S06 - Session O2 - Light use efficiency of various greenhouse systems in an arid environment.

Authors: Ilias Tsafaras, Jouke Campen, Feije de Zwart, Wim Voogt, Hessel van der Heide, Abdulaziz Al Harbi *, Khalid Al Assaf, Muien Qaryouti, Mohamed Ewis Abdelaziz

Photosynthetically Active Radiation (PAR) is the driving force for photosynthesis and thus for the growth and production of plants. Therefore, the abundant solar radiation in semi-arid and arid regions provides great potential for growing crops, provided water is available. To make use of this potential, greenhouses ensure that other environmental factors (such as temperature and humidity) can be controlled and are favorable for plant growth and production. The efficiency of the greenhouse as production system can be evaluated based on its ability to convert the available light to marketable yield (Light Use Efficiency - LUE). A wide range of greenhouses ranging from simple plastic tunnels to glasshouses with artificial illumination, mechanical cooling and CO 2 enrichment were compared with respect to their LUE. A rich data set consisting of a wide variety of experiments collected from more than 50 trials conducted with 3 vegetable crops (tomato, cucumber, sweet pepper) grown in 9 different greenhouse types was used to calculate the LUE of each greenhouse type and crop. The aforementioned research trials were all conducted during the last 5 years at the National Research and Development Center for Sustainable Agriculture (Estidamah) in Riyadh (KSA). The collected data showed a clear positive correlation between the level of (climate control) technology installed to the greenhouse and the achieved LUE. The transmissivity of the greenhouse cover was found to be positively related with production even in a place where yearly radiation sum exceeds 7.6 GJ/m 2 . On the other hand, there was no difference observed in LUE between identical greenhouses with different types of glass cover, i.e. clear and diffuse. Artificial light was found to decrease the LUE of the system. Finally, CO 2 enrichment resulted in higher LUE.