Optimization of the Yield, Total Phenolic Content, and Antioxidant Capacity of Basil by Controlling the Electrical Conductivity of the Nutrient Solution

Hydroponic cultivation using nutrient solution (NS) is the main cultivation method employed by plant factories with artificial lighting (PFALs). The electrical conductivity (EC) of NSs influences the yield and quality of vegetables. The purpose of this study was to optimize the yield and antioxidant accumulation of basil in a PFAL by EC management. In experiment 1, basil plants were grown under four different ECs (0.5, 1.0, 3.0, and 5.0 dS m(-1)) after transplanting. At 18 days after treatment, the highest levels of shoot fresh and dry weights, leaf fresh and dry weights, and leaf area were observed at an EC of 3.0 dS m(-1). However, low-EC treatments (0.5 and 1.0 dS m(-1)) generated total phenolic content (TPC) and antioxidant capacities that were higher than those of other EC treatments (3.0 and 5.0 dS m(-1)). In experiment 2, basil plants were grown at an EC of 3.0 dS m(-1) for 13 or 15 days, then treated with water or NS with low ECs (0.5 and 1.0 dS m(-1)) for 5 or 3 days before harvest. The short-term low-EC treatments, especially, water for 3 days and 0.5 dS m(-1) for 5 days, significantly increased the TPC and antioxidant capacity of leaves without significantly decreasing the yields of basil, compared with the control. In conclusion, yield of basil was optimized with an EC of 3.0 dS m(-1); however, the TPC and antioxidant capacity of basil were significantly increased by low ECs of 0.5 and 1.0 dS m(-1). Short-term low-EC treatments (0.5 dS m(-1) for 5 days or water for 3 days) could be used to promote the TPC and antioxidant capacity in leaves without sacrificing yield of basil significantly.