Ammonia Emissions from Stabilised Urea Fertiliser Formulations in Temperate Grassland.

National commitments to reduce ammonia emissions under the Gothenburg protocol along with pressures to reduce greenhouse gas emissions including N₂O have placed fertiliser N, which contributes to both, in sharp focus. Urea and urea stabilised with urease or nitrification inhibitors has shown promise for reducing N₂O emissions relative to ammonium nitrate. However these fertiliser N options are associated with differing impacts on NH₃ emissions. The relative NH₃ loss performance of a number of fertiliser N and stabilisers i.e. calcium ammonium nitrate (CAN), urea and urea in combination with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), the nitrification inhibitor dicyandiamide (DCD), or both inhibitors was evaluated. Fertiliser N was applied in five split applications at two temperate grassland sites in Ireland. Urea + Nutrisphere was tested at one site. Ammonia loss was measured using a system of windtunnels. Urea produced a higher, and importantly from a management and inventory perspective a more variable emission, compared with CAN. Inclusion of DCD was observed to increase, have no effect, and to decrease NH₃ emissions from urea. Nutrisphere had no effect on NH₃ emissions from urea. Promisingly, the urease inhibitor NBPT used with urea alone reduced emissions by 78% and to levels which were similar to CAN even where DCD was included. Thus an effective urease inhibitor provides opportunities to reduce and to stabilise NH₃-N loss from urea or urea with a nitrification inhibitor, allowing for implementation of select N₂O mitigation strategies without pollution swapping and also more reliable NH₃ inventory estimations compared with urea.