Suitable temperatures for open-field and tunnel-covered cultivation of head lettuce based on meteorological and crop statistical data in Japan

Lettuce (Lactuca sativa L.) is a major vegetable cultivated worldwide and an essential vegetable consumed throughout the year in Japan. However, the suitable temperatures for open-field and tunnel-covered cultivation have not been sufficiently clarified. The present study aimed to comprehensively and quantitively clarify the suitable temperatures for the cultivation of head lettuce in major production areas across Japan using 1-km resolution daily mean air temperature and statistical data on cropping type, production, and planted area, planting date, and harvesting date on the prefectural and municipal levels. The suitable temperature for open-field cultivation was found to be in the inter-quantile range (IQR) of 13.9-20.5°C. By contrast, the IQR in tunnel-covered cultivation, defined as the air temperature outside the tunnel, was estimated to be 4.3-9.8°C. Furthermore, the growing period tended to be longer at lower temperatures. These findings contribute to our understanding of the cultivability for head lettuce and may inform projections of the effects of climate change on lettuce cultivation.