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[EN] Agro-hydrological models are considered an economic and simple tool for quantifying crop water requirements. In the last two decades, agro-hydrological physically based models have been developed to simulate mass and energy exchange processes in the soil-plant-atmosphere system. Although very reliable, because of the high number of required variables, simplified models have been proposed to quantify crop water consumes. The main aim of this paper is to propose an amendment of the Food and Agricultural Organization (FAO) of the United Nations FAO-56 spreadsheet program to introduce a more realistic shape of the stress function, valid for mature olive orchards (Olea europaea L.). The modified model is successively validated by means of the comparison between measured and simulated soil water contents and actual transpiration fluxes. These outputs are finally compared with those obtained with the original version of the model. Experiments also allowed assessing the ability of simulated crop water stress coefficients to explain the actual water stress conditions evaluated on the basis of measured relative transpirations and midday stem water potentials. The results show that the modified model significantly improves the estimation of actual crop transpiration fluxes and soil water contents under soil water deficit conditions, according to the RMSEs associated with the revised model, resulting in significantly higher than the corresponding values obtained with the original version. (C) 2014 American Society of Civil Engineers.

Full spectral measurements (350–2500 nm) at tree canopy and leaf levels and the corresponding leaf water potentials (LWP) were acquired in an olive grove of Sicily, at different hours of the day, during summer season 2011. The main objective of the work was to assess, on the basis of the experimental data-set, two different approaches to detect crop water status in terms of LWP. Specifically, using existing families of Vegetation Indices (VIs) and applying Partial Least Squares Regression (PLSR) were optimised and tested. The results indicated that a satisfactory estimation of LWP at tree canopy and leaf levels can be obtained using vegetation indices based on the near infrared–shortwave infrared (NIR–SWIR) domain requiring, however, a specific optimisation of the corresponding “centre-bands”. At tree canopy level, a good prediction of LWP was obtained by using optimised indices working in the visible domain, like the Normalized Difference Greenness Vegetation Index (NDGI, RMSE = 0.37 and R2 = 0.57), the Green Index (GI, RMSE = 0.53 and R2 = 0.39) and the Moisture Spectral Index (MSI, RMSE = 0.41 and R2 = 0.48). On the other hand, a satisfactory estimation of LWP at leaf level was obtained using indices combining SWIR and NIR wavelengths. The best prediction was specifically found by optimising the MSI (RMSE of 0.72 and R2 = 0.45) and the Normalized Difference Water Index (NDWI, RMSE = 0.75 and R2 = 0.45). Even using the PLSR technique, a remarkable prediction of LWP at both tree canopy and leaf levels was obtained. However, this technique requires the availability of full spectra with high resolution, which can only be obtained with handheld spectroradiometers or hyper-spectral remote sensors.

Tree crops are representing one of most widespread agricultural systems in Mediterranean regions, thus contributing in a substantial way to the economy and productivity of primary sectors of the countries interested. Besides the aspects concerning their economical relevance, tree crops like vineyards, olive and orange orchards are also typical elements of the Mediterranean landscape, and their ecological role has been recently revitalised in consideration of their function as carbon sinks for the Kyoto agreement. The environmental and economical sustainability of these agricultural systems in arid and semi-arid zones has to cope with the availability and management of water resources for irrigation. During recent years there has been a substantial progress in understanding the evolution of evapotranspiration processes in cropping systems, and detailed models and measurement techniques have been set-up for describing the mass and energy exchanges in the soil-plant- atmosphere continuum. However, due to the complexity of rooting systems and aerial parts further steps are needed for a full comprehension of hydrological processes in tree crop systems, with special regard to water stress conditions. Within the research project P.R.I.N. 2008 “ Assessment of mass and energy fluxes for the irrigation management of Mediterranean tree crops ” different techniques for measuring evapotranspiration fluxes in tree crops will be developed and tested, from innovative methodologies based on remote sensing observations to in-situ observations (xylem-flow measurements and micro-meteorology). These data-sets have be interpreted by means of physical approaches, with a modelling perspective of the observed processes.

An operational use of the actual evapotranspiration estimates requires the integration from instantaneous to daily values. This can commonly be achieved under the hypothesis of daytime self-preservation of the evaporative fraction. In this study, it has been evaluated the effect of this assumption on the assessment of daily evapotranspiration from proximity sensing images acquired at hourly intervals over a homogeneous olive groove. Results have been validated by comparison with observations made by a micrometeorological (EC-flux tower) and an eco-physiological (sap flux) sensor. SEBAL model has been applied to thermal and multispectral images acquired during a clear day on August 2009 trough a FLIR A320G thermal camera and a Tetracam MCA II multispectral camera, installed on a tethered helium balloon. Thermal and multispectral images were characterized by very high spatial resolution. This experiment aims to analyze two effects: 1) the consistency of the self-preservation hypothesis for daily estimates of the actual evapotranspiration from hourly assessments at different times of the day; 2) the effects of the spatial resolution on the performances of the energy balance model. To evaluate the effects of the spatial resolution, semi-hourly observations made by a flux tower and sap-flow measures were compared to the evapotranspiration estimates performed using downscaled images at resolutions close to canopy sizes (2, 5 and 10 m). Results show that the best estimates are obtained with a spatial resolution comparable to the average size of the canopy with images taken approximately at 10 UTC.

Evapotranspiration estimation by micrometeorological techniques through the assessment of mass and energy exchanges in the soil-plant-atmosphere continuum (SPAC) is a very active research area, involving both well-known and novel measurement techniques. A crucial aspect in validating experimental results is the integration of independent measurements of mass and energy exchanges in the SPAC. To this aim, the development and validation of an integrated approach in major tree crop species, involving different independent techniques, are presented. Eddy covariance estimates of ET fluxes were compared to up-scaled sap flow measurements in olive, orange and grapevine, three important Mediterranean tree crop species with contrasting ecophysiological characteristics and responses to water deficits. These differences can affect directly the degree of coupling of the tree to the environment and, consequently, the degree of correspondence between instantaneous transpirational flux at tree level and the micrometeorological measurement of ET at orchard level. Data were analyzed to verify to what extent, in the three species, transpirational flow at orchard level is regulated by tree conductance, capacitance effects related to tree size or by environmental demand. Hourly observations were helpful in detecting physiological processes of the three species only when data were analyzed taking into consideration their diurnal changes.

Agro-hydrological models can be considered an economic and simple tool to quantify crop water requirements. In the last two decades, agro-hydrological physically based models have been developed to simulate mass and energy exchange processes in the soil-plant-atmosphere system. Although very reliable, due to the high number of required variables, simplified models have been proposed as simple tools to quantify crop water consumes. The main aim of the paper is to assess, for a Sicilian orchard of table olive, the suitability of FAO-56 agro-hydrological model to estimate the crop transpiration under soil water deficit conditions. The model validation is carried out by means of measurements of sap-flow and soil water contents, acquired during three years of field observations. An amendment of the model is suggested in order to take into account the water stress function and the soil water uptake ability as experimentally evaluated. The results show that the modified model improves the estimation of crop transpiration and soil water content, considered that the associated RMSEs resulted higher than the corresponding values obtained with the original version of the model.

Actual evapotranspiration from typical Mediterranean crops has been assessed in a Sicilian study area by using Surface Energy Balance and Agro-Hydrological models. Both modelling approaches require remotely sensed data to estimate evapotranspiration fluxes in a spatially distributed way. The first approach exploits visible (VIS), near-infrared (NIR) and thermal (TIR) observations to solve the surface energy balance equation. To this end two different schemes have been tested: the two-sources TSEB model, where soil and vegetation components of the surface energy balance are treated separately, and the widely used one-source SEBAL model, where soil and vegetation are considered as a sole source. Actual evapotranspiration estimates by means of the two surface energy balance models have been compared with the results of the Agro-Hydrological model SWAP, applied in a spatially distributed way to simulate one-dimensional water flow in the soil-plant-atmosphere continuum. In this latter model, remote sensing data in the VIS and NIR spectral ranges have been used to infer spatially distributed vegetation parameters needed to set up the upper boundary condition of SWAP. In the comparison presented here, actual evapotranspiration values obtained from the application of the soil water balance model SWAP have been considered as the reference. Considering that the study area is characterized by typical Mediterranean sparse vegetation, i.e. olive, citrus and vineyards, we focused the attention on the main conceptual differences between SEBAL and TSEB. Airborne hyperspectral data acquired during a NERC campaign in 2005 have been used. The results of the investigation evidenced that the remote sensing two-sources approach used in TSEB model describes turbulent and radiative surface fluxes in a more realistic way than the one-source approach.

L’uso razionale della risorsa idrica in agricoltura richiede, unitamente all’adozione di tecniche irrigue avanzate che assicurino la migliore efficienza degli interventi irrigui, l’individuazione dei tempi e dell’entità dei singoli interventi. Perché questi ultimi obiettivi siano raggiunti è necessario stimare con precisione i consumi di evapotraspirazione delle colture che, nell’ambiente mediterraneo, caratterizzato da un periodo vegetativo tipicamente non in fase con quello piovoso, si manifestano sotto condizioni di stress idrico. Nel presente lavoro è descritta un’applicazione a una piantagione di oliveto della tecnica scintillometrica, che permette una stima indiretta del flusso di calore latente attraverso l’equazione del bilancio energetico. Più in particolare, lo scintillometro è uno strumento ottico, che misura il flusso di calore sensibile dal sistema suolo-pianta sulla base degli effetti che tale flusso induce sull’indice di rifrazione della luce coerente emessa da un trasmettitore; misurando contemporaneamente la radiazione netta e il flusso di calore nel suolo, è possibile dedurre il flusso di evapotraspirazione come termine residuo dell’equazione che esprime il bilancio energetico di superficie. Sono in particolare presentati i risultati di un’indagine sperimentale effettuata nel corso della stagione irrigua 2007 nell’area di Castelvetrano, tipicamente vocata alla coltura dell’olivo. I dati di evapotraspirazione giornaliera ottenuti mediante la tecnica scintillometrica sono stati quindi confrontati con i corrispondenti valori stimati utilizzando il modello Agroidrologico SWAP, la cui applicazione ha richiesto una approfondita caratterizzazione biofisica dell’area di studio. I dati di evapotraspirazione giornaliera ottenuti mediante la tecnica scintillometrica sono stati confrontati con i corrispondenti valori stimati utilizzando sia il modello agroidrologico SWAP che la procedura semplificata proposta di recente dalla FAO che prevede l’adozione di un coefficiente colturale Kc,r che tiene conto delle eventuali condizioni di stress idrico.

The red/purple colour of some plant species is due to the presence of anthocyanins, a colourful class of flavonoids widely spread in the Plantae kingdom. Beside a doubtless aesthetic value of anthocyanin-rich species, the presence of these pigments confers them peculiar physiological and biochemical properties which make red species usually more tolerant to some environmental stresses, as occur in Mediterranean area. The ability of anthocyanins to partially absorb a proportion of light striking the mesophyll (mainly green and yellow wavebands) represents a useful feature against a condition of excessive light which not only occurs when plants are subjected to high irradiances, but also when other stressors (e.g., high temperature, low water availability) impair the photosynthetic process. The work elucidates as the presence of anthocyanins determines morpho-anatomical, biochemical and physiological effects. In particular, the roles of these pigments are described comparing the leaf ontogenesis of two genotypes of Prunus cerasifera, one with red (var. Pissardii) and one with green leaves (clone 29C). Red-leafed Prunus resulted better protected, especially during the leaf senescence. The presence of anthocyanins also promotes a delayed leaf senescence (4-week-longer leaf lifespan) which is a well-appreciated feature in the context of urban "greening".

The work aimed to discriminate among different soil management treatments in terms of beneficial effects by high-resolution thermal and spectral vegetation imagery using an unmanned aerial vehicle and open-source GIS software. Five soil management treatments were applied in two organic vineyards (cv. Sangiovese) from Chianti Classico terroir (Tuscany, Italy) during two experimental years. The treatments tested consisted of conventional tillage, spontaneous vegetation, pigeon bean (Vicia faba var. minor Beck) incorporated in spring, mixture of barley (Hordeum vulgare L.) and clover (Trifolium squarrosum L.) incorporated or left as dead mulch in late spring. The images acquired remotely were analyzed through map-algebra and map-statistics in QGIS and correlated with field ecophysiological measurements. The surface temperature, crop water stress index (CWSI) and normalized difference vegetation index (NDVI) of each vine row under treatments were compared based on frequency distribution functions and statistics descriptors of position. The spectral vegetation and thermal-based indices were significantly correlated with the respective leaf area index (R2 = 0.89) and stem water potential measurements (R2 = 0.59), and thus are an expression of the crop vigor and water status. The gravel and active limestone soil components determined the spatial variability of vine biophysical (e.g., canopy vigor) and physiological characteristics (e.g., vine chlorophyll content) in both farms. The vine canopy surface temperature, and CWSI were lower on the spontaneous and pigeon bean treatments in both farms, thus evidencing less physiological stress on the vine rows derived from the cover crop residual effect. In conclusion, the proposed methodology showed the capacity to discriminate across soil management practices and map the spatial variability within vineyards. The methodology could serve as a simple and non-invasive tool for precision soil management in rainfed vineyards to guide producers on using the most efficient and profitable practice.