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Jung D.H.,Seoul National University | Kim H.-J.,Seoul National University | Kim W.K.,Seoul National University | Kang C.I.,Science Laboratory Center Co. | Choi G.L.,South Korean National Institute of Animal Science
American Society of Agricultural and Biological Engineers Annual International Meeting 2013, ASABE 2013 | Year: 2013

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 hydroponic 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.


Jung D.H.,Seoul National University | Kim H.-J.,Seoul National University | Kim W.K.,Seoul National University | Choi G.L.,South Korean National Institute of Animal Science | Kang C.I.,Science Laboratory Center Co.
Acta Horticulturae | Year: 2014

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 hydroponic 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.


Jung D.H.,Seoul National University | Kim H.-J.,Seoul National University | Choi G.L.,South Korean National Institute of Animal Science | Kang C.I.,Science Laboratory Center Co.
American Society of Agricultural and Biological Engineers Annual International Meeting 2014, ASABE 2014 | Year: 2014

A recirculating hydroponic system based on EC-control has limited the ability to manage the composition of individual ions in the solution. This study reports on the automated management of hydroponic nutrients using an array of ion-selective electrodes (ISEs) and a nutrient dosing algorithm used in a closed lettuce growing system. 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 the LabVIEW program, 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. Changes in nutrient concentrations and water uptake were continuously monitored and their amounts were variably controlled when needed. The results showed that the NO3-K-Ca ISEs exhibited acceptable measurement performance, indicating that the ISEs provided concentrations within 12% of those forthe standard analyzers, i.e., 90.6 ±7.1%, 88.8 ±8.4%, and 89.6 ±4.0% for NO3, K and Ca ions, respectively. Using the automated management system, concentrations of the three ions were effectively maintained with a balanced concentration ratio of the three ions for two weeks. However, an improvement in the nutrient dosing algorithm and the identification of more nutrient salts were needed for better independent management of the three ions.


Kim H.-J.,Seoul National University | Kim W.-K.,Seoul National University | Roh M.-Y.,South Korean National Institute of Animal Science | Kang C.-I.,Science Laboratory Center Co. | And 2 more authors.
Computers and Electronics in Agriculture | Year: 2013

Automated sensing of macronutrients in hydroponic solutions would allow more efficient management of nutrients for crop growth in closed hydroponic systems. Ion-selective electrodes (ISEs) are a promising approach because they can directly measure the analyte with a wide range of sensitivity and are small and portable. However, signal drift and reduced accuracy over time are major concerns with an in-line management system based on continuous immersion of ISEs in a solution. An ISE-based, computer-controlled measurement system for automatic sampling, calibration, and electrode rinsing is a viable technique to improve accuracy and precision in the determination of nutrient concentration. This study reports on development and evaluation of such a system for direct measurement of macronutrients in recirculating hydroponic solutions. The sensitivity and selectivity of PVC membrane-based ISEs fabricated with TDDA-NPOE, valinomycin, and calcium ionophore II were satisfactory for measuring NO3-N, K, and Ca concentrations in single-ion solutions over ranges typical of hydroponic solutions. However, an acceptable Mg membrane was not identified. An ISE array incorporating the selected membranes, in combination with a computer-controlled measurement system, was evaluated for the direct measurement of NO3-N, K, and Ca concentration in paprika hydroponic nutrient solutions. Using previously developed baseline correction and two-point normalization methods, ISE-measured NO3-N and K concentrations in spiked or diluted hydroponic nutrient samples were strongly related to those determined using standard laboratory instruments (R2=0.85). However, the tested Ca electrode did not provide satisfactory results due to reduced sensitivity and poor selectivity in the hydroponic solution. The approach used in this research, where a base solution is used for both referencing the baseline and rinsing electrodes and two calibration solutions are injected to implement the two-point normalization method, could be used in an automated sensing system for hydroponic nutrients in greenhouses. Additional research is required to identify ion-selective membranes for Ca and Mg ions in hydroponic solutions. © 2013 Elsevier B.V.

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