Search

In the last two decades, research on water resource monitoring and management has mainly been aimed at reducing irrigation water volume and energy consumption. At the same time, the effects of climate change and agricultural policies have also been major research interests. Therefore, there is an interest in focusing on the assessment of irrigation performance to improve water management and to increase the sustainability of irrigated agricultural territories. Recent advances in optoelectronics, mechatronics, communication, and information technologies have allowed for the implementation of low cost, easy to operate, and virtual free maintenance of data acquisition systems to be used in soil-crop water status monitoring, as well as in smart irrigation systems. Agro-hydrological models have been recognized as an economic and simple tool to quantify crop water requirements in the decisionmaking processes for both farm and basin scales. They can simulate the mass and/or energy exchange processes in the soil-plant-atmosphere continuum under different spatial and temporal scales. In combination with new technologies such as sensors and remote sensing, these models are promising techniques that have accelerated spatial data collection substantially. Remote sensing and wireless sensor networks can cover scales from a single leaf to complete irrigation systems and can create data sets for large numbers of agricultural families and farming conditions. Hence, the agro-hydrological sensor-model based approach must be properly chosen and calibrated to increase its use on larger commercial farms, even using remote sensing data. This Special Issue consists of a collection of seven papers that cover a broad range of advances on modelling and partitioning evapotranspiration, modelling soil water and salt content, and modelling irrigation systems, with the aim to increase the sustainability of irrigation derived from the adoption of monitoring and optimum management practices

The SIMDualKc model was applied to evaluate the crop water use and the crop coefficient (Kc) of an irrigated olive grove (Olea europaea L.) located in Sicily, Italy, using experimental data collected from two crop seasons. The model applies the FAO56 dual Kc approach to compute the actual crop evapotranspiration (ETc act) and its components, i.e., the actual tree transpiration (Tc act), obtained through the basal crop coefficient (Kcb), and soil evaporation according to an evaporation coefficient (Ke). Model calibration was performed by minimizing the difference between the predicted Tc act and the observed daily tree transpiration measured with sap flow instrumentation (TSF field) acquired in 2009. The validation was performed using the independent data set of sap flow measurements from 2011. The calibrated Kcb was equal to 0.30 for the initial and non-growing season stages, 0.42 for the mid-season, and 0.37 for the end season. For both seasons, the goodness-of-fit indicators relative to comparing TSF field with the simulated Tc act resulted in root mean square errors (RMSE) lower than 0.27 mm d−1 and a slope of the linear regression close to 1.0 (0.94 ≤ b0 ≤ 1.00). The olive grove water balance simulated with SIMDualKc produced a ratio between soil evaporation (Es) and ETc act that averaged 39%. The ratio between actual (ETc act) and potential crop evapotranspiration (ETc) varied from 84% to about 99% in the mid-season, indicating that the values of ETc act are close to ETc, i.e., the adopted deficit irrigation led to limited water stress. The results confirm the suitability of the SIMDualKc model to apply the FAO56 dual Kc approach to tree crops, thus assessing the water use of olives and supporting the development of appropriate irrigation management tools that are usable by farmers. A different way to estimate Kcb is based on the approach suggested in 2009 by Allen and Pereira (A&amp, P), which involves the measured fraction of ground covered (shaded) by the crop and the height of the trees. Its application to the studied grove produced the mid-season Kcb values ranging from 0.40–0.45 and end-season Kcb values ranging from 0.35–0.40. The comparison between the A&amp, P-computed Tc act A&amp, P and TSF field shows RMSE values ranging from 0.27 to 0.43 mm d−1, which demonstrates the adequacy of the latter approach for parameterizing water balance models and for irrigation scheduling decision making.

This study aimed to develop a new model, valid for soil with and without expandable characters, to estimate volumetric soil water content (&theta, ) from readings of scaled frequency (SF) acquired with the Diviner 2000&reg, sensor. The analysis was carried out on six soils collected in western Sicily, sieved at 5 mm, and repacked to obtain the maximum and minimum bulk density (&rho, b). During an air-drying process SF values, the corresponding gravimetric soil water content (U) and &rho, b were monitored. In shrinking/swelling clay soils, due to the contraction process, the variation of dielectric permittivity was affected by the combination of the mutual proportions between the water volumes and the air present in the soil. Thus, to account for the changes of &rho, b with U, the proposed model assumed &theta, as the dependent variable being SF and &rho, b the independent variables, then the model&rsquo, s parameters were estimated based on the sand and clay fractions. The model validation was finally carried out based on data acquired in undisturbed monoliths sampled in the same areas. The estimated &theta, &theta, estim, was generally close to the corresponding measured, &theta, meas, with Root Mean Square Errors (RMSE) generally lower than 0.049 cm3 cm&minus, 3, quite low Mean Bias Errors (MBE), ranging between &minus, 0.028 and 0.045 cm3 cm&minus, 3, and always positive Nash-Sutcliffe Efficiency index (NSE), confirming the good performance of the model.

The objective of this paper was to assess the performance of Hydrus-2D model to simulate the effects of different on-farm irrigation strategies applied on potato crop. The ability of the model to simulate the stress coefficient (Ks), obtained as the ratio between actual and maximum transpiration, and to define the productive function of potato crop under the semi-arid conditions of central Tunisia were also evaluated. Experiments were carried out on potato crop under full (FI) and deficit irrigation (DI) and two different water qualities supplied by means of a subsurface drip irrigation system. Results evidenced that the model, despite some discrepancies locally observed, can fairly accurately predict soil water contents and electrical conductivity around buried emitters. Furthermore, under water and salt stress conditions, &ldquo, measured&rdquo, Ks, based on crop water stress index (CWSI) obtained on thermal images, resulted in a good correlation with the corresponding estimated by the model (R2 = 0.8). The database collected during the three growth seasons also allowed the definition of the crop productive function represented by a linear relationship between the relative yield loss and Ks. This function represents a useful guidelines for the sustainable use of irrigation water in countries characterized by a semi-arid climate and a limited availability of water for irrigation.

The present study reviews the research on the FAO56 crop coefficients of fruit trees and vines performed over the past twenty years. The main objective was to update information and extend tabulated single (K c ) and basal (K cb ) standard crop coefficients. The selection and analysis of the literature for this review have been done to consider only studies that adhere to FAO56 method, computing the reference ET with the FAO Penman–Monteith​ ET o equation and field measuring crop ET with proved accuracy. The crops considered refer to vine fruit crops, berries and hops, temperate climate evergreen fruit trees, temperate climate deciduous fruit trees and, tropical and subtropical fruit crops. Papers satisfying the conditions expressed above, and that studied the crops under pristine or appropriate eustress conditions, were selected to provide for standard K c and K cb data. Preference was given to studies reporting on the fraction of ground cover (f c ), crop height (h), planting density, crop age and adopted training systems. The K c and K cb values obtained from the selected literature generally show coherence relative to the crop biophysical characteristics and reflect those characteristics, mainly f c , h and training systems. The ranges of reported K c and K cb values were grouped according to crop density, particularly f c and h, and were compared with FAO56 (Allen et al., 1998) previously tabulated K c and K cb values, as well as by Allen and Pereira (2009) and Jensen and Allen (2016), which lead to define update indicative standard K c and K cb values. These values are aimed for use in crop water requirement computations and modeling for irrigation planning and scheduling, thus also aimed at supporting improved water use and saving in orchards and vines.

[EN] The knowledge of the crop response to soil water deficit is essential to predict the actual crop water requirements under limited soil water conditions. The mathematical schematization of the crop response under RDI can allow identifying the exact irrigation timing. The threshold of soil water status below which crop transpiration decreases represents a key parameter for the water stress functions. The main objective of this paper was to investigate the effects of several RDI treatments, applied during the three stages of fruit growth, on soil-plant-water relations of drip-irrigated mandarin trees. Experiments were carried out in seven irrigation treatments: a control, irrigated at 125% of potential evapotranspiration measured in weighting lysimeters, ETlys, during the whole year, and six RDI treatments in which 25% and 50% of ETlys were applied during each of the three stages of fruit growth. The critical threshold of soil water status expressed in terms of soil water depletion below which predawn (PLWP) and midday (MSWP) leaf water potential is affected by decreasing soil water content, were identified. The dependency of crop water status from the climate forcing, occurring under soil water contents higher than the critical threshold was also demonstrated. Moreover, a strong relationship between water stress integral ( ) evaluated during the three stages of fruit growth, and the corresponding amount of water applied (irrigation and precipitation) was observed after normalizing the variables. The robust relationship between these two variables (R2 = 0.83) confirmed that the water stress integral represents a good indicator of the plant-water relationship and allows the prediction of the total irrigation depth to be applied to achieve a desired stress level during the fruit growth. Moreover, this relationship depends on the irrigation schedule adopted to regulate the deficit, which includes the irrigation variables, such as irrigation dose and its variability., The research was carried out in the frame of Progetto Organizzazioni di Produttori-Illuminati Frutta-Rallo (University of Pisa, 1048 Ministero delle Politiche Agricole e Forestali-Regione Toscana) and ATMOSMART-dimostratore tecnologico (University of Pisa).

Accurate soil water status measurements across spatial and temporal scales are still a challenging task, specifically at intermediate spatial (0.1–10 ha) and temporal (minutes to days) scales. Consequently, a gap in knowledge limits our understanding of the reliability of the spatial measurements and its practical applicability in agricultural water management. This paper compares the cumulative EM38 (Geonics Ltd., Mississauga, ON, Canada) response collected by placing the sensor above ground with the corresponding soil water content obtained by integrating the values measured with an FDR (frequency domain reflectometry) sensor. In two field areas, characterized by different soil clay content, two Diviner 2000 access tubes (1.2 m) were installed and used to quantify the dimensionless fraction of transpirable soil water (FTSW). After the calibration, the work proposes the combined use of the FDR and electromagnetic induction (EMI) sensors to measure and map FTSW. A strong correlation (R2 = 0.86) between FTSW and EM38 bulk electrical conductivity was found. As a result, field changes of FTSW are due to the variability of soil water content and soil texture. As with the data acquired in the field, more structured patterns occurred after a wetting event, indicating the presence of subsurface flow or root water uptake paths. After assessing the relationship between the soil and crop water status, the FTSW domain includes a critical value, estimated around 0.38, below which a strong reduction of relative transpiration can be recognized.

The paper analyzes the performance of Hydrus-2D model to simulate the dynamic of soil water contents and transpiration fluxes in an olive orchard in which two different irrigation systems were used in 2011 and 2012. The relationship between measured midday stem water potential, MSWP, and simulated relative transpiration (ratio between simulated actual and maximum crop transpiration), Ks, was also identified with the aim to use the model for crop water status predictions. Finally, a scenario analysis was carried out for irrigation management purposes, by considering the level of crop water stress achieved in the different phases of the vegetative growth. The results evidenced that active roots (d

[EN] Micro-irrigation is considered one of the most efficient water distribution systems and allows increasing water use efficiency if coupled with effective water-saving irrigation management strategies as regulated deficit irrigation (RDI) or partial root-zone drying (PRD) techniques. However, application of these strategies makes it crucial the real-time monitoring of soil and crop water status, in order to identify appropriate irrigation scheduling parameters (irrigation timing and doses) and to prevent irreversible damage of plant system and/or crop yield reductions. Even if midday stem water potential (MSWP) is considered one of the most affordable indicator for direct determinations of crop water status, its measurement requires skilled operators, is destructive and time consuming, so that indirect and fast estimations are desirable. In this direction, agro-hydrological models can be considered an easy-to-use tool for indirect evaluations of soil and crop water status aimed to identify irrigation scheduling parameters even when micro-irrigation distribution systems and water saving management strategies are adopted. The paper, after examining the eco-physiological response of citrus orchards to soil water deficit, assessed the potential of FAO-56 agro-hydrological modelto identify the crop water stress under different irrigation management strategies. Experiments carried out during three years (2009–2011) allowed identifying the crop water stress response to soil water deficit conditions, also confirming the schematization proposed in FAO-56 paper for citrus orchards. Moreover, after evaluating the similarity between the measured MSWP with the simulated crop water stress coefficient, Ks, it was proved the fairly good performance of FAO-56 agrohydrological model to predict soil water content (RMSE = 0.04 m3 m−3), from one side, and the crop response to different irrigation management strategies, from the other. The obtained results evidenced that the crop water stress coefficient estimated by the model can be used as a suitable indicator to replace the tedious and time-consuming field measurements of MSWP. © 2016 Elsevier B.V. All rights reserved., Research was carried out in the frame of the PRIN 2010 projects, co-financed by Ministero dell'Istruzione, dell'Universita e della Ricerca (MIUR) and Universita degli Studi di Palermo. Authors wish to thank the Committee for International Relations Office (CORI) of University of Palermo to support the research cooperation with the Polytechnic University of Valencia.

A remote sensing-based approach to estimate actual evapotranspiration (ET) was tested in an area covered by olive trees and characterized by Mediterranean climate. The methodology is a modified version of the standard FAO-56 dual crop coefficient procedure, in which the crop potential transpiration, T p, is obtained by directly applying the Penman-Monteith (PM) equation with actual canopy characteristics (i.e., leaf area index, albedo and canopy height) derived from optical remote sensing data. Due to the minimum requirement of in-situ ancillary inputs, the methodology is suitable also for applications on large areas where the use of tabled crop coefficient values become problematic, due to the need of corrections for specific crop parameters, i.e., percentage of ground cover, crop height, phenological cycles, etc. The methodology was applied using seven airborne remote sensing images acquired during spring-autumn 2008. The estimates based on PM approach always outperforms the ones obtained using simple crop coefficient constant values. Additionally, the comparison of simulated daily evapotranspiration and transpiration with the values observed by eddy correlation and sap flow techniques, respectively, shows a substantial agreement during both dry and wet days with an accuracy in the order of 0.5 and 0.3 mm d−1, respectively. The obtained results suggest the capability of the proposed approach to correctly partition evaporation and transpiration components during both the irrigation season and rainy period also under conditions of significant reduction of actual ET from the potential one.

The 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.

Correct estimation of crop actual transpiration plays a key-role in precision irrigation scheduling, since crop growth and yield are associated to the water passing through the crop. Objective of the work was to assess how the combined use of micro-meteorological techniques (eddy covariance, EC) and physiological measurements (sap flow, SF) allows a better comprehension of the processes involving in the Soil–Plant–Atmosphere continuum. To this aim, an experimental dataset of actual evapotranspiration, plant transpiration, and soil water content measurements was collected in an olive orchard during the midseason phenological period of 2009 and 2010. It was demonstrated that the joint use of EC and SF techniques is effective to evaluate the components of actual evapotranspiration in an olive orchard characterized by sparse vegetation and a significant fraction of exposed bare soil. The availability of simultaneous soil water content measurements allowed to estimate the crop coefficients and to assess a simple crop water stress index, depending on actual transpiration that can be evaluated even in the absence of direct measurements of actual transpiration. The crop coefficients experimentally determined resulted very similar to those previously evaluated; in particular, in the absence of water stress, a seasonal average value of about 0.65 was obtained for the “single” crop coefficient, whereas values of a 0.34 and 0.41 were observed under limited water availability in the root zone. The comparison between the values of crop water stress index evaluated during the investigated periods evidenced systematically lower values (less crop water stress) in the first year compared to the second, according to the general trend of soil waters content in the root zone. Further researches are however necessary to extent the experimental dataset to periods characterized by values of soil evaporation higher than those observed, in order to verify the crop coefficients even under different conditions than those investigated.

[EN] The use of lay-flat polyethylene pipes to irrigate horticultural crops has been receiving widespread attention in the last decade, due to the significant improvements in their hydraulic performance, their potentially high application efficiency, and their limited installation costs. However, even if hydraulic design procedures for conventional microirrigation systems are fairly well established, there is still the need to know how different pipe-wall thicknesses of lay-flat pipes can affect the pipe geometry under different operating pressures as well as the related consequences on friction losses. This paper, after comparing two different procedures (caliper and photographic) to assess the geometry of lay-flat polyethylene pipes under different operating pressures, analyzes the friction losses per unit of pipe length, J, in order to identify and to assess a procedure for their evaluation. Hydrostatic tests, initially carried out on pipes with wall thicknesses of 6, 8, and 10 thousandth of an inch (mil), evidenced that the pipe dimensions measured with both methods are quite similar, despite the generally higher standard deviations characterizing caliper measurements when compared to photographic method. Tests allowed to verify that most of the changes in pipe dimensions occur within a range of pressure from 0 kPa to about 30 kPa, with pipe horizontal width and vertical height quite similar at higher pressures and pipes have a tendency to become circular. Additionally, due to the elasticity of the material, over a certain limit of water pressure, both the pipe dimensions tend to rise, with a trend depending on pipe thickness. According to the experimental data, the relationships between pipe effective diameter and water pressure were then determined for the three considered pipes. Moreover, based on measured friction losses and pipe effective diameters, it was confirmed that the relationship between the Darcy-Weisbach friction factor, f, and the Reynolds number, R, can be described by a power equation in which, by assuming a value of -0.25 for the exponent, it results a coefficient c = 0.285, lower than the theoretical. For the three investigated pipes the errors associated to estimated J were finally evaluated by considering (1) the experimental relationships between friction factor and Reynolds number as well as between pipe diameter and operating pressure (Case A); (2) the same value of c, but pipe effective diameters of 16.20, 16.10, and 15.85 mm corresponding to p = p(lim) (Case B); (3) the standard procedure, with a value of c = 0.302 and the pipe diameter equal to 16.10 mm, as suggested by the manufacturer. The results evidenced that suitable estimations of J need to account for the variations of the pipe effective diameter with water pressure. On the other hand, incorrect values of pipe diameter combined with inexact values of the friction factor generate inaccurate estimations of friction losses, with unavoidable consequences in pipe design. (C) 2015 American Society of Civil Engineers., The research was cofinanced by Universita di Palermo (FFR 2011) and Ministero dell'Istruzione, dell'Universita e della Ricerca (PRIN 2010). All the authors setup the research and discussed the results. V. Alagna and D. Autovino carried out the experimental measurements and G. Provenzano wrote the paper. A special thank to the Committee for International Relations Office (CORI) of University of Palermo to support the research cooperation with the University of Valencia.

Frequency domain reflectometry (FDR) downhole sensors have been increasingly used for soil moisture field monitoring because they allow measurement, even continuously, along a soil profile. Moreover, they can also be installed with minimal soil disturbance around the access tube. The objectives of the paper were to assess the field and laboratory calibration protocols for a FDR capacitance probe (Diviner 2000) for a range of soils characterized by different particle size distributions and shrink/swell potential and to propose a practical and effective protocol on the basis of undisturbed soil samples, accounting for soil shrinkage/swelling processes characterizing swelling clay soils. The experiments showed that on coarse-textured soils, field calibration under wet, moist, and dry conditions allows estimations of the volumetric soil water content, with root-mean-square error (RMSE) values always lower than 0.058 cm3 · cm-3. On the contrary, the problems occurring in the field on finer-textured soils, which are characterized by a clay content ranging between 36.7 and 45.1% and moderate to high shrink/swell potential, did not permit identification of suitable calibration equations and then accurate estimations of the soil water content. For such soils, in fact, a great dispersion of the experimental data and consequently high error values associated with the site-specific calibration equations, i.e., up to 0.121 cm3 · cm-3 for the soil characterized by the highest clay percentage, were observed. The laboratory experiments were carried out by using undisturbed soil monoliths which, compared with sieved soils, have the advantage of accounting for the natural soil structure surrounding the access tube and monitoring the soil shrinkage processes occurring in clay soils during sensor calibration experiments. The Diviner 2000 calibration equations obtained in the laboratory were characterized by error values generally lower than those obtained in the field and always smaller than 0.053 cm3 · cm-3. Finally, in the range of a soil water content between approximately 10% and the maximum observed, the scaled frequency measured by the sensor was almost constant at a decreasing soil water content. This circumstance can be ascribed to the normal phase of the shrinkage process determining the compensative effects between the reduction of the volumetric soil water content and the increasing soil bulk density. The maximum variations of scaled frequency were observed in the range of the soil water content, for which the resulting soil bulk density was approximately constant. The knowledge of the soil shrinkage characteristic curve therefore assumes a key role when calibrating FDR sensors on shrinking/swelling clay soils.

Reference evapotranspiration (ET 0 ) is widely used for irrigation scheduling, to promote an efficient use of water resources for a sustainable agro-ecosystem productivity, as well as to manage water quality and to face other environmental concerns. As suggested by ASCE-EWRI and FAO, standard Penman–Monteith methods are generally applied for an accurate estimation of ET 0 from hourly to daily scale. In absence of detailed meteorological information several simplified equations, using a limited number of variables, have been proposed as alternative. In this paper, the performance of different reference evapotranspiration methods, at hourly (Penman–Monteith, Pristley–Taylor, Makkink and Turc) and daily scale (Penman–Monteith, Blaney and Criddle, Hargreaves, Pristley–Taylor, Makkink and Turc), was evaluated against scintillometer measurements collected during six month in 2005 in an experimental plot maintained under “reference” conditions (alfalfa crop). The daily values of ET 0 obtained with the examined methodologies were then used as input in the FAO-56 agro-hydrological model, in order to evaluate, for an olive grove in a Mediterranean environment, the impact on simulated actual evapotranspiration. The experiment was carried out in South-West Sicily, in an area where olive groves are the major crop. The comparison between estimated and measured fluxes confirmed that FAO-56 Penman–Monteith (PM) standardized equation is characterized by the lowest mean bias error (−0.15 mm d −1 and 0.06 mm d −1 using daily or hourly data, respectively). Additionally, the analysis also highlighted that the Pristley–Taylor equation can be considered a valid alternative for an accurate estimation of ET 0 (mean bias error of 0.35 mm d −1 and 0.43 mm d −1 using daily or hourly data, respectively). The application of the FAO-56 water balance model on the investigated olive grove evidenced that the best estimations of actual evapotranspiration are obtained when the Pristley–Taylor ET 0 data are used as input, confirming that this approach can be considered a valid alternative to the standard Penman–Monteith.

This paper compares two agro-hydrological models that are used to schedule irrigation of a typical Mediterranean crop. In particular, a comparison between the Food and Agriculture Organization (FAO) model, which uses a black box approach, and the soil-water-atmosphere-plant (SWAP) model, which is based on the numerical analysis of Richards' equation, are shown for wine grape. The comparison was carried out for the 2005 and 2006 irrigation seasons and focused on hydrological balance components and on soil water contents. Next, the ordinary scheduling parameters were identified so that the performance of the two models, which aimed to evaluate the seasonal water requirements and the irrigation times, could be assessed. In the validation phase, both of the models satisfactorily simulated the soil water content, and comparable values of cumulative evapotranspiration were obtained. With the goal of recognizing the crop water stress condition in the field, the original algorithm of the FAO model was modified. This research provided evidence of how the two agrohydrological models, although characterized by different approaches in modeling the phenomena, showed a similar behaviour when used for scheduling irrigation under soil water deficit conditions.

Summary A coupled energy/hydrologic model was applied to simulate the exchange of energy and water in the soil–plant-atmosphere system (SPA). The model, which uses a “two-source” approach to estimate the energy fluxes, and the “force-restore” approach to represent the water balance, was validated by means of evapotranspiration measurements collected via scintillometry and soil moisture measurements collected via time domain reflectometry (TDR) in a Sicilian olive grove. The comparison between measured and estimated fluxes values at an hourly scale showed good agreement. Additional comparisons on a daily timescale confirmed the model’s applicability for quantifying crop water requirements. Also in terms of daily evapotranspiration and soil water content values, the obtained results confirmed the model’s applicability for those practical applications aiming to quantify the crop water requirement. Moreover, further studies should be conducted to test the feasibility of using this model for long term simulations over a broad range of conditions.

The authors deal with the quite interesting and actual problem of Diviner 2000 capacitance probe calibration and present some field and laboratory data obtained on two different layers (0–0.26 and 0.26–0.50 cm) of the same soil profile, characterized by different textural class. The importance of site-specific calibration of sensors used to monitor soil or plant water status assumes a particular relevance in semiarid environments where the application of precision irrigation represents an appropriate management strategy aimed to achieve high values of water use efficiency (Cammalleri et al. 2013). Moreover, in clay soils, physical properties are strongly influenced by soil water content (Provenzano et al. 2013), so that the correct measurement of this variable plays a key role to increasing crop yield and preserving water. However, the discussers would focus on some significant points to be corrected in the manuscript and some others that should have been specified in the methodology and considered in the final discussion, as following specified, for the benefit of potential readers. The need to adequately install the access tube, aimed to ensure the contact between the tube and the surrounding soil, is not only to avoid preferential flow of water down the walls of the tube, as considered in the paper, but also to reduce the air gap around the tube and to avoid rough measurements of scaled frequency, used to estimate soil water contents, whose values depend on the mutual proportion of soil, water, and air in the soil volume investigated by the sensor. With reference to the second part of Eq. (2) of original paper, it is necessary to precise that the function θwðSFÞ correctly results

[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.