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The aim of this study was to evaluate the robustness of infra-red thermometry to estimate stomatal conductance (gs) in grapefruit trees. For this purpose, the ability of several thermal indices to determine gs was tested for different: (i) irrigation strategies: full irrigation (FI) and regulated deficit irrigation (RDI), (ii) water sources: transfer water (TW) -optimal for agricultural uses- and saline reclaimed water (RW) and (iii) phenological stages: flowering-sprouting (FS) and fruit growth (FG). During two growing seasons, measurements of gs and canopy temperature (Tc) were taken in 14-year-old ´Star Ruby´ grapefruit trees (Citrus paradisi Macf.,). Air temperature (Ta) was also recorded and then the derived thermal indices: Tc-Ta, and CWSI (crop water stress index) were calculated. Subsequently, thermal-gs correlations were established at different averaged thermal data intervals, and VPD (vapour pressure deficit) and PAR (photosynthetically active radiation) conditions. The results indicated that both, water quality and deficit irrigation, affected negatively gs and Tc during FG. In addition, the highest r2 values in thermal indices-gs correlations were found when i) the thermal data was averaged 60 min before the gs measurement, ii) gs was measured over a wide range of VPD (between 0 and 3.5 kPa), and iii) PAR was 1200 µmol m−2 s−1. The ability of the thermal indices to estimate gs improved under RDI and RW conditions, when compared to the control treatment (TW-FI). Moreover, the thermal indices that more accurately estimated gs were Tc-Ta and CWSI in FS (P < 0.001), and the absolute values of Tc in FG (P < 0.001). Overall, thermal indices obtained by infra-red sensors could be a useful tool to estimate gs in grapefruit trees. However, irrigation treatment, water quality, tree phenological stage and environmental conditions (VPD and PAR) must be considered when interpreting thermal indices-gs correlations

BACKGROUND Non-conventional water sources and water-saving techniques can be valuable in semi-arid regions, although their long-term effects on citrus quality are little known. This study evaluated the effects of irrigation with two sources, transfer water (TW) and reclaimed water (RW), combined with two irrigation strategies, full irrigation (FI) and regulated deficit irrigation (RDI), on fruit quality of mandarins and grapefruits during eight growth seasons, RESULTS Reclaimed water irrigation in mandarin, without water restriction, influenced maturity index (MI) less than TW-FI, because titratable acidity (TA) increased to a greater degree than soluble solid contents (SSC). Nevertheless, juice quality standards were satisfied. Regardless of the irrigation treatment (FI or RDI), a trend towards increasing fruit weight was also detected with RW. In grapefruit, its rootstock (Citrus macrophylla) enhanced salinity resilience with respect to the rootstock of mandarin (‘Carrizo’ citrange) and, hence, MI was not affected by RW. The RDI strategy, without saline stress (TW-RDI), increased, to a similar degree, both SSC and TA in mandarin fruit, not affecting the MI. In grapefruit, the water stress of RDI did improve the MI due to the TA did not change and SSC increased significantly, the TA did not change. The combination of both strategies, RW-RDI, decreased the MI only in some years because TA increased proportionally more than SSC in mandarin, CONCLUSIONS The medium- and long-term feasibility of using RW and RDI to irrigate citrus was demonstrated. However, they must be performed cautiously and with appropriate management to avoid damaging fruit quality as a result of phytotoxic elements. © 2019 Society of Chemical Industry

The 70% worldwide surface of olive orchards is irrigated. The evaluation of non-conventional water resources and water-saving techniques has gained importance during the last decades in arid and semiarid environments. This study evaluated the effects of irrigation with two water sources: low-cost water DEsalination and SEnsoR Technology (DESERT) desalinated water (DW) ECw ∼1 dS m−1) and reclaimed water (RW) (ECw ∼ 3 dS m−1) combined with two irrigation strategies: full irrigation (FI) (100% of ETc) and regulated deficit irrigation (RDI, 50% of ETc) on fruit yield, ripening indices, and oil yield and quality of olive trees cv Arbosana planted in Mediterranean conditions. Our results showed that RW without water restrictions increased the fruit yield by 35% due to a slight increase in the fruit weight and, mainly, to a greater fruit set than the control trees; although this did not result in a higher oil yield (g tree−1) since the oil content per fruit dry weight was reduced. The RDI strategy did not decrease the fruit yield despite the fact that olive weight tended to decrease, and it increased the oil yield by ∼14.5%. The combination of both stresses (RW and RDI) neither decreased the fruit yield; however, it significantly reduced oil yield (25% less in 2018) since oil content per fruit dry weight was strongly reduced (40%) compared to control trees. Both RDI treatments, regardless water source, determined acidity levels in olive paste lower than in FI treatments; however, it reduced oil extractability and fatty yield. The finding about oil quality indicated that olive exposure to RW, regardless of the water amount, decreased oil quality mainly due to the reduction of oleic acid and the increase of C18:2/C18:3 ratio and peroxides; on the contrary, both RW and RDI improved the total polyphenols. In all cases, the parameters met the legislation. In short, with appropriate management, RW and RDI have great potential to manage oil olive production; nevertheless, studies

[SPA] El objetivo del trabajo fue evaluar los ritmos diarios de indicadores del estado hídrico de la planta, para la programación del riego de: (I) limeros (Citrus latifolia Tan., cv. Bearss) jóvenes cultivados al aire libre y bajo malla de sombreo, y (II) pomelos (Citrus paradisi Macf., cv. Star Ruby) adultos regados con agua de diferente calidad: agua del trasvase (CE≈1 dS/m) y agua salina regenerada (CE≈3,5 dS/m). Los indicadores mostraron un ritmo circadiano similar en todas las condiciones ensayadas. Los limeros cultivados bajo malla de sombreo presentaron una mayor conductancia estomática y fotosíntesis neta que los cultivados al aire libre. El potencial hídrico de tallo y la temperatura de copa fueron similares en ambas condiciones. Los pomelos regados con agua salina regenerada mostraron valores más bajos de intercambio gaseoso y potencial hídrico de tallo, y una temperatura de copa mayor. En conclusión, las condiciones de sombreo afectaron de forma significativa al intercambio gaseoso, favoreciendo la absorción de CO2. Las plantas regadas con agua regenerada salina mostraron un peor estado hídrico, resultado de que la alta concentración de sales presente en el suelo dificultó la absorción de agua por la planta. [ENG] The main objective of the work was to evaluate the diurnal courses of plant water status indicators for precision irrigation of: (I) young lime trees (Citrus latifolia Tan., cv. Bearss) grown under two growing conditions: open air and shade net, and (II) adult grapefruit trees (Citrus paradisi Macf., cv. Star Ruby) irrigated with two different quality water: Tagus-Segura transfer water (EC≈1 dS/m) and regenerated saline water (EC≈3.5 dS/m). Plant water status indicators showed circadian rhythms in all the studied conditions. Lime plants cultivated under shading net presented higher stomatal conductance and net photosynthesis than plants cultivated in the open air. Slight differences were found in stem water potential and canopy temperature betw

Climate change is one of the main challenges facing the agricultural sector as it strives to meet global food needs. In arid and semiarid areas, the scarcity of water imposes the use of alternative sources - such as reclaimed water (RW) or desalinated water (DW) - and of deficit irrigation strategies, such as regulated deficit irrigation (RDI), in order to maintain productivity. The impact of both alternative water sources and RDI strategies on soil microbial communities in conjunction with the crop response has been little studied, and far less in fruit trees. Here, we evaluated the effects of the irrigation water quantity (RDI or the optimal water amount) and quality (DW or saline RW) on: i) the biomass, composition, and activity of the soil microbial community, and ii) the plant agro-physiological response at the level of the water status, nutrients, vegetative growth, and yield of almond trees. The DW-RDI treatment had a lower vegetative growth than the rest, reducing the nutrient requirements and increasing the contents of organic carbon and nitrogen in soil. This coincided with a significant increase in the bacterial biomass and enzyme activities in soil, as well as with a decrease in plant nutrient use efficiencies and yield. Irrigation with RW increased the fungal biomass. When there were no water restrictions (RW-FI), none of the plant agro-physiological parameters were affected; when RDI was applied (RW-RDI), the highest soil sodicity was reached and vegetative growth and yield were negatively affected, although the plant nutrient use efficiencies did not decrease as much as with DW-RDI. In addition, the plant nutrient use efficiencies were negatively correlated with the soil enzyme activities. These results improve our knowledge of the functioning of plant-soil interactions in Mediterranean crops subjected to different irrigation strategies.

Regulated deficit irrigation (RDI) strategy using reclaimed water (RW) is becoming a common procedure in some Mediterranean regions. Full and regulated deficit irrigation were combined with desalinated (EC 1 dS m) and saline (EC 3 dS m) reclaimed water to irrigate young potted almond trees over a 3-year period. The full irrigation treatments received 130% of the crop evapotranspiration (ET) and the RDI treatments received 80% of ET during the kernel filling. Trunk diameter decreased in both RDI treatments at the end of the experimental period, although this response was more marked in the trees irrigated with saline RW. There were negative relationships between shoot growth and leaf Na and Cl contents in the saline treated trees, in which the accumulation of salts in leaves was associated with osmotic adjustment, which was responsible for maintaining midday leaf turgor. Plant water status, measured by the leaf and water potential, decreased in almond exposed to water deficit or irrigated with saline RW, indicating a slight dehydration in these plants due to the difficulty in water uptake from the substrate. Trees subjected to both deficit irrigation treatments showed lower stomatal conductance values than full irrigated treatments during the RDI period. However, at the end of experimental period, the lowest P values were found in plants irrigated with saline RW, especially in trees irrigated with saline RW combined with RDI strategy, verifying the relevance of duration of exposure to the stress. Saline and desalinated RW can be successfully used for irrigating almond trees, which might be of great economic and competitive significance for agriculture, but further research focused on a longer term should be carried out since detrimental effects might appear. Deficit irrigation combined with saline RW in P. dulcis is not recommended since it intensifies the negative effects of water and salt stress applied individually.

The European Union requires that benzene in the air is continuously measured due to its toxicity and widespread presence in the population nuclei, mainly motivated by vehicle emissions. The reference measuring technique is gas chromatography (GC). Automatic chromatographs used in monitoring stations must verify the operating conditions established in Standard EN 14662 part 3, which includes a type approval section with a number of tests that analysers must pass. Among these tests, the potential interference of a number of compounds is evaluated. The 2005 version of the mentioned standard requires the evaluation of the potential interference of tetrachloromethane (TCM). The 2015 version eliminates TCM as a potential interferent. Although most consumer uses of TCM have been banned, recent studies have measured significant concentrations of TCM in the air. In this paper, the potential interference of TCM in benzene measurements obtained with gas chromatography coupled to a photoionisation detector (GC-PID) has been investigated. Our study shows that the simultaneous presence of benzene and TCM causes a significant decrease in benzene readings. For TCM concentrations of 0.7 µg m−3 (typical of urban areas) and 4.5 µg m−3 (detected in the vicinity of landfills), the relative errors in benzene measurements were 34 % and 70 %, respectively, which are far too high compared to the maximum overall uncertainty allowed for benzene measurements (25 %). Possible mechanisms to qualitatively and quantitatively explain the behaviour of the PID when measuring benzene with and without TCM have been proposed.

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. La población mundial alcanzará unos 10.000 millones de personas en 2050, según recientes proyecciones (ONU, 2017). Para satisfacer la demanda de alimentos, la agricultura necesitará producir casi el 50% más en 2050 que en 2012. Así pues, el incremento de la productividad agrícola de una manera sostenible, conservando el agua y previniendo la contaminación del suelo debe de ser, actualmente, uno de los principales retos de la investigación agronómica a nivel de ecosistema. Es sabido que el agua es el factor de producción más limitante (CE, 2017), especialmente en áreas semiáridas, como la del Mediterráneo, donde el agua de riego no está siempre disponible debido a su escasez (Pedrero et al., 2015). Al mismo tiempo, las predicciones actuales sobre el cambio climático señalan que en el sur de Europa las olas de calor extremo y la reducción de las precipitaciones y del agua disponible limitarán más aún la productividad agraria dado que se está incrementando la frecuencia e intensidad de los periodos de sequía (García-Galiano et al., 2015; FAO, 2016). El uso de fuentes de agua no convencionales como el agua regenerada (AR) y de estrategias de riego deficitario controlado (RDC) podrían ser alternativas adecuadas para los agricultores. En este sentido, el AR puede ser beneficiosa para los cultivos dado que la presencia de macronutrientes (N, P, K) puede ayudar a reducir los requerimientos de fertilizantes, como el nitrato, dando lugar a importantes ahorros (Pedrero et al., 2013). No obstante, se requiere una gestión adecuada y cuidadosa del N para que sea absorbido por la planta y no se lixivie, contaminando así el suelo y los acuíferos (Laslo et al., 2012). En Murcia, una región agronómica semiárida, el 93% del AR tiene una conductividad eléctrica por encima de 2 dS·m-1 y un 37% por encima de 3 dS·m-1, según datos de ESAMUR. La salinidad está entre los factores ambientales más important, [ENG] This doctoral dissertation has been presented in the form of thesis by publication. World population will reach 10,000 million in 2050 by recent projections (ONU, 2017). To meet the demand for food, agriculture in 2050 will need to produce almost 50% more than in 2012. Thus, the increase of agricultural productivity in a sustainable way, conserving water and preventing soil contamination must be, currently, one of the main challenges of agronomic research at the ecosystem level. It is known that water is the most limiting factor of production (CE, 2017), especially in semi-arid areas, such as the Mediterranean, where irrigation water is not always available due to its scarcity (Pedrero et al., 2015). At the same time, current predictions on climate change indicate that extreme heatwaves and the reduction of rainfall and available water in southern Europe will limit agricultural productivity as the frequency and intensity of drought periods is increasing (García-Galiano et al., 2015, FAO, 2016). The use of unconventional water sources such as reclaimed water (RW) and strategies of regulated deficit irrigation (RDI) could be suitable alternatives for farmers. In this sense, RW can be beneficial for crops since the presence of macronutrients (N, P, K) can help reduce fertilizer requirements, such as nitrate, leading to significant savings (Pedrero et al., 2013). However, an adequate and careful management of the N is required so that it is absorbed by the plant and is not leached contaminating the soil and aquifers (Laslo et al., 2012). In Murcia, a semi-arid agronomic region, 93% of the RW has an electrical conductivity above 2 dS m-1 and 37% above 3 dS · m-1, according to recent data from ESAMUR. Salinity is among the most important environmental factors responsible for substantial losses of production in agriculture worldwide and is one of the serious problems confronting the long-term viability of agriculture in production systems irrigated with RW in semi-ar

[SPA] El objetivo de la investigación fue evaluar los efectos a largo plazo del riego con agua regenerada (AR) y agua del trasvase (AT) y diferentes estrategias de riego (control, C, y riego deficitario controlado, RDC) sobre la calidad de pomelos durante su almacenamiento en frío. Los resultados mostraron que el riego con AR y, principalmente, el RDC incrementaron la cantidad de solidos solubles, mejorando así el índice de madurez. Sin embargo, el AR combinada con RDC disminuyó el nº de frutos de la categoría de mayor tamaño al final del almacenaje y AT-RDC presentó el menor contenido en zumo. [ENG] The aim of our research was to discover the effects of the long-term irrigation with saline reclaimed (RW) and transfer (TW) water and different irrigation strategies: control (C) and regulated deficit irrigation (RDI) on fruit quality of grapefruit during cold storage. Result showed sugar/acid ratio was mainly increased by RDI, but also by RW, due to an important increase in soluble solid content. However, RDI combined with RW, significantly decreased the number of fruits in the largest category 5 at the end of cold storage and TW-RDI showed lower values of juice content.

The aim of our research was to discover the effects of the long-term irrigation with saline reclaimed (RW) and transfer (TW) water and different irrigation strategies: control (C) and regulated deficit irrigation (RDI) on yield and fruit quality of grapefruit at harvest and during cold storage. T W-RDI treatment decreased tree canopy (TC) and crop load, resulting in a 21% reduction of fruit yield. Regarding fruit quality, RW notably decreased peel thickness at harvest (about 8%); however, this difference was not remained during cold storage. Sugar/acid ratio was mainly increased by RDI, but also by RW, due to an important increase in soluble solid content (11% of average value for TW-RDI, RW-C and RW-RDI). In addition, RDI combined with RW, significantly increased the number of fruits in small category 5 at the end of cold storage. Finally, neither ratio yield/TC nor irrigation water productivity were affected by any irrigation treatments.

[SPA] Se evaluaron los efectos que tiene la aplicación de agua regenerada (AR), en combinación con estrategias de riego deficitario controlado (RDC), sobre los parámetros fisiológicos y de desarrollo de la planta de pomelo, destacando los posibles cambios en la eficiencia del uso del agua (EUA) y del nitrógeno (EUN) y realizando una caracterización de los elementos estructurales y constituyentes a nivel foliar. Se observó una mejora de la EUA en los tratamientos regados con AR y, por el contrario, una disminución de la EUN, del contenido en clorofila, de los niveles de intercambio gaseoso y, además, dio lugar a una potencial acumulación de sales a nivel foliar. [ENG] Effects of the application of reclaimed water (RW), combined with strategies of deficit irrigation (RDI) on physiological parameters and development of grapefruit plant were evaluated, highlighting the potential changes in water (WUE) and nitrogen (NUE) use efficiency and performing a characterization of structural elements and constituents at leaf level. RW improved the WUE and, conversely, decreased the NUE, the chlorophyll content and levels of gas exchange. In addition, the application of RW resulted in a potential accumulation of salts at the level foliar.

The aim of our research was to discover the effects of the long-term irrigation with saline reclaimed (RW) and transfer (TW) water and different irrigation strategies: control (C) and regulated deficit irrigation (RDI) on yield and fruit quality of grapefruit at harvest and during cold storage. TW-RDI treatment decreased tree canopy (TC) and crop load, resulting in a 21% reduction of fruit yield. Regarding fruit quality, RW notably decreased peel thickness at harvest (about 8%); however, this difference was not remained during cold storage. Sugar/acid ratio was mainly increased by RDI, but also by RW, due to an important increase in soluble solid content (11% of average value for TW-RDI, RW-C and RW-RDI). In addition, RDI combined with RW, significantly increased the number of fruits in small category 5 at the end of cold storage. Finally, neither ratio yield/TC nor irrigation water productivity were affected by any irrigation treatments.

[SPA] Se presenta un protocolo experimental diseñado para evaluar la respuesta agronómica y fisiológica de los cítricos al riego deficitario controlado (RDC) con aguas regeneradas (AR). Para ello se van a evaluar sus efectos sobre la planta (fisiología, producción, calidad y seguridad de la cosecha) y el medio ambiente (acumulación de sales y disponibilidad de nutrientes), además de analizar, desde un punto de vista integral, su sostenibilidad a medio-largo plazo. Los ensayos se están realizando en una finca comercial de cítricos, ubicada al noreste de la Región de Murcia. La parcela experimental de 1 ha está cultivada con árboles de pomelo 'Star Ruby´ (Citrus paradisi Macf) de 10 años de edad y árboles de mandarino (Citrus clementina cv. Orogrande) de 16 años de edad. Los objetivos del estudio son: i) evaluar la viabilidad de utilización de las AR en cultivos de cítricos, analizando su influencia en el crecimiento y producción, así como, en la calidad y seguridad de las cosechas obtenidas, ii) profundizar en el conocimiento de la respuesta de los cítricos al riego deficitario controlado (RDC), prestando especial atención a un aspecto novedoso en la aplicación de estas estrategias como es el riego con aguas de baja calidad y iii) determinar la eficiencia del uso del agua (EUA) a nivel de planta y sus patrones de extracción en función de los recursos hídricos utilizados y la eficiencia del uso del nitrógeno (EUN) para un manejo óptimo de la fertirrigación mediante técnicas de determinación de isótopos estables (13C, 18O y 15N). [ENG] We present an experimental protocol aiming to assess the agronomic and physiological response of citrus to deficit irrigation (RDI) with reclaimed water (RW). It focuses on the impact of RW use on both the plant (physiology, production, quality and safety of the harvest) and the environment (accumulation of salts and nutrient availability), and analyzing, from a holistic point of view, sustainability in the medium to long term. The trial

Citrus trees are strongly affected by salinity, especially in countries where irrigation is required as a semi-arid Mediterranean agronomic region. The aims of the study were i) to identify the best reliable plant-based water status indicator for field grown grapefruit trees irrigated with saline reclaimed water during five years of cultivation by measuring seasonal changes in physiological parameters (i.e. gas exchange and stem water potential measurements), leaf structural traits (i.e. leaf chlorophyll content, area-based leaf nitrogen and area-based dry mass), phytotoxic elements and yield; ii) to estimate phytotoxicity thresholds at leaf level. Our results showed that the chlorophyll content was the parameter with the highest number of measures with significant differences (p ≤ 0.05, ANOVA) between trees irrigated with reclaimed water and control trees throughout growing stages. Moreover, Chl a increased linearly with area-based leaf nitrogen (R2 = 0.63; p < 0.001) and area-based dry mass (R2 = 0.64; p < 0.001). We also determined the salt-induced phytotoxicity thresholds at which a reduction in yields occurs; these levels were Na: 0.1 g/100 g, Cl: 0.6 g/100 g and B: 100 ppm. In conclusion, we revealed the importance of leaf chlorophyll measurements as a significance diagnostic indicator of salt stress on field grown grapefruit trees. This parameter was also related to plantbased water status indicators such as stem water potential, stomatal conductance and net photosynthesis. Additionally, a salt accumulation potential at leaf level was shown, leading to possible risk in crop sustainability in the medium to long term.

Citrus trees are strongly affected by salinity, especially in countries where irrigation is required as a semi-arid Mediterranean agronomic region. The aims of the study were i) to identify the best reliable plant-based water status indicator for field grown grapefruit trees irrigated with saline reclaimed water during five years of cultivation by measuring seasonal changes in physiological parameters (i.e. gas exchange and stem water potential measurements), leaf structural traits (i.e. leaf chlorophyll content, area-based leaf nitrogen and area-based dry mass), phytotoxic elements and yield; ii) to estimate phytotoxicity thresholds at leaf level. Our results showed that the chlorophyll content was the parameter with the highest number of measures with significant differences (p . 0.05, ANOVA) between trees irrigated with reclaimed water and control trees throughout growing stages. Moreover, Chl a increased linearly with area-based leaf nitrogen (R2 = 0.63; p < 0.001) and area-based dry mass (R2 = 0.64; p < 0.001). We also determined the salt-induced phytotoxicity thresholds at which a reduction in yields occurs; these levels were Na: 0.1 g/100 g, Cl: 0.6 g/100 g and B: 100 ppm. In conclusion, we revealed the importance of leaf chlorophyll measurements as a significance diagnostic indicator of salt stress on field grown grapefruit trees. This parameter was also related to plantbased water status indicators such as stem water potential, stomatal conductance and net photosynthesis. Additionally, a salt accumulation potential at leaf level was shown, leading to possible risk in crop sustainability in the medium to long term.