Effects of diffused plastic cover materials on greenhouse microclimate, plant growth, fruit yield and quality, and energy use in greenhouse fruit vegetable production
Greenhouse cover materials affect not only the light quantity and quality entering the greenhouse but also heat loss to the outside, which thus have a large influence on greenhouse microclimate, plant growth, fruit yield and quality, and heating energy use. Diffused cover materials have the potential to improve the light distribution within crop canopy, and reduce high temperature stress and increase fruit yield and quality in the summer. Therefore, this study was initiated in 2013 with the aim to evaluate the performance of newly developed plastic cover materials by the industry on energy use, microclimate, plant growth, fruit yield and quality of greenhouse fruit vegetables. Two greenhouse trials were conducted using the 6 greenhouses covered with standard (STD) or newly developed diffused, double-layers and air-inflated polyethylene film (DPE), or twin-wall polycarbonate sheet (DPC), two greenhouses for each cover material. The STD, DPE and DPC all have the same calculated direct (perpendicular) light transmission (79%) while the proportion of diffused light is 50, 75 and 100%, respectively. It was found that the diffused cover materials (DPE and DPC) improved the vertical temperature and light distribution within crop canopy, increased light use efficiency, and improved fruit grades in the summer. The improvement in light use efficiency could only compensate for a small percentage of decrease in total light transmission. Therefore, DPE greenhouses had similar marketable fruit yield as STD even if its light transmission was a few percent lower than STD. DPE greenhouses also used similar amounts of energy as STD greenhouses. DPC greenhouses saved over 10% energy in comparison to STD and DPE greenhouses. However, its fruit yield was not as high as STD and DPE because of its much lower light transmission (11% less than STD), especially at lower solar angles during fall/winter production. Therefore, when plastic cover material manufacturers/developers try to increase the proportion of diffused light with their cover materials, the total light transmission should not be compromised.
Hao, X., Zheng, J.M., Zhang, Y., Little, C. and Khosla, S. (2017). Effects of diffused plastic cover materials on greenhouse microclimate, plant growth, fruit yield and quality, and energy use in greenhouse fruit vegetable production. Acta Hortic. 1182, 73-78
Cucumis sativus, Capsicum annuum, light transmission, vertical microclimate distribution