effects of nitrogen and rapeseed residues on grain yield and yield components of sunflower (helianthus annuus l.) and weed growth

abstract- crop residue is applied to amend soil properties and increase crop yield. in this study, the effects of rapeseed residues and different rates of nitrogen on grain yield and yield components of sunflower and weed dry matter were investigated. the experiment was conducted at the experimental farm of college of agriculture, shiraz university, located at badjgah, shiraz, iran in 2007-2008 and 2008-2009 growing seasons. treatments were nitrogen levels (150, 300 and 450 kg urea ha-1) as main plot and rates of residue rapeseed (25%, 50%, 75%) and without residues included weed free (r0) and weedy check (r1) as sub plot. the experimental design was a split plot based on randomized complete block in four replications. results showed that the lowest weed biomass, highest grain yield and yield components of sunflower were obtained at 150 and 450 kg n ha-1, respectively. compared to weedy conditions, the lowest weed biomass (2847.58 kg ha-1) and the highest yield (4087.67 kg ha-1) of sunflower were obtained at 75 and 25 % residue, respectively. optimum rates of nitrogen fertilizer and rapeseed residue to guarantee maximum grain yield and optimum suppression of weeds were 450 kg ha-1and 25%, respectively. generally, to increase sunflower yield and suppress weeds, it is recommended to integrate cultural practices with use of 450 kg urea ha-1 fertilizers and left over 25% of rapeseed residue, was the best treatment.