subsoil plow
心土犁
农机
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.