Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: June 3, 1996
Publication Date: N/A
Interpretive Summary: There is increasing concern about the impact of agricultural practices on drainage water quality. In response to general concerns about water quality computer models have been developed to predict water and salt transport. Only very few of these models are suitable for application to agricultural problems, where plant uptake of water must be considered. In this paper we review 3 rootzone models and compare model predictions in a realistic test case. We observed significant differences, based in part on differences in model assumptions and in part on inadequacies of computation algorithms. The example illustrate the fact that "validated" models may nonetheless contain serious errors and omissions which affect predictions.
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.