subsoil

Meanings

1. 1
   noun

   the layer of soil beneath the topsoil and above the underlying rock or parent material

   The roots reached through the dark topsoil into a dense clay subsoil.

2. 2
   verb

   to loosen or cultivate soil deeply below the normal plowing depth

   The farmer subsoiled the compacted field before planting the orchard.

A compound of sub-, 'under,' + soil. The noun names the earth directly below surface soil; the agricultural verb developed for working or breaking up that deeper layer.

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