SUMMARY

This research was carried out to determine the seed yield and some yield components of two dwarf hybrids compared with one standard height sunflower hybrid (Helianthus annuus L.) at different nitrogen rates and planting densities under natural rain fed conditions at the Thrace Agricultural Research Institute in Edirne-Turkey between 1999 and 2001. The experiments were set up in split-split plots in randomized Complete Block Design with three replications. Main plot treatments were three different height sunflower hybrids, DW-1, DW-2, and Trakya-80. The sub plots were three levels of nitrogen, 0, 60, and 120 kg N/ha. The sub-sub plots were three planting densities, 10X70 (142.850 plant/ha), 15X70 (95.230 plant/ha), and 20x70cm (71.430 plant/ha). Observations were taken on seed yield, oil content, oil yield, 1000 seed weight, test weight, seed hull rate, plant height, head diameter, time to flowering, and time to physiological maturity.

Nitrogen fertilizer increased significantly seed yield, oil content, oil yield, seed hull rate and head diameter of three different height sunflower hybrids in natural rain fed conditions. Based on marginal economical analyses, optimum economical seed yield from per ha was obtained at 50 kg N/ha for DW-1, 80 kg N/ha for DW-2 and Trakya-80 hybrids.

Increasing plant densities of three different height sunflower hybrids decreased 1000 seed weight, seed hull rate and head diameter but increased test weight in natural rain fed conditions. The highest seed yield was obtained on 15x70 cm (95.230 plant/ha) plant population for both dwarf hybrids.

The results of this research show that nitrogen and plant density have significant effects on seed yield and some yield components of different height sunflower hybrids.

Key words: Sunflower, dwarf, nitrogen, plant density.