Closed Hydroponic Nutrient Solution Management Using Multiple Water Sources

Purpose A properly ion-balanced nutrient solution is vital for plant growth. However, when reusing a nutrient solution, the nutrient balance is likely to fluctuate and become unsuitable for irrigation. Ionic imbalance problems that cause plant growth disorders in nutrient solutions can be minimized if the nutrient concentration of the various water sources can be determined and considered when making the nutrient solution. In this study, a closed hydroponic nutrient management algorithm for multiple water sources was developed. Methods The concentrations of NO 3 − , K + , and Ca 2+ ions in the nutrient solution and various water sources were measured in real time and calculated to automatically replenish insufficient ions. For this purpose, ion-selective electrodes (ISEs) were selected for the determination of NO 3 − , K + , and Ca 2+ ion concentrations and eight stock solutions for individual salt replenishment. Results Performance tests were conducted to verify the developed system’s ability to maintain NO 3 − , K + , and Ca 2+ ion concentrations at their target values. The nutrient solution dosing accuracy obtained in the stepwise management test was evaluated using root mean square error (RMSE). In addition, long-term performance evaluation of the developed algorithm was validated while growing lettuce using the closed nutrient film technique (NFT). The long-term accuracy of the developed system was RMSE 60.6, 21.0, and 9.86 mg/L for the NO 3 − , K + , and Ca 2+ ions, respectively. Conclusion The results of this study showed nutrient management using multiple water sources by applying three different ISE sensors, NO 3 − , K + , and Ca 2+ . With the further development of ISE technology, it would be possible to control all six macronutrients in the nutrient solution.