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Measuring soil dinitrogen (N2) emissions is notoriously challenging under field conditions. Hence, N2 emissions represent a significant uncertainty in the nitrogen mass balance of terrestrial ecosystems. The 15N gas flux (15NGF) method is the only method currently available for directly quantifying N2 emissions in situ. However, this method has rarely undergone independent validation under field conditions. In this study, our objectives were to: (1) Quantify N2 emissions and their role in the fertilizer N mass balance of a wheat rotation using the 15NGF method (2) Verify the obtained quantities of N2 emissions using a mass balance approach and (3) Verify the temporal N2 emission dynamics at the soil-atmosphere interface using vertical soil profiles of 15N2 enrichment.To achieve these objectives, we grew winter wheat in lysimeters and applied 15N enriched mineral fertilizers via fertigation in three doses (sum 170 kg N ha-1). We then analyzed gaseous (NH3, N2O, N2) and hydrological N losses, as well as fertilizer N fates in plant and soil, and 15N2 enrichment in soil air.Our results showed that N2 emissions directly measured using the 15NGF method amounted to 30 ± 4 kg N ha-1, which was equivalent to 18 ± 3 % of the applied fertilizer N. These measurements agreed with unrecovered fertilizer N obtained from the 15N fertilizer mass balance, although the latter had large inherent uncertainty (21 ± 21 kg N ha-1). N2O emissions, however, were negligible (0.14 ± 0.02 kg N ha-1). The temporal variability of measured N2 emissions after fertilizer additions was generally well explained by 15N2 enrichment in soil gas.Overall, we provide independent validation of the 15NGF method in measuring N2 emissions in the field and highlight the significant role of these emissions in the nitrogen balance of crop systems. Our data also suggest that soil gas measurements in combination with diffusion modeling could serve as an alternative method for quantifying N2 emissions. These results should encourage a wider application of the 15NGF method in order to improve our understanding of N2 emissions and reduce the current uncertainties in estimates of these emissions. |
