Comparison of CropSyst performance for water management in southwestern France using submodels of different levels of complexity

A comparison of the performance of the CropSyst model when using evapotranspiration (ET) and soil water transport submodels of different levels of complexity was conducted. ET submodels included Penman-Monteith, Priestley Taylor, and a temperature-based submodel. Soil water transport submodels included a finite difference numerical method and a simple cascading method. Simulations of biomass production, yield, and water use of irrigated maize, soybean, and sorghum were compared with experimental data collected at Auzeville, southwestern France. Experimental data for growing seasons 1986, 1989, and 1990 (dry years) were used, including three irrigation levels (full, deficit, and no irrigation) each year. Calibration of a small number of crop parameters was conducted using the most complex submodels. Using these most complex submodels, simulations compared well with measurements. with the Wilmott index of agreement fluctuating from 0.956 to 0.997 (an index of 1.0 indicating perfect agreement). The model appeared suitable for applications over a wide range of water availability and stress conditions. Using simpler submodels, the performance of CropSyst tended to decrease, but generally not significantly. A simple cascading method for soil water transport (non-constrained drainage) appeared to be a valid alternative to more complex numerical methods. All ET submodels predicted similar seasonal ET, but differences in vapor pressure deficit estimation led to growth overprediction in some cases. Simpler submodels would have performed similarly to the most complex submodels if used during calibration. Successful applications of the CropSyst model appear feasible for sites with limited weather and soil data. (C) 1997 Elsevier Science B.V.