SOYBEAN YIELD AND YIELD COMPONENTS AS INFLUENCED BY CANOPY HEIGHTS AND DURATION OF COMPETITION OF VELVETLEAF (ABUTILON-THEOPHRASTI MEDIK)

Soybean yields, pod and branch numbers were inversely related to the height of velvetleaf (Abutilon theophrasti). This effect was attributed to increasing interception of light with increasing height of A. theophrasti. Reductions in soybean yield and yield components were greater if A. theophrasti was maintained at various heights for only 3 weeks rather than 6 weeks following soybean emergence. This effect was attributed to a longer duration of light competition by the weed. Even when the A. theophrasti canopy was kept 25% below that of soybean for 4 weeks, soybean yields, pod and branch numbers decreased when the weed was allowed to regrow during the remainder of the season, but not if the weed was removed after the initial 4-week clipping period. No reduction in seed yields, pod and branch numbers was noted if A. theophrasti plants 25% shorter than soybeans were removed or allowed to resume growth after the initial 6 or 8 weeks of clipping. Soybean seed size was slightly affected by A. theophrasti canopy height and duration of competition.