Tomatoes are said to have originated in the Andes region of South America, but are now an important vegetable eaten all over the world, and in recent years, demand for tomatoes has been increasing in tropical and subtropical regions such as Southeast Asia. In 2018, tomato production in Southeast Asia and South Asia increased to 15 million tons and 26 million tons, respectively (FAOSTAT, 2018). In general, the optimal air temperature for growing tomatoes is 15-25°C. It is known that the yield and fruit quality will decrease if the tomatoes are grown in high air temperature environments such as tropical regions. Therefore, greenhouse cultivation is very important for stable tomato production by controlling a cultivation environment suited for tomato growth. Tomato cultivation under high air temperature environment is also becoming an important issue for Japan, where abnormal weather conditions such as heat wave are becoming more frequent.

As a countermeasure against high air temperature in greenhouse cultivation, various methods have been explored including ventilation, shading, cooling by heat pumps, and fog cooling using heat vaporization, etc. Recently, various kinds of covering materials have been investigated. According to a study conducted on Ishigaki island in Okinawa Prefecture, a subtropical region, a greenhouse covered by a heat insulation film reduces the wavelength range of light used by plants for photosynthesis (400-700 nm) by 22%; near-infrared rays (700-1050 nm) by 59%; and ultraviolet rays (250-400 nm) by 66% compared to a greenhouse covered with an agricultural polyolefin film (PO), a common greenhouse covering material. The maximum daily air temperature in the greenhouse with the heat insulation film was reduced by up to 3.6°C and the average daily air temperature by 0.4°C compared to the PO greenhouse. As a result, the yield of summer cultivation in greenhouse with the heat insulation film was higher than in the PO greenhouse, and fruit quality was also improved. This indicates that the use of the heat insulation film has the potential to improve the growing environment in Ishigaki island and tropical regions further south.

Reference
Nakayama M. et al., 2021. The effect of greenhouse cultivation under a heat insulation film covering on tomato growth, yield, and fruit quality in a subtropical area. Hort. J. https://doi.org/10.2503/hortj.UTD-249

Contributor: NAKAYAMA Masakazu (Tropical Agriculture Research Front)