Dig a deep hole and look at the wall. You will see horizontal layers stacked like pages in a book. That vertical cross-section is the soil profile, and each layer tells a story about how the soil formed and how it behaves.

Topsoil sits at the top, dark with organic matter and full of roots. Below it, the subsoil accumulates clay and minerals leached from above. Deeper still, weathered parent material transitions into bedrock. Not every soil has every layer, and thickness varies wildly from place to place.

Common horizon names

• O horizon, surface litter and decomposing organic matter
• A horizon, topsoil rich in organic matter
• B horizon, subsoil of accumulated clay and minerals
• C horizon, weathered parent material
• R horizon, solid bedrock

Farmers and agronomists read profiles to understand drainage, rooting depth, and nutrient movement. A shallow profile over bedrock drains fast and dries out quickly. A deep profile holds more water and supports larger root systems.