In-vitro method and model to estimate methane emissions from liquid manure management on pig and dairy farms in four countries

Methane (CH4) emissions from manure management on livestock farms are a key source of greenhouse gas emissions in some regions and for some production systems, and the opportunities for mitigation may be significant if emissions can be adequately documented. We investigated a method for estimating CH4 emissions from liquid manure (slurry) that is based on anaerobic incubation of slurry collected from commercial farms. Methane production rates were used to derive a parameter of the Arrhenius temperature response function, lnA', representing the CH4 production potential of the slurry at the time of sampling. Results were used for parameterization of an empirical model to estimate annual emissions with daily time steps, where CH4 emissions from individual sources (barns, outside storage tanks) can be calculated separately. A monitoring program was conducted in four countries, i.e., Denmark, Sweden, Germany and the Netherlands, during a 12-month period where slurry was sampled to represent barn and outside storage on finishing pig and dairy farms. Across the four countries, lnA' was higher in pig slurry compared to cattle slurry (p < 0.01), and higher in slurry from barns compared to outside storage (p < 0.01). In a separate evaluation of the incubation method, in-vitro CH4 production rates were comparable with in-situ emissions. The results indicate that lnA' in barns increases with slurry age, probably due to growth or adaptation of the methanogenic microbial community. Using lnA' values determined experimentally, empirical models with daily time steps were constructed for finishing pig and dairy farms and used for scenario analyses. Annual emissions from pig slurry were predicted to be 2.5 times higher than those from cattle slurry. Changing the frequency of slurry export from the barn on the model pig farm from 40 to 7 d intervals reduced total annual CH4 emissions by 46 %; this effect would be much less on cattle farms with natural ventilation. In a scenario with cattle slurry, the empirical model was compared with the current IPCC methodology. The seasonal dynamics were less pronounced, and annual CH4 emissions were lower than with the current methodology, which calls for further investigations. Country-specific models for individual animal categories and point sources could be a tool for assessing CH4 emissions and mitigation potentials at farm level.

Use of the range area in organic egg production systems: effect of climatic factors, flock size, age and artificial cover

(1) To evaluate the effect of climate, flock size, age and artificial cover on the use of range area, a study was conducted in 1994 to 1998, involving 5 farms with a total of 37 flocks of layers kept in commercial, free-range, organic systems. Flocks were visited regularly during the production period to record the number and distribution of hens on the range. (2) On average 9% of the flock used the range area, but with large variations both within and between flocks, and this was partly influenced by climatic factors. Range use was affected by temperature, wind, precipitation, season and age, and there was a tendency for reduced numbers of hens on the range with the time of day and increasing flock size. (3) Eight flocks (including houses and range areas) were divided into 8 paired units, and the range area of one unit in each of the flocks was provided with artificial cover. There were more hens on the range when artificial cover was present and the presence of cover attracted more hens away from the area immediately outside the hen house.

Comparative study of anchoring groups for molecular electronics: structure and conductance of Au-S-Au and Au-NH(2)-Au junctions

The electrical properties of single-molecule junctions, consisting of an organic molecule coupled to metal electrodes, are sensitive to the detailed atomic structure of the molecule-metal contact. This, in turn, is determined by the anchoring group linking the molecule to the metal. With the aim of identifying and comparing the intrinsic properties of two commonly used anchoring groups, namely thiol and amine groups, we have calculated the atomic structure and conductance traces of different Au-S-Au and Au-NH(2)-Au nanojunctions using density functional theory (DFT). Whereas NH(2) shows a strong structural selectivity towards atop-gold configurations, S shows large variability in its bonding geometries. As a result, the conductance of the Au-NH(2)-Au junction is less sensitive to the structure of the gold contacts than the Au-S-Au junction. These findings support recent experiments which show that amine-bonded molecules exhibit more well-defined conductance properties than do thiol-bonded molecules.

Evidence for a single hydrogen molecule connected by an atomic chain

Stable, single-molecule conducting-bridge configurations are typically identified from peak structures in a conductance histogram. In previous work on Pt with H2 at cryogenic temperatures it has been shown that a peak near 1G0 identifies a single-molecule Pt-H2-Pt bridge. The histogram shows an additional structure with lower conductance that has not been identified. Here, we show that it is likely due to a hydrogen decorated Pt chain in contact with the H2 molecular bridge.