Characteristics of N2 and N2O Fluxes from a Cultivated Black Soil: A Case Study through In Situ Measurement Using the 15N Gas Flux Method

Abstract

The magnitudes and source partitioning of soil dinitrogen (N2) 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 N2 fluxes following the basal application event of an ammonium-based fertilizer (labeled by 15N) for maize were simultaneously measured in situ by using the 15N gas flux (15NFG) method. During the two-month field experiment, the measured N2 and N2O fluxes cumulated to 1.61 ± 0.47 and 0.12 ± 0.01 kg N ha−1, respectively, showing N2O to N2O plus N2 ratios (RN2O) of 0.02–0.31 (0.15 on average). Temperature was identified as a key factor regulating the total soil N2 fluxes (r2 = 0.27, p < 0.01), despite the N2 fluxes originated from nitrate denitrification related to dissolved organic carbon concentrations (r2 = 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 RN2O 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 N2 emissions from black soil and the possible site- and/or time specificity of a soil factors-based parametrization of RN2O. In addition, this study implicates that labeling a nitrogen substrate of nitrification while using the 15N enrichment of N2O is necessary to more accurately quantify total soil N2 fluxes in situ by using the 15NFG approach even though further confirmation in future studies is still needed.