Introduction

Sesame (Sesamum indicum L.) is one of the important oilseed crops in warm and dry regions due to its high oil content, desirable fatty acid composition, and relative tolerance to drought stress. However, most sesame cultivars currently grown in Iran are dehiscent types, and seed shattering at maturity limits mechanical harvesting and causes considerable yield losses. Indehiscent sesame cultivars can reduce seed losses and provide better opportunities for mechanized harvesting and expansion of sesame cultivation. Achieving high yield in these cultivars requires appropriate management of agronomic factors, particularly plant density and nutrient management. Optimum plant density improves the efficient use of environmental resources and increases biomass production, while humic acid application can enhance root growth, nutrient uptake, and plant performance through improving soil properties. Considering that no comprehensive study has been conducted on the interaction between suitable plant density and optimum levels of organic fertilizer application for improving quantitative and qualitative yield of indehiscent sesame under the conditions of Khuzestan province, this study was carried out in 2021 in Behbahan, Khuzestan province, to evaluate the effects of plant density and humic acid application on growth characteristics, yield, and yield components of indehiscent sesame.

Materials and methods

This experiment was conducted during the 2021 growing season in Behbahan, Khuzestan province, Iran. The experiment was arranged as a factorial experiment based on a randomized complete block design with three replications, in 2021. The experimental treatments consisted of four plant densities (30, 40, 50, and 60 plants m⁻²) and four levels of humic acid application (0, 3, 6, and 9 L ha⁻¹). Morpho-physiological traits, yield components, seed yield, and oil yield were measured and statistically analyzed. The sesame cultivar used in this experiment was a non-shattering type named "Mohajer." This cultivar is single-stemmed and features an average yield of approximately 1 ton per hectare and a thousand-seed weight of about 3.5 grams, with a seed oil content ranging from 47% to 50%. Statistical analysis, including the assessment of residual normality, analysis of variance, and mean comparison, was performed using SAS v9.4 software. Mean comparisons were conducted using the LSD test at a 5% significance level. Graphs were plotted using Excel software.

Results and discussion

Statistical analysis results showed that the experimental factors investigated in this study had a significant effect on most morpho-physiological traits and the yield of the indehiscent sesame cultivar 'Mohajer'.The highest Grain yield (1252 kg ha⁻¹) was obtained at the planting density of 60 plants m⁻², whereas the lowest yield (763 kg ha⁻¹) was recorded at 30 plants m⁻². In addition, application of 6 L ha⁻¹ humic acid resulted in the highest Grain yield (1194 kg ha⁻¹) and oil product (412.8 kg ha⁻¹). The interaction between planting density and humic acid level had a significant effect on capsule length and plant height. The greatest capsule length (2.4 cm) and plant height (143 cm) were observed in the combination of 60 plants m⁻² and 6 L ha⁻¹ humic acid, while the lowest capsule length (1.4 cm) and plant height (109 cm) were recorded under 30 plants m⁻² and the control treatment (no humic acid application).

Conclusions

Sesame yield and yield components were influenced by planting density and humic acid application; a density of 60 plants per square meter combined with a foliar application of humic acid at a rate of 6 liters per hectare elicited a positive response from the plant. Increasing plant density and applying humic acid resulted in significant increases in grain yield, oil yield, and biological yield. Furthermore, the number of seeds per unit area, leaf area index, plant height, and capsule length also increased significantly in response to these treatments. Overall, the results indicated that optimizing plant density combined with humic acid application can play an effective role in improving quantitative and yield-related traits. The highest grain and oil yields were achieved at a density of 60 plants per square meter with a humic acid application rate of 6 liters per hectare. Therefore, the foliar application of humic acid and the selection of an appropriate planting density for shatter-resistant sesame can effectively increase grain production, biological yield, and oil yield. In summary, a density of 60 plants per square meter combined with an application rate of 6 liters per hectare is the best recommended treatment.