Mitigation of Nitrous Oxide Emissions From Grazed Grassland Soils in Ireland.

Irish agriculture accounts for 31% of national greenhouse gas (GHG) emissions with nitrous oxide (N₂O) from agricultural soils accounting for 12% of national emissions. The majority of N₂O emissions are from soil applied nitrogen fertiliser and animal excreta. Permanent grassland, grazed by ruminant animals, comprises 90% of the agricultural land area in Ireland. Between, 60-90% of ingested nitrogen (N) is returned to the pasture in urine and dung.  The amount of N deposited in a urine patch exceeds that which the pasture is able to take up, hence the surplus N is vulnerable to loss in pathways such as denitrification and leaching.  This is particularly important during the autumn/winter period when soil temperatures and pasture growth are low and rainfall is high. Nationally N₂O research has focused on improving inventory emission factors and investigating mitigation options for reducing emissions. Mitigation options for reducing N₂O emissions from soil focus on 1. Improving nitrogen use efficiency, 2. Reducing ruminant N excretion, 3. Synthetic N fertiliser formulation, 4. Use of urease and nitrification inhibitors. Improving manure N use efficiency through low ammonia (NH₃) emission spreading methods has been found to substantially reduce indirect N₂O emissions and does not increase direct emissions. Direct and indirect emissions of N₂O from urine patches was found to be linearly related to urine N content. Nitrate based fertilisers have been found to have substantially higher N₂O emissions than urea/ammonium (NH₄) fertilisers. Switching from nitrate to urea/NH₄ based fertilisers may increase N₂O emissions indirectly from NH₃ volatilisation, unless urea is amended with a urease inhibitor. Nitrification inhibitors have been found to significantly reduce direct and indirect N₂O emissions from urine, fertiliser and landspread animal manures. Further research is currently underway to further refine both N₂O inventories and practical cost effective mitigation options for farmers.