Methodology to simultaneously optimize the Macrocation and the Macroanion Composition of Nutrient Solutions, using Mixture Theory

To illustrate the use of mixture theory to simultaneously optimize the macrocation and the macroanion composition of a hydroponical nutrient solution, a {3,2;3,2} double lattice design was established in the double mixture factor space (K+, Ca2+, Mg2+, NO-3, H2PO-4and SO2-4). Only one response variable was considered: the calcium content of English ryegrass. The macronutrient composition significantly affected the calcium content of the ryegrass. A reduced second-degree double mixture model with 20 instead of 36 parameters was selected to represent the response surface over the experimental region. The macrocation composition had a more pronounced effect on the calcium content of the ryegrass than the macroanion composition.