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ISHS Acta Horticulturae 580: IV International ISHS Symposium on Artificial Lighting

PLANT RESPONSES UNDER AN EXPERIMENTAL NEAR INFRA-RED REFLECTING GREENHOUSE FILM

Authors:   E.S. Runkle, R.D. Heins, P. Jaster, C. Thill
Keywords:   far-red light, light quality, photoselective film, plant height, shade curtain, stem extension
DOI:   10.17660/ActaHortic.2002.580.16
Abstract:
When electromagnetic radiation levels are high, greenhouse air temperatures often become excessively warm and plants can experience heat stress. To reduce the temperature, many greenhouse growers use metalized shading fabrics. While the fabrics often reduce heat in the greenhouse, they also reduce photosynthetic active radiation (PAR, 400 to 700 nm), which can reduce crop quality and yield. Recently, a multilayered film was developed that reflects a significant portion of near infra-red radiation (NIR, 700 to 1100 nm) i.e., heat, with minimal PAR reduction. We performed an experiment to compare plant responses and environmental effects under two prototypes of the NIR film (as a solid screen and as a woven curtain) to a neutral density (N) metalized shading fabric in a commercial greenhouse located in a subtemperate climate. The solid NIR screen was constantly deployed, and the N and woven NIR curtains were installed into an automated retractable system. Depending on the angle of solar incidence, the maximum red (600 to 700 nm) to far-red (700 to 800 nm) ratio was 2.3 under the NIR film and 1.3 under the N curtain. Average daily air temperature under each treatment was within 0.6oC but PAR values were 30% to 100% greater under the NIR films. Ten bedding plant species were grown under each of the three filter environments. Compared to the N filter, internode length or plant height under the NIR screen was significantly shorter in impatiens, marigold, pansy, pepper, petunia, and salvia and was greater in tomato and vinca. Height under the NIR curtain was shorter in impatiens, pansy, petunia, and salvia but was taller in snapdragon. There were no consistent effects of curtain type on flowering percentage, node development, or flower number. This multilayered NIR film provides an alternative to metalized shading fabrics because it transmits more PAR per unit total radiant energy and simultaneously reduces internode elongation in sensitive species.
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