The Collaborative International Dictionary of English v.0.48:

Mangel-wurzel \Man"gel-wur`zel\, n. [G., corrupted fr.
   mangoldwurzel; mangold beet + wurzel root.] (Bot.)
   A kind of large field beet (Beta macrorhiza), used as food
   for cattle, -- by some considered a mere variety of the
   ordinary beet. See Beet. [Written also mangold-wurzel.]
   [1913 Webster]
   [1913 Webster]