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

Soil dinitrogen (N-2) emissions are a key nitrogen loss pathway of terrestrial ecosystems. However, the quantification of field N-2 emissions from terrestrial ecosystems remains challenging, as sensitive field methods for measuring N-2 fluxes are lacking. Here, we report a new approach to quantify field N-2 emissions by (i) param-eterizing the molar ratio of nitrous oxide (N2O) to N2O plus N-2 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 N-2 and N2O emissions were determined using the gas-flow-soilcore 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 RN z o against four easily measured soil factors (ammonia and nitrate concentrations, temperature, and moisture) (n = 20, r(2) = 0.92, P < 0.001) was developed. The seasonal N-2 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 N-2 and N-2 +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 N-2 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.