This research investigated the effect of long-term phosphorus (P) addition relative to carbon (C) availability on nitrous oxide (N₂O) emissions from an ungrazed grassland soil via two incubation experiments. No significant effect of soil P on N₂O was found under C-limited conditions, while under added-C, cumulative N₂O was significantly higher from low-P (p < 0.05) rather than high-P soils. CO₂ was not significantly different between P-levels. This highlights the influence of soil P on N₂O emissions under non C-limiting conditions. This is one of the first studies demonstrating available-C moderating the effect of P on N₂O emissions from temperate grassland soils.