Univrsity of Tehran Press Iranian Journal of Field Crop Science 2008-4811 56 4 2025 12 22 Foliar Application of Iron, Urea, and Amino Acids on Yield and Yield Components of Safflower (Carthamus tinctorius L.) under Irrigation Withholding during the Reproductive Stage Foliar Application of Iron, Urea, and Amino Acids on Yield and Yield Components of Safflower (Carthamus tinctorius L.) under Irrigation Withholding during the Reproductive Stage 93 103 105089 10.22059/ijfcs.2025.395809.655141 FA Sajad Saedi Department of Agrotechnology, Faculty of Agriculture, University of Tarbiat Modares, Tehran, Iran 0009-0004-5115-1957 Seyed Ali Mohammad Modarres-Sanavy Department of Agrotechnology, Faculty of Agriculture, University of Tarbiat Modares, Tehran, Iran 0000-0003-2037-0271 Ali Heidarzadeh Department of Agrotechnology, Faculty of Agriculture, University of Tarbiat Modares, Tehran, Iran 0000-0001-6680-9257 Hossein Sabourifard Department of Agricultural Science, National University of Skills (NUS), Tehran, Iran 0000-0002-6744-0452 Journal Article 2025 05 25 Introduction. Drought is widely regarded as one of the most critical abiotic stresses that can substantially impair plant growth and productivity, posing a significant threat to global food security. It can lead to a reduction in crop yield by as much as 70%, depending on the intensity, duration, and timing of the stress. The mechanisms through which drought stress affects plants include interference with the uptake and translocation of nutrients, induction of oxidative stress via the overproduction of reactive oxygen species (ROS), and disturbance of vital physiological and biochemical processes such as photosynthesis, stomatal conductance, and carbohydrate metabolism. Safflower (Carthamus tinctorius L.), an oilseed crop characterized by its considerable adaptability to water-deficit conditions, is not immune to such stresses. Particularly during the reproductive phase, drought can cause significant declines in seed yield and associated agronomic traits. In recent years, foliar application of nutrients has gained attention as a potentially efficient and practical approach to enhance plant tolerance to drought, especially in agro-ecological zones like Iran, where water scarcity and nutrient-poor soils often coexist. Among the foliar nutrients, iron, urea, and amino acids have shown promise in enhancing plant resilience against environmental stresses, due to their roles in improving nutrient use efficiency, activating antioxidant defense mechanisms, supporting protein and enzyme synthesis, and ultimately improving growth and yield performance. Materials and Methods. To investigate the potential of foliar-applied nutrients in alleviating the negative effects of drought stress, a comprehensive field experiment was conducted during the 2022–2023 growing season at the research farm of Tarbiat Modares University, Tehran, Iran. The experimental design was a split-plot arrangement within a randomized complete block design (RCBD) with three replications. The main plot factor consisted of three irrigation regimes: (i) full irrigation throughout the season with no water restriction, (ii) water deficit imposed from the onset of the flowering stage (representing early drought stress), and (iii) water deficit imposed from the beginning of the seed-filling stage (representing late drought stress). The subplot factor included nine foliar spray treatments: (1) 6% iron chelate, (2) 1% urea solution, (3) commercial amino acid solution at 1 g L⁻¹, (4) iron + urea, (5) iron + amino acid, (6) urea + amino acid, (7) iron + urea + amino acid (triple combination), (8) distilled water spray (as a spraying control), and (9) no foliar spray (as a negative control). A wide range of morphological and yield-related traits were measured to evaluate the effects of treatments. These traits included plant height, capitulum diameter and length, number of capitula per plant, number of seeds per capitulum, 1000-seed weight, biological yield, straw yield, grain yield, and harvest index. Results and Discussion. The results showed that drought stress significantly affected several yield components, most notably the capitulum dimensions. Capitulum length and diameter were particularly sensitive to water stress. The maximum capitulum length (65.17 mm) was recorded under late drought stress (with water withheld during the grain-filling stage), indicating that safflower plants tend to elongate floral structures under mild terminal drought conditions. In contrast, the minimum capitulum length (41.16 mm) was observed under early drought stress imposed at the flowering stage. Similarly, the highest capitulum diameter (74.26 mm) was recorded in the full irrigation treatment, while the lowest (47.22 mm) was observed when drought was applied during flowering. Interestingly, plant height did not differ significantly among irrigation regimes, indicating that this trait may be less sensitive to short-term water deficits or more genetically stable. The application of foliar nutrients had a considerable effect on reproductive output. The combined application of iron, urea, and amino acids produced the highest number of capitula per plant (7.69), suggesting a synergistic effect among these compounds in promoting flower development and retention under stress conditions. Full irrigation consistently resulted in superior reproductive parameters, including the highest number of seeds per capitulum (99.37) and the greatest 1000-seed weight (79.46 g). Conversely, early drought stress significantly reduced these values to 62.19 seeds per capitulum and 39.09 g for 1000-seed weight, respectively. Total biological yield and straw yield were strongly influenced by both the irrigation regime and foliar nutrient treatment. The highest biological yield (12,328 kg ha⁻¹) and straw yield (10,444 kg ha⁻¹) were obtained from the combined application of urea and amino acids under the late drought stress regime. Notably, this treatment combination also resulted in the highest grain yield (2627.78 kg ha⁻¹), confirming its effectiveness in enhancing crop productivity under water-limited conditions. In contrast, the lowest grain yield (1066.67 kg ha⁻¹) was recorded in the unsprayed control under drought, highlighting the detrimental effects of nutrient deficiency and water stress when unmitigated. Furthermore, the harvest index—a measure of resource allocation efficiency—was the highest under full irrigation and late drought stress, indicating that plants under these regimes were better able to convert assimilates into economic yield. Conclusion. The findings of this study underscore the critical importance of mitigating drought stress during sensitive phenological stages such as flowering and seed filling in safflower cultivation. While drought during flowering proved particularly harmful to yield components, the strategic use of foliar nutrients was effective in alleviating the negative impacts of water stress. Among the tested treatments, the combined application of iron, urea, and amino acids showed the most promising results, particularly when the stress occurred at the grain-filling stage. This integrated foliar fertilization approach enhanced not only morphological traits and reproductive parameters but also led to significant improvements in grain yield and biomass production. Given the increasing frequency and severity of drought in arid and semi-arid regions, this research provides valuable insights into sustainable agronomic practices for maintaining safflower productivity under water-limited conditions. Future studies may explore the physiological and molecular mechanisms behind these improvements and evaluate the economic feasibility of large-scale implementation in different agro-climatic regions Introduction. Drought is widely regarded as one of the most critical abiotic stresses that can substantially impair plant growth and productivity, posing a significant threat to global food security. It can lead to a reduction in crop yield by as much as 70%, depending on the intensity, duration, and timing of the stress. The mechanisms through which drought stress affects plants include interference with the uptake and translocation of nutrients, induction of oxidative stress via the overproduction of reactive oxygen species (ROS), and disturbance of vital physiological and biochemical processes such as photosynthesis, stomatal conductance, and carbohydrate metabolism. Safflower (Carthamus tinctorius L.), an oilseed crop characterized by its considerable adaptability to water-deficit conditions, is not immune to such stresses. Particularly during the reproductive phase, drought can cause significant declines in seed yield and associated agronomic traits. In recent years, foliar application of nutrients has gained attention as a potentially efficient and practical approach to enhance plant tolerance to drought, especially in agro-ecological zones like Iran, where water scarcity and nutrient-poor soils often coexist. Among the foliar nutrients, iron, urea, and amino acids have shown promise in enhancing plant resilience against environmental stresses, due to their roles in improving nutrient use efficiency, activating antioxidant defense mechanisms, supporting protein and enzyme synthesis, and ultimately improving growth and yield performance. Materials and Methods. To investigate the potential of foliar-applied nutrients in alleviating the negative effects of drought stress, a comprehensive field experiment was conducted during the 2022–2023 growing season at the research farm of Tarbiat Modares University, Tehran, Iran. The experimental design was a split-plot arrangement within a randomized complete block design (RCBD) with three replications. The main plot factor consisted of three irrigation regimes: (i) full irrigation throughout the season with no water restriction, (ii) water deficit imposed from the onset of the flowering stage (representing early drought stress), and (iii) water deficit imposed from the beginning of the seed-filling stage (representing late drought stress). The subplot factor included nine foliar spray treatments: (1) 6% iron chelate, (2) 1% urea solution, (3) commercial amino acid solution at 1 g L⁻¹, (4) iron + urea, (5) iron + amino acid, (6) urea + amino acid, (7) iron + urea + amino acid (triple combination), (8) distilled water spray (as a spraying control), and (9) no foliar spray (as a negative control). A wide range of morphological and yield-related traits were measured to evaluate the effects of treatments. These traits included plant height, capitulum diameter and length, number of capitula per plant, number of seeds per capitulum, 1000-seed weight, biological yield, straw yield, grain yield, and harvest index. Results and Discussion. The results showed that drought stress significantly affected several yield components, most notably the capitulum dimensions. Capitulum length and diameter were particularly sensitive to water stress. The maximum capitulum length (65.17 mm) was recorded under late drought stress (with water withheld during the grain-filling stage), indicating that safflower plants tend to elongate floral structures under mild terminal drought conditions. In contrast, the minimum capitulum length (41.16 mm) was observed under early drought stress imposed at the flowering stage. Similarly, the highest capitulum diameter (74.26 mm) was recorded in the full irrigation treatment, while the lowest (47.22 mm) was observed when drought was applied during flowering. Interestingly, plant height did not differ significantly among irrigation regimes, indicating that this trait may be less sensitive to short-term water deficits or more genetically stable. The application of foliar nutrients had a considerable effect on reproductive output. The combined application of iron, urea, and amino acids produced the highest number of capitula per plant (7.69), suggesting a synergistic effect among these compounds in promoting flower development and retention under stress conditions. Full irrigation consistently resulted in superior reproductive parameters, including the highest number of seeds per capitulum (99.37) and the greatest 1000-seed weight (79.46 g). Conversely, early drought stress significantly reduced these values to 62.19 seeds per capitulum and 39.09 g for 1000-seed weight, respectively. Total biological yield and straw yield were strongly influenced by both the irrigation regime and foliar nutrient treatment. The highest biological yield (12,328 kg ha⁻¹) and straw yield (10,444 kg ha⁻¹) were obtained from the combined application of urea and amino acids under the late drought stress regime. Notably, this treatment combination also resulted in the highest grain yield (2627.78 kg ha⁻¹), confirming its effectiveness in enhancing crop productivity under water-limited conditions. In contrast, the lowest grain yield (1066.67 kg ha⁻¹) was recorded in the unsprayed control under drought, highlighting the detrimental effects of nutrient deficiency and water stress when unmitigated. Furthermore, the harvest index—a measure of resource allocation efficiency—was the highest under full irrigation and late drought stress, indicating that plants under these regimes were better able to convert assimilates into economic yield. Conclusion. The findings of this study underscore the critical importance of mitigating drought stress during sensitive phenological stages such as flowering and seed filling in safflower cultivation. While drought during flowering proved particularly harmful to yield components, the strategic use of foliar nutrients was effective in alleviating the negative impacts of water stress. Among the tested treatments, the combined application of iron, urea, and amino acids showed the most promising results, particularly when the stress occurred at the grain-filling stage. This integrated foliar fertilization approach enhanced not only morphological traits and reproductive parameters but also led to significant improvements in grain yield and biomass production. Given the increasing frequency and severity of drought in arid and semi-arid regions, this research provides valuable insights into sustainable agronomic practices for maintaining safflower productivity under water-limited conditions. Future studies may explore the physiological and molecular mechanisms behind these improvements and evaluate the economic feasibility of large-scale implementation in different agro-climatic regions

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