Mike Roberts

Getting the Macronutrients and Micronutrients Right

All the research points to the fact that optimal citrus growth, fruit yields, and juice quality are all affected by nutrients. Furthermore, research also shows that deficiencies create low yields and affect revenue. Ensuring your citrus receives adequate nutrients is a must, for both macronutrients and micronutrients. The folks at UF/IFAS are working on new recommendations to guide BMPs, but there are nutrient recommendations that are evergreen for Florida citrus growers.

Recommendations for Macronutrients and Micronutrients

Macronutrients include primary macronutrients—the “big three” of nitrogen (N), phosphorus (P), and potassium (K)—and the secondary macronutrients of Calcium (Ca), magnesium (Mg), and sulfur (S). These macronutrients—especially the primary macronutrients—have the greatest impact on yield, growth, and fruit quality.

Micronutrients are those nutrients that help plants to take up and move macronutrients throughout the plant; these include boron, zinc, iron, manganese, copper, and others. Research has shown that micronutrients are especially important for citrus trees dealing with citrus greening.

Evergreen recommendations from UF/IFAS concerning macronutrients and micronutrients include:

  • To optimize yields, to ensure optimal and rapid tree growth, and to achieve the right pound solids and Brix/acid ratio in the juice, nitrogen (N) and potassium (K) should always be applied in equivalent ratios with phosphorus (P) being least in the ratio.
  • There are currently no recommendations for ratios for secondary macronutrients, but applying current recommendations for applications will help improve root health and immunity (Ca and S), metabolism (Mg), and growth (S).
  • Micronutrients should be applied to the root zone via fertigation or spreaders; this will improve root flushes and tree health.
  • Use supplemental foliar sprays to correct deficiencies in “real time.”

There are also recommendations that are meant to ensure the optimal availability of nutrients. These include:

  • Test soil pH and keep it in the optimal range of 5.8 to 6.5. Research shows this is especially important for citrus trees infected by citrus greening.
  • Nutrient soil testing is important, but do not rely on it. Use leaf tissue testing to ensure that all nutrients in the soil are available to the plant.
  • Use leaf tissue testing to get all nutrients in the optimal or high range of UF/IFAS recommendations.
  • If a leaf tissue test shows a nutrient in the excessive nutrient concentration range, consider omitting that nutrient in the next four to six months.
  • Utilize split applications of nutrients. For fertigation, that’s a minimum of 12 splits annually; for dry soluble fertilizer, use four split applications; for controlled or slow-release fertilizer, utilize two to three applications every year.

This column is sponsored by Griffin Fertilizer Co., and the opinions expressed herein may not reflect those of CFAN or of its advertisers.  

BIO: Mike Roberts is the Vice President of the Frostproof, Fla.-based Griffin Fertilizer Co. Roberts joined the company in November 2011. He has spent the majority of his career in the fertilizer/agchem industry. Roberts earned a Bachelor of Science degree in citrus production from Florida Southern College in Lakeland. For more information, visit griffinfertilizer.com.

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