مطالعه اثرات زمان های مختلف کنترل علف‌های هرز بر صفات ریخت‌شناسی، عملکرد و شاخص برداشت سه ژنوتیپ پاییزه کلزا

In order to study effects of competitive weeds (Sinapis arvensis, Hordeum spp., Secale montanum and Agrostemma githago) on morphological traits, yield and harvest index of winter rapeseed (Brassica napus L.) cultivars a factorial experiment was conducted in Islamic Azad University of Tabriz, during 2007-2008. Experimental factors were weeds controlling times included weeding in rosette (5-7 leaves stage), early stem elongation, early flowering and 50% flowering stages, full season competition and control; and Opera, SLM046 and Okapi cultivars. Results showed that number of branches per plant in control and full-season interference treatments were 4 and 2, respectively. Rapeseed biomass in whole season weed-infested plots reduced 40%, as compared with control. Weeds biomass in treatments those weeds were controlled at early stem elongation, early flowering and 50% flowering stages with 92, 86 and 87 g m^-2 had non-significant difference. Weeds could increase biomass up to 410 g m^-2 when grew with rapeseed along the season. Weeds controlling at rosette, early flowering and 50% flowering stages with 32%, 44% and 50% reduction value in seed yield, respectively, had significant difference with weed-free plots. When the weeds competition period extended a long time, allocation of biomass to seeds decreased. Seed oil percentage was not affected by cultivars and weeds competition periods. Reduction value in oil yield of rapeseed in different levels of weeds control were 32, 4, 45, 50 and 55%, respectively. Weeds controlling once in early stem elongation of all studied cultivars of rapeseed was recommended.