/yr was applied in five equal applications over the growing season at two grassland sites (one for MIP). Mean NH 3 -N losses from CAN were 85% lower than urea which had highly variable loss (range 45% points). The effect of DCD on NH 3 emissions was variable. MIP did not decrease loss but NBPT caused a 78.5% reduction, and when combined with DCD, a 74% reduction compared with urea alone. Mean spring and summer losses from urea were similar, although spring losses were more variable with both the lowest and highest loss levels.Maximum NH 3 -N loss usually occurred on the second day after application. These data highlight the potential of stabilised urea to alter urea NH 3 -N loss outcomes in temperate grassland, the need for caution when using season as a loss risk guide and that urea hydrolysis and NH 3 -N loss in temperate grassland is rapid. Micrometeorological measurements focused specifically on urea are needed to determine absolute NH 3 -N loss levels in Irish temperate grassland.

4In temperate grassland N source influences greenhouse gas emissions (GHG). Nitrification 5 and urea hydrolysis inhibitors can reduce these losses. The objective of this study was to 6 evaluate the impact of N source, urease inhibitors and nitrification inhibitors on temperate 7 grassland yields and N uptake. Experiments were conducted at three locations over two years 8 (6 site-years) on the island of Ireland, covering a range of soils and climatic conditions. 9Results showed that CAN, urea+NBPT, urea+NBPT+DCD and urea had equal annual DM 10 yield. Urea+DCD had lower DM yield than CAN for 3 site-years. Calcium ammonium nitrate 11 and urea+NBPT consistently had the same N uptake, and urea+DCD had lower N uptake than 12 CAN in 4 of 6 site-years, urea had lower N uptake than CAN in two site-years and 13 urea+NBPT+DCD had lower N uptake than CAN in one site-year. Urea+NBPT is a cost-14 effective alternative to CAN, which is consistently equal in terms of both yield and N uptake 15 in temperate grassland. 16 Corporation, St. Joseph, Michigan, USA). 106 Apparent fertilizer N recovery (AFR) was calculated as: 107 AFR (%) = ((N off-take treatment -N off-take control )/N rate) *100 108 Urea relative yield (URY) was calculated as: 109 URY (%) = (Yield urea_product / Yield CAN ) * 100 110 Grass Growing degree days (GDD) was calculated as: 111 GDD = (DailyTemp max +DailyTemp min /2 -T base ) (T base = 6°C for grass) 112 113 exchange capacity (CEC) and buffering capacity. 132 133 Statistical analysis 134 The effect of fertilizer N treatment on the dependent variables of grass yield and N uptake 135 were tested using the general linear mixed model for all site-years using the PROC 136 GLIMMIX procedure of SAS (© 2002-2010, SAS Institute Inc., Cary, NC, USA). The 137 factors in the model were site-year and fertilizer N and their interactions as fixed effects and 138 block as a random effect. Least significant differences are presented along with the pooled Teagasc Moorepark and Agri-Food and Biosciences Institute with their assistance on this 350 project. The authors would also like to thank Koch Agronomic Services for the supply of 351 fertilizer products.