1,721,032 research outputs found
PHYSICAL AND CULTURAL WEED CONTROL IN MINOR CROPS
No full textThis paper summarises the major European achievements with physical and cultural weed control methods in minor row crops. Minor crops, such as vegetables, sweet maize and potatoes, present two different situations for physical weed control of entirely different difficulty. Inter-row weeds are easily removed by inter-row cultivation while intra-row weeds, i.e. those growing between the crop plants in the rows, still constitute a major challenge aimed at minimising laborious hand weeding. Investigations have focussed on optimising the use of mechanical principles against intra-row weeds, e.g. harrowing, brush weeding and finger weeding. These methods have been successful in some transplants, potatoes and maize, and may become alternatives to chemical control. However, in sown crops with low initial growth rates and in general in organic farming, current intra-row mechanical methods have to act in combination with thermal and cultural methods to achieve sufficient control, though some subsequent hand weeding may be needed. As such, methods worth mentioning are: mulching with dead or living materials; intercropping (e.g. celery in transplanted leek); optimised crop spatial arrangement (e.g. in pigeon bean); and solarisation to reduce soil seed viability. Although the need for hand weeding has been reduced markedly, this is still to be fully achieved. The direction in research has thus moved to new methods. Robotic weeding is now being investigated for row crops with abundant and precise spacing between individual plants, and soil steaming prior to sowing row crops that develop dense crop stands shows promise of effective and prolonged control
Integrating Physical and Cultural Methods of Weed Control - Examples from European Research
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Report from an EWRS workshop on modelling weed population dynamics
Get PDFA three-day workshop on modelling weed population dynamics partially sponsored by the European Weed Research Society (EWRS) was held in October 2006 at Research Centre Flakkebjerg. 24 participants attended the workshop from 8 countries, mainly Europe and USA. The aim of the workshop was to gather some of those active and interested in the field, i.e. most of the participants had either published papers on weed population dynamic models or had a model under development. By gathering these people, it was our hope to learn from each other and possibly benefit by increasing the knowledge and use of each other's work. The EWRS saw the workshop as an opportunity to interconnect some of the work going on in (at least) three working groups: Weed Seed Germination and Early Growth, Crop-Weed Interactions and Physical and Cultural Weed Control.
The preparations of the workshop were initiated by the keynote paper on modelling weed population dynamics presented by N. Holst at the EWRS Symposium in Bari, Italy, 2005, which has recently been published in Weed Research. In connection with this, a database with a bibliography of publications on weed population dynamic models was created, and is public online at http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-3180.2007.00534.x. At the workshop, ten weed population dynamics models were presented, and all of these were available on computers for the participants to try. Many of the models are freely available on the Internet, although some must be paid for, and some are still under development.
The themes discussed at the workshop were presented under five headings: 1. Using models for understanding weed biology, 2. Modelling tools for understanding the dynamics of weed populations, 3. Using models for prediction purposes and decision support, 4. Understanding basic spatial-temporal dynamics through use of models and 5. Model analysis. A common understanding at the workshop, in respect of the fact that no model can accurately show the complexity of the real world, was that "All models are wrong – but some are useful". Some important discussion points brought up at the workshop were related to application domain and model complexity. Are the models used to explain what actually has happened, or are they used for forecasting. It was decided that some of the participants will collaborate on a common publication on this subject. Another topic was the required level of complexity also phrased as ‘How long do we keep on improving our models?’ Does added complexity make the model more realistic, or does it just add errors?
We also discussed how we could make better use of each other's work. In this regard it was decided to make a list of the presented models, including links to the models and where possible open source code, so that parts of generic models could be used by other modellers. In addition, a common database with parameters characterizing different life cycle stages of specific weed species was planned. Since participants agreed that this workshop was a very important opportunity for weed population dynamics modellers to convene, it was suggested that a new workshop should be arranged within 2-3 years, location depending on possibilities for sponsoring
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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