This study demonstrates that nutrient solutions can be defined as 'mixture systems'. A general methodology for design and analysis of mixture optimization experiments is developed. The emphasis is centered on multivariate investigation of the zone of optimal solution properties as a function of the ion composition and the total ionic strength of the solution. The study of the effects of ion interaction on well-defined solution properties is also possible by this multivariate approach. This work is a valuable tool in mineral nutritional research, because for the first time the chemical feasibility conditions of such solution, combined with additional chemical, physiological or economical constraints, form the foundation of the statistical experimental design theory, which makes the optimization of complex mixtures of ions in relation to well-defined response variables possible.