Effects of Plasma-Activated Water from a Flow-Through Arc Discharge System on the Growth and Fruit Quality of Melon under Controlled Soilless Cultivation

Abstract

     Plasma-activated water has attracted attention as an alternative nitrogen source for modern agriculture. This study developed and evaluated a flow-through arc-discharge plasma-activated water production system for melon (Cucumis melo L.) cultivation, comparing it with calcium nitrate and AB-mix fertilizer under both root-feeding and foliar-spray applications. Spectroscopic diagnostics confirmed the formation of reactive oxygen and nitrogen species in the gas phase and their transfer into the liquid, resulting in increased concentrations of nitrate, nitrite, and hydrogen peroxide, increased electrical conductivity, and a reduction in pH. These changes reflect nitrogen oxidation processes and water dissociation. Seed screening was conducted to reduce seedling variability at the early stage. X-ray imaging was used to non-destructively assess embryo integrity and internal structure, resulting in more uniform germination rates. After transplanting, irrigation was applied every two days, and mist spraying was performed twice a week, in accordance with the specified conditions. Morphological and physiological growth data were collected for 6 weeks, and yield was monitored for an additional 8 weeks. The experimental results showed that combining calcium nitrate and AB-mix fertilizer with foliar spraying of plasma-activated water produced the best performance. However, even though plasma-activated water contained five times less nitrate than chemical fertilizer, it still moderately promoted growth and yield. Foliar application enhanced plant growth and yield across all treatments. These findings indicate that plasma-activated water cannot yet replace primary nutrient sources, but it plays a role in improving macronutrient efficiency when used as a foliar spray in combination with chemical fertilizers.