Cocklebur and Velvetleaf Interference with Soybean Grown at Different Densities and Planting Patterns
- Khan Bahadar Marwat * and
- Emerson D. Nafziger*
Two common problems in soybean [Glycine max (L.) Merr.] fields are weeds and incomplete crop plant stands, and these problems may interact in their influence on soybean yield. A study was conducted in 1986 and 1987 to examine whether weed interference was influenced by soybean plant stand and planting pattern. In full stands (26 plants/m row) of soybean, common cocklebur (Xanthium strumarium L.) and velvetleaf (Abufilon theophrasti Medic.) spaced 1.5 m apart in the row decreased soybean yields 29 and 34%, respectively, in 1986 and 19 and 15%, respectively, in 1987. Decreasing the soybean stand 20, 40, and 60% without weeds resulted in yield losses of 8, 18, and 34% (across both years) in evenly spaced soybean plants, while similar stand losses caused by removal of sections of row resulted in yield losses of 14, 28, and 35%, across both years, respectively. When common cocklebur and velvetleaf were present, percentage yield decreases due to stand losses were similar to those in the weedfree treatment; there was no interaction between weed treatment and stand loss treatments. Light interception by the canopy, measured only in 1987, was higher in weedy plots than in weedfree plots, with the additional interception presumably due to the weeds. Common cocklebur produced more dry weight than did velvetleaf, but the two weeds had similar effects on soybean yield. These results indicate that, while weed competition and stand loss can both cause substantial yield losses in soybean, the effect of these factors is additive when both occur in the same field, and weed growth is not greatly enhanced by decreased competition resulting from loss of soybean stand.
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