Evaluation of growth, yield and yield components responses of black cumin (Nigella sativa L.) to nitrogen and methanol under drought stress

Drought stress is one of the environmental factors that affects the growth, yield and yield components of plants. Nitrogen and methanol play a key role in plant structure and metabolism. Black cumin (Nigella sativa L.) is one of the medicinal plants in the family of Ranunculaceae. The seed of Nigella sativa plant has been used since long to protect health and combat different diseases and its frequent application in the pharmaceutical industry. The plant is cultivated in different parts of Europe and Asia including Iran. The purpose of this study was to investigate the responses of growth indices and yield of the black cumin to nitrogen and methanol under water stress conditions.

Healthy seeds of black cumin were provided from Medicinal Plants Research Center, Shahed University. The experiment was a split split-plots study based on randomized complete block design with three factors and three replicates. The experiments were conducted in the farm of Zanjan University, Faculty of Agriculture (36° 41’ N latitude, 48°27’ E longitude, and altitude of 1620 m) during the year farming in 2019-2020. The factors were drought stress with 4 levels (control irrigation, irrigation at 80% soil capacity, irrigation at 60% soil capacity, irrigation at 40% soil capacity) as the main plots, nitrogen with 4 levels (control, 30, 60 and 90 kg per hectare) as the sub-plots and methanol with 3 levels (0, 10 and 30%) as the sub-sub-plots. In fact, for each level of methanol, two g l-1 glycine and one g l-1 tetrahydrofolate as catalysts and one g l-1 tween80 were added to increase the adhesion of methanol solution. In both areas, soil preparation, including plowing, leveling and paving was performed before planting. Black cumin seeds were weighed in the amount of 4 g and the seed was evenly distributed.
At the time of complete ripening, after removing the marginal effects, a random sample was selected from each plot and the plant height, root length crop growth rate (CGR) were measured.
Also, after the final ripening, sampling was done to determine the grain yield after removing the marginal effects and one square meter was taken from each experimental unit and the number of plants per square meter was counted and then the seeds were separated from the plants and weighed and then reported in kg ha-1. To measure yield components (number of capsules per plant, number of seeds per capsule and 1000-seed weight) at the time of harvest, 5 plants were randomly selected from each experimental unit and the number of capsules was counted and then the seeds were taken out of the capsules. To measure the weight of 1000 seeds from the harvested seeds related to grain yield, three thousand samples of seeds were counted and then weighed and their mean as 1000 seeds weight and were used for data analysis.

The results showed that with increasing irrigation stress, plant growth indices and yield decreased, while with increasing nitrogen and methanol concentrations, growth indices and yield increased. In total, application of 10% methanol and 30 kg ha-1 nitrogen increased root length plant height by 9 and 16% compared to the control treatment. The results showed that the triple interaction of control irrigation, application of 30 kg ha-1 nitrogen and 10% methanol increased crop growth rate by 17.44% compared to control treatment. The highest grain yield by interaction of without irrigation stress and application of 90 kg ha-1 nitrogen and application of 10 percent methanol in the amount of 715.40 g were observed. Application of high levels of nitrogen and methanol under severe stress reduced grain yield, while application of lower levels of nitrogen (30 kg ha-1) and methanol (10%) increased grain yield, and the triple interaction of non-stress irrigation, application of 90 kg ha-1 nitrogen and 10% methanol caused a significant increase in grain yield (3.6%).

The results showed that severe drought stress by reducing plant height, root length, crop growth rate, number of seeds per capsule and number of capsules per plant could reduce grain yield in black cumin and methanol application, especially at the level of 30%, with a positive effect on source strength (leaf area index) and reservoir strength (number and size of seeds) as well as root length, was able to increase black seed grain yield under water stress. The maximum crop growth length was obtained by triple interaction of control irrigation, application of 30 kg ha-1 nitrogen and 10% methanol foliar application at 35.31 g m-2 day and according to the importance and economic value of black cumin plant in the pharmaceutical industry The use of this treatment is recommended for producers of this plant.