You searched for: “true soil”
solum, true soil (s) (noun); sola, solums; true soils (pl);
The upper layer of a soil profile where the formation of new soil takes place: The solum is where most plant roots and soil animals are found.

The sola, or the top layers of the soil profiles, are affected by climate and vegetation, especially plant roots.

This entry is located in the following units: soil- + (page 3) sol-, -sol + (page 6)