1. The "A" horizon:
* This is the topmost layer of soil, often called the topsoil, in most soil classifications.
* It's characterized by being rich in organic matter (decomposed plant and animal material) and having a dark color.
* This is where most plant roots grow, and it's the most fertile layer of the soil.
2. The "O" horizon:
* This is the very top layer of soil, found in forested areas, consisting mostly of undecomposed plant matter like leaves, twigs, and needles.
* It's not technically part of the soil profile, but it breaks down over time to contribute to the "A" horizon.
In conclusion:
* The "A" horizon could be considered the "second layer" if you consider the "O" horizon to be the first layer.
* However, the "O" horizon is not always present, so it's more accurate to say that the "A" horizon is the first truly organic layer of soil.
For a more detailed understanding of soil layers, you can look into soil profiles and their horizons (O, A, E, B, C, R).
