A comparison of different rules of partitioning of crop growth between individual plants

Three contrasting rules to quantify the partitioning of crop dry matter between individual plants were incorporated into an overlapping zone of influence model. The model assumed that light was the limiting factor for growth and simulations were compared with growth observed in carrot (Daucus carota, L.) experiments. The simulations were compared with (i) the growth of individual plants at different positions in an imposed spatial planting pattern and (ii) the growth of plants of contrasting pre-competitive weight planted in a uniformly-spaced array. The simulation that gave a growth response closest to that in the experimental data was based upon an equation that partitioned crop dry matter between plants according to the degree of ‘crowding’ each plant experienced. This supports the view that plants alter their morphology in response to the presence of neighbours, thereby modifying the extent of growth interactions due to competition. The modification in growth was simulated by a simple modification to an overlapping zone model.