Effects of sowing date on the process of allocation of material photosynthesis on yield in direct seeded rice cultivars

In order to evaluate of sowing date on phonology and panicle development of rice cultivars in direct seeding condition. Four seeding date as 30th of April and 10، 20، 30th of May and three cultivars as Hashemi، Tarom and Elpaso were arranged in a split plot design as based on RCBD in 2007 with four replications. The results indicated that seeding date had significant effect on traits of productivity effort، days to panicle emergence، days to 50% panicle initiation، grain filling period، panicle weight and total plant dry weight. The second sowing date with a 25. 17 had the highest grain filling duration and had the highest operation in the amount of 5029 Kg/ha. All traits had affected by cultivar treatment. Tarom cultivar had the most seed filling duration (25. 88 days) and highest yield in the amount of 4444 Kg/ha. Cultivars and planting date interaction was significant in days to ear emergence، days to 50% panicle initiation، panicle weight، total plant dry weight and productivity effort. Elpaso cv had the highest days to panicle emergence (93. 75 days)، days to 50% panicle initiation (101 days) in the first planting date. It produced the highest panicle weight (681 g. m-2) and total dry matter (1139 g. m-2) in the second planting date and it was superior in productivity effort (0. 63) than others. Tarom cv had the highest grain filling duration (27. 50 days). Elpaso cv had the highest assimilate partitioning، because it had the highest productivity effort and grain filling rate. Because the sowing dates was considered based on temperature and time of harvest، the best sowing date، the second sowing date and best cultivar، cultivar Elpaso suggested. Because it have allocated the highest yield.