Calcium Ammonium Nitrate, Urea or Stabilised Urea: The Impact on Yield and Apparent Fertiliser Recovery in Intensive Grassland.

Approximately 12% of Ireland’s national emission of greenhouse gases is in the form of N₂O arising from chemical/organic nitrogen fertilizers. Fertiliser N selection offers a potential opportunity to maintain N input rates but mitigate N₂O losses. Urea is susceptible to ammonia (NH₃) volatilisation but this risk could be managed using urease inhibitors. The aim of this study was to evaluate the effects of switching from CAN to urea, urea with the urease inhibitor N- (n-butyl) thiophosphoric triamide (n-BTPT) (trade name Agrotain®) and/or the nitrification inhibitor dicyandiamide (DCD) on grass yield and N fertiliser recovery.

The study took place over two years at six permanent pasture sites located at: Johnstown Castle, Co. Wexford, Ireland; Moorepark, Co. Cork, Ireland and Hillsborough, Co. Down, Northern Ireland; covering a range of soil textures and drainage characteristics. The annual fertiliser N was applied at 200 kg N ha^-1 in five equal splits. Grass yield and N uptake were measured at the end of each fertiliser application cycle and fertiliser recovery calculated.  Results to date indicate that there was no significant difference in dry-matter yield between CAN and any urea based formulation apart from Urea with the nitrification inhibitor DCD which generated significantly lower yield than CAN in three out of six site years. On average apparent fertiliser recovery was highest for Urea with the urease inhibitor n-BTPT and lowest for Urea with the nitrification inhibitor DCD. Apparent fertiliser recovery for urea with the urease inhibitor compares favourably to CAN. Results indicate that as well as a mitigation strategy for N₂O emissions from CAN, the use of specific stabilised urea fertilisers also maintains yield and apparent fertiliser recovery at levels comparable to CAN in intensive grassland.