Perceptions and Acceptance of Desalinated Seawater for Irrigation: A Case Study in the Níjar District (Southeast Spain)

In the context of increasing demand for irrigation water—but, at the same time, with the constraints in the supply from traditional resources—desalinated seawater has been recognized as one of the alternative sources of water to increase the supply for agricultural irrigation. However, its use among farmers has not yet started to expand. Policy makers need to understand what is causing the low acceptance levels of farmers, and how their attitudes could be improved. This is the first study that has conducted an analysis of farmers’ perceptions and acceptance of the use of desalinated seawater for irrigation. The study is based on collected data from a survey completed by farmers in southeastern Spain who do not use desalinated seawater. The main results indicate that desalinated seawater as a water supply source has the lowest acceptance level for farmers. Barriers for its use are price, the need for additional fertilization, and the perception that it would negatively affect the yield and crop quality. The farmers’ general level of knowledge about the impact of using desalinated seawater in agriculture is extremely low. Furthermore, farmers consider it a priority that their startup investment should be subsidized and that water prices should be reduced. Based on the study findings, this paper makes recommendations for the decision-making process in order to improve farmers’ acceptance levels

Energy Efficiency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads

Evaporative cooling systems using a combination of evaporative pads and extractor fans require greenhouses to be hermetic. The greatest concentration of greenhouses in the world is located in southeast Spain, but these tend not to be hermetic structures and consequently can only rely on fogging systems as evaporative cooling techniques. Evaporative cooling boxes provide an alternative to such systems. Using a low-speed wind tunnel, the present work has compared the performance of this system with four pads of differing geometry and thickness manufactured by two different companies. The results obtained show that the plastic packing in the cooling unit produces a pressure drop of 11.05 Pa at 2 m·s−1, which is between 51.27% and 94.87% lower than that produced by the cellulose pads. This pressure drop was not influenced by increases in the water flow. The evaporative cooling boxes presented greater saturation efficiency at the same flow, namely 82.63%, as opposed to an average figure of 65% for the cellulose pads; and also had a lower specific consumption of water, at around 3.05 L·h−1·m−2·°C−1. Consequently, we conclude that evaporative cooling boxes are a good option for cooling non-hermetic greenhouses such as those most frequently used in the Mediterranean basin

Thermography and Sonic Anemometry to Analyze Air Heaters in Mediterranean Greenhouses

The present work has developed a methodology based on thermography and sonic anemometry for studying the microclimate in Mediterranean greenhouses equipped with air heaters and polyethylene distribution ducts to distribute the warm air. Sonic anemometry allows us to identify the airflow pattern generated by the heaters and to analyze the temperature distribution inside the greenhouse, while thermography provides accurate crop temperature data. Air distribution by means of perforated polyethylene ducts at ground level, widely used in Mediterranean-type greenhouses, can generate heterogeneous temperature distributions inside the greenhouse when the system is not correctly designed. The system analyzed in this work used a polyethylene duct with a row of hot air outlet holes (all of equal diameter) that expel warm air toward the ground to avoid plant damage. We have observed that this design (the most widely used in Almería’s greenhouses) produces stagnation of hot air in the highest part of the structure, reducing the heating of the crop zone. Using 88 kW heating power (146.7 W∙m−2) the temperature inside the greenhouse is maintained 7.2 to 11.2 °C above the outside temperature. The crop temperature (17.6 to 19.9 °C) was maintained above the minimum recommended value of 10 °C

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 GM1=√(∣∣G2T±G2w∣∣) , or Model 2, in which the flow is driven by the sum of two independent fluxes GM2=|GT±Gw| . 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)]

Dispositivo para medir el comportamiento de cimentaciones ante un esfuerzo de tracción o de comprensión

Número de publicación: ES2221783 A1 (01.01.2005) También publicado como: ES2221783 B1 (16.12.2006) Número de Solicitud: Consulta de Expedientes OEPM (C.E.O.)P200202403 (18.10.2002)Un dispositivo para medir el comportamiento de cimentaciones ante un esfuerzo de tracción o de compresión, que comprende: un bastidor (1, 2); un cilindro hidráulico (3) montado en el bastidor de modo que pueda pivotar alrededor de al menos un eje; medios de acoplamiento mecánico del cilindro hidráulico (3) a la cimentación; medios de medir el esfuerzo ejercido por el cilindro hidráulico sobre la cimentación; medios de medir el desplazamiento de la cimentación bajo el esfuerzo; y medios de alimentación hidráulica del cilindro hidráulico.Universidad de Almería. Universidad de Sevill

Assessment of response of greenhouse foundations to traction, and their simulation ussing finite elements

La causa de colapso de las estructuras de invernaderos son las succiones provocadas por el viento. Actualmente no se calculan las cimentaciones sometidas a esluerzos de tracción yes la experiencia de los técnicos de las empresas constructoras, o el deseo de los agricultores. lo que determina las dimensiones y distancia entre el/as. En este trabajo. se han ensayado prototipos a escala real de los distintos tipos de pilotes usados en la construcción de invernaderos. determinando laluerza máxima de tracción y el desplazamiento asociado a la misma que pueden soportar. En este artículo. se desarrollan modelos no lineales mediante el método de elementos finitos. que permiten el cálculo de este tipo de cimentaciones con mayor aproximación a los resultados reales que el obtenido mediante el uso delórmulas empíricas.rhe cause 01the col/apse 01the structures 01greenhouses is the suction induced by wind. Currently, the design olthe loundations is not based on calculations oltraction. rhe experience 01the construction company or 01thelarmer determine the dimensions and separation 01greenhouse loundations. In this work. we tested prototypes 01diflerent types olpileloundations. used in the construction 01 greenhouse, to determine the maximumlorce 01 traction and the associated displacement which they can support. In this article. non-linear models using finite elements. are developed that enable more accurate calculation olthe actual results than obtained with empiricallormulas

Software for the geometric characterisation of insect-proof screens

Novel software has been developed for the geometric characterisation of agrotextiles intended for installation in greenhouse vents as a means of crop protection. This characterisation of insect-proof screens is essential with a view to keeping insects out and also from an aerodynamic point of view. The method of analysis is based on digital images taken by microscope or scanner. The geometric procedure considers that each hole of the screen represents a quadrilateral, as it is defined by four threads of monofilament that cross over each other. The software developed using Visual Basic allows us to identify the coordinates of the vertices of the quadrilaterals and therefore to carry out a complete characterisation of the agrotextiles: number of threads per unit length, porosity of the sample, dimensions of the holes, thickness of the threads, area of the holes and the largest circle contained in the holes. The analysis of the data provided by the software allows us to study the uniformity of the material and also to detect flaws in its manufacture. The software includes a pattern for identifying the vertices with a high percentage of accuracy. For instance, it analysed over 40,000 vertices with only 1.14% error, mostly due to dirt on the screen. The software developed includes procedures to detect these errors, to alert the user to the type of error and to correct them. There is no other specific procedure to measure the characteristic dimensions of insect-proof screens and, therefore, it is no possible to contrast in this way the results that are obtained with the proposed method. Consequently, the measurement method has been verified using a set of screens of known dimensions manufactured for this very purpose. The results obtained are excellent, revealing that the differences between the expected values and the measured ones are well below the sensitivity of the device used to obtain the digital images

Scheduling vegetable sales to supermarkets in Europe: The tomato case

This article analyzes the temporal programming of sales for a horticultural marketing company, e.g. a cooperative. The empirical study references the European tomato market, where most of the production is sold through the retail channel dominated by large distribution chains. We study the marketing schedule for an individual company, or even a prominent farmer, using a modified Markowitz model, assuming that his decisions do not affect the balance of market prices. As a result, this model can manage risk and improve decision-making. The data also provide information on the risk borne by marketers depending on their sales calendar, which often depends on their geographic locatio

Determining the emissivity of the leaves of nine horticultural crops by means of infrared thermography

he present study was carried out with the aim of analysing the variability of the emissivity values of nine of the most characteristic horticultural crops of the greenhouse productive system in the Mediterranean region. A thermographic camera was used for both qualitative and quantitative emissivity measurement by evaluating radiation emission from the leaves. The real temperature of the leaves was also measured with a contact probe in order to calculate emissivity. The differences in emissivity between crops for the upper side of leaves are below standard deviation values, the average values are all close to 0.98. For upper side of leaves we obtained the following average values of emissivity: 0.980 ± 0.010 for Lycopersicum esculentum Mill., 0.978 ± 0.008 for Capsicum annuum L., 0.983 ± 0.008 for Cucumis sativus L., 0.985 ± 0.007 for Cucurbita pepo L., 0.973 ± 0.007 for Solanum melongena L., 0.978 ± 0.006 for Cucumis melo L., 0.981 ± 0.009 for Citrullus lanatus Thunb., 0.983 ± 0.006 for Phaseolus vulgaris L. and 0.983 ± 0.005 for Phaseolus coccineus L. Considerable differences have been observed between the emissivity values on the opposite sides of the leaves in some horticultural crops, such as green bean and particularly red bean, with a difference of 0.029 in the average emissivity value. Emissivity values of 0.98 are recommended as a reference for measuring the temperature of horticultural crops other than those studied here whenever there is no other possibility to determine the emissivity

Effects of surrounding buildings on air patterns and turbulence in two naturally ventilated mediterranean greenhouses using tri‐sonic anemometry

The aim of the present study is to increase the available information concerning the influence of surrounding buildings on air patterns and turbulence characteristics of the ventilation airflow in greenhouses. With a view to evaluating the possible effect of different obstacles close to greenhouse vents, sonic anemometry has been used. At the side opening, the airflow was mainly horizontal, while at the roof vent it was upward or downward. The vicinity of obstacles to the greenhouse side openings reduced the incoming mean flow up to 79% and increased turbulence. Larger ventilation rates were observed for the leeward roof vent, since the wind impacts directly with the windward side opening without obstacles, with a maximum of 31.6 air exchanges per hour. However, when the roof vent is on the windward side, the wind is partially blocked by another similar greenhouse located upwind, as the outside air enters through the roof vent and exits through the two side openings. In this situation, the maximum ventilation rate observed was 14.5 air exchanges per hour. Natural ventilation was more effective in eliminating heat from the part of the greenhouse with a crop when the air entered through the side openings and exited through the roof vent. In this case, the ventilation efficiency for temperature ( T) was greater than 1. The maximum turbulence levels were associated with low air speeds and were observed mainly at the points located close to the side openings influenced by surrounding buildings. The turbulent energy levels of the airflow were higher at the windward openings without obstacles