Characteristics of N-2 and N2O Fluxes from a Cultivated Black Soil: A Case Study through In Situ Measurement Using the N-15 Gas Flux Method

The magnitudes and source partitioning of soil dinitrogen (N-2) and nitrous oxide (N2O) emissions are not well documented, yet. To address both issues for black soil subject to a typical cool temperate climate, soil N2O and N-2 fluxes following the basal application event of an ammonium-based fertilizer (labeled by N-15) for maize were simultaneously measured in situ by using the N-15 gas flux ((15)NFG) method. During the two-month field experiment, the measured N-2 and N2O fluxes cumulated to 1.61 +/- 0.47 and 0.12 +/- 0.01 kg N ha(-1), respectively, showing N2O to N2O plus N-2 ratios (R-N2O) 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 N2O fluxes and the R-N2O values, respectively (p < 0.01). Moreover, the process(es) other than autotrophic nitrification and heterotrophic denitrification could be of substantial importance for the soil N2O 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-N2O. In addition, this study implicates that labeling a nitrogen substrate of nitrification while using the N-15 enrichment of N2O 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.