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

Nitrogen 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 (NH 3 ) and nitrous oxide (N 2 O) emissions remains a scientific challenge. We conducted soil column experiments to investigate the combined effects of straw incorporation (with/without), nitrogen (N) management (deep placement vs. surface broadcast of urea vs. nitrification inhibitor DMPP-amended urea) on NH 3 and N 2 O emissions in three typical Chinese upland soils. With surface broadcast fertilizer, straw incorporation significantly increased NH 3 emissions in the acidic Latosol and Black soil, while no effect on NH 3 emissions was observed in the alkaline Fluvo-aquic soil. The increased NH 3 emissions can be explained by the associated increase in soil pH caused by straw incorporation. Notably, deep placement reduced NH 3 emissions to negligible levels (1-4% of applied N) under all N and straw management strategies in the three soils. Straw incorporation significantly increased N 2 O 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, N 2 O 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 NH 3 and N 2 O emissions between N, straw and soil properties, showing that deep placement of DMPP-amended urea can effectively reduce both NH 3 and N 2 O emissions with straw incorporation across the three contrasting upland soils in China. • We examined NH 3 and N 2 O emission under N and straw management in three upland soils • Straw return increased NH 3 emissions in acidic soils and N 2 O emissions in all soils • Combining DMPP and deep placement minimized straw-induced NH 3 and N 2 O emissions • Enhanced NH 3 emissions by straw return can be attributed to the increase of soil pH