The Effect of Irrigation Interval and Iron and Zinc Foliar Application on Some Morpho-Physiological Characteristics and Yield of Sunflower

Sunflower is one of the five important oil plants in Iran that because of the relative resistance to drought stress and high oil quality (absence of cholesterol) had a wide range of country land that devoted to the cultivation of this crop. Drought stress is one of the most important factors that limiting the growth and yield of many crops, especially in the arid and semi-arid region in the world.The use of micro-nutrients is one of the ways to reduce the negative effects of water stress on crops. This research was carried out to investigate the response of sunflower to the foliar application of iron (Fe) and zinc (Zn) micro fertilizers under drought stress conditions and to evaluate the role of these nutrients for reducing drought stress damages and plant tolerance to the drought stress.
Material and This experiment was carried out as a split-plot based on randomized completely block design with three replications in Zarghan Agricultural Research Station, Fars province in spring and summer of 2014. The irrigation interval in three levels (irrigation after 60, 120 and 180 mm evaporation from A-class pan evaporation) were used as the main plot and foliar application of micronutrients in four levels (foliar application with water (control), ferrous sulfate (3 g L-1) zinc sulfate (3 g L-1) and the combination of ferrous sulfate and zinc sulfate each one at a rate of (3 g L-1)) served as the subplot. In this experiment, physiological traits (chlorophyll content, proline, soluble carbohydrates, relative water content and electrolyte leakage percent of leaf), morphological traits (leaf area index and height) as well as grain yield were evaluated. The results showed that the main effects of irrigation interval and foliar application were significant for all traits, but their interactions only were significant for proline and soluble carbohydrates. Delaying in irrigation from 60 to 180 mm evaporation significantly decreased 5.6, 31.2, 37.5, 17 and 37 percent relative water content (RWC), chlorophyll content, plant height, leaf area index (LAI) and grain yield, respectively. With the delaying in irrigation also, leaf electrolyte leakage increased by 20 percent. In foliar application treatments, compared to the control, the foliar application of Fe and Zn caused to increase the RWC, chlorophyll content, proline and soluble sugars content of leaves, plant height, LAI and grain yield and oil as well as reduced electrolyte leakage in leaf significantly. The interactions mean comparison of irrigation and foliar application on proline and soluble carbohydrates showed that in all three levels of irrigation use of Fe and Zinc together increased these traits. Foliar application of Fe and Zn improved physiological traits under drought stress condition. Hence, the increase in metabolites particularly soluble carbohydrates and reducing lipid peroxidation, by foliar application of these two elements, could have a positive effect on the mechanisms of drought tolerance and increased sunflower grain yield and oil.