Effects of using LED supplementary lighting to improve photosynthesis on growth and yield of strawberry forcing culture
Most strawberry fruits in Japan are produced under forced-production culture, using June-bearing cultivars. Strawberry plants are transplanted in a heated greenhouse in autumn and the normal harvest period is from late November to June. Insufficient solar radiation for fruit loading during the winter sometimes causes a decline in growth and yield. Therefore, we investigated the effects of supplementing natural light with artificial lights using light-emitting diodes (LEDs). The experiment was conducted in a greenhouse (2400 m2 in area) located in Yamamoto town, Miyagi prefecture, Japan (37.961°N, 140.877°E). Strawberry plants were transplanted in an elevated bed. We ran two experiments: experiment 1 was on light quality [photosynthetic photon flux density (PPFD) ratio of red light to blue light], while experiment 2 examined various lamp positions relative to the plants. In experiment 1, strawberry plants were exposed to three different qualities of light (red-to-blue ratios of 2:1, 3:1, and 4:1) with LED lamps (peak blue wavelength 450 nm, peak red wavelength 660 nm, SFL 120 BR-ERx). In experiment 2, LED lamps of two light qualities (red-to-blue ratios of 3:1 and 4:1) were installed in three different positions (above, in the middle, and at the bottom of treatment containers). Yields increased in almost all supplementary-light treatments relative to controls in both experiments. In experiment 1, the yield was higher when the PPFD ratio was 3:1 or 4:1 than when it was when 2:1. In experiment 2, strawberry yield increased by about 10% relative to the control, but no significant difference was observed among light positions or light quality. In addition, no increase in total dry weight was observed as a result of supplemental lighting, but the fruit distribution ratio (fruit dry matter/total dry matter) increased. It is possible that morphological changes caused by supplemental LED lighting led to the increase in fruit yield.
Goto, N., Honma, Y., Yusa, M., Sugeno, W., Iwasaki, Y., Suzuki, H., Yoneda, T., Hikosaka, S., Isigami, Y. and Goto, E. (2018). Effects of using LED supplementary lighting to improve photosynthesis on growth and yield of strawberry forcing culture. Acta Hortic. 1227, 563-570
fruit load, dry matter, fruit distribution, solar radiation, PPFD ratio of red and blue