Fruit trees, like all plants, need 13 mineral elements plus water, sunlight and oxygen to grow and thrive. If the site was well prepared, most of the required nutrients will be readily available in the soil. Since fruit trees are perennial plants, not all nutrients must come from the soil each year. Much of the nutrients that are taken up one year are available in subsequent years for growth and metabolism. The most common nutrient deficiencies on fruit trees in Utah’s home orchards come from a lack of nitrogen, iron, or zinc.
Nitrogen deficiency is often characterized by small leaves with a light green color. The pale color is evident first in older leaves. Another symptom is a lack of adequate growth of new shoots.
The actual amount of supplemental Nitrogen needed depends on the amount of organic matter in the soil, and the soil texture and nutrient holding capacity. A beginning point for nitrogen application is 1 ounce of actual Nitrogen per year of tree age, not to exceed 8 oz of Nitrogen per tree per year. Requirements may be higher for sandy soils and less for loam or clay soils. The actual amount to apply is based on the nitrogen concentration of the fertilizer. For example, ammonium sulfate is about 20% nitrogen. To apply 1 oz of nitrogen, you would need to apply 5 oz of ammonium sulfate fertilizer.
The best gauge for nitrogen fertilizer application is the amount of tree growth. If new growth is excessive, reduce Nitrogen application.
Deficiencies of mineral nutrients, particularly micronutrients are diagnosed through tissue analysis. Collect leaves from the midpart of current season growth and submit to a testing lab for analysis. Your local county Extension office can help with this.