Effect of Foliar Application of Kaolin and Different Sources of Potassium on Yield, Growth and Physiological Characteristics of ‘Asgari’ Grapevine Under Rainfed Conditions

Global warming and recent droughts are one of the main factors in reducing agricultural products. This research was conducted in order to increase the adaptability of ‘Asgari’ grapevine against drought stress in rainfed conditions. In this research, foliar spraying with kaolin (6%) and potassium sources (1.5% and 3% each of potassium nitrate, potassium sulfate and potassium chloride) was done during two seasons on 30-year-old vines located in Shiraz. Kaolin is a highly durable antiperspirant for vineyards, and it is a realistic and attractive strategy to protect grape clusters from excessive heat and sunburn. The results showed that the application of different sources of potassium caused an increase in berry weight, fruit cluster length, soluble solids, chlorophyll, leaf and fruit potassium content, relative leaf water content, and a decrease in the activity of antioxidant enzymes and leaf temperature compared to the control treatment. On the contrary, kaolin treatment decreased these traits and increased the activity of antioxidant enzymes compared to the control treatment. Potassium sources in both concentrations were able to improve the morphological and physiological characteristics of the, resulting in the greater resistance of ‘Asgari grapevine’ to drought and increase in yield compared to the control treatment. But the application of kaolin had no positive effect on studied traits, which may have been due to the inappropriate concentration used in this study.