The effects of different organic fertilizers on yield and quality in black cumin (Nigella sativa L.) cultivation

This research was carried out in Tokat Gaziosmanpaşa University Agricultural Research and Application Farm during the 2022 and 2023 growing seasons. The goal of this research is to investigate the effects of various types and application rates of organic fertilizers on the yield and quality characteristics of black cumin (Nigella sativa L.). The experiment followed a Split Plot Design in Randomized Blocks with three replications. The 'Çameli' variety of Nigella sativa L. was used as the plant material in the experiment. The main plots were assigned five types of organic fertilizers: leonardite, vermicompost, solid humus, chicken manure and sheep manure. Each fertilizer type was applied at four different rates (0, 150, 300, and 600 kg/da) in the subplots. Additionally, urea (46% N) was used as a chemical fertilizer at rates of 0, 4, 8, and 12 kg/da for comparison. Key parameters evaluated over both years included plant height (cm), number of branches per plant, number of capsules per plant, number of seeds per capsule, thousand seed weight (g), seed yield (kg/da), biological yield (kg/da), harvest index (%), fixed oil content (%), oil yield (kg/da), fatty acid composition (%), essential oil content (%), essential oil yield (kg/da), essential oil components (%), thymoquinone content (%) and antioxidant activity (measured by DPPH, FRAP and TEAC methods in µmol TE/g seed). The results showed that plant height ranged from 39.76 to 54.33 cm, branches per plant from 6.22 to 6.35, capsules per plant from 13.43 to 14.88, seeds per capsule from 98.56 to 104.00 and thousand seed weight from 2.50 to 3.11 g. Seed yield varied between 135.26 and 135.41 kg/da, biological yield between 433.31 and 445.91 kg/da, and harvest index between 30.26% and 30.94%. Fixed oil content ranged from 26.17% to 26.19%, oil yield from 35.52 to 35.63 kg/da, essential oil content from 0.24% to 0.59% and essential oil yield from 0.36 to 0.80 kg/da. Thymoquinone content ranged from 36.82% to 41.75%, linoleic acid from 57.17% to 58.02%, palmitic acid from 22.81% to 30.20%, oleic acid from 11.78% to 15.35% and stearic acid from 0.07% to 4.59%. Antioxidant activity ranged from 11.30 to 17.09 µmol TE/g (DPPH), 37.94 to 60.52 µmol TE/g (FRAP) and 59.25 to 59.44 µmol TE/g (TEAC). Statistical analysis revealed significant differences (p<0.01) across all measured traits. Among the treatments, chicken manure at 300 kg/da resulted in the highest yield, while sheep manure and vermicompost at 600 kg/da positively influenced quality parameters. These findings suggest that organic fertilizers can serve as effective alternatives in black cumin cultivation, enhancing both yield and quality while supporting environmentally and economical sustainable agricultural practices.