Static Magnetic Field and 10 Hz Pulsed Electromagnetic Field Priming Improve Early Rice Seedling Establishment Under Salinity with Redox Remodeling and Improved Ion Balance

Salinity limits early rice establishment by imposing osmotic stress, ionic imbalance, and poor early seedling growth. Magnetic-field seed treatment has been explored mainly using static magnetic fields (SMFs), whereas low-intensity pulsed electromagnetic fields (PEMFs) remain less defined as physical seed-treatment inputs under salinity. Here, we directly compared SMF and 10 Hz PEMF under matched low-intensity conditions to determine whether PEMF can function as an effective physical seed treatment in rice. Seeds of Oryza sativa L. cv. Phitsanulok 2 were exposed to SMF (2.0 mT) or PEMF (10 Hz, approximately 2.0 mT peak) using three protocols—1 h before sowing, 10 min daily after sowing, or a combined schedule—followed by germination under 150 mM NaCl. Magnetic exposure had limited effect on final germination percentage, but a single 1 h pre-sowing treatment with either SMF or PEMF significantly increased the germination rate index under salinity. This protocol also improved root length, seedling dry weight, and seedling vigour, whereas repeated daily exposure produced less consistent benefits. Redox analysis showed that PEMF increased H2O2 at 48 h but reduced H2O2 at 96 and 120 h compared with the untreated saline control at the corresponding sampling time. PEMF also produced the clearest increase in extractable DPPH radical-scavenging activity at 120 h. Ion analysis showed that the 1 h pre-sowing treatment improved tissue ion balance, as reflected by lower Na+ accumulation, improved K+ status, and a reduced Na+/K+ concentration ratio, particularly in roots. Overall, this study identifies a timing-specific low-intensity magnetic-treatment window for improving early rice establishment under salinity and positions 10 Hz PEMF as a testable non-chemical physical treatment associated with redox remodeling and improved ion homeostasis.