IMO comparing the lime requirements of a clay subsoil of a pond basin to surface growing crops I think will give just 'ball park' estimates. The clay subsoils 'could' have a higher pH and more calcium present than the surface topsoils due to topsoils having more organic decomposiiton creating humic acid and less calcium leaching and added plant calcium extraction. If one wants the best answer, do a soil test of the pond basin. These tests are often free or very low cost at agricultural supply facilities who usually sell lime.

Remember that lime additions to ponds and farm fields to maintain the proper alkalinity / pH need to be done on a regular basis. Periodic testing determines the need for lime additions.