Impact of irrigation intervals with fertigation timing on Washington navel orange tree productivity and leaf nutrient content.

Recently, as a result of citrus trees in some Nubaria region expose to intermittent forced irrigation, study in Egypt evaluated the effects of prolonged irrigation intervals and fertilizer doses timing , on twelve-year-old Washington navel orange trees on sour orange, under drip irrigation system (Nile river water) in Al- Bustan region, El-Behira governorate during 2020, 2021and 2022 seasons. Ten treatments contained T0: every day and fertigation done 30 min-before end irrigation period (control), T1, T2, T3 were every two, three and four days, respectively. Each of T1, T2, T3 had three timing of fertigation (a) 15 min - after beginning, (b) at middle time and (c) 15 min - before the end of irrigation period. Treatment were arranged in complete randomize block design. Irrigation every four days plus fertilizers at the 3^rd time significantly increased leaf proline content, reduced fruit peel %,  TSS %, TSS/Acid ratio &V.C .Irrigation every three days plus fertilizers at the 3^rd time improved leaf macro- elements% , fruit weight, number of fruits, yield as kg / tree and reduced juice acidity. Irrigation every two days plus fertilizers at the 3^rd time gave highest number of fruitlets in May, then decreased and fixed in June & July. Control treatment significantly reduced fruit-splitting% during August, September, October &November, while irrigation every four days plus fertilizers at the 1st time was the highest. Moreover, the highest fruit-splitting values noticed at September for all studied treatments. Irrigation every two days plus fertilizers at the 1^st time increased fruit juice.