1,720,973 research outputs found
Dispositivo per il monitoraggio di superfici vegetali
No full textLa presente invenzione si riferisce al settore della diagnostica ambientale poiché fornisce un dispositivo che consente il monitoraggio dello stato fisiologico dei tappeti erbosi e di altre tipologie di coperture naturali che può essere anche impiegato per una accurata caratterizzazione e gestione delle coperture vegetali quali ad esempio campi sportivi, aree verdi naturali o artificiali e il relativo
metodo
Detection of crop water status in mature olive orchards using vegetation spectral measurements
Get PDFLeaf/stem water potentials are generally considered the most accurate indicators of crop water status (CWS) and
they are quite often used for irrigation scheduling, even if costly and time-consuming. For this reason, in the last
decade vegetation spectral measurements have been proposed, not only for environmental monitoring, but also in
precision agriculture, to evaluate crop parameters and consequently for irrigation scheduling.
Objective of the study was to assess the potential of hyperspectral reflectance (450-2400 nm) data to predict the
crop water status (CWS) of a Mediterranean olive orchard.
Different approaches were tested and particularly, (i) several standard broad- and narrow-band vegetation indices
(VIs), (ii) specific VIs computed on the basis of some key wavelengths, predetermined by simple correlations and
finally, (iii) using partial least squares (PLS) regression technique.
To this aim, an intensive experimental campaign was carried out in 2010 and a total of 201 reflectance spectra,
at leaf and canopy level, were collected with an ASD FieldSpec Pro (Analytical Spectral Devices, Inc.) handheld
field spectroradiometer. CWS was contemporarily determined by measuring leaf and stem water potentials with
the Scholander chamber.
The results indicated that the considered standard vegetation indices were weakly correlated with CWS. On the
other side, the prediction of CWS can be improved using VIs pointed to key-specific wavelengths, predetermined
with a correlation analysis. The best prediction accuracy, however, can be achieved with models based on PLS
regressions.
The results confirmed the dependence of leaf/canopy optical features from CWS so that, for the examined crop, the
proposed methodology can be considered a promising tool that could also be extended for operational applications
using multispectral aerial sensors
Modeling olive ecophysiological response to soil water deficit.
No full textObjective of the work was to define critical thresholds of soil water status determined according to measured leaf and stem xilematic potentials, as well as tree transpiration. Furthermore, the performance of existing models, simulating the potential transpiration reduction coefficients as a function of the soil water status, was assessed. Soil water retention curve was used to determine soil matric potentials according to measured soil water contents. Transpiration was monitored with Thermal Dissipation Probes, whereas leaf and stem water potentials were measured with the Scholander chamber. An almost constant transpiration value was obtained for soil water contents higher than a critical threshold; lower and lower values of actual transpiration were recognized at decreasing soil water content. A similar threshold was obtained when xylematic potentials were considered. The best performance of models evaluating the potential transpiration reduction coefficient was obtained when non-linear functions are assumed
Modeling olive orchard response to water stress and definition of critical thresholds of soil water status.
No full textThe knowledge of the plant response to water stress is very important to predict the dynamic of potential
transpiration reduction under limited soil water condition. The water stress response is influenced by soil, plant
and climate and in particular by soil matric potential, hydraulic conductivity, osmotic head (in saline ecosystem)
and evapotranspirative atmospheric demand, as well as by root spatial distribution and plant properties.
The macroscopic approach, taking into account global stress indicator (relative transpiration, xylematic water
potential, etc), can allow to assess empirical functions, able to describe the plant response to water stress, on the
basis of the observed plant response to soil water status. Using the macroscopic approach it is not necessary to
evaluate separately difficult and time consuming soil and plant parameters, like the gradient of water potential at
the interface between the roots surface and the soil.
Modelling the plant response under water stress condition is crucial to identify the exact irrigation timing. In order
to assess the water stress functions, is necessary to estimate critical thresholds of soil water status, below which
plant transpiration starts to strongly decrease.
The main objective of the work is to investigate the relationships between soil matric potential and measured
transpiration, as well as to define the critical plant water status conditions, determined according to measured
leaf and stem xilematic potentials. Furthermore, the performance of existing models, simulating the relative
transpiration as a function of the soil matric potential, is assessed.
The soil water retention curve was used to determine, at the different depths, the soil matric potential according to
the measured of soil water contents obtained with capacitive sensors (Diviner 2000, Sentek).
Actual transpiration was monitored by measuring the sap flows with thermal dissipation probes (TDP), while the
leaf and stem water potentials were determined by using the Scholander pressure bomb.
The study area is located in the South-Western coast of Sicily (Italy); the dominant crop is represented by
table olive grove and it is characterized by typical Mediterranean semi-arid climate. According to the USDA
classification, the soil can be classified as silty clay loam. The investigation period included 2008 and 2009
irrigation seasons. Meteorological data were collected by means of a weather station of the SIAS (Servizio
Informativo Agrometeorologico Siciliano), located nearby the study area.
Experimental data allowed to define the critical threshold values of the soil water status (soil water content and
matric potential) below which the actual transpiration tends to reduce when soil water content decreases. For
values of soil water content greater than the critical threshold, the actual transpiration resulted almost constant. A
similar behaviour was observed when the xylematic potentials are used to quantify the crop water stress.
The investigation also showed that the best performance of the examined models, used to estimate transpiration,
can be obtained when non-linear models are considere
Modeling olive orchard response to water stress and definition of critical thresholds of soil water status
Get PDFThe knowledge of the plant response to water stress is very important to predict the dynamic of potential
transpiration reduction under limited soil water condition. The water stress response is influenced by soil, plant
and climate and in particular by soil matric potential, hydraulic conductivity, osmotic head (in saline ecosystem)
and evapotranspirative atmospheric demand, as well as by root spatial distribution and plant properties.
The macroscopic approach, taking into account global stress indicator (relative transpiration, xylematic water
potential, etc), can allow to assess empirical functions, able to describe the plant response to water stress, on the
basis of the observed plant response to soil water status. Using the macroscopic approach it is not necessary to
evaluate separately difficult and time consuming soil and plant parameters, like the gradient of water potential at
the interface between the roots surface and the soil.
Modelling the plant response under water stress condition is crucial to identify the exact irrigation timing. In order
to assess the water stress functions, is necessary to estimate critical thresholds of soil water status, below which
plant transpiration starts to strongly decrease.
The main objective of the work is to investigate the relationships between soil matric potential and measured
transpiration, as well as to define the critical plant water status conditions, determined according to measured
leaf and stem xilematic potentials. Furthermore, the performance of existing models, simulating the relative
transpiration as a function of the soil matric potential, is assessed.
The soil water retention curve was used to determine, at the different depths, the soil matric potential according to
the measured of soil water contents obtained with capacitive sensors (Diviner 2000, Sentek).
Actual transpiration was monitored by measuring the sap flows with thermal dissipation probes (TDP), while the
leaf and stem water potentials were determined by using the Scholander pressure bomb.
The study area is located in the South-Western coast of Sicily (Italy); the dominant crop is represented by
table olive grove and it is characterized by typical Mediterranean semi-arid climate. According to the USDA
classification, the soil can be classified as silty clay loam. The investigation period included 2008 and 2009
irrigation seasons. Meteorological data were collected by means of a weather station of the SIAS (Servizio
Informativo Agrometeorologico Siciliano), located nearby the study area.
Experimental data allowed to define the critical threshold values of the soil water status (soil water content and
matric potential) below which the actual transpiration tends to reduce when soil water content decreases. For
values of soil water content greater than the critical threshold, the actual transpiration resulted almost constant. A
similar behaviour was observed when the xylematic potentials are used to quantify the crop water stress.
The investigation also showed that the best performance of the examined models, used to estimate transpiration,
can be obtained when non-linear models are considered
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
Evaluating the performance of reference evapotranspiration equations with scintillometer measurements under Mediterranean climate and effects on olive grove actual evapotranspiration estimated with FAO-56 water balance model
Get PDFThe concept of reference potranspiration is widely used to support water resource management in
agriculture and for irrigation scheduling, especially under arid and semi-arid conditions. The Penman-Monteith
standardized formulations, as suggested by ASCE and FAO-56 papers, are generally applied for accurate
estimations of ETo, at hourly and daily scale. When detailed meteorological information are not available, several
alternative and simplified equations, using a limited number of variables, have been proposed (Blaney-Criddle,
HargreavesSamani, Turc, Makkinen and Pristley-Taylor).
In this paper, scintillometer measurements collected for six month in 2005, on an experimental plot under
“reference” conditions, were used to validate different ETo equations at hourly and daily scale. Experimental plot
is located in a typical agricultural Mediterranean environment (Sicily, Italy), where olive groves is the dominant
crop.
As proved by other researches, the comparison confirmed the best agreement between estimated and measured
fluxes corresponds to FAO-56 Penman-Monteith standardized equation, that was characterized by both the
lowest average error and the minimum bias. However, the analysis also evidenced a quite good performance of
Pristley-Taylor equation, that can be considered as a valid alternative to the more sophisticated PenmanMonteith
method.
The different ETo series, obtained by the considered simplified equations, were then used as input in the FAO-56
water balance model, in order to evaluate, for olive groves, the errors on estimated actual evapotranspiration ET.
To this aim soil and crop model input parameters were settled by considering previous experimental researches
already used to calibrate and validate the FAO-56 water balance model on olive groves, for the same study area.
Also in this case, assuming as the true values of ET those obtained using the water balance coupled with Penman-
Monteith ETo input values, the Priestley-Taylor equation, requiring a limited number of input meteorological
data, was characterized by the best performance if compared to the other equations used to evaluate ETo. Under
environments conditions similar to those considered therefore, according to the good performance associated
to the Priestley-Tailor approach, FAO-56 model can allow realistic estimation of ET, even in absence of a full meteorological dataset
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