Effects of nitrification inhibitor and maize straw application on N2O and N2 emissions from two agricultural soils: A 15N tracer study

N2O and N2 emissions from two soils after urea addition were quantified in the lab.The Inceptisol (alkaline) emitted much more N2O and N2 than the Mollisol (acidic).NI application mitigated N2O emissions in both soils but differed on N2 emission.Straw application mitigated N2O emissions in Mollisol but had little effects on N2 emissions. The application of nitrification inhibitors (NIs) and crop straw with nitrogen (N) fertilizers is a common practice aimed at enhancing soil N conservation and improving crop N use. However, their effects on gaseous N emissions from soils, particularly for N2, are less understood. We conducted a 60-day soil incubation experiment under controlled conditions (80% water-filled pore space and 25 degrees C) to investigate the effects of NI or maize straw application on N2O and N2 emissions from two typical upland soils: a Mollisol and an Inceptisol, which have contrasting pH values. Both soils were fertilized with 15N-labeled urea. During the incubation period, cumulative N2O and N2 emissions for the urea-only treatment in the Mollisol were 0.5 and 12 mg N kg-1 soil, respectively, while emissions in the Inceptisol reached 15 and 176 mg N kg-1. The application of NI (dicyandiamide) reduced N2O emissions by 66%-72% in both soils and decreased N2 emissions by 81% in the Inceptisol, although it increased N2 emissions by 15% in the Mollisol. Straw application also reduced N2O emissions by 60% in the Mollisol and by 4% in the Inceptisol, but it increased N2 emissions by 75%-96% in both soils. Notably, the increased N2 emissions following straw incorporation were primarily soil-derived rather than fertilizer-derived in both soils. These findings reveal that the applications of NIs or straw have varying impacts on N2O and N2 emissions across different soils, and that NI application could be a promising strategy to reduce high gaseous N losses in Inceptisol following N fertilization.