The dataset originates from a two-year field experiment (2022–2024) at Teagasc Johnstown Castle, Wexford, Ireland. It captures nitrous oxide (N₂O) emissions, emission intensities, and emission factors from grassland systems fertilised with either digestate (from an anaerobic digestion plant) or calcium ammonium nitrate (CAN). Four grassland community compositions were tested: perennial ryegrass monoculture, ryegrass with white clover, ryegrass with red clover, and a six-species mixture including grasses, legumes, and herbs. The dataset therefore integrates greenhouse gas fluxes, soil characteristics, climatic records (temperature, rainfall, air pressure), soil moisture, and agronomic performance data (yields, nitrogen uptake) across fertiliser treatments and grassland types