EFFECT OF EXTERNALLY MOUNTED SHADING SCREEN ON MICROCLIMATIC CONDITIONS OF GREENHOUSE CANTALOUPE CROP EQUIPPED WITH EVAPORATIVE COOLING SYSTEM

The aim of this experimental work was to investigate the effect of two different types of cooling pads with and without externally mounted shading screen on growth, development, productivity, and fruit quality of cantaloupe crop. Two similar gable-even-span greenhouses were utilized at EL-Sabahia Horticultural Research Station (latitude and longitude angles, respectively, are 31.22ºN and 30.50°E, and 3.00 m mean altitude underneath the sea level), Alexandria, to grow and produce cantaloupe crop during summer of two successive growing seasons (2009 and 2010). Each greenhouse was equipped with complete evaporative cooling system based on cooling pads and extracting fans and shaded using shading screens mounted externally to reduce solar radiation inside the greenhouse and consequently increase the effectiveness of evaporative cooling systems. Two different cooling pads (one of locally available materials (LPM), and the other of cross-fluted cellulose pads (CCP) were functioned with shading to cool the two greenhouses. The obtained data revealed that, the indoor air temperatures of the shaded greenhouse were lower than the greenhouse without shading. The maximum indoor air temperatures without operating the evaporative cooling system reached to 37.8 and 41.9^oC for the shaded and not-shaded greenhouses, respectively. The hourly average indoor air temperatures when operating the two evaporative cooling systems with two different cooling pads (LPM and CCP), respectively, were 28.4 and 27.3 ^oC. The maximum indoor air temperatures for the two greenhouses when operating the evaporative cooling systems with and without shading screen were 28.5 and 31.4ºC, respectively. The maximum indoor temperatures were 29.75 and 28.85 ^oC, while, the hourly average indoor air temperatures were 27.50 and 26.37 ^oC for the two greenhouses with operating evaporative cooling system and shading screens, respectively. The obtained results also showed that, the hourly average vapour pressure deficit (VPD) of the indoor air during daylight times for the two greenhouses with shading screen was 1.458 and 1.480 kPa, consequently the cantaloupe plants were not heat stressed under these levels of VPD (danger level > 2.0 kPa). Utilizing the evaporative cooling systems for the two greenhouses with shading screens have had the same effect on the growth, development, productivity of fresh yield, and quality of fruit characteristics.