Effects of soil fertility methods on the quantitative yield and oil of medicinal plant black cumin (Nigella sativa L.)

To investigate the effects of soil fertility methods on the quantitative yield and oil of medicinal plant black cumin (Nigella sativa L.), an experiment was conducted in a randomized complete blocks design with three replications. Experimental treatments included different levels of NPK chemical fertilizers, different levels of manure, combination of NPK+manure, and combination of NPK+manure with Azorhizobium biofertilizer inoculation. The results showed that plant nutrition increased plant height, plant dry weight, number of lateral branches, leaf area index, number of capsules per plant, number of seeds per capsule, grain yield, biological yield, relative leaf water content, and percentage and oil yield. The highest quantitative and qualitative characteristics were obtained in the chemical nutrition in the treatment of NPK: 120-96-120 (kg ha-1) and in the manure nutrition in the treatment of manure: 20 ton ha-1. In the chemical+manure combined method, the treatment of NPK: 40-32-40 (kg ha-1)+manure: 30 ton ha-1 was the best one. In the chemical+manure+biological combined method, the treatment of manure: 30 ton ha-1+ Azorhizobium+ NPK: 40-32-40 (kg ha-1) was observed as the most appropriate treatment. Overall, the combined treatment of NPK: 40-32-40 (kg ha-1) + manure: 30 ton ha-1+ Azorhizobium had the most positive effect on improving the biological yield and black cumin oil percentage, which also had the lowest amount of chemical fertilizer.