Landscape-Scale Modeling of Cotton Across Variable Pedology and Weather.

Cotton production in the semi-arid Southern Ogallala Aquifer region is highly reliant on irrigation using water from the non-recharging aquifer in combination with highly variable growing season precipitation. The mechanics of varying irrigation amounts across cotton fields has been developed. Variable rate irrigation equipment is becoming more available and will provide producers options for managing both spatial and temporal irrigation requirements across fields. However, specific logic and decision support tools needed by managers to prescribe irrigation amounts are under development. Cotton simulation models allowing continuous updating of interactions between weather, management, and physical variables impacting cotton growth across the field and throughout the season are likely components for these tools. The PALMScot model is an approach towards modeling pivot irrigated cotton systems at a landscape-scale; allowing integration and continuous accounting of mass and energy balances and interactions between management, surface hydrology, the soil, above and below ground plant physiological processes, and atmosphere. The PALMScot model’s ability to correctly calculate soil water content and cotton crop height has been evaluated against field measured values at multiple locations within two > 50 ha production fields of contrasting textural class. The model has exhibited acceptable levels of model efficiency across variability in pedology and divergent inter-seasonal weather. Values of mean absolute error for soil water content were consistently < 0.015 m³ m^‑3 in a fine-loamy soil and between 0.010 – 0.024 m³ m^‑3 in a fine soil; both sets of results showed positive modified coefficients of efficiency. Values of mean absolute error in cotton crop height calculations have consistently been < 0.05 m in a fine-loamy soil and < 0.08 m in a fine soil. The PALMScot model calculates soil water contents and plant heights at levels of precision supportive of management decisions in pivot irrigated cotton systems.