Effect of Air Temperature on Tipburn Incidence of Butterhead and Leaf Lettuce in a Plant Factory

Abstract

In a plant factory with completely controlled environments, incidence of tipburn in the middle growth stage was observed only in butterhead lettuce at 30/25°C (day/night) when head development was in progress. At 20/15°C in later stage, tipburn was observed 100% in butterhead lettuce and 50% in leaf lettuce. Growth of both lettuces was affected by air temperature, which increased photosynthesis and ion leakage. Highest photosynthesis and growth were observed at 30/25°C until the middle stage. In later stage, on the other hand, photosynthesis was the highest at 20/15°C in both lettuces, while growth of leaf lettuce was the fastest at 30/25°C, and butterhead lettuce did not show any difference between 30/25°C and 20/15°C. Ion leakage in both lettuces was 2.2–2.6 times higher at 30/25°C than that at 10/7°C. Butterhead lettuce was more sensitive to tipburn compared to leaf lettuce. Mass production of quality lettuce in the plant factory can be achieved through optimal temperature management since growth rate is closely related to tipburn incidence. In this experiment, optimum day temperature for butterhead and leaf lettuces was 22 to 26°C in the initial and middle growth stages and 20 to 24°C in the later growth stage. Optimum night temperature was 15 to 20°C.