Modeling plant nitrogen uptake and grain nitrogen accumulation in wheat

Grain nitrogen (N) concentration is one of the main quality parameters of wheat grains. Since few reports have quantified the processes of N accumulation in both grain and vegetative parts in wheat (Triticum aestivum L.), this study was undertaken to develop a dynamic model for simulating plant N uptake and grain N accumulation in wheat by focusing on the variation of N accumulation rate in individual grains. Five different experiments involving genotypes, N fertilization rates and water regimes were conducted to support model development and model evaluation. The model proposed that the rate of individual grain N accumulation was determined by the N availability and the interaction of influencing factors as temperature, water and nitrogen conditions within plants over the time course. N availability of individual grain was the sum of N uptake and remobilization from the vegetative parts post-anthesis. Post-anthesis N uptake exhibited an exponential relationship to grain weight and N accumulation at the time of anthesis which was determined by pre-anthesis N uptake. N remobilization from the leaves was assumed to decrease with leaf area index (LAI). N remobilization from the stems and chaffs (spikes without grains) was dependent on the curvilinear or linear decreases of the N concentrations and the weights of stems and chaffs during grain filling. Two genotypic parameters were incorporated into the model, i.e. the maximum rate of individual grain N accumulation and physiological filling duration of specific cultivars. The overall performance of the model was validated with independent data sets from three field experiments spanning 3 years and comprising various genotypes, nitrogen and water levels. The RMSE values for model components with all treatments were averaged 11%, indicating a good fit between the simulated and observed data. It appears that the model can give a reliable prediction for grain N accumulation and protein formation in different wheat cultivars under various growing conditions.