This paper aims at studying the capacity of an individual-based morphogenetic crop model of sugar beet growth - GreenLab - to predict the effects of population density on growth and yield. A field experiment was carried out for three homogeneous population densities to measure detailed plant development and growth of one cultivar. A set of in situ measurements were used to observe some model inputs (organs' expansion times and life-spans) and destructive data of dry masses were collected for model calibration. For all density conditions, the plasticity of total biomass production and allocation patterns was accurately simulated using the sets of optimized parameters. Most of them reveal stable across different spacing, and a few parameters vary with density: specific blade mass, time after which phyllochron increases, petiole sink and the characteristic surface used to compute Beer's law at individual level. These results are a first step towards developing a predictive capacity regarding crop spacing.