Role of Calcium in Citrus Production
Calcium is a key component of cell walls and also has a direct influence on the regulation of enzyme systems, phytohormone activities and nutrient uptake.
Calcium also influences pollen tube elongation and seed formation.
Calcium nitrate and yield - Florida
Annual, cumulative use of calcium produces high yields. This was confirmed in a controlled, low pH environment experiment in Florida where high rates of calcium on its own increased tree growth rate and yield of navel oranges over an eight year period.
Calcium nitrate and Ammonium nitrate
Calcium nitrate ensures higher yields compared to ammonium nitrate. Maximum yields in this fertigated trial (Valencia oranges, Brazil) were achieved with lower N rates applied by calcium nitrate. In a long-term series of trials, calcium nitrate has consistently proven to be the most effective form of fertilizer for producing high orange crop yields.
Yield on limed soils - Valencia oranges, Florida
Regular use of soluble forms of calcium is also beneficial on high calcium carbonate soils or those that are regularly limed. After seven years of regular use, calcium boosted orange yields in USA trials by up to 56%. The nutrient also has a significant effect on reducing many fruit disorders.
Ca and tree loss - oranges, Florida
Research in Florida across three citrus species, confirms that tree loss due to citrus blight (Fusarium spp.) is significantly lower where calcium nitrate is the main form of fertilizer. For the most responsive cultivar Hamlin, 15% of trees treated with ammonium nitrate as part of the fertilizer programme were unproductive after ten years, compared to just 7% where calcium nitrate was the only form of N-fertilizer used.
Ca in fruit - Valencia orange, Brazil
Applications of calcium as calcium nitrate to the soil, as well as the crop, reduce the incidence of fruit disorders. This is as a result of increasing calcium levels in the fruit.
Foliar Ca sprays and splitting
Foliar Ca sprays, reduce splitting, creasing (=albedo breakdown) and pitting diseases of oranges and mandarins. For example, Spanish works showed that two calcium nitrate sprays during the summer, reduced splitting of oranges and mandarins.
Calcium effect at growth stages
| Stage | Calcium effect |
| Flowering | To aid leaf growth, pollination and fruit set |
| Fruit Set | Provide good fruit productivity and quality |
| Fruit Enlargement and Maturation | Boost leaf growth and tree vigor and reduce skin disordersincluding fruit splitting and albedo breakdown |
| Post Harvest | To maintain tree root health and productivity and to encourage leaf flush |
See more on Citrus Growth Stages.
General guidelines for Calcium application
Annual, cumulative use of calcium produces high yield. Calcium nitrate ensures higher yields compared to ammonium nitrate. Fertigation using calcium nitrate is a highly effective way of maximizing Ca nutrition and yield. Significant fruit set improvements come from calcium nitrate applications made immediately prior to and during flowering.
Calcium deficiencies in citrus
There are few visual signs of calcium deficiency in the leaf. Leaves may show interveinal symptoms similar to iron or manganese deficiencies but these are rare. Leaves with calcium levels below 1.6% are deficient, however, trees lack vigor and start defoliating when the leaf calcium level falls below 3%.
Calcium deficient trees are stunted due to poor root development, with dark green foliage. The main impacts of calcium deficiency are root systems that are more susceptible to root diseases and fruit which is more prone to albedo breakdown and splitting.
