1,720,994 research outputs found
Characterization of Root System Architectures from Field Root Sampling Methods
No full textBackground and objectives: The root system architecture (RSA) of a plant determines the plant’s ability to capture resources efficiently from the soil and directly linked to plant performance. The development and distribution of plant’s root systems are determined by the soil and surrounding environmental conditions. With the emerging methods of phenotyping techniques and the necessity of improving crop yield with limited resources, root phenotyping for developing new genotypes is given increasing attention to fulfill the increasing food demand of the world. Therefore, characterizing the behavior of root system with its surrounding environment and identifying beneficial traits are of attention in the agricultural industry. However, obtaining the information about root systems and their interaction with soil of all stages of root systems of field-grown crops is a challenging task because of the hidden nature of roots. Traditionally, the root information is extracted from field root sampling methods, which provide limited information about root growth and distribution. Therefore, obtaining a wide range of information such as the entire root system architecture can be identified as one of the main challenges in this regard. Moreover, the influence of soil and climatic factors on root growth has not been studied extensively. Thus, estimating distribution and functions of root systems that grow in different soil and climatic conditions are poorly understood. Root architecture models are becoming increasingly popular to study root growth and its functions successfully to understand and explain the mechanisms of root growth functions and to be used as a tool for exposing “hidden” root systems. Therefore, in this study, we demonstrate the use a RSA model to characterize root system traits from classical field root sampling schemes based on synthetic experiments and evaluate the differences in simulated root growth patterns and measured dynamic root development data in terms of different crops, soil, and environmental conditions.
Materials and Methods: The quantification of parameter sensitivities was conducted based on a synthetic experiment that mimics the root growth and root sampling procedure in the real field. The root system architecture (RSA) model CRootBox was used along with root architecture parameters to simulate winter wheat and maize root systems in a virtual field plot, similar to real field practices and subsequently used sampling methods; soil coring, root counting in trenches and weekly observation of roots through rhizotubes from a camera to sample roots virtually. Then, the sampling data was converted to root system measures to investigate the parameters of RSA that are sensitive to root system measures. Moreover, the principal component analysis (PCA) was carried out to understand the parameter correlations. The selected most sensitive parameters of RSA of winter wheat from core sampling method were estimated with the Markov chain Monte Carlo DREAM(Z S) sampler. Since the stochasticity of forward model leads to unstable log-likelihood estimates, we averaged the log-likelihood of 32 forward model runs and modified the MCMC acceptance mechanism. Furthermore, the log-likelihood was inflated to account the unknown data dependencies that cause the overfitting problem. After 15000 iterations, we compared the differences between true parameter values and posterior distribution of estimated parameters. To evaluate the influence of soil and climatic factors on root growth of winter wheat and maize crops, we carried out field experiments to measure root growth in two different soil types and collected data from the rhizotron facility in Selhausen, Germany. The collected data were used to simulate root growth based on functions implemented in CRootBox RSA model to compare the differences between measured and simulated data, and to investigate whether root simulation is representative of real field measurements.
Results: The sensitivity analysis results indicate that most of the parameters of zero-order roots are the most sensitive; especially number (NB), maximum length (maxl0 ), inter-branch distance (ln0 ), and elongation rate (r0 ) of zero-order toots and the higher-order roots are less sensitive to characteristic root system measures. The PCA analysis results indicate parameter pairs, such as number (NB)- inter-branch distance (ln0 ), gravitropism (tr0 )-insertion angle (theta0 ) of zero-order roots, are highly correlated. Bayesian sampling for posterior took a long inversion run time (3 weeks for three chains run in 32 parallel processors). The approximate posterior distributions of NB, maxl0, ln0, r0, theta0 parameters are narrowly centered and the other parameters show large parameter uncertainty. A few of the estimated parameters of zero-order roots show approximate posterior distributions that are narrowly centered around true parameter values. Yet the other zero-order and higher-order root parameters are not well resolved and show a large posterior uncertainty. The field measurements indicate significant differences in root length density (RLD) between the root growth in silty loam and stony soil. A higher root length density values were reported in root growth in silty loam soil than the stony soil of both wheat and maize crops and higher development of roots in depth below 60 cm and lower amounts of roots within the first 40 cm in silty loam soil was reported. The simulation results are not representative of measured data and the differences observed in measured data are not successfully reproduced by the model.
Conclusions: The root growth of the same type of crop could alter significantly with the growth medium and surrounding environmental conditions. However, these differences are not well incorporated into root growth models. Moreover, root length density measurements that are obtained from minirhizotron methods require reviewing thoroughly for use in simulation studies due to lack of calibration for converting root density to root length density values and the influence of tubes, soil conditions that alter root growth patterns of rhizotron methods should be investigated properly. The classical field sampling methods contain enough information about the root system traits, or root architectures parameters of zero-order roots such as NB, maxl0, ln0, r0 and Bayesian inference of core sampling data could be used to characterize some of the zero-order roots of wheat crop
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Zwischenfruchtbau an wasserlimitierten Standorten: eine Feld- und Modellierungsstudie zu hydrologischen und Bodenstruktureffekten von Zwischenfrüchten und ihrer Auswirkung auf die Wasserbilanz
No full textZwischenfruchtbau ist eine verbreitete Agrarumweltmaßnahme zum Boden- und Grundwasserschutz. Ziel der Studie war die Analyse des Wasserverbrauchs durch Zwischenfrüchte unter semiariden Bedingungen für ein verbessertes Management an wasserlimitierten Standorten. Biomassebildung, Bodenbedeckung und Wurzelparameter von Phacelia, Winterwicke, Roggen und Senf wurden charakterisiert. Effekte auf die Wasserbilanz wurden mit einer Feldmessstelle untersucht und detaillierte Messungen der Infiltration im Makroporenbereich durchgeführt. Die Wasserdynamik wurde mit der FAO Pflanzen-Koeffizienten-Methode sowie dem Modell HYDRUS 1D analysiert. Biomassebildung und Bodenbedeckung von Senf, mit starker Haupt- und dichten Seitenwurzeln, erwiesen sich am stabilsten gegenüber Trockenheit. Wicke zeigte eine geringe Wurzeldichte, jedoch eine homogene Tiefenverteilung, die eine hohe Biomassebildung erlaubte. Das Wurzelsystem von Phacelia war nahe der Sprossbasis konzentriert und nahm in vertikale und horizontale Richtung rasch ab. Roggen erreichte auch unter günstigen Bedingungen eine geringe Bodenabdeckung im Herbst, zeigte jedoch eine hohe Durchwurzelungsintensität. Bei herbstlicher Trockenheit lag die Verdunstung der Begrünungen über der Brache, wobei der Pflanzenanteil nur zwischen 17,6 % und 52,6 % der gesamten Evapotranspiration ausmachte. Wasseranteilunterschiede zur Brache reduzierten sich über Winter auf 2,8 %. Die Infiltration im Makroporenbereich zeigte eine hohe räumliche und zeitliche Variabilität. Es konnte jedoch eine Makroporenstabilisierung durch die Zwischenfrüchte gezeigt werden. Die Ergebnisse bestätigen die Möglichkeit des Zwischenfruchtbaus in semiariden Gebieten ohne überhöhtes Risiko von Ertragsverlusten. Stabilisierung der hydraulischen Bodeneigenschaften über Winter und Verringerung der Bodenverdunstung durch eine rasche Bodenbedeckung im Spätsommer tragen zu einem Ausgleich des potentiell höheren Wasserentzugs während der Wachstumszeit der Begrünungen bei.Cover cropping is a common agro-environmental instrument for soil and groundwater protection. The objective of this study was to assess the risk of soil water depletion by cover crops in a semi-arid environment to improve management for water limited conditions. Aboveground biomass, soil cover and rooting parameters of phacelia, hairy vetch, rye and mustard were characterized. Soil water status under the cover crops and a fallow control was monitored with a field measurement site and infiltration in the macropore range was investigated in detail. Water dynamics were analysis using the FAO Dual Crop Coefficient method and the model HYDRUS 1D. Mustard was most stable under dry conditions with an intense vertical and lateral root system. Vetch had a low rooting density, but a homogeneous depth distribution of roots that could sustain a high biomass growth. The root system of phacelia was intense near the stem base with a high decrease in the vertical and horizontal direction. Rye had only low soil cover before winter, but provided a high root biomass and dense rooting of the soil. Cover crops showed a higher cumulative evapotranspiration compared to fallow under dry conditions in autumn. Plant transpiration accounted for only 17.6 % to 52.6 % of total evapotranspiration. Soil moisture differences to fallow during cover crop growth were reduced over winter to 2.8 % in spring. Water infiltration in the macropore range showed high temporal and spatial variability. A certain stabilization of macropores over winter was found for the cover crops. The study showed that cover cropping in a semi-arid region is feasible without higher risk of yield losses due to water storage depletion. Stabilization of soil structure related hydraulic properties over winter and the reduction of evaporation losses in late summer by plants with a fast canopy cover contribute to equilibrate potential higher water extraction from deep soil layers during the main growing period of the cover crops.submitted by Gernot BodnerAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheWien, Univ. für Bodenkultur, Diss., 200
Zwischenfruchtbau an wasserlimitierten Standorten: eine Feld- und Modellierungsstudie zu hydrologischen und Bodenstruktureffekten von Zwischenfrüchten und ihrer Auswirkung auf die Wasserbilanz
No full textZwischenfruchtbau ist eine verbreitete Agrarumweltmaßnahme zum Boden- und Grundwasserschutz. Ziel der Studie war die Analyse des Wasserverbrauchs durch Zwischenfrüchte unter semiariden Bedingungen für ein verbessertes Management an wasserlimitierten Standorten. Biomassebildung, Bodenbedeckung und Wurzelparameter von Phacelia, Winterwicke, Roggen und Senf wurden charakterisiert. Effekte auf die Wasserbilanz wurden mit einer Feldmessstelle untersucht und detaillierte Messungen der Infiltration im Makroporenbereich durchgeführt. Die Wasserdynamik wurde mit der FAO Pflanzen-Koeffizienten-Methode sowie dem Modell HYDRUS 1D analysiert. Biomassebildung und Bodenbedeckung von Senf, mit starker Haupt- und dichten Seitenwurzeln, erwiesen sich am stabilsten gegenüber Trockenheit. Wicke zeigte eine geringe Wurzeldichte, jedoch eine homogene Tiefenverteilung, die eine hohe Biomassebildung erlaubte. Das Wurzelsystem von Phacelia war nahe der Sprossbasis konzentriert und nahm in vertikale und horizontale Richtung rasch ab. Roggen erreichte auch unter günstigen Bedingungen eine geringe Bodenabdeckung im Herbst, zeigte jedoch eine hohe Durchwurzelungsintensität. Bei herbstlicher Trockenheit lag die Verdunstung der Begrünungen über der Brache, wobei der Pflanzenanteil nur zwischen 17,6 % und 52,6 % der gesamten Evapotranspiration ausmachte. Wasseranteilunterschiede zur Brache reduzierten sich über Winter auf 2,8 %. Die Infiltration im Makroporenbereich zeigte eine hohe räumliche und zeitliche Variabilität. Es konnte jedoch eine Makroporenstabilisierung durch die Zwischenfrüchte gezeigt werden. Die Ergebnisse bestätigen die Möglichkeit des Zwischenfruchtbaus in semiariden Gebieten ohne überhöhtes Risiko von Ertragsverlusten. Stabilisierung der hydraulischen Bodeneigenschaften über Winter und Verringerung der Bodenverdunstung durch eine rasche Bodenbedeckung im Spätsommer tragen zu einem Ausgleich des potentiell höheren Wasserentzugs während der Wachstumszeit der Begrünungen bei.Cover cropping is a common agro-environmental instrument for soil and groundwater protection. The objective of this study was to assess the risk of soil water depletion by cover crops in a semi-arid environment to improve management for water limited conditions. Aboveground biomass, soil cover and rooting parameters of phacelia, hairy vetch, rye and mustard were characterized. Soil water status under the cover crops and a fallow control was monitored with a field measurement site and infiltration in the macropore range was investigated in detail. Water dynamics were analysis using the FAO Dual Crop Coefficient method and the model HYDRUS 1D. Mustard was most stable under dry conditions with an intense vertical and lateral root system. Vetch had a low rooting density, but a homogeneous depth distribution of roots that could sustain a high biomass growth. The root system of phacelia was intense near the stem base with a high decrease in the vertical and horizontal direction. Rye had only low soil cover before winter, but provided a high root biomass and dense rooting of the soil. Cover crops showed a higher cumulative evapotranspiration compared to fallow under dry conditions in autumn. Plant transpiration accounted for only 17.6 % to 52.6 % of total evapotranspiration. Soil moisture differences to fallow during cover crop growth were reduced over winter to 2.8 % in spring. Water infiltration in the macropore range showed high temporal and spatial variability. A certain stabilization of macropores over winter was found for the cover crops. The study showed that cover cropping in a semi-arid region is feasible without higher risk of yield losses due to water storage depletion. Stabilization of soil structure related hydraulic properties over winter and the reduction of evaporation losses in late summer by plants with a fast canopy cover contribute to equilibrate potential higher water extraction from deep soil layers during the main growing period of the cover crops.submitted by Gernot BodnerAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheWien, Univ. für Bodenkultur, Diss., 200
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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