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 is a potential mechanism for the control of ion concentrations in nutrient solutions. In this study equilibrium constants for two cation exchange resins and three anion exchange resins were determined at 25°C in low ionic strength systems. The measured constants were used to successfully predict the resin combinations required to achieve desired solution equilibrium concentrations. The effectiveness of these resins in buffering solution ion concentrations was evaluated by examining their release characteristics in circulating systems from which aliquots of solution were withdrawn and replaced with deionised water to simulate plant uptake. Buffering of NO₃ and SO₄ concentrations was effective when manual control of one anion was imposed. The cation resins 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 form.