<p>Agricultural soils are a major source of nitrous oxide (N₂O), a potent greenhouse gas. Legume pastures, such as white clover (Trifolium repens), and non-legume pastures, like tall fescue (Festuca arundinacea), can emit N₂O as a result of soil nitrogen (N) transformations. However, N fertilizer application typically amplifies these emissions by increasing nitrogen availability for nitrification and denitrification. Biochar a carbon-rich amendment derived from crop residues, may mitigate N₂O through modifying soil physicochemical and microbial processes. However, its interaction with different N fertilizers in not well understood in perennial pastures. We conducted a 12-month field experiment in white clover and tall fescue pastures using ammonium sulphate (AS) and urea (U), applied alone or with rice husk biochar (5 and 10 t ha⁻¹). AS had significantly lower soil pH more than U in tall fescue. Furthermore, AS maintained higher ammonium (NH₄⁺-N) than U in tall fescue and lower nitrate (NO₃⁻-N) than U in white clover, corresponding to its lower annual average daily N₂O fluxes (57 vs. 107&#xa0;µg N m⁻² h⁻¹), and 40.8% cumulative emissions than U in white clover. ASB5 treatment had the lowest cumulative and yield-scaled N₂O emissions in white clover accompanied also by the higher NH₄⁺-N concentration than sole AS. The significant negative correlation between NH₄⁺-N and NO₃⁻-N in tall fescue could suggest that, biochar co-applied with N fertilizer reduced nitrification and N₂O emissions. However further analyses for N₂O associated functional genes is required to elucidate the processes. These findings highlight the importance of pasture species and the potential of AS co-applied with optimum biochar rate of 5 t ha⁻¹ to reduce N₂O emissions in white clover.</p>