In order to study the effect of sowing date and plant density on growth analysis and seed yield, of two winter rapeseed varieties, an experiment was conducted in karaj in 1994. A split- split plot design with four replications was used. Four sowing dates, from 16.9.93 at ten day intervals , two winter rapeseed varieties (Belinda and Ceres ) and three planting density (40,80 and 120 plant/rn2) were carried out. There was a significant difference between the date of sowing for plant height and seed yield .Late sowing decrease the plant height, total dry weight, crop growth rate and seed yield. Both varieties showed significant differences for plant height and seed yield. Belinda variety was superior to Ceres variety for plant height , total dry weight and crop growth rate, but Ceres was superior to Belinda for ralative growth rate and seed yield . In this study, it was found that the Belinda variety with 264 days of growth period requires about 2900 thermal units and Ceres with 266 days needs about 2950 thermal units in Karaj region. There was a significant difference between the levels of density for plant height and seed yield . Plant density with 40 and 80 plant /m2 showed higher and lower total dry weight respectively. Plant density of 40 and 80 plant /m2 had higher and lower crop growth rate , while plant density with 80 and 120 plant/rn2 showed highest and lowest of seed yield respectively.
)