This study was carried out during the 2019 & 2020 seasons on 15-year-old Washington navel orange trees budded on sour orange rootstock grown at 5 x 5 meters a part in loamy sand soil under surface irrigation on the private farm at Kom Hamada, El-Behera Governorate, Egypt. The main goal of this investigation was directed towards improving productivity and fruit quality of Washington navel orange trees associated with lower production cost through investigating the minimizing of chemical N fertilizers by Bio-N. Anyhow, the eight treatments involved in this study were summarized as follows: T1- Chemical N (adopted N fertilization in the farm) at 3.5kg/tree from (NH4)₂SO₄, T2- Urea, T3- Ammonium sulphate (NH4)₂SO₄, T4- Ammonium nitrate (NH₄)₂NO₃, T5- Nitroben (bio-N), T6- Urea + Nitroben (bio-N), T7- Ammonium sulphate + Nitroben (bio-N) and T8- Ammonium nitrate + Nitroben (bio-N). Data obtained revealed that all investigated treatments positively responded to fruit (set % and retention %), and yield/tree and fruit quality were also improved. However, T8- Ammonium nitrate+ Nitroben (bio-N) was statistically superior in this concern. Moreover, T7 - Ammonium sulphate + Nitroben (bio-N) ranked statistically second in this concern. Consequently, it can be recommended that minimizing 50 % chemical N fertilizers by Nitroben at the rate of 500cm³ per tree + 50% chemical-N (Ammonium nitrate 2.5 Kg per tress) enhanced productivity and fruit quality of Washington navel orange trees under the same conditions.