Abstract
Abstract. The loss of N2 from intensively managed agro-ecosystems is an important part of the N budget. Flux monitoring of N2 emissions at the field scale, e.g., by eddy correlation or aerodynamic gradient method, is impossible due to the large atmospheric N2 background (78%). The acetylene (C2H2) inhibition technique (AIT) is a rather simple and frequently used, albeit imperfect, method to determine N2 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 C2H2 injection. A survey of total denitrification losses (N2 + N2O) 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.
Highlights
Nitrogen (N) is an essential nutrient for ecosystem functioning and food production in the world
Using a gas chromatography (GC) allowed the determination of small background fluxes, which occur most of the time, the problem of leakage could not be solved by changing the trace gas detection device
The size of the soil cores was a compromise between the following aspects: (1) the samples, measured in the laboratory, should be as close as possible to field conditions, (2) the C2H2 should penetrate the sample and reliably reach the active denitrification micro-sites by diffusion, and (3) the produced N2O should escape into the headspace as soon as it is produced in the sample
Summary
Nitrogen (N) is an essential nutrient for ecosystem functioning and food production in the world. The increased demand for food and energy production on a global scale has altered the nitrogen cycle by introducing ever greater quantities of reactive nitrogen (Nr) in the environment. The plant usable N is in form of nitrate (NO−3 ) , ammonium (NH+4 ) and possibly monomeric organic N (Schimel and Bennett, 2004; Nasholm et al, 2009). In an intensively fertilized mown grassland system, the N uptake by the plant is largely dominated by the uptake of NO−3 and to a lesser extent of NH+4. On a global scale Galloway and Cowling (2002) indicated that only about 31 % of produced N fertiliser shows up in harvested biomass
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