VOLUME 19 NUMBER 1 (January to June 2026)

Effects of different treatments of atmospheric pressure plasma on the germination and seedling development of soybean (Glycine max) seeds

Soybean (Glycine max) is a major source of vegetable protein and an important agricultural commodity in the Philippines; however, its thick seed coat limits germination efficiency. This study investigated the effects of argon–nitrogen atmospheric pressure plasma on soybean seed germination and seedling growth through direct, indirect, and combined treatments. In direct treatment, seeds were exposed to plasma for 3–7 s, while indirect treatment used plasma-activated water (PAW) generated for 5–15 min. The combined method applied both direct plasma (3–7 s) and PAW (5 min). Optical emission spectroscopy (OES) confirmed the presence of reactive and excited argon, nitrogen, and trace oxygen species in the plasma. Scanning electron microscopy (SEM) revealed surface microcracks and wax removal after plasma exposure, while contact angle analysis showed increased hydrophilicity and water uptake with longer treatment times. PAW displayed reduced pH and elevated nitrate levels compared to the control. The combined treatment demonstrated the most pronounced and consistent improvements in germination potential by 22%, shoot length by 54–66%, shoot fresh weight by 31–43%, and shoot air-dried weight by 44–77%. In contrast, direct plasma treatment consistently enhanced root-related early growth performance, with increases of 16–20% in germination rate, 22–29% in root length, 40–50% in root fresh weight, and 31–44% in root air-dried weight. These findings highlight plasma technology as a promising approach to improve soybean seed germination and early growth.