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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.

Water supplies have been decreasing in several semi-arid regions, and it is therefore necessary to adopt irrigation strategies aimed at maximizing water use efficiency. In this paper, the effects of saline and deficit irrigation on water use efficiency and on potato crop response, based on observations of soil and plant water status, were investigated. Experiments were carried out in Central Tunisia, by monitoring potato crop growth during two seasons in four distinct treatments (T1&ndash, T4), represented by two different irrigation doses and two water qualities. For irrigation scheduling purposes, thresholds of soil matric potential, soil water content and Crop Water Stress Index (CWSI) were identified with the aim to quantify the effects of water and/or salinity stress on the achievable yield. Experiments allowed verifying that crop yield is strongly affected by the seasonal amount and quality of applied water. Despite differences of crop yield between treatments T2, T3 and T4 not being statistically significant (P &lt, 0.05), crop yield varied between 26.3 t/ha (T3 in 2015) to 16.3 t/ha (T4 in 2015). However, crop yield decline of 17.0 t/ha and 12.0 t/ha per each 100 mm decrease of applied water were observed under the application of water electrical conductivity of 1.6 dS/m and 4.1 dS/m respectively. On the other hand, an increase of 1.0 dS/m in water electrical conductivity caused a yield decline rate of about 10%. The results achieved showed that under the semi-arid climate of Tunisia, potato crop irrigation should be scheduled to avoid water deficit, however, the possibility to reduce water supply can be envisaged when water availability is limited, but with the awareness to accept the shortage of production. Finally, when saline water is the only source available to the farm, it is necessary to avoid the reduction of irrigation doses, to prevent excessive salt accumulation in the root zone with unavoidable effects on crop yield.

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

Actual evapotranspiration is assessed via surface energy balance at an hourly rate. However, a robust estimation of daily evapotranspiration from hourly values is required. Outcomes of surface energy balance are frequently determined via measures of eddy covariance latent heat flux. Surface energy balance can be applied on images acquired at different times and spatial resolutions. In addition, hourly actual evapotranspiration needs to be integrated at a daily rate for operational uses. Questions arise whether the validation of surface energy balance models can benefit from complementary in situ measures of latent heat flux and sap flow transpiration. Here, validation was driven by image acquisition time, spatial resolution, and temporal integration. Thermal and optical images were collected with a proximity-sensing platform on an olive orchard at different acquisition times. Actual latent heat fluxes from canopy and sap flux at tree trunks were measured with a flux tower and heat dissipation probes. The latent heat fluxes were then further analyzed. A surface energy balance was applied over proximity sensing images re-sampled at different spatial resolutions with resulting latent heat fluxes compared to in situ ones. A time lag was observed and quantified between actual latent heat fluxes from canopy and sap flux at the tree trunk. Results also indicate that a pixel resolution comparable to the average canopy size was suitable for estimating the actual evapotranspiration via a single source surface energy balance model. Images should not be acquired at the beginning or the end of the diurnal period. Findings imply that sap flow transpiration can be used to measure surface energy balance at a daily rate or when images are found at an hourly rate near noon, and the existing time lag between the latent heat flux at the canopy and the sap flow at the trunk does not need to be taken into account.

The knowledge of soil water content (SWC) dynamics in the upper soil layer is important for several hydrological processes. Due to the difficulty of assessing the spatial and temporal SWC dynamics in the field, some model-based approaches have been proposed during the last decade. The main objective of this work was to assess the performance of two approaches to estimate SWC in the upper soil layer under field conditions: the physically-based thermal inertia and the Hydrus model. Their validity was firstly assessed under controlled laboratory conditions. Thermal inertia was firstly validated in laboratory conditions using the transient line heat source (TLHS) method. Then, it was applied in situ to analyze the dynamics of soil thermal properties under two extreme conditions of soil-water status (well-watered and air-dry), using proximity remote-sensed data. The model performance was assessed using sensor-based measurements of soil water content acquired through frequency (FDR) and time domain reflectometry (TDR). During the laboratory experiment, the Root Mean Square Error (RMSE) was 0.02 m3 m−3 for the Hydrus model and 0.05 m3 m−3 for the TLHS model approach. On the other hand, during the in situ experiment, the temporal variability of SWCs simulated by the Hydrus model and the corresponding values measured by the TDR method evidenced good agreement (RMSE ranging between 0.01 and 0.005 m3 m−3). Similarly, the average of the SWCs derived from the thermal diffusion model was fairly close to those estimated by Hydrus (spatially averaged RMSE ranging between 0.03 and 0.02 m3 m−3).

[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.

[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.