Dynamic monitoring of nutrient species in hydroponic solutions for advanced life support

The next-generation of plant hydroponic systems for advanced life support will most likely require a dynamic monitoring capability for their nutrient species in solution for two reasons: (1) to be able to optimize nutrient use, which would help to reduce the mass and volume of stored inorganic chemicals; and (2) to be able to dynamically correlate the fluctuations in uptake of individual nutrient species with the plant's physiological state (e.g., stress) over time under microgravity conditions. The latter in turn will provide advanced physiological diagnoses for the crops and could help reduce the astronaut man-hours for crop maintenance. The results of this study suggested that a combination of inductively coupled plasma (ICP) spectroscopy and ion selective electrodes (ISEs) could be a competent strategy for designing a dynamic nutrient-monitoring capability for hydroponic systems. The ICP used had a dynamic range that adequately encompassed the varying concentrations of Ca, K, Mg, P, B, Cu, Fe, Mn, Mo and Zn in the sweetpotato hydroponic solution, with accuracy and reproducibility of the measurements at 1-4% ± 5%, respectively. Likewise, the ISE used had a dynamic range that adequately encompassed the varying concentrations of NO₃^- in the sweetpotato hydroponic solution, with accuracy and reproducibility of the measurements at 1-5% and ± 2%, respectively.