Ammonium-Based Compound Fertilisers Mitigate Nitrous Oxide Emissions in Temperate Grassland

Nitrogen fertiliser application represents the largest anthropogenic source of nitrous oxide (N₂O) emissions, and the magnitude of these emissions is dependent on the type of fertilisers applied in the agroecosystems. Despite N-P-K compound fertilisers being commonly used in agricultural soils, a lack of information exists regarding their effects on N₂O emissions. This study aims at examining the effects of different commonly used N-P-K compound fertiliser formulations with contrasting nitrate to ammonium ratios (0.05 to 0.88) on N₂O emissions, yield, and nitrogen use efficiency (NUE) in temperate grassland and to compare these variables with common straight N fertilisers. Compound fertilisers with varying NPK inclusion rates (18-6-12, 10-10-20, 24-2.2-4.5, and 27-2.5-5), and calcium ammonium nitrate (CAN) and urea + N-(n-butyl) thiophosphoric triamide (NBPT) were applied at 80 kg N ha⁻¹ to experimental plots in managed grassland on two occasions in a growing season. Fluxes of N₂O during the experiment period, yield and NUE following two harvests were measured. The cumulative N₂O emission from urea + NBPT, 18-6-12, 10-10-20, and 24-2.2-4.5 treatments were significantly reduced by 44%, 43%, 37%, and 31% compared with CAN treatment under conducive soil moisture condition. Under the same soil condition, 18-6-12 and 10-10-20 treatments showed higher yield, N uptake, and NUE although did not significantly differ from the other fertiliser treatments. Our results suggest that ammonium-based compound fertilisers have a potential to reduce N₂O emissions while maintaining yields. Further long-term study is needed to capture the full magnitude of variations in N₂O emissions, including ammonia (NH₃) volatilization from nitrate and ammonium-based compound fertiliser applications from multiple soil types and under different climatic conditions.