Modelling nitrogen uptake and redistribution in wheat

A new mechanistic model of N uptake and redistribution in wheat crops incorporating the effects of N shortages through variation in leaf area is described. The model is based on the assumption that the concentration of N in green tissue can be approximated as constant per unit leaf area and that. excess N is stored in non-green tissue. Two hypotheses about how grain demand for N is set, were also tested. These were that N-demand by the grain is set mostly in response to total N content in the crop (source determined), or that the N-demand is set according to the grain number per unit area (sink determined). The model was tested using data from widely separated, independent experiments. The model produced substantial improvement in the simulation of green area index (GAI) compared with an alternative older model, particularly in response to changes in N-supply, while retaining the ability to simulate biomass accumulation and grain growth accurately. Of the two hypotheses on the determination of grain N-demand, the source determined model gave substantially better estimates of final grain N concentration that were highly correlated with observations over a wide range of values, whereas the sink determined simulations were uncorrelated with observations. The study demonstrated that most of the variations caused by different N supply regimes can be simulated using a very simple mechanism, and that the inclusion of this more mechanistic approach conveys little extra complexity in a wheat simulation model. (C) 2000 Elsevier Science B.V. All rights reserved.