Question

which soil horizon is considered the topsoil and generally contains the most humus?
a horizon
b horizon
c horizon
o horizon

Explanation:

Soil horizons: The A horizon is the topsoil layer. It is rich in organic matter (humus) from decomposed plant and animal material, has high biological activity, and is where most plant roots grow. The O horizon is mainly organic matter (litter), B horizon is subsoil with accumulated minerals, C horizon is parent material, and O horizon is organic but not the main topsoil with humus in the mineral - soil context. So the A horizon is the topsoil with the most humus.

Answer:

A. A horizon