Interference and Temperature Effects on Growth in Soybean (Glycine max) and Associated C3and C4Weeds

Effects of temperature and interference were examined in a replacement series experiment with soybean [ Glycine max (L.) Merr. ‘Ransom’], common cocklebur ( Xanthium pensylvanicum Wallr.), and smooth pigweed ( Amaranthus hybridus L.). Plants were grown in controlled-environment greenhouses at day/night temperatures of 32/23, 29/20, or 26/17C and harvested 14 and 34 days after planting. In all species, height, dry weight, and leaf area at both harvests, and dry matter and leaf area duration for the harvest interval, increased significantly with temperature. Net assimilation rate in all species peaked at 29/20C. Dry weight and leaf area at day 34, and dry matter production and leaf area duration for the harvest interval, were reduced in plants subjected to interference. Temperature modified the effects of interference upon growth in smooth pigweed, but not in the other species. Common cocklebur and soybean were roughly equivalent as competitors at all temperatures and were superior to smooth pigweed.