Validation and application of AquaCrop for irrigated cotton in the Southern Great Plains of US

Dwindling water resources and weather variability present two of the major limiting factors for irrigated cotton production in the Southern Great Plains (SGP) of the United States. Under these conditions, there is a dire need to understand the trends and fluctuations in cotton yields to help producers make better irrigation and crop management decisions. Crop models coupled with long-term weather data provide an opportunity for evaluating yield variabilities by simulating numerous potential scenarios. In this study, the AquaCrop model was calibrated and validated for cotton at two sites in the SGP. The validated model was then applied to investigate the effect of variable irrigation capacity (IC) on cotton yield during a 33-year period (1981-2013). The AquaCrop model performed with acceptable accuracy for simulating canopy cover, soil water content, evapotranspiration and yield indicating that it is a potential tool for evaluating variable cotton irrigation scenarios in the SGP. The response of cotton yield to IC was highly dependent on heat unit availability. Yields increased significantly with increase in water availability in years when total growing season heat units were above 1100 degrees C day. The yield response to irrigation diminished considerably as the magnitude of growing season heat units decreased. No significant increase in mean cotton yield was found at IC higher than 0.3 L s(-1) ha(-1).