Particulate organic matter drives 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 controls subfield variation in denitrification potential by regulating availability of dissolved organic C (DOC), the form of OC used by denitrifiers. Among 20 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-1 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.