Closed hydroponics (recirculating) is increasingly recognized as a sustainable approach for conserving water and fertilizer resources. However, concerns remain among growers regarding ionic imbalances and yield instability during nutrient–solution recirculation. This study aimed to clarify these issues through continuous ionic monitoring of drainage water and optimization of nutrient compensation intervals in commercial tomato (Solanum lycopersicum L.) cultivation. Two greenhouse systems, an open (non-recirculating) and a closed (recirculating) system, were compared. Electrical conductivity (EC), pH, and major ions (NO₃⁻, K⁺, Ca²⁺, Mg²⁺, SO₄²⁻, PO₄³⁻, and Na⁺) were analyzed using ion chromatography. Based on ionic fluctuation trends, compensation intervals of 0, 2, and 4 weeks were evaluated in the closed system. Contrary to expectations of growers, open hydroponics exhibited greater ionic imbalance due to uncontrolled leaching. Periodic compensation (every 4 weeks) stabilized ionic ratios, reduced fertilizer input by 67–69%, and decreased water use by 33–36% compared with the open system. These findings demonstrate that drainage-based ionic monitoring and interval-based compensation can improve the environmental and economic performance of closed hydroponics.

Platycodon grandiflorum is a medicinal plant primarily cultivated in Korea, China, and Japan. The roots of Platycodon grandiflorum are high in saponins. This making them effective for protecting the respiratory system, which is why they are extensively used as medicinal materials, as well as in processed food and cosmetics. However, a proper lighting environment for the large-scale production of Platycodon grandiflorum in a closed-type plant production system (CPPS) has not been established. Therefore, this study was conducted to elucidate the optimal light intensity and photoperiod for Platycodon grandiflorum. The seedlings were cultivated in a walk-in chamber at 24.9 ± 0.9°C temperature and 53.7 ± 10.9% relative humidity for 48 days. Light intensities of 100, 150, and 200 ± 10 µmol•m-2 •s-1 were used, along with photoperiods of 10/14, 12/12, and 14/10 h (light/dark). The highest growth of the shoot was observed at the highest light intensity of 200 µmol•m-2 •s-1 , showing no significant differences between the photoperiods of 12/12 and 14/10 h. In 200 µmol•m-2 •s-1 , the internode length at photoperiod of 12/12 h was significantly shorter compared to the photoperiod of 14/10 h. In 200 μmol•m-2 •s-1 , the root characteristics showed enhanced growth at photoperiod of 14/10 h compared to photoperiod of 12/12 h. In conclusion, a light environment of 200 µmol•m-2 •s-1 with a photoperiod of 12/12 h is deemed suitable for the plug seedling production for seedling of Platycodon grandiflorum.

This study aimed to evaluate the shoot and root growth, changes in photosynthetic pigments, and nursery period of Korean angelica plug seedlings under different CO 2 concentrations in plant factories with artificial lighting systems (PFALs). Korean angelica seeds were sown in 72-cell plug trays, and the seedlings were grown for 40, 50, and 60 days to evaluate their morphological characteristics and chlorophyll contents. The internal CO 2 concentrations in PFALs were set at three levels: ambient (475 ± 40 µmol•mol-1), 'high concentration' ('HC', 758 ± 29 µmol•mol-1), and 'very high concentration' ('VHC', 1,197 ± 37 µmol•mol-1). CO 2 supply started 20 days after sowing when cotyledons were fully extended, and the first true leaf was observed. As a result, from 50 days after sowing, the crown diameter, leaf area, root development, and dry weight were higher in HC and VHC than in ambient, indicating a faster growth speed. However, there was statistically no significant difference in the dry matter accumulation between HC and VHC. From a morphological point, VHC had the longest petioles and the widest leaf area at 60 days after sowing, and the canopy expanded horizontally. The chlorophyll a, b, and total chlorophyll content were also the lowest. Additionally, the leaf area index was higher compared to the ambient, and the specific leaf weight, which indicates leaf thickness, was reduced. This is thought to be because the growth speed is fast, resulting in competition between individuals within the narrow plug tray environment. Therefore, the appropriate CO 2 concentration for shortening the nursery period of Korean angelica is considered to be approximately 800 µmol•mol-1 and the appropriate nursery period in 800 µmol•mol-1 condition is 50 days.