Assessing Ammonia Volatilization As Influenced By Fertilizer Nitrogen Source and Inhibitors in Temperate Grassland.

A proposed strategy for mitigating N fertilizer related nitrous oxide (N₂O) emissions in Irish agriculture is switching N source from calcium ammonium nitrate (CAN) to urea or urea with a urease inhibitor (N-(n-butyl) thiophosphoric triamide) and or a nitrification inhibitor (dicyandiamide). CAN is a ready source of nitrate (NO₃-N) which is vulnerable to leaching and to de-nitrification loss pathways under the cool humid conditions of Ireland. Switching to urea has the potential to decrease N₂O emissions and reduce direct fertiliser costs as urea is less expensive per unit N compared with CAN. Adoption of urea to reduce N₂O emissions presents a potential pollution swopping risk via ammonia (NH₃-N) volatilization.  Such loss is problematic for several reasons: i) it represents an economic loss of N, ii) it contributes to eutrophication in aquatic and low-N input ecosystems through atmospheric transport and deposition, and iii) Ireland has committed to reduce emissions of gases including ammonia under the Gothenburg Protocol and the National Emissions Ceiling Directive. This study is using a system of windtunnels to evaluate how NH₃-N loss potential is impacted by fertilizer N source and the N inhibitors in temperate grassland. Initial results show that NH₃-N losses were greater from urea compared with CAN. The urease inhibitor alone and when combined with the nitrification inhibitor, successfully mitigated NH₃-N losses from urea. Results to date indicate that the potential for pollution swapping when switching N source from CAN to urea can be addressed using specific urea inhibitor combinations in intensively managed grassland.