I got more curious and thus found some more stuff directly linking it to American tradition. 1896 is the date so once more it can't be blamed on Supernatural.

"Salt, as a preservative principle, is a talisman and protection against evil spirits" (58)

Title: Memoirs of the American Folk-Lore Society. Vol. IV. Current Superstitions
Author(s): Fanny D. Bergen and W. W. N.
Source: The Journal of American Folklore, Vol. 9, No. 32 (Jan. - Mar., 1896), pp. 55-66
Stable URL: http://www.jstor.org/stable/532996