Abstract: 【Objective】Grain protein content is an important quality index in rice. The objective of this study was to develop a process based simulation model for predicting the content and accumulation of grain protein under different cultural conditions. 【Method】On the basis of the field experiments involving different eco-sites, cultivar types and nitrogen rates, the fundamental relationships between grain protein accumulation and environmental and genetic factors were quantified by modeling the processes of nitrogen assimilation and partitioning within plant. 【Result】The model proposed that the rate of individual grain nitrogen accumulation was determined by the nitrogen availability restricted by source and nitrogen accumulation rate restricted by sink. Nitrogen availability of individual grain restricted by source was the sum of nitrogen uptake and remobilization from the vegetative organs post-anthesis, whereas nitrogen accumulation rate restricted by sink was dependent on potential nitrogen accumulation rate and interactive effects of temperature, water and nitrogen factors. Post-anthesis nitrogen uptake exhibited a logarithmic relationship to increasing grain weight. Nitrogen remobilization from the vegetative organs was provided from nitrogen accumulated in both leaves and stems. Relative nitrogen contents in leaves and stems pre-anthesis linearly increased with the accumulative growing degree-days after sowing, while those post-anthesis linearly decreased with the growing degree-days. The model was tested using the independent data sets of different years, eco-sites, cultivars, nitrogen rates, and it exhibited a good fit between the simulated and observed values, with the R2 of 0.968, 0.980, 0.974, 0.970 and 0.976, and RMSE of 16.55%, 13.24%, 9.53%, 10.93% and 9.29% for nitrogen uptake amounts of leaf and stem before anthesis, grain nitrogen uptake amount after anthesis, and nitrogen translocation amount of leaf and stem after anthesis, respectively, with the RMSE of 7.82% and R2 of 0.930 for grain protein content, respectively.【Conclusion】The simulation model based on nitrogen assimilation and translocation in rice could give a reliable prediction of plant nitrogen uptake and translocation amounts, and grain protein content and accumulation under different cultural conditions, which would provide a quantitative tool for grain quality prediction.

Key words: rice, nitrogen accumulation, nitrogen translocation, grain, protein, simulation model