In citrus trees, calcium is the most abundant mineral element by weight. Similarly, it accounts for a % of dry weight in all plants. Most important, Ca is involved in cell division.
Also, Calcium is crucial for root development and functioning. Elemental deficient plants’ root growth is severely restricted. Roots become more prone to bacteria and fungi infections. Furthermore, Calcium activates several enzyme systems and neutralizes organic acids. Therefore, an inadequate Ca supply reduces plant growth long before symptoms appear.
Additionally, Alkaline soils have an abundance of Calcium because they contain limestone. Despite the quantity of Ca in soils, plants can suffer from a range of deficiency disorders.
A Calcium deficiency in citrus is expressed as a fading of green along leaf margins and between the main veins during the winter months (Figure 1). Small necrotic (dead) spots can develop in the faded areas. Also, calcium deficiency produces small, thickened leaves, causes loss of vigor, thinning of foliage, and decreased production. Additionally, severely deficient trees can develop twig dieback.
These leaves show calcium deficiency.
How Deficiencies Occur in Plants
First, deficiencies usually occurs on acidic soils where native Ca has leached away. Furthermore, continuous use of ammonium-containing fertilizer, particularly ammonium sulfate, accelerates loss from soils. Similarly, using Muriate of potash and Sulfur causes losses.
Fixing Deficiencies in Plants
- Gypsum can correct deficiencies and reduce the harmful effect of Salts
- Short-term deficiencies become addressed by using a water-soluble Ca source such as calcium nitrate
- Liming is the most effective and economic practice to supply Ca to crops.
The movement of Ca in plants
First, plants’ calcium movement is one-directional, moving up from the roots and generally routed to young tissue. Then, once in a leaf, it is not used again, even under stressful conditions.
Additionally, foliar-applied calcium usually is immobile but can be induced to translocate by the saturation of leaves with chelation.
Furthermore, in woody plants, movement is relatively slow, with much accumulation in the bark and little in the wood. Similarly, in an herbaceous plant, Ca is rapidly immobilized, whereas, in the apple, Ca continues to move up the tree over a number of seasons.
Lastly, this Ca comes from reserves in the root and lower shoot and is a significant source of calcium for new growth at the beginning of the season.