SHADING EFFECTS ON GREENHOUSE MICROCLIMATE AND CROP TRANSPIRATION IN A CUCUMBER CROP GROWN UNDER MEDITERRANEAN CONDITIONS

The aim of this study was to investigate the effects of greenhouse shading on greenhouse microclimate and energy balance, and on crop production. Experiments were carried out in the experimental farm of the University of Thessaly at Velestino, in three similar, plastic-covered greenhouses using hydroponically-grown cucumbers as a test crop. One of the greenhouses was used as a control (without shading); the other two were shaded using two different shade nets (shading intensity of approximately 35% and 50%, respectively). Climatic parameters were measured during two growing seasons from April to June and from September to November 2008 and seven selected days of the above periods are presented. The results showed that shading could not keep greenhouse air temperature and vapor pressure deficit below 30 degrees C and 1.5 kPa, respectively, values that are considered acceptable for cucumber crop growth (Growers Books, 1980; Bakker et al., 1987; Olympios and Hanan, 1992). From the crop production data it was found that shading intensity should not exceed 35%. The analysis of greenhouse microclimate and energy balance showed that shading is necessary from the middle of spring, while even shading of approximately 50% was not sufficient to cool the greenhouse during noon time of summer days in Central Greece and that an additional cooling system was required