A test of a field‐based ¹⁵ N –nitrous oxide pool dilution technique to measure gross N ₂ O production in soil

Soils are both a major source and sink of nitrous oxide ( N 2 O ), but the proportion of soil N 2 O production released to the atmosphere (termed the N 2 O yield) is poorly constrained due to the difficulty in measuring gross N 2 O production. The quantification of gross N 2 O fluxes would greatly improve our ability to predict N 2 O dynamics across the soil‐atmosphere interface. We report a new approach, the 15 N 2 O pool dilution technique, to measure rates of gross N 2 O production and consumption under laboratory and field conditions. In the laboratory, gross N 2 O production and consumption compared well between the 15 N 2 O pool dilution and acetylene inhibition methods whereas the 15 NO 3 − tracer method measured significantly higher rates. In the field, N 2 O emissions were not significantly affected by increasing chamber headspace concentrations up to 100 ppb 15 N 2 O . The pool dilution model estimates of 14 N 2 O and 15 N 2 O concentrations as well as net N 2 O fluxes fit observed data very well, suggesting that the technique yielded robust estimates of gross N 2 O production. Estimated gross N 2 O consumption rates were underestimated relative to rates calculated as the difference between gross and net N 2 O production rates, possibly due to heterogeneous and/or inadequate tracer diffusion to deeper layers in the soil profile. Gross N 2 O production rates were high, averaging 8.4 ± 3.2 mg N m −2 day −1 , and were most strongly correlated to mineral nitrogen concentrations and denitrifying enzyme activity ( R 2 = 0.73). Gross N 2 O production rates varied spatially, with the highest rates in soils with the best drainage and the highest mineral N availability. Estimated and calculated N 2 O consumption rates constrained the average N 2 O yield from 0.70 to 0.84. Our results demonstrate that the 15 N 2 O pool dilution technique can provide well‐constrained estimates of N 2 O yields and field rates of gross N 2 O production correlated to soil characteristics, improving our understanding of terrestrial N 2 O </jat