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Development of a method for sequential Si extraction from soils
No full textThe soil under savanna woody species is often enriched in nutrients in what is termed an ‘island of fertility'. We tested for positive feedbacks between encroaching woody plants and soil fertility in two co-occurring shrub species at three sites. One of these shrub species is nitrogen-fixing, Acacia mellifera, and the other is non‑nitrogen-fixing, Tarchonanthus camphoratus; we compared these effects to the grasslands surrounding the shrub patches. We found that soil nutrient concentrations were usually related to shrub size rather than the species. Fertile patches developed underneath large shrubs as indicated by higher carbon and nitrogen concentrations, a higher CECeff(especially sodium, which is a limiting nutrient for grazing livestock) and a pH near 6. We found no difference in soil nitrogen between the N-fixing A. mellifera and T. camphoratus. Plant cover under large shrubs was less than in open grassland. There are ‘islands of fertility' under large shrubs. However, the development of fertility islands did not facilitate understorey growth. Thus, increased soil fertility had no positive feedback on overall vegetation composition. Negative effects of the woody vegetation may override the positive effects of increased soil nutrient availability
Optimising the extraction of amorphous silica by NaOH from soils of temperate-humid climate
No full textTesting a new method for sequential silicon extraction on soils of a temperate - humid climate
No full textThe importance of silicon (Si) compounds in agriculture and geochemical cycles has received increasing attention over the last decade; however, quantitative data on non-crystalline pedogenic Si phases in soils are still rare. Recently, the authors developed a method for sequential Si extraction from soils, in order to improve the quantification of different Si compounds in soils. The method has been tested on samples of known composition. Here, the method is applied for the first time to complete soil profiles. Six different soil types from south-west Germany that have developed since the end of the last glacial period were selected. Most of the Si in these soils was bound in primary and secondary silicates. In mineral soil horizons, the second-highest proportion of Si was in precipitates of amorphous silica (minerogenic amorphous silica), whereas in some O horizons, the second-most important Si fraction was in biogenic amorphous silica. Topsoil horizons and clayey subsoil horizons of a Luvisol and a Stagnosol especially accumulate amorphous silica. Silicon from bio-opal contributed up to 14% to the total Si in Oa horizons of the studied soils. The smallest amounts of Si were found in the mobile and adsorbed Si fractions. Some methodological limitations are identified and discussed; however, the new sequential method of Si extraction enabled separation of different Si fractions in typical soils of a temperate–humid climate
Review of methodologies for extracting plant-available and amorphous Si from soils and aquatic sediments
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
The loess-paleosol profile Datthausen, on the penultimate-glacial terrace of the upper Danube River: Luminescence dating and interpretation
No full textThe loess-paleosol profile Datthausen, on the penultimate-glacial terrace of the upper Danube River: Luminescence dating and interpretation
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