Prediction of wheat yield loss due to competition by wild oats (Avena spp.)

Field experiments were conducted to determine the effect of varying the density of wheat (cv. Gamut) and wild oats (Avena fatua and A. sterilis ssp. ludoviciana) on the grain yield of wheat. Wheat grain yields were reduced by wild oats through the reduction in number of tillers, and this competitive effect could be reduced by increasing the density of wheat. Increasing wheat plant density beyond the weed-free optimum was found to be unsatisfactory for wild oat control. The best model to describe the data comprised a parabolic wheat yield-density component and a hyperbolic yield loss component. Parameters in the yield-density component were calibrated using 36 data sets to account for variation in sowing date and available soil water. The parabolic model best described the effect of limiting soil water on the wheat yield-density relationship. The yield loss component, which included weed and crop density as variables, indicated that wheat and wild oats behaved as near-equal competitors.The predictive ability of the yield loss model varied when tested on several independent data sets collected from commercial wheat crops. This variation was caused by changes in the relative competitive ability of the crop and weed which resulted in significant variation in values of the yield loss parameters. Further refinement and generalization of the model will be possible if the yield loss parameters can be related to genetic and environmental variables