Lysimeter-based full fertilizer 15N balances corroborate direct dinitrogen emission measurements using the 15N gas flow method

The ${}^{15}$N gas flux (${}^{15}$NGF) method allows for direct in situ quantification of dinitrogen (N${}_2$) emissions from soils, but a successful cross-comparison with another method is missing. The objectives of this study were to quantify N${}_2$ emissions of a wheat rotation using the ${}^{15}$NGF method, to compare these N${}_2$ emissions with those obtained from a lysimeter-based ${}^{15}$N fertilizer mass balance approach, and to contextualize N${}_2$ emissions with ${}^{15}$N enrichment of N${}_2$ in soil air. For four sampling periods, fertilizer-derived N${}_2$ losses (${}^{15}$NGF method) were similar to unaccounted fertilizer N fates as obtained from the ${}^{15}$N mass balance approach. Total N${}_2$ emissions (${}^{15}$NGF method) amounted to 21 ± 3 kg N ha− 1, with 13 ± 2 kg N ha− 1 (7.5% of applied fertilizer N) originating from fertilizer. In comparison, the ${}^{15}$N mass balance approach overall indicated fertilizer-derived N${}_2$ emissions of 11%, equivalent to 18 ± 13 kg N ha− 1. Nitrous oxide (N${}_2$O) emissions were small (0.15 ± 0.01 kg N ha− 1 or 0.1% of fertilizer N), resulting in a large mean N${}_2$:(N${}_2$O + N${}_2$) ratio of 0.94 ± 0.06. ... mehrDue to the applied drip fertigation, ammonia emissions accounted for < 1% of fertilizer-N, while N leaching was negligible. The temporal variability of N${}_2$ emissions was well explained by the δ${}^{15}$N${}_2$ in soil air down to 50 cm depth. We conclude the ${}^{15}$NGF method provides realistic estimates of field N${}_2$ emissions and should be more widely used to better understand soil N${}_2$ losses. Moreover, combining soil air δ${}^{15}$N${}_2$ measurements with diffusion modeling might be an alternative approach for constraining soil N${}_2$ emissions.