Particulate organic matter predicts spatial variation in denitrification potential at the field scale

High spatiotemporal variability in soil nitrous oxide (N₂O) fluxes challenges quantification and prediction of emissions to evaluate the climate change mitigation outcomes of sustainable agricultural practices. Triggers for large, short-lived N₂O emission pulses, such as rainfall and fertilization, alter soil oxygen (O₂) and nitrate (NO₃^–) availability to favor N₂O production via denitrification. However, the organic C (OC) needed to fuel denitrification may exhibit subfield variation that constrains the potential for high denitrification rates to occur, leading to spatial variation in N₂O hot moments. We tested the hypothesis that the particulate organic matter (POM) fraction of soil organic matter (SOM) controls subfield variation in denitrification potential by regulating availability of dissolved organic C (DOC), the form of OC used by denitrifiers. Among 38 soil samples collected across a maize field in central Illinois, USA, we found that potential denitrification rate was best predicted by POM C concentration (R² = 0.35). Using multiple linear regression analysis that included other soil properties as explanatory variables, we found that POM C fraction of bulk soil (mg POM C/g SOC) was the most important predictor based on regression coefficient size (P < 0.01). Our results, which provide support for our hypothesis, suggest that consideration of the link between C and N cycling may be a key to predicting spatiotemporal variation in soil N₂O emissions when denitrification is the dominant N₂O source process.