Yes, potassium fertilizer can be used at this time. Potassium dihydrogen phosphate can be used. This time application is beneficial to the coloration and quality of the fruit. If the apple tree leaves are light in color, a small amount of nitrogen fertilizer may be added to the foliar spraying fertilizer. The amount of nitrogen fertilizer used in the later stage of fruit tree growth is not large. The concentration of potassium dihydrogen phosphate and urea sprayed together is not higher than 0.5%.
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