The greenhouse cover has previously been shown to have large effects upon the greenhouse environment, crop productivity and energy use. However, in most cases, because of inadequate treatment replication, the extent of these effects has been impossible to quantify with confidence. In the fall of 1987, a new greenhouse complex of 9 mini greenhouses (6.4m × 7.2m, each) was constructed at the Harrow Research Station on the principles of the 3×3 Latin Square experimental design and with glass, double polyethylene film and double acrylic panel greenhouse covers as the three levels of treatment in the Latin Square. During the spring seasons of 1988 and 1990 the greenhouse cucumber cultivar Corona was cropped in rockwool in all 9 mini greenhouses, under 3 day air (DAT: 18°C, 21 °C and 24°C) and 3 night air temperatures (NAT: 16°C, 18°C and 20°C), superimposed across the rows and columns of greenhouses, respectively, to estimate yield and energy use response to DAT, NAT and greenhouse cover variation. Early marketable yield was highest at the 18/18 and 18/20°C DAT/NAT combinations and final marketable yield was highest at 18°C DAT regardless of NAT. Yield differences due to the greenhouse cover were insignificant. However, there were consistent differences in greenhouse air RH due to greenhouse cover (60%, 70% and 75% daily averages for glass, double polyethylene and double acrylic, respectively). Also, there were significant energy savings with the use of double polyethylene or double acrylic, as compared to glass greenhouse cover, and with low DAT and NAT (28%, 15% and 12% energy use reduction, respectively).
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