عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The dry weight and weed density are the important factors and have obvious effects on crop yield that can be achieved by several methods including time, amount and method of application to apply the appropriate management of these factors. In order to study of nitrogen effect on critical period of weed control in sunflower (Heliantus annus L.) in Birjand region, a split plot experiment based on randomized complete block design was conducted with 24 treatments and 3 replications in research farm of college of agriculture of Birjand University in 2010. The main factor was 3 levels of nitrogen (0, 100 and 200 Kg ha-1) and the sub factor was different weed competition periods on sunflower growth stages. The dominant weeds in farm were Pigweed, Common mallow, European bindweed, Amaranth, Lambs quarter and Hoary cress. Increasing in time of weed interference was increased weed dry weight per unit area established, so that reached to its maximum amount of in all season interference. This maximum for fertilizer levels of 0, 100 and 200 kg ha-1 nitrogen, were 80.49, 143.43 and 118.7 g m-2, respectively. The sunflower seeds yield was significantly affected by weed competition and continued to the end of weed presence which reduced grain yield intensely. However, with the increase in time of interference, weed density decreased, but their dominance count was preserved. With increasing the density of the weed-free time weeds were strongly reduced at the end of the season. The highest dry matter and weed competition and as a result, the lowest yield of sunflower competition treatments recovered in the level of 100 kg ha-1 nitrogen.