A field experiment was conducted during 2008 and 2009 growing seasons in sandy soil of Bustan area, Tawfik EL- Hakem village, Behera governorate, Egypt. The objective of this study was to evaluate the influences of foliar application with mixture of potassium, calcium and magnesium on fruit set, fruit growth rate, fruit splitting, yield and fruit quality of Washington Navel orange trees. The tested variables were:T1: Control (Only Sprayed with tap water).T2, T3 and T4: Trees sprayed with 300ppm liquid potassium plus 100 ppm chelated calcium plus 20 ppm magnesium sprayed once; on May, 10, twice; on May, 10 and June, 10 and thrice, on May, 10, June, 10 and July, 10 respectively. T5, T6 and T7: Trees sprayed with 600 ppm liquid potassium plus 200ppm chelated calcium plus 40ppm magnesium also sprayed at the same dates mentioned above. Mature (6 years old) of Washington Navel orange budded on sour orange rootstock and spaced at 5m apart were used. Results indicated that spraying Washington navel orange trees with potassium, calcium and magnesium once, twice or thrice with two concentrations resulted in a higher number of fruit set / branch, number of fruits/ tree and yield. Different spraying treatments increased fruit growth rates, fruit weight, diameter, rind thickness and juice volume. Fruit acidity and T.S.S. was increased only in one season, while,
fruit length and Vitamin C content was not affected. The results also showed a marked decrease in fruit splitting percentage. Different foliar applications increased potassium, calcium and magnesium in the leaves.