Field experiments at six Irish grassland sites (2013–2014) examined the influence of nitrogen (N) fertiliser type and application rate on nitrous oxide (N₂O) emissions. Calcium ammonium nitrate (CAN) replaced with urea-based fertilisers, particularly when stabilised with inhibitors such as NBPT or DCD, reduced direct N₂O emissions by up to 80% while lowering costs. Emission factors (EFs) were strongly influenced by fertiliser formulation and rate, with CAN consistently producing higher and more variable emissions than urea. Stabilised urea (urea + NBPT) was least sensitive to increasing rates. Collectively, these studies highlight that fertiliser choice and rate are key management levers for mitigating agricultural greenhouse gases and underscore the need for country-specific emission factors to improve national greenhouse gas inventories.