Response of an eggplant crop grown under Mediterranean summer conditions to greenhouse fog cooling N. Katsoulas a , D. Savvas b , I. Tsirogiannis c , O. Merkouris a , C. Kittas a, * a Department of Agriculture Crop Production and Rural Environment, School of Agricultural Sciences, University of Thessaly, N. Ionia-Volos, Magnesia, Greece b Department of Crop Science, Agricultural University of Athens, Athens, Greece c Department of Floriculture and Landscape Architecture, Faculty of Agricultural Technology, Technological Educational Institute of Epirus, Arta, Greece 1. Introduction Greenhouses in the Mediterranean region are generally rudimentarily equipped (Baille, 2001). Crops cultivated during summer in such greenhouses are negatively affected by stressful temperature and humidity conditions, which in turn influence yield and product quality. However, there is a continuous trend for structural and equipment improvements and adaptations so that skilful management of the greenhouse and crop systems can be obtained. A challenge for researchers, engineers and growers is to extend crop cultivation period with satisfactory levels of market- able quality produce, in order to obtain higher net income for greenhouse businesses. Extension of cultivation period during summer and optimal greenhouse climate conditions for plant growth could be obtained by proper greenhouse climate control, using various cooling methods. Natural ventilation is usually the simplest cooling method due to its low cost and simplicity, but is generally not sufficient for extracting the excess energy during sunny summer days. High ventilation rates are not a priori the best solution for reducing water stress in greenhouses under summer conditions since ventilation reduces greenhouse overheating, but increases the risk for water stress due to leaf stomatal conductance restriction (Kittas et al., 2001) or transpiration rate increase (Seginer, 1994). Furthermore, based on the greenhouse energy balance, ventilation alone cannot decrease greenhouse air temperature below the outside air temperature. Outside air temperature levels currently observed in Mediterranean countries during summer are very high (T > 35 8C). Evaporative cooling techniques have recently become more popular in areas like the Mediterranean basin (Montero, 2006). The recent interest in evaporative cooling is associated with the common use of insect proof screens, which strongly reduce air exchange rate and therefore, strongly increase greenhouse air temperature during summer. However, greenhouses equipped with fog cooling systems require less ventilation (Boulard and Baille, 1993) and, for that reason, incorporation of insects proof screens in fog-cooled greenhouses does not have negative effects on greenhouse cooling. Evaporative cooling systems do not only decrease air temperature but also increase absolute Scientia Horticulturae 123 (2009) 90–98 ARTICLE INFO Article history: Received 22 December 2008 Received in revised form 8 July 2009 Accepted 10 August 2009 Keywords: Fog system Water consumption Crop transpiration Fruit temperature ABSTRACT The effects of greenhouse cooling using a high-pressure fog system on greenhouse microclimate and on eggplant (Solanum melongena) crop response were studied at the coastal area of western Greece. Measurements were carried out in two distinct greenhouse compartments involving: (1) no air humidity control and (2) a fog system operating in order to obtain a greenhouse air relative humidity of 80%. Fog cooling reduced mean fruit temperature by about 3 8C and maintained greenhouse air temperature below 32 8C, while maximum temperature without cooling reached 40 8C. Furthermore, fogging reduced air vapor pressure deficit by about 55% and increased crop stomatal conductance by about 73%. These changes, in combination with alterations in crop aerodynamic conductance, resulted in around 31% decrease of crop transpiration rate. Fog system cooling efficiency was relatively low (46%) resulting in relatively high water consumption for fog cooling, reaching an equivalent to about 60% of crop water uptake. Nevertheless, since fog cooling decreased crop water needs, total greenhouse water consumption with fog cooling was only 19% higher than with no air humidity control. These results indicate the need to increase the cooling efficiency of fog systems in order to reduce greenhouse water consumption. Furthermore, the fog system enhanced mean fruit weight and marketable fruits, but appreciably reduced total fruit number per plant. Finally, fog cooling did not affect fruit quality characteristics such as fruit resistance to penetration, skin colour, fruit titratable acidity and total soluble solids. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +30 2421093012; fax: +30 2421093234. E-mail address: ckittas@uth.gr (C. Kittas). Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti 0304-4238/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2009.08.004