Optimizing Macronutrients and Micronutrients

Tacy CalliesNutrition, Tip of the Week

A sign of nitrogen deficiency is yellow leaves.

By Davie Kadyampakeni

Nutrients are needed for optimal tree growth, fruit yield and juice quality. Any nutrient deficiencies could result in low yields and decreased revenue. It is important to make sure citrus trees always receive adequate nutrient supplies.

Nutrients are categorized into two groups: macronutrients and micronutrients.

Macronutrients are those nutrients needed in large quantities to influence yield, growth and fruit quality. The primary macronutrients include nitrogen (N), phosphorus (P) and potassium (K). The ratio of N:P:K is important if yield is to be optimized. While P is always least in this ratio, N and K should be applied at equivalent ratios of about 1:1, or somewhere close to that. This will help realize rapid tree growth and the right pounds solid and brix/acid ratio in the juice.

Calcium (Ca), magnesium (Mg) and sulfur (S) belong to the group of secondary macronutrients. While there is no specific ratio for these nutrients, when they are applied following current recommendations, they will help improve root health and immunity (Ca and S), metabolism (Mg) and growth (S). In addition, Ca and S can help moderate pH to optimal levels. For example, when pH is low, additional lime (which contains Ca) or dolomite (which contains Ca and Mg) can raise the pH to the required level. When pH is high, elemental S can lower it to the desired level.

Micronutrients, though required in minute quantities, are equally important. Examples of micronutrients include boron, zinc, iron, manganese, copper and others. Micronutrients are known to improve the accessibility and movement of macronutrients in the plant, particularly for trees affected by citrus greening. Apply micronutrients to the rootzone via fertigation or spreaders to ensure improved root flushes and overall tree health. Supplemental foliar sprays are encouraged to ensure any deficiencies are corrected in real time.

For optimal availability of nutrients, the following should be observed:

  • Periodically do a soil test for pH and keep the soil pH between 5.8 and 6.5. Results have shown that this is the optimal range for nutrient availability in citrus-producing soils.
  • Do leaf tissue tests and make sure every nutrient is in the optimal or high range according to current University of Florida Institute of Food and Agricultural Sciences recommendations.
  • Do a soil test but watch for the leaf tissue results because while some soil tests may show high nutrient content, the nutrient may not be readily available to the plant.
  • When a leaf nutrient test shows excessive nutrient concentration, consider omitting that nutrient in the next four to six months to make sure the nutrient reverts to the optimal or high ranges. Excessive nutrient concentration may result in too much vegetative growth at the expense of fruit yield and juice quality.

Davie Kadyampakeni is an assistant professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.

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