THE EFFECTS OF SOWING DATE ON GROWTH, SEED YIELD AND OIL CONTENT OF SUNFLOWER (HELIANTHUS ANNUUS L.) CULTIVARS UNDER RAINFED CONDITIONS
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This study was conducted at Research Farm of Ahi Evran University in Kirehir Province of Turkey in 2012 and 2013 to determine effects of sowing date on yield and agronomic characteristics of sunflower hybrid cultivars in rainfed conditions. Five sowing dates 10 days apart set on 10th April, 20th April, 1st May, 10th May and 20th May and 6 hybrid sunflower cultivars (LG-5580, SanayMr, SanbroMr, Sirena, Tarsan and Transol) were used. The study was taken place in both rainy (2012) and dry (2013) warm conditions due to different weather. In this way, the effects of both sowing dates and extreme climatic conditions were tested. Sunflower yield and yield components were higher in 2012 than 2013, except dehulled/hulled seed weight and oil content. When sowing date was delayed, seed and oil yields declined. The highest plant height (151.18 cm), 1000-seed weight (51.72g), crude oil content (46.18%), seed yield (2.55 t ha(-1)) and oil yield (1.18 t ha(-1)) were obtained on the second sowing date (20th of April) while the highest ratio of dehulled/hulled seed weight (70.04%) and head diameter (20.49 cm) were obtained on the first sowing date (10th of April) in 2012. However, the first sowing date in early April resulted in higher yield and agronomic characteristics than delayed sowing due to a decrease in rainfall during the growing period of both research years. SanbroMr cultivar in the first year and Transol cultivar in the second year reached the higher yields with best yield components. In conclusion, by considering the spring last frost date, the sowing date of 20th April provided significant improvements in yield and yield parameters due to the longer growing season with suitable soil moisture, allowing sufficient time for vegetative growth and head and achenes filling.