Modelling nitrogen translocation to grain under elevated carbon dioxide in wheat

• Grain N yield response to CO2 was 33 % under water stress, low (1 %) under low N-supply. • Results show decline in grain N concentration under eCO2 despite increased N supply. • Models’ accuracy was similar to the experimental error for harvest grain N yield. • Models did not predict well observed post-anthesis decline in grain N concentration. • Models need better post-anthesis dynamics to capture the flux of N into grain. Rising atmospheric CO2 concentration tends to increase grain yields and decreases grain N concentration in cereal crops, reducing nutritional content. The robustness of APSIM-Wheat, DSSAT-Nwheat and OLEARY-CONNOR models were tested for their performance in predicting grain N yield and grain N concentration under elevated CO2 (eCO2) across two environments with varied environmental stresses including temperature, in-season water, and N supply. Observed grain N yield response to eCO2 was 33 % increase under water stressed conditions but low (1 %) under low N-supply conditions. Models’ responses to eCO2 were similar and close to the experimental error for harvest grain N yield and N concentration, but with large error in stressed environments. The biomass N concentration by anthesis and grain N concentration during post anthesis were not well simulated by the models in all conditions. While each model showed some advantage in some treatments, all models need better post-anthesis N dynamics to capture the flux of N into grain. The models would benefit from improvements in the following: potential excess soil N availability, initial and early flux of N to grain, heat and water stress interactions with eCO2, soil N dynamics in wet conditions. Specifically, for APSIM-Wheat mechanisms that increase grain N concentration decline post anthesis, for DSSAT-Nwheat mechanisms that decrease grain N concentration decline early after anthesis and for OLEARY-CONNOR model reinstating the original multilayer soil profile for both water and N balances. All these results point to the need for a specialised modelling framework for cereal nitrogen dynamics after anthesis.