Multielectrolyte Solution Preparation for the Groundwater Salinity Experiment.

An experimental program to determine the effect of groundwater salinity on groundwater uptake by wheat grass is underway at the San Joaquin Valley Agricultural Sciences Center, USDA-ARS. Six different treatments having groundwater salinities varying from nonsaline to 32 dS/m are applied with four replicates in 32 column lysimeters. The salts are calcium chloride, sodium chloride and sodium bromide which is used as a tracer for detection of groundwater uptake by the wheat grass. We have developed a prediction function for the electrical conductivity (EC) of such mixed electrolyte solutions based on a generalization of the theory of EC for single electrolytes. Through constrained optimization of this prediction function we obtained estimates for the concentrations of each salt needed to produce a multielectrolyte solution having a specified EC. The constraints were defined as (1) the concentration of calcium equals that of sodium and (2) the sodium bromide must contribute 1.6 dS/m to the overall EC of the solution. Using this method we prepared solutions of 8,16,24 and 32 dS/m.