Evaluation of DSSAT-Nwheat Performance Across a Wide Range of Current and Future Growing Conditions.

Crop models are widely used in agricultural impact studies. However, large uncertainties have been reported from single-model-based simulation analysis suggesting the need for multi-model simulation capabilities. In this study, the APSIM-Nwheat model was integrated in to the Decision Support System for Agro-technology (DSSAT) to create a multi-model simulation capability for wheat cropping systems analysis. The new model in DSSAT (DSSAT-Nwheat) was evaluated using more than 1000 observations from field experiments of 65 treatments including a wide range of nitrogen fertilizer applications, water supply (irrigation and rainout shelter), planting dates, elevated atmospheric CO₂concentrations, temperature variations, cultivars and soil types in diverse climatic regions representing main wheat growing areas around the world.

   DSSAT-Nwheat reproduced the observed grain yields in general well with an overall root mean square deviation (RMSD) of 0.89 t/ha. Nitrogen applications, water supply and planting dates had large effects on observed biomass and grain yields and these crop responses were well reproduced by the model. Crop total biomass and nitrogen uptake were reproduced well despite relatively poor simulations of observed leaf area measurements during the growing season. The response of DSSAT-Nwheat to temperature variations and elevated atmospheric CO₂concentrations was close to observed responses. When compared with the two other DSSAT-wheat models (CERES and CROPSIM), these responses were similar, except for extreme dry environments. The comprehensive evaluation of the DSSAT-Nwheat model with field measurements including a comparison with two other DSSAT-wheat models created a multi-model simulation platform allowing now the quantification of model uncertainties in wheat impact assessments.

Key words: DSSAT-Nwheat, model evaluation, multi-model simulations