Abstract: By analyzing and extracting the quantitative relationships of suitable nitrogen index dynamics of rice and wheat to their cultivar types, cultural techniques, and eco-environments, a design model for the suitable nitrogen index dynamics of rice and wheat  was developed. The model was driven by the physiological development time-based relative growing degree days, with the relative nitrogen indices as modeling parameters, and could be used to generate the time-course indices such as the nitrogen accumulation and concentration of rice and wheat under different growth conditions. Case studies with the datasets from 3-year field experiments in Nanjing showed that the average RMSEs of the simulated to measured plant nitrogen accumulation and concentration were 0.1245 and 0.1316 for rice, and 0.1166 and 0.1301 for wheat, respectively. It was suggested that this model could reliably  guide the dynamics of major nitrogen indices of rice and wheat, which would help with the quantitative nitrogen diagnosis and precision nitrogen management of rice and wheat  under different eco-environments, cultivar types, and production conditions.

Key words: rice, wheat, nitrogen index dynamics, relative growing degree days (RGDD), precision management, Loess Plateau dryland, apple orchard, soil moisture, dry soil layer.