Models for the relationship between the population development of barnyard grass and the yield reductions of soyabeans.
Dynamic yield reductions of soyabeans in relation to the population development of barnyardgrass (Echinochloa crus-galli) was investigated at different growth stages in 5 soyabean fields in the Beijing region. Comparison of plant height, DM and product of relative plant height × DM (PRHM) of barnyardgrass in relation to the yield reduction of soyabeans were made. A close relationship that can be best presented by Richard's function with 4 parameters was found between the yield reduction of the crop and the PRHM of the weed. By using this model, least error occurred in predicting the yield reduction of soyabeans due to barnyardgrass at a given growth stage of the crop after emergence.