Th is work compares the performance of AquaCrop, a crop simulation model developed by FAO, with that of two well established models, CropSyst and WOFOST, in simulating sunfl ower (Helianthus annuus L.) growth under diff erent water regimes in a Mediterranean environment. Th e models diff er in the level of complexity describing crop development, in the main growth modules driving the simulation of biomass growth, and in the number of input parameters. AquaCrop is exclusively based on the water-driven growth module, in that transpiration is converted into biomass through a water productivity (WP) parameter; Cropsyst is based on both water and radiation driven modules, while WOFOST simulates crop growth using a carbon driven approach and fraction of intercepted radiation. Th e data used in the analysis were obtained in fi eld experiments with hybrid Sanbro_MR, performed in a typical Mediterranean area of Southern Italy in 2005 and 2007. Th e models were calibrated on data from a full irrigation treatment in 2007, and were validated on a full irrigation treatment in 2005 and several defi cit irrigation (DI) treatments, including regulated defi cit irrigation (RDI) and rain-fed (RF) conditions. Although AquaCrop required less input information than CropSyst and WOFOST, it performed similarly to them in simulating both biomass and yield at harvesting. Th e use of diff erent numbers of parameters and crop growth modules by the tested models did not infl uence substantially the simulation results. Th erefore, for management purposes and in conditions of limited input information, the use of simpler models should be encouraged.

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