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When irrigation is optimized to maximize net economic returns, some level of deficit irrigation is required. However, the theoretical, technical, and practical challenges associated with deficit irrigation scheduling are far more complex than conventional (full) irrigation. Oregon State University and the NRCS have cooperatively developed a web-based application for optimum irrigation management. This system, Irrigation Management Online (IMO), explicitly analyzes irrigation efficiency, accounts for spatial variability of soil properties and irrigation uniformity, performs simultaneous scheduling for all fields in the farm, accounts for energy use and its associated costs, and uses both ET and soil moisture measurements to enhance the accuracy of the irrigation schedules. IMO has been developed specifically to support irrigation management when either water supplies or delivery system capacities are limited. To mitigate the complexities of irrigation constraints the system has been designed so that the irrigation manager is an integral part of the irrigation optimization procedure.