evaluation of sunflower (helianthus annuus l.) response to weed interference in deficit irrigation condition

an experiment was conducted in 2011 to evaluate the effect of weed interference on sunflower yield in deficit irrigation and to study the grass and broadleaf weeds growth at different moisture condition. the experiment was arranged as factorial, randomized complete blocks with four replicates per treatment. treatments included different moisture conditions [40%, 60%, 80%, and 100 percent of crop water requirement (cwr)], and two weed interference levels: hand weeding and weedy condition. a plot with furrow irrigation was kept as control. the results showed that sunflower grain yield was significantly affected both by moisture condition and weed interference. weed competition decreased crop grain yield by 23%, 21%, and 30% in tape irrigation at 100% and 80% cwr and furrow irrigation treatments, respectively. weed biomass severely decreased as water deficiency increased. the maximum weed biomass was observed in the tape irrigation with supplying the 100% of cwr, which was 17% greater than the furrow irrigation. weed biomass also decreased with increasing the water stress up to 64%. in regions where water resources are limited and farmers have to use deficit irrigation, the joint effect of weed competition and drought stress may be severely harmful to crop yield; therefore, controlling weeds at the earliest possible time is crucial to save the stored moisture for crops.