A good liming programme is the best supplier of calcium to plants.

Deficiency symptoms:

Deficiency causes stunting of new growth in stems, flowers and roots. Symptoms range from distorted new growth to black spots on leaves and fruit. Yellow leaf margins may also appear.

Functions in plant:

Calcium activates enzymes, is a structural component of cell walls, influences water movement in cells and is necessary for cell growth and division.

Mobility in plant:Calcium, once deposited in plant tissue, is immobile (non-translocatable) so there must be a constant supply for growth.
Influence of soil pH: Calcium deficiency occurs only on very acid soil (< pH 5.0). Even soils that are moderately acid(between pH 5.0 and 6.0) generally contain sufficient calcium for plants.
Factors affecting levels: Poor plant growth on these soils is usually due to excess soluble aluminum, manganese and/or iron rather than inadequate calcium.or where excessive quantities of potassium or magnesium have been used. Calcium deficiency symptoms sometimes occur when the root system has been so damaged by nematodes, insects or diseases that the plant cannot take up adequate calcium.

Correcting deficiencies:

Calcium in plants is a relatively immobile element.
Where deficiencies exist and foliar sprays are used to  correct the deficiency, it is very important to cover the young terminal growth with calcium. Applications on older leaves will not benefit the plant. The suggested rate for foliar application of calcium is 1 to 2 pounds of calcium in 30 gallons of water, using either calcium chloride or calcium nitrate. Agricultural lime should be used to correct calcium deficiency on acid soils. Calcitic lime is suggested when the Ca/Mg equivalent ratio is less than 1.