RELEASE CHARACTERISTICS OF ION-EXCHANGE RESINS AS BUFFERS IN LOW IONIC-STRENGTH NUTRIENT SOLUTIONS

The use of synthetic ion-exchange resins as buffers of nutrient ions i s a potential mechanism for the control of ion concentrations in nutri ent solutions. In this study equilibrium constants for two cation exch ange resins and three anion exchange resins were determined at 25 degr ees C in low ionic strength systems. The measured constants were used to successfully predict the resin combinations required to achieve des ired solution equilibrium concentrations. The effectiveness of these r esins in buffering solution ion concentrations was evaluated by examin ing their release characteristics in circulating systems from which al iquots of solution were withdrawn and replaced with deionised water to ;simulate plant uptake. Buffering of NO3 and SO4 concentrations was ef fective when manual control of one anion was imposed. The cation resin s were ineffective in buffering the concentrations of Ca and Mg with a tendency for the resins to retain most of the Ca and Mg in adsorbed f orm.