4,285 research outputs found
Adapting FAO-56 Spreadsheet Program to estimate olive orchard transpiration ?uxes under soil water stress condition
No full textSistema intelligente per la misura dei flussi evapotraspirativi reali
No full textScopo della presente invenzione è quello di fornire un dispositivo per la determinazione dell’evapotraspirazione reale della superficie vegetata di un terreno, migliorato rispetto a quelli descritti dalla tecnica nota.
Secondo l’invenzione, tale scopo viene raggiunto grazie ad un dispositivo comprendente:
- un evaporatore poroso composito, almeno una porzione del quale ha una resistenza al flusso di vapore acqueo che dipende da un parametro, detto evaporatore avendo una superficie superiore esposta all’atmosfera,
- un serbatoio di acqua liquida sottostante all’evaporatore al quale è connesso da un tubo di aspirazione, e provvisto di un misuratore di livello,
- un sensore di misura dell’umidità del terreno, e
- una “central process unit” (CPU) che è configurata per controllare detto parametro da cui dipende la resistenza al flusso di vapore acqueo attraverso l’evaporatore, in dipendenza dal valore di umidità del terreno rilevata da detto sensore
Estimation of water potential components and pressure-volume curve parameters - Goetz Program Recap
No full textOsmotic and turgor water potentials are the principal components of a global potential term; they are
usually measured by pressure methods in vegetative organs, like leaves or pieces of shoot. Considering
that the components of plant water potential have opposite sign (negative for osmotic and positive for
turgor water potential), the simple measurement of total water potential does not provide any information
about its components. To this aim, is therefore necessary to plot, together with the Pressure–Volume (P-
V) curve, the components of leaf water potential versus leaf water contents. In the literature, this kind of
plot is known as “Höfler diagram” (Richter, 1978), .
The knowledge of the P-V curve, allows to identify specific parameters (turgor loss point and osmotic
potential at saturation) indicating the drought tolerance of a certain vegetation species. Moreover,
volumetric bulk elastic modulus, reflecting the mechanical propertied of cell walls, can be
mathematically derived.
Proximal spectral reflectance in the visible, near-infrared, and shortwave-infrared (VIS–NIR–SWIR)
regions (350–2500 nm) have been successfully used for an accurate and rapid estimation of vegetation
water status, as well as of biochemical and bio-agronomic properties involved into important
physiological processes such as water exchange, photosynthesis, biochemistry of plant pigments, etc.
Estimation of energy status of water in vegetative organs via proximal spectral reflectance is a convenient
and rapid field-scale measurement approach, although it is applicable only to characterize the vegetation
surface. Despite several field and laboratory experimental studies have been investigated the interactions
between energy and water status, a poor scientific focus has been aimed to study the intrinsic interaction
between the energy and the elementary components of the vegetation water potential, as well as the
relationship between the energy and the mechanical properties of the cell walls. Only a research carried
out by Peñuelas et al. (1993) presented some considerations about the effects of volumetric elastic
module parameter on the reflectance response of gerbera plants. However, this study did not include the
parametric approach to estimate the behavior of vegetative organs expressed in terms of Pressure-Volume
curve.
Considering that the proximal spectral reflectance signatures contains information about vegetation water
status and biomass structure, it can be assumed that the parameters describing the P-V patterns should be
related to the vegetation spectral response
SYSTEM FOR THE DETERMINATION OF THE REAL EVAPOTRANSPIRATION OF A VEGETATED SURFACE
No full textThe present invention relates to a device for determining the real evapotranspiration (ETr) of a natural or cultivated vegetated surface.
US 2010/212 409 A1 describes an atmometer comprising an evaporator having an upper surface exposed to the atmosphere, a liquid water tank provided with a level meter and underlying the evaporator to which it is connected by a suction tube, a measurement sensor of the soil humidity value, and a CPU which controls the flow of water vapor through the evaporator depending on the soil humidity value.
An object of the present invention is to provide a device for determining the real evapotranspiration of the vegetated surface of a soil, improved with respect to those described by the prior art.
According to the invention, this object is achieved with a device comprising:
- a composite porous evaporator, at least a portion of which has a resistance to the flow of water vapor that depends on a parameter, said evaporator having an upper surface exposed to the atmosphere,
- a tank of liquid water underlying the evaporator to which it is connected by a suction tube, and provided with a level meter,
- a sensor for measuring the soil humidity, and
- a central processing unit (CPU) which is configured to control said parameter on which the resistance to the flow of water vapor through the evaporator depends, in dependence on the humidity value of the soil detected by said sensor
Modelli di bilancio agro-idrologico per la previsione dello stress idrico di colture arboree mediterranee
No full textIl 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
Farm scale application of EMI and FDR sensors to measuring and mapping soil water content
No full textSoil water content (SWC) controls most water exchange processes within and between the soil-plants-atmosphere continuum and can therefore be considered as a practical variable for irrigation farmer choices. A better knowledge of spatial SWC patterns could improve farmer’s awareness about critical crop water status conditions and enhance their capacity to characterize their behavior at the field or farm scale.
However, accurate soil moisture measurement across spatial and temporal scales is still a challenging task and, specifically at intermediate spatial (0.1–100 ha) and temporal (minutes to days) scales, a data gap remains that limits our understanding over reliability of the SWC spatial measurements and its practical applicability in irrigation scheduling.
In this work we compare the integrated EM38 (Geonics Ltd. Canada) response, collected at different sensor positions above ground to that obtained by integrating the depth profile of volumetric SWC measured with Diviner 2000 (Sentek) in conjunction with the depth response function of the EM38 when operated in both horizontal and vertical dipole configurations.
On a 1.0-ha Olive grove site in Sicliy (Italy), 200 data points were collected before and after irrigation or precipitation events following a systematic sampling grid with focused measurements around the tree. Inside two different zone of the field, characterized from different soil physical properties, two Diviner 2000 access tube (1.2 m) were installed and used for the EM38 calibration. After calibration, the work aimed to propose the combined use of the FDR and EMI sensors to measuring and mapping root zone soil water content.
We found strong correlations (R2 = 0.66) between Diviner 2000 SWC averaged to a depth of 1.2 m and ECa from an EM38 held in the vertical mode above the soil surface. The site-specific relationship between FDR-based SWC and ECa was linear for the purposes of estimating SWC over the explored range of ECa monitored at field levels.
Volumetric SWC changes in the root zone were observed by differencing the maps, where differences in the observed ECa are primarily the result of changes in soil water status. As with the data showed in the research, more structured patterns occur after wetting event, indicating the presence of subsurface flow or root water uptake paths.
A vision for the future at hydrological watershed scale is to combine EMI measurements with FDR-based sensor networks, the last with the scope to constrain calibration of the EMI measurements
Modelli di bilancio agro-idrologico per la previsione delle dinamiche di stress idrico di colture arboree Mediterranee
No full textDefining irrigation volumes and timing under slight or moderate water stress conditions
requires to monitor the water status in the soil–crop
system and identify indicators to guide irrigation
scheduling.
Leaf water potential (LWP) is a commonly used variable
to describe crop water status and, when measured
at pre-dawn or mid-day, is an indicator of any
instantaneous crop water stress condition. Even if leaf
water potential measurements are considered one of
the most reliable methods for direct determinations of
crop water status, these determinations are destructive
and time consuming and require skillful operators.
Agro-hydrological models can be considered an easyto-use
tool for indirect determination of soil and crop
water status, as well as to estimate other parameters
related to crop development. However, the application
of these models requires the preliminary calibration
and validation of the algorithms used for the different
processes occurring in the Soil-Plant-Atmosphere
continuum. Therefore, a reasonable use of the models
to predict crop water stress conditions should be
based on site-specific experimental investigations and
requires an improvement of sub-models related to the
specific crop response to changes in soil water deficit.
Several models have been proposed to quantify the
water stress coefficient as linear or nonlinear functions
of soil water status, expressed in terms of matric
potential or soil water depletion. For a certain crop,
the water stress function is applied once it is known
its shape and the thresholds values identifying the soil
water status beyond which crop water stress occurs
and the level of maximum stress.
This review aims to demonstrate how the use of agrohydrological
models is able to predict the water stress
dynamics of two important Mediterranean tree crops
(olive and citrus), which have a different eco-physiological
water stress response to soil water deficit conditions.
After examining the eco-physiological
response of both crops to soil water deficit, we
assessed the potential of FAO-56 agro-hydrological
model to identify crop water stress under different irrigation
management strategies.
The proposed the water stress functions are the result
of recent experiments based on long term series of
field measurements of soil (volumetric water content)
and plant (xylem water potential and transpiration
flows) water status of olive and citrus trees.
Experiments carried out during three years in a
Sicilian olive grove and a Valencian citrus orchard
allowed to identify the specific crop water stress
response to soil water deficit conditions and confirm
for citrus the original schematization proposed in
FAO-56 paper. Moreover, after evaluating the similarity
between the measured midday stem water potential
using the simulated crop water stress coefficient, the
fairly good performance of FAO-56 agro-hydrological
model to predict soil water content was proven.
The obtained results evidenced that the crop water
stress coefficient estimated by the model is used as a
suitable indicator to replace the tedious and time-consuming
field measurements of midday stem water
potential. On the other side, when specific crop water
stress function are implemented, the FAO-56 agrohydrological
model can predict soil water content and
the crop water requirement, even when water saving
strategies are used
Modelling eco-physiological response of table olive trees (Olea europaea L.) to soil water deficit conditions
No full textThe knowledge of crop response to water stress is crucial to predict transpiration reductions under limited soil water conditions and for a rational scheduling of irrigation.
In order to assess whatever water stress model, it is necessary to estimate critical thresholds of soil water status, below which plant transpiration starts to decrease.
The main objective of the work is to identify the shape and to determine the parameters of table olive orchards (Olea europaea, var. Nocellara del Belice) water stress function, assessed according to relative transpiration or leaf/stem water potential.
In order to assess different water stress functions describing the eco-physiological field response to soil water status, an experimental campaign was carried out in a farm located in South-West coast of Sicily. Meteorological data and soil and crop water status were monitored during irrigation seasons 2008 and 2009.
A value of soil matric potential of about −40 m was identified as the threshold below which actual transpiration decreases with decreasing soil water content. For values of soil matric potential higher than the critical threshold, actual transpiration resulted almost constant. A similar behavior was observed when the xylematic leaf/stem water potentials were used to quantify the crop water stress. Investigation also showed that the non-linear models better reproduced the initial phase of the transpiration reduction process; for the examined crop, in fact, convex shape models, typical of xerophytes, better reproduce the reductions of actual transpiration under the soil water deficit conditions recognized in the field
Indirect estimation of calibration equation parameters for Sentek Diviner 2000 capacitance probe by means of soil physical properties
No full textMeasurements of soil water content (SWC) are often used for irrigation scheduling. Accurate monitoring of SWC is
necessary, for example, to identify the exact irrigation timing and the amount of water volume to supply according
to the crop requirement.
The use of capacitance probes, measuring the apparent soil dielectric permittivity, indirectly related to soil water
status, have been increasing during the last decade, as proved by the numerous researches carried out to determine,
for different soil types, site-specific calibration relationships between SWC and the scaled frequency (SF) measured
by the sensor. However, for swelling/shrinking clay soils, there is a lack of knowledge on how the changes of
soil bulk density associated to variations of soil water content influence the apparent dielectric permittivity and
therefore the sensor calibration relationship, as a consequence of the different contribute that soil, water and air,
have on the measure provided by the sensor.
The main objectives of the work are i) to determine the site specific calibration equations for a Sentek Diviner 2000
capacitance probe for soils characterized by different texture, ii) to investigate on the effects of soil bulk density
and its variability with soil water content, on the calibration equation and iii) to proceed to the indirect estimation
of calibration parameters by means of easily-measurable soil physical properties.
Experiments were carried out on nine different soils collected from Sicilian irrigated area, characterized by a clay
percentage ranging between 9% and 45%. Undisturbed soil samples (25 cm diameter and 25 cm height), allowed to
determine, for each soil, the corresponding site-specific calibration equation. On the other hands, samples having
the same dimensions, but filled with sieved soil and compacted at two different bulk densities ( b), were used
to investigate on the effects of soil texture and bulk density on the measured SF. On each undisturbed or sieved
sample and for all the investigated soils, the shrinkage characteristic curve, b(U) and the U(SF) relationship were
contextually determined.
The experiments on sieved soil samples, allowed to verify that the scaled frequency measured by the sensor also
depends on b. According to this result, the generally used calibration equation was modified and a new empirical
model U(SF, b), introducing the relationship b(U) as a factor, was proposed. Of course, for swelling/shrinkage
clay soil the suggested calibration equation results implicit, if considering that b is also a function of U.
The experiments also allowed to verify that parameters of the calibration equation depend on soil clay percentage
and then to identify empirical relationships for their estimation, that were finally validated by using measurements
acquired on undisturbed soil samples and some data collected by the literature
Modellistica agro-idrologica per la stima dei consumi traspirativi di colture Mediterranee e schematizzazione della funzione di stress idrico
No full textI modelli di simulazione agro-idrologica permettono la schematizzazione dei fenomeni che si manifestano nel sistema suolo-vegetazione-atmosfera (SVA) su un ampio range di scale spaziali e temporali. Ogni singolo comparto del sistema è caratterizzato da comportamenti complessi dovuti, ad esempio, alle strategie adattative della pianta in risposta a condizioni di deficit idrico del suolo. Con riferimento a quest’ultimo aspetto, nella stima degli attingimenti radicali e quindi dei consumi traspirativi effettivi, di cruciale importanza risulta la corretta schematizzazione della funzione di stress idrico, descritta in generale utilizzando coefficienti riduttivi della traspirazione potenziale in funzione del deficit idrico del suolo. La forma di tale funzione dipende, oltre che dalle proprietà idrauliche del suolo, anche dal tipo di risposta ecofisiologica della coltura al variare dello stato idrico del suolo.
Il lavoro si propone di evidenziare come, per colture arido-resistenti quali l’olivo, la schematizzazione di una funzione di stress idrico di forma convessa (Rallo e Provenzano, 2013), può migliorare sensibilmente le stime dei flussi traspirativi ottenute con il modello di bilancio agro-idrologico proposto dalla FAO (Allen et al., 1998). D’altra parte, per la coltura dell’agrume che non presenta particolari comportamenti eco-fisiologici in risposta allo stress idrico, viene verificato come l’uso della originaria funzione di stress idrico, proposta nel quaderno FAO-56, fornisca una schematizzazione idonea alla corretta stima dei flussi traspirativi
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