Agronomic and physiological basis for automating regulated deficit irrigation in sweet cherry trees

Mención Europeo / Mención Internacional: Concedido[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. La tesis estudia el funcionamiento hídrico del cerezo a partir del empleo de diferentes estrategias de riego y técnicas de cultivo. Para ello, se evaluaron las respuestas agronómica y fisiológica del cultivo y se estudiaron y compararon diferentes indicadores del estado hídrico del continuo suelo, planta, atmósfera con el fin último de aumentar la productividad del uso de agua.[ENG] This doctoral dissertation has been presented in the form of thesis by publication. The global sweet cherry production has sharply increased in the last decades. As consumer interest in this seasonal fruit keeps growing, growers from areas where cherries have not been traditionally cultivated exhibit interest and consider its cultivation due to a demand exceeding the offer. These new areas are interested in extending sweet cherry season and providing high quality fruit when there is a low supply on the market. To achieve these goals, it has been necessary to adopt new orchard systems, new cultivar/rootstock combinations adapted to different edaphoclimatic conditions, and drip irrigation systems.Los artículos que componen la tesis son los siguientes:: Artículo I. Blanco, V., Domingo, R., Pérez-Pastor, A., Blaya-Ros, P.J., Torres-Sánchez, R., 2018. Soil and plant water indicators for deficit irrigation management of field-grown sweet cherry trees. Agricultural Water Management, 208:83-94. DOI: 10.1016/j.agwat.2018.05.021. Artículo II. Blanco, V., Martínez-Hernández, G.B., Artés-Hernández, F., Blaya-Ros, P.J., Torres-Sánchez, R., Domingo R., 2019. Water relations and quality changes throughout fruit development and shelf life of sweet cherry grown under regulated deficit irrigation. Agricultural Water Management, 217:243-254. DOI: 10.1016/j.agwat.2019.02.028. Artículo III. Blanco, V., Torres-Sánchez, R., Blaya-Ros, P.J., Pérez-Pastor, A., Domingo, R., 2019. Vegetative and reproductive response of ‘Prime Giant’ sweet cherry trees to regulated deficit irrigation. Scientia Horticulturae, 249:478-489. DOI: 10.1016/j.scienta.2019.02.016. Artículo IV. Blanco, V., Zoffoli, J.P., Ayala, M., 2019. High tunnel cultivation of sweet cherry (Prunus avium L.): physiological and production variables. Scientia Horticulturae, 251:108-117. DOI: 10.1016/j.scienta.2019.02.023.Escuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Técnicas Avanzadas en Investigación y Desarrollo Agrario y Alimentario por la Universidad Politécnica de Cartagen

Precision irrigation in citrus with different water qualities

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. El cambio climático hará que la temperatura de la Tierra aumente 2,2 ◦C de aquí a 2040. Se prevé que este aumento de la temperatura del aire vaya acompañado de una reducción de las precipitaciones, lo que aumentará la intensidad y la frecuencia de los episodios de sequía. Paralelamente, la población mundial es más de tres veces mayor que a mediados del siglo XX y seguirá aumentando en los próximos años, lo que incrementará la demanda de agua para la producción de alimentos. En la actualidad, la producción mundial de alimentos mediante regadío representa más del 40 % del total y sólo utiliza alrededor del 20 % de la superficie destinada a este fin. Los cítricos son una de las principales especies cultivadas en todo el mundo, repartidas en más de 140 países. Esta especie depende del riego y tiene una demanda de agua media-alta. Para hacer frente a la sequía, la agricultura de regadío se ve obligada a realizar los máximos esfuerzos para mejorar la eficiencia en el uso del agua. En este contexto, la presente tesis doctoral tiene como objetivo evaluar la sostenibilidad del riego de precisión de cultivos de cítricos (pomelo y lima), con especial atención al estudio de la evapotranspiración del cultivo (ETc) y al uso de indicadores del estado hídrico de suelo y planta. Para alcanzar estos objetivos se han llevado a cabo varios experimentos (Artículos del I al IV). Un buen conocimiento de la ETc es necesario para decidir "cuándo" regar y "cuánta" agua aplicar. En el Artículo I, se calculó la ETc de limeros jóvenes por el método del balance hídrico del suelo utilizando lisímetros de pesada. A lo largo del ciclo de cultivo, la ETc fue más alta en Julio (2,56 L planta-1día-1), debido al elevado consumo de agua durante la última fase de crecimiento del fruto. Cuando los cambios en la biomasa de la lima fueron insignificantes, las variaciones en el peso de las macetas servían para validar la ETc calculada por el método del balance hídrico (r2=0,92***). En este artículo, se propone un prototipo de lisímetro de pesada escalable, sencillo y robusto, para árboles jóvenes cultivados en maceta, que proporciona una forma práctica y rentable de medir la ETc durante todo el año. En limeros jóvenes cultivados al aire libre y bajo malla de sombreo se midieron indicadores discretos del estado hídrico de la planta, como el potencial hídrico del tallo (Ψstem), la conductancia estomática (gs) y la fotosíntesis neta (Pn), así como indicadores continuos como la temperatura de la copa (Tc) (Artículos II y III). En el Artículo II, el sombreado incrementó un 54 y 37 % la gs y la Pn diaria acumulada, respectivamente. Además, bajo malla se incrementó el Ψstem en 0,05 MPa y se redujeron los valores de la diferencia de temperatura entre la copa y el aire (Tc-Ta) en 1,7 ◦C según los Artículos II y III. Estos hechos apuntaron un mejor comportamiento fisiológico de los limeros en condiciones de sombreado. En el Artículo III, se evaluó el efecto combinado del sistema de cultivo y el riego deficitario en los indicadores de estado hídrico del suelo y de la planta. Los resultados indicaron que cuando el estrés hídrico del suelo fue moderado, las condiciones de sombreado amortiguaron el efecto negativo sobre el estado hídrico del suelo y de la planta, permitiendo posponer el déficit hídrico. Sin embargo, cuando el estrés hídrico del suelo fue severo, se observaron valores igualmente bajos de estos indicadores tanto en campo abierto como en condiciones de sombreado. Además, se proponen dos nuevos índices basados en la Tc, que mostraron una respuesta diferente según el sistema de cultivo y el tratamiento de riego considerado. La programación del riego basada en indicadores del estado hídrico del suelo y de la planta permite ajustar la dosis de riego a las necesidades hídricas del cultivo. En esta tesis, el riego de los limeros se gestionó automáticamente, en base a valores umbrales del contenido de agua del suelo medidos en la zona radicular activa. El uso de este protocolo de riego promovió un estado hídrico óptimo de la planta, como se observó en los limeros cultivados en maceta (Artículo I) y en el suelo (Artículos II y III). En cuanto a los indicadores del estado hídrico de la planta, la medida de la Tc a distancia y en tiempo real supone una gran ventaja para la gestión del riego. En este sentido, en el Artículo III, se propusieron valores umbrales de la Tc-Ta de 2,4 y 0,8 ◦C para limeros bien regados cultivados al aire libre y bajo malla de sombreo, respectivamente. En el Artículo IV, se evaluó la robustez de varios índices basados en la Tc para estimar la gs en pomelos adultos regados con diferentes cantidades (riego completo y deficitario) y calidades de agua (trasvase y agua regenerada) de riego durante dos estados fenológicos (floración-brotación y crecimiento del fruto). Además, se comprobó la capacidad de diferentes índices térmicos para determinar la gs en diferentes intervalos de datos térmicos y en diferentes condiciones de déficit de presión de vapor (VPD) y de radiación fotosintéticamente activa (PAR). Los resultados sugirieron que los índices térmicos y la gs tenían el mayor grado de correlación cuando los datos térmicos se promediaron a 60 min, a VPD entre 0 y 3,5 kPa, y a PAR 1200 μmol m-2 s-1. En estas condiciones, los árboles con riego deficitario y los regados con agua regenerada fueron los que mostraron las mejores correlaciones entre los índices térmicos y la gs. El índice de estrés hídrico del cultivo (CWSI) y la Tc-Ta estimaron mejor la gs durante la floración-brotación, y los valores absolutos de Tc durante el estado fenológico de crecimiento del fruto, independientemente de la calidad y cantidad de agua aplicada. Esto indicó que durante floración-brotación la Tc dependía principalmente de las condiciones climáticas más que del estado hídrico de la planta, mientras que durante el período de crecimiento del fruto la Tc estaba más influenciada por factores intrínsecos de la planta (apertura estomática). En general, los índices térmicos han demostrado ser buenos indicadores del estado hídrico de la planta para una gestión precisa del riego en cítricos. [ENG] This doctoral dissertation has been presented in the form of thesis by publication. In the coming years, climate change will cause the earth's temperature to rise 2.2 ◦C by 2040. This increase in air temperature is expected to be accompanied by a reduction in precipitation, which will increase the intensity and frequency of drought events. In parallel, the world’s population is more than three times larger than it was in the mid-twentieth century. It will continue increasing in the subsequent years, driving up water demand for food production. Currently, global food production from irrigation represents more than 40 % of the total and uses only about 20 % of the land area designated to this end. Citrus is one of the main species cultivated worldwide, spread in more than 140 countries. This species is irrigation-dependent, and it has a medium-high water demand. In order to cope with this water scarcity, irrigated agriculture is forced to make utmost efforts to improve water use efficiency. In this context, this thesis is aimed to assess the sustainability of precise irrigation of citrus crops (grapefruit and lime), with special attention to the study of crop evapotranspiration (ETc) and the use of soil and plant water status indicators. To achieve these objectives several experiments were carried out (Articles I to IV). A sound knowledge of ETc is necessary to decide ‘when’ to irrigate and ‘how much’ water to apply. In Article I, young lime’s ETc was calculated by soil water balance method using drainage-weighing pot-lysimeters. Along the crop cycle, ETc was the highest in July (2.56 L plant-1day-1), due to the elevated water consumption during the last fruit growth stage. When lime tree biomass changes were negligible, pot weight variations served for ETc-water balance validation (r2=0.92***). A prototype of a simple and robust scalable drainage-weighing lysimeter for young potted trees was proposed, which provided a practical and cost-effective way to measure ETc throughout the year. Discrete plant water status indicators, as stem water potential (Ψstem), stomatal conductance (gs) and net photosynthesis (Pn), as well as continuous ones like canopy temperature (Tc) were measured on lime trees grown in shaded and in open-field conditions (Articles II and III). In Article II, shading increased by 54 and 37 % daily accumulated leaf gs and Pn, respectively. Moreover, in shaded conditions Ψstem was increased by 0.05 MPa and canopy to air temperature difference (Tc-Ta) values were reduced by 1.7 ◦C according to Articles II and III. These facts pointed to a better physiological performance of lime trees under shading conditions. In Article III, the combined effect of cropping system and deficit irrigation on soil and plant water status indicators was evaluated. The results indicated that when soil water stress was moderate, shading conditions cushioned the negative effect on soil and plant water status, allowing to postpone water deficits. However, when soil water stress was severe, similar low values of these indicators were observed in open-field and in shaded conditions. Additionally, two new thermal-based indices were proposed, which showed a different response by cropping system-irrigation treatment considered. Irrigation scheduling based on soil and plant water status indicators allows adjusting the irrigation dose to crop water needs. In this thesis, irrigation of lime trees was automatically managed, based on soil water content threshold values measured in the active root zone. This irrigation protocol promoted an optimal plant water status, as proved in pot grown (Article I), and in field grown (Articles II y III) lime trees. Regarding plant water status indicators, remote and real-time Tc measurement supposes a great advantage for irrigation management purposes. In this sense, in Article III, Tc-Ta threshold values of 2.4 and 0.8 ◦C were proposed for full irrigated lime trees in open-field and shaded conditions, respectively. In Article IV, the robustness of several thermal-based indices to estimate gs for different irrigation strategies (full and deficit irrigation), water sources (transfer and reclaimed water) and phenological stages (flowering-sprouting and fruit growth) in grapefruit trees were evaluated. In addition, the ability of thermal indices to determine gs at different averaged thermal data intervals, vapour pressure deficit (VPD) and photosynthetically active radiation (PAR) conditions, was tested. The results suggested that thermal indices and gs had the highest degree of correlation at 60 min thermal average data, VPD between 0 and 3.5 kPa and PAR 1200 μmol m-2 s-1. In these conditions, trees under deficit irrigation and those irrigated with reclaimed water showed the best thermal indices-gs correlations. Crop water stress index (CWSI) and Tc-Ta estimated gs better during flowering-sprouting (FS), and Tc during fruit growth (FG), independently of quality of the irrigation source and the amount of water applied. This fact indicated that in FS stage Tc depended mainly on climatic conditions rather than on plant water status, whereas in FG stage it was more influenced by intrinsic plant factors (stomatal opening). Overall, thermal-based indices have demonstrated to be suitable plant water status indicators for precise irrigation management of citrus trees.Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. Está formada por un total de cuatro artículos: Article I: Mira-García, A.B., Vera, J., Conejero, W., Conesa, M.R., Ruiz-Sánchez, M.C., 2021. Evapotranspiration in young lime trees with automated irrigation. Scientia Horticulturae 288, 110396. DOI: 10.1016/j.scienta.2021.110396 Article II Mira-García, A.B., Conejero, W., Vera, J., Ruiz-Sánchez, M.C., 2020. Leaf water relations in lime trees grown under shade netting and open-air. Plants 9(4), 510. DOI: 10.3390/plants9040510 Article III Mira-García, A.B., Conejero, W., Vera, J., Ruiz-Sánchez, M.C., 2022. Water status and thermal response of lime trees to irrigation and shade screen. Agricultural Water Management 272, 107843. DOI: 10.1016/j.agwat.2022.107843 Article IV Mira-García, A.B., Romero-Trigueros, C., Bayona-Gambín, J.M., Sánchez- Iglesias, M.P., Nortes-Tortosa, P.A., Nicolás-Nicolás, E., 2023. Estimation of stomatal conductance by infrared thermometry in citrus trees cultivated under regulated deficit irrigation and reclaimed water. Agricultural Water Management 276, 108057 DOI: 10.1016/j.agwat.2022.108057Escuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Técnicas Avanzadas en Investigación y Desarrollo Agrario y Alimentari

Deficit Irrigation in Mediterranean Fruit Trees and Grapevines: Water Stress Indicators and Crop Responses

In regions with Mediterranean climate, water is the major environmental resource that limits growth and production of plants, experiencing a long period of water scarcity during summer. Despite the fact that most plants developed morphological, anatomical, physiological, and biochemical mechanisms that allow to cope with such environments, these harsh summer conditions reduce growth, yield, and fruit quality. Irrigation is implemented to overcome such effects. Conditions of mild water deficit imposed by deficit irrigation strategies, with minimal effects on yield, are particularly suitable for such regions. Efficient irrigation strategies and scheduling techniques require the quantification of crop water requirements but also the identification of pertinent water stress indicators and their threshold. This chapter reviews the scientific information about deficit irrigation recommendations and thresholds concerning water stress indicators on peach trees, olive trees, and grapevines, as case studies

Using Soil Moisture Sensors for Automated Irrigation Scheduling in a Plum Crop

The growing scarcity and competition for water resources requires the urgent implementation of measures to ensure their rational use. Farmers need affordable irrigation tools that allow them to take advantage of scientific know-how to improve water use efficiency in their common irrigation practices. The aim of this study is to test under field conditions, and adjust where required, an automated irrigation system that allows the establishment of regulated deficit irrigation (RDI) strategies in a stone fruit orchard. For this, an automated device with an algorithm which combines water-balance-based irrigation scheduling with a feedback adjustment mechanism using 15 capacitive sensors for continuous soil moisture measurement was used. The tests were carried out in 2016 and 2017 in Vegas Bajas del Guadiana (Extremadura, Spain) on an experimental plot of ‘Red Beaut’, an early-maturing Japanese plum cultivar. Three irrigation treatments were established: control, RDI and automatic. The control treatment was scheduled to cover crop water needs, a postharvest deficit irrigation (40% crop evapotranspiration (ETc)) strategy was applied in the RDI treatment, while the Automatic treatment simulated the RDI but without human intervention. After two years of testing, the automated system was able to “simulate” the irrigation scheduling programmed by a human expert without the need for human intervention.info:eu-repo/semantics/publishedVersio

Updated single and dual crop coefficients for tree and vine fruit crops

ReviewThe 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 (Kc) and basal (Kcb) 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 ETo 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 Kc and Kcb data. Preference was given to studies reporting on the fraction of ground cover (fc), crop height (h), planting density, crop age and adopted training systems. The Kc and Kcb values obtained from the selected literature generally show coherence relative to the crop biophysical characteristics and reflect those characteristics, mainly fc, h and training systems. The ranges of reported Kc and Kcb values were grouped according to crop density, particularly fc and h, and were compared with FAO56 (Allen et al., 1998) previously tabulated Kc and Kcb values, as well as by Allen and Pereira (2009) and Jensen and Allen (2016), which lead to define update indicative standard Kc and Kcb 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 vinesinfo:eu-repo/semantics/publishedVersio

Programación de riego y déficit hídrico controlado en frutales de hueso

[SPA] La escasez y baja calidad de los recursos hídricos junto a la presión del desarrollo turístico, industrial y residencial hace que la agricultura en las regiones semiáridas afronte serias restricciones de forma casi permanente. Para mejorar esta situación se requiere un esfuerzo colectivo entre quién gestiona los recursos hídricos y quién los utiliza. Los primeros deben buscar nuevas políticas de gestión y sistemas de gobernanza participativa mientras que los segundos deben cambiar sus prácticas de modo que consigan producciones más elevadas y de mejor calidad con una menor utilización de recursos hídricos. Los agricultores, apoyados por los estudios de investigación y la introducción de nuevas tecnologías, pueden paliar las consecuencias de la escasez de agua mediante varias opciones complementarias: riego de precisión, riego deficitario y uso de aguas no convencionales. En los últimos años han cobrado gran importancia los estudios que abordan la aplicación de estrategias de riego deficitario controlado (RDC), las cuales además del ahorro hídrico que suponen, pueden incluso resultar en mejoras de algunos aspectos cualitativos de las cosechas obtenidas. La presente tesis se ha dividido en cuatro capítulos independientes pero relacionados entre sí. Los objetivos y resultados de cada capítulo se presentan a continuación: En el primer capítulo, se realizaron medidas de potencial hídrico de tallo (Ψt) y máxima contracción diaria del tronco (MCD) durante 3 años consecutivos en melocotoneros adultos de la variedad “Catherine” con el objetivo de obtener ecuaciones de referencia que permitan la programación del riego a partir de medidas automáticas de MCD. La MCD se relacionó con parámetros climáticos como la ET0, temperatura y déficit de presión de vapor (DPV) (máxima y al mediodía) así como con el t, el indicador del estado hídrico de la planta reconocido como estándar. Los resultados indicaron que los registros de MCD presentaban una mayor correlación con la temperatura, durante el período de crecimiento del fruto, y con el DPV en post-cosecha. Las relaciones entre la MCD y Ψt difirieron interanualmente, aunque se encontraron ecuaciones de referencia similares entre estaciones de crecimiento para los distintos períodos post-cosecha. Sin embargo, estas relaciones variaron en gran medida con el estado fenológico del árbol y la carga de frutos de cada año. En el segundo capítulo, los objetivos fueron, en primer lugar, cuantificar las necesidades hídricas de la planta, a partir de las medidas de MCD, y normalizar estas medidas respecto al tratamiento control, estableciendo una intensidad de señal de la MCD (ISMCD). Así, los tratamientos aplicados fueron 3: Un control sobre-regado, un control ajustado donde se mantuvieron los valores de ISMCD en torno a la unidad durante todo el ciclo de cultivo y un tratamiento RDC donde se mantuvo un valor de ISMCD en torno a la unidad en todos los estados fenológicos del cultivo excepto en los periodos no críticos durante los cuales se mantuvo en torno a 2. El ahorro hídrico del tratamiento deficitario se situó alrededor del 43-65% respecto a la ETc durante los 3 años de la experiencia y no se observaron diferencias significativas en el crecimiento de los frutos, aunque sí en el crecimiento vegetativo. El hecho de que el control ajustado presentara niveles de Ψt y MCD similares al control sobre-regado, además de una producción y calidad del fruto sin diferencias significativas, indicó que los melocotoneros bajo este tratamiento de precisión no fueron afectados por el protocolo de riego impuesto, por lo que, en ausencia de drenaje podría considerarse como una herramienta para estimar los valores de Kc cuando éstos no se conozcan a nivel local. En el tercer capítulo se procedió a evaluar el efecto del RDC en la respuesta fisiológica y productiva de melocotoneros de la variedad “Catherine” durante 3 años consecutivos. Para ello, el riego se programó mediante el empleo de valores umbrales de Ψt. Se establecieron tres tratamientos: Un control sobre-regado y dos tratamientos deficitarios: moderado (-1,5 MPa de Ψt durante fase II de crecimiento del fruto y post-cosecha, y severo, -1,8 MPa de Ψt durante fase II de crecimiento del fruto y -2 MPa en post-cosecha). Los resultados mostraron una reducción en el agua aplicada de entre 38 y 68% respecto a la ETc. El crecimiento vegetativo y la poda se vieron reducidos en ambos tratamientos de RDC respecto al control, efecto que no se observó en la evolución del tamaño del fruto ni en la cosecha. Se demostró que el uso de valores umbral de Ψt para programar el riego es una opción viable para ahorrar agua sin comprometer la producción. Sin embargo, estos efectos deben estudiarse a largo plazo para evaluar la sostenibilidad de estas estrategias, así como para adaptar los umbrales Ψt a otras condiciones de suelo y clima. En el último capítulo se evaluó el efecto del RDC en albaricoqueros adultos de la variedad “Búlida” durante 3 años consecutivos. Los tratamientos establecidos fueron dos: control regado al 100% de la ETc durante todo el ciclo de cultivo y un tratamiento de riego deficitario controlado (RDC) regado al 100% de la ETc durante los estados fenológicos críticos y cuyo porcentaje de riego aplicado en los periodos no críticos fue función del estado fenológico de la planta. Los resultados indicaron que el albaricoquero es una especie apropiada para el establecimiento de estrategias de RDC debido a la clara separación entre el crecimiento vegetativo y reproductivo. El déficit hídrico impuesto no afectó significativamente el crecimiento vegetativo ni reproductivo. Algunas características de calidad como el índice de madurez aumentaron bajo RDC, lo que según estudios previos puede influir favorablemente en las decisiones de mercado de esta fruta. Estas razones, junto con ahorros hídricos de alrededor del 33%, demuestran que el RDC es una estrategia de manejo del agua de riego adecuada para las zonas con escasez de recursos hídricos como el sureste español. [ENG] Water resources scarcity and low quality, together with the pressure of tourist, industrial and residential developments, makes that agriculture in semiarid regions must deal with water-limiting situations almost permanently. Irrigated agriculture consumes more than 70% of available water resources causing, in some cases, overexploitation of groundwater resources and the loss of water quality. However, it is difficult to tackle the problem due to several reasons such as: - The consequences of excessive water use and fertilizers in intensive agriculture are not taken into account at the medium and long terms. - The effective management of water resources is a collective task since its implementation requires the involvement of all the agents, both water resource managers and farmers or end users. - User limited awareness about the dimensions of the problem of water scarcity and its consequences, in some cases. - Low utilization of tools / techniques to save water in agriculture. In order to improve this situation, a collective effort between who manages water resources and who uses them is required. The first ones should seek new management policies and participatory governance systems, while the second ones must change their practices to get higher yields and better crop quality with a lower use of water resources. Farmers, supported by research studies and the introduction of new technologies, can mitigate the consequences of water shortages through several complementary options: 1) Precision irrigation: this strategy seeks to minimize water losses that usually occur during irrigation events. It requires an efficient system and an irrigation scheduling methodology that takes into account water relations in the soil-plant-atmosphere system. 2) Deficit irrigation: the fact that crop response to water deficit is variable depending on the plant growth stage allows for reducing water application through irrigation during non-critical phenological stages without causing losses in the final yield. 3) Use of unconventional water: municipal reclaimed water represents a considerable volume of total agricultural consumption, thus often occur in nearby agricultural areas. These water resources also contain a high concentration of minerals and organic matter that could partially cover plan nutritional needs. For these reasons, in recent years the studies that address the implementation of regulated deficit irrigation strategies (RDI) have become very important, due to the water savings they entail, which can even result in qualitative improvements in some aspects of the harvests obtained (Fereres and Soriano, 2007). Based on this, plant based water status measurements have gained interest because they integrate the effect of both the soil water availability and the evaporative demand and, therefore, provide more suitable information for determining the water restrictions effect on plant physiological activity and irrigation scheduling (Jones, 2004). These water status indicators may be distinguished in two groups, if they allow for continuous data collection (maximum daily trunk shrinkage, MDS) or not (stem water potential, Ψs), in order to automate irrigation.[ENG] Water resources scarcity and low quality, together with the pressure of tourist, industrial and residential developments, makes that agriculture in semiarid regions must deal with water-limiting situations almost permanently. Irrigated agriculture consumes more than 70% of available water resources causing, in some cases, overexploitation of groundwater resources and the loss of water quality. However, it is difficult to tackle the problem due to several reasons such as: - The consequences of excessive water use and fertilizers in intensive agriculture are not taken into account at the medium and long terms. - The effective management of water resources is a collective task since its implementation requires the involvement of all the agents, both water resource managers and farmers or end users. - User limited awareness about the dimensions of the problem of water scarcity and its consequences, in some cases. - Low utilization of tools / techniques to save water in agriculture. In order to improve this situation, a collective effort between who manages water resources and who uses them is required. The first ones should seek new management policies and participatory governance systems, while the second ones must change their practices to get higher yields and better crop quality with a lower use of water resources. Farmers, supported by research studies and the introduction of new technologies, can mitigate the consequences of water shortages through several complementary options: 1) Precision irrigation: this strategy seeks to minimize water losses that usually occur during irrigation events. It requires an efficient system and an irrigation scheduling methodology that takes into account water relations in the soil-plant-atmosphere system. 2) Deficit irrigation: the fact that crop response to water deficit is variable depending on the plant growth stage allows for reducing water application through irrigation during non-critical phenological stages without causing losses in the final yield. 3) Use of unconventional water: municipal reclaimed water represents a considerable volume of total agricultural consumption, thus often occur in nearby agricultural areas. These water resources also contain a high concentration of minerals and organic matter that could partially cover plan nutritional needs. For these reasons, in recent years the studies that address the implementation of regulated deficit irrigation strategies (RDI) have become very important, due to the water savings they entail, which can even result in qualitative improvements in some aspects of the harvests obtained (Fereres and Soriano, 2007). Based on this, plant based water status measurements have gained interest because they integrate the effect of both the soil water availability and the evaporative demand and, therefore, provide more suitable information for determining the water restrictions effect on plant physiological activity and irrigation scheduling (Jones, 2004). These water status indicators may be distinguished in two groups, if they allow for continuous data collection (maximum daily trunk shrinkage, MDS) or not (stem water potential, Ψs), in order to automate irrigation.Universidad Politécnica de CartagenaPrograma Oficial de Posgrado en Técnicas Avanzadas en Investigación y Desarrollo Agrario y Alimentari

Extrapolating base-line trunk shrinkage reference equations across olive orchards

preprintMaximum daily trunk shrinkage is a common measurement in irrigation scheduling of fruit trees. But the strong relationship between these measurements and the environment severely limit field applications. Reference baselines are the solution for understanding the influence of environmental conditions. Nevertheless, the extrapolation out of the original conditions is not clear. The aim of this study was to compare several approaches to estimate a reference baseline in an olive orchard where there were no previous data from other seasons. Two orchards, separated 60. m, with different tree density were used. Orchard 1 had greater tree density than orchard 2, though the age and the cultivar were the same. Trunk diameters of both orchards were similar but the crown volume of orchard 2 was slightly lower than orchard 1. The current reference baselines of maximum daily trunk diameter in both orchards were not significantly different between them (p<0.05). In orchard 1, the previous reference baseline was calculated in a 5-year study (the so called multi-seasons approach). The multi-seasons approach was not significantly different in slope but it was in the y-interception to the current reference baselines in both orchards (p<0.05). This approach over-estimated the values in both orchards. Two additional approaches were tested. These latter approaches used data before massive pit hardening to estimate the current reference baseline. One of them used the early data to estimate a complete reference baseline (the so-called early approach). The other (the so-called y-early approach) used the same data only to estimate the y-interception and assumed that the slope was the same as in the multi-seasons approach. The early approach under-estimated the value of maximum daily trunk shrinkage. The early-y approach provided a satisfactory estimation of the reference baseline and improved those obtained with the multi-seasons approach. The limitations and uses in irrigation scheduling are also discussed.MINECO AGL2010-19201-CO4-03AECID D/030431/1

Sensitivity to water deficit of the second stage of fruit growth in late mandarin trees

In citrus fruits, phases I and II of fruit growth are sensitive to water deficit, and for this reason, deficit irrigation (DI) has been usually restricted to the final ripening phase. However, the optimal timing and intensity of stress during sensitive phases have not been clearly defined. The main objective was to determine the sensitivity of the second stage of fruit growth to water deficit in adult mandarin trees, and to explore the suitability of different soil and plant water status indicators, including the leaf-scale spectrum, according to the water stress level. Four irrigation treatments were tested: a control (CTL) irrigated at ~ 80% of ETc during the entire crop cycle, and three irrigation suppression treatments, in which no water was applied during the end of phase I and the beginning of phase II (DI1), the second half of phase II (DI2), and phase III of fruit growth (DI3), respectively. Phase II of fruit growth can be considered as a non-critical phenological period until the fruit reaches approximately 60% of its final size, with the application of a water deficit using an irrigation threshold of midday stem water potential of − 1.8 MPa, and a cumulative water stress integral close to 28 MPa day. The novel visible infrared ratio index (VIRI) showed a high sensitivity for trees subjected to moderate and severe water stress and can be complementarily used to estimate on a larger temporal and spatial scale the plant water status. Wavelengths in the short-wave infrared (SWIR) region allowed differentiation between non-stressed, moderately, and severely water-stressed trees, and can be considered as an initial basis for determining the water status of mandarin trees at various stress intensities by remote sensing.This study was supported by the European Commission H2020 (Grant 728003, DIVERFARMING Project) and National Research Agency of Spain (PID2019-106226RB-C22)