1,721,019 research outputs found
Modelli di bilancio agro-idrologico per la previsione dello stress idrico di colture arboree mediterranee
Full text linkIl contributo si propone di dimostrare come l‟uso della modellistica agro-idrologica possa consentire una corretta previsione delle dinamiche di stress idrico di due importanti colture arboree Mediterranee (olivo e agrume), caratterizzate da una diversa risposta eco-fisiologica a condizioni di deficit idrico del suolo.
In particolare viene analizzata in dettaglio la tematica della modellizzazione della risposta eco-fisiologica delle due colture e viene affrontata la questione relativa all‟implementazione delle funzioni di stress all‟interno dei modelli di bilancio agro-idrologico di tipo a serbatoio, in modo da simulare l‟effettivo stato idrico della pianta.
Con riferimento alle colture esaminate, è nello specifico approfondita la schematizzazione della funzione di stress attraverso l‟analisi di lunghe serie di dati acquisiti nel corso di sperimentazione in campo, relative allo stato idrico del suolo (contenuti idrici volumetrici) e della pianta (potenziali idrici xilematici e flussi traspirativi).
È infine discussa l‟applicabilità del modello semplificato descritto nel quaderno FAO n. 56 (Allen et al., 1998) per la predizione delle dinamiche di stress idrico delle colture ed è approfondita l‟importanza che riveste una specifica schematizzazione della funzione di stress idrico nel miglioramento delle performance del modello.The contribute aims to demonstrate how agro-hydrological models are able to predict the water stress dynamics of two important Mediterranean arboreal crops, i.e. olive and citrus, characterized by different eco-physiological water stress response to soil water deficit conditions.
In particular, the topic related to the crop water stress function and its implementation into agro-hydrological bucket models is analyzed in order to improve the estimations of actual crop water status.
With reference to the examined crops, the proposed schematization of the water stress functions is based on long time series of field measurements of soil (volumetric water contents) and plant (xylem water potentials and transpiration fluxes) water status.
The applicability of the bucket model proposed by FAO (Allen et al., 1998) to predict the crop water stress dynamics is also discussed in order to emphasize the importance of a specific schematization of the stress function to improve the model's performance
Agro-hydrological models and field measurements to assess the water status of a citrus orchard irrigated with micro-sprinkler and subsurface drip systems
No full textCompared to the micro-sprinkler irrigation, traditionally used in citrus orchards, subsurface drip systems (SDS) allow increasing the water use efficiency (WUE); when coupled with water-saving strategies, like regulated deficit irrigation (RDI), further increase of WUE are possible.
Combining measurements of soil water content (SWC) and weather data with measurements of midday stem water potential (MSWP) makes it possible to identify irrigation scheduling parameters for the RDI. However, measurements of MSWP are destructive and time-consuming, and also require skilled operators. For all these reasons, the use of the agro-hydrological models, such as the FAO-56 model, can be considered a surrogate aimed at the indirect evaluation of soil and crop water status.
Objective of this work was to assess the potential of the FAO-56 model to predict soil and crop water status of a citrus orchard under subsurface drip and traditional micro-sprinklers and different irrigation strategies, as well as to identify the model outputs that can be used for irrigation scheduling purposes.
Experiments were carried out in a citrus orchard during 2018 and 2019. The field was irrigated with micro-sprinkler and SDS. In the latter, two different irrigation strategies, i.e. full and regulated deficit irrigation, were applied. A standard weather station and probes to measure SWC were installed in the orchard. Additionally, Predawn Leaf Water Potential and Midday Stem Water Potential were monitored.
After a site-specific calibration, the predicted average SWC fitted fairly well with the corresponding measured in the layer 0-50cm, with root mean square errors (RMSE) lower than 0.028 m3/m3. The performance of the model to identify the crop response to soil water deficit was also assessed by considering the observed similarity between the temporal dynamic of simulated crop water stress coefficient, Ks, with the measured MSWP. Even extending the analysis, the model was able to estimate the seasonal water stress integrals characterizing the examined treatments, demonstrating that even this variable can be used for irrigation scheduling purpose
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
Assessing actual evapotranspiration in irrigation districts using Landsat TM images and SEBAL model: Potential uses for irrigation monitoring
Full text linkSatellite imagery allows the observation of large land stretches and the acquisition of worthwhile information that can be used efficaciously in agro-hydrologic systems. On the other hand, remotely sensed data coupled with energy balance models represent reliable tools to estimate actual evapotranspiration (ET).
Objective of the research was to propose a methodology to estimate ET by using Landsat TM images and surface energy balance, thus allowing the monitoring of current irrigation practices and/or possible vegetation stress.
The proposed methodology was applied in an irrigation district managed by “Consorzio di Bonifica Agrigento 3”, Castelvetrano, Sicily (Italy), in which water is distributed by a pressurized distribution network operating on-turn.
Satellite information retrieved by a set of Landsat TM images allowed to implement the surface energy balance model (SEBAL) in order to map the spatial distribution of instantaneous ET over two main crops (olives and grapevines), during irrigation seasons (from May to September) 2009 and 2010. These instantaneous values were then up-scaled to daily values based on the hypothesis of self-preservation of evaporative fraction. Finally, daily acquisitions were used to derive ET within longer time intervals, by assuming the by assuming proportionality to temporal dynamics of the reference evapotranspiration (ET0) computed using standard ground meteo-data.
With reference to the acquisition days, the comparison between SEBAL outputs and maximum daily crop evapotranspiration (ETc) estimated with the FAO 56 approach, showed notable stress levels for both the investigated crops, except for the images acquired in May, when significant rainfall occurred in both years. Moreover, measurements of eddy covariance fluxes collected by a tower located in the district within an olive orchard, evidenced the general reliability of daily ET retrieved by the model and consequently the validity of the self-preservation hypothesis applied to upscale instantaneous ET. Even if the applied methodology can be considered a valuable tool to monitor irrigation practices, the availability of cloud-free satellite images, as well as the temporal frequency of sensing, are critical issues for the proposed applications
Soil structure and bypass flwo processes in a Vertsol under sprinkler and drip irrigation.
Full text linkIn this paper morphological and physical characteristics, as well as flow behaviour of a Mediterranean Vertisol under the influence of two different irrigation systems currently used for irrigation, i.e. drip and sprinkler systems, were compared. No differences in soil texture, compaction and in potential cracking were found on cores from the two fields. However, field application of methylene blue showed the presence of continuous macropores, penetrating up to depths of 20-25 cm from the soil surface, in the field where the drip system was in use (field 1). This was considered to be the pre-existing soil structure. Instead, macropores terminating at a depth ranging between 5 and 10 cm from the soil surface were observed in the sprinkler irrigated field (field 2). The same difference in terms of macropores' continuity was also observed on soil cores sampled from the two irrigated fields. The higher raindrop impact and the non-point water application involved in the sprinkler irrigation system were assumed to have determined, during several years, the different depth of penetration of the macropores in the two fields. A different hydraulic behaviour was evidenced by laboratory measurement of bypass flow on soil cores taken from the two fields. Specifically, higher values of the saturated hydraulic conductivity were found in the cores from the drip irrigated field compared to those sampled in the sprinkler field. In addition no bypass flow was measured in the columns under the sprinkler field, while high rates and amounts of bypass flow were obtained in the cores taken from the drip irrigated field. The different hydraulic behaviour observed in the cores taken from the drip and from the sprinkler irrigated field was in agreement with the difference in terms of macropores' continuity between the two fields. Being bypass flow a mechanism inducing leaching of solutes, results of this investigation suggest that irrigation systems affecting soil structure, and altering macropores' continuity, should be avoided in clay soils. (c) 2006 Published by Elsevier B.
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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