Sunflower-nitrogen calibration based on the amount of mineral nitrogen in soil under rainfed conditions in thrace region

Sunflower is grown under both rainfed and irrigated conditions in all regions to meet the vegetable oil needs of Türkiye, however, in the Thrace region, it is the main rotation crop grown under rainfed conditions after wheat. This study was conducted in the Thrace Region between 2013 and 2016 in order to evaluate the parameters that can be used as an index for nitrogen fertilization recommendations for sunflower plant. For this purpose, organic matter and saturation were determined in soil samples taken from 0-20 cm depth before the experiment and ammonium and nitrate contents were determined in soil samples taken from 0-30 cm, 30-60 cm, and 60-90 cm depths. Within the scope of the study, 27 field trials were conducted over four years. Nitrogen levels of 0 (control), 3, 6, 9, and 12 kg da-1 were implemented in the trials conducted in a Latin square experimental design. In this study, log (279.9-y) = log279.9-0.090b1-0.117x Mitscherlich calibration equations were determined based on 0-30 cm ammonium+nitrate content in the soil.