During a recent workshop, a speaker talked about calcareous soil.  He mentioned that calcareous areas have an abundance of calcium.  That didn't sound right to me, since I remember from soils class that calcareous meant the presence of calcium carbonate, not calcium.

From Dr. John Sawyer, Iowa State University, calcareous soils:

• have a pH of 7.2 to 8.5
• contain various amounts of solid calcium carbonate (1 to 20% CaCO₃ by weight)
• CaCO₃ controls soil pH
• CaCO₃ (solid) + 2 H+ = Ca⁺² + CO₂ + H₂O

If calcium carbonate is present (as a solid), then how much soluble (i.e. plant available) calcium is there?  I don't know, but will be working to find out.  It seems to me, that it would be conceivable to need more calcium for plant growth & development, even though the pH is above neutral.