Nutrition Remains a Critical Element as New Therapies Roll Out

Growers have largely adopted new trunk-injection therapies to fight the effects of HLB in citrus groves. In addition, plant growth regulators have helped improve tree health and fruit retention. One University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) scientist reminds growers to maintain their fertilizer programs as the new therapies are deployed. 

Davie Kadyampakeni, UF/IFAS associate professor of citrus water and nutrient management, says nutrients are needed for optimal tree growth, fruit yields 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.

KNOW YOUR MACROS AND MICROS

Nutrients are categorized into two groups: macronutrients and micronutrients. Macronutrients are those nutrients needed in large quantities to influence yield, growth and fruit quality. They 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 close to that in order to ensure optimal and rapid tree growth and the right pounds solids and Brix/acid ratio in the juice. P tends to be high on Florida sandy soils, so conducting soil and leaf analyses at least once per year is recommended to see whether additional P application is needed.

“While there is no specific ratio for the macronutrients Ca, Mg and S, these nutrients when applied following current recommendations help the citrus trees with improved root health and immunity,” Kadyampakeni says. “In addition, Ca and S can moderate the soil pH to the 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, addition of elemental S can lower the pH to the desired level.”

Micronutrients, though required in small quantities, are equally important, especially for trees impacted by citrus greening. 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.

“It is encouraged to apply these micronutrients to the root zone via fertigation or fertilizer spreaders to ensure improved root flushes and overall tree health. Supplemental foliar sprays are also encouraged about three to four times per year to ensure any deficiencies are corrected in real time,” Kadyampakeni says.

KEY POINTS

To ensure optimal availability of nutrients, Kadyampakeni recommends the following:

• Periodically take a soil test for pH and keep the soil pH between 5.8 to 6.5. Research results have shown that this is the optimal range for nutrient availability in citrus-producing soils, especially for trees affected by citrus greening.
• Always take a leaf tissue test and make sure every nutrient is in the optimal or high range, according to current UF/IFAS recommendations.
• Conduct soil tests 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, which should show up in leaf tissue results.
• When leaf tests show 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 for best tree performance. 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, make a minimum of 12 to 30 applications per year. If using dry soluble fertilizer, four split applications are ideal. When using controlled or slow-release fertilizer, two to three applications per year are recommended.
• When using slow-release, controlled-release or conventional granular fertilizer sources, it is highly recommended those blends have both macronutrients and micronutrients included to achieve the best tree response.