This study was conducted during three successive seasons of 2013/2014, 2014/ 2015 and 2015/2016, on 6-year-old Valencia orange (Citrus sinensis, L. Osbeck ) trees budded on sour orange rootstock and grown in sandy soil at 4 × 5 m  under drip irrigation system. Forty-eight trees were subjected to 12 N fertilization treatments using ammonium nitrate (33.5%N) fertilizer. The N fertilizer was added through fertigation, soil application and trunk injection at different rates and periods. Trees fertigated at 1000 g N/ tree/year 3 times/ week gained the highest fruit set and fruit retention percentages in the three seasons. Trunk injected trees induced also higher percentages although they consumed very small amounts of N (0.2 – 0.3% of the recommended rate). Leafy inflorescences exhibited higher fruit set and fruit retention percentages than leafless ones. Fruit retention percentage on leafy inflorescences was 21.71, 3.14 and 2.97 folds its percentage on leafless ones in the three seasons, respectively. The highest yield and number of fruits/ tree as well as cropping efficiency were gained by trees fertigated at 1000 g N/tree/year 2 or 3 times/ week, followed by those soil applied at the same rate 3 times/ year and those trunk injected without significant differences between them in most cases. The produced fruits on trees of these treatments contained higher vitamn. C and lower total soluble solids (TSS)/ acid ratio. Trunk injected trees not only consumed very small amounts of fertilizers, but also produced comparable higher yield of  fruits with higher firmness, juice volume, TSS/ acid ratio and vitamn. C content. They gave lower TSS and total acidity percentages in comparison with the other tested fertilization treatments in the three seasons.