The Acetylene Inhibition Method for Short‐term Measurement of Soil Denitrification and its Evaluation Using Nitrogen‐13

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Abstract
Acetylene was found to effectively inhibit the reduction of N2O by anaerobic soils. With concentrations of C2H2 above 0.1 atm, added NO3‐ was quantitatively converted to N2O, and added N2O was reduced at an insignificant rate. Experiments with 13N demonstrated that at low soil nitrate concentrations at least 0.1 atm C2H2 was required for effective inhibition. Denitrification rates determined by 13N and by C2H2 inhibition methods correlated well, as did determinations of N2O/(N2 + N2O). The methods also revealed that an acceleration in denitrification rate occurred within a few hours after soil was exposed to anaerobic conditions. The acetylene method was generally used to measure denitrification rates in soils incubated as anaerobic slurries, but was also used to determine rates for field moist aggregrates incubated anaerobically and aerobically. When assayed as anaerobic slurries, initial denitrification rates ranged from 0.1 to 0.7 nmoles N gas · soil−1 · min−1 for the mineral soils examined. The denitrification rate in aerobic aggregrates was approximately 1,000 times less, showing the strong inhibitory effect of O2 on the indigenous denitrifying enzymes.
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