Have you ever taken a look at a hillside that has been cut through to make a road? You can usually see many different layers that might be different colors or obviously made up of different materials. What you see are the more or less horizontal layers of soil and rock that have developed in that particular place. Let’s start digging! Find out more about soil horizons!
O horizon – Also called humus, this is the top-most layer of any soil with a significant amount of plant life above it. Humus is a layer of organic material (hence the ‘O’), like dead grass, fallen leaves, etc. that collects on the ground’s surface.
A Horizon – The A horizon is topsoil, the upper layer of actual dirt. It’s made of broken up bits of rock and dust as well as organic matter. If a soil has a deep A horizon, that likely means it is older and has had a lot of plants growing in it over time. In terms of plants and farming, this is the nutrient-rich layer that plants love to get their roots into.
B Horizon – This layer is also made of finely ground up rock bits (AKA dirt and dust!) and some organic matter, though much less than in the A horizon. The subsoil is also hard-packed and dense. In some tropical areas with a lot of rainfall, heavy minerals such as iron and nickel can get washed out of the upper soil layers (“leaching”) and deposit in the subsoil, causing it to be heavy and hard, and also to take on a different color.
C Horizon – The C horizon is the parent material from which the soil formed by erosion and plant activity. This usually means large chunks of partially broken-up rock, very little organic material. In sedimentary deposits, the C horizon can include a sedimentary rock layer if it is the parent material of the soil and a different type of roc than the bedrock.
R Horizon – ‘R’ stands for rock, and in this case, bedrock. Bedrock is considered to be solid rock that formed in place and is the underlying foundation of an area. It will be the bottom-most layer, above which soil development takes place.
Check out our interesting article about Soil Layers!