Impact of Using a Passive Electromagnetic Device on Lettuce Growth

Amidst escalating global food insecurity and climate volatility, non-chemical technologies are critical for boosting productivity in controlled-environment agriculture. This study evaluated the biostimulatory potential of low-intensity electromagnetic fields (EMF) at extremely low frequency (4.4 Hz ELF) and radio frequency (5.0 MHz), generated by resonant circuit rings, on two Lollo rosa lettuce cultivars (‘Carmesi’ and ‘Carmelian’) grown hydroponically in a Nutrient Film Technique (NFT) system under red-blue LED lighting (200 µmol m?² s?¹ PPFD, 16/8 h photoperiod). Seven-day-old seedlings were continuously exposed from the 3–4 true-leaf stage until harvest at 28 days post-transplantation, with unexposed plants as controls. Both EMF treatments significantly enhanced vegetative growth in a frequency- and genotype-dependent manner: the 5.0 MHz field markedly increased plant height (up to +33.7 % in ‘Carmesi’), stem diameter (up to +22.0 %), and leaf number (up to +35.9 % in ‘Carmesi’), while the 4.4 Hz ELF treatment preferentially boosted aboveground fresh biomass (15.9–23.3 % gains, outperforming 5 MHz in both cultivars), yielding overall shoot fresh mass increases of 14.8–23.3 %. Root responses were complex, with 5 MHz preserving or enhancing root volume (+20 % in ‘Carmelian’) but 4.4 Hz consistently suppressing root length (−8.6 to −44.9 %), indicating resource reallocation toward aerial development. Strong linear correlations (R² = 0.90–0.96) confirmed dose-response relationships, with ‘Carmesi’ showing greater responsiveness than ‘Carmelian’. These outcomes suggest that 5 MHz promotes structural elongation and meristematic activity via auxin redistribution and ion-channel modulation, whereas 4.4 Hz ELF optimizes photosynthetic efficiency and carbohydrate partitioning through mild ROS signaling. Low-intensity EMF thus emerges as a promising, zero-residue physical biostimulant capable of 10–36 % growth enhancement in hydroponic lettuce, offering a sustainable pathway to higher yields and resource-use efficiency in vertical farming systems.