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.

Abstract. Methane (CH 4 ) from ruminants contributes onethird of global agricultural greenhouse gas emissions. Eddy covariance (EC) technique has been extensively used at various flux sites to investigate carbon dioxide exchange of ecosystems. Since the development of fast CH 4 analyzers, the instrumentation at many flux sites has been amended for these gases. However, the application of EC over pastures is challenging due to the spatially and temporally uneven distribution of CH 4 point sources induced by the grazing animals. We applied EC measurements during one grazing season over a pasture with 20 dairy cows (mean milk yield: 22.7 kg d −1 ) managed in a rotational grazing system. Individual cow positions were recorded by GPS trackers to attribute fluxes to animal emissions using a footprint model. Methane fluxes with cows in the footprint were up to 2 orders of magnitude higher than ecosystem fluxes without cows. Mean cow emissions of 423 ± 24 g CH 4 head −1 d −1 (best estimate from this study) correspond well to animal respiration chamber measurements reported in the literature. However, a systematic effect of the distance between source and EC tower on cow emissions was found, which is attributed to the analytical footprint model used. We show that the EC method allows one to determine CH 4 emissions of cows on a pasture if the data evaluation is adjusted for this purpose and if some cow distribution information is available.

We compared (i) nitrous oxide (N 2 O) fluxes from a 9-month field experiment established on a temperate, newly sown, intensively managed meadow using automated chambers with fine time resolution, and (ii) fluxes measured at several occasions throughout the experiment under controlled laboratory conditions. Twenty tonnes dry matter ha −1 greenwaste biochar were added to three plots and compared with three control plots. Cumulated N 2 O field measurements revealed a reduction of 21.5% in the plots with biochar. The reductions for samples where the biochar was added at the beginning of the experiment in the field and samples which were collected each month and measured in the laboratory were in the same range (11.4-39.2%). Emission reductions from laboratory incubations when biochar was freshly mixed with soil in the laboratory were about twice as large (46.5-58.0%). Our results indicate provisionally that, at our site, biochar controls N 2 O emission through its capacity for reducing NO 3 − availability to denitrifiers, with the efficiency being related to the effectiveness of mixing of biochar in soil.

Abstract. Biochar, a carbon-rich, porous pyrolysis product of organic residues may positively affect plant yield and can, owing to its inherent stability, promote soil carbon sequestration when amended to agricultural soils. Another possible effect of biochar is the reduction in emissions of nitrous oxide (N 2 O). A number of laboratory incubations have shown significantly reduced N 2 O emissions from soil when mixed with biochar. Emission measurements under field conditions however are more scarce and show weaker or no reductions, or even increases in N 2 O emissions. One of the hypothesised mechanisms for reduced N 2 O emissions from soil is owing to the increase in soil pH following the application of alkaline biochar. To test the effect of biochar on N 2 O emissions in a temperate maize cropping system, we set up a field trial with a 20 t ha −1 biochar treatment, a limestone treatment adjusted to the same pH as the biochar treatment (pH 6.5), and a control treatment without any addition (pH 6.1). An automated static chamber system measured N 2 O emissions for each replicate plot (n = 3) every 3.6 h over the course of 8 months. The field was conventionally fertilised at a rate of 160 kg N ha −1 in three applications of 40, 80 and 40 kg N ha −1 as ammonium nitrate. Cumulative N 2 O emissions were 52 % smaller in the biochar compared to the control treatment. However, the effect of the treatments overall was not statistically significant (p = 0.27) because of the large variability in the data set. Limed soils emitted similar mean cumulative amounts of N 2 O as the control. There is no evidence that reduced N 2 O emissions with biochar relative to the control is solely caused by a higher soil pH.