1,721,016 research outputs found
Root traits in cover crop mixtures of blue lupin and winter rye
No full textAbstract Purpose Mixtures of cover crops are gaining importance in farming systems. While complementarity between species is a potentially important mechanism underlying mixture benefits, there is little quantitative evidence about complementarity of root growth. Therefore, we aimed to gain detailed knowledge about mixture effects of specific root traits. Methods Blue lupin ( Lupinus angustifolius L.) and winter rye ( Secale cereale L.) were grown as sole and intercrops in a two-year organically managed field experiment in Germany. Crops were analysed for shoot biomass and nutrient uptake as well as for root mass density (RMD), root length density (RLD) and specific root length (SRL). We used Fourier transform infrared (FTIR) spectroscopy to discriminate the root mass species-specifically in the mixtures. Results In the shoot, overyielding was only found for N and P uptake in the 75:25 mixture of lupin and rye, whereas positive mixture effects of RLD, RMD, and root mass complementarity occurred only in the 50:50 mixture in one year. Consistently positive mixture effects of SRL were found. Root biomass proportion of rye was higher in topsoil, that of lupin higher in subsoil. Vertical niche differentiation in RMD between sole crops and mixtures was not observed. Conclusion Among all root traits analysed, consistent mixture effects were observed only for SRL. Mechanisms behind mixture effects of root traits need further research. FTIR spectroscopy discriminated intercrop root mass well. Discrimination of mixture partners’ root length would help to better understand complementarity of root growth in mixtures
Oil radish, winter rye and crimson clover: root and shoot performance in cover crop mixtures
No full textAbstract Purpose The current knowledge of belowground interactions in intercropping systems is limited due to methodological constraints. The current study aimed to investigate cereal-brassica and cereal-legume-brassica cover crop mixtures regarding mixture effects on root and shoot biomass as well as root traits, vertical root niche differentiation, and complementarity. Methods Sole crops and two- and three-species-mixtures of winter rye ( Secale cereale L.), crimson clover ( Trifolium incarnatum L.), and oil radish ( Raphanus sativus L. var. oleiformis Pers.) were grown in Germany in a two-year organic field experiment. Root traits were analysed using the monolith method. For discrimination of species root mass Fourier transform infrared (FTIR) spectroscopy was used. Results Oil radish dominated mixtures above- and belowground. Oil radish and its mixtures had highest root length density (RLD) and root mass density (RMD) in subsoil. Rye had highest root biomass and RLD in topsoil. Clover was uncompetitive and had low RLD and RMD. Large but non-significant mixture effects occurred in the shoot, especially for shoot nutrient uptake. Mixture effects were positive for RLD and RMD in subsoil and positive for specific root length (SRL) throughout the whole profile. There was no clear evidence for vertical root niche differentiation and root mass complementarity. Conclusion Oil radish as a mixing partner increased rooting in subsoil. When comparing mixtures and sole crops, morphological changes, i.e. higher SRL in mixtures, were found. Contrary to expectations, changes in root allocation patterns, such as vertical niche differentiation or complementarity of root mass, were not observed.Bundesanstalt für Landwirtschaft und Ernährung http://dx.doi.org/10.13039/501100010771Rheinische Friedrich-Wilhelms-Universität Bonn 50110000813
Root growth of sole and mixed cover crops in organic farming
Get PDFCover crops are an important tool in arable farming systems. They provide many different agroecosystem services. For many of these functions, such as nutrient uptake, erosion prevention and soil structure formation, the roots of cover crops are of central importance. In recent years, cover crop mixtures have become increasingly popular in agricultural practice. Mixtures can have advantages over sole crops in terms of productivity and agroecosystem services. In agricultural practice and consulting, the advantages of mixtures are often mentioned with regard to the rooting of cover crop stands, and complementarity in the root zone as well as increased rooting across the entire soil profile are postulated.
The aim of the present thesis is to test different cover crop species for their rooting intensity and, in a further step, to investigate the root traits in cover crop mixtures and possible below-ground mixture effects. In addition, the potential of cover crops to create large-sized biopores is assessed. Different methods for determining root length density are compared.
In 2018/19 and 2019/20, sole and mixed cover crops were investigated for shoot and root traits in the field. The latter were determined using the monolith and profile wall method. Species-specific root masses in mixtures were analysed by Fourier transform infrared spectroscopy.
The results showed that winter hardy cover crop species increased root length over winter. Oil radish, winter turnip rape and phacelia rooted intensively into large-sized biopores in the sub-soil. Positive mixture effects partly occurred in the shoot, whereby these were higher for nutrient content than for biomass. There were no significant mixing effects for root mass. Weak partners were suppressed in root mass. In mixtures with oil radish, there were positive mixture effects for root length and root mass density in the subsoil. For the specific root length, positive mixture effects were found in all mixtures. Neither a vertical niche differentiation for root mass density nor complementarity effects for root mass could be clearly found. The biopore genesis potential of cover crops was low, but highest for blue lupin.
Compared to the monolith method, the root length density estimated with the profile wall method was underestimated, especially in highly rooted zones. High agreement between both methods was found for the cumulative root distribution. The influence of soil depth was very decisive for the comparison of both methods.
Overall, it was shown that for the cover crop mixtures tested in this thesis mixture effects of root traits were rather small. Complementarity in the root zone and increased rooting over the entire soil profile could not be found. In addition, future perspectives for root research on cover crop mixtures as well as agronomic management options for cover cropping are discussed
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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