Measurement of short‐term nutrient uptake rates in cranberry by aeroponics

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Abstract
Aeroponics, a soil‐less plant culture system in which fresh nutrient solutions are intermittently or continuously misted on to plant roots, is capable of sustaining plant growth for extended periods of time while maintaining a constantly refreshed nutrient solution. Although used relatively extensively in commercial installations and in root physiology research, use of aeroponics in nutrient studies is rare. The object of this study was to examine whether nutrient uptake rates could be calculated for aeroponic systems by difference using measurements of concentrations and volumes of input and efflux solutions. Data were collected from an experiment with cranberry plants (Vaccinium macrocarpon Ait. cv. Stevens) cultured aeroponically with nutrient solutions containing various concentrations of ammonium‐N and isotopically labelled nitrate‐N. Validation of the calculated uptake rates was sought by: (1) evaluating charge balance of the solutions and total ion uptake (including proton efflux) and (2) comparison with N‐isotope measurements. Charge balance and proton efflux calculations required use of chemical modelling of the solutions to determine speciation of dissolved phosphate and acid‐neutralizing capacity (ANC). The results show that charge balance requirements were acceptably satisfied for individual solution analyses and for total ion uptake when proton efflux was included. Relative rates of nitrate/ammonium uptake determined by difference were in agreement with those determined by isotopic techniques. Additional information was easily obtained from this experimental technique, including evidence of diurnal variation in nutrient uptake, correlation between ammonium uptake and proton efflux, and the relationship between ion concentration and uptake. Use of aeroponic systems for non‐destructive measurement of water and ion uptake rates for numerous other species and nutrients appears promising.