Modelling CO2 effects on wheat with varying nitrogen supplies

Crop simulation models are an essential tool for testing whether predicted global atmospheric changes are likely to have impact on food production. An y confidence in model predictions must be based on their ability successful ly to predict performance in experiments. Accordingly, the predictions of t hree daily time step wheat simulation models (AFRCWHEAT2, FASSET and Sirius ) were tested against data from wheat (Triticum aestivum L.) experiments in AZ in which the amount of applied N and the atmospheric CO2 concentration were both varied. Although there were differences between predicted and obs erved yields, all the three models predicted yield trends with treatments v ery similar to those observed. They all predicted, both in absolute terms a nd in the magnitude of responses, very similar effects of the variations on green area index (GAI), shoot and grain biomass accumulation. and shoot an d grain biomass yield to observations and to each other. Comparison of simu lated and observed results showed that CO2 effects were expressed through e ffects on light use efficiency (LUE), whereas N effects were expressed by c ausing variations in GAI. The exercise showed that the models used have pot ential for assessing climate change impacts on wheat production. (C) 2000 E lsevier Science B.V. All rights reserved.