THE EFFECT OF SECONDARY GLAZING AND FIXED SCREENS ON GREENHOUSE ENVIRONMENT AND CROP RESPONSE OF TOMATOES.

Two energy saving techniques were installed into 6.7m span houses to study the effects on environment and response of tomatoes, grown in NFT, from a sowing date of 14 October 1983. Double glazing consisted of glass plus 75μ Melinex 071 polyester, which was in place throughout the crop, was compared with fixed screens of 50μ anti-condensate polythene, in position for five weeks during January 1984. These treatments were compared with standard single glazed units.
Higher average day temperatures and day humidities were observed when the fixed screens were in place and in the double glazed houses, particularly before ventilation frequency increased from June onwards.
Despite attempts to decrease day humidity by applying minimum ventilation positions, during February and March, the vapour pressure deficits fell to low levels, particularly under the fixed screens in January and in the secondary glazed houses in March.
These high humidities resulted in shorter leaves and increased incidence of calcium deficiency in leaves compared to single glazing.
Early yields from February to April were similar, despite smaller fruit from the energy saving units.
Yields in May and June were significantly lower than from single glazing, but were similar from July to the end of crop.
It is thought that high day humidities decrease transpiration causing a reduction in fruit size on initial trusses and affects subsequent trusses, picked in May and June by reductions in potential leaf area during January to March.

Symposium Greenhouse Climate and its Control

N.G. Starkey

https://doi.org/10.17660/ActaHortic.1985.174.43