الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
In 2011/2012 and 2012/2013 seasons four and five years old Washington Navel orange (WN) trees on Sour orange (So) rootstock received fertigation with different N : K ratios, namely 1 : 0.6 (control), 1 : 1.2 and 1 : 1.8. In addition, Mg foliar spray was applied three times on 50% of the trees in March, April and May. The main objective of the study was to overcome the relatively slow vegetative and fruiting activities of the trees on So rootstock in the early years after planting compared to other citrus rootstocks. The obtained results revealed a clear promotion in tree volume, and shoot and leaf parameters in the second season with N : K ratios of 1 : 1.2 and 1 : 1.8 compared to the control (1 : 0.6). The ratios of 1 : 1.2 and 1 : 1.8 also promoted N, K, Fe and Cu levels in the leaves, While depressed Ca, S and Mn levels. Also, the ratios of 1: 1.2 and 1: 1.8 tended to increase chlorophyll a, b and total chlorophyll in leaves. The ratios of 1 : 1.2 and 1 : 1.8 decreased number of flowers per branch, while promoted the number of retained fruits per branch. The fruit weight, peel thickness and weight, pulp weight were dependent on number of fruits/tree rather than the N : K ratio or Mg foliar spray. The largest fruit juice weight and volume came from control fruits (1 : 0.6 without Mg spray). The differences in TSS, acidity and TSS/acid ratio were more clear in the second season (2012/2013) where the ratios of 1 : 1.2 and 1 : 1.8 gave higher juice TSS, acidity and ascorbic acid values than the control (1 : 0.6). The N : K ratio of 1 : 1.2 produced the uppermost values for total weight of fibrous roots/kg soil as well as for the roots weight at 0.5 and 1.5 m from the trunk compared to the control (1 : 0.6). In conclusion, under the same conditions the obtained results make possible to recommend promoting potassium fertilization of young Washington navel orange trees on sour orange rootstock to reach a N : K ratio of 1 : 1.2. Such fertilization would encourage vegetative and fruiting development of the young trees on this rootstock beside their higher fruit quality compared to other citrus rootstocks.