This research was carried out to determine the effects of six phosphorus (P205) rates and two application time on sunflower (Helianthus annuus L.) seed yield and yield components. The sunflower hybrid used in the experiments was Edirne-87. The research lasted for two years, 1991 and 1992, and it was conducted at the Thrace Agricultural Research Institute in Edirne, Turkey.

The experiments were established in a split plot arrangement in randomized complete block design in three replicates. Phosphorus application times were used as main plots. These were autumn and spring time applications. Six rates of phosphorus were used as sub-plots: 0, 20. 40, 60, 80, and 100 kg/ha P2O5.

Mean values of time to flowering, time to physiological maturity, plant height, head diameter, seed yield/ha, 1000 seed weight, oil content, and oil yield were determined in each plot and analyzed using ANOVA.

According to the two-year results of this research, relationship between sunflower grain yield and phosphorus rates was found significant (R=0.922 ** ) in Edirne conditions. Phosphorus rates can be expressed by following regression equation Y: 1321 + 10.39 X - 0.066 X2. Based on 1996 phosphorus fertilizer and sunflower crop prices for optimum economical sunflower production it was recommended that the application rate of phosphorus should be 70 kg/ha in Edirne conditions.