Effects of nitrate and water content on acetylene inhibition technique bias when analysing soil denitrification rates under an aerobic atmosphere

The acetylene inhibition technique (AIT) is the most widely used indirect method of determining denitrification fluxes. Although AIT bias has long been recognised, the contributions of soil denitrification-related parameters to this bias have not yet been well quantified. Using a direct-N-2 method as a baseline, we determined the composition of AIT bias and quantified the effects of soil nitrate (NO3-) and water contents on AIT bias under an aerobic atmosphere. The results showed that the AIT severely underestimated the denitrification rate by 5-26 times and failed to capture the dynamic of denitrification with increasing soil water content. The bias increased with increases in the soil NO3- and water contents. Acetylene-catalysed nitric oxide (NO) oxidation accounted on average for 60% (ranging from 31 to 79%) of the bias. The remaining bias was caused by incomplete acetylene inhibition of nitrous oxide (N2O) reduction. Our results indicate that the AIT method is not recommended for denitrification determination under an aerobic atmosphere, especially for soils with high NO3- and water contents