Evaluation of the Newly-Linked DSSAT-Oryza Compared to Oryza V3 for Rice Crop Simulation Under Potential, Water-Limited, and N-Limited Conditions.

The use of multiple model approaches is a valuable objective to evaluate uncertainty of crop models for their response to climatic, soil, and management factors.  There were two objectives in this work.  The first objective was to incorporate the rice crop simulation model, ORYZA, into the DSSAT software platform.  This followed a wrapper approach in which the ORYZA code was integrated into the DSSAT Cropping System Model (CSM), and thus uses the soil water balance and the soil carbon-nitrogen balance of the CSM.  The second objective was to evaluate the performance of the linked DSSAT-ORYZA model by comparing to the original standalone ORYZA model under potential production, water-limited, and N-limited production situations.  For potential production, the simulated outputs were exactly equivalent for the two ORYZA versions.  For the water-limited cases, the models gave different outputs, with DSSAT-ORYZA showing lower biomass and grain accumulation, along with much higher soil evaporation and slightly lower transpiration.  Under N-limited conditions, DSSAT-ORYZA gave lower biomass and grain accumulation with lower N uptake.  In neither case, can we say which model is right, because ORYZA over-predicted under water and N limitation, but the DSSAT-ORYZA under-predicted.  Further examination is underway to evaluate water and N-limited causes for these variations.