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

Background and Aims: The application of nitrification inhibitor (NI) and crop straw with nitrogen (N) fertilizer is a common practice to increase soil N conservation and crop N use in cropping systems. However, their effects on gaseous N emission from soils are less understood, especially for N₂. Methods: We conducted a 60-day soil incubation experiment to study the effects of NI or maize straw application on N₂O and N₂ emissions from two typical upland soils, namely a Mollisol and an Inceptisol with contrasting pH values, fertilized with ¹⁵N-labeled urea. Results: During the incubation period, cumulative N₂O and N₂ emissions for urea-only addition treatment in the Mollisol were 0.5 and 12 mg N kg^-1 soil, respectively, while they were 15 and 176 mg N kg^-1 soil in the Inceptisol. The co-application of NI (dicyandiamide) decreased cumulative N₂O emissions by 66%-72% in both soils and decreased N₂ emissions by 81% in the Inceptisol. However, it increased N₂ emissions by 15% in Mollisol. The co-application of straw also decreased cumulative N₂O emission by 60% in the Mollisol and by 4% in the Inceptisol, but increased N₂ emission by 75%-96% in both soils. Interestingly, the increased N₂ emissions after straw incorporation were mainly soil-derived rather than fertilizer-derived in either soil. Conclusions: Our findings reveal that the applications of NI or straw have various impacts on N₂O and N₂ emissions in different soils, and NI application could be a promising measure to reduce the high gaseous N losses in Inceptisol following N fertilization.