REAL-TIME CONTROL OF HYDROPONIC MACRONUTRIENTS FOR CLOSED GROWING SYSTEM

A recirculating hydroponic system based on EC-control is not efficient in managing the composition of individual ions in the solution, thereby resulting in a high increase in total concentration of the nutrients and an imbalance of the nutrient salts. This study reports on the development and evaluation of a computer-controlled system with an array of ion-selective electrodes (ISEs) and four diaphragm pumps for direct measurement and individual control of macronutrients in recirculating hydro¬ponic solutions. The ability of three PVC membrane-based ISEs for simultaneous determination of NO₃, K⁺, and Ca²⁺ ions in the closed soilless system was evaluated. A computer program was developed with NI LabVIEW, which could calculate the volumes of individual nutrient stock solutions to be supplied based on real-time measurements of NO₃-K-Ca ions, and vary the injection times of the metering pumps working at constant injection rates. A performance test of the developed sensing and control system was conducted by varying the concentrations of macronutrients in original lettuce solution contained in a hydroponic tank. The results showed that the NO₃-K-Ca ISEs exhibited satisfactory performance in measuring nutrient concentrations in hydroponic solution and the target concentrations were prepared as expected when using the automated nutrient management system, showing linear relationships with high determination coefficient of >0.9 between the ISE- dosing methods and standard analyzers.