Effect of water stress and amount of nitrogen fertilizer on grain yield, yield components, essential oils and thymoquinone content in Black Cumin (Nigella sativa L.)

Effects of water stress on plants are complex and depend on the developmental stage and their growth stages. Limitation of the amount of moisture in the soil will be adversely affected plants yield through reductions in photosynthesis, leaf area production, nutrient absorption and assimilates transportation to grains. To evaluate effects of water stress applied at various growth stages combined with different nitrogen fertilizer amounts on grain yield, yield components, essential oil and thymoquinone content of Black Cumin (Nigella Sativa L.) a split plot experiment based on RCBD was conducted with three replications in 2011 at Agricultural Research Station, Zahak, located at 20 km south of Zabol. Water stress was considered as the main plot and stress treatments were created by withholding irrigation at different plant growth stages including: W1 (control), W2 (withholding irrigation at stem elongation stage until flowering), W3 (withholding irrigation at flowering stage until the beginning of grain filling) and W4 (withholding irrigation at flowering stage until the termination of grain filling) and four levels of nitrogen fertilizer including N1 (control), N2 (30 kg N.ha-1), N3 (60 kg N.ha-1) and N4 (90 kg N.ha-1) were assigned as sub plots. Results showed that water stress imposed at each growth stage led to a reduction in grain yield of Nigella Sativa. The maximum reduction rate (about 40.9%) was observed at W4 treatment. Water stress significantly reduced the biological yield, number of branches per plant, number of follicles per plant, number of seeds per follicle, number of seeds per plant and 1000- seed weight, whereas significantly increased the essential oil and thymoquinone contents. The maximum impact on all these traits was observed at W4 treatment. Among the nitrogen levels, N3 had the greatest impact on yield, yield components, essential oil percentage and thymoquinone in Nigella Sativa. In this experiment, interaction effect between water stress and nitrogen had only significant impact on essential oil and seed thymoquinone content, while it had no significant effect on all other studied traits. The maximum amount of essential oil and thymoquinone was obtained at W4N3 treatment.