evaluation effect of different wheat residue and sunflower densities on growth and yield of sunflower

mulches often use for weed control, hold soil moisture, decrease soil temperature, soil fertility, soil conservation, soil against rain and soil quality in organic farming. a field experiment was conducted to evaluate the effect of different wheat residue and sunflower densities on sunflower growth and yield during 2007 growing season at the research field of birjand university. the experimental design was randomized complete block in factorial with three replications. the experiment treatments were wheat residue at the rates of 0, 1250, 2500, 3750, 5000 kg.ha-1 and burning residue and three levels of sunflower density (50000, 70000 and 90000 plant.ha-1). results showed that effect of wheat residue and sunflower density levels was significant on sunflower biomass, height and grain yield. with increasing wheat residue and sunflower density, sunflower biomass, height and yield increased significantly. results showed that by increasing wheat residue, sunflower biomass increased 61.77, 52.08 and 42.71% more than control respectively in 3, 6 and 9 weeks after planting. in this three weeks, with increasing density, sunflower height increased 66.82, 49.48 and 50.16%, respectively. also, sunflower grain yield increased 29.86 and 31.73 % with increasing wheat residue and plant density, respectively. results showed that maximum sunflower growth and yield were obtained by using of 2500 kg.ha-1 wheat residues and the highest density of sunflower.