Response of an eggplant crop grown under Mediterranean summer conditions to greenhouse fog cooling

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 °C and maintained greenhouse air temperature below 32 °C, while maximum temperature without cooling reached 40 °C. 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.