What is "fragipan"

n. A diagnostic soil horizon of the USDA soil taxonomy, an altered subsurface soil layer that restricts water flow and root penetration.

A fragipan is a diagnostic horizon in USDA soil taxonomy. They are altered subsurface soil layers that restrict water flow and root penetration. Fragipans are similar to a duripan in how they affect land-use limitations. In soil descriptions, they are commonly denoted by a Bx or Btx symbol.