底そこ土つち

noun

subsoil

Refers to the layer of soil beneath the surface soil, often in agricultural, geological, or construction contexts.

• この地ち域いきの底そこ土つちは粘ねん土ど質しつだ。

  The subsoil in this area is clayey.

• 底そこ土つちを耕たがやすことで排はい水すい性せいが改かい善ぜんされた。

  Tilling the subsoil improved drainage.