USE OF ECOPHYSIOLOGICAL MODELS FOR CROP-WEED INTERFERENCE - RELATIONS AMONGST WEED DENSITY, RELATIVE-TIME OF WEED EMERGENCE, RELATIVE LEAF-AREA, AND YIELD LOSS

The performance of a mechanistic simulation model of crop-weed competition was evaluated with data on the effects of weed density, relative time of weed emergence, and environmental conditions on crop yield for three different crop-weed combinations. Reductions in crop yields due to weed competition were simulated accurately for all experiments, except for one case in which severe water stress combined with weed competition altered crop morphological development (height and leaf area). The mechanistic model was then used to assess the potential and constraints of two empirical models of crop-weed competition, one based upon weed density and relative time of emergence, and the other on relative leaf area. The empirical model describing the relationship between relative leaf area of the weeds shortly after crop emergence and yield loss appeared to have several advantages for management applications, whereas the mechanistic model is more suited for research purposes.