Modeling Center Pivot Irrigated Cotton At Field Scale.

Pivot irrigation equipment may take several days to complete a cycle around a field. This long cycle magnifies the spatial and temporal variability of water and energy balance dynamics and presents some complex challenges for modeling activities at field scale, e.g., 1 km². One such challenge is the spatial and temporal representation of irrigation input data. This data is becoming more available as producers in the Southern High Plains of Texas adopt the use of pivot monitoring devices that provide information on pivot position and flow. The PALMScot model, a combination of the PALMS (Precision Agricultural-Landscape Modeling System) and the Cotton2K models, can use hourly data from these pivot monitoring devices as spatially and temporally representative irrigation input. Features in PALMScot that integrate the surface and subsurface hydrology and plant growth, in combination with the ability to use representative irrigation input, allow simulation of water and energy balance dynamics at the field scale and a detailed resolution within pivot irrigated cropping systems. Simulation results have shown that PALMScot can represent the spatial and temporal variability of soil profile water content across a large (~ 50 ha) production cotton field that is heterogeneous in elevation and soil type. Further, our results have shown that the use of pivot monitoring device input data as temporally and spatially representative irrigation can improve accuracy and reduce bias in field-scale modeling of volumetric soil water content when compared to results using  more general irrigation input; root mean squared deviations between measured volumetric water content and simulated values have been reduced by ~ 20%.