Estimating field N 2 emissions based on laboratory-quantified N 2 O/(N 2 O + N 2 ) ratios and field-quantified N 2 O 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 (N 2 O) emissions has advanced significantly; however, despite several attempts, in situ dinitrogen (N 2 ) measurement is still a great challenge and is poorly understood due to the high atmospheric N 2 background. This study aimed at estimating field-scale inferred N 2 emissions using data of field N 2 O emissions and laboratory-measured N 2 O/(N 2 O + N 2 ) ratios and correlating those emissions with the soil-environmental factors. Materials and methods Closed static chamber and He/O 2 direct measurement methods were used at field and laboratory scale, respectively. For each treatment (varying N fertilizer rates), on each sampling date, N 2 O and N 2 emissions were measured at laboratory and N 2 O emissions at field-scale, allowing the calculation of field-scale inferred N 2 emissions. Results The results demonstrate that field-scale inferred cumulative N 2 emissions were 1.35, 1.48 and 1.60 times greater than laboratory-measured cumulative N 2 emissions in low nitrogen level (LNL), medium nitrogen level (MNL) and high nitrogen level (HNL) treatments, respectively. This suggests that estimating N 2 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 N 2 O and N 2 emissions. Both positive and negative relationships between soil-environmental parameters and N 2 O, N 2 and their N 2 O/(N 2 O + N 2 ) ratios at field and laboratory-based indicate their heterogeneous roles in N 2 O formation and reduction processes. Conclusion The results provide complementary insights into field-scale N 2 emissions in agricultural soil and help in closing the knowledge gap in the N balance. Linear relationships between the emissions (N 2 O and N 2 ) and N fertilizer rates observed suggest that climate change mitigation options could be achieved by optimizing the N fertilization rates since N 2 O and N 2 emissions are enhanced by increasing N inputs. As our results present the field-scale inferred N 2 emissions, there is still a need to design a robust methodological approach that will enable researchers to directly quantify field N 2 emissions.