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Cover crops have long been proposed as an alternative soil management for minimizing erosion rates in olive stands while providing additional ecosystem services. However, the trade-off between these benefits and the competition for water with the trees makes the definition of optimal management practices a challenging task in semiarid climates. This work presents an improved version of OliveCan, a process-based simulation model of olive orchards that now can simulate the main impacts of cover crops on the water and carbon balances of olive orchards. Albeit simple in its formulation, the new model components were developed to deal with different cover crop management strategies. Examples are presented for simulation runs of a traditional olive orchard in the conditions of southern Spain, evaluating the effects of different widths for the strip occupied by the cover crop (Fcc) and two contrasting mowing dates. Results revealed that high Fcc resulted in lower olive yields, but only when mowing was applied at the end of spring. In this regard, late mowing and high Fcc was associated with lower soil water content from spring to summer, coinciding with olive flowering and the earlier stages of fruit growth. Fcc was also negatively correlated with surface runoff irrespective of the mowing date. On the other hand, net ecosystem productivity (NEP) was substantially affected by both Fcc and mowing date. Further simulations under future climate scenarios comparing the same management alternatives are also presented, showing substantial yield reductions by the end of the century and minor or negligible changes in NEP and seasonal runoff., Project funding: This work was supported by “Consejería de Transformación Económica, Industria, Conocimiento y Universidades” (“Junta de Andalucía”, Spain) through a project cofunded by ERDF [grant number 27425]. In addition, part of the work was conducted under two projects funded by “Ministerio de Ciencia, Innovación y Universidades”, Spain, [grant numbers PID2019-110575RB-I00 and PCI2019-103621], one of which into the framework of the MAPPY project (JPI-Climate ERA-NET, AXIS call). The authors also acknowledge financial support from “Ministerio de Ciencia, Innovación y Universidades”, through the Severo Ochoa and María de Maeztu Program for Centers and Units of Excellence in R&D [grant number CEX2019-000968-M]. Postdoctoral fellowships were granted to the first and second authors by “Consejería de Transformación Económica, Industria, Conocimiento y Universidades” (“Junta de Andalucía”, Spain) [grant number POSTDOC-21-00381] and “Ministerio de Universidades (‘María Zambrano’ scholarship) [grant number 2021/86493], respectively., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2019-000968-M).

In this work, an open-circuit fault detection scheme for the converter of a wind power generation system is proposed and evaluated, which is robust to false detections under grid disturbance conditions such as sags and swells. The wind energy system is composed of a doubly-fed induction generator (DFIG) that supplies energy to the electrical grid through a power electronics converter based on the neutral point-clamped topology in a back-to-back configuration (NPC-BTB). The converter operates with a field-oriented-control (FOC) scheme, whereas the fault detection method is based on the processing of the current signals flowing through the converter at the rotor and stator sides of the generator using the discrete wavelet transform (DWT) with the Haar and Daubechies4 wavelet types. The fault detection scheme is evaluated verifying that false detections do not arise, analyzing cases where magnitude variations in the grid voltage of 15%, 30% and 50% occur, with respect to the nominal operating condition.

Better knowledge of the evapotranspiration and carbon exchange of fruit trees is needed to optimize the trade-off between water use and carbon assimilation and to better understand the role of agriculture in the biogeochemical cycles. In this work, we measured water and carbon fluxes with eddy covariance and transpiration with sap flow in a drip-irrigated peach orchard of 70% ground cover located in southern Spain for 2 years. The empirically measured crop coefficient (Kc) under good watering conditions in the summer ranged from 1 to 1.1. The daytime net ecosystem exchange (NEE) flux of the orchard averaged 30 g CO2 m2 day−1 during the period of maximum activity in July. The daytime ecosystem water use efficiency (WUE) of the orchard reached a minimum in late June, flattened around 4 g CO2 L−1 throughout the summer, and increased in autumn, but was unaffected by fruit removal or post-harvest irrigation reduction imposed by the farm (30% reduction). The response of instantaneous peach ecosystem WUE to VPD was also investigated. Both Kc, NEE, leaf water potential and stomatal conductance decreased sharply after harvest. Transpiration data from some purposely over-irrigated experimental trees demonstrated that the post-harvest alterations we found were not caused by fruit removal, but are result of mild water stress originated by the irrigation reduction. Hence, the often-observed alterations in water relations after harvest in well-watered trees were not observed in this experiment. This work adds insight on peach irrigation efficiency and on the contribution of orchards to agricultural carbon budgets., This study was funded by the project CONSOLIDER-RIDECO [grant number CSD2006-00067], of the Spanish Ministry of Science and Education through European Union ERDF funds.

As radial root resistance (Rp) represents one of the key components of the soil–plant–atmosphere continuum resistance catena modulating water transport, understanding its control is essential for physiologists, modelers and breeders. Reports of Rp, however, are still scarce and scattered in the scientific literature. In this study, we assessed genetic variability in Rp and its dependence on temperature in five widely used olive cultivars. In a first experiment, cultivar differences in Rp at 25 °C were evaluated from flow–pressure measurements in excised roots and subsequent analysis of root traits. In a second experiment, similar determinations were performed continually over a 5-h period in which temperature was gradually increased from 12 to 32 °C, enabling the assessment of Rp response to changing temperature. Despite some variability, our results did not show statistical differences in Rp among cultivars in the first experiment. In the second, cultivar differences in Rp were not significant at 12 °C, but they became so as temperature increased. Furthermore, the changes in Rp between 12 and 32 °C were higher than those expected by the temperature-driven decrease in water viscosity, with the degree of that change differing among cultivars. Also, Rp at 25 °C reached momentarily in the second experiment was consistently higher than in the first at that same, but fixed, temperature. Overall, our results suggest that there is limited variability in Rp among the studied cultivars when plants have been exposed to a given temperature for sufficient time. Temperature-induced variation in Rp might thus be partly explained by changes in membrane permeability that occur slowly, which explains why our values at 25 °C differed between experiments. The observed cultivar differences in Rp with warming also indicate faster acclimation of Rp to temperature changes in some cultivars than others., This work was supported by Ministerio de Economía y Competitividad (grant number AGL-2015-69822) and ERA-NET FACCE SURPLUS (grant number 652615, project OLIVE-MIRACLE), the latter co-funded by INIA. In addition, A.L.-B. and O.G.-T. were supported by postdoctoral fellowships of the ‘Juan de la Cierva-formación’ programme funded by Ministerio de Economía y Competitividad (grant numbers FJCI-2015-24109 and FJCI-2017-34086).

Induction motors (IM) are susceptible to mechanical failures with severe consequences for production lines; hence, detection and classification of IM faults have been of great interest for researchers in last years. Broken rotor bars (BRB) are one of the most difficult faults to detect, since this fault does not give any indication of deterioration increasing significantly the production costs; hence, it is quite important to detect them in early states. Several methodologies have been proposed to extract information about the motor condition relying on motor-current-signature analysis (MCSA); however, they usually require high-computational-complexity algorithms to reach trustworthy result. In this work, a novel methodology for early detection and classification of BRB faults in IM is proposed. This methodology consists of obtaining two spectrograms using fixed-width windows, which are segmented through Otsu algorithm to visualize the time evolution of fault frequencies. The fault severity classification is performed through Kurtosis computation from non-stationary components. Obtained results from real experimentation validate the proposed-method high efficiency, reaching an overall 100% accuracy on detecting and classifying half, one, two BRBs, and healthy condition.

A new stochastic weather generator, ClimaSG, is presented and evaluated under a wide range of climates. The model requires monthly means data as inputs to generate daily weather data. Validation tests revealed that ClimaSG performed well in capturing monthly rainfall variability but showed some limitations for generating extreme temperatures. Solar radiation, air humidity, and wind speed were reproduced acceptably. The weather generator was particularly accurate in predicting mean and extreme values of ET0, which indicates that ClimaSG may be used as the basis for calculating crop water requirements and for irrigation design and planning purposes. The suitability of synthetic weather series generated with ClimaSG for crop modelling applications was further assessed by running the model OliveCan for low density rainfed (LD) and super high density irrigated (SHD) olive orchards for several locations in Spain. Yield distributions simulated with synthetic weather rarely differed significantly from those obtained with actual weather data, although the coefficient of variation (CV) was usually underestimated. Considering its low input requirements and satisfactory performance, ClimaSG represents a promising source of weather data for different practical applications., This work was supported by Ministerio de Ciencia, Innovación y Universidades, Spain, through two projects [grant numbers PID2019–110575RB-I00 and PCI2019–103621], one of which into the framework of the MAPPY project (JPI-Climate ERA-NET, AXIS call), and the “María de Maeztu” program for centers and units of excellence in research and development [grant number CEX2019–000968-M]. In addition, part of the work was conducted under ERA-NET FACCE SURPLUS project OLIVE-MIRACLE [grant number 652615], co-funded by INIA, Spain. Álvaro López-Bernal was supported by a postdoctoral fellowship [grant number POSTDOC-21–00381] from Junta de Andalucía (Conserjería de Transformación Económica, Industria, Conocimiento y Universidades)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2019–000968-M).

“Dehesas”, the Iberian semi-natural woodlands based on large holm oak (Quercus ilex L.) trees, represent a key agroforestry system in Spain and Portugal sustaining relevant economic activities (e.g. “iberico” pork feeding, truffle) and ecosystem services. Despite of their importance, scarce information is still available regarding both the transpiration (Ep) and photosynthesis of holm oaks growing in dehesas and the effects of irrigation on these fluxes. Two experiments were performed in Espiel and Hinojosa del Duque (southern Spain) where sap flow was measured in large trees between 2009 and 2011 and photosynthesis was measured with a transitory-closed chamber in smaller trees at different moments of 2009. In 2009, half of the trees equipped with sap flow sensors were drip irrigated and half were rainfed. However, the supply of irrigation barely affected Ep and shoot water potential. The seasonal course of Ep peaked in late spring and decreased gradually, reaching minimum values during winter. Vapor pressure deficit (VPD) exerted a strong control over canopy conductance and its seasonal variation was identified as a major driver for the observed patterns of Ep. Photosynthesis showed a similar course as that of Ep but there was a second smaller peak in autumn. Seasonal water use efficiency was remarkably high due to the reduced summer Ep. Our results also indicate that hyperbolic models of canopy conductance and water use efficiency in response to VPD may be used to estimate diurnal and seasonal Ep and net photosynthesis of holm oak if the tree size and leaf area density are known.

The water potential (Ψp), has been widely used as an indicator of plant water status for irrigation management purposes. The simple infrastructure needed for its measurement and its direct relation to basic plant physiological processes, have contributed to the popularity of the methodology. When used for irrigation scheduling, it is commonly assumed that an unavoidable relationship exists between plant transpiration (T), soil water content and Ψp. Nevertheless, it is worth remembering that variations in Ψp are not solely related to changes in soil water content, but are also an expression of the interaction between the plant and its environment. We used a soil-plant-atmosphere-continuum (SPAC) model to highlight the importance of considering such interactions through a series of in silico experiments. Our analysis shows that evaporative demand, the hydraulic architecture of the plant, and the texture and depth of the soil play key roles in the final Ψp observed. To establish irrigation programs based on Ψp, without considering the environmental and plant factors that influence it, can create the paradox of having a plant that suffers greater water stress even when high irrigation volumes are applied. The conclusions from our in silico analysis provide some warnings that should be considered when using Ψp to schedule irrigation., This work was supported by project RTA2015-00089-C02-02 from the Ministry of Economy and Competitiveness of the Spanish government and by the European Union’s Horizon 2020 research and innovation program (No 730253). The authors would like to thank the “Juan de la Cierva Formación” funded by the Spanish Ministry of Economy and Competitiveness [grant numbers FJCI-2017-34086 andFJCI-2015-24109] for providing the funds for Dr. Omar Garcia-Tejera and Dr. Alvaro Lopez-Bernal.

There is growing interest in the use of canopy temperature to evaluate the water status of crops for irrigation water management. One of the main indicators currently used is the Crop Water Stress Index (CWSI). In this index, the canopy temperature is normalized by the environmental conditions to account for the evaporative demand of the atmosphere. The theoretical framework, based on the Penman-Monteith equation, defined the CWSI as one minus the ratio between actual and potential water use (Jackson et al., 1981). For the first time in tree crops, we have related the actual transpiration of almond trees measured with heat-pulse sap flow probes with the CWSI, calculated using an empirical Non-Water Stress Baseline. The relationship obtained between the CWSI and the relative transpiration fitted the theoretical relationship, although it showed a large scatter (R2=0.69; RMSE=0.13). The variability in micrometeorological conditions among different parts of the canopy, the scatter of the NWSB, or inherent measurement errors are identified as probable causes of this scatter. Finally, the effect of this scatter on the accurate assessment of actual transpiration from canopy temperature is analyzed for practical irrigation management purposes. We found an error of about 10% in the relative transpiration, which seems acceptable for irrigation management applications., This work was funded by the Spanish Ministry of Science and Innovation (RTI2018–096754-J-I00 and AGL2015–66141-R). V.G-D. was supported by a ‘Ramon y Cajal’ grant (RYC2018–024994-I) provided by the Spanish Ministry of Science, Innovation and Universities. A.L-B. was supported by a postdoctoral scholarship from the ‘Juan de la Cierva–formación 2015′ program Spanish Ministry of Economy and Competitiveness (FJCI-2015–24109).

Rational fertilizer management is crucial in the efficient use of resources that are basically non-renewable and that can have a great environmental impact when used without scientific basis. The availability of scientifically sound decision-making tools for rational fertilization is scarce. We have developed a Windows program to calculate the required seasonal N, P and K rates, and the most cost-effective combination of commercial fertilizers. The tool also provides estimates of the Ca, Mg and S balances in the field resulting from the fertilizer program chosen. Novel aspects of the calculations include the development of stochastic flexible fertilizer programs for N and the calculation of acidification and N losses. Regarding P and K, estimations are provided on the grounds of threshold values of usual availability indexes, something frequently unknown by final users. Also, it allows the users to determine the best complex fertilizer for pre-plant applications to avoid blending of simple fertilizers at the farm, a task usually complex for farmers. The application may be useful both to the fertilizer supply and demand sides. In addition, it may be used for teaching as it helps understanding the rationale behind this management practice., This work was supported by ERA-NET FACCE SURPLUS (Grant number APCIN 652615, project OLIVE-MIRACLE), being co-funded by INIA of Spain.

In olive (Olea europaea L), deficit irrigation (DI) has proven to be an effective management strategy to improve water productivity (WP, yield per unit of water used), particularly under localized irrigation. However, despite the significant research efforts made to adapt irrigation programs to each particular cropping environment, little has been done to study the response of tree root systems to DI. The present paper analyzes the effect of water stress on olive root morphology and studies olive ideotypes best suited to DI. To do so, the results of a two-year field experiment using two irrigation treatments, a well-watered control irrigation (CI) and a regulated deficit irrigation (RDI), are combined with simulations using a soil-plant-atmosphere continuum (SPAC) model. Results of the field experiment show that olive root systems forage for water resources when RDI is imposed, i.e. they try to maximize the soil area explored. However, simulations indicate that under DI, foraging might not be the best strategy. Instead, a root system that tends to concentrate new growth inside the wet bulb will increase daily net assimilation (An) by up to 16%. The present analysis shows that tree performance under DI could be optimized to trigger a new leap in WP.

Olive orchards represent a key agricultural system with high economic and environmental prominence. Expected future climate tendencies over the Mediterranean could threaten the sustainability of such strategic tree crop. This study evaluates the productive and environmental performance of olive orchards under different climate change scenarios and management strategies across the main olive-farming regions over southern Europe using the process-based model OliveCan. Simulations were performed for low density LD (100 trees ha−1), high density HD (400 trees ha−1) and super high density SHD (1650 trees ha−1) olive orchards over baseline period (1980-2010) and future scenarios (2041–2070 and 2071–2100 for RCP4.5 and RCP8.5). Results showed that the future increase in CO2 concentration may compensate the negative effects of higher evaporative demand and diminished water supply resulting in an enhancement of water use efficiency and carbon capture potential in olive orchards. Irrigation requirement for the maximum productivity are expected to increase by 5−27%. Moreover, rainfed low density orchards will be the most vulnerable to expected climate changes, in particular in the driest areas. In fact, a decrease in yield up to 28 % with an increase in its interannual variability of 20 % is expected over the Iberian Peninsula while yield increased up to 26 % over the centre of the Mediterranean. Deficit irrigation and intensification will improve olive orchard productivity and carbon sequestration capacity. Besides, the decrease in winter chilling is not expected to be enough to produce significant flowering anomalies or failures over the study area. Even though findings of this research showed that olive orchards may benefit from future conditions, assessment of management alternatives at local scale will be a must for a better adaptability of olive orchards., This study was supported by the Spanish Ministry of Economy and Competitiveness (project AGL-2015-69822-R) and co-funded by ERA-NET FACCE SURPLUS and INIA (project OLIVE-MIRACLE, grant No. 652615) and by EU-FEDER and the department of Economy, Knowledge, Companies and Universities of the Andalusian Regional Government (project UCO 27425). Besides, H-M was funded by a research doctorate scholarship from The Italian Ministry of Education, University and research - University of Perugia. L-R was funded by the EU project LIFE OLIVE4CLIMATE (LIFE15 CCM/IT/000141).

In this paper, we analyse the combined effect of wetted area and irrigation volume and its impact on olive tree transpiration (E p) after validating a multi-compartment SPAC model in a drip-irrigated hedgerow olive tree plantation. Modelled E p is compared with 2 years of calibrated sap flow records under two different irrigation treatments: a control (C) that was watered using a crop coefficient (K c) of 0.75 and a regulated deficit irrigation (RDI) in which applied irrigation was gradually reduced in relation to the K c of the control (50, 25 and 20% from June to August). The simulated midday leaf water potential (Ψ l) was also compared with measurements performed twice a month in each treatment and for both years. The model accurately predicted E p in both years for the two treatments (R 2 = 0.81 and RMSE = 0.29 mm/day), while midday Ψ l was slightly underestimated. Simulation analysis showed that (a) the use of drip irrigation systems always limits the maximum attainable E p for a given environment; and (b) irrigation design should depend on available water. If irrigation water is limited, the wetted area should be minimized to reduce losses from soil evaporation, thus maximizing the water devoted to E p; by contrast, if water is available, the maximum E p would be reached when wetting at least 30–40% of tree space. The model was accurate enough to capture the trends in E p and Ψ l of trees submitted to different irrigation regimes., This work was supported by Projects AGL2010-20766 and AGL2015-69822 of the Spanish Ministry of Economy, Industry and Competitiveness (former Ministry of Science and Innovation), by the European Community’s Seven Framework Programme-FP7 (KBBE.2013.1.4-09) under Grant Agreement No. 613817 (MODEXTREME, modextreme.org) and by the Programme ERA-NET FACCE SURPLUS “OLIVE MIRACLE” call 2015, ID 118. We wish to thank the “FPI” programme of the aforementioned ministry for providing the Ph.D. scholarships for Omar Garcia-Tejera.

En el actual contexto de rápidos e incesantes desarrollos tecnológicos, existe una necesidad creciente de incorporar nuevas herramientas basadas en las Tecnologías de la Información y la Comunicación (TIC) en los procesos de enseñanza-aprendizaje en ingeniería. Este artículo describe las principales características de FertiliCalc, una novedosa aplicación Windows concebida como herramienta de apoyo en la docencia del cálculo de necesidades de nutrientes y fertilizantes de los cultivos. La aplicación permite al usuario determinar las cantidades estacionales requeridas de nitrógeno, potasio y fósforo y la combinación más barata de fertilizantes comerciales para 149 cultivos. Más aún, se han desarrollado versiones de FertiliCalc y videos tutoriales de uso en hasta 25 idiomas, haciendo posible su empleo en diferentes universidades alrededor del mundo y que cualquier estudiante pueda aprender la terminología relacionada en otros idiomas. Las primeras evaluaciones del uso de la aplicación en un curso reducido perteneciente al Grado de Ingeniería Agroalimentaria de la Universidad de Córdoba han revelado mayores tasas de éxito por parte de los estudiantes en el cálculo de las necesidades de fertilizantes en relación a ediciones pasadas del mismo. Se concluye que FertiliCalc representa una prometedora y potente herramienta para la docencia. Under the current context of fast and constant technological developments, there is a major call for the introduction of new tools based on the new available Information and Communication Technologies (TIC) in the processes of teaching-learning in engineering. This article describes the main characteristics of FertiliCalc, a novel Windows application conceived as a support tool for teaching the calculation of nutrient and fertilizer requirements of crops. The application allows the user to calculate the seasonal amounts of nitrogen, potassium and phosphorous needed and the most cost-effective combination of commercial fertilizers for up to 149 crops. Moreover, versions of FertiliCalc and video tutorials have been developed in up to 25 languages, so that it can be used in different universities across the world and allows students to learn the related terminology in foreign languages. The first assessments of the use of the application in a course belonging to the Degree on Agricultural Engineering of the University of Córdoba revealed a higher success rate among students in the calculation of fertilizer requirements in relation to past editions of that course. It is concluded that FertiliCalc represents a promising and powerful tool for teaching.

Harvest timing in olive orchards has a strong effect on the quality and quantity of oil yield, but many farmers still lack simple and affordable quantitative tools for rationally deciding appropriate harvest dates. This study presents and tests a conceptual model for predicting fruit oil content (Of, g oil fruit−1) from inexpensive measurements of fruit dry weight (wf). The model presents two physiologically relevant parameters, the fruit dry weight at the onset of the oil accumulation phase (wf0) and the ratio of accumulated oil per unit of fruit dry weight increase during the oil accumulation period (β), the latter assumed invariable throughout ripening. A compilation of data on wf and Of dynamics collected from four experiments including six olive cultivars and contrasting conditions of water supply and crop load was used to test the model. Our results suggest that β could be fairly independent of crop load or watering regime and, probably, genetically controlled. By contrast, wf0 is clearly affected by both the cultivar and the availability of assimilates for fruit growth preceding oil accumulation, which makes it orchard- and year-specific. According to those premises, once cultivar-specific β values are available wf0 could be easily calibrated by either a single determination of Of and wf at any time during the oil accumulation phase (Approach A) or by directly measuring wf0 if the date for the onset of oil accumulation can be estimated (Approach B). Validation tests with an independently calibrated β showed an excellent performance for reproducing Of patterns from wf data using Approach A. Approach B satisfactory predicted oil accumulation rates, but absolute estimates of Of were less reliable. Regardless of the calibration approach, the model is easy to implement and has a minimal cost, which satisfies the demand for inexpensive tools for monitoring oil accumulation dynamics., This work was supported by the Spanish Ministry of Economy and Competitiveness [project AGL-2015-69822] and also by National Funds by FCT - Portuguese Foundation for Science and Technology [project UIDB/04033/2020]. The former project provided the funding for setting up Experiment I. Experiment II was performed under the framework of a project [P10-AGR-6456] funded by the Andalusian Regional Government. Experiment III was supported by the PRODER program of the Portuguese Ministry of Agriculture [project PA-44662-IF0019]. Experiment IV was funded by the AGRO-INIA program of the Portuguese Ministry of Agriculture [project AGRO175] and by the PhD fellowship [SFRH/BD/18441/2004] awarded to AF-S by the Foundation for Science and Technology of the Portuguese Ministry of Science, Technology and Education. AL-B enjoyed a JAE-Pre PhD scholarship during Experiment II (funded by CSIC) and a ‘Juan de la Cierva-Formación’ postdoctoral fellowship (funded by the Spanish Ministry of Economy and Competitiveness, grant number [FJCI-2015-24109]) during the execution of Experiment I.

The water footprint (WF), defined as the volume of water used per unit food produced, is becoming a popular indicator in a variety of assessments that relate food production to water use. The complexities underlying the phrase “water used” already point to the difficulties in computing an indicator with robust and general meaning.

Olive (Olea europaea L.) is a widely spread tree species in the Mediterranean. In the last decades, olive farming has known major management changes with high economic and environmental impacts. The fast track expansion of this modern olive farming in these recent years casts doubts on the sustainability of such important tree plantation across the Mediterranean. In this work, we performed a spatial modelling analysis to investigate the implications of climate variability and farming management on the productivity and environmental performances of olive orchards around the Mediterranean. Implementation of this research is based on the use of OliveCan; a process-based model able to illustrate responses of water and carbon balances to weather variables, soil characteristics and management techniques enabling the comprehension of olive orchard dynamics under heterogeneous conditions of climate and agricultural practices. Four main intensification levels were adopted to reflect the main olive grove types from traditional to new intensive plantations: low density LD (100 trees ha−1), medium density MD (200 trees ha−1), high density HD (400 trees ha−1) and super high density SHD (1650 trees ha−1). Managements tested were intensification, water supply (rainfed, deficit and full irrigated) and the fate of pruning residues (exported or left on the soil). Two cases studies in two of the main Mediterranean olive-growing regions with contrasting environmental conditions, Tuscany and Jaen regions, focused on mitigation alternative managements for carbon sequestration. Results showed that olive orchards responses in terms of yield and Net Ecosystem Productivity (NEP) vary along with climatic conditions. Water supply was the main driver with a production function that varies for different atmospheric demands. Application of deficit irrigation proved to boost water use efficiency. Besides, intensification from LD to SHD, presented the greatest improvements, 28–73% for yield and 50–100% for NEP. The C sequestration potential of olive orchards was confirmed. In fact, soil organic carbon (SOC) increased continuously over 400 years of simulation, reaching a state of equilibrium. Moreover, intensification and irrigation improved total carbon sequestration. Management of incorporating pruning residues in the soil increased SOC of 10.5 t C ha−1 for Tuscany and 10.8 t C ha−1 for Jaen. Findings of this research enabled the identification of the main drivers influencing the productive and environmental performance of olive groves in the different Mediterranean sub-climates. Impacts of management innovations on olive farming sustainability were also quantified which may help improve production systems for a more sustainable olive cultivation., The research leading to these results was supported by the Spanish Ministry of Economy and Competitiveness (project AGL-2015-69822-R) and co-funded by ERA-NET FACCE SURPLUS and INIA (project OLIVE-MIRACLE, grant No. 652615) and by EU-FEDER and the Department of Economy, Knowledge, Companies and Universities of the Andalusian Regional Government (project UCO 27425). Besides, H-M was funded by a research doctorate scholarship from The Italian Ministry of Education, University and research - University of Perugia. L-R was funded by the EU project LIFE OLIVE4CLIMATE (LIFE15 CCM/IT/000141). We acknowledge the E-OBS dataset from the EU-FP6 project UERRA (http://www.uerra.eu) and the Copernicus Climate Change Service, and the data providers in the ECA&D project (https://www.ecad.eu).

The abundance of scientific papers dealing with olive reproductive phenology contrasts with the scarce information available in relation to the winter dormant state of olive vegetative structures. In this study, three experiments with young olive trees were performed in Southern Spain, aiming to provide insight into some features of the winter rest period in this evergreen species. Experiment 1 evaluated the environmental cues triggering dormancy induction by measuring leaf appearance rates in trees subjected to different conditions of temperature and daylength over the course of the 2012 autumn. In Experiment 2, several sets of plants were placed into a greenhouse at different dates along the 2013/2014 winter, testing the ability of dormant plants to resume growth upon the return of favourable temperatures. Finally, Experiment 3 was carried out during the autumns of 2016 and 2017 in two locations, and was devoted to assess differences between five cultivars in the onset of dormancy under natural conditions. Our findings revealed that dormancy induction is not controlled by photoperiod, but by low temperatures. The subsequent winter rest state seems to be easily reversed after 1–2 weeks of exposure to warm conditions, irrespective of the initial date of exposure. With regard to cultivar variability, differences in the timing of growth cessation was found to be rather small. Finally, two simple models for predicting the onset of dormancy based on the accumulation of a certain amount of chilling (either considering or not a reversal of chilling by warm temperatures) are presented. Calibration and validation was performed with independent datasets from Experiments 1, 2 and 3. Validation tests highlighted the reliability of both models in reproducing the date of growth cessation., This work was supported by Ministerio de Economía y Competitividad [grant numbers AGL-2010-20766, AGL-2015-69822]; ERA-NET FACCE SURPLUS[grant number 652615, project OLIVE-MIRACLE], the latter co-funded by INIA [PCIN-2015-259]. In addition, AL-B was supported by a postdoctoral fellowship of the ‘Juan de la Cierva-formación’ programme funded by Ministerio de Economía y Competitividad [grant number FJCI-2015-24109].

[Aims] To evaluate the effects of changes in water stress and variable evaporative demand on water potential (Ψ), relative water content (RWC) and gas exchange during two consecutive years (2005 and 2006) providing insight into the mechanisms of stomatal control in the little-studied cultivar ‘Cobrançosa’., [Methods] Measurements of water potential, gas exchange in olive trees subjected to three irrigation treatments: rainfed (T0), continuous deficit irrigation (T1) and well irrigated (T2) that received 0, 30 and 100 % of estimated crop evapotranspiration., [Results] Both the differences in irrigation amounts and the prolonged summer drought conditions characteristic of the study area (Northeast Portugal) resulted in considerable divergences among treatments, with T2 showing the highest values of both Ψ, RWC and gas exchange rates and T0 the lowest. Stomatal conductance exhibited a strong down-regulation under increasing vapor pressure deficit (VPD), with water stress leading to parallel reductions in stomatal conductance values at any given VPD and sensitivity to changes in VPD. These effects might be associated to the deduced drought-induced declines in leaf specific hydraulic conductance (KL)., [Conclusions] The results indicated that Cobrançosa olive trees have a near-isohydric behavior with a tendency to maintain a constant root-to-leaf water gradient (∆Ψ)., This study was supported by project AGRO 175 of AGRO-INIA programme of Ministério da Agricultura (Portugal) and Fundação para a Ciência e a Tecnologia do Ministério da Ciência, Tecnologia e do Ensino Superior (Portugal) by the doctoral fellowship (SFRH/BD/18441/2004) awarded to AA Fernandes-Silva. This study has also benefited from additional funding through projects AGL-2010-20766 of Spanish Ministry of Natural, Rural and Marine Environment and by the European Community’s Seven Framework Programme-FP7 (KBBE.2013.1.4-09) under Grant Agreement No. 613817 (MODEXTREME, modextreme. org).

The measurement of bulk net assimilation (A) in fruit tree species is hindered by the need for sophisticated and complex instrumentation. The aim of this study is to present a simple alternative for estimating A from sap flow measurements and meteorological records. The proposed method was tested in a mature hedgerow olive orchard of 22.2 ha. Within the orchard, an irrigation experiment was established in a small plot including three treatments: a full irrigated control (CI), regulated deficit irrigation (DI) and a treatment mimicking customary orchard irrigation management (FI). Determinations of sap flow, water potential (Ψ) and trunk diameter variations (TDV) were conducted in the three treatments for 3 years. Also, measurements of net ecosystem exchange (NEE) were performed with an eddy covariance system in the centre of the orchard for the first season. The validity of the method was supported by the fact that estimates of A were consistent with both the measured values of NEE and published data regarding the same species under similar environmental and management conditions. Also, differences in A between irrigation treatments were generally in agreement with irrigation applied, transpiration (Ep), Ψ and TDV. It is concluded that the proposed sap flow-based method represents a user-friendly approach to estimate A at the canopy level with potential to study the effects of DI on biomass accumulation., This work was funded by the Andalusian Regional Government (Junta de Andalucía, Project P10-AGR-6456), the Spanish Ministry of Economy and Competitiveness (MINECO, project AGL-2010-20766) and European Regional Development Fund (ERDF). In addition, we thank the Spanish Research Council (CSIC) predoctoral JAE program and again the aforementioned project AGL-2010-20766 for providing the PhD scholarship granted to the first and second author, respectively. Besides that, the authors also acknowledge the excellent technical support provided by Mr Rafael del Río, Mr Ignacio Calatrava and Mr José Luis Vazquez.

A disturbance of water relations in response to chilling have long been observed in potted plants growing under controlled conditions, but information is lacking for field plants. The aim of this study was to assess the effects of winter low temperatures on the water relations of mature olive trees. To this end, water potential, sap flux density, soil temperature and meteorological data were monitored in a hedgerow olive orchard near Córdoba, southern Spain, throughout two consecutive winters. Water stress symptoms were found in terms of midday Ψ, despite adequate water supply and low evaporative demand. These effects were associated with changes in the soil-to-trunk hydraulic resistance (Rroot), which increased by December–January to much higher values than those previously reported in the literature, particularly in the year of higher fruit load. The contribution of viscosity (η) to the observed Rroot dynamics was almost negligible as deduced from measurements of soil temperature, so the high winter values of Rroot were likely to have originated from other causes such as reductions in membrane permeability and root growth. The findings of this work raise new major issues that deserve further research such as the impact of the winter water stress on stomatal conductance and photosynthesis rates in mature olive trees., This work was funded by the Spanish Ministry of Science and Innovation (MICINN, project AGL-2010-20766) and European Regional Development Fund (ERDF). We thank the Spanish Research Council (CSIC) predoctoral JAE program and the aforementioned project for providing the Ph.D. scholarship granted to the first and second author, respectively.

In the context of fractional calculus (FC), this paper is devoted to model thermal processes in trees based on the measurement of the temperature difference (ΔT) between sensors located above and below a heater inserted in the tree trunk. By evaluating several temperature curves taken from real trees of different species, the current approach shows that the temperature in each probe can be successfully described by the two-parameter Mittag- Leffler function Eα,β. Then, a simple methodology is followed to derive a novel expression of the heat-pulse velocity (v) as a function of ΔT and the parameter α of the mentioned Eα,β function. Experimental results are given to validate the goodness of the current proposal.

Increased water scarcity demands more efficient use of water in the agricultural sector which is the primary consumer of water. Precise determination of irrigation requirements based on specific crop parameters is needed for accurate water applications. We conducted a 4-year study on almond evapotranspiration using a large weighing lysimeter. Tree canopies changed from 3 to 48 % ground cover during the course of the study. Sap flow measurements made on the lysimeter tree provided a continuous record of tree transpiration. We propose to use the daily fraction of photosynthetically active radiation intercepted by the canopy (fIRd) as a predictor of almond orchard maximum transpiration. The transpiration coefficient (T/ETo or KT) was related to the fIRd of the last two years, and the ratio between fIRd and KT stayed more or less constant around a value of 1.2. Such value extrapolated to the size of a mature orchard with 85 % intercepted radiation gives a KT of around 1.0, a number above the standard recommendations, but fully compatible with the maximum Kc values of 1.1–1.15 recently reported., M Espadafor is a recipient of research fellowship BES-2010-033883 from the Spanish Ministry of Science and Innovation. Financial support from the Spanish Ministry of Science and Innovation (AGL2009-07350) is also acknowledged.

This article is part of the Research Topic: Advances in Oil Crops Research—Classical and New Approaches to Achieve Sustainable Productivity.-- Edited by: Dragana Miladinović, Johann Vollmann, Leire Molinero-Ruiz and Mariela Torres., Several simulation models of the olive crop have been formulated so far, but none of them is capable of analyzing the impact of environmental conditions and management practices on water relations, growth and productivity under both well-irrigated and water-limiting irrigation strategies. This paper presents and tests OliveCan, a process-oriented model conceived for those purposes. In short, OliveCan is composed of three main model components simulating the principal elements of the water and carbon balances of olive orchards and the impacts of some management operations. To assess its predictive power, OliveCan was tested against independent data collected in two 3-year field experiments conducted in Córdoba, Spain, each of them applying different irrigation treatments. An acceptable level of agreement was found between measured and simulated values of seasonal evapotranspiration (ET, range 393 to 1016 mm year-1; RMSE of 89 mm year-1), daily transpiration (Ep, range 0.14–3.63 mm d-1; RMSE of 0.32 mm d-1) and oil yield (Yoil, range 13–357 g m-2; RMSE of 63 g m-2). Finally, knowledge gaps identified during the formulation of the model and further testing needs are discussed, highlighting that there is additional room for improving its robustness. It is concluded that OliveCan has a strong potential as a simulation platform for a variety of research applications., The research leading to these results has received funding from Ministerio de Economía y Competitividad (Grant Nos. AGL-2010-20766 and AGL2015-69822), from Junta de Andalucía (Grant No. P08-AGR-04202), from the European Community’s Seven Framework Programme-FP7 (KBBE.2013.1.4-09) under Grant Agreement No. 613817. 2013–2016 “MODelling vegetation response to EXTREMe Events” (MODEXTREME, modextreme.org) and from ERA-NET FACCE SURPLUS (Grant No. 652615, project OLIVE-MIRACLE), the latter co-funded by INIA (PCIN-2015-259). Besides, ÁL-B was funded by a postdoctoral fellowship (‘Juan de la Cierva-Formación 2015’ Programme, FJCI-2015-24109) from Ministerio de Economía y Competitividad.

Under localized irrigation, even when applying non-limiting amounts of water, there could be transpiration (T) limitations due to a limited wetted soil volume. To study under field conditions how drip-irrigated almond trees responded to a change in wetted soil volume, two treatments were established in summer 2012 in a drip irrigated almond orchard in Cordoba, Spain. One treatment (“Large volume”) was initially irrigated with micro-sprinklers (MS) to wet the entire ground surface, and then reverted to drip irrigation, while other was always kept under drip irrigation (“Small volume”). Continuous monitoring of T and measurements of soil moisture content, tree water status and trunk growth were carried out. Even though trees in both treatments were supplied with sufficient water, the MS application induced an increase in T and an improvement in water status in “Large volume” relative to “Small volume”. A reduction in the hydraulic resistance of the tree was also detected in “Large volume”, as well as an enhancement in canopy conductance and tree growth. We concluded that there are situations in the field where almond tree transpiration is limited by an insufficient wetted soil volume, even when supplied with adequate water, due to a high hydraulic resistance during times of high evaporative demand., This study has been financially supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) projects ALWAT (AGL2009-07350), RIPAO (AGL2012-35196) and SORIAL (AGL2015-66141-R), by project P12-AGR2521 funded by Junta de Andalucia, and by project INNOVA-NUTS (AVA.AVA201601.18) funded by the European Regional Develpment Fund (FEDER). M Espadafor was a recipient of research fellowship BES-2010-033883 from MINECO.

Stomatal oscillations have long been disregarded in the literature despite the fact that the phenomenon has been described for a variety of plant species. This study aims to characterize the occurrence of oscillations in olive trees (Olea europaea L.) under different growing conditions and its methodological implications. Three experiments with young potted olives and one with large field-grown trees were performed. Sap flow measurements were always used to monitor the occurrence of oscillations, with additional determinations of trunk diameter variations and leaf-level stomatal conductance, photosynthesis and water potential also conducted in some cases. Strong oscillations with periods of 30-60 min were generally observed for young trees, while large field trees rarely showed significant oscillations. Severe water stress led to the disappearance of oscillations, but moderate water deficits occasionally promoted them. Simultaneous oscillations were also found for leaf stomatal conductance, leaf photosynthesis and trunk diameter, with the former presenting the highest amplitudes. The strong oscillations found in young potted olive trees preclude the use of infrequent measurements of stomatal conductance and related variables to characterize differences between trees of different cultivars or subjected to different experimental treatments. Under these circumstances, our results suggest that reliable estimates could be obtained using measurement intervals below 15 min.

The accurate assessment of respiration by woody vegetation, still a challenge in plant productivity models, is generally a problem of correctly scaling-up the process from organs to the whole plant. We used a large (41.6 m3), canopy chamber to enclose mature olive trees and to measure aboveground respiration (R ag) under natural environmental conditions in an irrigated olive orchard in Córdoba (Spain). The 3-year study assessed nocturnal and seasonal R ag patterns in terms of temperature (T), plant dry matter composition, and phenology. The relative contributions of maintenance and growth respiration to R ag were determined empirically via an independent experiment. Although short-term variations in R ag rates were explained mainly by T variations, over seasonal time-scales this relationship was modulated by the vegetative composition of the olive trees and the contribution of growth respiration to R ag when the plants, in different seasons, allocated most of the new assimilates to actively growing shoots, flowers or fruits. Leaf mass and fruit load were the main determinants of R ag, which was weakly affected by differences in woody biomass since woody tissue respiration accounted for just 15 % of R ag. Respiration in olive trees during fruit setting periods is composed of approximately 30 % growth and 70 % maintenance. This study provides an independent evaluation of how, and to what degree, seasonally varying plant organ composition determines total respiration. Improved modelling of ecosystem respiration can be achieved by accounting for plant biological patterns characterising energy-requiring growth and maintenance processes, since biochemical kinetics alone cannot explain the observed seasonal variability. © 2014 Springer Science+Business Media Dordrecht., This work was co-funded by Spanish Science Ministry projects CGL2011-15276-E, AGL-2004-05717 and CONSOLIDER CSD2006-67, and Andalusian regional projects P08-AGR-4202 and RNM-7186, with European Regional Development Fund (ERDF) support. OPP is funded by a postdoctoral fellowship from the European Commission (FP7) through GHG-Europe project (Call FP7-ENV-2009-1.1.3.1; Project Code 244122).

Crop coefficients (the ratio of actual and reference evapotranspiration, ET/ETo) can be derived from vegetation indices (VIs) obtained by remote sensing. If ground meteorological stations are available to calculate ETo, then the FAO method for estimating the ET of actual crops may be applied in combination with series of satellite images if it is assumed that the crops are not water stressed. This approach was evaluated for two annual crops (cotton and garlic) and three tree crops (mandarin, olive, and peach) using measurements of evapotranspiration, made with the eddy covariance method, as ground truth. Thirty images acquired by the Landsat 5 TM and Landsat 7 ETM+ sensors were used to calculate VIs and derive crop coefficients. The assessment (based on 557 data pairs) led to an overall positive valuation of the method. The root-mean-square deviation over all estimates was 0.75 mm day−1. It was concluded that the VI-ETo method is valid and robust for estimating spatially distributed evapotranspiration in large, irrigated areas. Weaknesses of the method were identified and new research to overcome these deficiencies is proposed.

Improving current approaches to quantify the transpiration of fruit trees is needed for water allocation purposes and to enhance the precision of water applications under full and deficit irrigation. Given that transpiration of tree crops is mainly modulated by canopy conductance (Gc) and vapour pressure deficits, we developed a functional model of tree transpiration by quantifying an average daily Gc based on radiation use efficiency and CO2 assimilation. For model calibration, an extensive experimental dataset of tree transpiration (Ep) was collected in many of the main temperate fruit tree species, namely, apricot, apple, citrus, olive, peach, pistachio, and walnut, all under non-limiting water conditions, in different orchards in Spain and California (USA). In all species, Ep was assessed by measuring sap flux with the Compensation Heat Pulse method for several months, and a transpiration coefficient (Kt) was calculated as the ratio of measured Ep to the reference evapotranspiration. For three deciduous species (apricot, peach and walnut) Kt showed maximum values close to 1, a value which stayed more or less constant throughout the summer in peach and walnut. The maximum Kt values were measured in pistachio (1.14) while they only reached 0.35 in olive and citrus trees. In the latter two species, Kt varied seasonally between 0.2 and 0.6 depending on the weather. The average Gc in July was high for apple, walnut, peach and pistachio (range 0.240–0.365 mol m−2 s−1) and low for olive and orange (range 0.074–0.100 mol m−2 s−1). The calibrated model outputs were compared against measured Ep data, suggesting the satisfactory performance of a functional model for Ep calculation that should improve the precision of current empirical approaches followed to compute fruit tree water requirements.

The aim of this study was to assess the effect of different irrigation strategies in virgin olive oil (VOO) composition and quality of cv. Cobrançosa, integrated in a protected denomination of origin of >Azeite de Trás-os-Montes> in the Northeast of Portugal. Three irrigation treatments were applied: T2-full irrigation that received a seasonal water equivalent to 100% of estimated crop evapotranspiration (ETc), T1-continuous deficit irrigation (30% ETc) and T0- rainfed treatment. Data were collected from two consecutive crop years (2005-2006). Irrigation regimes had a minor effect on standard quality indices (free fatty acids, peroxide value, K232 and K270) of VOO and in fatty acid composition. Total polyphenols decreased up to treatment T2, and were strongly related to the water stress integral, suggesting that the effect of irrigation on this variable occurs along the crop season and not just during the oil accumulation phase. A strategy of continuous deficit irrigation with only 30% of maximum ETc may have an advantageous effect, as it increased oil yield to more than double that of rainfed conditions while VOO quality was similar., This study was supported by project AGRO 175 of AGRO-INIA program of Ministério da Agricultura (Portugal) and Fundação para a Ciência e a Tecnologia do Ministério da Ciência, Tecnologia e do Ensino Superior (Portugal) which supported a PhD grant (SFRH/BD/18441/2004).

The aim of this study was to assess the effect of different irrigation strategies on the sensory quality of virgin olive oil (VOO) from the cv. >cobrançosa> integrated into a protected denomination of origin of >Azeite de Trás-os-Montes> in the Northeast of Portugal. Three irrigation treatments were applied: (T2)-full irrigation, which received a seasonal water equivalent of 100% of the estimated crop evapotranspiration (ETc), (T1)-continuous deficit irrigation (30% ETc) and (T0)- rainfed treatment. Data were collected from two consecutive crop years (2005-2006). Olive oil samples were analyzed for volatiles by GC-MS and the results compared with sensory evaluation data. Total volatile compounds tended to decrease with the amount of water applied. The characteristics pungent and bitter were more pronounced in olive oils from T0 and T1, which had higher polyphenolic concentrations, with a strong positive relationship with this variable and the bitter attribute. The Principal Components Analysis clearly separates the three olive oils from 2005, the driest year, and aggregates into a single group the three samples from 2006, suggesting no effect of irrigation on volatile compounds in years with a rainy spring and a marked effect in years with severe drought, suggesting that the effect of the trees' water status on these variables occurs throughout the crop season and not just during the oil accumulation phase. In general, olive oil from the cv. Cobrançosa is more bitter than pungent and has a typical nutty sensory attribute shown by a strong positive relationship between benzaldehyde and the sensory notes of almonds and nuts., This study was supported by the project AGRO 175 of AGRO-INIA program of Ministério da Agricultura (Portugal) and Fundação para a Ciência e a Tecnologia do Ministério da Ciência, Tecnologia e do Ensino Superior (Portugal) which supported a PhD grant (SFRH/BD/18441/2004).