Performance evaluation of commercial ion-selective electrodes for hydroponic cultivation system

The performance evaluation of commercial ion-selective electrodes (ISE) is important for real-time, ion-based nutrient management in hydroponic crop cultivation systems as the fabrication, ion-sensing membrane’s composition and contamination, storage duration, ion interference, use time, and solution types of ISE cause sensing errors.
In this research, the performance of K⁺, NO₃^–, and Ca²⁺ ion-selective electrodes were evaluated in regard to measurement error, potential drift, and calibration for building an effective nutrient management system.
A recycle-type aeroponic nutrient management test bench was designed and fabricated.
The K⁺, NO₃^–, and Ca²⁺ ISE were attached and tested in the ion-sensing chamber of that test bench.
A LabVIEW-coded program and NI-DAQ device were used for data collection.
The measurement error percentage was checked in five different levels of nutrient solution.
ISE sensors were immersed into a known nutrient level solution for 15 days to check the potential drift trends, and a two-point calibration technique was applied to minimize error effects.
A linear relationship was found while testing the measurement error of K⁺, NO₃^–, and Ca²⁺ ISE in five different levels of nutrient solution, where R² and RMSE were 0.98, 36.86 ppm; 0.99, 22.25 ppm, and 0.99, 12.94 ppm, respectively.
The ISE showed continuous upward (R²=0.94, RMSE=54.66 ppm), upward (R²=0.85, RMSE=1.24 ppm), and downward (R²=0.86, RMSE=4.53 ppm) potential drifts, respectively.
Two-point calibration to reduce errors showed R² values of 0.99, 0.99 and 0.99 for K⁺, NO₃^–, and Ca²⁺ ISE, respectively.
These results indicated that the performance of commercial ISE needs to be evaluated for improved real-time nutrient ion monitoring in hydroponic cultivation systems.

International Symposium on Advanced Technologies and Management for Innovative Greenhouses: GreenSys2019

M. Chowdhury, B.E. Jang, M.S.N. Kabir, D.H. Lee, H.T. Kim, T.S. Park, S.O. Chung

hydroponics, nutrient ions sensing, ion-selective electrodes, sensing errors

https://doi.org/10.17660/ActaHortic.2020.1296.105