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

Abstract

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. Due 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.

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