Pigweed density number per m2

Fig. 8.6. Yield loss in maize as a function of redroot pigweed (A. retroflexus) density and date of pigweed emergence (redrawn from Knezevic et al., 1994).

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Even the timing of fertilizer application will determine the competitive outcome. For example, two cultivars of sugarbeet (Beta vulgaris var. sacchariferal) were more competitive with wild mustard (Sinapsis arvensis) if there was a late season nitrogen fertilizer application, and more competitive with lambsquarters if nitrogen was applied earlier in the season (Paolini et al., 1999). Similar results were found when nitrogen was applied later in winter wheat (Triticum aestivum), thereby reducing the competitive effect of ivy-leaved speedwell (Veronica hederifolia) (Agnonin et al., 1996).

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