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  • 1
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd
    Grass and forage science 56 (2001), S. 0 
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Bracken (Pteridium aquilinum) is a major weed of considerable economic concern in upland pastures in Bulgaria and elsewhere in Europe. Between 1993 and 1998, a field experiment was carried out to test methods for restoring productive meadows. Initially, spraying asulam (4·8 kg a.i. ha−1) was used to control the bracken on the site; this was achieved in terms of reduced frond densities and a higher level of grassland establishment. This grassland was dominated by Vicia cassubica and the perennial grasses Agrostis vulgaris, Dactylis glomerata, Festuca rubra, Holcus lanatus and Poa pratensis.After 2 years, a fertilizer addition experiment was started with four treatments (no fertilizer; addition of phosphorus; addition of nitrogen and phosphorus; addition of nitrogen, phosphorus and potassium. The phosphorus and potassium fertilizers were applied annually in the early spring at 80 kg of P ha−1 year−1 and 50 kg of K ha−1 year−1, and nitrogen was added at the start of grass growth at 60 kg of N ha−1 year−1. At the same time, a twice-yearly hay-cutting regime was implemented. Fertilizer addition increased both the quantity and the quality of the resulting grassland. The herbage dry matter was increased by at least a factor of two depending on fertilizer combination, and there was an increase in grass and legume cover and a decrease in both weed cover and bracken recovery. However, although bracken recovery was inversely related to grassland production, there was a consistent increase in bracken density across all treatments between 1997 and 1998, suggesting that increasing herbage biomass merely delays bracken recovery. The implications of these findings are discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Boston, MA, USA : Blackwell Science Inc
    Restoration ecology 9 (2001), S. 0 
    ISSN: 1526-100X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: High soil pH has been highlighted as a constraint to the restoration of heathland on ex-arable land. Previous studies at the Minsmere Reserve of the Royal Society for the Protection of Birds (RSPB) in England have shown that it is possible to acidify ex-arable soils using elemental sulfur and bracken litter, although sulfur (S) is more effective. Current recommendations suggest that 4 tS/ha need to be applied to reduce soil pH below pH 4, control vigorous ruderal species, and create conditions suitable for Calluna vulgaris (heather) establishment. However, S is relatively expensive, and as bracken litter is moderately abundant within the reserve, it made economic sense to evaluate the potential for mixing S with bracken to see if adequate pH reductions could be achieved at lower S rates. Accordingly an experiment was designed to test the effects of combining S (0–8 t S/ha) and bracken litter (0–10 cm depth layers) on (1) soil pH, (2) cover of ruderal species, and (3) the developing plant community. Significant interactions were detected, especially in the period immediately after application. Where bracken litter was applied the soil pH fell immediately; in contrast, S took at least six months to start reducing pH. Where mixtures were applied there was a synergistic effect, which produced a lower pH than the S or bracken litter applied alone. These effects were most marked at low S application rates, between 0.5–4 t S/ha. The effects of the bracken litter addition also reduced the growth of ruderal species in the period immediately after application, probably through a combination of acidification and physical smothering. There is, therefore, a clear potential to acidify ex-arable soils using combinations of S and bracken litter in schemes designed to restore Calluna heathland.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 27 (1987), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of six grass growth retardants, maleic hydrazide (±2,4-D), mefluidide, paclobutrazol, EL500 and a mixture of mefluidide with paclobutrazol on a grass/clover sward were compared over a 3-year period. Maleic hydrazide, which is the most commonly used retardant, gave poor levels of growth control except when used with 2,4-D. Greatest growth suppression, a 38% reduction in dry matter production from May to July, was obtained from a mixture of mefluidide and paclobutrazol. Differences were observed between the effects of the shoot-acting retardants, maleic hydrazide and mefluidide and the root-acting retardants, paclobutrazol and EL500. Shoot-acting retardants were less effective in wet weather and lasted for a shorter period than root-acting retardants. They also increased compensatory growth after a period of growth suppression, and increased the proportion of clover in the sward.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Weed research 45 (2005), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Agriculture plays a major role in the economic and social development of Sudan. The most important agricultural area in Sudan is the irrigated Gezira Agricultural Scheme (GAS), which takes water from the Sennar Dam on the Blue Nile. This study investigated weed communities in relation to geographical location and crop rotation in 2000 and 2001. Five agricultural units were sampled from the central sector of the GAS; within each unit we surveyed weed communities in different phases of the crop rotation: cotton, groundnuts, sorghum, and a fallow. The distribution of weed species showed some similarities in the 2 years sampled, with most species being found in all agricultural units but their relative proportions differed. Broad-leaved weeds were dominant, suggesting that herbicides selected for weed control in the Gezira scheme need to be effective against this group of species. Agricultural unit and crop type affected weed communities in both years. The weed flora was largest in cotton, intermediate in groundnuts and sorghum, and smallest in the fallow. Although most weeds were found in all agricultural units; however, their relative abundances differed greatly, either as a result of differences in management between the units, or some other spatial effect. As such, weed control programmes need to be tailored at the agricultural unit scale.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for the pulsatile release of luteinizing hormone releasing hormone (LHRH) can be reduced to a FitzHugh–Nagumo model subject to regular and quasiregular (i.e., with slight random variation in the interstimulus interval), discrete-time stimulation. The relationship of output pulse frequency (OPF) to stimulus frequency is compared between the excitable and oscillatory forms of the model and discussed in the context of results from other pulse-driven model systems. Some examples of the changes in OPF caused by quasiregular and purely Poissonian stimuli are given for the excitable case. The unstimulated system frequently interacts with the stimulation in such a complex manner that the OPF bears little resemblance to the frequency of stimulation or of the unstimulated system. Furthermore, the inability of the oscillatory form of the model to allow complete suppression of output pulses for moderate stimulation frequencies suggests that the LHRH system can be more appropriately described by the excitable form of the model. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 204-209 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Recombination of slow highly charged ions at the surface of a target foil can be used as a source of x rays for a projection x-ray microscope. In a first test of this concept, a low emittance beam of Ar18+ and Ar17+ ions from an electron beam ion trap was focused with einzel lenses to a 20 μm full width at half maximum spot on a beryllium target foil. The 3 keV x rays from radiative deexcitation of the ions were used to obtain a magnified image of an electroformed nickel mesh with 20 μm resolution by projection onto a CCD camera. Prospects for substantial improvements in resolution and intensity are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2338-2342 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-throughput von Hámos-type Bragg crystal spectrometer is described that is operated with the Livermore electron beam ion trap. The spectrometer is employed to measure high-resolution x-ray spectra from highly charged heliumlike and neonlike ions. Data from heliumlike Ti20+ and Fe24+ and from neonlike Au69+ are presented to demonstrate the utility of the new instrument.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 941-944 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A super electron beam ion trap has been used to produce bare U92+ ions at an electron beam energy of 198 keV. Evaporative cooling with light ions was used to trap a population of 5×104 highly charged uranium ions for many seconds and reduce their temperature to less than 2q eV, suggesting that a very low emittance source of these ions is possible. Roughly 10 U92+ and 500 U91+ ions were present in the Super electron beam ion trap as determined from x-ray emission spectra of the trapped ions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 2806-2811 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Several key features of the electron-beam ion trap (EBIT) enable it to provide superior ion-source performance for many applications requiring ultra-high-charged ions. This paper briefly reviews these features and the operating conditions in the existing EBITs. The present performance of the EBIT as an ion source is demonstrated by producing and extracting ions up to Th80+ and U70+ at microsecond-wide ion beam pulses of about 104 ions per second. Using as examples the production of U92+, U90+, and Dy66+, modeling results are presented to show how the fundamental processes limit the quality and quantity of ions that can be obtained from an upscaled EBIT.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-5036
    Keywords: Amendments ; Kaolin mining wastes ; Leaching ; Mica ; Nutrient loss ; Overburden ; Sand ; Top-soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The chemical composition and leaching loss of applied fertilizers were measured from four waste materials derived from china clay extraction. Two waste materials, overburden and mica, had a higher nitrogen and calcium concentration, and were more efficient than sand wastes for the retention of these elements when applied as fertilizers. The possibility of using overburden and mica wastes as amendments for sand waste reclamation is briefly discussed.
    Type of Medium: Electronic Resource
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