A dynamic model was developed enabling calculation of the DM yields of species in a mixture on day n + 1 from the DM yields on day n, by means of parameters derived from a spacing experiment with the species grown at 2 densities and harvested at intervals. Differences of growth in height between the species are taken into account. The model is evaluated by means of experiments with oats, barley and peas. It is applicable under conditions of near optimum supply of water and nutrients, i.e., where the species mainly interfere by competition for light. A simple non-destructive method for measuring the relative light interception of species in mixed stands is described.-A.M.H. (Abstract retrieved from CAB Abstracts by CABI’s permission)