Both Calcium salts are very useful. The Carbonate is sparingly soluble and
the Chloride is highly soluble which would allow foliar spraying on some
plants (tomatoes).
According to this url: http://en.wikipedia.org/wiki/Calcium_chloride
chloride has multiple uses but don't get it in your mouth.
It is less harmful to plants when used as a de-icer than other salts.
This one discusses the use of Calcium to treat sodic soil
They both appear to have a good application for treating plants with Calcium
deficiencies and certain apples cannot be raised in many places without a
Calcium supplement.