Effects of Nutrient Solution Electromagnetic Properties, Droplet Size, and Spray Control Methods on the Growth Characteristics of Aeroponic Lettuce

This study investigated the effects of nutrient solution magnetization, droplet size, and spray control strategy on the growth characteristics of aeroponically grown lettuce. Two experimental groups were established. Group A employed a two-factor design under timer control to evaluate the effects of magnetic field intensity and droplet size, whereas Group B adopted an incomplete block design to examine the combined effects of magnetic field intensity, droplet size, and spray control mode, including timer control and temperature–humidity-based intelligent control. The interaction between magnetic field intensity and droplet size significantly affected root length, shoot growth traits, and the root-to-shoot ratio. Magnetic field intensity significantly influenced root length, shoot length, canopy area, biomass, and the root-to-shoot ratio, while droplet size primarily affected canopy area and biomass. Spray control strategy had a highly significant effect on the root-to-shoot ratio, and intelligent control improved biomass allocation compared with timer control. The results from Group B generally confirmed the trends observed in Group A, indicating that moderate magnetic field intensity and an appropriate droplet size were more favorable for lettuce growth than excessively high magnetic field intensity or unsuitable droplet size. Multi-objective optimization indicated that a moderate magnetic field intensity of approximately 260 mT, a droplet size of approximately 57.55 μm, and temperature–humidity-based intelligent control provided the most favorable balance between shoot growth and root-to-shoot allocation. These findings provide a preliminary reference for parameter selection in aeroponic system design and protected vegetable production under controlled conditions. However, the optimized parameters should be further validated across different lettuce cultivars, growth stages, and larger-scale production systems.