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The aim of this research was to assess the effect of both the salinity level and the type of growing system on the vegetative health of a tomato crop (Solanum lycopersicum). The study was carried out in Almería (Spain) in a local typical greenhouse. Two different growing media were tested: (i) the artificial soil "enarenado" and (ii) a coconut fiber substrate. Each of these growing media was irrigated with water with three different saline concentrations: (i) T1 with an electrical conductivity of 0.6 dS/m, (ii) T2 with 1.5 dS/m, and (iii) T3 with 3.0 dS/m. Using the European and Mediterranean Plant Protection Organization (EPPO) regulations, two diseases were identified: (i) powdery mildew (Leveillula taurica) with a lower disease incidence in tomato plants grown in soil and in plants irrigated with decreasing salinity treatments and (ii) crown and root rot in tomato (Fusarium f. sp. radicis-lycopersici) with a lower incidence in tomato plants grown in soil and a higher incidence in tomato plants grown in coconut substrate. A higher yield was observed in tomato plants transplanted in enarenado than in coconut substrate, although a higher level of Brix degrees was observed in the crops with higher disease severity and salinity stress. [ABSTRACT FROM AUTHOR]

The purpose of this study was to analyse the effect of different evaporative cooling systems compared to natural ventilation on the microclimate, photosynthetic activity and yield of a tomato crop (Lycopersicum esculentum Mill.) in a spring-summer cycle. In this study, the expenditure of electricity and water caused by the different refrigeration systems and their economic cost was analysed. The study was carried out in three multi-span greenhouses: (i) a greenhouse with evaporative pads and fans and natural ventilation (PS + NV); (ii) a greenhouse with a fog system and natural ventilation (FS + NV); (iii) a greenhouse only with natural ventilation (NV). The photosynthetic activity was higher in the greenhouse with natural ventilation (14.7 µmol CO2 m−2 s−1) than in the greenhouse with the pad-fan system (14.6 µmol CO2 m−2 s−1; without a statistically significant difference) and in the greenhouse with fog system (13.4 µmol CO2 m−2 s−1; with a statistically significant difference). The production was higher in the greenhouse with the pad-fan system (5.0 kg m−2) than in the greenhouse with natural ventilation (4.8 kg m−2; without a statistically significant difference) and in the greenhouse with a fog system (4.5 kg m−2; with a statistically significant difference). In general, photosynthetic activity and crop production increased as the maximum temperature (and the number of hours of exposure to high temperatures) decreased. It has been observed that the improvement in temperature conditions inside the greenhouses in spring-summer cycles produces increases in the photosynthetic activity of the tomato crop and, consequently, growth in production. The energy and water consumption derived from the use of active-type cooling systems have not been offset by a representative improvement in photosynthetic activity or crop production. [ABSTRACT FROM AUTHOR]

The efficient use of light is one of the most important factors for the development of greenhouse crops. It is increasingly necessary to use film covers that enhance transmittance and the proportion of diffuse light to generate a more homogeneous light distribution. The objective of this study was to evaluate the effect that an experimental film cover with high transmittance and high light diffusivity produces on the microclimate and the growth and yield of tomato crops (Solanum lycopersicum L.), compared with a commercial thermal film cover. The trial was developed during a spring–summer growing cycle in a multispan greenhouse divided into two compartments (sectors) separated by a vertical polyethylene sheet. In the East sector, a commercial film was installed (transmittance of 85% and diffusivity of 60%) and in the West sector, an experimental film was used (transmittance of 90% and diffusivity of 55%). The results show an increase in the marketable yield of 0.25 kg·m−2 in the sector with the experimental film, which represents 3.2% growth with respect to the commercial film. The photosynthetic activity measured in tomato leaves was 21.5% higher in plants growing in the sector with the experimental film, with had the highest transmittance. The increase in radiation transmittance of 14% produced greater photosynthetic activity without generating a higher inside air temperature at the crop level (at the height of 2 m above the floor). However, the mean temperature of the soil surface was statistically higher on the side with the diffuse experimental cover film, as a logical consequence of the higher level of intercepted solar radiation. [ABSTRACT FROM AUTHOR]

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)]. [ABSTRACT FROM AUTHOR]