The AquaCrop model is a well-known crop-water model, developed and maintained by the Food and Agricultural Organization of the United Nations. AquaCrop accurately reproduces biomass accumulation, canopy cover development, and grain yield of multiple crops, including winter wheat, under various environmental conditions. However, the small subset of studies validating AquaCrop with winter wheat under arid or semi-arid climates reported widely different values for the calibrated parameters, raising questions about the applicability and transferability of these previously validated dataset in Uzbekistan. To address this issue, we use two-years of field data gathered under a cold semi-arid climate in Southern Uzbekistan to calibrate and validate AquaCrop for simulating the growth of winter wheat under various irrigation managements.

Applying an objective methodology for calibrating the AquaCrop model and strictly following AquaCrop guidelines, we calibrated five input parameters. Using the calibrated parameters, AquaCrop adequately simulated biomass accumulation (R² > 0.91, RMSE ≤ 1.2, and EF ≥ 0.83) and canopy cover growth (R² > 0.91, RMSE ≤ 9.2, and EF ≥ 0.91) during 2010-2011. During the second year (2011-2012), simulations of biomass and canopy cover were also satisfactory (R² > 0.70, RMSE ≤ 35.5, and EF ≥ 0.93). The insignificant effect of different irrigation managements on the AquaCrop simulations can be attributed to i) a limited number of irrigation events (only two), and ii) the proactive replenishment of soil moisture to prevent water stress conditions. During both growing seasons, simulated grain yields were consistently lower than the measured values obtained from the experimental field owing to the simulated winter wheat experiencing low temperature stress during its vegetative stage.

Under typical climate conditions of Karshi, results of the field experiment and AquaCrop simulations indicate that adopting furrow deficit irrigation do not significantly decrease grain yield of winter wheat and has the potential to conserve water resources in this semi-arid region. The decrease in irrigation water does not translate into meaningful saving for farmers due to the low price of water and policy makers should provide means to further encourage water saving irrigation practices.