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A study was conducted during four seasons to evaluate the performance of mature Valencia orange trees converted to pressurized irrigation systems. Trees irrigated by trickle, bubbler, spray, and sprinkler systems were compared to trees irrigated by the traditional border-flood irrigation method used in the southwestern Arizona desert region. During the first year only trees irrigated by the sprinkler system grew significantly less than trees irrigated by border-flood. During the second year after conversion, trees irrigated by border-flood grew significantly more than trees irrigated by any of the pressurized systems. However, there were no differences in tree growth during the third and fourth years, suggesting that the trees adapted to the new irrigation systems. Effects of irrigation treatments on leaf concentrations of N, P, Fe, Zn, Mn, and Cu were minimal. There were significant differences in orange yields from trees among the different irrigation treatments within years. However, average or total tree yields over the four-year period did not vary due to irrigation treatment. Similarly, there were no consistent differences in fruit or juice quality. Overall, results from this study indicate that mature Valencia orange trees can be converted to pressurized irrigation systems with minimal effects on fruit yield and quality. Under the conditions imposed in the studies, 33% less irrigation water was utilized with the pressurized systems compared to border-flood.