OPTIMIZING IRRIGATION MANAGEMENT FOR POLLUTION-CONTROL AND SUSTAINABLE CROP YIELD

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/optimizat ion management model. The included constraint equations maintain a wat er volume balance and salt transport in the unsaturated zone. Implicit finite difference forms of the unsaturated water flow equation (Richa rds' equation), the diffusion-convection solute transport equation, fu nctions describing the hydraulic properties of the medium, a root extr action function, and other constraints are used. The model uses a larg e discretization in time. A cyclic prediction and correction type of a pproach is adopted to eliminate the inaccuracy that would otherwise re sult from the coarse discretization. As a result of the procedure pres ented, intercell water and mass flux rates in the optimization model h ave the same accuracy as those in a more finely discretized simulation model. The model is applied to a research farm in Huntington, Utah, w here salty water is used for irrigation. In that process detailed soil water and salt profiles are computed and spatially distributed moistu re content and concentration constraints are satisfied.