Document Type : Research Paper - Agroecology

Authors

• Hamid Alahdadi ¹
• Alireza Yadavi ²
• Mohsen Movahedi Dehnavi ²
• Hamidreza Balouchi ²

¹ M.Sc. Student of Agrotechnology, Department of Agronomy and Plant Breeding, Faculty of Agriculture, Yasouj University, Yasouj, Iran

² Professor, Department of Agronomy and Plant Breeding, Faculty of Agriculture, Yasouj University, Yasouj, Iran

Abstract

Introduction
Safflower (Carthamus tinctorius L.) is a multipurpose crop with medicinal and oil-producing applications, primarily cultivated for edible oil and industrial dyes. Its adaptability to arid and semi-arid climates makes it a valuable crop for regions facing water scarcity. Water scarcity and drought stress significantly impact its growth and yield, particularly in arid regions such as Iran. Sulfur, the fourth most consumed nutrient by plants, plays a crucial role in photosynthesis and cell membrane integrity. However, excessive application of chemical sulfur fertilizers can lead to soil salinity, making biofertilizers a sustainable alternative. Biofertilizers, such as Thiobacillus spp., not only provide essential nutrients but also improve soil health and reduce environmental pollution. Thiobacillus spp. bacteria enhance plant growth by supplying sulfate and improving soil properties.
Materials and Methods
This study investigated the effects of chemical and biological sulfur sources, including bentonite sulfur and Thiobacillus bacteria, on the shoot nutrient content (N, P, K, S, Fe, and Zn), physiological characteristics, and seed yield of safflower under water stress. The experiment was conducted in the summer of 2023 at the research farm of Yasouj University, Faculty of Agriculture, located in Dashtrom. A split-factorial design based on a randomized complete block design (RCBD) with three replications was used. Irrigation regimes at three levels (full irrigation, irrigation cutoff from flowering to maturity as severe drought stress, and irrigation cutoff from seed filling to maturity as moderate drought stress) were the main factor, while bentonite sulfur application at three levels (0, 150, and 300 kg/ha) and Thiobacillus bacteria application (with and without) were the secondary factors.
Results and Discussion
Statistical analysis showed that bentonite sulfur fertilizer and Thiobacillus bacteria significantly improved nutrient content in shoot, physiological traits, and grain yield under drought stress. The combined application of sulfur and Thiobacillus bacteria enhanced the plant’s ability to withstand water deficit conditions by improving nutrient availability and stress-related enzymatic activities. Under severe drought stress (irrigation cutoff from flowering to maturity), the highest nitrogen (2.33%), sulfur (0.149%), iron (44 mg kg^-1), and zinc (25.66 mg kg^-1) levels were observed with the combined application of 300 kg ha^-1 of bentonite sulfur and Thiobacillus bacteria. The interaction between irrigation regime, bentonite sulfur, and Thiobacillus bacteria significantly influenced total chlorophyll content, carotenoid content, total soluble carbohydrates, and antioxidant enzyme activities (catalase and peroxidase). The highest values for these traits in each irrigation regime were obtained with the application of 300 kg ha^-1 of bentonite sulfur and Thiobacillus bacteria. This demonstrates the potential of sulfur-based treatments to enhance stress tolerance mechanisms in safflower. Malondialdehyde (MDA) content increased under water deficit conditions (flowering and seed-filling stages), but decreased with bentonite sulfur and Thiobacillus bacteria. Seed yield was significantly enhanced by the application of 300 kg ha^-1 of bentonite sulfur and Thiobacillus bacteria, with increases of 25.28% under full irrigation, and 45.54% under moderate drought stress. 
 Conclusion
The findings suggest that drought stress, particularly irrigation cutoff from flowering to maturity, reduces physiological traits and seed yield in safflower. However, the application of 150 kg ha^-1 of sulfur-bentonite combined with Thiobacillus bacteria not only mitigates the adverse effects of water stress but also enhances nutrient uptake, biofertilizer efficiency, and seed yield while reducing the need for chemical fertilizers. This study provides valuable insights into the role of sulfur and biofertilizers in improving safflower resilience under water-limited conditions, contributing to sustainable agricultural practices in arid regions.

Keywords

• Biofertilizer
• Irrigation cutoff
• Malondialdehyde
• Seed yield
• Shoot elements

Main Subjects

• A: Agroecology