Developing a good intuition around how your tree’s leaves look will be your best bet in determining where a deficiency or deficiencies lie. Keep your eyes peeled! Early identification will lead to a quicker course correction thereby reducing the duration of time in which your tree is unhealthy.
The recommended NPK ratio for your citrus fertilizer is 3-1-1 or 2-1-1
Yellowing of the leaves may present itself when watering is an issue or your tree really needs more nitrogen. Naturally, nutrients leave the soil as they are used up by the plant or leached away it rains or you supply water.
Replenish your soil by adding more citrus fertilizer and/or amending with organic blood meal. Blood meal is rich in nitrogen while adding relatively little or no phosphorus or potassium to the soil.
After identifying your tree is zinc deficient, what’s the remedy? The percent of zinc required for healthy tree is far less than that of all macro nutrients. Most commonly, citrus fertilizer will contain a very small amount of zinc. Try applying some more of that fertilizer. Oftentimes, this is all this needed.
Read the packaging. Perhaps it’s worth finding a fertilizer with a little more zinc it than your go to citrus fertilizer to use in this situation.