Evaluation The Effects of Planting Date on Some Growth Indices and Grain Yield of Two Oil Sunflower Cultivars in Damghan Province

A factorial experiment of randomized complete block design with 4 replications was designed in 2002 at Islamic Azad University experimental station in Damghan Branch to evaluat the effects of planting Date on some growth indices and grain Yield of two oil sunflower cultivars in damghan province. The results showed that the variation pattern of total dry matter accumulation, leaf area index, crop growth rate, relative growth rate and net assimilation rate of two cultivars was the same at all planting dates. The Record cultivar had the highest dry matter accumulation (1258 gr) and the highest leaf area index (4.67) in all planting dates. Increases in to total dry matter accumulation accelerated after 600 GDD and reached it’s maximum at 1700 GDD. The maximum and minimum amount of total dry matter accumulation and leaf area index of both cultivars were obtained from planting date of 7 May and 2 June, respectively. Both cultivars had the highest value of crop growth rate at planting date of 7 and 21 May and the lowest value at planting date of 24 April and 2 June. There was no difference between them in regard to crop growth rate up to 800 GDD. But the decrease in Zaria crop growth rate started soon that of Record cultivar. Realative growth rate of both cultivars reached Zero at 1400 GDD. The maximum relative growth rate of both cultivars obtained at planting date of 7and 21 May but the minimum of it's at 24 April and 2 June planting date. Net assimilation rate had a mild increase up to 600 GDD and then after a faster rate it reached to Zero at 1200 GDD. The maximum (4237.9 kg/ha) and the minimum (3490.5 kg/ha) grain yield were obtained from 7 May and 2 June planting dates,respectively. The grain yield of Record cultivar was % 14.8 higher than Zaria cultivar.There was a positive correlation between grain yield with leaf area index and crop growth rate. According to the condition of experiment and the earned result, it can be suggested that the Record cultivar, because of highest total dry matter, leaf area index and grain yield, is a more suitable cultivar to be planting dates at 7 and 21May in Damghan province.