Effect of Plasma-Activated Water (PAW) Generated With Various N₂/O₂ Mixtures on Soybean Seed Germination and Seedling Growth

This work aimed to evaluate the physicochemical properties of plasma-activated water (PAW) treated with different gas compositions, as well as to investigate their effect on the early-stage growth of soybean sprouts. The carrier gas with different N-2/O-2 mixing ratios of 100/0, 80/20, 50/50, 20/80, and 0/100 was applied to generate PAW via the atmospheric-pressure plasma jet (APPJ) system. As controlling the N-2/O-2 ratio at 50/50, the nitrate concentration of PAW was successfully increased to 166.4 mg/L, relative to 0.2 mg/L in distilled water (DW) without plasma treatment. Moreover, as compared with seeds immersed in DW, nearly doubled plant lengths were achieved as treated in PAW with an N-2/O-2 ratio of 80/20 and 50/50, corresponding to better electrical conductivities and higher nitrate concentrations in PAW. This work demonstrated that the generation of reactive species under an appropriate proportion of N-2/O-2 altered the physicochemical properties of PAW, effectively promoting seedling growth.