عنوان مقاله [English]
Introduction: The DSSAT consists of a series of popular and widely used process-based crop growth simulation models. The models have been used worldwide to simulate crop biomass and yield, and soil nitrogen leaching under different management practices and various climatic conditions. The DSSAT has also proven to be a useful tool for selecting improved agricultural practices. Among all management agronomic factors, nitrogen fertilizer and crop species are major effective aspects impacting crops production. Although limited use of nitrogen fertilizer seems likely to reduce crop yield, high application rates of nitrogen causes serious adverse environmental effects. Thus, management of nitrogen fertilizer consumption decreases production costs and environmental pollution in agroecosystems. Therefore, the objectives of the present study were: (1) to determine the genetic coefficients and calibrate the CERES-Maize model (2) to evaluate the performances of the CERES-Maize model in simulating maize cultivars growth, development and grain yield for different fertilizer nitrogen application rates under Kermanshah climate condition.
Materials and Methods: This experiment was carried out in a split-plot design with 5 levels of nitrogen fertilizer application (0, 138, 238, 350 and 483 kg ha-1 urea) as main plots, 3 current maize cultivars SC-704, BC-678 and Simon as sub plots, and 4 replications in 2014. The required model inputs describe field management, daily weather condition, soil profile characteristics, and cultivar characteristics. The cultivar coefficients were obtained under optimum conditions (i.e., minimum stress in weather and nutrients). The genetic coefficients (P1, P2, P5, G2, G3 and PHINT) of the maize cultivars i.e. SC-704, BC-78 and Simon were determined using the GenCal software of DSSAT v 4.6 for 350 kg Urea ha-1 treatment (optimum nitrogen fertilizer amount based on the results of soil library). Model performance was evaluated by comparing simulated and measured values of maize cultivars phonological development stages (DVS), leaf area index, total dry weight and grain yield for independent nitrogen fertilizer treatment (0, 138, 238 and 483 kg Urea ha-1) by root mean square error (RMSE), normalized RMSE (nRMSE) and index of agreement (d).
Results and Discussion: The coefficients of P1, P2, P5, G2, G3 and PHINT ranged between 275 to 286 °C day, 0.576 to 1.80 days hr-1, 910 to 950 °C day, 940 to 990 number per plant, 7.0 to 7.9 mg day-1 and 51.70 to 51.97 °C day , respectively, for all cultivars. The CERES-Maize model was able to accurately simulate growth, development stages and yield for maize cultivars. For both simulated and measured conditions, leaf area index, total dry weight and grain yield were improved by increasing the application of nitrogen fertilizer. Simon cultivar had higher simulated (9925 kg.ha-1) and measured (10467 kg.ha-1) grain yield in respect to other cultivars. The validation results also indicated that the CERES-Maize model gave a reliable estimate of growth, development stages and grain yield for maize cultivars in the different fertilizer nitrogen application rates. The value of RMSE and nRMSE for leaf area index of SC-704, BC-78 and Simon cultivars were 0.56, 0.46 and 0.36 and 25.5%, 21.8% and 16.3%, respectively. The index of agreement (d) for leaf area index ranged from 0.94 to 0.98. The RMSE and nRMSE magnitudes for total dry weight of SC-704, BC-78 and Simon cultivars were 440.1, 569.6 and 419.7 and 6.2%, 8.2% and 5.8%, respectively. The index of agreement (d) for total dry weight ranged from 0.94 to 0.95. The RMSE and nRMSE values for SC-704, BC-78 and Simon grain yield were equal to 163.7, 345.2 and 314.4 and 4.3%, 11.4% and 8.1%, respectively. The index of agreement (d) for grain yield ranged from 0.93 to 0.98.
Conclusion: The results indicated that the CERES-Maize was parameterized reliably for three maize cultivars under Kermanshah climate conditions. The results of validation also showed that the CERES-Maize model was able to give an accurate simulation of all studied traits of maize cultivars except leaf area index in different fertilizer nitrogen application rates.