A new procedure (HMR) for soil-atmosphere trace-gas flux estimation with static chambers is presented. It classifies data series into three categories according to criteria based on the application of a particular nonlinear model and provides statistical data analyses for all categories. The two main categories are non-linear and linear concentration data, for which data are analysed by, respectively, the non-linear model and linear regression. The third category is represented by concentration data within the range of experimental error, or noise, from sites with no significant flux. Data in this category may be analysed by linear regression or simply classified as no flux. The particular non-linear model has been selected among alternatives because its exponential curvature generally fits non-linear static chamber concentration data well, and because it can be proven, mathematically, to be robust against horizontal gas transport through the soil or leaks in the chamber. The application of the HMR procedure is demonstrated on 244 data series of nitrous oxide accumulation over time. On average, 47% of these data were non-linear, with an average flux increase over linear regression of 52%. The classification and analysis of data with a small signal-to-noise ratio requires special attention, and it is demonstrated how diagnostic graphical plots may be used to select the appropriate data analysis. The HMR procedure has been implemented as a free add-on package for the free software R and is available for download through CRAN (http://www.r-project.org).

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Slurry acidification before storage is known to reduce NH(3) emissions, but recent observations have indicated that CH(4) emissions are also reduced. We investigated the evolution of CH(4) from fresh and aged cattle slurry during 3 mo of storage as influenced by pH adjustment to 5.5 with sulfuric acid. In a third storage experiment, cattle slurry acidified with commercial equipment on two farms was incubated. In the manipulation experiments, effects of acid and sulfate were distinguished by adding hydrochloric acid and potassium sulfate separately or in combination, rather than sulfuric acid. In one experiment sulfur was also added to slurry as the amino acid methionine in separate treatments. In each treatment 20-kg portions of slurry (n = 4) were stored for 95 d. All samples were subsampled nine to 10 times for determination of NH(3) and CH(4) evolution rates using a 2-L flow-through system. In all experiments, the pH of acidified cattle slurry increased gradually to between 6.5 and 7. Acidification of slurry reduced the evolution of CH(4) by 67 to 87%. The greatest reduction was observed with aged cattle slurry, which had a much higher potential for CH(4) production than fresh slurry. Sulfate and methionine amendment to cattle slurry without pH adjustment also significantly inhibited methanogenesis, probably as a result of sulfide production. The study suggests that complex microbial interactions involving sulfur transformations and pH determine the potential for CH(4) emission during storage of cattle slurry, and that slurry acidification may be a cost-effective greenhouse gas mitigation option.

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Animal manure contributes about 40% of the total methane (CH4) and 20% of the total nitrous oxide (N2O) emissions in Denmark. We measured the CH4 and N2O emissions from stored cattle slurry and fermented slurry during fall 1996 and summer 1997 and evaluated the effect of surface covers consisting of straw, floating leca pebbles, or a natural surface crust on the patterns of these emissions. No emission of N2O was measured during periods with more rain than evaporation from the slurry stores and no emission was measured from uncovered slurry, irrespective of climatic conditions. During the summer storage with drying conditions, N2O emissions of up to 25 mg N m−2 h−1 were recorded from slurry with surface covers. Total N2O emission was highest from digested slurry. The emission of CH4 from stored fermented slurry and cattle slurry varied between <0.01 and 1.4 or 0.7 g CH4—C m−3 h−1, respectively. The log‐transformed emissions were linearly related to the inverse temperature. Emission of CH4 was reduced, on average, by 38% with surface covers. The reduction was probably due to CH4 oxidation in the surface covers or in the interface between the cover and liquid in the store. Fermentation did not reduce CH4 emissions during storage of the slurry.

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Disturbances typically associated with the study of soil microbial communities, i.e., sieving, storage, and subsequent incubation at elevated temperatures, were investigated with phospholipid fatty acid (PLFA) analyses. Treatment effects were quantified by statistical analyses of the mole percentage distribution of the individual fatty acids. Changes in the concentrations of individual fatty acids over a 7-week storage period at 4.5°C were generally not statistically significant. Sieving effects (mesh size, 4 or 2 mm) on CO2 evolution and the PLFA profile were monitored over 3 weeks; the physical disturbance had only minor effects, although some damage to fungal hyphae by the first sieving (<4 mm) was suggested by a decrease in the signature fatty acid 18:2 w6c. Temperature effects were investigated by incubating soil for up to 3 weeks at 4.5, 10, or 25°C. Principal component analyses demonstrated a significant shift in the PLFA composition at 25°C over the first 2 weeks, while changes at the other two temperatures were minor. Several of the changes observed at 25°C could be explained with reference to mechanisms of temperature adaptation or as a response to conditions of stress, including a decrease in the degree of unsaturation, an increased production of cyclopropyl fatty acids, and increased ratios of the branched-chain fatty acids iso-15:0 and iso-17:0 over anteiso-15:0 and anteiso-17:0, respectively. A decrease in the total amount of PLFA was also indicated.