Plasma activated water (PAW) is produced when plasma generated by high-voltage discharge is delivered to an atmospheric gas and interacts with water to create a new solution containing reactive species. The resulting water contains nitrate nitrogen (ca. 20-176 ppm N), small amounts of nitrite and ammonium, as well as reactive oxygen species. The benefits of PAW use for agricultural crops can include improved germination, increased seedling vigor and health, resistance to pests and disease, an alternative nitrogen source, and an overall improved plant health and yield. However, further research is needed to understand the characteristics of PAW, PAW shelf-life stability, crop specific PAW application and timing, and its overall effects in plant production. Our overall objective is to determine if PAW can enhance plant quality/yield in organic greenhouse tomato production. Studies were conducted to evaluate tomato germination and seedling growth in response to PAW application. A study was conducted to evaluate if germination of tomato seeds and subsequent growth in seedling trays with container media is affected when soaked prior to seeding with plasma water or tap water for three, six, or 12 hours. The study was replicated four times over time, with each replicate lasting for 15 days. Data was collected on daily germination, weekly heights and widths, and fresh mass, dry mass, and leaf area at harvest. Most seed treatments for 6 or 12 hours, regardless of water treatment, enhanced germination on day 5 and day 6 compared to control. However, by final harvest at day 15 there were no significant differences between treatments and control. Our second phase of research evaluated PAW application during organic tomato seedling production stage. Seedlings were treated with a drench of 4 mL per cell of different PAW sources generated for 5, 10, 30, or 60 minutes for a total of three applications every three days. On day 7, 30-minute PAW had significantly greater germination counts compared to the control. At final harvest on day 22 60-minute PAW had significantly greater fresh mass, dry mass, and leaf area compared to the control. In conclusion, a pre-seed soaking treatment for 12 hours is recommended for earlier germination and a drench application of PAW generated at a duration of 60 minutes is recommended for greater seedling growth. Further research includes PAW application timing and frequency and its carry-over effects in tomato crops grown to fruiting.
