Impact of Nutrient Solution Volume during Hydroponic Production on Growth, Nutrient Content and Postharvest Characteristics of Four Leafy Greens Species

Efficient nutrient management is critical for successful hydroponic crop production. However, limited research exists on optimizing nutrient solution (NS) volume for various leafy green vegetables in recirculating hydroponic cultivation. To address this gap, we evaluated partial nitrogen budgets, growth, tissue nutrient composition, and postharvest quality of four leafy greens species [butterhead lettuce ( Lactuca sativa ‘Salanova Red Butter’), arugula ( Eruca sativa ‘Standard’ ), kale (Brassica oleracea ‘Red Russian’), and the emerging crop Malabar spinach ( Basella alba ‘Rubra’)] using a nutrient film technique (NFT) hydroponic system under two NS volumes [moderate (2 L/plant) and high (4 L/plant)] in a greenhouse during both summer and fall seasons. Electrical conductivity (EC) of 1.8 mS . cm −1 and pH of 5.8 to 5.9 were maintained daily across treatments. Using a moderate NS volume resulted in higher nitrogen (N) uptake efficiency and lower N retained in the NFT system in both trials. NS volume had no impact on growth and yield parameters, but it influenced nutrient composition and quality attributes of leafy greens. Leaf N and potassium (K) increased with high NS volume in summer, whereas phosphorus (P) and K followed a similar trend in the fall. Moderate NS volume reduced nitrate levels in shoots of arugula, lettuce, and Malabar spinach during both trials, suggesting that reduced volume may help minimize excessive nitrate levels in plant tissues. In contrast, kale consistently exhibited nitrate concentrations above the reported classification range regardless of treatment. In addition, NS volume influenced leaf color, total phenolics, and antioxidant capacity. These findings highlight the importance of crop-specific NS management to optimize plant health, improve nutrient use efficiency, minimize nitrate accumulation and nutrient waste, and support sustainable hydroponic production.