Theoretical and practical limitations of the acetylene inhibition technique to determine total denitrification losses

Abstract

Abstract. The loss of N 2 from intensively managed agroecosystems is an important part of the N budget. Flux monitoring of N 2 emissions at the field scale, e.g., by eddy correlation or aerodynamic gradient method, is impossible due to the large atmospheric N 2 background (78 %). The acetylene (C 2 H 2 ) inhibition technique (AIT) is a rather simple and frequently used, albeit imperfect, method to determine N 2 losses from intact soil cores. In principle, AIT allows an estimation of total denitrification at high temporal resolution and on small spatial scales, with limited workload and costs involved. To investigate its potential and limitations, a laboratory system with two different detection systems (photoacoustic IR spectroscopy and gas chromatography) is presented, which allowed simultaneous measurements of up to 7 intact soil cores in air-tight glass tubes in a temperature controlled cabinet (adjusted to field conditions) with automated C 2 H 2 injection.A survey of total denitrification losses (N 2 + N 2 O) over 1.5 yr in soil cores from an intensively managed, cut grassland system in central Switzerland supports previous reports on severe limitations of the AIT, which precluded reliable estimates of total denitrification losses. Further, the unavoidable sampling and transfer of soil samples to the laboratory causes unpredictable deviations from the denitrification activity in the field.

Advances in understanding, models and parameterizations of biosphere-atmosphere ammonia exchange

“…Whether nitrification significantly reduces NH 3 emission factors depends on nitrification rates, which have ] was roughly a factor of 50 higher than in the study by Felber et al (2012). Such variability highlights the need to give nitrification proper consideration in models of NH 3 volatilisation.…”

Topography and land use effects on spatial variability of soil denitrification and related soil properties in riparian wetlands

“…The acetylene block technique is based on the ability of acetylene to inhibit the reduction of N 2 O to N 2 during denitrification. Although the acetylene block technique has a number of limitations (Yu et al, 2010;Felber et al, 2012;Qin et al, 2012), it is still amenable to large-scale comparisons of soil denitrification, especially for systems with moderate or high NO 3 − concentrations (Groffman et al, 2006). For potential denitrification rate assays, 50 g of homogenised fresh soils from each sampling site were weighed into a 250-mL serum bottle with 30 mL of incubation solution (final concentrations: 0.1 g/L KNO 3 , 0.18 g/L glucose and 1 g/L chloramphenicol).…”

N<sub>2</sub>O, NO, N<sub>2</sub> and CO<sub>2</sub> emissions from tropical savanna and grassland of northern Australia: an incubation experiment with intact soil cores

“…This is, in part, due to the reluctantly accepted, but currently well-proven fact, that the previously widely used acetylene-inhibition technique fails to accurately quantify N 2 loss from soil (e.g., Felber et al, 2012).…”

“…In addition to these natural and semi-natural landscapes, farmers have introduced improved pastures in northern Australia since the 1880s to increase productivity and their area expanded by approximately 2500 km −2 yr −1 during the 1980s (Lonsdale, 1994). Savanna systems experience pronounced intra-annual variability of rainfall (dry season conditions from 2 to 9 months) in addition to substantial inter-annual climatic fluctuations (Frost et al, 1986). In the tropical savanna zone of Australia the wet season is controlled by the Asian monsoon and occurs from October to March.…”