Søren O. Petersen

O2 uptake, C metabolism and denitrification associated with manure hot-spots

O2, C and N metabolism in organic hot-spots (sites where the intensity of microbial respiration creates a high O2 demand) was studied with fresh or anaerobically digested liquid cattle manure as substrates. A gel-stabilized mixture of soil and manure, 16 mm thick, was sandwiched between layers of soil with a water content adjusted to field capacity, and incubated at 15°C for up to 3 wk. When fresh manure was used, O2 microprofiles demonstrated an O2 penetration into the hot-spot of < 1 mm after 1–3 d, increasing to ca. 2 mm after 3 wk. During this time, O2 uptake rates decreased from 100–150 to ca. 50 nmol O2 cm−2 h−1. With digested manure, the lower C availability in this substrate resulted in O2 penetration depths of 3–4 mm and O2 uptake rates of <30 nmol O2 cm−2 h−1 throughout the 3 wk. Maximum denitrification rates were also consistently lower with digested manure (4 nmol N cm−2 h−1) than with fresh manure (18 nmol N cm−2 h−1). A numerical model of NO3− transport indicated that denitrification was limited by the availability of NO3− during the first week in the fresh manure treatment, and that the soil was the only significant source of NO3− during at least 3 d; after this time nitrification at the soil-manure interface became increasingly important. After the first week with fresh manure, and throughout the experiment with digested manure, C availability apparently regulated denitrification.

Effects of Cattle Slurry Acidification on Ammonia and Methane Evolution during Storage

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.

Reorganization of membrane lipids during fast and slow cold hardening in Drosophila melanogaster

Abstract Rapid cold hardening is a naturally occurring phenomenon in insects that is thought to be responsible for increased cold tolerance during diurnal variations in temperature. The underlying physiological mechanisms are still not fully resolved but, in Drosophila melanogaster (Meigen 1830), rapid cold hardening is accompanied by specific changes in the membrane lipid composition. To further understand the link between rapid cold hardening and adjustments in the membrane lipid composition, the present study investigates how different rates of cooling affect thermotolerance and the composition of phospholipid fatty acids. Female Drosophila are cooled gradually from 25 to 0 °C at 0.01, 0.05, 0.1 or 0.5 °C min−1, respectively, and, subsequently, phospholipid fatty acid composition and survival after a 1‐h cold shock at −5 °C is measured. The rapid cold hardening treatments all influence cold tolerance differently so that short and intermediate rapid cold hardening treatments (0.05, 0.1 or 0.5 °C min−1 cooling rates) increase cold shock survival, whereas the slow cooling treatment (0.01 °C min−1) decreases survival relative to an untreated control. The intermediate rapid cold hardening treatments (0.05 or 0.1 °C min−1) induce a similar type of response characterized by an increase in the molar percentage of linoleic acid, 18:2(n‐6), at the expense of 16:0 and 18:1(n‐9), which leads to an increase in the degree of unsaturation. The slowest cooling treatment (0.01 °C min−1) results in a large increase in cis‐16:1(n‐7) and significant reductions in the saturated phospholipid fatty acids 16:0, 18:0 and the unsaturated 16:1(n‐9) and 18:2(n‐6) fatty acids. These changes cause a slight decrease in the average length of the phospholipid fatty acids and an increase in the overall ratio of unsaturated vs. saturated fatty acids. These findings demonstrate that the rate of cooling is important for both the reorganization of membrane lipids, and for the degree of acquired cold tolerance during rapid cold hardening, and they suggest an important role for rapid cold hardening during diurnal rather than seasonal temperature changes.

Ester-linked polar lipid fatty acid profiles of soil microbial communities: a comparison of extraction methods and evaluation of interference from humic acids

Abstract Analyses of polar lipid fatty acids isolated from soil are frequently used for characterization of microbial communities, and any interference from fatty acids derived from dead organic material is assumed to be negligible. We studied the initial extraction of lipid material from eight different soils and from purified humic acids using four different combinations of solvent (chloroform or dichloromethane), methanol and buffer (potassium phosphate, pH 7.4 or sodium citrate, pH 4). The quantitative yields of polar lipid fatty acids (PLFA) and PLFA composition of soils and humic acids were compared with absorbance spectra (200–850 nm) of lipid extracts for evaluation of extraction efficiency and potential interference. Chloroform + citrate buffer generally gave the highest, and dichloromethane + phosphate buffer the lowest PLFA yields, and it was estimated that

Developments in greenhouse gas emissions and net energy use in Danish agriculture – How to achieve substantial CO2 reductions?

Greenhouse gas (GHG) emissions from agriculture are a significant contributor to total Danish emissions. Consequently, much effort is currently given to the exploration of potential strategies to reduce agricultural emissions. This paper presents results from a study estimating agricultural GHG emissions in the form of methane, nitrous oxide and carbon dioxide (including carbon sources and sinks, and the impact of energy consumption/bioenergy production) from Danish agriculture in the years 1990-2010. An analysis of possible measures to reduce the GHG emissions indicated that a 50-70% reduction of agricultural emissions by 2050 relative to 1990 is achievable, including mitigation measures in relation to the handling of manure and fertilisers, optimization of animal feeding, cropping practices, and land use changes with more organic farming, afforestation and energy crops. In addition, the bioenergy production may be increased significantly without reducing the food production, whereby Danish agriculture could achieve a positive energy balance.

Phospholipid fatty acid profiles and C availability in wet-stable macro-aggregates from conventionally and organically farmed soils

Abstract Whole soil samples and four aggregate size classes (2–8 mm, 1–2 mm, 0.5–1 mm and 0.25–0.5 mm) from organically or conventionally farmed sandy loam soils were compared with respect to texture, C content and C mineralization potential, microbial biomass C and phospholipid fatty acid (PLFA) composition. The PLFA concentration of organically farmed soils (44–56 nmol g−1 dry wt.) was larger than in soils under conventional management (28–32 nmol g−1 dry wt.) and correlated with biomass C. Principal component analyses demonstrated only minor differences between whole soil samples with respect to PLFA composition. The texture of soil fractions obtained by wet-sieving deviated strongly from the texture of whole soil, paticularly in the 0.25–0.5 mm and 0.5–1 mm size classes. These fractions also appeared to include some non-aggregate particulate organic matter. The C mineralization during a 13-week incubation increased significantly with decreasing aggregate size class in four of the six soils. Biomass C declined during the incubation, and the decline in most cases could account for the C mineralized. No consistent differences were observed between conventionally and organically farmed soils or between aggregate size classes with respect to taxonomic composition or physiological status of the microbial community.

Short-term nitrous oxide emissions from pasture soil as influenced by urea level and soil nitrate

Nitrogen excreted by cattle during grazing is a significant source of atmospheric nitrous oxide (N2O). The regulation of N2O emissions is not well understood, but may vary with urine composition and soil conditions. This laboratory study was undertaken to describe short-term effects on N2O emissions and soil conditions, including microbial dynamics, of urea amendment at two different rates (22 and 43 g N m−2). The lower urea concentration was also combined with an elevated soil NO3− concentration. Urea solutions labelled with 25 atom%15N were added to the surface of repacked pasture soil cores and incubated for 1, 3, 6 or 9 days under constant conditions (60% WFPS, 14 °C). Soil inorganic N (NH4+, NO2− and NO3−), pH, electrical conductivity and dissolved organic C were quantified. Microbial dynamics were followed by measurements of CO2 evolution, by analyses of membrane lipid (PLFA) composition, and by measurement of potential ammonium oxidation and denitrifying enzyme activity. The total recovery of15N averaged 84%. Conversion of urea-N to NO3− was evident, but nitrification was delayed at the highest urea concentration and was accompanied by an accumulation of NO2−. Nitrous oxide emissions were also delayed at the highest urea amendment level, but accelerated towards the end of the study. The pH interacted with NH4+ to produce inhibitory concentrations of NH3(aq) at the highest urea concentration, and there was evidence for transient negative effects of urea amendment on both nitrifying and denitrifying bacteria in this treatment. However, PLFA dynamics indicated that initial inhibitory effects were replaced by increased microbial activity and net growth. It is concluded that urea-N level has qualitative, as well as quantitative effects on soil N transformations in urine patches.

Dynamics of a pasture soil microbial community after deposition of cattle urine amended with [13C]urea.

ABSTRACT Within grazed pastures, urine patches are hot spots of nitrogen turnover, since dietary N surpluses are excreted mainly as urea in the urine. This short-term experiment investigated 13C uptake in microbial lipids after simulated deposition of cattle urine at 10.0 and 17.1 g of urea C m−2. Confined field plots without or with cattle urine amendment were sampled after 4 and 14 days, and soil from 0- to 5-cm and 10- to 20-cm depths was analyzed for content and composition of phospholipid fatty acids (PLFAs) and for the distribution of urea-derived 13C among individual PLFAs. Carbon dioxide emissions were quantified, and the contributions derived from urea were assessed. Initial changes in PLFA composition were greater at the lower level of urea, as revealed by a principal-component analysis. At the higher urea level, osmotic stress was indicated by the dynamics of cyclopropane fatty acids and branched-chain fatty acids. Incorporation of 13C from [13C]urea was low but significant, and the largest amounts of urea-derived C were found in common fatty acids (i.e., 16:0, 16:1ω7c, and 18:1ω7) that would be consistent with growth of typical NH4+-oxidizing (Nitrosomonas) and NO2−-oxidizing (Nitrobacter) bacteria. Surprisingly, a 20‰ depletion of 13C in the cyclopropane fatty acid cy17:0 was observed after 4 days, which was replaced by a 10 to 20‰ depletion of that in cy19:0 after 14 days. Possible reasons for this pattern are discussed. Autotrophic nitrifiers could not be implicated in urea hydrolysis to any large extent, but PLFA dynamics and the incorporation of urea-derived 13C in PLFAs indicated a response of nitrifiers which differed between the two urea concentrations.

Emissions of Sulfur-Containing Odorants, Ammonia, and Methane from Pig Slurry: Effects of Dietary Methionine and Benzoic Acid

Supplementation of benzoic acid to pig diets reduces the pH of urine and may thereby affect emissions of ammonia and other gases from slurry, including sulfur-containing compounds that are expected to play a role in odor emission. Over a period of 112 d, we investigated hydrogen sulfide (H(2)S), methanethiol (MT), dimethyl sulfide (DMS), dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS), as well as ammonia and methane emissions from stored pig slurry. The slurry was derived from a feeding experiment with four pig diets in a factorial design with 2% (w/w) benzoic acid and 1% (w/w) methionine supplementation as treatments. Benzoic acid reduced slurry pH by 1 to 1.5 units and ammonia emissions by 60 to 70% for up to 2 mo of storage, and a considerable, but transitory reduction of methane emissions was also observed after 4 to 5 wk. All five volatile sulfur (S) compounds were identified in gas emitted from the slurry of the control treatment, which came from pigs fed according to Danish recommendations for amino acids and minerals. The emission patterns of volatile S compounds suggested an intense cycling between pools of organic S in the slurries, with urinary sulfate as the main source. Diet supplementation with methionine significantly increased all S emissions. Diet supplementation with benzoic acid reduced emissions of H(2)S and DMTS compared with the control slurry and moderately increased the concentrations of MT. Sulfur gas emissions were influenced by a strong interaction between methionine and benzoic acid treatments, which caused a significant increase in emissions of especially MT, but also of DMDS. In conclusion, addition of 2% benzoic acid to pig diets effectively reduced ammonia volatilization, but interactions with dietary S may increase odor problems.

Manure management for greenhouse gas mitigation

Ongoing intensification and specialisation of livestock production lead to increasing volumes of manure to be managed, which are a source of the greenhouse gases (GHGs) methane (CH4) and nitrous oxide (N2O). Net emissions of CH4 and N2O result from a multitude of microbial activities in the manure environment. Their relative importance depends not only on manure composition and local management practices with respect to treatment, storage and field application, but also on ambient climatic conditions. The diversity of livestock production systems, and their associated manure management, is discussed on the basis of four regional cases (Sub-Saharan Africa, Southeast Asia, China and Europe) with increasing levels of intensification and priorities with respect to nutrient management and environmental regulation. GHG mitigation options for production systems based on solid and liquid manure management are then presented, and potentials for positive and negative interactions between pollutants, and between management practices, are discussed. The diversity of manure properties and environmental conditions necessitate a modelling approach for improving estimates of GHG emissions, and for predicting effects of management changes for GHG mitigation, and requirements for such a model are discussed. Finally, we briefly discuss drivers for, and barriers against, introduction of GHG mitigation measures for livestock production. There is no conflict between efforts to improve food and feed production, and efforts to reduce GHG emissions from manure management. Growth in livestock populations are projected to occur mainly in intensive production systems where, for this and other reasons, the largest potentials for GHG mitigation may be found.