Which soil horizon is considered topsoil?

Which soil horizon is considered topsoil?

• A. Horizon B
• B. Horizon A
• C. Horizon C
• D. Horizon D

Answer: (B)

Topsoil is the uppermost mineral layer in the soil profile where most plant roots grow and nutrients are readily available. In standard soil descriptions, this is the A horizon. It forms as the surface materials weather and mix with organic matter from decaying plants and roots, so it tends to be darker in color and crumbly in texture due to humus and a lively mix of minerals and organisms. That combination makes it the most fertile and biologically active part of the soil, ideal for seedling establishment and root development. Below the topsoil sits the subsoil, the B horizon, where minerals like clays and oxides accumulate and the material generally becomes denser and less fertile. Deeper still is the C horizon, the weathered parent material that is less altered and slower to support plant roots. An organic surface layer, the O horizon, may sit atop these mineral layers, consisting of litter and decomposing material; in everyday language some people call topsoil the surface layer, but in formal terms the topsoil is the A horizon.

Topsoil is the uppermost mineral layer in the soil profile where most plant roots grow and nutrients are readily available. In standard soil descriptions, this is the A horizon. It forms as the surface materials weather and mix with organic matter from decaying plants and roots, so it tends to be darker in color and crumbly in texture due to humus and a lively mix of minerals and organisms. That combination makes it the most fertile and biologically active part of the soil, ideal for seedling establishment and root development.

Below the topsoil sits the subsoil, the B horizon, where minerals like clays and oxides accumulate and the material generally becomes denser and less fertile. Deeper still is the C horizon, the weathered parent material that is less altered and slower to support plant roots. An organic surface layer, the O horizon, may sit atop these mineral layers, consisting of litter and decomposing material; in everyday language some people call topsoil the surface layer, but in formal terms the topsoil is the A horizon.