Every plant needs calcium to grow. Once fixed, calcium is not mobile in the plant. It is an important constituent of cell walls and can only be supplied in the xylem sap. Thus, if the plant runs out of a supply of calcium, it cannot remobilize calcium from older tissues.
If transpiration is reduced for any reason, the calcium supply to growing tissues will rapidly become inadequate. Without adequate amounts of calcium, plants experience a variety of problems.
The Benefits of Calcium
Calcium plays a very important role in plant growth and nutrition, as well as in cell wall deposition.
The primary roles of calcium:
As a soil amendment, calcium helps to maintain chemical balance in the soil, reduces soil salinity, and improves water penetration.
Calcium plays a critical metabolic role in carbohydrate removal.
Calcium neutralizes cell acids.
The role of calcium in plants must not be overlooked.
Factors Affecting Calcium Availability
Calcium is found in many minerals in soil, but is relatively insoluble in this state. Calcium is not considered a leachable nutrient. Many soils will contain high levels of insoluble calcium such as calcium carbonate, but crops grown in these soils will often show a calcium deficiency.
High levels of other cations such as magnesium, ammonium, iron, aluminum and especially potassium, will reduce the calcium uptake in some crops. A common misconception is that if the pH is high, adequate calcium is present. This is not always true.
Calcium deficiency symptoms in crops are often called physiological disorders.
Symptoms of calcium deficiency:
necrosis at the tips and margins of young leaves;
bulb and fruit abnormalities;
deformation of affected leaves;
highly branched, short, brown root systems;
severe, stunted growth;
It must be remembered that these problems are caused by an inadequate supply of calcium to the affected tissues. These deficiencies can occur even when the soil appears to have an adequate presence of calcium.
For all practical purposes, calcium is not considered to be toxic to plants. Although rare, excess calcium levels in the soil can reduce a plant’s uptake of other nutrients such as phosphorus, potassium, magnesium, boron, copper, iron, or zinc, resulting in deficiencies of these nutrients.
Using Calcium in a Fertility Program
When calcium is needed, it is not necessary to apply a material such as limestone that will affect the pH level in the soil. Fertilizer can supply 100 percent of the recommended soluble calcium and will not affect soil pH levels. In today’s crop production, this effect is most desirable because the soluble calcium can be applied through an irrigation system when needed and in the amounts that are needed. Because calcium does not relocate in the plant, a soluble source of calcium applied throughout the growing season is preferred, especially in vegetables and other fast growing crops.