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Th e modeling of yield response to water is expected to play an increasingly important role in the optimization of crop water productivity (WP) in agriculture. During 3 yr (2004)(2005)(2006)(2007), fi eld experiments were conducted to assess the crop response to water stress of quinoa (Chenopodium quinoa Willd.) in the Bolivian Altiplano (4000 masl) under diff erent watering conditions (from rain fed, RF, to full irrigation, FI). Crop physiological measurements and comparisons between simulated and observed soil water content (SWC), canopy cover (CC), biomass production, and fi nal seed yield of a selected number of fi elds were used to calibrate the AquaCrop model. Subsequently, the model was validated for diff erent locations and varieties using data from other experimental fi elds and from farmers' fi elds. Additionally, a sensitivity analysis was performed for key input variables of the parameterized model. AquaCrop simulated well the decrease of the harvest index (HI) of quinoa in response to drought during early grain fi lling as observed in the fi eld. Further-on, the procedure for triggering early canopy senescence was deactivated in the model as observed in the fi eld. Biomass WP (g m −2 ) decreased by 9% under fully irrigated conditions compared with RF and defi cit irrigation (DI) conditions, most probably due to severe nutrient depletion. Satisfactory results were obtained for the simulation of total biomass and seed yield [validation regression R 2 = 0.87 and 0.83, and Nash-Sutcliff effi ciency (EF) = 0.82 and 0.79, respectively]. Sensitivity analysis demonstrated the robustness of the AquaCrop model for simulation of quinoa growth and production, although further improvements of the model for soil nutrient depletion, pests, diseases, and frost are also possible. available water in the soil between fi eld capacity and permanent wilting point; WP, water productivity; WP*, water productivity, normalized for ET o ; Y, total seed yield; Z x , maximum rooting depth.

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