Modeling nitrogen management effects on winter wheat production using RZWQM and CERES-wheat

Agricultural system models can provide an alternative, less time-consuming and inexpensive means of determining the optimum crop N requirement under varied soil and climatic conditions. In this context, we parameterized the Root Zone Water Quality Model (RZWQM) for winter wheat (Triticum aestivum L.) production and then evaluated it along with the CERES-Wheat model to assess their potential as N management tools at Akron, Co. Both models were evaluated with data from five N treatments (0, 28, 56, 84, and 112 kg N ha(-1)) and three crop seasons (1987-1988, 1988-1989, and 1989-1990). Data from 1987-1988 zero-N treatment were used for model calibration, and the rest of the data were used for model validation. Genetic coefficients for winter wheat (cv. TAM 107) were developed for the CERES-Wheat model. The crop parameters required for the generic crop model of RZWQM were parameterized using information from the literature or by calibration. Both models were calibrated first for soil moisture and then for biomass and grain yield. Grain yield predictions had a root mean square error (RMSE) of 500 and 363 kg ha(-1), respectively, for CERES-Wheat and RZWQM. Aboveground biomass was predicted with RMSEs of 1247 and 1441 kg ha(-1), respectively. Long-term simulations of both RZWQM and CERES for winter wheat growth using historical weather data (1912-2001) showed that 56 kg ha(-1) N applied as broadcast incorporated is a viable N management option in eastern Colorado, taking into account the grain yield, crop N uptake, N leaching into groundwater, and residual soil N at harvest. Model simulations also showed that the wheat-fallow cropping system is less water use efficient than a continuous wheat system under rainfed agriculture in eastern Colorado.