The overall goal of this research was to modify and apply the
ISE-based macronutrient sensing system of Kim et al. (2007) for
real-time and direct measurement of macronutrients in recirculating
hydroponic solutions based on automatic sampling and electrode
rinsing. Specific objectives were to (1) identify ion-selective
membranes suitable for measuring typical ranges of macronutrient
concentrations in hydroponic solutions with respect to their sensitivity,
lower detection limits, and selectivity against interferences
of other ions, and (2) evaluate the ability of a sensor array consisting
of the selected ion-selective membranes, in combination with a
laboratory-made automated test stand, to directly estimate NO3–N,
K, and Ca concentrations in hydroponic nutrient solutions.