Responses of sunflower (Helianthus annuus L.) to irrigation and nitrogen fertilization rates

This study was conducted to determine the effects of different nitrogen rates (0, 40, 80, 120, 160, 200 and 240 kg ha -1 N) on the yield, its components and the quality characters of sunflower (Helianthus annuus L.) and to identify the economic optimum N rate for maximum profit under both irrigated and non-irrigated conditions during a 2-year period (2007)(2008). As the N rates increased, all of the traits measured significantly increased, except the crude oil content, under both irrigation treatments. Based on the 2-year average, the highest seed yield (2713.6 to 2751.2 kg ha -1 ) and crude oil yield (1012.7 to 1042.5 kg ha -1 ) were obtained using 160 kg ha -1 N and the higher N rates, with increases of 47.8% and 39.4%, respectively, compared to the control (0 kg ha -1 N). Similar trends were also obtained for the other traits, except the crude oil content, which was the highest (39-41%) at 0 kg ha -1 N but the lowest (36-38%) under the higher N rates. The highest mean values for the crude protein content and 1000-seed weight were obtained under the highest N rates (200 and 240 kg ha -1 N). In 2007, the economic optimum nitrogen rate (EONR) for sunflower was 148.5 kg ha -1 N under non-irrigated conditions, as compared with 190.0 kg ha -1 N with irrigation. In 2008, the EONRs for sunflower under non-irrigated and irrigated conditions were 145.1 and 176.7 kg ha -1 N, respectively. Although the EONR for irrigated conditions was approximately 30-40 kg ha -1 N more than that for non-irrigated conditions, the seed yield under the irrigation conditions was approximately 65-79% higher compared with the non-irrigated conditions. As a result, it was determined that the economic optimum N rate for sunflower was 145-150 kg ha -1 N under non-irrigated conditions and 177-190 kg ha -1 N under irrigated conditions.