Test of a greenhouse covered by polyethylene film that reflects near-infrared radiation
The aim of this work was to study the effects of a new polyethylene (PE) 'silver' film [with high reflection and absorption in the Near Infrared Radiation (NIR)] on greenhouse microclimate and on growth and production of a hydroponic tomato crop. The experiments were carried out from November 2004 to July of 2005 in two similar greenhouses covered by different PE films: one covered by a PE film with high reflection and absorption to NIR radiation (NIR-PE) and one by a common PE film (control greenhouse, C-PE). The spectral properties of the cover materials were measured by a portable spectroradiometer equipped with an integrating sphere. The greenhouse and the outside microclimate parameters were recorded. Furthermore, tomato crop growth and production and quality measurements were also carried out. The reflectance and absorbance of the films to radiation from 700 to 1100 nm were found to be 20 and 16% for the NIR-PE and 12 and 5% for the C-PE, respectively. The respective values of the transmittance to 400-700 nm were 62 and 79%, for the NIR-PE C-PE, respectively. However, the results of the microclimate measurements showed that the air temperature and vapour pressure deficit levels were similar in both greenhouses. The mean height of the tomato plants measured during winter was higher in the C-PE greenhouse while during summer was higher in the NIR-PE greenhouse. No differences were found in the number of nodes of plants. The leaf area index of the tomato crop was higher under the NIR-PE greenhouse during the summer period. The total crop production was similar between the two greenhouses for both winter and summer period. However, marketable tomato production was higher in the NIR-PE greenhouse. In conclusion, the lower solar radiation levels observed under the NIR-PE covered greenhouses did not affect the growth and production of tomato plants but increased slightly the marketable production of the crop. © ISHS 2012.