Effects of genotypes and weed removal on the competitive ability of grain sorghum

Studies of weed interference in grain sorghum [Sorghum bicolor (L.) Moench] are limited. Improved knowledge of morphological differences of sorghum hybrids and their influence on weed interference could contribute to selection of crops with greater competitive ability. Consequently, we evaluated velvetleaf (Abutilon theophrasti Medic.) interference with three-grain sorghum hybrids in field experiments during 1996 and 1997 at Havelock and Mead, Nebraska. Our research objectives were: (1) to determine the effects of velvetleaf interference on light interception, growth, dry matter accumulation, and yield in grain sorghum; (2) to evaluate the effects of sorghum interference on light interception, growth, dry matter production, and reproductive fitness of velvetleaf; (3) to parameterize an ecophysiological. model for interplant competition (INTERCOM) for light. Sorghum hybrids used were FS2 (tall), DK54 and X260 (medium-stature). Weed treatments included sorghum in monoculture, sorghum kept weed-free for two weeks, and sorghum and velvetleaf grown in mixture for the entire season. In monoculture, light interception and dry matter production did not differ among sorghum hybrids. The medium stature sorghum hybrids developed greater leaf area indices and leaf area ratios than the tall hybrid. Light interception, growth parameters, dry matter production, and grain yield did not differ between sorghum in monoculture and sorghum weed free for the first two weeks. Sorghum hybrids produced greater biomass and grain yield in monoculture than in mixture. The tall sorghum hybrid intercepted more light and produced more biomass and grain yield than the medium-stature hybrids when grown in mixture with velvetleaf. Velvetleaf intercepted more light and produced greater biomass and more capsules in monoculture than in mixture with sorghum. Velvetleaf light interception, growth, dry matter production, and reproductive fitness were more affected by the tall sorghum hybrid than the medium stature hybrids. In this study, sorghum height was the characteristic most associated with competitiveness. Integrating sorghum hybrids with improved weed suppressive ability into a well-designed weed management program can increase the profitability and sustainability of crop production systems