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In recent years, associated extreme events to climate change are being experienced more frequently and with greater intensity, worldwide but particularly affecting to Mediterranean basin countries. The DANA phenomenon (Spanish acronym for depresión aislada en niveles altos, meaning upper-level isolated atmospheric depression) occurs normally in autumn due to convective storms generated by the existence of cold air in the upper layers of the atmosphere combined with warm winds coming from the Mediterranean Sea. Its effects are devastating, provoking storms of great intensity that cause violent flash-flooding and run-off with a huge capacity for soil erosion. This field experiment focuses on the effects of DANA event of 12-13 September 2019 in Southern Spain on plant water status and thermal response of nectarine trees. Two irrigation treatments were applied during the summer-autumn postharvest (DOY, Day of the year, 158-329): well-irrigated (CTL) and non-irrigated (DRY). Volumetric soil water content (θv), air temperature (Ta) and canopy temperature (Tc) were real-time monitored and the crop water stress index (CWSI) was calculated. Stem water potential (Ψstem) and leaf gas exchange were measured on representative days of the experimental period. The effects of DANA forced to disconnect the soil water content sensors, precluding to measure Ψstem and leaf gas exchange from DOY 255 to 275. Before DANA, withholding irrigation caused a gradual decline in soil and plant water status in the DRY treatment. Minimum values of Ψstem = -2.63 MPa and θv = 13% were obtained at DOY 246. Significant differences were obtained in the Tc, Tc-Ta, and CWSI between treatments. CWSI in the DRY treatment was maximum (0.94) at DOY 232. The effects of DANA reduced the differences between treatments in thermal data, what required to establish different baselines for CWSI calculation. In this sense, the relationship Tc-Ta vs. VPD improved the coefficient of determination after DANA (from R2=0.71*** to 0.83***) in well-irrigated trees. Similar values of Ψstem and leaf gas exchange were found in both treatments after DANA. Only thermal indices showed significant differences between treatments. Furthermore, the strong relationship found between Tc-Ta vs. Ψstem worsened after DANA event (from R2=0.81*** to 0.32*). This work underlined the robustness of infra-red thermography to continuously monitor plant water status under this type of natural weather disaster. Acknowledgements: This work was funded by Spanish Agencia Estatal de Investigación (PID2019-106226RB-C21/AEI/10.13039/501100011033). MR. Conesa thanks to the Spanish Juan de la Cierva programme (IJC2020-045450-I) funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR.

This work studies the feasibility of using automated drip irrigation based on the volumetric soil water content measured with capacitance probes in early maturing nectarine trees (Prunus persica L. Batsch, cv. ‘Flariba’) grown in a clay–loam soil in Mediterranean conditions. An automated irrigation treatment (AUTO), based on the management allowed depletion (MAD) concept (with a feed-back control system), was compared with an irrigation-scheduling method based on the conventional crop evapotranspiration (100% ETc) as Control, under high (HWA) and low (LWA) water availability scenarios, each during three consecutive growing seasons. With HWA (no water restriction), the AUTO treatment maintained the soil water content at near field capacity (α = 10% depletion of available soil water content), and there were no significant differences between treatments in terms of the plant–soil water status, nectarine yield, or fruit quality parameters. Under LWA conditions (water deficit), the AUTO treatment (α = 10% during pre-harvest and 30% post-harvest) provided 43% less water than the Control, promoting a moderate plant water deficit, which led to a decrease in vegetative growth (winter pruning and tree canopy cover) but no significant differences in total yield and fruit quality parameters (although the total soluble solid content increased). The water use efficiency values in the AUTO treatment increased by an average of 34%. It was concluded that automated irrigation, based on MAD seasonal threshold values and monitored by means of real-time soil water content sensors, could be considered a promising tool for application in semi-arid Mediterranean agro-systems subjected to water scarcity., This research was supported by the Spanish Research Agency, co-financed with European Union FEDER funds (AGL2013-49047-C02-2R, and AGL2016-77282-C03-1R), PID2019-106226RB-C21/AEI/10.13039/501100011033, and the Seneca Foundation of the Region of Murcia (19903/GERM/15) projects. M.R. Conesa acknowledges the postdoctoral financial support received from the Juan de la Cierva Spanish Postdoctoral programme (FJCI-2017-32045)

This work studied the sensitivity of the postharvest period of early maturing nectarine trees (Prunus persica L. Batsch, cv. Flariba) to water stresses. Along with a well-irrigated treatment (T-0), three water deficit treatments (by withholding irrigation) were applied: T-1: early postharvest (June–July), T-2: late postharvest (August–September), and T-3: the whole postharvest period (June–September). Soil water content (θv) and midday stem water potential (Ψstem) were measured throughout the study. During winter dormancy, L-arginine, starch, and phosphorus content in the roots were analyzed. Yield, fruit quality, and metabolites were determined at harvest. Ψstem reached −1.7 and −2.3 MPa at the end of the early and late postharvest periods, respectively. Total yield and number of fruits per tree were significantly reduced in all deficit treatments with respect to T-0, while no significant differences were observed in physicochemical fruit quality. The T-2 treatment showed the highest percentage of cracked fruits. Significantly, lower values of L-arginine and phosphorus were observed in the roots of T-2 trees, with respect to T-0, while they were similar in T-1 trees. Although the early postharvest stage is key for the application of RDI strategies, our results indicated that the late postharvest period was also a sensitive period to severe drought, as the accumulation of winter root reserves (L-arginine and phosphorus) was reduced, which limited yield.

Citrus latifolia is increasingly being cultivated in Mediterranean areas, where the need for precise irrigation implies a sound knowledge of the crop's water requirements, which is carried out by monitoring the tree water status in the plant-soil-atmosphere system. Two year-old lime trees (Citrus latifolia Tan. cv. Bearss) were cultivated in 45 L weighing pot-lysimeters filled with a clay-loam soil and equipped with soil water sensors for recording the real-time soil water status. Irrigation, drainage, pot weight, and agro-meteorological variables were also recorded in real-time. Plant water relations - stem (Ψ) and leaf (Ψ) water potentials, and leaf gas exchange - were periodically measured throughout the experiment. The automated irrigation protocol based on the volumetric soil water content was set to prevent tree water stress (with mean seasonal values of Ψ above -0.8 MPa and 7 μmol m s and 80 mmol m s, for net phtosynthesis and stomatal conductance, respectively). From the soil water pot balance, the computed fortnightly ET mean values throughout the growing season varied from 0.25 to 2.56 L plant day in winter and summer months, respectively. Maximum ET values occurred in July when evaporative demand was highest and lime fruits were in their most active growing phase. For day length, lime tree biomass changes were negligible, and the pot tree weight variations served for ET water balance validation (r=0.92***). The contribution of this work is that it establishes a scalable weighing lysimeter prototype for determining the ET of lime trees grown in Mediterranean semi-arid conditions, using real-time soil water balance monitoring managed by an irrigation automation protocol. This approach could be replicated for precise ET measurements in other crops., This research was supported by Spanish National Plan-FEDER-UE-AGL2016-77282-C03-1 R and PID2019-106226RB-C2 1/AEI/10.13039/ 501100011033, and Seneca Foundation of Region of Murcia (19903/ GERM/15) projects. Conesa M.R. acknowledges the postdoctoral financial support received from the Spanish Juan de la Cierva program (FJCI -2017 -32045)

La escasez de agua y la necesidad de abastecer de alimentos de mayor calidad nutricional y organoléptica a una demanda cada vez más exigente y sensible por los sistemas de producción ha propiciado una gran tecnificación del riego. Esta tecnificación incluye el riego localizado, la fertigación y las mejoras en la toma de decisiones basadas en las necesidades hídricas del cultivo en cada etapa fenológica. Una de esas mejoras es la incorporación de sensores de contenido de agua para monitorizar la humedad del bulbo. En este trabajo se compara la respuesta de dos tipos de sensores comerciales de contenido volumétrico de agua en el suelo basados en la estimación de la constante dieléctrica: EnviroPro (capacitivo) y Acclima-TDR (Time Domain Reflectometry), instalados a 0,2, 0,4 y 0,6 m de profundidad y a 0,1 m del gotero, en una parcela de limeros (Citrus latifolia Tan. cv. Bearss) cultivados en meseta, en la finca experimental del CEBAS-CSIC (Santomera, Murcia) en un suelo franco-arcilloso. La gestión del riego localizado consistió en establecer umbrales de inicio y parada del riego basados en un agotamiento máximo permisible de agua en el perfil del suelo (MAD, de sus siglas en inglés Maximum Allowable Depletion) del 30%. EL MAD considera una fracción de la reserva de agua útil, que varía desde capacidad de campo (CC) hasta el punto de marchitez (PM), parámetros estrechamente ligados a la textura del suelo. Los valores de contenido de agua en el suelo determinados con Acclima-TDR fueron ligeramente superiores a los obtenidos mediante el modelo matemático (dependiente de los porcentajes de arena, limo, arcilla y materia orgánica, y de la compactación del suelo): 0,35 m3 m-3 para capacidad de campo y 0,30 m3 m-3 para el 30% de MAD. Sin embargo, las lecturas correspondientes medidas con EnviroPro fueron de 0,54 y 0,38 m3m-3 respectivamente. Además, las tendencias observadas en las curvas de agua en el suelo no fueron paralelas durante el ensayo, con una respuesta a la humectación y su redistribución más rápida en el caso de los sensores de capacitancia. De estos resultados cabe concluir que la gestión del riego de precisión requiere sensores cuyas características de exactitud, precisión y volumen de suelo explorado sean compatibles con el rango de MAD establecido (en este caso 0,04 m3 m-3), lo que se consiguió con los sensores TDR.

En nectarinos extra-tempranos cultivados en condiciones mediterráneas, se evaluó la idoneidad del largo periodo de postcosecha (mayo-octubre) para desarrollar estrategias de riego deficitario controlado. Para ello, se establecieron 4 tratamientos de riego: (i) Control (T‐CTL): regado al 100% ETc durante todo el año; (ii) Estrés 1 (T‐E1): supresión del riego en la postcosecha temprana (junio y julio); (iii) Estrés 2 (T‐E2): supresión del riego en la postcosecha tardía (agosto y septiembre), y iv) Estrés 3 (T‐E3): supresión del riego durante todo el período postcosecha (junio‐septiembre). Salvo en las fases de estrés, todos los tratamientos recibieron idénticas dosis de riego que T‐CTL. La producción total y el número de frutos por árbol fue mayor en T-CTL y T-E1, que en el resto de tratamientos de estrés. Además, el tratamiento T-E2 registró el mayor porcentaje de frutos agrietados. El análisis de reservas en raíz mostró valores significativamente más altos de arginina y fósforo en los árboles del tratamiento T‐E1 seguido de T‐CTL. No se observaron diferencias significativas entre tratamientos en los parámetros de calidad físico-química estudiados. Estos resultados sugieren que el periodo de postcosecha tardía (agosto‐septiembre), es más sensible que el de postcosecha temprana (junio-julio) al déficit hídrico severo, pues disminuye la acumulación de reservas nutricionales, afectando al rendimiento del cultivo.

Although mycorrhizae applications have been widely used to improve the establishment and growth of agricultural crops, there have been no studies on their application in field-grown nectarine trees. In this work, a commercial arbuscular mycorrhizal fungus (AMF; Glomus iranicum var. tenuihypharum) was applied by means of fertigation to inoculate young “Flariba” nectarine trees grown in south-eastern Spain to evaluate its effect on plant water status, and vegetative and reproductive growth. Using minirhizotrons to measure the root dynamics over a complete growing season, revealed that AMF substantially increased root growth (51% increase compared with untreated trees), while no changes in plant water status or canopy development were noted. The productive response improved in inoculated trees, as demonstrated by a significantly higher yield, fruit size, number of fruits per tree and greater crop load efficiency values than in untreated trees. Given that the same amount of irrigation solution was applied in both treatments, the irrigation water use efficiency increased by 19.5% in AMF compared with untreated trees. The findings of this study suggest that a simple inoculation of AMF can be considered a good practice in semi-arid agro-systems to firmly establish efficient young nectarine trees and enhance their adaptation to field conditions.

Lime tree growing area is increasing in Mediterranean temperate regions. In these areas, climate change scenario is expected to raise air temperature and water shortages. Such scenario requires new approaches to implement a precision irrigation in agriculture. In order to use water more efficiently, it becomes necessary to accurately determining the crop water needs, which are estimated by crop evapotranspiration computations (ETc). In this study the ETc of young lime trees grown under Mediterranean conditions were determined using the soil water balance method. For this purpose, two-year old lime trees (Citrus latifolia Tan., cv. Bearss) grafted on C. macrophylla rootstock were cultivated in pot-lysimeters, equipped with capacitance and granular matric sensors for real-time monitoring of the soil water status. Irrigation, drainage, and pot weight were also monitored continuously. All measurements were integrated into a telemetry platform. Agro-meteorological variables, plant water status (stem (Ψstem) and leaf (Ψleaf) water potentials), and leaf gas exchange parameters (stomatal conductance (gs) and net photosynthesis (Pn)) were measured. Along the experiment, an automated irrigation protocol based on volumetric soil water content (θv) threshold values were programmed, guaranteeing an adequate lime tree water status. Irrigation dose was calculated based on a feed-back strategy maintaining θv within 30% management allowed depletion.During the experimental period, the lime trees were well irrigated as revealed midday Ψstem values that were maintained above -0.8 MPa. Also, the mean seasonal values of ≈ 7 µmol m−2 s−1 and 80 mmol m−2 s−1, for Pn and gs, respectively, indicated optimal gas exchange values. The computed water balance parameters yielded values for the crop evapotranspiration from 0.25to 2.56 mm day-1, in winter and summer months, respectively, with maximum values in July when evaporative demand conditions were the highest. This soil water balance was daily validated by the pot weight balance through the year.In conclusion, the automated irrigation of young potted lime trees, using soil water content as a control system variable, has ensured an adequate lime tree water status. A simple, robust weighing/drainage lysimeter, with real-time monitoring of the soil water balance parameters, has been proved practical and economical tool for crop evapotranspiration measurements.Acknowledgments: This work was funded by Spanish Agencia Estatal de Investigación (PID2019-106226RB-C2-1/AEI/10.13039/501100011033) and Fundación Séneca, Región de Murcia (19903/GERM/15) projects.

In a low water availability scenario, as is increasingly frequent in Mediterranean areas threatened by climate change and endemic water scarcity, to achieve the best irrigation water efficiency is of vital importance. This study aimed to assess the feasibility of an automated irrigation scheduling strategy based on real-time threshold volumetric soil water content values (VSWC), monitored with capacitance probes, in adult early-maturing nectarine orchard (Prunus persica (L.) Batsch cv. `Flariba’, on GxN-15 rootstock). Two drip irrigation practices were tested: one control treatment (T-0) based on conventional crop evapotranspiration calculations (ETc, FAO-56), and one automated treatment (T-A) based on management allowed depletion (MAD) threshold values, derived from VSWC data, with a feed-back control system. Furthermore, for both treatments agro-physiological responses were evaluated under two different water availability scenarios (each one comprised of three consecutive growing seasons): no water restrictions (high water availability), and deficit irrigation (low water availability), in which reduced water to irrigate nectarine trees involved regulated deficit irrigation criteria. In the high water availability scenario, T-A (MAD = 10%) and T-0 (ETc = 100%) irrigation treatments showed no significant differences in the plant-soil water status, vegetative growth, yield, and nectarine fruit quality parameters. The VSWC was not a limiting factor and full irrigating to achieve a maximum yield was a profitable option. In the low water availability scenario, the T-A treatment (subjected to MAD = 10% during pre-harvest and 30% during post-harvest) received 43% less water than the control, which promoted moderate plant and soil water deficits, leading to a decrease in vegetative growth (winter pruning weight and tree canopy cover), without compromising the total yield and nectarine fruit quality parameters (including an increase in the total soluble solid content). The crop water use efficiency increased by an average of 34%. The proposed automated irrigation strategy, based on MAD seasonal threshold values, combined with regulated deficit irrigation phenological criteria could be considered a promising tool that could be eventually extrapolated to other stone fruit orchards under water scarcity conditions. Acknowledgements: This work was funded by Spanish Agencia Estatal de Investigación (PID2019-106226RB-C21/AEI/10.13039/501100011033) and Fundacion Séneca, Región de Murcia (19903/GERM/15) projects.

El objetivo principal del trabajo es el de evaluar los efectos de diferentes sistemas de cultivo: al aire libre (en meseta, sin meseta) y bajo malla de sombreo, en la producción y el crecimiento vegetativo de limeros (Citrus latifolia Tan., cv. Bearss) jóvenes. El ensayo se llevó a cabo durante dos campañas (2018 y 2019) en la finca experimental del CEBAS-CSIC en Murcia. El crecimiento vegetativo se evaluó con medidas del diámetro del tronco y del ancho y alto de copa, y el crecimiento de fruto con medidas de su diámetro ecuatorial. En el momento de la recolección se determinaron los kilos de fruta y número de frutos por árbol y se calculó el peso unitario medio del fruto. Los resultados obtenidos apuntan a que los árboles cultivados bajo malla de sombreo mostraron un mayor volumen de copa que los cultivados al aire libre, debido a una significativa mayor altura. La producción fue también mayor (aunque no significativa) en los árboles bajo sombreo, debido a un mayor tamaño de las limas durante la última fase de su crecimiento. La disminución de la radiación incidente en las condiciones de sombreo, propiciaron la creación de un microclima más favorable para la asimilación de carbono, lo que parece provocar unas mejores condiciones para el desarrollo vegetativo de los árboles y la producción de limas de calidad. El trabajo se ha financiado con los proyectos AGL2016-77282-C03-1R y PID2019-106226RB-C2-1 (Plan Nacional AEI-Fondos FEDER-UE) y 19903/GERM/15 (Ayudas Grupos de Alto Rendimiento, Fundación Séneca, Región de Murcia).

En este trabajo se evalúan los efectos de diferentes condiciones de manejo del riego sobre la producción, calidad y conservación de nectarina extratemprana. Se aplicaron 3 tratamientos: dos con programación del riego en base a 100% ETc, con un lateral de riego (T-Simple) y dos laterales (T-Doble), y programación del riego automática (T-Automático) en base a sensores de agua en el suelo. A pesar de la doble superficie de suelo humectada en T-Doble se observó un déficit ligero durante la postcosecha (disminución de potencial hídrico de tallo a mediodía (Ψt,md) de 0,15 MPa respecto a T-Simple), que no afectó de forma significativa a la producción y calidad de la nectarina. La programación automática en base a sensores generó un déficit moderado, con diferencias de Ψt,md de 0,25 MPa respecto a TSimple durante la postcosecha. T-Automático supuso un ahorro de agua del 35%, sin afectar a los parámetros de producción (salvo un aumento del contenido en sólidos solubles totales, SST) y mejorando la eficiencia del uso del agua, EUA (32% > T-Simple). Durante el periodo de conservación (10 días a 0 ºC + 5 días a 15 ºC), las nectarinas del T-Automático mostraron los valores más altos de SST y del índice de madurez, mientras que las del TDoble mostraron los valores más altos de luminosidad (L). Los frutos de todos los tratamientos se evaluaron sensorialmente como aptos para la comercialización, no obstante, los del T-Automático fueron los mejor clasificados por el consumidor. El trabajo se ha financiado con los proyectos AGL2016-77282-C03-1R y PID2019-106226RB-C2-1 ( y 19903/GERM/15 (Fundación Séneca, Región de Murcia). M.R. Conesa agradece la ayuda posdoctoral disfrutada del programa Juan de la Cierva (FJCI-2017-32045).

© 2020 by the authors., Physiological plant water status indicators are useful for managing precision irrigation in regions with limited water resources. The aim of this work was to evaluate the effect of shade netting on the diurnal and seasonal variations of several plant water status indicators in young lime trees (Citrus latifolia Tan., cv. Bearss), grown at the CEBAS-CSIC experimental station in Murcia, Spain. Stem water potential (Ψstem), leaf gas exchange (net photosynthesis (Pn) and stomatal conductance (gs)), and canopy temperature (Tc) were measured on representative days of winter and summer. The Ψstem daily pattern was quite similar in both seasons under both conditions. However, the circadian rhythm of leaf gas exchange was affected by shade conditions, especially in summer, when shaded leaves showed maximum gs values for a longer time, allowing higher net photosynthesis (37%). Canopy temperature behaved similarly in both conditions, nevertheless, lower values were recorded in open-air than in shaded trees in the two seasons. The canopy-to-air temperature difference (Tc − Ta), however, was lower in shaded trees during the daylight hours, indicating the higher degree of leaf cooling that was facilitated by high gs values. The possibility of continuously recording Tc makes it (or the proposed canopy thermal index, CTI) a promising index for precise irrigation scheduling. Shade netting was seen to favour gas exchange, suggesting that it may be considered alternative to open-air for use in semi-arid areas threatened by climate change., This study was supported by the Spanish Research Agency and co-financed by European Union FEDER funds (AEI/FEDER, UE, AGL2016-77282-C3-1R) and “Fundación Séneca, Agencia de Ciencia y Tecnología” of the Region of Murcia under the Excellence Group Program (19903/GERM/15) projects.

This work aimed to ascertain the effects of diff; erent irrigation management practices on yield, fruit quality (nutritional and sensorial) and storage performance of early-maturing nectarine fruits during three consecutive growing seasons (2016/2017–2018/2019) under Mediterranean conditions. Three irrigation treatments were studied: two based on maintaining non-limiting soil water conditions (100 % crop evapotranspiration, ETc) with one (T-Single) or two (T-Double) lines of emitters; and one based on volumetric soil water content (VSWC) threshold values (T-Auto). Despite the greater wetted surface in the T-Double treatment, a mild plant water deficit was observed during the post-harvest period, which did not significantly affect the yield and nectarine fruit quality. The T-Auto irrigation based on VSWC, which received 43 % less water than the T-Single treatment, caused a moderate water deficit, without yield penalty in any of the growing seasons studied and an increase in the water use efficiency of 34 % respect to the T-Single treatment. Furthermore, nectarine fruits from the T-Auto treatment had higher TSS levels (°Brix) at harvest. There were no significant differences in the physico-chemical quality among treatments after 10 days of cold storage (0 °C) plus 5 days of shelf-life (15 °C), showing fruits from the T-Single treatment the highest weight loss values. The use of precise agronomic criteria with soil water sensors is an avant-garde alternative for irrigation scheduling compared to the conventional ETc-based irrigation that improved water use efficiency and contributed to the sustainability of agriculture. The T-Double treatment has not provided any advantage in terms of production and quality compared to the T-Single treatment., This research was supported by Spanish National Plan-FEDER (AGL2013-49047-C02-2R, AGL2016-77282-C03-1R and PID2019-106226RB-C2-1) and Seneca Foundation of Region of Murcia (19903/GERM/15) projects. Conesa M.R. acknowledges the postdoctoral financial support received from the Spanish Juan de la Cierva program (FJCI -2017 -32045)

A growing international human population and rising living standards are increasing the demand for agricultural products. Under higher pressure over natural resources, environmental concerns are increasing as well, challenging current water use decision-making processes in irrigated agriculture. Higher agricultural productivity means water should be applied more efficiently, which requires instant information on weather, soil, and plant conditions throughout the growing season. An information-based irrigation scheduling application tightened to the spatiotemporal variability of the fields is critical for enhancing the current irrigation system and making better irrigation scheduling decisions. The aim of this study is to review current irrigation scheduling methodologies based on two case studies (woody and field crops) located in semi-arid areas of Southeast Spain. We realize that optimal irrigation programming requires consistent investment in equipment, expenditure on operation and maintenance, and qualified technical and maintenance services. These technological approaches will be worthwhile in farms with low water availability, high profitability, and significant technical-economic capacity.

In the context of a water scarcity scenario, typical of Mediterranean climates, the agronomic and physiological responses of early-maturing peach trees, such as tree growth pattern (including root dynamics), to different deficit drip irrigation strategies are discussed. An estimation of local crop, basal, and irrigation coefficients is also presented. Compared with full irrigation, a deficit irrigation strategy, managed continuously during the growing season, induces a reduction in yield, fruit size, and vegetative growth, whereas a regulated deficit irrigation strategy, performed during specific phenological periods (outside stage III of fruit growth), induces maximum water saving despite a reduction in yield but no changes in fruit size or quality at harvest, leading to the highest water use efficiency. For optimal yield, stem water potential should be maintained above −0.9 MPa during summer. Automatic irrigation based on soil water content status monitoring and plant phenology allows feedback irrigation scheduling with no penalization in yield.

[ESP] El objetivo de la Tesis se centró en desarrollar las bases necesarias para programar el riego del melocotonero (Prunus persica (L.) Batsch, cv. Flordastar, injertados sobre pie de GF-677) utilizando exclusivamente medidas de la máxima contracción diaria del tronco (MCD). Este objetivo global se abordó a partir de los siguientes objetivos parciales: a) evaluación de la sensibilidad de la MCD como indicador del estado hídrico, b) comparación de la programación del riego utilizando medidas de la MCD y el flujo de savia, c) elaboración de ecuaciones de referencia de la MCD, y d) evaluación de la utilización de estas ecuaciones de referencia en la programación del riego. Los resultados indicaron que la MCD es un indicador más sensible y consistente que el flujo de savia para diagnosticar cambios en el estado hídrico del melocotonero. Las bajas necesidades de mantenimiento del instrumental, junto con el suministro de información en tiempo real confirmaron sus potencialidades como herramienta de precisión para la programación automática del riego. En este sentido, cabe destacar que se pudo programar el riego del melocotonero utilizando exclusivamente medidas de la máxima contracción diaria del tronco, ya que las dosis de riego se pudieron ajustar de forma precisa conforme se generaba la información suministrada por el indicador, no induciendo ninguna situación de déficit hídrico ni afectando la producción ni la calidad del melocotón. Por el contrario, la programación del riego utilizando medidas de flujo de savia mostró una inferior precisión en los ajustes de las dosis de riego, induciendo situaciones de déficit hídrico moderado y afectando el tamaño de los frutos recolectados. Complementariamente, pudo demostrarse que el riego programado manteniendo la intensidad de señal de la MCD en valores muy cercanos a la unidad es una prometedora herramienta para la estima de las necesidades de riego de los cultivos. Por otro lado, los ajustes diarios de las dosis de riego suponen un claro aumento de la precisión del riego en periodos de alta variabilidad como el crecimiento del fruto. Pudieron obtenerse ecuaciones de referencia para la MCD respecto de las variables climáticas, si bien, sólo cuando se utilizan valores de la evapotranspiración del cultivo de referencia, el déficit de presión de vapor medio diario o la temperatura media diaria fue posible obtener ecuaciones de referencia con validez interanual. Para la elaboración de estas líneas de base es necesario considerar que las variaciones diarias del diámetro del tronco tienen que contemplarse no sólo en el contexto del balance hídrico de la planta sino en el del balance de carbono, lo que obliga a considerar periodos fenológicos concretos, evitando la consideración conjunta de toda la estación de crecimiento. La comparación de la respuesta al riego programado utilizando ecuaciones o árboles de referencia mostró como la programación con árboles de referencia es más precisa durante el periodo de crecimiento del fruto. No obstante, los resultados obtenidos durante la postcosecha sugirieron que el uso de ecuaciones de referencia elaboradas sobre la base de datos de más años constituirá un adecuado procedimiento para programar de forma precisa el riego. [ENG] The research reported in this Thesis was carried out to test the hypothesis that irrigation scheduling in peach trees (Prunus persica (L.) Batsch, cv. Flordastar, grafted on GF-677) can be based exclusively on maximum daily trunk shrinkage (MDS) measurements. For this, we studied i) the sensitivity of MDS and sap flow (SF) as indicators of the plant water status in response to a cycle of water stress and recovery, ii) the comparison of irrigation scheduling using MDS and SF measurements, iii) the feasibility of obtaining MDS baselines for use in irrigation scheduling, and iv) the plants response to irrigation scheduled using these reference equations. Our findings indicated that MDS in peach trees is a more suitable plant-based indicator than SF because it is more sensitive and reliable in detecting changes in plant water status. Moreover, other complementary aspects, including that the sensors did not need repositioning during the observation period, low labour costs and the possibility of obtaining automatic information in real time, confirm the suitability of using MDS as an indicator for irrigation scheduling Peach tree irrigation scheduling can be based on MDS measurements alone, because it is possible to adjust the irrigation schedule according to the daily information provided by MDS without affecting plant water status, yield and fruit size. In addition, MDS signal intensity-driven irrigation schedules at MDS signal intensity values very close to unity could be applied to derive better irrigation protocols when local Kc values are not available. On the contrary, peach irrigation scheduling using SF measurements showed a lower precision, inducing mild water stress situations and affecting fruit size. Daily irrigation scheduling improved irrigation precision in periods of high MDS variability as fruit growth period. Reference relations between MDS and climatic variables in trees under non-limiting soil water conditions were established, with the characteristic that it was possible to predict MDS reference values using inter-seasonal equations only when climatic variables measured on a whole-day basis (crop reference evapotranspiration, mean daily vapour pressure deficit and daily mean air temperature) were used. The fact that during the experiment the fits for individual periods were better than those obtained for the seasonal regressions, confirmed that daily stem diameter variations must be considered not only in the context of the water status of the plant but also in the context of the carbon status of the plant, because, under non-limiting soil water conditions, MDS values were closely related to the presence or absence of a sugardemanding sinks. The comparison of the plant response to irrigation scheduled using reference equations or reference trees showed that during fruit growth the use of reference trees is more convenient. Nevertheless, the results obtained after harvest induce to think that the use of reference equations elaborate on more data years basis will be a suitable procedure to obtain reference MDS values for precise irrigation scheduling., Escuela Internacional de Doctorado, Universidad Politécnica de Cartagena, Programa de Doctorado de Tecnología agraria y alimentaria

BACKGROUND Biochemical and enzymatic responses to long-term regulated deficit irrigation (RDI) at harvest, during cold storage and after the retail sale period of ‘Flordastar’ early peaches were evaluated. Irrigation strategies were Control, and two RDI applied during post-harvest period (RDI1, severe; RDI2, moderate), based on different thresholds of maximum daily shrinkage signal intensity (RDI1, 1.4 to dry; RDI2, 1.3 to 1.6). RESULTS Both RDI provoked stress in the plant. This meant higher antioxidant concentration [averaging 1.30 ± 0.27 g ascorbic acid equivalents (AAE) kg−1 fresh weight (FW) for control and 1.77 ± 0.35 and 1.50 ± 0.30 g AAE kg−1 FW for RDI1 and RDI2, respectively]. Antioxidant levels decreased with storage by polyphenoloxydase action, which increased (from 0.04 ± 0.01 U mg−1 protein to 0.32 ± 0.08 U mg−1 protein). Vitamin C was initially higher in RDI samples (44.22 ± 0.05 g total vitamin C kg−1 FW for control vs. 46.77 ± 0.02 and 46.27 ± 0.03 g total vitamin C kg−1 FW for RDI1 and RDI2, respectively). CONCLUSION The way RDI was applied affected bioactive fruit composition, being catalase and dehydroascorbic acid good water stress indicators. RDI strategies can be used as field practice, allowing water savings while enhanced healthy compound content in early peaches. © 2015 Society of Chemical Industry

Seasonal Ψstem is a useful diagnostic tool for peach tree irrigation management.The autumn rainfall events point to the resilient behaviour of the peach cultivar studied.The soil water content was the main contributor to Ψstem estimation.Ψstem was estimated by regression equation of soil water content, GDH and VPDm data. In the last decade deficit irrigation strategies allowed growers to deal with water shortages, while monitoring stem water potential (Ψstem) is deemed essential for maximising fruit yield and quality. However, because of the intensive labour involved in measuring Ψstem, alternative methods are desirable. The experiment described was conducted in Murcia (Spain) with adult peach trees (Prunus persica (L.) Batsch cv. Flordastar) submitted to different drip irrigation treatments, measuring Ψstem with a pressure chamber and the soil water content with a neutron probe. Agro-meteorological variables were recorded. Seasonal patterns of stem water potential provide a useful diagnostic tool for irrigation management in peach trees. Rainfall events and the meteorological conditions prevailing in autumn pointed to the resilient nature of the peach cultivar studied. Fitting Ψstem by linear regression analysis as a function of soil and atmosphere yielded a significant correlation, with the soil water content being the main contributor to estimating Ψstem. Linear regression analysis highlighted the importance of considering plant water status as a function of the peach tree cultivar, the atmospheric conditions in which it develops and the soil water conditions resulting from irrigation. A multiple linear regression equation based on soil water content in the soil profile, mean daily air vapour pressure deficit (VPDm) and growing degree hours (GDH) data explained 72% of the variance in Ψstem, and is proposed as an alternative to the field measurement of Ψstem.

The objectives of the paper were to study the pattern of root growth (measured by minirhizotrons) in relation to trunk, fruit and shoot growth and the effects of crop load on tree growth and yield in peach trees. Two crop load (commercial and low) treatments were applied in a mature early-maturing peach tree orchard growing in Mediterranean conditions. Root growth dynamics were measured using minirhizotrons during one growing season. Shoot, trunk and fruit growth were also measured. At harvest, all fruits were weighed, counted and sized. Roots grew throughout the year but at lower rates during the active fruit growth phase. Root growth was asynchronous with shoot growth, while root and trunk growth rates were highest after harvest, when the canopy was big enough to allocate the photo-assimilates to organs that would ensure the following season’s yield. Shoot and fruit growth was greater in the low crop load treatment and was accompanied by a non-significant increase in root growth. High level of fruit thinning decreased the current yield but the fruits were more marketable because of their greater size.

The paper identifies and quantifies how crop load influences plant physiological variables that determine stem diameter variations to better understand the effect of crop load on drought stress indicators. Stem diameter (D stem) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two D stem derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit growth stages.

Summer pruning (SP) in fruit trees can be performed with the aim of improving fruit quality by permitting better light penetration and carbon allocation, reducing the needs for winter pruning (WP). This paper deals with the effects of SP on the plant water status, vegetative growth, yield and fruit quality of two Prunus persica fruit trees of different ages: mature (peach trees) and young (nectarine trees). Pruning provided a total of 8 and 12 kg dry matter tree−1, being the SP contribution of 56% and 34%, of young and mature Prunus trees, respectively. Tree cover (obtained with zenithal image analysis) was significantly lower in the SP treatment, which resulted in an improvement in the plant water status of about 0.30 MPa with respect to WP trees in summer, leading to a reduction in water consumption during periods of highest evaporative demand (postharvest), equivalent to 10% of annual requirements under WP conditions. No significant differences were detected between WP and SP in the yield components studied. Our findings highlight the importance of considering the tree age/size as a key factor for the application of SP in trees grown under commercial conditions. Summer pruning can be considered a sensible cultural practice to mitigate the drought effects in early-maturing Prunus persica, maintaining yield with no extra costs.

The aim of this study was to establish threshold TGR and MDS values which could be used in regulated deficit irrigation in future work. Three irrigation treatments were performed during three seasons in a 37 year-old table olive orchard in Seville (Spain). Control treatment was irrigated with 125% of the crop evapotranspiration. Regulated deficit irrigation (RDI) treatments were performed according to the phenological stage of the trees and different water stress levels. RDI trees were irrigated only when the threshold values of water stress level was reached. Water stress conditions were applied during the massive pit hardening period (phase II, RDI-2) or during this period and the shoot-flowering period (phase I, RDI-12). The water stress level was performed with the trunk growth rate (TGR) during phase I and recovery and maximum daily shrinkage signal (MDS signal) during phase II. Both parameters were calculated as relative values of the Control trees. TGR threshold values varied from equal to Control (RDI-2) or 0.25μm day-1 less than Control (RDI-12) during phase I. MDS signal (ratio between MDS in RDI vs MDS Control) threshold values varied from 0.5 (RDI-12) to 0.75 (RDI-2). In the recovery period, trees were irrigated when TGR values were lower than Control. This scheduled changed the amount of applied water between high and low fruit load seasons. The total amount of applied water in RDI trees oscillated from 38 to 160mm, depending on the season and the treatment. The yield was not significantly different between Control and deficit treatments. Fruit volume and number of fruits was affected for the irrigation. Limitations and management of TDF in irrigation scheduling is discussed., This research was supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) (AGL2007-66279-C03-02/AGR and AGL2010-19201-CO4-03). The stay of D. Morales was supported by the AECID project D/030431/10.

A 4-year long experiment was conducted using drainage lysimeters to determine the basal crop coefficients of an early season drip irrigated peach tree cultivar growing in a clay loam textured soil in southern Spain. The lysimeters were equipped with irrigation and drainage water meters and access tubes for monitoring the soil water content by neutron probe. Crop evapotranspiration (ET c ) was obtained from the water balance equation. Following the dual crop coefficient approach, K c was split into the basal crop coefficient ( K cb ) and the soil evaporation coefficient ( K e ). The effect of tree size on K cb was determined for two canopy covers. The K cb for full yield peach trees changed during the growing season gradually increasing from 0.15 at the beginning of the year (January) to a maximum of 1.0 during July, followed by a rapid fall to 0.15 at the end of year. The proposed curvilinear K cb pattern fitted well with the phenological stages and their water use, and could serve for irrigation scheduling for early maturing peach trees growing in Mediterranean semi-arid climatic conditions.

No information exits on the effects of water stress on pomegranate ( Punica granatum L.) fruits. In this paper, the influence of three irrigation treatments on the physical and chemical characteristics of the fruits of adult pomegranate trees was studied. Control (T0) plants were drip irrigated (60% ETo from the beginning of the season to the end of the first half of linear fruit growth phase, 117% ETo during the second half of linear fruit growth phase and 99% ETo during the end of fruit growth and ripening phase) in order to guarantee non-limiting soil water conditions, T1 plants were drip irrigated according to the criteria frequently used by the growers in the area (32% ETo from the beginning of the season to the end of the first half of linear fruit growth phase, 74% ETo during the second half of linear fruit growth phase and 36% ETo during the end of fruit growth and ripening phase) and T2 plants were irrigated as T1, except during the second half of linear fruit growth phase, in which irrigation was withheld. To ensure the recovery of T2 plants re-irrigation was performed at the levels used in T0. T1 plants achieved a moderate water stress level, whereas T2 plants achieved a more pronounced water stress level, from which they completely recovered when plants were rewatered. During ripening the peel of pomegranate fruits changes to show higher luminosity and greater red saturation. Also, the colour of the arils changes to a more perceptible red colour as a consequence of the increasing total anthocyanin content. However, neither the intense red colour of the arils nor their total phenolic compounds content was correlated with the juice antioxidant capacity. Considerable differences were observed in the response of pomegranate fruits to both deficit irrigation treatments. In this sense, fruits from T1 plants showed a decrease in fruit growth, leading to a lower final fruit size and lower total yield, and some changes in colour and chemical characteristics, which reflected earlier ripening. In contrast, a more pronounced water stress during the second half of the fruit growth phase (T2) was more critical for fruit size than for the chemical characteristics of the fruit, probably because under this situation carbon assimilation should be allocated to the synthesis of primary metabolites, which did not exceeded the amount used for fruit growth to the detriment of the synthesis of carbon-based secondary metabolites.

Ministerio de Economía y Competitividad AGL2013-49047-C02-2R

BACKGROUND: Iron (Fe) chlorosis is a serious problem affecting the yield and quality of numerous crops and fruit trees cultivated in alkaline/calcareous soils. This paper describes the efficiency of a new class of natural hetero-ligand Fe(III) chelates (Fe-NHL) to provide available Fe for chlorotic lemon trees grown in alkaline/calcareous soils. These chelates involve the participation in the reaction system of a partially humified lignin-based natural polymer and citric acid. RESULTS: First results showed that Fe-NHL was adsorbed on the soil matrix while maintaining available Fe for plants in alkaline/calcareous solution. The effects of using three different sources as Fe fertilisers were also compared: two Fe-NHL formulations (NHL1, containing 100% of Fe as Fe-NHL, and NHL2, containing 80% of Fe as Fe-NHL and 20% of Fe as Fe-ethylenediamine-N,N′-bis-(o-hydroxyphenylacetic) acid (Fe-EDDHA)) and Fe-EDDHA. Both Fe-NHL formulations increased fruit yield without negative effects on fruit quality in comparison with Fe-EDDHA. In the absence of the Fe-starter fraction (NHL1), trees seemed to optimise Fe assimilation and translocation from Fe-NHL, directing it to those parts of the plant more involved in development. CONCLUSION: The field assays confirmed that Fe-NHL-based fertilisers are able to provide Fe to chlorotic trees, with results comparable to Fe-EDDHA. Besides, this would imply a more sustainable and less expensive remediation than synthetic chelates. Copyright © 2012 Society of Chemical Industry

Adult pomegranate trees ( Punica granatum (L.) cv. Mollar de Elche) were submitted to three irrigation treatments. Control (T0) plants were drip irrigated in order to guarantee non-limiting soil water conditions, T1 plants (deficit irrigation) were drip irrigated according to the criteria commonly used by the growers in the area and T2 plants were subjected to water withholding and recovery periods of 34 and 6 days, respectively, during the summer of 2009. The results indicated that pomegranate plants confront water stress by developing stress avoidance and stress tolerance mechanisms. From the time of deficit irrigation (T1) and water withholding (T2) began to be applied, leaf conductance decreased in order to control water loss via transpiration and to avoid leaf turgor loss (stress avoidance mechanism). Close to the end of the stress period, when maximum stress levels had developed, active osmotic adjustment was triggered, contributing to the maintenance of leaf turgor (stress tolerance mechanism). Other drought tolerance characteristics commonly seen in xeromorphic plants were also observed, such as high relative apoplastic water content (42–58%), which would contribute to the retention of water at low leaf water potentials.

SUMMARYAdult early maturing peach trees (Prunus persica(L.) Batsch cvar Flordastar) grafted ontoP. persica×Prunus amygdalusGF-677 peach rootstock, were subjected to low water availability (water stress) and recovery periods for 28 and 7 days, respectively, during summer 2009. Control plants were irrigated daily at 1·3 estimated crop reference evapotranspiration (ETC) in order to obtain non-limiting soil water conditions. Active osmotic adjustment was observed at the end of the stress period. However, the magnitude of this osmotic adjustment (0·18 MPa) was not sufficient to modify the leaf water potential at turgor loss point. The observed active osmotic adjustment that maintained turgor was in contrast to other results in potted peach trees, where no osmotic adjustment was observed, and highlights the importance of field studies in which water stress is developed gradually over a prolonged period. Relative apoplastic water content (RWCa) values were high and decreased as a result of water stress. The rapid decrease in leaf conductance from the beginning of the stress period, together with the delay in stomatal reopening after rewatering, indicated that stomatal behaviour was not a simple passive response to water deficit. The results indicate that drought resistance in early maturing peach trees is based both on avoidance mechanisms, such as stomatal control and tolerance mechanisms, including active osmotic adjustment and high RWCa.

Trunk diameter fluctuations (TDFs) have been suggested as an irrigation-scheduling tool for several fruit trees, but the works in olive trees has not obtained successful results with any of the indicators (maximum daily shrinkage (MDS) and trunk growth rate (TGR)) that are calculated from the daily TDF curves. No studies of olive trees have ever used reference trees to reduce the influence of the environment, as in work for other fruit trees. In this work, we compare different continuous and discrete water status measurements in a drought cycle. We suggest the calculation of a new and related indicator (DTGR), the difference between the TGR of stressed trees, and the TGR of reference trees. Negative DTGR values always indicate water stress conditions. The current work describes the variations of this new indicator (DTGR) in relation to water stress, and compares DTRG to the midday stem water potential, maximum leaf conductance and to the MDS. The midday stem water potential and the maximum leaf conductance describe the stress cycle clearer than the trunk diameter fluctuation indicators. No significant differences were found in the values of MDS between stressed and reference trees. On the other hand, the DTGR pattern values were near that of the stem water potential, though positive values were recorded in some dates during the water stress cycle. These variations indicate that DTGR is not a cumulative water stress indicators, as is water potential. Therefore, according to our data, water potential is a better indicator than the TDF parameters when no deficit irrigation scheduling is performed in olive trees. DTGR seems to be a good indicator of water stress from a threshold value around -1.4. MPa in olive trees. In addition, higher variability of DTGR than stem water potential may also be reduced with the increase in the number of sensors.

Measurements of midday stem water potential (Ψstem) and maximum daily trunk shrinkage (MDS) were taken over a 4-year period in early maturing peach trees (Prunus persica (L.) Batsch cv. Flordastar) grafted on GF-677 rootstock. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that seasonal reference equations can be obtained for MDS and Ψstem using crop reference evapotranspiration (ETo), daily mean vapour pressure deficit (VPDm) and mean daily air temperature (Tm) in the case of MDS, and ETo and VPDm in the case of Ψstem. In this way, VPDm was seen to be the best predictor of MDS and Ψstem, without both were influenced significantly by yield or crop load variations between years. When the postharvest regression between MDS or Ψstem and the meteorological parameters mentioned were broken down into early and late postharvest periods, the correlation coefficients improved and were closely related to the presence or absence of sugar-demanding sinks, such as active root growth. A negative linear relationship between MDS and Ψstem was found, pointing to unchanging radial hydraulic conductivity in the bark tissues and suggesting that MDS depends to a great extent of the water potential.

The effects of high crop load (unthinned trees, 22�23 fruits cm-2 of trunk cross-sectional area (TCSA)), commercial crop load (3�4 fruits cm-2 of TCSA), and no crop load (all fruitlets removed) on maximum daily trunk shrinkage (MDS), trunk growth rate (TGR) and stem water potential (?stem) were studied during the fruit growth period and 20 days following harvest in fully irrigated early maturing peach trees, Prunus persica (L.) Batsch, cv. Flordastar. Even though crop load did not affect plant water status, the MDS and TGR values increased and decreased, respectively, as a result of the crop load effect. In this sense, for the same ?stem value, there was a linear increase in MDS with crop load, with a slope of 6.6 µm MPa-1 per unit of crop load increment. The effects of environmental conditions on daily MDS values were also dependent on crop load, suggesting that MDS reference values should be obtained by representing the relations between MDS and the climatic variables (daily mean air temperature, daily mean vapour pressure deficit and daily crop reference evapotranspiration) for a given crop load. The constancy of the relation between MDS and ?stem across crop load underlined the constancy of the elastic properties of the bark tissues.

Adult Fino lemon trees (Citrus limon L. Burm. fil.) grafted on sour orange (Citrus aurantium L.) and irrigated above their crop water requirements (T0 treatment) were compared with plants where water was applied according to maximum daily trunk shrinkage (MDS) (T1 treatment), in order to maintain MDS signal intensity [actual (T1) MDS/control (T0) MDS] threshold values close to unity. When MDS signal intensity on at least 2 of 3 consecutive days did not exceed the signal intensity threshold value, irrigation was reduced by 10%. In contrast, when the MDS signal intensity on at least 2 of 3 consecutive days exceeded the threshold value, the irrigation rate was increased by 10%. The results indicated that lemon tree irrigation scheduling can be based on MDS measurements, avoiding the appearance of any plant water stress situation without affecting yield or fruit quality. Also, the cumulative amounts of applied water in T1 plants can be considered as an estimate of lemon tree water requirements, because they were only 9% above the estimated crop evapotranspiration (ETc) and drainage did not occur. Nevertheless, to improve the precision of irrigation management, some changes in the irrigation protocol for periods of variable evaporative demand were proposed: for instance, increasing the irrigation scheduling frequency and/or using changes in the daily irrigation rate higher than those proposed in the protocol.