Evaluation of the acetylene‐inhibition technique for the measurement of denitrification in grassland soils

Abstract

AbstractThe acetylene inhibition technique has been evaluated for its suitability for routine field measurements of denitrification in two soils under grass. Acetylene was introduced into the soil air by radial diffusion from probes inserted vertically into the soil and, using a soil cover, total denitrification was determined as the loss of nitrous oxide (N2O) from the acetylene‐treated soil. Acetylene concentrations of 0.1–1.0% (v/v), which are effective in inhibiting the reduction of N2O, were established within 1–2 h of commencing the supply of acetylene to soil at field capacity; the N2O flux equilibrated within the same period. Treatment and equilibration times were longer after rainfall on to a soil at field capacity and shorter in spring, summer and autumn when soil water content was less than field capacity. Spatial variability in N2O flux from acetylene‐treated soil was generally ±25% and was probably associated with variability in air‐filled pore spaces in the soil. Repeated treatments, as required in routine measurements of denitrification, did not affect the distribution of soil inorganic N between NH4+ and NO3‐ which suggests that concurrent inhibition of nitrification by acetylene was not a significant constraint in the field application of the technique. The efficiency with which acetylene inhibits the reduction of N2O was not affected by repeated treatments of soil nor was there any evidence for acetylene decomposition. Repeated treatments did not affect dry matter yield or mineral contents of herbage. The findings of this study suggest that the acetylene‐inhibition technique may be applied to routine measurements of denitrification in both small and large plot studies of the fate of fertilizer N.