Effect of Redroot Pigweed (Amaranthus retroflexus L.) density and time of emergence on yield and yield components in Sunflower (Hybrid Hysun-33)

In order to study effect of redroot pigweed (Amaranthus retroflexus L.) interference in sunflower, hybrid Hysun 33, a field experiment was carried out in the field research station of Islamic Azad University of Tabriz in 2004 cropping season. Three different pigweed densities of 5, 15 and 25 plants per meter of row and three time of emergence of 0, 15 and 30 days after sunflower emergence (DAE). The experiment of design was a randomized complete blocks with factorial arrangement and three replications. Emergence of sunflower and redroot pigweed seeds occurred after 4 days. Evaluated studied traits were stem height at the flowering stage, disc diameter, seed number in each disc, unfilled seed percentage, 1000 seeds weight, seed yield, oil percentage and oil yield. Analysis of variance indicated that difference between treatments due for studied traits were significant. The highest 1000 seeds weight (67.12g) and grain yield (3467kg ha-1) obtained from density of 5 plants m-1 in row and interference time of 30 DAE. Seed oil percentage in all treatments except three treatments including; first level of density at difference levels of interference time decreased in comparison with control treatment. The highest (1539kg ha-1) and the lowest (818.19 kg ha-1) seed oil yield obtained from density of 5 plants per meter in row and interference time of 30 DAE and density of 25 plants per meter in row and interference time of emerging with sunflower, respectively. It can be concluded that, redrect pigweed density has higher effect than it’s interference time on seed oil percentage and yield loss is more affected by interference time than by density.