Impact of Nitrogen Application Timing and Boron-Zinc Spray on "Fuerte" Avocado

This study was carried out throughout two successive seasons of 2015 and 2016 at Horticulture Research Station at El-Kanater El-Khayria, Qalyubeia Governorate on 20-year-old avocado trees (Persea americanaMill.) "Fuerte" cultivar grafted on Dayouk rootstock and irrigated through farrow (surface) irrigation system. In this sequence (N1) as the control or untreated trees and other trees were treated with four treatments of different addition times of nitrogen soil fertilization (N2, N3, N4, and N5) all only once and once with boron and zinc as foliar spraying in concentrations (1, 2 and 3 g/L) beside combination between them. Nitrogen fertilization rated 1200 g /tree in 3 times as (NH4No3) 33. 5%. Boron was used as sulaphate boron (17, 5%) and zinc was used as sulphate zinc (34%) where each treatment was sprayed independently or in combination three times during (October, January, April). Pollen germination, fruit set as well as yield, fruit weight, flesh weight, oil content percentage and vitamin C were determined to assess the effect of the treatments. The obtained results showed that nitrogen soil application time and boron and zinc foliar spraying were significantly affected on improving all the tested parameters compared with control trees. The study also showed that, nitrogen soil application time N2 with boron and zinc combination at 1g/L/tree was more effective than the other treatments and gave significantly the highest values in comparison of other tested treatments in both seasons of study.