Have you ever thought about the ground that’s beneath your feet and what is it composed of? We might think it’s just plain dirt, but scientists have determined that six different soil horizons make up the different soil profiles of the ground. Learn more about these soil horizons and what impact they can have on your gardening efforts.
What is a Soil Horizon?
Simply put, a soil horizon is a distinct layer in the ground. These six layers are made up of different substances that either look different, have different chemical makeups, or are physically different from the other layers.
Soil horizons act as the history of the soil in a particular area. The layers are formed in a specific way due to the original composition of the land, the weather, the vegetation of the area, and other factors. Think of this as the biography of the soil.
What are the Six Soil Horizons?
The six soil horizons are labeled with a letter denotation and are O, A, E, B, C, and R. Each of these soil horizon layers are unique. O is the soil horizon that is made up of organic materials. Soil horizon A is the layer that is made up of minerals. E is the soil horizon that’s comprised of eluviated soil, or soil layers that have gained materials from other layers by water movement. Soil horizon B is made up of subsoil. C is the soil horizon that contains parent material. Finally, R is the soil horizon that’s bedrock.
Soil Horizon O
Soil horizon O is made up of the organic matter or humus that falls on the soil. This organic matter has decomposed down and created a layer of soil. The O soil horizon can vary when it comes to the size of the segment.
Soil Horizon A
When you think of dirt, you probably imagine soil horizon A. It is the topsoil. It has a combination of organic matter and minerals located in it. Soil horizon A is the best for growing plants. It is always at the surface of the soil, as that is where it forms; however, it can show up again deeper in the layers. If there is a natural event, such as flooding or a landslide, that moves the ground, this layer can go deeper into the soil profile. This layer is often dark in color.
Soil Horizon E
Soil horizon E is a complex layer that is mostly sand, quartz silt particles, and other material that can’t be leached away. It is formed by the organic materials, clay, and any minerals being leached out of the soil. Anything that can’t be leached out of the soil is left behind and makes up this layer. Soil horizon E is often found in forests and areas with old soil that hasn’t been disturbed in a long time. This layer is often lighter in color than other layers because much of it has leached into lower layers.
Soil Horizon B
Soil horizon B is the subsoil layer. All of the materials, such as minerals that are leached from the soil horizon A and E, make up this layer in the soil profile. Often, it has iron, soluble salts, and clay accumulated in it. Erosion can sometimes expose this layer to the surface, in addition to some manmade causes. Bulldozers and landscaping can also result in erosion that exposes it.
Soil Horizon C
Soil Horizon C is the parent material layer. The Earth’s surface deposits created this layer. It could have been produced by glaciers moving across the earth, lake sediment, or the exposure of bedrock.
Soil Horizon R
Soil horizon R is made up of bedrock. The rocks typically found in this layer include limestone, quartzite, sandstone, basalt, and granite. In areas where the bedrock is exposed at the surface of the ground, these materials will weather. The materials that weather off of the bedrock become the soil horizon C. This horizon is technically not soil and is usually found under soil horizon C.
Does All Soil Have All Six Soil Horizons?
There is no specific reason for soil horizons. Some soil profiles will have every single one of the six soil horizons in it. Other areas will have fewer soil horizons in their soil compositions. An example would be some may have just O, or O, E, and B, or A and C. In some spots, there may be soil horizons that repeat in different layers. An example here would be A, B, E, and B. Keep in mind that the majority of soil profiles will have A, B, and C horizons in them. Also, some may also include an O horizon in addition to these three major soil horizons.
Not only can soil profiles have all six soil horizons, fewer than six soil horizons, or have repeating profiles, they can be found in any order. Soil horizons don’t have a set order for how the horizons appear in the soil profile. It all depends on how the soil was formed over time and the surrounding conditions.
Gardeners and Soil Horizons
Gardeners may not think too much about the soil horizons in their garden plots or the history of their soil, but it can help them to make informed decisions. Examining the soil horizons in the area you plan on planting can give you an idea of whether or not you may need to add some soil amendments to make the soil more fertile or to add loosen up soil that has a high clay content. Knowing your soil horizons can help you to determine what’s necessary to get your garden growing healthy and strong.
The soil horizons that make up your backyard may be exactly what you need to have a bountiful garden that doesn’t need much help. That scenario isn’t always what happens, so learning about soil horizons can be applied to your gardening efforts. Your garden soil will thank you with beautiful blooms and a nice harvest.