There have been several simulation studies of the effects of increasing CO2 concentration ([CO2]) on crop productivity, but confidence in these would be substantially enhanced if the models used in the studies are shown to mimic the effects of increasing [CO2] and interactions with other variables such as nitrogen and water supplies. Since rice is one of the major staple crops in the world, it is highly desirable to evaluate the climate change impacts on this crop. In this study, we tested Oryza2000 model against the observed growth and yield of rice plants in a 3-year field experiment, where rice plants were subjected to elevated [CO2] with free air carbon dioxide enrichment (FACE) under varying nitrogen (N) fertilization rates in farmers’ rice paddies in northern Japan. The simulation results showed that the model greatly overestimates the increase in peak green leaf area index due to elevated [CO2], but that it simulates the enhancement of total plant biomass with only a minor overestimation. The model was successful in simulating the increase in rice yield due to the CO2 enrichment, but it failed to reproduce the observed interaction with N in the rice yield response to elevated [CO2].

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