What does the abbreviation "Ap" refer to in soil horizons?

The abbreviation "Ap" refers specifically to a soil horizon that has been altered by human activity, such as plowing or other disturbances. This horizon is typically characterized by a mixing of organic material with mineral soil due to cultivation practices, which changes the natural structure and composition of the soil.

In an "Ap" horizon, the upper layer is often lighter in color and may show signs of depletion of certain minerals and nutrients as a result of agricultural activities. This distinct horizon is essential for soil evaluators as it signifies the degree of disturbance the soil has undergone, impacting its health, fertility, and overall ecosystem function. Understanding this helps in assessing land use practices and their effects on soil quality.