Using field-measured soil N2O fluxes and laboratory scale parameterization of N2O/(N2O+N2) ratios to quantify field-scale soil N2 emissions

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Soil dinitrogen (N2) emissions are a key nitrogen loss pathway of terrestrial ecosystems. However, the quantification of field N2 emissions from terrestrial ecosystems remains challenging, as sensitive field methods for measuring N2 fluxes are lacking. Here, we report a new approach to quantify field N2 emissions by (i) parameterizing the molar ratio of nitrous oxide (N2O) to N2O plus N2 emissions (RN2O) in the laboratory and (ii) measuring field N2O emissions and soil factors. Soil samples were taken from a maize field and incubated in the laboratory under simulated field conditions. Soil N2 and N2O emissions were determined using the gas-flow-soil-core method. The measurements revealed that the RN2O values were significantly higher (0.06–0.67) following urea fertilization and soil rewetting compared to those periods with no fertilization (0.03–0.08) (P < 0.01). A multivariate, nonlinear parameterization of RN2O against four easily measured soil factors (ammonia and nitrate concentrations, temperature, and moisture) (n = 20, r2 = 0.92, P < 0.001) was developed. The seasonal N2 emissions at the field scale were calculated by combining the laboratory-measured RN2O with the field-measured N2O emissions and the soil factors. Based on this approach, the cumulative emissions of N2 and N2+N2O for the maize season were 7.2 ± 2.8 and 9.6 ± 2.1 (standard error) kg N ha−1, respectively. Using a fixed RN2O, i.e., disregarding the temporal and spatial variability of RN2O, resulted in approximately 50%–70% lower estimates. Our study shows that a combination of field N2O and soil factors measurements and laboratory parameterization of RN2O allows field N2 emissions from croplands to be constrained. With additional measurements, including other soil properties, the development of a generalized parameterization of RN2O may become feasible. This approach would allow for a better understanding of gaseous N losses from agricultural ecosystems.