Effect of sowing date on yield and yield components of sunflower(Helianthus annus L.)

High yields of grain and sunflower oil need to match of vegetative and reproductive growth stages of the plant with favorable weather conditions by selecting appropriate sowing date. A split plot experiment, according a randomized complete block design (RCBD) with three replications was performed in the research field of Scientific and Practical Center, Education Complex of Jahad-Agriculture of Hamedan, Iran in 2012. Main plot were sowing date (20 May, 5 and 20 June) and sub-plots were six sunflower cultivars (Pomar, Euroflor, Master, Sirna, Azargol and Armaviruski). Results showed that between cultivars, was significant for grain yield, biological yield, head diameter, stem diameter, stem height, grain empty percent, head dry weight, dry weight of stems and leaves. Grain yield of Euroflor (556.3 g m-2) was the most of the other varieties. The superiority of this variety was due to increased diameter and dry weight of head, stem diameter and biomass. Study planting dates showed that between cultivars was no significant for grain yield, but with delayed planting, decreased stem diameter. The effect of sowing date was significant difference for thousand-grain weight and number of grains per head, so that delays in planting increased grain weight. That was due to reduced number of grains per head.