الفهرس 
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Abstract
This investigation was conducted over three successive seasons; 1985, 1986 and 1987 on mature ttBalady orange1t and “Balady mandarin” trees grown in the orchard of the Faculty of Agriculture, Assiut University. All trees were budded on sour orang rootstocks and planted in clay soil.
This experiment was arranged in a split plot design with five replicates each consisted of one tree in each cul— tivar. The objective is to study the effect of nitrogen fertilization rate and certain growth regulator treatments at different concentrations on fruit set, DROP, yield and fruit quality of both cultivars.
Three levels of nitrogen fertilizations were chosen, i.e., 0, 600 and 1200 gm N/tree/year. Each level was monthly added at 6 equal doses starting on March of each season. Within each plot of nitrogen level there are seven growth regulator treatments as follows:
Control (untreated trees), GA3 (Gibberellic acid) at
50 and 100 ppm and both 2,4—D (2,4-Dichiorophenoxyacetic
acid) or NAA (Naphthalineacetic acid) each were applied at
10 and 20 ppm.
The growth regulator treatments were sprayed during ;full bloom of two investigated cultivars.