GMAS 5th Grade Science Practice Test

Topsoil is the uppermost part of soil where most nutrients, organic matter, air, and water are available for plants. This layer supports root growth and tends to be darker and crumbly from decaying leaves and organisms, making it the most fertile part of the soil for plant life. Minerals in bedrock sit below this layer, not in the topsoil, and the deepest layer of soil is much lower down than the surface. The area below the roots is deeper than the surface layer that plants primarily use, so it isn’t the topsoil either. So the best definition is the uppermost portion of the soil that directly supports plant growth.