The influence of wheat density and spatial arrangement on annual ryegrass, Lolium rigidum Gaudin, competition

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Abstract
The influence of wheat (Triticum aestivum L.) planting arrangement and density on the competitive effect of the weed, annual ryegrass (Lolium rigidum Gaudin), was examined in field experiments over three climatically contrasting years on the central western slopes of New South Wales. Results for three experiments conformed to a common trend. Geometrical arrangement of the crop (rectangularities of 1 to 6.4) at any one of a range of crop densities had no significant effect (P > 0.05) on ryegrass competition, expressed as relative wheat grain yield reduction. However, the effect of ryegrass was substantially reduced by increasing wheat sowing density from 40 or 75 to 200 plants m-2. In analysing models of weed competition a reciprocal yield model (I/ Y = 0.0092 + 0.0037X, r2= 0.89) predicted yield reduction (Y, as per cent of weed-free controls), especially when used with the ratio of weed density to crop density (X), with residual sums of squares lower than for other models.

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