simulation of sugar beet growth and yield under different nitrogen levels

models can be used to predict crop yield and inputs levels such as fertilizer, in order to conduct programming for the management of probable future crisis. in this study, based on the model, the effect of nitrogen fertilizer on dry matter partitioning in shoot and root of sugar beet was predicted. for model construction, data were collected from an experiment conducted in karaj city in 2001. inputs consisted of solar radiation, applied nitrogen, and some sugar beet morphophysiological parameters such as radiation use efficiency (rue), specific leaf area (sla), and root and shoot partitioning coefficients. eleven variables including six independent parameters and five parameters with interaction effects were determined in this model (less variable number than similar models). radiation use efficiency and sla were calibrated for karaj region. for model validation, results of the experiments conducted in karaj, in 2001-03 and 2009, respectively were used. simulated data for total and root dry matter and also crop cover were fitted to the observed data properly and the effect of nitrogen application on dry matter partitioning into different organs was determined. in this model, the sugar yield was estimated on the basis of optimum nitrogen level. root mean square error (rmse) for the simulated and observed data for total root and plant dry matter and sugar yield were 12.86, 17.57 and 20.62, respectively which showed optimum fitness of the model to total root and dry matter and also sugar yield for the studied nitrogen levels.