Lysimetric Evaluations of RZWQM2 Simulations of Corn ET in the Southern High Plains.

Fresh water scarcity due to increasing demands from competing human enterprises is being further exacerbated by global warming associated with increasing atmospheric greenhouse gas (GHG) concentrations.  In this scenario, accurate quantification of crop evapotranspiration (ET) is critical in optimizing irrigation water productivity, especially, in the semiarid regions of the world where limited rainfall is supplemented by irrigation for sustainable crop production. Cropping system models are potential tools for predicting irrigation water demands in agriculture across soils and climates, and prescribing adaptation decision support.  The objective of this study was to evaluate accuracy of RZWQM2 simulated silage corn daily ET against their water use measured with large precision lysimeters in the Texas High Plains. Nimah and Hanks approach was used for crop water uptake simulations. Simulations of leaf area index, biomass, soil water storage, and ET were found to be reasonably accurate for irrigation water management applications. Fallow soil evaporation before and after corn planting also were simulated with a high level of accuracy verifying the robustness of the model in simulations across cropping seasons.  Simulated crop coefficients (Kc) computed for both grass and alfalfa reference ET estimates also compared well with lysimetric data.