1,721,049 research outputs found
Differential Regulation of Kernel Set and Potential Kernel Weight by Nitrogen Supply and Carbohydrate Availability in Maize Genotypes Contrasting in Nitrogen Use Efficiency
Get PDFSub-optimal nitrogen (N) conditions reduce maize yield due to a decrease in two sink components: kernel set and potential kernel weight. Both components are established during the lag phase, suggesting that they could compete for resources during this critical period. However, whether this competition occurs or whether different genotypic strategies exist to optimize photoassimilate use during the lag phase is not clear and requires further investigation. We have addressed this knowledge gap by conducting a nutrient solution culture experiment that allows abrupt changes in N level and light intensity during the lag phase. We investigated plant growth, dry matter partitioning, non-structural carbohydrate concentration, N concentration, and 15N distribution (applied 4 days before silking) in plant organs at the beginning and the end of the lag phase in two maize hybrids that differ in grain yield under N-limited conditions: one is a nitrogen-use-efficient (EFFI) genotype and the other is a control (GREEN) genotype that does not display high N use efficiency. We found that the two genotypes used different mechanisms to regulate kernel set. The GREEN genotype showed a reduction in kernel set associated with reduced dry matter allocation to the ear during the lag phase, indicating that the reduced kernel set under N-limited conditions was related to sink restrictions. This idea was supported by a negative correlation between kernel set and sucrose/total sugar ratios in the kernels, indicating that the capacity for sucrose cleavage might be a key factor defining kernel set in the GREEN genotype. By contrast, the kernel set of the EFFI genotype was not correlated with dry matter allocation to the ear or to a higher capacity for sucrose cleavage; rather, it showed a relationship with the different EFFI ear morphology with bigger kernels at the apex of the ear than in the GREEN genotype. The potential kernel weight was independent of carbohydrate availability but was related to the N flux per kernel in both genotypes. In conclusion, kernel set and potential kernel weight are regulated independently, suggesting the possibility of simultaneously increasing both sink components in maize.publishedVersio
Plant community impacts on the structure of earthworm communities depend on season and change with time
No full textDeclining plant diversity potentially threatens essential ecosystem functions driven by the decomposer community, such as litter decomposition and nutrient cycling. Currently, there is no consensus on the interrelationships between plant diversity and decomposer performance and previous studies highlighted the urgent need for long-term experiments. In the Jena Experiment we investigated the long-term impacts of plant community characteristics on the structure of earthworm communities representing key decomposers in temperate grassland. We repeatedly sampled plots varying in plant species richness (1-16 species), plant functional group richness (1-4 groups), and presence of certain plant functional groups (grasses and legumes) three, four, and six years after establishment of the experiment in spring and autumn. The results show that earthworm performance is essentially driven by the presence of certain plant functional groups via a variety of mechanisms. Plant productivity (root biomass) explained most of the detrimental grass impacts (decrease in earthworm performance), while beneficial legume effects likely were linked to high quality inputs of plant residues (increase in earthworm performance). These impacts depended on the functional group of earthworms with the strongest effects on surface feeding anecic earthworms and minor effects on soil feeding endogeic species. Remarkably, effects of plant community characteristics on the composition and age structure of earthworm communities varied between seasons. Moreover, plant diversity effects reported by a former study decreased and detrimental effects of grasses increased with time. The results indicate that plant community characteristics, such as declining diversity, indeed affect the structure of earthworm communities; however, loss of key plant functional groups is likely to be more important than plant species number per se. However, in frequently disturbed ecosystems plant species richness might be important for the recovery and resilience of belowground functions. Moreover, the results accentuate the importance of long-term repeated measurements to fully appreciate the impacts of plant community composition and diversity on ecosystem properties. Single point observations may be misleading and potentially mask the complexity of above-belowground interrelationships. (C) 2009 Elsevier Ltd. All rights reserved
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
Ammonia (NH₃) and nitrous oxide (N₂O) emissions from agricultural soils as affected by production management
Get PDFThe goal of this research was to quantify event-based NH₃ and N₂O emissions in various farming systems and to propose emission-avoidance strategies.
Emission measurements were made on pasture land (Allgaeu, Hohenheim) and on cultivated fields (Hohenheim, Biberach). These measurements were made after applying organic and mineral fertilizers, after incorporating crop residues, and after freeze / thaw cycles; furthermore, experiments were conducted using container plants of different species (leguminous, and non-leguminous) and different fertilizers.
NH3 emissions data was gathered under field conditions using the wind tunnel method and the IHF method (Integrated Horizontal Flux). In the container experiments, data was gathered by taking photo-acoustic measurements. N₂O emissions data was compiled using closed chambers (Hohenheim measuring chambers) and using an open-chamber system in which an exchange occurred between the air in the chambers and the ambient air. N₂O levels were determined using a gas chromatograph or by photo-acoustic measurements. The NH₃ emissions after applying liquid manure to pasture land varied between 11 and 40% of the total nitrogen applied. Emission levels of less than 20% occurred when it rained shortly after spreading liquid manure causing it to be washed into the soil. The application technique (splash plate, surface banding and liquid manure injection) had no apparent influence on NH₃ emissions under these conditions.
The N₂O emissions after liquid manure fertilization on pasture land in Hohenheim were 0.16% of the total NH4+-N. In comparison, the emissions in the Allgäu were between 1.7 and 2.3% of the total NH4+-N applied. Liquid manure injection led to higher emissions as did application using a splash plate. In the Allgäu, the N₂O emissions after mineral-nitrogen fertilization were markedly lower (0.3 to 0.8% of applied N) than after liquid manure application. In Hohenheim, the nitrogen form had no distinct influence on the emissions (<0.16% of applied N). Definitive differences between the two locations were observed during the experiments. These differences were based on N₂O losses due to the respective soil and weather conditions (precipitation, temperature). The higher emissions after applying liquid manure compared to those after applying mineral nitrogen fertilizer are explainable in that aside from the nitrogen compounds found in liquid manure, carbon compounds which promote the microbial formation of N₂O were also entering the soil.
The NH3 emissions after liquid manure fertilization on cultivated fields using a splash plate varied between 25 and 35% of the applied NH4+-N. By using a slurry cultivator which combines application with immediate incorporation, the NH3 emissions can be clearly reduced to 6% of the applied NH4+-N. Application with a drag hose, in comparison to using a splash plate, did not always result in an emission reduction; however, in taller plants, a readable emission reduction was measured.
The N₂O emissions after liquid manure application on cultivated fields varied between 0.1 and 2.2% of the applied NH4+-N whereby the emissions after guided application with the drag hose were always higher than after using a splash plate. Mineral fertilizer had lower N2O emissions (<0.13% of applied N), especially when ammonium fertilizer was brought out in combination with a nitrification inhibitor.
The incorporation of green manure crops notedly increased N₂O emissions. N₂O emission after the incorporation of legumes was especially high. In the container experiments, a diurnal rhythm of the N₂O and NH₃ flows in growing rape and vetch was observed. This indicated a stomatal flow of these gaseous nitrogen forms.
N₂O emissions also occurred outside of the vegetation period at temperatures between 0 and 5°C, with the N₂O emissions from the nitrogen fertilized parcels being greater than the emissions from the unfertilized parcels. In container experiments, the N₂O emissions after freeze / thaw cycles were greater from white clover than from perennial rye grass. In fallow soil columns, the N₂O emissions after freeze / thaw cycles were especially high if the content of nitrate and water-soluble organic carbon in the soil was large.
The results of this research show that the emission of nitrogen-containing compounds after organic and inorganic fertilization can be reduced through application methods (immediate incorporation), appropriate fertilization technology (addition of nitrification inhibitors), but also through fertilizer application under favourable weather conditions to include seasonal and volume adjustment of the fertilizer based on the growth requirements of the plants. Because high N₂O emissions can also occur at low temperatures, cultivation practices that influence the availability of mineral nitrogen and easily degradable organic substances in the soil during cold weather have a large impact on the N₂O emissions from agricultural land.Ziel der Untersuchungen war es, ereignisbezogene Emissionen an NH₃ und N₂O in landwirtschaftlichen Betriebssystemen zu erfassen. Messungen wurden bei der Ausbringung von Flüssigmist sowie bei mineralischer Düngung auf Acker und Grünland durchgeführt. Des Weiteren fanden N₂O-Emissionen während Frost / Tau-Zyklen statt. Der Einfluss von Pflanzenbeständen auf den NH₃- und N₂O-Haushalt wurde ebenfalls untersucht. Die Untersuchungen fanden auf Standorten im Allgäu, Oberschwaben, in Hohenheim (Filderebene) sowie in Gefäßversuchen statt.
Die NH₃-Emissionen nach Flüssigmistdüngung auf Grünlandflächen variierten zwischen 11 und 40% des ausgebrachten NH4+-N. Niedrige Emissionen (< 20%) traten immer dann auf, wenn kurz nach der Düngung Niederschläge auftraten und somit der Flüssigmist in den Boden eingeschwemmt wurde. Die Ausbringungstechnik (Prallteller, Schleppschlauch, Gülleinjektion) hatte unter diesen Bedingungen keinen deutlichen Einfluss auf die NH₃-Emission.
Die N₂O-Emission nach Flüssigmistdüngung auf Grünland lag am Versuchstandort Hohenheim bei 0,16% des ausgebrachten NH4+-N. Im Vergleich dazu lagen die Emissionen im Allgäu zwischen 1,7 und 2,3% des ausgebrachten NH4+-N. Gülleinjektion führte zu höheren N₂O-Emissionen als die Ausbringung mit dem Prallteller. Im Allgäu war die N₂O-Emission nach mineralischer N-Düngung deutlich geringer (0,3 bis 0,8% des gedüngten N) als nach Gülledüngung. Die N-Düngerform in Hohenheim hatte keinen deutlichen Einfluss auf die Emissionen (<0,16% des gedüngten N). Es zeigten sich somit deutliche Unterschiede zwischen den beiden Versuchsstandorten bezüglich der N₂O-Verluste, die zum einen auf die unterschiedlichen Bodeneigenschaften und zum anderen auf die unterschiedlichen Witterungsbedingungen (Niederschlag, Temperatur) während der Versuche zurückzuführen sind. Die gemessenen höheren Emissionen nach Düngung von Flüssigmist im Vergleich zu mineralischen N-Düngern sind dadurch zu erklären, dass mit dem Flüssigmist neben N auch C-Verbindungen in den Boden gelangen, die sich fördernd auf die mikrobielle N₂O-Bildung auswirken.
Die NH₃-Emissionen nach Flüssigmistdüngung auf Ackerflächen mit dem Prallteller variierten zwischen 25 und 35% des ausgebrachten NH4+-N. Durch Ausbringung mit einem Güllegrubber, bei dem eine sofortige Einarbeitung des Flüssigmistes im selben Arbeitsgang erfolgte, wurden die NH3-Emissionen deutlich vermindert (6% des ausgebrachten NH4-N). Die Ausbringung mit dem Schleppschlauch führte im Vergleich zur Pralltellerausbringung nicht immer zu einer Verringerung der Emissionen. In höheren Pflanzenbeständen allerdings wurden mit dem Schleppschlauch geringere NH₃-Emissionen gemessen.
Die N₂O-Emissionen nach Flüssigmistdüngung auf Ackerflächen variierten zwischen 0,1 und 2,2% des ausgebrachten NH4-N, wobei die Emissionen nach platzierter Ausbringung mit dem Schleppschlauch immer höher waren als nach Ausbringung mit dem Prallteller. Mineralische Düngung war mit geringerer N₂O-Emission verbunden (<0,13% des ausgebrachten N), vor allem wenn Ammoniumdünger zusammen mit einem Nitrifikationshemmstoff ausgebracht wurden.
Die Einarbeitung von Zwischenfrüchten führte zu einer deutlichen Erhöhung der N₂O-Emission. Dabei war die Emission nach Einarbeitung von Leguminosen besonders hoch. Bei Gefäßversuchen zeigte sich eine diurnale Rhythmik der N₂O- und NH₃-Flüsse in wachsenden Raps- und Wickebeständen, die als Hinweis für einen stomatären Fluss dieser N-Verbindungen gewertet werden können.
Auch bei Temperaturen zwischen 0 und 5°C, also außerhalb der Vegetationszeit, traten N₂O-Emissionen auf, die auf N-gedüngten Ackerflächen höher waren als auf ungedüngten Flächen. In Gefäßversuchen war nach Frost / Tau-Ereignissen die N₂O-Emission aus einem Weißkleebestand (Pflanzen und Boden) höher als aus einem Weidelgrasbestand (Pflanzen und Boden). In unbewachsenen Bodensäulen traten nach Frost / Tau-Ereignissen nur dann besonders hohe N₂O-Emissionen auf, wenn die Bodengehalte an Nitrat und wasserlöslichem organischen Kohlenstoff hoch waren.
Aus den Ergebnissen wird gefolgert, dass die Emissionen von NH₃ und N₂O nach organischer und anorganischer N-Düngung durch geeignete Ausbringungstechnik (unmittelbare Einarbeitung), geeignete Düngertechnologie (z.B. Zusatz von Nitrifikationshemmstoffen) sowie durch Ausbringung bei günstiger Witterung und gute zeitliche und mengenmäßige Anpassung der Düngung an den wachstumsbedingten Bedarf der Pflanzen verringert werden können. Da auch bei tiefen Temperaturen hohe N₂O-Emissionen auftreten können, haben pflanzenbauliche Maßnahmen, welche die Verfügbarkeit an mineralischem N und leicht abbaubarer organischer Substanz im Boden während der kalten Jahreszeit beeinflussen, eine große Bedeutung für die N₂O-Emission von landwirtschaftlichen Nutzflächen
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
Mineral Management in African Indigenous Vegetable Production Systems
Get PDFDurch ihre Umwelt- und Nährwertvorteile erweckten Afrikanische indigene Blattgemüse – „African Indigenous Vegetables“ (AIV) in letzter Zeit Aufmerksamkeit als „Supergemüse“ (Cernansky 2015). Da mehrere Spezies aus unterschiedlichen botanischen Familien innerhalb der AIVs vertreten sind, ist ein besseres Verständnis Spezies spezifischer Eigenschaften, wie z.B. Ernährungswert und agronomischem Management nötig, um diese Vorteile voll ausschöpfen zu können. In dieser Arbeit haben wir Afrikanisch indigene Blattgemüsearten aus fünf Familien, inklusive C3 and C4 Spezies und Leguminosen und nicht-Leguminosen (Brassica carinata/Cruciferae - Ethiopian Kale, Amaranthus cruentus/Amaranthaceae - Amaranth, Vigna unguiculata/Leguminosae - Cowpea, Solanum scabrum/Solanaceae - African Nightshade, Cleome gynandra/Capparaceae - Spiderplant) mit einer importierten und in Kenia häufig angebauten Gemüseart (Brassica oleracea acephala/Cruciferae - Exotic Kale) verglichen. Wir betrachteten die Pflanzenarten hinsichtlich ihrer Konzentrationen an wertgebenden und toxischen Elementen in Blättern als Index für den Nährwert, ihrer Reaktionen auf unterschiedliche zur Verfügung gestellten Mengen und Formen an Phosphor (P) als Index für die Adaptation an suboptimale chemische Bodenbedingungen und ihre erntebedingten Nährstoffausfuhren aus dem Boden als Index für den Düngerbedarf. Die Arbeit war in das interdisziplinäre Forschungsprogramm HORTINLEA (Horticultural Innovation and Learning for Improved Nutrition and Livelihood in East Africa) eingebunden.African Indigenous Vegetables (AIVs) have recently captured considerable attention as “super vegetables” due to their nutritional and environmental benefits (Cernansky 2015). As AIVs include many species belonging to different botanical families, more species-specific knowledge e.g. on nutritional value and agronomic management is needed to fully exploit those benefits. In this thesis we compared leafy AIV species from five families including C3 and C4 species, and a legume and non-legume species (Brassica carinata/Cruciferae - Ethiopian kale, Amaranthus cruentus/Amaranthaceae - amaranth, Vigna unguiculata/Leguminosae cowpea, Solanum scabrum/Solanaceae - African nightshade, Cleome gynandra/Capparaceae - spider plant) with a non-indigenous species, which is commonly grown in Kenya (Brassica oleracea acephala/Cruciferae - “exotic kale”). We compared the leaf concentrations of beneficial nutrients and heavy metals as an index for the nutritional value, the performance under different rates and forms of phosphorus (P) supply as an index for adaptation to suboptimal chemical soil conditions, and the harvest-related nutrient outflow from soil as an index for fertilizer need. The thesis was embedded in the interdisciplinary research program HORTINLEA (Horticultural Innovation and Learning for Improved Nutrition and Livelihood in East Africa)
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