I also have to determine the deepest layer of mature soil--would it be the A Horizon, since it is decomposed organic matter? E Horizon is leaching, and anything downward is rock decomposing, so I think it has to be the A Horizon but I wanted to check.
To determine the deepest layer of mature soil, you need to understand the different soil horizons and their characteristics.
The A horizon, also known as topsoil, is composed of decomposed organic matter mixed with mineral particles. It is the uppermost layer of the soil profile and is rich in nutrients. While the A horizon plays an important role in supporting plant growth, it is not necessarily the deepest layer of mature soil.
The E horizon, also called the leaching zone, is located below the A horizon. It is characterized by the loss of minerals through the process of leaching, which occurs when water percolates downward, carrying dissolved substances with it. The E horizon is usually lighter in color and less fertile than the A horizon.
Below the E horizon, you have the B horizon, which contains accumulated minerals that have leached from above. It is often referred to as the subsoil and can vary in color, texture, and composition depending on the specific location.
Finally, beneath the B horizon is the C horizon, which consists of partially weathered parent material. It is and partially broken down rock, with less organic matter and nutrients compared to the upper horizons.
In order to determine the deepest layer of mature soil, you would need to look for the transition between the B horizon and the parent material in the C horizon. This transition zone is where the weathered rock begins to break down into soil and is often considered the bottom of the mature soil profile.
So, to accurately determine the deepest layer of mature soil, you should inspect the soil profile and identify the transition from the B horizon to the C horizon. This will help you identify the termination point of mature soil formation.