Soluble Calcium is Critical During Heavy Fruit Loads

CompleteCitrus Newsletter, March 19, 2020

With Valencia’s in bloom and approaching spring flush, now is the opportunity to set fruit, provide for maximum sizing and develop a canopy to generate maximum carbohydrate production. Trees have benefited from cooler temperatures a few weeks ago – aiding in bud and fruit retention. But this increased fruit load now demands the right nutrient strategy to maintain this advantage through filling. A soluble calcium fertilizer source, like YaraLiva TROPICOTE, is needed to supply calcium to the flower bud during the 10-12 week window of opportunity. Once leaf development begins calcium flow is greatly reduced to the fruit. Calcium must be available now – later is too late. The high solubility of YaraLiva’s calcium provides that soluble calcium for optimum fruit set and persistence while the window of opportunity is open.

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The anticipated heavy initial crop set will require more leaf area to produce the additional carbohydrates required to meet the desired solids in the crop. Capacity to expand and develop leaf surface area is largely dependent on calcium levels in the tissue. Soluble calcium increases fruit set and strengthens tree resistance to stress that would cause fruit abortion. Adequate levels of calcium are critical for optimum leaf health – leading to lower incidence of leaf disease and vector penetration.

Keys to maintaining maximum fruit set during filling

  • Increased flowering reduces critical nutrient concentrations per fruitlet in the first weeks of fruit development.
  • Since each flower, regardless of whether it develops into fruit, will draw upon the nutritional supply available to the tree, it is critical to have essential nutrients available in abundant supply during early filling.
  • Developing flower buds are a low respiration/transpiration site, causing higher demand for supplemental nutrition until flush.
  • Calcium directly influences pollen tube elongation (fruit set), mitosis (cell division) and abscission layer development (fruit drop).

Avoid ammonium toxicity to citrus

Ammonium toxicity affects most plants but the threshold at which symptoms of toxicity show differs among plant species. The most sensitive plants include tomatoes, potatoes, strawberries, lettuces, and citrus species. The symptoms of ammonium toxicity include chlorosis of leaves, decreased growth and poor root development.

Ammonium toxicity occurs when there is too much ammonium available for plant uptake in the soil and plants absorb harmful amounts of it. The preferred form of nitrogen for plant uptake is nitrate and the conversion of urea and ammonium into nitrate-nitrogen in the soil is a biological process governed by temperature, moisture, and soil pH.

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Ammonium toxicity can be prevented by following appropriate cultural practices. When it comes to choosing your spring nitrogen fertilizer, the use of ammonium containing fertilizers or fertilizers that are converted to ammonium (urea) can have a negative impact on crops due to toxicity from ammonium. By reducing the amount of nitrogen in the ammonium form and using a nitrate-nitrogen fertilizer we can avoid ammonium toxicity. There is clear evidence that better root growth is attained when plants receive nitrate-nitrogen. Also, nitrate-nitrogen promotes uptake of critical nutrients such as calcium, magnesium, and potassium, increasing crop quality.

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Improved root growth in citrus trees fertilized with YaraLiva Calcium Nitrate.
Quaggio et al., unpublished data.


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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.