1,721,080 research outputs found
Recent advances in crop modelling to support sustainable agricultural production and food security under global change
No full textGrowth of Individual Tomato Fruits under Assimilate Limitation Associated with Successively-later Set Fruits
Full text linkThe time course of growth of individual tomato fruits (Solanum lycopersicum) was analyzed in relation to the fruit initiation date and cumulative degree days of growth. Experimental data of dry weight (DW), fresh weight (FW), radial diameter (FDIAM), and dry matter concentration (DMC) of three different cohorts of fruits of determinate fresh-market tomato cultivar Florida 47 were determined under field conditions in Florida during spring of 2006 and 2007. Successively later cohorts (1 week intervals) had longer lags prior to rapid growth, slower maximum growth during the rapid phase, and smaller DW, FW, and FDIAM at maturity. These growth patterns were analyzed by fitting the data to a three-parameter Gompertz function for DW, FW, and FDIAM, and to a four-parameter modified Gompertz function for DMC. The good agreement of predicted and measured values indicates that the growth of individual tomato fruits followed the classical S-shaped Gompertz function. The Gompertz function was suitable to describe the slow growth that occurs in tomato fruits immediately after fertilization. The equation was able to predict the increasing duration of this lag and slower maximum growth and smaller final DW, FW, and size for successively later initiated cohorts of fruits. These results confirm the role of sink-source relationships (time of fruit set) on the growth of tomato fruits over time. This study will provide information potentially useful to improve existing tomato crop growth models that are presently limited because they do not predict practical outputs such as fresh weight and size of individual fruits.Fil: Rybak, Maria Raquel. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cerro Azul; ArgentinaFil: Boote, Kenneth J. University of Florida. Department of Agronomy; Estados UnidosFil: Jones, James W. University of Florida. Department of Agricultural and Biological Engineering; Estados Unido
Editorial Introduction to the Special Issue “Modelling cropping systems under climate variability and change: impacts, risk and adaptation”
No full textImproving a Tomato Growth Model to Predict Fresh Weight and Size of Individual Fruits
Full text linkTesis para obtener el grado de Doctor (PhD), de la University of Florida, en 2009A new version of the CROPGRO-Tomato model was developed to include a subroutine for predicting dry matter concentration, fresh weight and size of fruits over time. This subroutine builds on already existing crop model predictions of dry mass per fruit and fruit thermal age. The model was calibrated with field data obtained on tomato cultivar ‘Florida 47’ in Gainesville Florida during spring 2007 and evaluated with an independent data set obtained during spring 2006. The dynamics of dry weight accumulation, fresh weight, dry matter concentration, and fruit size were simulated by the model and compared with independent data of fruits tagged at anthesis in the field study at three successive weekly dates. These results demonstrated that the model was able to explain and predict the time-series growth and development of individual fruits on a cohort basis, to include delayed growth, slower growth, and smaller size of
progressively later-set fruits. Overall, the standard deviation of model error was less than 20 percent of the mean for all the variables evaluated (dry weight, fresh weight, fruit dry matter concentration, and fruit size). In addition, the Willmot index was always above 0.9.
The effects of water and N stress on the growth of individual fruits were studied by withholding drip irrigation for three periods and withholding N supply beginning at 14 days after transplanting. The main effects of water stress on the growth of individual fruits were reduced fresh mass and size and an increase in dry matter concentration, while N stress on the other hand, caused a decrease in dry matter concentration of fruits. The existing water and N stress factors in the CROPGRO model were linked to the new equations that affect dry weight growth and dry matter concentration of individual fruits, and were successfully used to predict the stress-induced
variations in dry matter concentration, and reductions in dry and fresh weight growth and size of single fruits. The newly-added subroutine for predicting dry matter concentration, fruit fresh weight, and size, along with coupling to water and N stresses make the improved model a valuable risk assessment tool for predicting fresh market production and quality of tomato.EEA Cerro AzulFil: Rybak, Maria Raquel. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Cerro Azul; Argentin
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
Adapting the CROPGRO model to simulate alfalfa growth and yield
Full text link14 Pags.- 6 Figs.- 6 Tabls. Available freely online through the author-supported open access option.
Copyright © 2018 by the American Society of Agronomy. This is an open access article distributed under the CC BY-NC-ND license.Despite alfalfa’s global importance, there is a dearth of crop simulation models available for predicting alfalfa growth and yield with its associated composition. The objectives of this research were to adapt the CSM-CROPGRO Perennial Forage Model for simulating alfalfa growth and yield and to describe model adaptation for this species. Data from six experimental plots grown under sprinkler irrigation in the Ebro valley (Northeast Spain) were used for model adaptation. Starting with parameters for Bracharia brizantha, the model adaptation was based on values and relationships reported from the literature for cardinal temperatures and dry matter partitioning. A Bayesian optimizer was used to optimize temperature effects on photosynthesis and daylength effects on partitioning and an inverse modeling technique was employed for nitrogen fixation rate and nodule growth. The calibration of alfalfa tissue composition was initiated from soybean composition analogy but was improved with values from alfalfa literature. There was considerable iteration in optimizing parameters for the processes outlined above where comparisons were made to measured data. After adaptation, the Root Mean Square Error and d-statistic of harvested herbage averaged across 58 harvests (yield range: 990–4617 kg ha–1) were 760 kg ha–1 and 0.75, respectively. In addition, good agreement was observed for Leaf Area Index (LAI) (LAI range: 0.1–6.7) with d-statistic of 0.71. Simulated belowground mass was within the range of literature values. The results of this study showed that CROPGRO-PFM-Alfalfa can be used to simulate alfalfa growth and development. Further testing with more extensive datasets is needed to improve model robustness.This work was funded by the Ministry of Economy and
Competitiveness of the Spanish Government through the research
grants (AGL2013-48728-C2-2-R). We thank this Ministry for
awarding Wafa Malik a predoctoral fellowship and financial support
for research abroad internship at the University of Florida.Peer reviewe
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
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