evaluation the effects of seeding rate and delaying sowing dates on yield and yield companents of three winter rapeseed cultivars.

In order to study the effects of delayeing sowing date and seeding rate on on Yield and Yield Components in three winter rapeseed (Brassica napus L.) cultivars, two field experiment was carried out as split-split plot arrangement in complete block design with three replications in agricultural research station of Agricultural and Natural Resources Research Center of Markazi Province, Arak (Iran) during 2006-2008 growing seasons. Three rapeseed cultivars (Okapi, Modena and Licord), three sowing dates (October 2, 12 and 22) and three seeding rate (6, 8 and 10 kg/ha) were randomized in main plot, subplot and sub-subplot respectively. Rapeseed cultivars had significant differences for all traits except seed oil content (%). Licord cultivar had the highest grain yield, lOOO-seed weight, seed number per pod, pod number per plant, plant height, days to end flowering, length of flowering, days to maturity, length of maturity, oil yield. Modena cultivar showed the highest pod number per plant, second branch number per plant, seed oil content (%) and the least 1000- seed weight, seed number per pod respectively. Okapi cultivar had the least grain yield, pod number per plant, plant height, second branch number per plant, days to initial flowering, days to end flowering, days to maturity, oil yield. There were significant differences among sowing dates for grain yield (P:sO.O 1). The first sowing date, had superiority to other sowing dats for all traits except length of flowering. The ieast grain yield (1723 kg/ha), 1000-seed weight (3.34 g), seed number per pod (22.01), pod number per plant (70.34), plant heigth (110.8 em), second branch number per plant (2.92), days to end flowering (244.79), length of maturity (29.22), seed oil content (45.5%), oil yield (806 kglha) was obtained on third sowing date and delaying sowing datc declined grain yield, oil yield. The interaction effect between sowing date*cultivar was significant for 10aO-seed weight and pod number pcr plant at 5% and I % probability level respectively. The interaction effect between cultivar*seeding rate for seed number per pod, pod number per plant and second branch number per plant was significant at I % probability level. The interaction effect between sowing date*seeding rate was significant for grain yield, seed number per pod, pod number per plant, plant height, second branch number per plant, length of flowering and oil yield at 1 % probability level. Also the interaction effect between cultivar*sowing date* seeding rate was significant for seed number per pod, pod number per plant, plant height and second branch number per plant at 1 % probability level. There was positive and significant correlations between grain yield and the most traits such as 1 aaO-seed weight, seed number per pod, pod number per plant, plant height, second branch number per plant, days to maturity, length of maturity, seed oil content (%), oil yield, except days to initial flowering and days to end flowering but correlation coefficient between grain yield and length of flowering was negative and significant. Keywords: Delaying Sowing Date, Seeding Rate, Quantitative and Qualitative Traits, Rapeseed