Monitoring the temporal variations of nitrate, potassium and manganese in sweetpotato hydroponic solutions for space life support application

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 results showed that the variations in nitrate concentrations over time resulted in fairly reasonable r-squares, and thus fairly reasonable regularity, both for the standard solution and the doubled-N by nitrate treatment. The regularity of the variations over time is important since significant deviation from the regular pattern could suggest a condition of stress for the plant. The results also showed that for a given nutrient regime, one nutrient species might exhibit regularity of time variation while another nutrient species might not. In addition, the relative quickness in the uptake of manganese rendered it undesirable for comparing nutrient uptake patterns to decipher the occurrence of plant stress.