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

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 headspace 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.