The Collaborative International Dictionary
Subsoil plow
Subsoil \Sub"soil`\, n. The bed, or stratum, of earth which lies immediately beneath the surface soil.
Subsoil plow, a plow having a share and standard but no
moldboard. It follows in the furrow made by an ordinary
plow, and loosens the soil to an additional depth without
bringing it to the surface.
--Knight.