الفهرس 
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Abstract
This work was carried out in the three successive seasons of 2008, 2009 and 2010 on thirty two 15-year-old Washington navel orange trees [C. sinensis (L.) Osbeck] grown in clay soil at 5 m apart in a private citrus orchard located at Minia El-Kamh district, Sharkia Governorate. The experiment included two factors: the first consisted of spraying urea at 2% three times a year (1st Dec., 1st Jan. and 1st Feb.), GA3 and NAA at 10 ppm 3 times/ year (beginning of flowering, full bloom and after fruit set), beside water spray as a control. The second factor was adding nitrogen at 1000 g N/ tree/ year (819.5 kg ammonium sulfate 20.5% /fed.) at 3 or 4 doses. The first N dose was added at 100 kg ammonium sulfate/ fed. at early Dec. in four doses treatment. The three doses either in 3 or 4 doses treatments were equally added at February, May and August.
Spraying GA3 three times a year at 10 ppm, four N applications (early Dec., Feb., May and August) and their interaction gave the maximum fruit set, fruit retention percentage, fruit weight, number of fruits/ tree and yield/ tree, but reduced total fruit DROP percentage. Juice fruits of trees sprayed with water and received four N applications contained the highest TSS and the lowest total acidity percentages and consequently the highest TSS/ acid ratio as well as total, non-reducing and reducing sugars percentages compared with those sprayed with GA3 and received the same N doses.
Trees received 4 n doses/ year with or without spraying urea at 2 % three times a year caused earlier flowering for about one week in comparison with other tested treatments.