Accurate prediction of the allocation and redistribution of crop biomass is essential for simulating the impact of crop traits and management approaches on field-scale outcomes. The Agricultural Production system Simulator (APSIM) Plant Modelling Framework (PMF) uses a generic ‘arbitration’ approach to allocate biomass among plant organs. Crop models’ handling of biomass partitioning is not often described in detail or explicitly tested, in spite of its central importance. Our aim was to describe and test the partitioning approach currently implemented in APSIM PMF. For that we used two experiments with maize and wheat crops where N supply was varied with different fertilizer application, and dry matter (DM) supplies were varied with different irrigation treatments. Detailed analysis of the models’ predictions of biomass partitioning over the duration of these crops allowed for a number of improvements in their parameterization and showed the theory and implementation of the arbitration approach in the PMF to be sound.