Fertiliser N Formulation Impacts Yield, Nitrous Oxide and Ammonia Emissions in Temperate Grassland.

Fertiliser nitrogen (N) is a cornerstone input in many intensive agricultural systems including those prevalent in Irish temperate grassland. However, N fertiliser is associated with environmental loss of the potent greenhouse gas nitrous oxide (N₂O) and the air pollutant ammonia (NH₃). Nitrogen fertiliser form and the use of N stabilisers have potential to improve fertiliser efficiency and reduce N₂O and NH₃ emissions while sustaining the N rates which underpin production. In the current work fertiliser form along with an N stabiliser from the urease inhibition class, N-(n-butyl) thiophosphoric triamide (NBPT), and/or a stabiliser from the nitrification inhibitor class, dicyandiamide (DCD), were tested. Five N fertiliser formulations; calcium ammonium nitrate (CAN), urea, urea+NBPT, urea+DCD and urea+NBPT+DCD were evaluated for agronomic and environmental loss parameters at six site-years on a range of soils in temperate maritime grassland. With the exception of urea+DCD which had significantly lower yield than the other treatments at three site-years all fertiliser options gave similar annual yields. However, urea and urea+DCD had significantly lower apparent fertiliser recovery efficiency than CAN and urea+NBPT which were consistently equal. The urea+NBPT treatment had significantly lower NH₃ emissions compared with urea; on average 78.5% lower. The addition of the nitrification inhibitor resulted in inconsistent effects on NH₃ emissions. Emissions of the greenhouse gas N₂O were highest and most variable for CAN (1.5% c.v. 61%). Emissions for the urea treatments were lower at all site-years (0-0.5%) and less variable (c.v. 14-38%). Fertiliser formulation including the use of nitrogen stabilisers is a useful tool for meeting agronomic and environmental goals without reducing the N rates that underpin production. Based on this work, policy makers are assessing impact of incorporating N fertiliser formulation as an emission mitigation strategy to aid national goals of growing agricultural output while meeting emission reduction commitments.