responses of morphological characteristics, yield and yield components of rapeseed (brassica napus l.) as the second crop after rice to plant density and weed interference duration

in order to determine the responses of morphological characteristics, yield and yield components of rapeseed (brassica napus l.) to plant density and weed interference duration, a factorial experiment was conducted using a randomized complete block design with 3 replications at the rice research institute of iran (rrii) in rasht, in the 2008 growing season. the factors comprised plant density at 2 levels (80 and 57 plants m2) and weed interference duration at 7 levels (including weed competition with canola until the end of crop emergence, 2, 4, 8 leaf stages, and formation of flower buds). after the above mentioned growth stages, weeds of each treatment were removed manually until harvest. two check treatments including weedy and weed free were also selected as control. the traits evaluated in this research were plant height, number of secondary branches plant1, height of the lowest pod bearing branch, pod length, pod number plant1, grain number pod1, 1000 grain weight and grain yield. the results indicated that plant density, weed interference duration and their interaction had significant effects on all traits except pod length. in addition, the 1000 seed weight showed significant response to separate effect of each factor, but was not influenced by their interaction. the highest value of grain yield was related to a density of 80 plants m2 on total weed free check (full season weed free) and the lowest value of this trait was obtained from a density of 57 plants m2 on weedy check (fullseason weed infested) treatment.