Effectiveness of acetylene inhibition of N2O reduction for measuring denitrification in soils of varying wetness

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Abstract
The use of acetylene (C2H2) in the inhibition of N2O to N2 is widely used for measuring denitrification. The objective of this study was to determine the effectiveness of acetylene inhibition of N2O reduction for short‐term and prolonged incubation studies in soils of varying water saturation, and to find out the possible reasons for lower N2O recovery in continuously sealed incubations. Two experiments carried out in the laboratory reconfirmed that acetylene was very effective in inhibiting the reduction of N2O in denitrification even for the prolonged incubation period (up to 96 h) under moist to saturated soil water contents. With 90 and 120% water‐filled pore space (WFPS), the accumulated N2O in containers kept sealed throughout the study period, was 28 to 41% less than total headspace N2O produced in containers that were opened, flushed and fresh C2H2 added every 24 h. Interpretation of our results suggest the lower N2O amount recovered from continuously sealed containers at high WFPS, as compared to short‐term incubations (flushed containers), resulted primarily from delayed N2O release from soil and not greater N2O dissolved in soil solution, lower rates of denitrification, or decomposition/loss of C2H2 during prolonged incubation. Reduction of N2O diffusion from soil cores showed direct relationship with head space concentration‐of N2O and soil WFPS. From these results it is concluded that to obtain quantitative recovery of N2O produced via denitrification, especially from soil with high WFPS soil cores should be vigorously shaken before head‐space N2O analysis.