Characteristics of N 2 and N 2 O Fluxes from a Cultivated Black Soil: A Case Study through In Situ Measurement Using the 15 N Gas Flux Method

The magnitudes and source partitioning of soil dinitrogen (N 2 ) and nitrous oxide (N 2 O) emissions are not well documented, yet. To address both issues for black soil subject to a typical cool temperate climate, soil N 2 O and N 2 fluxes following the basal application event of an ammonium-based fertilizer (labeled by 15 N) for maize were simultaneously measured in situ by using the 15 N gas flux ( 15 NFG) method. During the two-month field experiment, the measured N 2 and N 2 O fluxes cumulated to 1.61 ± 0.47 and 0.12 ± 0.01 kg N ha −1 , respectively, showing N 2 O to N 2 O plus N 2 ratios ( R N 2 O ) of 0.02–0.31 (0.15 on average). Temperature was identified as a key factor regulating the total soil N 2 fluxes ( r 2 = 0.27, p < 0.01), despite the N 2 fluxes originated from nitrate denitrification related to dissolved organic carbon concentrations ( r 2 = 0.39, p < 0.01). Differently, both temperature and soil moisture jointly accounted for 85% and 74% of the variances in the N 2 O fluxes and the R N 2 O values, respectively ( p < 0.01). Moreover, the process(es) other than autotrophic nitrification and heterotrophic denitrification could be of substantial importance for the soil N 2 O emissions. Our findings emphasized the importance of temperature in regulating N 2 emissions from black soil and the possible site- and/or time specificity of a soil factors-based parametrization of R N 2 O . In addition, this study implicates that labeling a nitrogen substrate of nitrification while using the 15 N enrichment of N 2 O is necessary to more accurately quantify total soil N 2 fluxes in situ by using the 15 NFG approach even though further confirmation in future studies is still needed.