MEASUREMENT OF SHORT-TERM NUTRIENT-UPTAKE RATES IN CRANBERRY BY AEROPONICS

Aeroponics, a soil-less plant culture system in which fresh nutrient s olutions are intermittently or continuously misted on to plant roots, is capable of sustaining plant growth for extended periods of time whi le maintaining a constantly refreshed nutrient solution, Although used relatively extensively in commercial installations and in root physio logy research, use of aeroponics in nutrient studies is rare, The obje ct 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 co llected from an experiment with cranberry plants (Vaccinium macrocarpo n Ait, cv, Stevens) cultured aeroponically with nutrient solutions con taining 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 (in cluding proton efflux) and (2) comparison with N-isotope measurements, Charge balance and proton efflux calculations required use of chemica l modelling of the solutions to determine speciation of dissolved phos phate and acid-neutralizing capacity (ANC). The results show that char ge balance requirements were acceptably satisfied for individual solut ion analyses and for total ion uptake when proton efflux was included. Relative rates of nitrate/ammonium uptake determined by difference we re in agreement with those determined by isotopic techniques, Addition al information was easily obtained from this experimental technique, i ncluding evidence of diurnal variation in nutrient uptake, correlation between ammonium uptake and proton efflux, and the relationship betwe en ion concentration and uptake, Use of aeroponic systems for non-dest ructive measurement of water and ion uptake rates for numerous other s pecies and nutrients appears promising.