Mitigating NH₃ and N₂O emissions through deep placement of DMPP-amended urea with straw incorporation in upland soils

Nitrogen (N) fertilization and straw return play a pivotal role in enhancing crop productivity and soil fertility and yet designing management approaches that reduce both soil ammonia (NH₃) and nitrous oxide (N₂O) emissions remains a scientific challenge. We conducted soil column experiments to investigate the combined effects of straw incorporation (with/without), N management (deep placement vs. surface broadcast of urea vs. nitrification inhibitor DMPP-amended urea) on NH₃ and N₂O emissions in three typical Chinese upland soils. With surface broadcast fertilizer, straw incorporation significantly increased NH₃ emissions in the acidic Latosol and Black soil, while no effect on NH₃ emissions was observed in the alkaline Fluvo-aquic soil. The increased NH₃ emissions can be explained by the associated increase in soil pH caused by straw incorporation. Notably, deep placement reduced NH₃ emissions to negligible levels (1–4% of applied N) under all N and straw management strategies in the three soils. Straw incorporation significantly increased N₂O emissions with all N application techniques in all three soils, except for under deep placement of urea in the Latosol. When DMPP was applied with urea, N₂O emissions were significantly reduced and only represented 0.01–0.09% of the applied N. Our results provide novel insights into the tripartite interactions governing both NH₃ and N₂O emissions between N, straw and soil properties, showing that deep placement of DMPP-amended urea can effectively reduce both NH₃ and N₂O emissions with straw incorporation across the three contrasting upland soils in China.