Performance reaction and biochemical properties of black cumin under the influence of different regimes of nitrogen, menthol and drought stress

The purpose of this study was to investigate the responses of growth indices and yield of the black cumin to nitrogen and methanol under drought stress conditions. The experiment was a split split plots based on randomized complete block design with three factors and three replicates in the research farm of Medicinal Plants Research Center, Shahed University, Tehran, Iran, during 2019– 2020. The factors were drought stress with 4 levels (non-stress, mild, moderate, and severe) as the main factor, nitrogen with 4 levels (0, 30, 60, and 90 kg ha -1 nitrogen from the source of urea) as the sub-factor and methanol with 3 levels (0, 10, and 30%) as sub-sub-factor. Nitrogen treatments (except the 0 level) were each applied in three stages of black seed growth: 1) one-third at the same time as planting, 2) one-third at the stage of 4–6 leaves, and 3) one-third at the beginning of flowering. Methanol foliar application was done once at the first capsule formation stage and again at an interval of seven days later. Two days after the second time of methanol spraying, the data on biochemical traits (chlorophyll, proline and protein contents) and in the end of generative stage, agronomical (seed yield) and phytochemical compounds were measured. The results indicated that main effects and interactions significantly affected all biochemical traits and yield. The results showed that the yield under drought stress conditions decreased (11.67%) in comparison to the control, while the yield increased (5.7%) in comparison to control by applying the nitrogen and methanol. The interaction of methanol and nitrogen had significant effects on the amount of grain yield, chlorophyll, proline, protein, carotenoid contents and oil of seed. The results indicated that the interaction of drought stress-nitrogen, drought stress-methanol and nitrogen-methanol had significant effects on chlorophyll, proline, protein, carotenoid contents, oil seed and yield. The results showed the highest seed oil (717 kg/ha) in the interaction of without drought stress, 90 kg/ha nitrogen. Therefore, the application of 10% methanol and 90 kg/ha nitrogen under drought stress was the most effective treatments on increasing the yield and phytochemical compounds in black cumin.