Quantitative Analysis of the Sources of N₂O Emissions on Maize-cultivated Fluvo-aquic Soil

Quantifying the sources of N₂O emissions is essential for clarifying the N₂O production mechanism and estimating the emission factor of nitrogen (N) fertilizer. Most published studies focused on the N₂O which emitted directly from N fertilizer, while there were only limited reports determined the patterns of native soil-derived N₂O emissions following N fertilization. In this study, a pot experiment was carried out to elucidate the impacts of the ¹⁵N fertilization and plant cropping (maize) on fertilizerand native soil-derived N₂O emissions in a fluvo-aquic soil. Four treatments, i. e., no N fertilization and no plant maize (N0P0), plant maize without N fertilization (N0P1), N fertilization without plant maize (N1P0), and N fertilization plus plant maize (N1P1), were established in the experiment. Results show that the total N₂O emissions were stimulated by N fertilization. The soiland fertilizer-derived N₂O emissions accounted for 22.5% and 77.5% of the total emissions, respectively. Compared with non-N-fertilized control, N fertilization significantly enhanced soil-derived N₂O emissions by 162%-460% (P < 0.05), and this increased soil-derived N₂O emissions (4.16-6.98 mg N₂O-N·m^-2) contributed about 13.7%-18.1% to the total emissions. N fertilization also enhanced CO₂ fluxes, and a significant linear relationship between CO₂ emissions and the change of soil-derived N₂O emissions was observed (P < 0.05), which suggests that the stimulated soil-derived N₂O emissions were highly related to the promoted soil organic matter turnover. The results of the two-way ANOVA indicate that the interactions between N fertilization and plant maize had a significant effect on the rates and sources of N₂O emissions (P < 0.01). Compared with N1P0, N₂O emissions under N1P1 were significantly reduced by 55.0% (P < 0.05); but the proportion of the stimulated native soil-derived N₂O emissions was higher under N1P1. The total inorganic N (NO₃^--N and NH₄⁺-N) content under N1P0 was significantly (P < 0.05) higher than that under N1P1 treatment, but contrary trends were found for NH₄⁺-N content, indicating that plant cropping significantly affected the fates and dynamics of soil N. In conclusion, in the soil-crop system, the exogenous N application stimulated not only the fertilizer-derived N₂O emissions but also the emissions from native soil and the participation of the plant has significant impacts on the source of N₂O emission. Our study highlights that, in intensively farmed fluvo-aquic soils, future N₂O mitigation strategies should pay more attention to the emission from native soil.