Effects of Regulated Deficit Irrigation and Superabsorbent Polymer on Fruit Yield and Quality of \u27Granny Smith\u27 Apple

Water resource limitation has caused increasing interest in changing irrigation strategy to improve water use efficiency. In this study, effect of regulated deficit irrigation (RDI) (75 and 50% ETC) in combination with different concentration of superabsorbent polymer (SAP) (0, 100, 200 and 300 g/tree) on fruit yield and quality of \u27Granny Smith\u27 apple was investigated during two consecutive growing seasons. The tree irrigated with 100 ETC was used as control. No significant difference was found between control and RDI and SAP treatments for apple fruit yield. But in the second year of the experiment, apple trees treated with 200 g/tree superabsorbent showed by 15% greater fruit weight. The fruit soluble solid content (SSC) was significantly affected by irrigation regimes and superabsorbent polymer. The highest SSC was found in RDI50 in two years and 200 g/tree superabsorbent in the first year. In the first season, titratable acidity (TA) was significantly affected by SAP levels. The apple trees that received 300 g/tree of SAP, had the highest content of TA in the first season. No significant difference was observed among treatments regarding dry matter percentage and firmness. Total phenolic content of apple fruits was significantly affected by both RDI and SAP treatments in both seasons. In each level of SAP application, by reducing RDI percent total phenolic content increased. The highest phenolic content was found when the trees were treated with 50% RDI with and without SAP treatment