This investigation studied the effects of foliar sprays of urea (0.5%), a mixture of Zn (0.4%), Mn (0.3%), Fe (0.5%), and Cu (0.3%) in sulfates from 23% Zn, 28% Mn, 19% Fe, and 30% Cu, respectively, and two growth regulators (GA3 at 25 ppm and α-NAA at 10 ppm), as well as number and date of sprays, on the number of fruit/tree, average fruit weight, and yield/tree in kilograms. Spraying `Washington' navel orange trees with urea and/or micronutrients significantly increased the number of fruit/tree, average fruit weight, and yield/tree expressed in kilograms. However, the treatment including both of them was the most effective in 1991–92 and 1992–93. Application of GA3 and NAA effectively increased the value of the three traits compared with the control; however, spraying the trees with NAA was responsible for higher fruit numbers, while GA3 was more effective in increasing fruit weight. Two sprays of urea, micronutrients, and NAA (or GA3), the first applied 3 weeks before flowering and the second 4 weeks after fruit set, were more effective than spraying once at any of the two dates in producing high numbers of fruit/tree, average fruit weight and yield per tree by weight.
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