نقش عناصر ریزمغذی آهن و روی و محلول‎پاشی اسید سالیسیلیک در بهبود تحمل ذرت (Zea mays L.) به خشکی

Introduction
Maize (Zea mays L.) is a vital global crop, serving as a significant food source and primary income for farmers, particularly in developing countries. It is also a key raw material for various industries, including biofuel (ethanol) production. Environmental stresses, especially drought, are the primary limiting factors for maize yield, severely impacting its growth and productivity. Sustainable and eco-friendly solutions, such as the application of micronutrients and plant growth regulators, can effectively enhance a plant's drought tolerance. Essential micronutrients like zinc (Zn) and iron (Fe) play crucial roles in plant physiological and biochemical processes; zinc is involved in chlorophyll synthesis and carbohydrate metabolism, while iron is vital for nitrogen fixation and antioxidant enzyme activity. Additionally, salicylic acid (SA), a plant growth regulator, is known to improve drought resistance. Given the arid and semi-arid climate of Iran and the scarcity of water resources, it is essential to investigate innovative strategies to improve maize performance under these conditions. This study aims to evaluate the effects of the combined application of iron and zinc micronutrients with salicylic acid on the growth and yield characteristics of maize under drought conditions.

Materials and methods
To investigate the effects of iron (Fe), zinc (Zn), and salicylic acid (SA) on alleviating drought stress in maize, we conducted a factorial split-plot experiment using a randomized complete block design with three replications at the University of Gonabad during the 2019-2020 growing season, employing minimum tillage practices. The experimental design comprised two irrigation regimes: Non-drought (control) and drought during seed filling stage (drought stress) in main plots and factorial combinations of micronutrient treatments (Fe, Zn, and control-no micronutrient application) and SA application (foliar spray vs. no spray) in sub plots. Minimum tillage was employed for land preparation. The data were analyzed using SAS (version 9.4) and Excel (version 14) software. Mean comparisons were performed using Duncan's multiple range test at a 5% probability level.

Research findings
The results demonstrated that the simultaneous foliar application of salicylic acid (SA) with Fe and Zn significantly improved most of the studied traits under drought stress. Specifically, the combined application of SA and micronutrients (Fe and Zn) led to a significant increase in the number of seeds per plant compared to treatments lacking foliar application. The highest thousand-seed weight (426.40 g) was observed in the non-drought treatment combined with the simultaneous foliar application of SA and Zn. In stark contrast, the lowest value for this trait (132.87 g) was recorded in the drought-stressed control group, which did not receive any foliar treatment. Furthermore, under drought stress conditions during the seed-filling stage, the foliar application of iron and zinc combined with salicylic acid substantially enhanced crop productivity. Compared to the control, this treatment increased grain yield by 94.36% (for Fe+SA) and 87.35% (for Zn+SA) and raised the harvest index by 77.42% (for Fe+SA) and 99.42% (for Zn+SA), respectively.

Conclusion
This research confirms that the foliar application of salicylic acid, iron, and zinc are effective strategies for alleviating the adverse effects of drought stress on maize. The combined application of these substances significantly improved the plant's yield and physiological characteristics. While each micronutrient (iron or zinc) combined with salicylic acid yielded positive results, future studies should explore the synergistic effects of a combined application of both iron and zinc with salicylic acid. Such research could further elucidate the metabolic pathways of drought resistance, such as antioxidant enzyme activity and phytohormone synthesis, to develop optimized solutions for increasing maize productivity in arid and semi-arid regions.