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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 35 (1995), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Three years of experiments with spring barley showed significant differences in weed suppression ability among varieties. Weed dry matter in the most suppressive variety, Ida, was 48% lower than the mean weed dry matter of all varieties, whereas it was 31% higher in the least suppressive variety, Grit. Ranking varietal responses to weed competition in terms of grain yield loss corresponded well to ranking weed dry matter produced in crop weed mixtures. There was no correspondence between the varietal grain yields in pure stands and their competitiveness, suggesting that breeding to optimize both yielding and competitive ability may be possible. Non-linear regression models were fitted to canopy height and light interception data for each variety in all three years. The canopy height model provided a precise description of development and maximum canopy height of the varieties. A light interception model was developed to describe the light interception profiles of the varieties. A study of the estimated parameters showed significant correlation between weed dry matter, rate of canopy height development and the light interception profile. However, when estimates were standardized to eliminate the effect of year, there was no correlation between weed dry matter and the light interception profile parameters, indicating that varietal competitiveness was not related to this trait. A multiple regression analysis showed that a model comprising parameters of maximum canopy height, maximum light interception and temporal displacement of light interception provided a good description of the varietal differences.
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  • 2
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: For implementation of simple yield loss models into threshold-based weed management systems, a thorough validation is needed over a great diversity of sites. Yield losses by competition wsth Sinapis alba L. (white mustard) as a model weed, were studied in 12 experiments in sugar beet (Beta vulgaris L.) and in 11 experiments in spring wheat (Triticum aestivum L.). Most data sets were heller described by a model based on the relative leaf area of the weed than by a hyperbolic model based on weed density. This leaf area model accounted for (part of) the effect of different emerging times of the S. alba whereas the density model did not. A parameter that allows the maximum yield loss to be smaller than 100% was mostly not needed to describe the effects of weed competition. The parameter that denotes the competitiveness of the weed species with respect to the crop decreased the later the relative leaf area of the mustard was determined. This decrease could be estimated from the differences in relative growth rate of the leaf area of crop and S. alba. However, the accuracy of this estimation was poor. The parameter value of the leaf area model varied considerably between sites and years. The results strongly suggest that the predictive ability of the leaf area model needs to be improved before it can be applied in weed management systems. Such improvement would require additional information about effects of abiotic factors on plant development and morphology and the definition of a time window for predictions with an acceptable level of error.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 34 (1994), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In dose-response experiments with the herbicide combinations MCPA+dichlorprop and ioxynil+mecoprop in barley, winter wheat, and winter rye varieties, oilseed rape (Brassica napus L.) was used as a substitute for weeds. The results showed a significant interaction between the competitive ability of varieties and herbicide performance. A negative exponential model with variety as categorical variable was used to analyse the data and to assess the competitive effect of the varieties on herbicide efficacy.A target level of 5 g weed dry matter m−2 in all varieties at the end of flowering was used to derive a varietal calibration factor of the herbicide dose. The results showed significant differences in calibration factors between species of winter wheat, barley, and rye, and between varieties of spring barley and winter wheat. In the winter wheat variety Sleipner it was necessary to use a 154% higher herbicide dose than in the winter barley variety Trixi, whereas in the winter rye variety Petkus II, herbicide dose could be reduced by 31% compared with Trixi. The differences between spring barley varieties were smallerbut significant. Competition entre culture et mauvaises herbes, et efficacité herbicide chez différentes espèces et variétés de céréales Dans des expériences dose-effet avec les combinaisons herbicides MCPA+dichlorprop et ioxynil+mécoprop dans différentes variétés d'orge, de blé d'hiver et de seigle d'hiver, le colza (Brassica napus L.) était utilisé comme modèle de mauvaise herbe. Les résultats ont montré une interaction significative entre l'aptitude à la concurrence des variétés et l'efficacité herbicide. Un modèle exponentiel négatif avec la variété comme variable catégorielle, a été utilisé pour analyser les données et pour déterminer l'effet de l'aptitude à la compétition des variétés sur l'efficacité herbicide.Un objectif de 5 g de matière sèche de mauvaise herbe par m2 pour toutes les variétés à la fin de la floraison a été utilisé pour déterminer un facteur de calibration varietal de la dose d'herbicide. Les résultats ont montré des différences significatives entre les facteurs de calibration déterminés pour les espèces blé d'hiver, orge et seigle, ainsi qu'entre les variétés d'orge de printemps et de blé d'hiver. Avec la variété de blé d'hiver Sleipner, U était nécessaire d'utiliser une dose d'herbicide supérieure de 154%à celle nécessaire pour la variété d'orge d'hiver Trixi, alors que dans le seigle d'hiver Petkus II, la dose herbicide pouvait ßtre réduite de 31 % par rapport à Trixi. Les différences entre variétés d'orge de printemps étaient plus faibles mais significatives. Konkurrenz zwischen Kulturpflanzen und Unkraut und Herbizidwirkung bei Getreidearten und -Sorten In Dosis-Wirkungs-Untersuchungen mit den Herbiziden MCPA+Dichlorprop und loxynil+Mecoprop wurde in Gersten-, Winterweizen- und Winterroggensorten Raps (Brassica napus L.) als Unkraut eingesetzt. Die Ergebnisse zeigten eine signifikante Wechselwirkung zwischen der Konkurrenzkraft von Sorten und der Herbizidwirkung. Ein negativ exponentielles Modell mil der Sorte als Kategorie wurde angewandt, um die Da ten zu analysieren und den Einfluß der Sorten auf die Herbizidwirksamkeit zubestimmen. Es wurde eine Zielgröße von 5 gm−2 Unkrauttrockenmasse in allen Sorten zum Endeder Blüte gesetzt, um einen sortenbezogenen Kalibrierungsfakt or für die Herbiziddosis zu erhalten. Es wurden signifikante Unterschiede der Kalibrierungsfaktoren zwischen den Getreidarten Winterweizen, Gerste und Roggen und zwischen den Sommergersten- und Winterweizensorten gefunden. Bei der Winterweizensorte Sleipner war es erforderlich, eine 154 % höhere Herbiziddosis als bei der Wintergerstensorte Trixi anzuwenden, während die Herbiziddosis bei der Winterroggensorte Petkus II im Vergleich zu Trixi um 31 % reduziert werden konnte. Die Unterschiede waren bei Sommergerstensorten geringer, jedoch signifikant.
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  • 4
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . Species of Tetrahymena, including T. vorax, T. thermophila, T. pyriformis, and T. pigmentosa, were tested for cloning efficiency in proteose peptone and in synthetic nutrient media to which were added hemin, protoporphyrin IX, chlorophyllin, or asolectin, an impure mixture of phospholipids. All species could be cloned with high efficiency in the crude media. In unsupplemented synthetic medium the cloning efficiencies were 0–10%, around 50%, around 50%, and 90–100% for T. thermophila, T. vorax, T. pyriformis, and T. pigmentosa, respectively. The first three were all stimulated to 90–100% by addition of the porphyrin or phospholipid compounds mentioned above. Uroporphyrin III and coproporphyrin I and III had no effect. We suggest that cells unable to form clones suffer from a lack of cellular energy. This situation may be alleviated by our additions: certain porphyrin rings may be built into cytochromes and phospholipids may be used as fuel. Thus, the synthetic media used so far for these ciliates have not been optimal.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 36 (1998), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Database information on geology, hydrology, and hydrometeorology may form an excellent basis for studying ground water flow and seepage to surface water in a catchment. In a field case study of a 114 km2 catchment, geological database information was used to determine layer thicknesses and boundary conditions as well as to parameterize a ground water flow model. Hydraulic head and stream flow data were used to estimate the model parameters by nonlinear regression. The uncertainty of the estimated parameters and of the predicted stream flow gains was quantified by individual likelihood method confidence intervals. During four stages of calibration, ranging from using only head data to also using an extensive set of measured stream flow gains, no parameter estimates changed significantly, but the number of parameters was increased from 12 to 14 in order to fit local stream flow gains. This indicates that the geology-based parameterization is firm.Adding stream flows to the calibration data reduced the uncertainty of the estimated parameters significantly. However, the uncertainty of some of the parameters was significant even when an extensive set of measured stream flow gains and hydraulic heads was used to calibrate the model. Parameter uncertainty is reflected in the uncertainty of the predicted stream flow gains. When an extensive set of stream flow data was used during calibration, the prediction uncertainty is up to ±25% in large streams, and up to ±60% in smaller streams. The confidence intervals in general are skewed, and they are very skewed in the case where no stream flow measurements were used to calibrate the model.The case study shows that even when relatively extensive geological information and calibration data are available, there may be significant uncertainty connected with the prediction of local discharge of ground water to streams. Reducing uncertainty in such cases will require extensive field investigations in order to improve the definition of recharge areas and to describe the local fluxes and flow patterns in the aquifers.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 9 (1992), S. 0 
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 86 (1992), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Adding fresh roots to intact soil cores resulted in marked increases in microbial and microfaunal activity at the resource islands. Microbial activity increased in two phases following root addition. Respiratory activity and concentration of respiratory enzyme (dehydrogenase) in soil adhering to the roots was very high during the first three weeks resulting in anaerobic conditions in the soil. After a period of low respiratory activity and enzyme content, these quantities increased from 6 to 20 weeks, but not enough to maintain anaerobic conditions. Numbers of protozoa peaked earlier than the nematodes. Based on yield coefficients of microbes and bacterivores, the increase in bacterivores was in accordance with root-induced respiration activity. In soil adhering to roots, numbers of bacterial grazers (protozoa and nematodes) were up to 80 and 30 times higher, respectively, than in the surrounding soil. This effect is up to 20 times higher than observed around live root systems, which may suggest that the rhizosphere effect on microbivores could for the major part result from the decomposition of dead segments of the root system.
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  • 8
    Map available for loan
    Map available for loan
    Stuttgart : Bundesanstalt für Geowissenschaften und Rohstoffe
    Associated volumes
    Call number: K 94.0022 / Fach 23
    In: Geologische Übersichtskarte
    Type of Medium: Map available for loan
    Location: Upper compact magazine
    Branch Library: GFZ Library
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