Temperature

Temperature is one of the most influencing factors on the growth and development of plants besides light, CO2_2, humidity, and nutrient. The optimal temperature varies depending on plant species and the stages of growth and development. In the vegetative stage, when the plant is young, temperature plays an important role in building biomass. It was shown in the study of Heuvelink that the young tomato at 24°C has significantly higher biomass compared to 18°C. The reason is that at a higher temperature, plants develop more leaves and hence gain more light interception and grow faster. In the generative stage, the photosynthesis process is not so sensitive the day/night temperature regime. However, the fruit set is more vulnerable and show a remarkable reduction in the number of fruit at a high temperature stress (Suguru Sato et al.). On the other hand, too low temperature can have unwanted effects such as smaller fruit, mis-shapen fruits (A. Tiwari et al.) Besides the average temperature, the difference in temperature between day and night (DIF) is also important. Usually temperature is higher during daytime, if temperature is higher during nighttime we have an inversed DIF. An inversed DIF results in a reduction of both plant growth and development but the reduction of plant growth due to inversed DIF is more obvious. To control temperature in a greenhouse, we use greenhouse facilities such as ventilation, fogging system, thermal screen, and heating system. When it is too warm inside greenhouse, ventialtion is the most effective and cheapest way to discharge energy by exchanging hot air inside greenhouse with cooler air outside. Fogging system should be used just in case the greenhouse air is dryer than expected. When it is too cold inside greenhouse, we can deploy energy screen and/or turn on heating system. During nighttime, it is suggested to close energy screen and turn on heating at the same time for energy saving. However, during daytime when the amount of PAR enters greenhouse matter we need to be more thoughfull about wheter close energy screen or not. Usually it is suggested to close energy screen during daytime on cloudy and cold days.