subsoil

Plow deep and subsoil all wheat-lands, except those on a gravelly or sandy bottom.

Often where lime has been used in excess, it has sunk to the subsoil, where it remains inactive.

Burrowing animals, by throwing up the soil and subsoil, expose these to be dried and blown away by the wind.

The Common Spruce and its allies are nearly all failures on light dry soil, especially where the subsoil is gravel.