Development of an ion-selective electrode-based monitoring and dosing channel control system for closed-loop hydroponics

Abstract

Closed-loop hydroponic systems can reduce the use of water and fertilizer compared to open systems. However, conventional closed systems based on electrical conductivity (EC) control may cause ion imbalances in the nutrient solution over time. Supplying fertilizers individually based on current ion concentrations in the solution may allow to maintain balance in the nutrient solution. In this study, a venturi dosing channel control system and an ion monitoring system using ion-selective electrodes was developed for closed-loop hydroponics to adjust the amount of fertilizers variably. The system was designed to control each solenoid valve for the venturi dosing channel at different time intervals. Ion monitoring system was consisted of an array of NO3, K electrodes and buffering circuits. The system was validated at the Gyeonggi Agricultural Research & Extension. The root mean square error (RMSE) of injected ions mass ratio to the target ion mass ratio was 5.22%, and the minimum error was 0.02%. The RMSE of NO3, K measurements using ISEs were 26.60 and 19.20 mg L-1, respectively. The results proved that the developed systems could be applied to ion-specific variable fertigation for the closed-loop hydroponics. © 2025 International Society for Horticultural Science. All rights reserved.