Response of Spring Wheat Cultivars to Different Fall Sowing Dates in Neishabour

In order to determine the optimum sowing date for different spring wheat cultivars, a field experiment was conducted in Neishabour during 2003/04 and 2004/05 cropping seasons, using a split plot based on a randomized complete block design with three replications. Five sowing dates of Oct. 7(D1), Oct. 22(D2), Nov. 6(D3), Nov. 21(D4) and Dec. 6(D5) were assigned to main plots and sub-plots were consisted of eight spring wheat cultivars, Marvdasht, Cross Arvand, Mahdavi, Pishtaz, Falat, Shiraz, Chamran and BC Roshan. Results of combined analysis of variance indicated significant differences between many of traits and grain yield of planting dates and between cultivars. Due to temperature fell down below zero (-7  C) in April of the second year, and severe damage imposed to early sowing date, results between two years were completely different. Mean grain yield in first and second years, were 6600 and 6417 kg/ha, respectively that showed weather was desirable in first year. Stepwise regression showed No. of spike/m2, date of heading and No. of grain/spike determined 73% of grain yield in first year, and HI, plant height and No. of spike/m2 explained 70% of grain yield in second year. Partial coefficient of determination showed No. of spike/m2 in the first and the second years were 63 and 4% respectively, that indicated freezing at second year caused tillers were similar uniform with no difference between tillers. In general, results showed that for the best performance, date of sowing was Nov. 6 and Shiraz was the best cultivar, because the highest grain yield was obtained in this combination.