Impact of super absorbent polymers (hydrogels) on water use parameters of Plum trees under water stress conditions

: The present study was conducted during two successive seasons 2019 and 2020 on five years old "Kelsey" Plum trees ( Prunus salicina L . ), budded on Mariana rootstock. The trees were planted in sandy soil in a private orchard located in Salah Al-Abd Village, Bostan Area, West Nubaria, Behaira Governorate, Egypt (Lat. 30.598  and Long. 30.228  ). The study was conducted to test the effect of irrigation practices;100, 80, and 60% of reference evapotranspiration (ET 0 ) and water retaining materials (hydrogel polymers) Barbary Plant, "BP" and Aqua Gool, "AG" at rates of 75, 100, and 125 g/tree in addition to the control treatment. The irrigation was controlled via the operating time using the drip irrigation system. The results revealed that fruit yield was improved by the application of AG and BP treatments. The treatments of AG125 and BP125 gave the highest significant values in yield and yield parameters as compared to the control (not treated trees). The increases over the control treatment were 25.65 and 27.84% for AG125 and 22.41 and 24.05% for BP125 in the 2019 and 2020 growing seasons, respectively. On the other side, the highest value of fruit yield and parameters was recorded for 100% of ET 0 treatment and then decreased with decreasing irrigation rate. The calculated crop evapotranspiration (ETc) of Plum trees reached 774.1, 619.3, and 464.5 mm during the 2019 growing season for 100, 80, and 60% of ET0, respectively. The corresponding values for the 2020 growing season are 662.3, 529.8, and 397.4 mm, respectively. The applied irrigation water of Plum trees was 3251.13, 2600.90, and 1950.68 m 3 /fed during the 2019 growing season for 100, 80, and 60% of ET0, respectively. The corresponding values were 2920.23, 2367.28, and 1813.06 m 3 /fed, respectively, for the 2020 growing season. As for the irrigation water use efficiency (IWUE) of Plum trees, the GA125 and BP125 treatments were found to increase IWUE by about 26.63 and 21.57% over the control treatment in the first growing season, respectively while it was 27.78 and 23.32 %, respectively in the second growing season. The treatments in terms of water use efficiency came in descending order as follows GA125, BP125, BP100, GA100, BP75 then GA75. Irrigation water use efficiency was increased under irrigation deficit by about 13.52 and 12.90% for 80 and 60% of ET 0 in the 2019 growing season, respectively as compared to 100% of ET 0 . The corresponding values for the 2020 growing season were 12.52 and 9.68%, respectively. Accordingly, the use of hydrogel as a water preservative and or deficient irrigation can be an appropriate strategy to obtain a good yield of Plum trees under conditions of water shortage, taking into account that the incomplete irrigation should be moderate, with the need to study its long-term effects on the strength of growth and productivity of trees