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Water Resources Research





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Irrigation strategies which maximize crop yield while preventing salt from leaching to the groundwater or undesirable salt increases in the root zone are computed by using a one-dimensional simulation/optimization management model. The included constraint equations maintain a water volume balance and salt transport in the unsaturated zone. Implicit finite difference forms of the unsaturated water flow equation (Richards' equation), the diffusion-convection solute transport equation, functions describing the hydraulic properties of the medium, a root extraction function, and other constraints are used. The model uses a large discretization in time. A cyclic prediction and correction type of approach is adopted to eliminate the inaccuracy that would otherwise result from the coarse discretization. As a result of the procedure presented, intercell water and mass flux rates in the optimization model have the same accuracy as those in a more finely discretized simulation model. The model is applied to a research farm in Huntington, Utah, where salty water is used for irrigation. In that process detailed soil water and salt profiles are computed and spatially distributed moisture content and concentration constraints are satisfied.