This study was carried out during the 2022 and 2023 seasons on 12-year-old Washington navel orange trees budded on Sour orange rootstock planted at 5 x 5 meters apart (168 trees/fed.) under the surface irrigation system of a private orchard at Moshtoher village, Toukh region, Qalubia Governorate, Egypt, to study the effect of foliar spray with different potassium forms, i.e., Nano potassium nitrate (KNO₃ NPs) 20% it's commercial name is Biota (46% K and 13% N) beside two traditional potassium fertilizer forms, potassium citrate (K₃C₆H₅O₇) 37.5% K (Citro pro commercial name) and potassium polysulfide ( K₂S_x) 45% contain (33% K, 25% S), on the leaf nutritional status, productivity, and fruit quality of Washington navel orange trees. Each potassium source was applied, covering the whole foliage of each tree canopy, whereas 5 liters were sufficient in this regard. Besides, it is periodically applied five times per season at a one-month interval (in the 1^st week of March, April, May, June, and July).   The obtained results showed that all potassium forms induced a remarked promotion in leaf nutritional status. Also potassium forms enhanced yield , fruit physical and chemical characteristics compared with  water sprayed trees (control). The best results with regards to foliar application were obtained by Nano potassium nitrate (KNO₃-NPs) at 20% at 3 cm which significantly superior in this concern compared with control (water spray) and other potassium treatments ,thus it could be recommended to spray Washington navel orange trees with Nano potassium nitrate (KNO₃-NPs) at 20% at 3 cm 5/L/tree ,five times per season at a one-month interval (in the 1^st week of March, April, May, June, and July). to improve leaf nutritional status , maximize yield and enhanced fruit quality traits under the same experimental conditions.