In the Central High Plains, the predominant crop rotation is winter wheat (Triticum aestivum L.)-fallow. Producers are looking to add diversity and intensity to their cropping systems and improve water use efficiency by adding summer crops, however, the elimination of summer fallow may increase the risk of crop failure. The objective of this study was to use crop simulation modeling to compare the productivity of two fixed rotations [winter wheat-corn (Zea mays L.)- fallow and winter wheat-corn-spring triticale (Triticosecale rimpaui Wittm.)] with a simulated flexible fallow rotation. The flexible fallow rotation makes the decision to plant triticale or to use summer fallow prior to winter wheat seeding based on the soil water available in spring. Data from three years of field studies at two sites, Sidney, NE and Akron, CO, were used to calibrate and test the model, AquaCrop, for the crop simulation. Fifty years of historical weather data from the High Plains region were used to simulate crop production from all three rotations. Average and standard deviation of simulated yields were determined to assess the advantages and disadvantages of using a flexible fallow rotation over set rotations.