evaluation of sowing date influence on quantitative and qualitative yield in four rapeseed cultivars adapted to cold regions in arak, iran

in order to evaluate the influence of different sowing dates on quantitative and qualitative yield in four winter rapeseed cultivars (brassica napus l.), two field experiments were carried out as split plot arrangement in complete block design with four replications. this research was performed in agricultural experimental station of agricultural and natural resources research center of markazi province, arak (iran) during growth seasons 2007-2008 and 2008-2009. four planting dates (september 11, 21 and october 1 and 11) and four canola cultivars (licord, opera, okapi and modena) were randomized in main plot and sub-plot, respectively. results showed that at the second sowing date, plants produced the most grain yield (4518 kg ha-1). the least grain yield (3786 kg ha-1) was obcained the fourth sowing date. the delayed sowing dates decreased grain yield due to decrease of pod number per plant. in this research, modena cultivar had more seed yield in comparison with other cultivars due to genetic diversity and high using of sources such as nutrient elements, soil moisture and solar radiation. the best sowing date forarak region was september 11 to october 1.