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The study evaluates the accuracy of measured and estimated crop evapotranspiration fluxes (ETc) on Citrus in a semiarid Mediterranean climate (Sicily, Italy). Specifically, ETc rates derived from in situ techniques [eddy covariance (EC) and sap flow heat pulse velocity (HPV)] and modelling approaches [Food and Agricultural Organization of the United States (FAO) Irrigation and Drainage Paper No. 56 (FAO-56) single and dual crop coefficient (Kc)] were compared under deficit irrigation scenarios. Results of the comparison showed that the single and dual Kc approaches provided similar ETc estimates (292 and 324 mm), even if these approaches overestimated ETc measured by EC (ETEC) (17% and 30% respectively). HPV was able to show transpiration (T) reductions caused by deficit irrigation strategies when compared with T under full irrigation condition (ranging from 70% to 82%). Overall, the assessed methodologies were able to capture ETc trends, but the selection of the most appropriate one will depend on the specific crop and study site characteristics. [ABSTRACT FROM AUTHOR]

Environmental and economic sustainability of agricultural systems has to face the general decreasing trend of water resources through the adoption of strategies aimed at improving water-use efficiency. In the study, during three consecutive summer seasons, the effects of deficit irrigation (DI) treatments applied on mature orange trees [Citrus sinensis (L.) Osbeck] cv. "Tarocco Meli" were analyzed. Two different DI strategies supplying 70 and 50% of crop evapotranspiration (ETc) were compared with irrigation at the full rate of ETc; the comparisons were carried out in terms of plant physiological response, crop production, quality, and nutritional status. The orange trees became less sensitive to moderate water restrictions (DI = 70% ETc) permitting approximately 80 mm of water saving (i.e., corresponding to a threshold for water stress integral of 60 MPa) per season without any significant impact on their water status and on agronomic performances. Severe water restrictions (DI = 50%ETc) reduced fruit weight and crop production every year, with water-use efficiency values similar to those of the moderate DI (70% ETc). The study does not evidence crop mineral nutrition imbalances and yield decrease caused by mild water reductions. A moderate water restriction can be applied in commercial orange orchards because it saved water and improved fruit quality by increasing total soluble solids and titratable acidity while the fruit maturity was delayed. [ABSTRACT FROM AUTHOR]

In this study, the adaptation characteristics of orange trees, related to the application over a decade of deficit irrigation (DI) strategies, have been explored. To this purpose, the analysis of a minimal dataset composed of physiological information (stem water potential - Ψ stem and sap flow - SF measurements), yield (fruits number and weight) and qualitative parameters (titratable acidity, TA; and total soluble solids, TSS) was performed with reference to the last irrigation seasons (i.e. 2018–19). The applied irrigation treatments were the following: sustained deficit irrigation (SDI); regulated deficit irrigation (RDI); partial root-zone drying (PRD), each distributing a water deficit of about 19%, 29% and 52%, respectively, compared to the control treatment (FI) supplying the full irrigation level (100% ET c). In general, higher water use efficiencies (WUE) have been obtained in DI treatments, which guarantee greater water savings (up to 50%), without affecting yield and quality characteristics. In particular, the most stressed treatment (PRD), while reaching the lowest Ψ stem values (− 1.8 to − 2.0 MPa), as also shown by SF versus Ψ stem clusters, resulted in WUE values for yield (WUE Y), TA (WUE TA) and TSS (WUE TSS) parameters of approximately 2.6, 2.9, and 3.1 times greater than FI, respectively. Overall, this study allowed identifying the cumulative adaptation characteristics of the orange trees under study to the application of long-term DI strategies and showing that trees were able to achieve yields and qualitative features similar to those obtained with FI, even after 10 years of application of deficient irrigation regimes. • Water savings up to 53% were reached for citrus grove under deficit irrigation (DI). • Higher water use efficiencies for DI regimes than for full irrigation conditions. • Orange trees showed adaptation effects after long-term DI application. • Long-term water deficit application did not affect orange yield and quality. [ABSTRACT FROM AUTHOR]

The article presents the results of research consisting of the application of deficit irrigation (DI) criteria, combined with the adoption of micro-irrigation methods, on orange orchards (Citrus sinensis (L.) Osbeck) in Sicily (Italy) during the irrigation season of 2015. Regulated deficit irrigation (RDI, T3) and partial root-zone drying (PRD, T4) strategies were compared with full irrigation (T1) and sustained deficit irrigation (SDI, T2) treatments in terms of physiological, biochemical, and productive crop response. A geophysical survey (electrical resistivity tomography, ERT) was carried out to identify a link between the percentages of drying soil volume in T4 with leaves abscisic acid (ABA) signal. Results highlight that the orange trees physiological response to water stress conditions did not show particular differences among the different irrigation treatments, not inducing detrimental effects on crop production features. ABA levels in leaves were rather constant in all the treatments, except in T4 during late irrigation season. ERT technique identified that prolonged drying cycles during alternate PRD exposed more roots to severe soil drying, thus increasing leaf ABA accumulation. [ABSTRACT FROM AUTHOR]

The study aims to identify the responses of citrus orchards (C. sinensis (L.) Osbeck), grown under typical Mediterranean climatic conditions, to deficit irrigation (DI) regimes applied over more than a decade (2010-2020). In particular, the DI regimes were declined at the study site in terms of sustained deficit irrigation, regulated deficit irrigation, partial drying of the root-zone, with increasing severity of the water deficit, from 25% to 50% of the crop evapotranspiration, using surface and sub-surface micro-irrigation techniques. Long-term monitoring was set up for identifying the main processes acting at the soil-plant-atmosphere continuum (SPAC) level through direct in situ measurements of mass and energy fluxes (i.e., via micrometeorological technique) and the estimation of ETc and transpiration fluxes (i.e., via sap flow method), and the soil-plant-water processes (via geoelectrical techniques). In addition, the main physiological, qualitative, and quantitative parameters were evaluated since the beginning of the experiment. The results of the long-term experiment demonstrated the great adaptability of the crop species to sustain even the highest water reductions without substantial alterations of the main marketable productive and qualitative characteristics, evidencing the importance of controlling the SPAC dynamics for correctly applying the water restriction regimes. [ABSTRACT FROM AUTHOR]