Mitigation of N₂O emissions by different nitrification inhibitors in Mollisols of Northeast China

Objectives The use of nitrification inhibitors (NIs) is a common measure to reduce N₂O emissions from croplands. Here, we examined the effects of different types of NIs on N₂O emissions from the Mollisols upland to help developing effective mitigation strategies.

Methods A maize field experiment was set up in the typical Mollisols in Heilongjiang Province. The six treatments were no nitrogen fertilizer (N0), conventional N application rate (N200), 20% reduction of N rate (N160), 20% N reduction combined with dicyandiamide (N160+DCD), 3,4-dimethyl-pyrazole phosphate (N160+DMPP), and 2-choloro-6(trichloromethyl)-pyridine (N160+CP). We monitored the N₂O fluxes, soil temperature and moisture across the whole year, and measured the contents of soil ammonium (NH₄⁺-N), nitrate (NO₃⁻-N) and dissolved organic carbon (DOC) during the maize growing season.

Results All the five N fertilization treatments significantly increased soil NH₄⁺-N content, and the NH₄⁺-N contents were not significantly different among them. NIs application reduced soil NO₃⁻-N content, N160+DCD and N160+DMPP treatments exhibited levels similar to that of N0 treatment. Soil DOC content was slightly affected by the application of N fertilizer and NIs. Soil N₂O mainly emitted during maize growing season (May−October), accounting for 79%−95% of the annual emissions. DCD and DMPP significantly reduced the peak value and frequency of N₂O flux peak. The annual N₂O emissions in N200 was 3.83 kg/hm², which was significantly higher than 0.76 kg/hm² in N0. The N160 decreased 31% of annual N₂O emissions (2.65 kg/hm²), and the application of DCD and DMPP further reduced N₂O emissions to 0.98 and 1.34 kg/hm², with mitigation efficiency of 63% and 49%, respectively. However, CP had no significant effect on N₂O emissions. The N₂O emission factor for N160+DCD and N160+DMPP were 0.14% and 0.36%, respectively, which were significantly lower than those of the other treatments (1.14%−1.53%). N fertilization significantly increased maize yield, however, N200 and N160 treatments increased the yield-scaled N₂O emission by 3.5 and 2.1 times respectively, while DCD and DMPP decreased yield-scaled N₂O emission to the level of N0.

Conclusions Reducing N fertilizer input could significantly reduce N₂O emissions from Mollisols, and the combination with DCD and DMPP could further significantly reduce annual N₂O emissions. Among the three types of NIs considered in this study, DCD showed the most satisfactory effect on N₂O reduction, followed by DMPP and CP. NIs did not affect maize yield, but DCD and DMPP could significantly reduce yield-scaled N₂O emission. DCD is recommended for the mitigation of N₂O emissions in Mollisols region in Northeast China.