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  • 2000-2004  (5)
  • 1990-1994  (1)
  • 1985-1989  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Seasonal variation in white clover content and nitrogen fixing (acetylene reducing) activity in a cut upland sward (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Grass and forage science 43 (1988), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The seasonal variation in herbage mass and nitrogen fixing (acetylene reducing) activity of white clover in an upland sward, cut weekly to 3·5 cm from mid-May until mid-October, was measured. Acetylene reducing activity (ARA) was measured over a 24-h period at 3-weekiy intervals starting on 3 March 1983. Clover leaf and Stalon biomass was measured by harvest of the assay truces, and from mid-May quadrat euts to 3·5 cm above the soil surface provided estimates of herbage accumulation.Little A RA was detected in March, but activity increased substantially after 10 cm soil temperatures reached 〉 3°C, and peak activity per unit of clover leaf dry weight occurred in June and July; standing clover leaf dry matter increased during the season to a maximum of 60·5 g m−1 in June. Acetylene reducing activity was positively correlated with the number of rooted nodes, and Stalon and leaf dry weights in early spring. Thereafter, except during a period of summer drought, ARA was positively correlated with the amount of clover leaf material.Clover population density increased during the season and maximum growing point numbers (5540 m−1) occurred in September; maximum leaf number per unit area (12 984 m−1) was found in October, prior to the final cutting of the site.Results suggest that higher levels of nitrogen fixation in upland swards should be obtained if sward management regimes, which encourage a high clover leaf area, are adopted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2494.1988.tb02150.x
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  • 2
    Electronic Resource
    Electronic Resource
    The long-term effects on upland sheep production in the UK of a change to extensive management (2002)
    Oxford, UK : Blackwell Science Ltd
    Grass and forage science 57 (2002), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Extensification (a reduction in fertilizer inputs and stocking rate of grassland) is seen as one way of increasing the conservation value and of reducing the environmental impact of upland sheep production in the UK, but little is known about the consequences of such a change. This study determines the changes in animal production over ten years following the introduction of four extensive grazing management strategies to perennial ryegrass/white clover pastures at two upland sites. Fertilizer-free treatments were maintained with sward heights of: 4 cm (treatment 4/4U) or 8 cm (8/8U) during the whole of the grazing year, 4 cm during summer and 8 cm during autumn (4/8U) and 8 cm during summer and 4 cm during autumn (8/4U). A control treatment that received 140 kg N ha−1 year−1 was also maintained with a sward surface height of 4 cm (4/4F). Scottish Blackface sheep grazed all treatments.The 4/4F treatment carried the greatest number of animals (3746 grazing days ha−1 year−1); the 4/4U and the 8/8U treatments carried 0·73 and 0·43 of this number respectively. The number on the 4/8U treatment was similar to that on the 4/4U while the 8/4U treatment carried 1·41 of that on the 8/8U treatment (0·61 of 4/4F). Mean individual animal performance was greatest on the 8 cm swards and tended to be lowest on the 4/4F treatment. However, the 4/4F treatment produced the greatest live weight of lamb (623 kg ha−1 year−1) with the 4/4U producing 0·77, and the 8/8U producing 0·55, of this amount. Although there was year-to-year variation in agricultural output, it was concluded that the lower levels of sheep production that result from a change to extensive systems of grazing management can be maintained for at least 10 years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2494.2002.00309.x
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  • 3
    Electronic Resource
    Electronic Resource
    The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK: 7. Sustainability of white clover in grass/clover swards with reduced levels of fertilizer nitrogen (2004)
    Oxford, UK : Blackwell Science Ltd
    Grass and forage science 59 (2004), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The sustainability of white clover in grass/clover swards of an upland sheep system, which included silage making, was studied over 5 years for four nitrogen fertilizer rates [0 (N0), 50 (N50), 100 (N100) and 150 (N150) kg N ha−1]. A common stocking rate of 6 ewes ha−1 was used at all rates of N fertilizer with additional stocking rates at the N0 fertilizer rate of 4 ewes ha−1 and at the N150 fertilizer rate of 10 ewes ha−1. Grazed sward height was controlled, for ewes with their lambs, from spring until weaning in late summer by adjusting the proportions of the total area to be grazed in response to changes in herbage growth; surplus pasture areas were harvested for silage. Thereafter sward height was controlled on separate areas for ewes and weaned lambs. Areas of pasture continuously grazed in one year were used to make silage in the next year. For treatments N0 and N150, white clover stolon densities (s.e.m.) were 7670 (205·4) and 2296 (99·8) cm m−2, growing point densities were 4459 (148·9) and 1584 (76·0) m−2 and growing point densities per unit length of stolon were 0·71 (0·015) and 0·67 (0·026) cm−1 respectively, while grass tiller densities were 13 765 (209·1) and 18 825 (269·9) m−2 for treatments N0 and N150 respectively. White clover stolon density increased over the first year from 780 (91·7) cm m−2 and was maintained thereafter until year 5, reaching 8234 (814·3) and 2787 (570·8) cm m−2 for treatments N0 and N150 respectively. Growing point density of white clover increased on treatment N0 from 705 (123·1) m−2 to 2734 (260·7) m−2 in year 5 and it returned to the initial level on treatment N150 having peaked in the intermediate years. Stolon density of white clover was maintained when the management involved the annual interchange of continuously grazed and ensiled areas. The non-grazing period during ensiling reduced grass tiller density during the late spring and summer, when white clover has the most competitive advantage in relation to grass. The increase in stolon length of white clover in this period appears to compensate for the loss of stolon during periods when the sward is grazed and over winter when white clover is at a competitive disadvantage in relation to grass. The implications for the management of sheep systems and the sustainability of white clover are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2494.2004.00426.x
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  • 4
    Electronic Resource
    Electronic Resource
    Changes in species composition of abandoned sown swards after imposing seasonal cutting treatments (2003)
    Oxford, UK : Blackwell Science Ltd
    Grass and forage science 58 (2003), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Seasonal cutting treatments were imposed on abandoned perennial ryegrass/white clover swards at three sites in the UK to determine the impact on species diversity and the contribution of different species to biomass. Before the cutting experiment, the abandoned swards had received no fertilizer applications and had been neither grazed nor cut for 3 years. The original sown species, Lolium perenne and Trifolium repens, had virtually disappeared during this period. Self-sown grasses, including Agrostis capillaris, Dactylis glomerata, Festuca rubra, Holcus mollis, Poa pratensis and P. trivialis, had become dominant at two sites. Ranunculus repens was the dominant species at the third site, and self-sown grasses, such as Holcus lanatus and P. trivialis, and Juncus and Carex species were also present. The standing herbage in 2·5 m × 2·5 m subplots was cut to 2·5 cm above ground level and removed annually in either June or October for 7 years at two sites and 6 years at the third site. Total biomass removed was generally 〈 4 t dry matter (DM) ha−1, and both total and live biomass decreased over time in the June cutting treatment at two sites. There were large changes in species composition after initiating the two cutting treatments. The numbers of grass and dicot species increased, although many new species had a low frequency of occurrence. The contribution of species to biomass changed over time, with species showing a vegetative regenerative strategy decreasing over time at one site. At this site, annual cutting in June was slightly more effective than cutting in October in reducing the dominance of R. repens; cutting in early October effectively reduced Juncus spp. At two sites, there was a decrease in the contribution of the species group showing seasonal regeneration by seed, and differences between cutting dates for two species within this group at one site. L. perenne and T. repens remained at much lower levels than in adjacent unfertilized, grazed swards. Reseeding may be necessary to create species assemblages for ecological and agricultural objectives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2494.2003.00350.x
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamics of perennial ryegrass and white clover in sown swards in NW Greece (2000)
    Oxford UK : Blackwell Science Ltd
    Grass and forage science 55 (2000), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Seasonal dynamics of white clover and perennial ryegrass were examined in sown perennial ryegrass/white clover swards subject to a 2 × 2 factorial treatment combination of defoliation (rotational grazing by sheep and cutting) and nitrogen fertilizer application (0 and 40 kg N ha–1 year–1) in NW Greece. Sward surface height and percentage cover were measured before and after five defoliation periods in 1996 within permanent microplots (30 × 30 cm, divided into nine cells) in which white clover was either initially present or absent. Both white clover and perennial ryegrass achieved maximum height and cover in April–May. Defoliation treatment and whether white clover was present initially significantly affected height and cover of both species. Total plant cover was similar prior to all defoliation periods except in July, a time of drought. Cover of perennial ryegrass was greater where white clover was initially absent, but total plant cover was greater in microplots containing white clover and the extent of the differences varied during the year. In contrast, N fertilizer application had little effect on species cover, other than small reductions in white clover cover. When white clover was present in April, it was found in virtually every microplot cell until July, but if it was absent in April there was little colonization of the microplot.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2494.2000.00219.x
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  • 6
    Electronic Resource
    Electronic Resource
    Systematic Investigations of the Influence of Molecular Structure on the Transport of Peptides Across Cultured Alveolar Cell Monolayers (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 7-14 
    Details
    ISSN: 1573-904X
    Keywords: transport of peptides ; molecular structure ; molecular size ; cultured alveolar cell monolayers ; alveolar permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To determine how the structures of peptides influence theiralveolar permeability. Methods. The studies were performed using 14 synthetic ‘model’peptides, labelled with a novel, non-intrusive amino acid fluorophore, andtheir transport studied using rat alveolar cell monolayers cultured onpermeable supports. Results. The passage of the peptides across the epithelial cellmonolayers is shown to be primarily paracellular, with an inverse dependenceon molecular size, and an enhanced flux observed for cationic peptides.The apparent permeability coefficients (P app ) for the peptides(together with those for other organic solutes, taken from the literature) areshown to be well-modelled assuming two populations of ‘pores’ in themonolayers, modelled as cylindrical channels of radii 15 Å and 22nm. The former pores are shown to be numerically equatable withthe monolayer tri-junctional complexes, and the latter are taken asmonolayer defects. Conclusions. The various monolayer P app values correlatewell with the results from in vivo transport experiments, and the conclusion isdrawn that the pulmonary delivery of peptide drugs is perfectlyexploitable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007514121527
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  • 7
    Electronic Resource
    Electronic Resource
    Blockade of insulin sensitive steady-state R-type Ca2+ channel by PN 200-110 in heart and vascular smooth muscle (1992)
    Springer
    Molecular and cellular biochemistry 117 (1992), S. 93-106 
    Details
    ISSN: 1573-4919
    Keywords: heart cells ; vascular smooth muscle ; Ca2+ channels ; insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The effect of high K− concentration, insulin and the L-type Ca2− channel blocker PN 200-110 on cytosolic intracellular free calcium ([Ca2+]i) was studied in single ventricular myocytes of 10-day-old embryonic chick heart, 20-week-old human fetus and rabbit aorta (VSM) single cells using the Ca2+-sensitive fluorescent dye, Fura-2 microfluorometry and digital imaging technique. Depolarization of the cell membrane of both heart and VSM cells with continuous superfusion of 30 mM [K+]o induced a rapid transient increase of [Ca2+]i that was followed by a sustained component. The early transient increase of [Ca2+]i by high [+]o was blocked by the L-type calcium channel antagonist nifedipine. However, the sustained component was found to be insensitive to this drug. PN 200-110 another L-type Ca2+ blocker was found to decrease both the early transient and the sustained increase of [Ca2+]i induced by depolarization of the cell membrane with high [K+]o. Insulin at a concentration of 40 to 80 μU/ml only produced a sustained increase of [Ca2+]i that was blocked by PN 200-110 or by lowering the extracellular Ca2+ concentration with EGTA. The sustained increase of [Ca2+], induced by high [K+]o or insulin was insensitive to metabolic inhibitors such as KCN and ouabain as well to the fast Na+ channel blocker, tetrodotoxin and to the increase of intracellular concentrations of cyclic nucleotides. Using the patch clamp technique, insulin did not affect the L-type Ca2+ current and the delayed outward K+ current. These results suggest that the early increase of (Ca2+]i during depolarization of the cell membrane of heart and VSM cells with high [K+]o is due to the opening and decay of an L-type Ca 2+ channel. However, the sustained increase of [Ca2+]i during a sustained depolarization is due to the activation of a resting (R) Ca 2+ channel that is insensitive to lowering [ATP]i and sensitive to insulin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230415
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