Introduction
The production of oilseeds is very important in the economy of every country, because the consumption of oil in the world has an upward trend, so that it is predicted that by 2030, the global need for edible oil will reach one billion kilograms. Sesame, as an annual oilseed plant, is widely cultivated in arid and semi-arid regions of the world. Although sesame is more drought tolerant than other oilseeds, its production is affected by high levels of drought stress. In general, the results of various researches show that sesame reacts to water stress and its sensitivity to drought stress should be evaluated accurately. Since the effects of deficit irrigation during the sesame flowering stage have not been well investigated, in the present study, an attempt has been made to investigate the effect of drought stress on sesame production, and the possible effects of humic acid and silicon foliar application in reducing the negative effects of drought stress.
 
Materials and Methods
The experiment was conducted as split factorial based on RCBD with three replications. The experiment factors were irrigation (I₁: full irrigation and I₂: irrigation interrupting at flowering stage) in main plot and humic acid and silicon as sub plot. Three levels of humic acid (0.0, 3.0 and 6.0 kg ha^-1) and silicon (0.0, 1.0 and 2.0 mM) were employed. At maturity, grain yield and related traits including, capsule number per plant, grain number per capsule, 1000-grain weight, plant height, biological yield, harvest index, oil yield and protein yield were measured. To measure oil yield, seed oil percentage was first measured (using Soxhlet apparatus) and then the indices of seed oil percentage and seed yield were used. Seed protein percentage was also measured using Kjeldahl apparatus.
 
Results and Discussion
Under irrigation interrupting at flowering stage, water consumption decreased by 36% and seed protein increased by 10%. Water deficit stress decreased the number of capsules per plant, number of seeds per capsule, plant height, 1000-grain weight and grain oil by 12.5, 32, 26, 9 and 7%, respectively. The highest number of capsules per plant, number of seeds per capsule, plant height, biological yield, oil percentage and seed protein percentage were recorded in the foliar application of 6 kg ^-1 of humic acid, which were 20%, 52%, 64%, 18%, 4% and 11% more than that of no humic acid application treatment, respectively. Similar results were recorded for the consumption of 2 mM silicon where silicon foliar application led to the improvement of indicators related to the yield and quality of sesame seeds. The highest number of capsules per plant, number of seeds per capsule, plant height, harvest index, oil percentage and seed protein percentage were obtained with the consumption of 2 mM silicon, which is 21, 26, 38, 6, 4 and 13% more than the treatment which did not use silicone. The use of 6 kg ^-1 of humic acid and 2 mM silicon increased the yield of oil and protein by 60 and 82%, respectively. The highest water productivity of sesame water (0.756 kg m^-3) was obtained in the treatment of interruption of irrigation and consumption of 6 kg ^-1 of humic acid and 2 mM silicon. Finally, it can be stated that the consumption of two 6 kg ^-1 of humic acid and 2 mM silicon can reduce the effects of water shortage stress on sesame.
 
Conclusion
In this study, applying limited irrigation reduced the production of sesame seeds and oil (by 25 and 30%, respectively). However, since in the drought stress treatment, water consumption was lower than in full irrigation, the water productivity for seed production increased by 58% in the treatment of interruption of irrigation. Humic acid and silicon increased the tolerance of sesame to drought and improved seed yield and related traits. According to the fact that in the present study, the interruption of irrigation was necessarily applied in the flowering stage based on the conditions of the region, it is necessary to investigate the effects of interruption of irrigation in the vegetative growth stages in order to support the idea that probably the interruption of irrigation in the vegetative growth stage increases water productivity in sesame without serious impact on seed yield, gave a more accurate answer.