Estimating field N2 emissions based on laboratory-quantified N2O/(N2O + N2) ratios and field-quantified N2O emissions.

Purpose: The key environmentally beneficial process that substantially removes reactive nitrogen from biosphere is a complete denitrification. The science of measuring and constraining nitrous oxide (N₂O) emissions has advanced significantly; however, despite several attempts, in situ dinitrogen (N₂) measurement is still a great challenge and is poorly understood due to the high atmospheric N₂ background. This study aimed at estimating field-scale inferred N₂ emissions using data of field N₂O emissions and laboratory-measured N₂O/(N₂O + N₂) ratios and correlating those emissions with the soil-environmental factors. Materials and methods: Closed static chamber and He/O₂ direct measurement methods were used at field and laboratory scale, respectively. For each treatment (varying N fertilizer rates), on each sampling date, N₂O and N₂ emissions were measured at laboratory and N₂O emissions at field-scale, allowing the calculation of field-scale inferred N₂ emissions. Results: The results demonstrate that field-scale inferred cumulative N₂ emissions were 1.35, 1.48 and 1.60 times greater than laboratory-measured cumulative N₂ emissions in low nitrogen level (LNL), medium nitrogen level (MNL) and high nitrogen level (HNL) treatments, respectively. This suggests that estimating N₂ emissions at the field-scale in agricultural soil could give more insight on N cycling processes. Moreover, N fertilizer application rates increased linearly both field and laboratory cumulative N₂O and N₂ emissions. Both positive and negative relationships between soil-environmental parameters and N₂O, N₂ and their N₂O/(N₂O + N₂) ratios at field and laboratory-based indicate their heterogeneous roles in N₂O formation and reduction processes. Conclusion: The results provide complementary insights into field-scale N₂ emissions in agricultural soil and help in closing the knowledge gap in the N balance. Linear relationships between the emissions (N₂O and N₂) and N fertilizer rates observed suggest that climate change mitigation options could be achieved by optimizing the N fertilization rates since N₂O and N₂ emissions are enhanced by increasing N inputs. As our results present the field-scale inferred N₂ emissions, there is still a need to design a robust methodological approach that will enable researchers to directly quantify field N₂ emissions. [ABSTRACT FROM AUTHOR]