Managing Macronutrients and Micronutrients

By Davie Kadyampakeni

Nutrients are needed for optimal citrus tree growth, fruit yields and juice quality. Any nutrient deficiencies could result in low yields and decreased revenue. Make sure citrus trees receive adequate macronutrients and micronutrients at all times.

Macronutrients are those nutrients needed in large quantities to influence yield, growth and fruit quality. Macronutrients are further divided into two groups as primary and secondary macronutrients. The primary macronutrients include nitrogen (N), phosphorus (P) and potassium (K). Calcium (Ca), magnesium (Mg) and sulfur (S) belong to the group of secondary macronutrients.

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 always be applied at equivalent ratios of about 1:1, or somewhere close to ensure optimal and rapid tree growth and the right pound solids and Brix/acid ratio in the juice.

While there is no specific ratio for the macronutrients Ca, Mg and S, these nutrients, when applied following current recommendations, help improve root health and immunity (Ca and S), metabolism (Mg) and growth (S). In addition, Ca and S can help moderate pH to the optimal level. 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, the addition of elemental S can lower the pH to the desired level.

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

To ensure optimal availability of nutrients, follow these tips:

• Periodically do a soil test for pH and keep the soil pH between 5.8 to 6.5. Results have shown that this is the optimal range for nutrient availability in citrus-producing soils, especially for trees affected by citrus greening.
• Perform a leaf tissue test and make sure every nutrient is in the optimal or high range according to current University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) 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 it reverts to the optimal or high range. Excessive nutrient concentration may result in too much vegetative growth at the expense of fruit yield and juice quality.
• Split applications of nutrients are encouraged. For example, if using fertigation, apply a minimum of 12 splits per year. If using dry soluble fertilizer, four split applications are ideal. When using controlled or slow-release fertilizer, make two to three applications per year.

Davie Kadyampakeni is an assistant professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

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