Mediterranean Greenhouses Research Articles

Ventilation surface area: key to modify morphology, quality and photosynthetic activity of tomato crops in Mediterranean greenhouses

Ventilation surface area: key to modify morphology, quality and photosynthetic activity of tomato crops in Mediterranean greenhouses

Effects of the increase of ventilation surface area on the microclimate and yield of a tomato crop in Mediterranean greenhouses

Effects of the increase of ventilation surface area on the microclimate and yield of a tomato crop in Mediterranean greenhouses

Effect on temperature of lightweight plant cover enveloping papaya fruit (Carica papaya L.) in a naturally ventilated Mediterranean greenhouse

Effect on temperature of lightweight plant cover enveloping papaya fruit (<i>Carica papaya</i> L.) in a naturally ventilated Mediterranean greenhouse

A Flexible Tool for Modeling and Optimal Dispatch of Resources in Agri-Energy Hubs

The dispatch of energy and resources in agricultural systems often involves the definition and resolution of optimization problems. This paper presents a novel tool composed of a set of MATLAB® and Simulink® files that has been developed to ease such tasks. In contrast to other alternatives, it allows the consideration of multiple kinds of resources in the problem and the relationships between the inputs and outputs of the system; its parametrization can be defined graphically in Simulink® without requiring third party software, and the entire package is freely available on Github. The package can generate the constraints in MATLAB® code and can get the optimal dispatch schedule for the deterministic mixed-integer linear problem that represents the defined system. Its main functions and blocks as well as a case study based on a traditional Mediterranean greenhouse and a photovoltaic parking lot located in Almeria (Spain) are included to demonstrate its use and clarify how the problem is formulated. The simulation performed validates the tool as being useful for decision-making (schedule irrigation and CO2 enrichment, as well as managing storage systems) in these and similar environments. Future implementations are intended to incorporate the interconnection of agents with opposed interests and robust optimization strategies for uncertain scenarios.

Automatic Tomato and Peduncle Location System Based on Computer Vision for Use in Robotized Harvesting

Protected agriculture is a field in which the use of automatic systems is a key factor. In fact, the automatic harvesting of delicate fruit has not yet been perfected. This issue has received a great deal of attention over the last forty years, although no commercial harvesting robots are available at present, mainly due to the complexity and variability of the working environments. In this work we developed a computer vision system (CVS) to automate the detection and localization of fruit in a tomato crop in a typical Mediterranean greenhouse. The tasks to be performed by the system are: (1) the detection of the ripe tomatoes, (2) the location of the ripe tomatoes in the XY coordinates of the image, and (3) the location of the ripe tomatoes’ peduncles in the XY coordinates of the image. Tasks 1 and 2 were performed using a large set of digital image processing tools (enhancement, edge detection, segmentation, and the feature’s description of the tomatoes). Task 3 was carried out using basic trigonometry and numerical and geometrical descriptors. The results are very promising for beef and cluster tomatoes, with the system being able to classify 80.8% and 87.5%, respectively, of fruit with visible peduncles as “collectible”. The average processing time per image for visible ripe and harvested tomatoes was less than 30 ms.

How mulching and canopy architecture interact in trapping solar radiation inside a Mediterranean greenhouse

This work evaluates roles and interactions of ground albedo (ag) and canopy architecture in capturing solar radiation inside Mediterranean greenhouses. Both incident and reflected solar radiation were measured over the ground surface and the greenhouse roof cover during a series of greenhouse experiments where common types of mulch and crop architecture were combined. In the experiments without crop around winter, changes in the daily mean ag from 0.06 to 0.38 induced changes in the greenhouse cover albedo (ac), which ranged from about 0.20 to 0.42. In measurements carried out around winter, both the ag and ac decreased when the ratio of the outdoor diffuse-to-solar radiation increased, independently of the ground surface, indicating that a higher percentage of solar radiation was trapped by the greenhouse under diffuse than under sunny conditions. In crops grown horizontally (not vertically trained), the effect of ground mulching over ag vanishes progressively with the increase in leaf area of the crops, resulting in an asymptotic trend of ag close to 0.23 at full ground covering, independently of the mulch type. In crops grown with high-wire production systems (plants grown in separated rows with the canopy distributed vertically up to 1.5–4.0 m high), asymptotic ag values were also reached but they were lower and dependent on the mulch type and the canopy architecture (0.08 for with black mulch and 0.12 to 0.19 with a gravel mulch). Then, crops with high-wire production systems, common in greenhouses, presented a higher efficiency in trapping solar radiation inside greenhouses. A model, which predicts fairly well the ac from the knowledge of ag and the cover shortwave reflectance, was proposed and used.

Supplementary LED Interlighting Improves Yield and Precocity of Greenhouse Tomatoes in the Mediterranean

In Northern Europe, the use of light–emitting diodes (LEDs) is widely adopted in protected horticulture, enabling to enhance plant growth by ensuring needed radiative fluxes throughout seasons. Contrarily, the use of artificial lighting in Mediterranean greenhouse still finds limited applications. In this study, the effects of supplemental LED interlighting on vegetative development, fruit growth, yield, and fruit quality of high-wire tomato plants (Solanum lycopersicum L. cv. ‘Siranzo’) during spring and summer season were addressed in a hydroponic greenhouse in Italy. Plants were either grown under natural solar radiation (control), or by adding supplemental LED interlighting. LED treatment featured red (R) and blue (B) light (RB ratio of 3) and a photosynthetic photon flux density of 170 µmol m−2 s−1 for 16 h d−1. Supplemental LED interlighting enhanced yield as a result of increased fruit weight and dimension. While no effects on soluble solids content and fruit color at harvesting were observed, supplemental LED interlighting accelerated ripening by one week in spring and two weeks in summer and this also resulted in increased cumulated productivity (+16%) as compared to control treatment. Overall, supplemental LED interlighting can represent a feasible technology for tomato greenhouse production also in the Mediterranean region.

Comparative study of two predatory mites Amblyseius swirskii Athias-Henriot and Transeius montdorensis (Schicha) by predator-prey models for improving biological control of greenhouse cucumber

Suppression of the whitefly Bemisia tabaci (Gennadius) and the thrips Frankliniella occidentalis (Pergande) by the predatory mite Amblyseius swirskii Athias-Henriot on greenhouse cucumbers can be considerably affected by cooler conditions in winter. In this study, this well known mite was tested simultaneously with a more recent predatory mite Transeius montdorensis (Schicha), to find out which of them was better at controlling pests on cucumbers in winter in Mediterranean greenhouses. We developed a mathematical predator-prey model which involved releasing both predators with populations of the two naturally occurring pests in a greenhouse cucumber trial. T. montdorensis provided pest control that was similar to and as effective as that by A. swirskii. T. montdorensis exhibited higher populations than A. swirskii, specifically when climatic conditions were colder. However, as the weather became warmer, the A. swirskii population increased quickly. Therefore, releasing T. montdorensis in winter, followed with releases of A. swirskii in spring, may be a good pest control strategy for greenhouse cucumbers.

Vegetable Crops Grown under High Soil Water Availability in Mediterranean Greenhouses

The soil water availability of six vegetable crop cycles, irrigated with water of 0.4 dS m−1 electrical conductivity, was modified by varying the irrigation frequency in typical Mediterranean greenhouses at SE Spain. The soil matric water potential (SMP) in the middle of the loamy soil layer where most roots usually grow was maintained between −10 and −20 kPa (H), −20 and −30 kPa (C), and −30 and −50 kPa (L) for the crops grown under high, conventional and low soil water availability, respectively, while the total irrigation water applied was similar for the three treatments. The high soil water availability (H) did not improve the fresh weight of total, marketable and first class fruits, or the shoot biomass and partitioning. The irrigation frequency did not affect the total root biomass at the end of the autumn–winter cucumber, but the crop under L distributed its root biomass more homogenously throughout the soil profile than the crop under H. Regulating the soil water availability (maintaining the SMP higher than or close to the level at which crop water stress may occur) over the cycle as a function of crop conditions or farmers’ requirements appears to be a useful management practice for controlling soil root distribution or shoot partitioning.

Off-seasonal soilless production of green vegetables in reused substrates in Mediterranean unheated greenhouses

Off-seasonal soilless production of green vegetables in reused substrates in Mediterranean unheated greenhouses

Effects of Cover Whitening Concentrations on the Microclimate and on the Development and Yield of Tomato (Lycopersicon esculentum Mill.) Inside Mediterranean Greenhouses

This work analyzes the influence of whitening a greenhouse roof on the microclimate and yield of a tomato crop. In the west sectors of two multi-span greenhouses, a whitening concentration of 0.250 kg L−1 was used as a control. In an autumn–winter cycle, a lower (0.125 kg L−1) and an increased (0.500 kg L−1) concentration were used in the east sectors of greenhouses 1 and 2. In a spring–summer cycle, the whitening concentrations in the east were varied depending on outside temperature. The effect of whitening on photosynthetic activity, production, plants’ morphological parameters, and the quality of the fruits were also analyzed. To evaluate the effect on microclimate, solar and photosynthetically active (PAR) radiations, air and soil temperatures, and heat flux in the soil were measured in greenhouse 1. Results show that excessive whitening leads to reductions of inside PAR radiation that decreases photosynthesis and crop yield. A whitening concentration of 0.500 kg L−1 is proposed at the beginning of the autumn–winter crop cycle, washing the cover when inside temperature drops to 35 °C. At the end of the spring–summer cycle, a concentration of 0.125 kg L−1 is recommended when inside temperature increases to 35 °C.

Growth, Yield, and Water Productivity Responses of Pepper to Sub-Irrigated Planter Systems in a Greenhouse

A sub-irrigated planter (SIP) is a container irrigation technique in which water is supplied to the crop from the bottom, stored in a saturated media-filled reservoir beneath an unsaturated soil, and then delivered by capillary action to the root zone. The aim of this study was to optimize the water management and to assess the performance of this technique in terms of water use efficiency, soil moisture, and solute distribution in comparison with surface irrigation in a Mediterranean greenhouse. The experiment consisted of four SIP treatments, with a constant water level in the bottom reservoir in order to evaluate the effect of two different irrigation salinities (1.2 and 2.2 dS m−1) and two depths of substrate profiles (25 and 15 cm). The results showed that SIP is capable of significantly improving both water-use efficiency and plant productivity compared with surface irrigation. Also, a 24% average reduction in water consumption was observed while using SIP. Moreover, SIPs with a higher depth were recommended as the optimum treatments within SIPs. The type of irrigation method affected the salinity distribution in the substrate profile; the highest salinity levels were registered at the top layers in SIPs, whereas the maximum salinity levels for the surface treatments were observed at the bottom layers. SIPs provide a practical solution for the irrigation of plants in areas facing water quality and scarcity problems.

Reducing nitrate leaching losses from vegetable production in Mediterranean greenhouses

Reducing nitrate leaching losses from vegetable production in Mediterranean greenhouses

Solar Cooling: A renewable energy solution

A sustainable and environmentally alternative to commonly used air conditioning systems can be the solar cooling system due to the use of renewable and clean energy. Solar absorption systems can be used for greenhouse cooling in areas with high outdoor temperatures and solar radiation levels. These systems take advantage of the simultaneity between the solar energy availability and the greenhouse cooling demand allowing the reduction of conventional electricity and water consumption. This paper presents the results of the application of a solar cooling plant for the climate control of a greenhouse at the University of Bari, Italy. The experimental plant consists of a Mediterranean greenhouse, having a surface of 300 m2, and of a single effect LiBr-H2O absorption chiller fed by evacuated-tube solar collectors. Two different localized systems were chosen for the distribution of cold inside the greenhouse: the first system presents pipes placed centrally on the cultivation vessels; the second consists of pipes in contact with aluminium plates and of a transparent EVA film, used to border an area close to plants. The distribution system of cold with pipes, plate and EVA film provided a slightly higher cooling capacity due to the presence of the plates which increases the ability to dissipate energy.

Application of Semi-Empirical Ventilation Models in A Mediterranean Greenhouse with Opposing Thermal and Wind Effects. Use of Non-Constant Cd (Pressure Drop Coefficient Through the Vents) and Cw (Wind Effect Coefficient)

The present work analyses the natural ventilation of a multi-span greenhouse with one roof vent and two side vents by means of sonic anemometry. Opening the roof vent to windward, one side vent to leeward, and the other side vents to windward (this last vent obstructed by another greenhouse), causes opposing thermal GT (m3 s−1) and wind effects Gw (m3 s−1), as outside air entering the greenhouse through the roof vent circulates downward, contrary to natural convection due to the thermal effect. In our case, the ventilation rate RM (h−1) in a naturally ventilated greenhouse fits a second order polynomial with wind velocity uo (RM = 0.37 uo2 + 0.03 uo + 0.75; R2 = 0.99). The opposing wind and thermal effects mean that ventilation models based on Bernoulli’s equation must be modified in order to add or subtract their effects accordingly—Model 1, in which the flow is driven by the sum of two independent pressure fields G M 1 = | G T 2 ± G w 2 | , or Model 2, in which the flow is driven by the sum of two independent fluxes G M 2 = | G T ± G w | . A linear relationship has been obtained, which allows us to estimate the discharge coefficient of the side vents (CdVS) and roof vent (CdWR) as a function of uo [CdVS = 0.028 uo + 0.028 (R2 = 0.92); CdWR = 0.036 uo + 0.040 (R2 = 0.96)]. The wind effect coefficient Cw was determined by applying models M1 and M2 proved not to remain constant for the different experiments, but varied according to the ratio uo/∆Tio0.5 or δ [CwM1 = exp(−2.693 + 1.160/δ) (R2 = 0.94); CwM2 = exp(−2.128 + 1.264/δ) (R2 = 0.98)].

Antioxidant Seasonal Changes in Soilless Greenhouse Sweet Peppers

This study was commissioned to study the effect of the growing season on the antioxidant components of greenhouse sweet pepper crops, which is of scientific interest because of their possible beneficial health effects. The total antioxidant activity (estimated by ferric reducing antioxidant power-FRAP assay) major antioxidants (ascorbic acid, phenolics and carotenoids) and taste fruit quality characteristics (soluble solids, titratable acidity, dry matter and sugars) were recorded in soilless-grown sweet pepper cultivars of red, orange, yellow and green color at four harvesting season months, i.e., February (winter), May (spring), July (summer) and October (autumn). The results showed seasonal variations in antioxidant components and activity of pepper fruits. In most cases measured parameters showed higher values in spring (May) and summer (July) compared with winter (February) and autumn (October) growing seasons. This study indicates that during late autumn and winter, lower levels of solar irradiance, ultraviolet radiation and temperature in Mediterranean greenhouses can be insufficient to stimulate phytochemicals production in peppers; thus, plant–light interception must be more actively managed.

Effects of Cooling Systems on Greenhouse Microclimate and Cucumber Growth under Mediterranean Climatic Conditions

Two experiments were conducted in different cropping seasons under Mediterranean climatic conditions to investigate the impact of two cooling systems (fan-pad evaporative as opposed to fan ventilation) on greenhouse microclimate and soilless cucumber growth. The second objective of the experiment was to determine the most appropriate irrigation regime (between 0.24 and 0.32 L m−2) in relation to crop water uptake and greenhouse fertigation effluents. The use of a fan ventilation system enhanced the vapor pressure deficit; thus, the crop transpiration improved by 60% in relation to the transpiration rates of plants grown under the fan-pad system. Higher transpiration rates alleviated the heat load as the external–inside greenhouse air differences declined from 6.2 °C to 3 °C. The leaf–air temperature differential indicated that plants were not facing any water stress conditions for both cooling systems tested; however, fan ventilation reduced drainage emissions outflows (95% decrease) compared with evaporative cooling. Results also demonstrated that an irrigation regime of 0.24 L m−2 can be applied successfully in soilless cucumber crops, keeping the drainage to a minimum (20% of the nutrient solution supply). These results suggest that fan ventilation cooling system in conjugation with an appropriate irrigation regime prevents overheating and minimizes the nutrient and water losses in spring-grown soilless cucumber crops in Mediterranean greenhouses without compromising yield.

The effects of phosphorus supply limitation on photosynthesis, biomass production, nutritional quality, and mineral nutrition in lettuce grown in a recirculating nutrient solution

In this study, we investigated the impact of phosphorus (P) supply levels (0.8, 1.3 and 1.8 mM) in two green leaf lettuce (Lactuca sativa L.) types, namely ‘Romaine’ (cv. Nader), and ‘Lollo’ (cv. Bionda) grown in a recirculating nutrient solution. The biomass yield of the Romaine type was reduced by 15% at the lowest P supply (0.8 mM) and plants showed reduced photosynthetic function (i.e., net photosynthesis, stomatal conductance, quantum yield and electron flow) and increased root/shoot ratio. On the other hand, the Lollo type maintained photosynthetic rates and biomass accumulation in all cases and proved less sensitive to low P levels in the NS. At the lowest P supply, the P concentration in the recirculating solution declined to 0.1 mM and showed a decline in leaf P and Ca concentrations and an increase in total sugar and nitrate content, depending on the cultivar. Also, lowering P supply boosted P-use efficiency (kg biomass kg−1 P supply) in both types of lettuce. Nutrient to water uptake ratios of macro nutrients N, P, K, Ca and Mg were determined as follows: (i) 16.0, 1.3, 9.1, 3.1 and 0.9 mmol L−1, respectively for Romaine, and (ii) 16.4, 1.3, 9.1, 3.3 and 0.9 mmol L−1, respectively for Lollo. The current experimental results suggest that, reducing the P supply to lower levels than those currently recommended for lettuce crops grown in closed hydroponics considerably improves the P use efficiency in Mediterranean greenhouses without compromising yield.

Analysis of the Effect of Concentrations of Four Whitening Products in Cover Transmissivity of Mediterranean Greenhouses.

The present work analyses the traditional method of applying whitening products on Mediterranean greenhouses. Four commercial whitening products (agricultural solar protectors, ASPs), applied at four doses, were compared with a non-whitened cover. The traditional product “Blanco de España” with 99% calcium carbonate (CaCO3) and other three products with 97% CaCO3 that incorporate adhesives were tested. The use of adhesives in ASP did not influence the effect of the different products on the inside temperature, and at the same dose all four products show a similar behaviour. The findings support the maximum dose recommended by other authors of 0.50 kg L−1 (50/100), above which the transmissivity of the greenhouse cover decreases by over 50%. The effect of ASP on the transmissivity of the cover depends principally on the dose applied, but also on the climatic conditions (solar radiation, cloud cover, etc.) and on the time of year (solar elevation). The habitual use of a constant dose throughout the year does not seem to be the most adequate. Recommended doses should vary according to the time of year and the desired degree of transmissivity reduction. The adhesive components are shown to provide a high degree of protection against heavy rain. The study recommends a standardised method of ASP application, establishing a method that allows the grower to verify the concentration of the product that will remain on the greenhouse cover.

Organic Photovoltaics on Greenhouse Rooftops: Effects on Plant Growth

Abstract Greenhouse agriculture is a high-growth and high-volume market that rapidly expands worldwide to address the societal needs for food production. The increasing demand for energy to cover their requirements, coupled with the limited amount of available fossil fuels, has turned the agriculture community in the exploitation of renewable energy sources. Intensive research is currently focuses on the use of solar energy in agriculture constructions. Organic Photovoltaics (OPVs) are constantly gaining ground among other PV technologies due to their low weight, tunable optical transmittance, flexibility and high conformability. In this work, semi-transparent OPVs based on the blend of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) were integrated on the rooftop of the 24 m2 experimental Mediterranean greenhouse covering the 22% of its total area in order to investigate its effect on the growth and behavior of cultivated pepper plants (Capsicum annuum). Under the shade of OPVs, the pepper plants produced 20.2% more fruit mass compared to the control ones. In addition, at the end of the growing season, the height of the shaded plants was 21.8% larger than the remaining plants.