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

Abstract Acetylene was found to effectively inhibit the reduction of N 2 O by anaerobic soils. With concentrations of C 2 H 2 above 0.1 atm, added NO 3 ‐ was quantitatively converted to N 2 O, and added N 2 O was reduced at an insignificant rate. Experiments with 13 N demonstrated that at low soil nitrate concentrations at least 0.1 atm C 2 H 2 was required for effective inhibition. Denitrification rates determined by 13 N and by C 2 H 2 inhibition methods correlated well, as did determinations of N 2 O/(N 2 + N 2 O). 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 O 2 on the indigenous denitrifying enzymes.