1
general::
Phrase(s): plow something under (something)
to turn something under the surface of soil by plowing. • The farmer plowed the wheat stubble under the surface of the soil. • The farmer plowed the stubble under.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Cause to vanish, overwhelm, as in The independent bookstores are being plowed under by the large chains. This term alludes to the farmer's burying vegetation by turning it into the soil with a plow. [Second half of 1900s]
American Heritage Idioms