This study investigated the influence of different electrical conductivity (EC) levels on cucumber growth and yield in pot soil under controlled conditions. Four EC treatments were tested: control, T1 (0.5 dS·m^-¹), T2 (1.5 dS·m^-¹), and T3 (2.5 dS·m^-¹), over a 53-day period. Irrigation and drainage dynamics were monitored alongside plant growth, fruit production, and leaf gas exchange. Plants in T2 and T3 required higher irrigation volumes but showed lower drainage rates (16.4%-17.2%), whereas the control and T1 required less irrigation but had higher drainage (24.8%-29.0%). Nutrient leaching was most pronounced in T3 at 51 days after treatment (DAT). Growth and yield parameters were significantly influenced by EC treatments: the highest plant height, leaf area, and fruit fresh weight were observed in T2 and T3 at 53 DAT, while T3 reduced fruit number and quality. Photosynthetic rate peaked in T3 (12.7 µmol m^-² s^-¹) but was associated with lower drainage pH and higher electrolyte leakage. In contrast, T2 improved overall growth and yield performance. Water use efficiency (WUE) was highest in T2 (2.82 g L^-¹) and lowest in T1 (2.22 g L^-¹). The highest Fertilizer use efficiency (FUE) was observed in T1 and the lowest in T3. Principal component analysis revealed that traits such as fruit fresh weight, fruit dry weight, leaf length, leaf width, leaf fresh weight, and leaf dry weight were strongly associated with T2. These findings demonstrate that a moderate EC level of 1.5 dS·m^-¹ optimizes cucumber productivity in controlled pot soil cultivation.

Closed hydroponic systems for strawberries (Fragaria × ananassa Duch.) are infrequently used because the crop is highly sensitive to salt accumulation and prone to root diseases, resulting in yield reduction. This study investigated semi-closed hydroponic systems using various drainage recycling ratios (30%, 50%, and 70% of drainage EC) to determine their impact on yield, fruit quality, and antioxidant properties. Recycling at moderate levels (30–50%) effectively maintained ionic balance, particularly with respect to K/N and K/Ca ratios, which enabled stable yields and increased fruit weight similar to the control (open hydroponic system) group. Conversely, a high recycling ratio (70%) led to ionic imbalances—characterized by increased K/N ratios and higher concentrations of Na⁺, Cl⁻, and SO₄²⁻—that were associated with decreased fruit size. Measures of antioxidant capacity, such as total phenol and flavonoid content, ferric reducing antioxidant power, and DPPH activity, were not significantly influenced by the recycling ratio alone. Nevertheless, the relatively elevated antioxidant activity observed at the 70% recycling level indicates a mild ionic and osmotic stress response likely caused by increased salt concentration. Changes related to the cropping system season, rather than ion variations from recycling, exerted a stronger influence on antioxidant accumulation. In summary, moderate drainage recycling facilitates optimal fruit production without negatively affecting quality, while excessive recycling may increase antioxidant activity but leads to reduced yields. The results provide practical recommendations for optimizing nutrient reuse in semi-closed strawberry hydroponic systems.

Drainage recycling management in recycling hydroponic systems affects root-zone conditions and fruit metabolism. However, its interaction with fruit developmental stages on strawberry biochemical quality and mineral content is unclear. Therefore, this study investigated how developmental stages and drainage recycling ratio influence antioxidant properties, pigment contents, carbohydrate accumulation, and mineral composition in hydroponically grown 'Seolhyang' strawberry. The experiment was conducted from 20 September 2024 to 31 March 2025 in a smart greenhouse. Plants were grown in coconut coir in a closed hydroponic system with 30%, 50%, 70% and 100% (open-system) drainage recycling ratios. Fruits were harvested at green, white, turning, and red stages on March 11, 2025. Fruit developmental stages primarily determined biochemical composition, while drainage recycling ratio modified traits in a stages-dependent way. Antioxidant properties including total phenolic content (TPC), total flavonoid content (TFC), ferric reducing antioxidant power (FRAP), and 2,2-diphenyl-1-picrylhydrazy (DPPH) radical-scavenging activity were highest in green fruit, especially under 30% drainage, reaching 45.8 mg GAE g⁻¹ FW for TPC and 5.5 mg QE g⁻¹ FW for TFC. Conversely, anthocyanin and soluble sugar accumulation increased during ripening, with 50% drainage recycling yielding the highest concentrations in red fruit (30.0 and 17.8 mg g⁻¹ DW, respectively) and lower starch accumulation. Chlorophyll a, chlorophyll b, and total chlorophyll were also highest in green fruit and enhanced by 30% drainage. Mineral responses were less pronounced and primarily driven by developmental stages. Correlation analysis showed associations among phenolic compounds, antioxidant capacity, pigments, Ca, and Mg, while soluble sugars were negatively associated with early-development traits. Partial least squares analysis identified DPPH, TPC, TFC, FRAP, and anthocyanins as key variables distinguishing developmental stages and drainage recycling treatments. Drainage recycling management does not have a single optimum for strawberry fruit quality; its effects depend on the developmental target. A 30% drainage recycling regime favored phenolic-antioxidant characteristics in early-stages fruit, while 50% drainage recycling enhanced sugar accumulation and pigmentation at full ripeness. In contrast, a 70% drainage recycling ratio promotes the accumulation of Na⁺, Cl⁻, and SO₄²⁻, disrupts nutrient balance, whereas an open system showed lower phytochemical accumulation. This stages-specific response helps guide drainage recycling management based on the harvest goals and shows that immature strawberries may be a useful source of phytochemicals.