Abstract:

To explore the regulatory effect of LED far-red side light (730nm) supplementation (based on red and blue light) before harvest on the growth and quality of hydroponic lettuce, an experiment was conducted using Italian lettuce as the test material in a fully intelligent and environmentally controlled plant factory. In this experiment, the top lighting of the hydroponic tank on the growing rack was used as the main light source, and side LED supplementary lighting was added 6d before harvesting. The control treatment (CK) received red and blue light (4:1, light intensity 150.0μmol·m⁻²·s⁻¹, duration of 3h), while the experimental groups were supplemented with far-red light at 5 different intensities (12.5, 25.0, 50.0, 75.0 and 150.0μmol·m⁻²·s⁻¹) on the basis of CK treatment. By analyzing the effects of different light treatments on lettuce yield and quality, this study aimed to alleviate the problem of insufficient side light for lettuce on planting racks and provide a theoretical basis and technical parameters for improving the quality and efficiency of hydroponic lettuce in plant factory with artificial light. The results showed that compared with CK, supplementary far-red light significantly increased the shoot fresh weight, dry weight and leaf area of lettuce in the 1^st row (closest to the side lamps) and the 2^nd row. The magnitude of the increase rised as the intensity of the far-red light increases. At a far-red light intensity of 150.0μmol·m⁻²·s⁻¹, the shoot dry weight was 93% higher than that of CK. The complementary far-red side light also increased the ascorbic acid content in the 1^st to 3^rd leaf layers of lettuce in the 1^st and 2^nd rows. Specifically, at a far-red light intensity of 50.0μmol·m⁻²·s⁻¹, the ascorbic acid content in the 2^nd leaf layer of the 1^st row reached the highest level (213μg·g⁻¹). However, as far-red light intensity increased, the contents of photosynthetic pigments, soluble proteins, soluble sugars, total phenols and flavonoids in the 1^st to 3^rd leaf layers of lettuce in the 1^st and 2^nd rows gradually decreased, reaching the lowest values at 150.0μmol·m⁻²·s⁻¹. This trend was negatively correlated with the indicators such as the shoot fresh weight, shoot dry weight and leaf area of lettuce growth. Comprehensively considering lettuce yield, quality indicators and energy consumption for supplementary lighting, the far-red side light supplementation treatment at 50.0μmol·m⁻²·s⁻¹ achieved the best cultivation effect.

Key words: Side lighting, Far-red light, Growth, Quality, Plant factory with artificial light