Measuring denitrification and the N$_{2}$O:(N$_{2}$O + N$_{2}$) emission ratio from terrestrial soils

Denitrification, a significant pathway of reactive N-loss from terrestrial soils, impacts on agricultural production and the environment. Net production and emission of the denitrification product nitrous oxide (N$_{2}$O) is readily quantifiable, but measuring denitrification's final product, dinitrogen (N$_{2}$), against a high atmospheric background remains challenging. This review examines methods quantifying both N$_{2}$ and N$_{2}$O emissions, based on inhibitors, helium/O$_{2}$ atmosphere exchange, and isotopes. These methods are evaluated regarding their capability to account for pathways of N$_{2}$ and N$_{2}$O production and we suggest quality parameters for measuring denitrification from controlled environments to the field scale. Our appraisal shows that method combinations, together with real-time monitoring and soil-gas diffusivity modelling, have the potential to significantly improve our quantitative understanding for denitrification from upland soils. Requirements for instrumentation and experimental setups however highlight the need to develop more mobile and easily accessible field methods to constrain denitrification from terrestrial soils across scales.