Technical Abstract: Prediction of the impact of agricultural practices on concentrations of salt and toxic elements in irrigation return flows requires knowledge of water and salt transport and relevant chemical processes. Despite the relatively large number of transport models in the literature, there are only a few models which include transient water flow and solution chemistry, factors that are necessary for simulation of both ion concentrations in the root zone and concentrations and volumes of drainage water. We review three available models, discussing the differences in approach and model complexity. Model predictions are compared for a case based on two years of irrigation with a sodic, high alkalinity water under conditions of little or no leaching. Significant differences are observed among the model predictions, based in part on the differences in model assumptions and in part on the differences in methods of calculation.