2,471 research outputs found

    Indicator systems - resource use in organic systems

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    A balanced use of resources within organic farming systems is required to maintain sustainable systems. Hence, it is essential to have tools that can assess the use of resources within the farming system and their impact on the environment. The range of tools that have been developed include those assessing local farm-scale issues together with those that assess impacts at the global scale. At the global scale assessments are usually made on the basis of a unit of product whereas at the local scale assessments can also be made on an area basis. In addition, the tools also assess a variety of issues, e.g. biodiversity, pollution potential, energy and water use. The level of detail required for the different assessment tools differs substantially; nevertheless it is essential that the indicator systems developed are based on sound knowledge, are acceptable to the farmers and can guide their future actions

    The Prediction of Biological Nitrogen Fixation

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    In organic farming systems, biological nitrogen (N) fixation is crucial for short-term productivity and long-term sustainability. However, the estimation of biological N fixation is fraught with difficulties, and many equations attempt to estimate the process. As part of an organic research programme, biological N fixation was measured by the 15N dilution technique in the ley phases of 2 experimental organic ley-arable rotations at 2 sites, between 1997 and 2000. Hence, N fixation has been determined on N partitioned to above-ground biomass. The measured values have been compared with N fixation estimates calculated from the equations proposed by Korsaeth & Eltun (2000) and Hogh-Jensen et al. (2004)

    Internal Friction of Amorphous Silicon in a Magnetic Field

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    The internal friction of e-beam amorphous silicon was measured in a magnetic field between 0 and 6 T, from 1.5-20 K, and was found to be independent of the field to better than 8%. It is concluded that the low energy excitations observed in this experiment are predominantly atomic in nature.Comment: 4 pages, 4 figures, REVTe

    Elastic response of [111]-tunneling impurities

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    We study the dynamic response of a [111] quantum impurity, such as lithium or cyanide in alkali halides, with respect to an external field coupling to the elastic quadrupole moment. Because of the particular level structure of a eight-state system on a cubic site, the elastic response function shows a biexponential relaxation feature and a van Vleck type contribution with a resonance frequency that is twice the tunnel frequency Δ/\Delta/\hbar. This basically differs from the dielectric response that does not show relaxation. Moreover, we show that the elastic response of a [111] impurity cannot be reduced to that of a two-level system. In the experimental part, we report on recent sound velocity and internal friction measurements on KCl doped with cyanide at various concentrations. At low doping (45 ppm) we find the dynamics of a single [111] impurity, whereas at higher concentrations (4700 ppm) the elastic response rather indicates strongly correlated defects. Our theoretical model provides a good description of the temperature dependence of δv/v\delta v/v and Q1Q^{-1} at low doping, in particular the relaxation peaks, the absolute values of the amplitude, and the resonant contributions. From our fits we obtain the value of the elastic deformation potential γt=0.192\gamma_t=0.192 eV.Comment: 19 pages, 5 figure

    Quantifying N2O emissions from intensive grassland production: the role of synthetic fertilizer type, application rate, timing and nitrification inhibitors

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    SUMMARYIncreasing recognition of the extent to which nitrous oxide (N2O) contributes to climate change has resulted in greater demand to improve quantification of N2O emissions, identify emission sources and suggest mitigation options. Agriculture is by far the largest source and grasslands, occupying c. 0·22 of European agricultural land, are a major land-use within this sector. The application of mineral fertilizers to optimize pasture yields is a major source of N2O and with increasing pressure to increase agricultural productivity, options to quantify and reduce emissions whilst maintaining sufficient grassland for a given intensity of production are required. Identification of the source and extent of emissions will help to improve reporting in national inventories, with the most common approach using the IPCC emission factor (EF) default, where 0·01 of added nitrogen fertilizer is assumed to be emitted directly as N2O. The current experiment aimed to establish the suitability of applying this EF to fertilized Scottish grasslands and to identify variation in the EF depending on the application rate of ammonium nitrate (AN). Mitigation options to reduce N2O emissions were also investigated, including the use of urea fertilizer in place of AN, addition of a nitrification inhibitor dicyandiamide (DCD) and application of AN in smaller, more frequent doses. Nitrous oxide emissions were measured from a cut grassland in south-west Scotland from March 2011 to March 2012. Grass yield was also measured to establish the impact of mitigation options on grass production, along with soil and environmental variables to improve understanding of the controls on N2O emissions. A monotonic increase in annual cumulative N2O emissions was observed with increasing AN application rate. Emission factors ranging from 1·06–1·34% were measured for AN application rates between 80 and 320 kg N/ha, with a mean of 1·19%. A lack of any significant difference between these EFs indicates that use of a uniform EF is suitable over these application rates. The mean EF of 1·19% exceeds the IPCC default 1%, suggesting that use of the default value may underestimate emissions of AN-fertilizer-induced N2O loss from Scottish grasslands. The increase in emissions beyond an application rate of 320 kg N/ha produced an EF of 1·74%, significantly different to that from lower application rates and much greater than the 1% default. An EF of 0·89% for urea fertilizer and 0·59% for urea with DCD suggests that N2O quantification using the IPCC default EF will overestimate emissions for grasslands where these fertilizers are applied. Large rainfall shortly after fertilizer application appears to be the main trigger for N2O emissions, thus applicability of the 1% EF could vary and depend on the weather conditions at the time of fertilizer application.</jats:p

    Using legume-based mixtures to enhance the nitrogen use efficiency and economic viability of cropping systems - Final report (LK09106/HGCA3447)

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    As costs for mineral fertilisers rise, legume-based leys are recognised as a potential alternative nitrogen source for crops. Here we demonstrate that including species-rich legume-based leys in rotations helps to maximise synergies between agricultural productivity and other ecosystem services. By using functionally diverse plant species mixtures, these services can be optimised and fine-tuned to regional and farm-specific needs. Replicated field experiments were conducted over three years at multiple locations, testing the performance of 12 legume species and 4 grass species sown in monocultures, as well as in a mixture of 10 of the legumes and all 4 grasses (called the All Species Mix, ASM). In addition, we compared this complex mixture to farmer-chosen ley mixtures on 34 sites across the UK. The trials showed that there is a large degree of functional complementarity among the legume species. No single species scored high on all evaluation criteria. In particular, the currently most frequently used species, white clover, is outscored by other legume species on a number of parameters such as early development and resistance to decomposition. Further complementarity emerged from the different responses of legume species to environmental variables, with soil pH and grazing or cutting regime being among the more important factors. For example, while large birdsfoot trefoil showed better performance on more acidic soils, the opposite was true for sainfoin, lucerne and black medic. In comparison with the monocultures, the ASM showed increased ground cover, increased above-ground biomass and reduced weed biomass. Benefits of mixing species with regard to productivity increased over time. In addition, the stability of biomass production across sites was greater in the ASM than in the legume monocultures. Within the on-farm trials, we further found that on soils low in organic matter the biomass advantage of the ASM over the Control ley was more marked than on the soils with higher organic matter content. Ecological modelling revealed that the three best multifunctional mixtures all contained black medic, lucerne and red clover. Within the long term New Farming Systems (NFS) rotational study, the use of a clover bi-crop showed improvement to soil characteristics compared to current practice (e.g. bulk density and water infiltration rate). Improvements in wheat yield were also noted with respect to the inclusion of a clover bi-crop in 2010, but there was evidence of a decline in response as the N dose was increased. Cumulatively, over both the wheat crop and the spring oilseed rape crop, the clover bi-crop improved margin over N. The highest average yield response (~9%) was associated with the ASM legume species mix cover cropping approach

    Soft Interaction Between Dissolved Dendrimers: Theory and Experiment

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    Using small-angle neutron scattering and liquid integral equation theory, we relate the structure factor of flexible dendrimers of 4th generation to their average shape. The shape is measured as a radial density profile of monomers belonging to a single dendrimer. From that, we derive an effective interaction of Gaussian form between pairs of dendrimers and compute the structure factor using the hypernetted chain approximation. Excellent agreement with the corresponding experimental results is obtained, without the use of adjustable parameters. The present analysis thus strongly supports the previous finding that flexible dendrimers of low generation present fluctuating structures akin to star polymers.Comment: 20 pages, 4 figures, submitted to Macromolecules on July 24, 200

    Restoration of CD28 Expression in CD28− CD8+ Memory Effector T Cells Reconstitutes Antigen-induced IL-2 Production

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    The control of many persistent viral infections by Ag-specific cytolytic CD8+ T cells requires a concurrent virus-specific CD4+ Th cell response. This reflects in part a requirement of activated effector CD8+ T cells for paracrine IL-2 production as a growth and survival factor. In human CMV and HIV infection, the majority of differentiated virus-specific CD8+ T cells notably lose the ability to produce IL-2 but also lose expression of CD28, a costimulatory molecule. Analysis of the fraction of memory CD8+ T cells that continue to express CD28 revealed these cells retain the ability to produce IL-2. Therefore, we examined if IL-2 production by CD28− CD8+ T cells could be restored by introduction of a constitutively expressed CD28 gene. Expression of CD28 in CD28− CD8+ CMV- and HIV-specific CD8+ T cells reconstituted the ability to produce IL-2, which could sustain an autocrine proliferative response after Ag recognition. These results suggest that the loss of CD28 expression during differentiation of memory/effector CD8+ T cells represents a decisive step in establishing regulation of responding CD8+ T cells, increasing the dependence on CD4+ Th for proliferation after target recognition, and has implications for the treatment of viral disease with adoptively transferred CD8+ T cells
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