بهبود جنبه‌های فیزیولوژیک و عملکرد ذرت (Zea mays L.) با کاربرد خاکی و افشانه کردن عنصر روی تحت شرایط متفاوت رطوبتی

Introduction
Water deficit is the most significant environmental stress that limits plant growth in the world. Meanwhile, zinc is recognized as a vital micronutrient that plays a crucial role in the normal growth of plants. Its application has been shown to enhance both the quantity and quality of agricultural products by increasing the photosynthesis rate, activity of antioxidant enzymes, and some osmolyte compounds such as proline. This enhancement can mitigate the adverse effects of environmental stresses, including drought. In the present study, the effects of various amounts and methods of zinc application were investigated on the activity of antioxidant enzymes as well as the growth and grain yield of maize under drought stress conditions. The aim of this experiment was to improve the physiological aspects, growth and yield of maize under various droght conditions.

Materials and methods
This research was conducted as split-plot in a randomized complete block design with three replications in research field of the Faculty of Agriculture, University of Zanjan, Zanjan, Iran, in 2020. The maize variety studied in this research was grain maize SC704, belonging to the late-maturing group with a growing period of 125 to 135 days. The main factor included drought stress at three levels (by applying irrigation at 90%, 60%, and 30% of field capacity) and sub-factor was the rates and methods of zinc application at six levels (including no zinc application, soil application of zinc sulfate at 10 and 25 kg.ha^-1, and foliar application of 5 g.Lit^-1 zinc at stem elongation, tassel emergence and milking stages. The characteristics evaluated in this study included grain iron, zinc, and phosphorus concentrations, the activity of antioxidant enzymes of catalase, ascorbate peroxidase, guaiacol peroxidase, and superoxide dismutase, as well as proline content, malondialdehyde content, hydrogen peroxide concentration, leaf chlorophyll index, leaf area index, grain yield, and biological yield. Data analysis including analysis of variance and comparison of means by least significant difference (LSD) test at a probability level of 5% were performed using SAS software version 9.3, and graphs were drawn using Excel software.

Research findings
The results of the analysis of variance showed that the effect of drought stress and application of zinc was significant on all evaluated traits in the SC704 variety. The interaction of zinc × drought stress was also significant on all evaluated traits, except grain yield and biological yield. The results showed that drought stress significantly reduced the grain iron, zinc, and phosphorus concentrations, the activity of antioxidant enzymes including superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase, as well as leaf chlorophyll index and leaf area index in the SC704 variety. On the other hand, hydrogen peroxide, malondialdehyde, and proline contents increased by 197%, 256% and 129%, respectively, with increasing drought stress intensity. In contrast, the application of zinc with enhancing these traits, led to decrease in the production of hydrogen peroxide and malondialdehyde. Furthermore, drought stress reduced grain yield and biological yield, but zinc application especially soil application of 25 kg.ha^-1, significantly improved the grain yield and biological yield of SC704 variety by 62% and 44%, respectively.

Conclusion
The findings of this study showed that drought stress, especially at high intensities, by disrupting the absorption of nutrient from the soil, soil, led to a decrease in the concentration of grain elements, leaf area index, leaf chlorophyll index, and antioxidant enzyme activities, and an increase in proline content. In contrast, the application of zinc, especially its soil application of kg.ha^-1, by changing (intensifying) the mentioned traits, improved the physiological and morphological aspects and grain yield of maize, so that its application under moderate drought stress reduced hydrogen peroxide and malondialdehyde contents, and increased proline content and antioxidant enzymes activities. Also, the results of this experiment showed that foliar application of zinc was more effective in increasing the concentration of grain elements than soil application.