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Evaluation of Foliar Application of Sulfuric Acid, Humic Acid, and Potassium Nitrate on Seed Yield and Some Physiological Indices of Pot Marigold (Calendula officinalis L.)
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Parasto Nourelahi   , Alireza Abdali Mashhadi , Ahmad Koochekzadeh * , Mohamad Hossain Gharineh |
| Plant Production and Genetics Department |
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Abstract: (147 Views) |
Marigold (Calendula officinalis L.) is an ornamental plant also valued for its medicinal compounds and seed oil. In calcareous soils with high pH, nutrient uptake is restricted. Sulfuric acid increases the solubility of elements by reducing soil pH. Humic substances enhance plant performance by chelating nutrients and improving photosynthesis. Potassium is also effective through enzyme activation and stress mitigation. This study aimed to investigate the effects of potassium nitrate, sulfuric acid, and humic acid on the reproductive and some physiological indices of marigold. The experiment was conducted as a split-plot factorial arranged in a randomized complete block design with three factors and four replications at the Agricultural Sciences and Natural Resources University of Khuzestan. The factors were: potassium nitrate at three levels (control, 250, and 500 mg·kg⁻¹ soil), sulfuric acid at two levels (control and 5 L·ha⁻¹), and humic acid at two levels (control and 16 kg·ha⁻¹). The results showed that the highest plant dry weight (574 g·m⁻²), seed yield (343 g·m⁻²), and seed oil yield (49.9 g·m⁻²) were obtained with the combined application of 500 mg·kg⁻¹ potassium nitrate and 16 kg·ha⁻¹ humic acid, indicating their synergistic effect on nutrient uptake. The highest SPAD chlorophyll index (39.7) was observed under the combined treatment of sulfuric acid and humic acid. The three-way interaction of all factors increased plant fresh weight to 3791 g·m⁻², confirming the pivotal role of humic acid in enhancing biomass. It is concluded that the integrated application of potassium nitrate, sulfuric acid, and humic acid improves soil conditions, nutrient uptake, and microbial activity, thereby enhancing the growth traits, seed yield, and oil yield of marigold.
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| Keywords: Calcareous soil, Harvest index, Seed, Soil pH |
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Type of Study: Research |
Subject:
Special
Received: 2026/04/25 | Accepted: 2026/05/16 | Published: 2026/05/16
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