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The long-term hypothesis of this study is that the patterns in uptake of certain nutrient species in the hydroponic nutrient solution can serve as an early-warning stress detector for specific hydroponically grown crops. This is a two-part hypothesis: first, it posits that the time variation in the uptake of specific nutrient species under a given nutrient regime shows fairly reasonable regularity; and, second, it posits that deviations from such regularity actually correlate with the occurrence of certain plant stress. Addressing the first part of the hypothesis, the objective of the current study was to determine the temporal variations in the concentrations of nitrate, potassium, and manganese under the following four nutrient regimes used for sweetpotato hydroponics: standard or control, elevated nitrogen by ammonium, elevated nitrogen by nitrate, and elevated potassium conditions.

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.