Irrigation with saline waters is a major problem in many parts of the world. Economic questions have usually been addressed using synthesized production functions and theoretically based soil salinity relations. The purpose of this paper is to estimate functions relating crop yield and salt accumulation in the soil to initial soil salinity and water quantity and quality. Crop response functions and dynamic salt balance relations are estimated from experimental data for alfalfa and cotton. The estimated functions are then used in a dynamic programming model to determine optimal water applications for different levels of initial soil salinity and crop and water prices.