The “Donnan Theory” in Development of Plant Growth Media from Ion‐Exchange Resins1

Abstract

AbstractSynthetic ion‐exchange resins were prepared to serve as plant growth media. The resin was considered as an exchanger phase present for the purpose of controlling the solution phase composition within a range known to be satisfactory for plant growth. The “Donnan Theory”, an assumed Ca++ concentration of the solution phase based on the carbonate equilibrium, and known desirable solution phase concentrations were employed for determination of resin treatments. Treatment variables were introduced to test the functioning of the “Donnan System” in the resin media. The exchanger and solution phases of prepared media were separated and analyzed. Although differences were found between theoretical and experimental values, the data are considered to support the functioning of the system. Uncertainties due to unknown activity coefficients and lack of proved procedures are considered responsible for the observed discrepancies.Wheat (Triticum vulgare, L.), tomato (Lycopersicon esculentum, Mill.), and sunflower (Helianthus annuus, L.) were grown in the resin media, in a fertilized mixture, and in nutrient solutions. Plant yields were about equal from resin media and soils, but much less from nutrient solutions. The cation nutrient composition, including micro‐nutrients, of plants grown in resin media was essentially the same as in soil‐grown plants.