1. Three field sites: Clay loam at 3. Methods Three grassland field sites in Ireland: Drainage impeded at Hillsborough, Co. Down Moderately drained at Johnstown Castle, Co. Wexford Well drained at Moorepark, Co Cork. Fertiliser N formulations evaluated in year 1 (2013/14) and year 2 (2014/15): CAN, Urea, Urea + n-BTPT, Urea + DCD and Urea + n-BTPT + DCD. Fertiliser N rates (0 – 500 kg N ha -1 yr -1 ) applied in five equal splits, the 200 kg N ha -1 yr -1 rate is presented. N 2 O-N emissions measured using static chambers (Fig. 1) and NH 3 emissions measured using wind tunnels (Fig 2.) to give indirect N 2 O emissions. interaction (P<0.001) The impact of fertiliser formulation on N 2 O emissions Mary Harty 1,3, Patrick J. Forrestal 1, Rachael Carolan 2, Karen L. McGeough 2, Catherine J. Watson 2,3, Ronnie J. Laughlin 2, Dominika Krol 1, Gary Lanigan 1 and Karl G. Richards 1 1 Teagasc, Johnstown Castle, Environmental Research Centre, Co. Wexford, Ireland. 2 Agri-Food and Biosciences Institute, Belfast, Northern Ireland. 3 Queen’s University Belfast, Northern Ireland. mary.harty@teagasc.ie 1. Objective: To evaluate the effect of switching from calcium ammonium nitrate (CAN) to urea or urea with the urease inhibitor N-(n- butyl) thiophosphoric triamide (n-BTPT) and/or a nitrification inhibitor dicyandiamide (DCD) on nitrous oxide (N 2 O) emissions. 2. Introduction: Approximately 11.8% of Ireland’s national GHG emissions are due to fertiliser N application to agricultural soils (EPA, 2014). Use of nitrate-N (NO 3 –N) based fertilisers in a temperate maritime climate may result in fertiliser N 2 O-N emission factors (EFs) higher than the IPCC default of 1%. Switching from CAN to urea based fertilisers could potentially reduce N 2 O loss by managing the soil NO 3 –N pool, a key risk factor for denitrification. 4. Results : Table 1 – Direct N 2 O EFs (EFs in red indicate ≥ IPCC default of 1%) This work is funded by the Walsh Fellowship programme and Department of Agriculture Food and Marine, Research Stimulus Fund The authors would like to acknowledge the help of the technical and lab staff at Teagasc and AFBI. Reference: Environmental Protection Agency. 2014. Ireland National Inventory Report – 2014, page 116. Forrestal et al., 2015. Ammonia emissions from stabilised urea fertiliser formulations in temperate grassland. Soil Use and Management (in review) 6. Summary: Urea formulations generated sig. lower direct N 2 O emissions than CAN in five of six site years (Table 1) Nitrification inhibitor (DCD) was highly effective in lowering N 2 O emissions (Table 1) Incorporation of indirect N 2 O EFs in overall N 2 O EFs brings urea EF closer to IPCC default value of 1% although overall urea emissions are still significantly lower than overall CAN emissions (Figure 3) The addition of urease inhibitor (n-BTPT) reduced urea indirect N 2 O EFs to levels comparable to CAN (Figure 3) Use of urea with urease and or nitrification inhibitor shows potential as a mitigation strategy for N 2 O emissions (direct and indirect) relative to CAN. The magnitude of N 2 O emissions from CAN are site and rainfall dependent. Multi-site and year datasets are critical for developing meaningful national N 2 O EFs. *Treatment differences determined using F protected LSD test (P<0.05). Direct N 2 O emissions for CAN significantly different to all other urea treatment s except Urea+n-BTPT in Johnstown in Year 1. ** Hillsborough LTAR based on average rainfall data from 1995-2011, Johnstown and Moorepark LTAR based on average rainfall data from 1981-2010. Fig 1 – Static Chambers Fig 2 – Wind Tunnels interaction (P<0.001) 5. Results : Figure 3 – Year 2 N 2 O EFs Direct and Indirect Johnstown Hillsborough