The application of cold plasma technology in agriculture includes its use as a nitrate fertilizer, offering an alternative to traditional chemical fertilizers. This study investigated the effects of using plasma-activated water (PAW) as a nitrate source on the growth and flowering of Vanda orchids through two integrated experiments. Plants were treated with different nitrate concentrations (0, 100, 200, 300, and 400 mg/L) and fertilizing frequencies (weekly vs. biweekly), in combination with varying plant ages (1-, 2-, and 3-year-old plants). The analysis focused on several variables, including plant height, the number of leaves, fresh and dry biomass, and flowering traits, such as time to bloom, inflorescence length, floret number, floret diameter, and vase life. The leaf nitrate, total nitrogen, and gas exchange parameters were also recorded. The results demonstrate that the plants receiving 100 mg/L PAW-NO₃⁻ exhibited significantly greater plant height, fresh weight, and dry weight than the control (0 mg/L), with a trend toward a higher leaf number. Flowering occurred earlier in the 100 mg/L treatment group, with the first, second, and third inflorescences emerging at 208, 284, and 304 days after treatment, respectively. Additionally, this concentration produced the highest floret number per inflorescence and the longest vase life (12.63 days). Weekly fertilization resulted in more pronounced vegetative growth than biweekly application, particularly in 3-year-old plants—the only group to flower. Fertilizing frequency, however, had no effect on flower quality regarding the inflorescence length, floret number, or floret size. These findings suggest that 100 mg/L nitrate from plasma-activated water, applied weekly, optimally enhances growth and flowering performance in Vanda orchids.

Flower senescence during transport is a major concern for exporters, as physiological disorders reduce quality and price. Extending vase life is crucial, and while 1-MCP is widely used, it requires low temperatures and is less effective in disease control. Cold plasma generated by dielectric barrier discharge produces reactive oxygen and nitrogen species (RONS), offering an alternative method for preserving cut flowers. This study compared the effectiveness of cold plasma and 1-MCP treatments on the vase life of Vanda ‘Pachara Blue’ orchids. Flowers were treated with T1 (control at 25 °C), T2 (1-MCP), and T3 (cold plasma). Both 1-MCP and cold plasma significantly reduced ethylene production (26.15 and 25.20 µL C₂H₄/kg/hr, respectively) and respiration rate (63.92 and 57.44 mg CO₂/kg/hr, respectively) compared to the control (40.93 µL C₂H₄/kg/hr and 118.21 mg CO₂/kg/hr). Vase life was extended to 19.33 days in both treatments, an 87.12% increase over the control (10.33 days). Additionally, cold plasma slightly improved water uptake and reduced petal discoloration. These findings indicate that cold plasma is a promising alternative to 1-MCP, offering effective flower preservation without the need for low-temperature conditions and potential additional benefits in floral quality.

Nitrogen (N) form is a key factor influencing plant growth, N utilization efficiency (NUE), and sustainable crop production. Information on N-source effects on N uptake, allocation, and growth of ‘Daruma’ wasabi remains limited. This study evaluated the effects of nitrate (NO₃⁻), ammonium (NH₄⁺), and their combination on plant growth, N uptake and allocation, NUE, and selected free amino acid concentrations using a ¹⁵N tracer approach in a sterilized sand culture system. Five N treatments were applied: N-free solution; 2.5 mM ¹⁵NO₃⁻ + 2.5 mM NH₄⁺; 2.5 mM NO₃⁻ + 2.5 mM ¹⁵NH₄⁺; 5.0 mM ¹⁵NO₃⁻; and 5.0 mM ¹⁵NH₄⁺. Measurements were conducted at 90 and 180 days after treatment initiation. Plants supplied with NO₃⁻ alone or combined with NH₄⁺ showed greater growth and biomass than those under sole NH₄⁺ or N-free conditions. Total plant N increased with NO₃⁻ supply. Isotopic analysis showed preferential allocation of NO₃⁻-derived N to leaves and petioles, whereas NH₄⁺-derived N was largely retained in the rhizome. At 90 DAIT, sole NO₃⁻ supply showed the highest ¹⁵NUE, whereas at 180 DAIT, the NO₃⁻-labelled fractions under sole and mixed-N supply showed the highest ¹⁵NUE. NO₃⁻ supply was also associated with higher concentrations of selected free amino acids. The 50:50 NO₃⁻/NH₄⁺ supply may therefore support NUE and stable wasabi growth under the present conditions.