The Influence of Weed Seed Dispersion Versus the Effect of Competition on Crop Yield

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Abstract
A theoretical model was developed to assess the relative importance of weed competition and seed dispersal in determining long-term crop yield reductions imposed by weeds. Weed seed dispersal by cultivation, natural means, and harvest machines was incorporated into a weed and crop population model. Model simulations were conducted with green foxtail and spring wheat demographic data from the literature. Simulations indicated that seed dispersal from a weed species invading a field may have a more important influence on crop yield than the relative competitive ability of the weed with respect to the crop. However, if a weed species has a uniform or a high frequency random distribution, there is less difference in the relative importance of dispersal versus competitive ability in determining crop yield reductions. Harvest machines may be an important mechanism for dispersing weed seeds that are harvested with the crop. The practical implication is to make harvesters weed seed ‘predators’ rather than dispersal agents and thereby reduce herbicide and mechanical weed control inputs.