CompleteCitrus Newsletter

November 2019


Sustaining Optimum Nutrition for Citrus Fruit, Roots and Canopy During Fall and Winter

Maintaining balanced nutrient levels going into the fall and winter is critical to the next crop. Nutrient uptake is dependent on a healthy vigorous root system. With the onset of cooler conditions, we need sources of nitrogen and calcium that will be immediately available for uptake to ensure maximum response. The CompleteCitrus by Yara Hybrid Program, including the Optimal Citrus 9-1-14 Blend with YaraLiva® TROPICOTE®, YaraVita® PROCOTE® BMZ, and YaraTera NITRAKAL works together to ensure a vigorous healthy root system allowing your crop to obtain its full potential, this year and next. Healthy trees have higher resistance to pest pressure and produce more profits.

Key Points fo Fall and Winter Nutrition in Citrus:

  • During the period from late August to December, fruit will increase in fresh and dry weight significantly.
    • Hamlin will gain 42% of its final fresh weight and 35% of its final dry weight.
    • Valencia will gain 42% of its fresh weight and 53% of its dry weight.
  • Valencia will continue to develop into March-April and may respond favorably from the January/February application.
  • Failure to supply sufficient nutrients to meet fruit and tree needs will weaken both.
  • Trees that become stressed due to heavy crop load are more susceptible to disease pressure.
  • Fall fertilizer application needs to reflect the needs of the fruit crop in order to maximize grower return on fertilizer investment.

Fertilization studies with the University of Florida on Flatwoods citrus between 1992 and 1998 revealed that the fruit uptake for Hamlin and Valencia were similar for the period of October through December for potassium. Similar but not the same, Valencia took up 27 pounds of K2O per acre for a 500 box crop while Hamlin’s uptake was 22 pounds. Potassium is easily leached from Florida soils and the recent heavy rainfall may have removed this much needed nutrient. If you haven’t done a fall application of potassium to meet your crop’s needs you still have some time for your Hamlin crop. Valencia will need another 15 pounds of K2O during January till harvest, this is in addition to the needs of next year’s crop needs.


A healthy root system supports the canopy’s needs and that of developing fruit. Nitrate-nitrogen and calcium are the most critical element for supporting increased canopy development. Ensuring adequate levels of available calcium will increase number of growth points and the ultimate size and thickness of leaves. It is important to have large, thick leaves to collect solar energy to produce photosynthates which create dollars. Healthy leaves are like healthy roots, they attract fewer insects and resist invasion of bacteria and fungi. Calcium nitrate will supply both nitrogen and calcium immediately for uptake and metabolism ensuring large, healthy leaves.

citrus - Ca x no-Ca pathogens.png

A dense canopy structure has the added benefit of supporting more root development by producing the starches needed by the roots for growth and development. It is important to maintain a good root to shoot ratio and not create an imbalance due to excessive vegetative growth from over-application of fertilizers or damage due to misapplication. This happens easily from over-applying fertilizers with higher salt indexes. The result is that soil moisture levels decrease, and the root mass is damaged. The need to select the right sources can’t be over emphasized. Many growers are now experiencing the results of applying the wrong sources based on price rather than plant needs and agronomic merit. Given the plant stress environment currently in our groves, cheaper priced fertilizers are now costing some growers everything.

Calcium Loves Citrus Fun Fact

Leaves hold the most Ca. They live for a long time if proper nutrition is applied and it's the same thought process as solar panels. Quantity and size leads to increase in energy and tree production.

Calcium (Ca) is one of the most important nutrients in a balanced nutritional program for HLB-infected citrus. Cell division or mitosis will not occur without it. Plant cell walls and plasma membranes are weak and limited without Ca resulting in easier access for pathogens and less efficient water and nutrient uptake. Root hair, which are the primary nutrient uptake vessels for plants, require Ca to grow. Also, when water-soluble Ca is removed from growing trees, shoots, leaves and more importantly roots suffer. Healthy roots must be continually grown to replace ineffective HLB infected roots and Ca is a key nutrient for this to occur. But most important of all, Ca is the messenger for initiation of HLB defense by the plant protection mechanism along with K. Therefore, we must apply adequate soluble Ca and K to obtain the immune effect. Interestingly, essentially all HLB-infected trees are Ca deficient.

citrus tree picture.png

Without an adequate root system, essential nutrient and water uptake is greatly inhibited resulting in canopy collapse which further reduces the root system. A downward spiral begins.

Matching tree and fruit needs throughout the year is key to profitability. Calcium Nitrate helps growers meet these needs without loading the root zone with high rates of salts and ammonium causing root damage, reducing vital nutrient uptake and exposing susceptible damaged roots to fungi infestation. Healthy roots allow the nutrients to support canopy development that later protects the fruit from scaring and provide more sugars to be stored in the fruit. Here is a simple concept: more fruit containing more sugar equals more income. Making a fall application of the CompleteCitrus by Yara Hybrid Program provides the nutrient balance, profitability, and results Florida’s groves need for success.

To learn more about the CompleteCitrus by Yara Hybrid program, contact your local Yara representative.


Trey Cutts
Crop Manager, Yara North America


About this newsletter...

Yara's CompleteCitrus Newsletters represent many years of knowledge with concentration on Florida citrus nutrition. Articles address nutrition's role in the plant processes which influences the final outcome as the season progresses. The goal of the newsletter is to provide citrus growers with the best available information with which to manage their production optimally, with minimum environmental impact, consistently from one year to the next. Tree health is recognized as a major element in sustainable production. Nutrition is also fundamental in establishing and maintaining optimal performance and tree longevity. The "whys" are addressed with the "how to" in a straightforward and practical manner.

YaraLiva Calcium Nitrate Fertilization of Citrus

The following brief video reviews the reasons why YaraLiva Calcium Nitrate is superior to ammonium nitrate for citrus fertilization. Bill Easterwood, Ph.D., Yara North America's Director of Agronomic Services, reviews research supporting the use of calcium nitrate to improve tree health, citrus yield and quality.

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