Understanding Soil Horizons
Looking back at the soil test you performed, lets dig deeper into understanding your soil composition. Below your vegetation is not just a uniform soil layer, there are different levels that have a direct effect upon your vegetation, referred to as a soil horizon. Those individual horizons serve a specific purpose and can identify if soil is healthy.
Just below your vegetation is the O horizon or organic layer. This layer is made up of decomposing clippings, leaves, sticks and old plant matter. Those materials listed are excellent at absorbing moisture and providing protection to the soil from sunlight and wind. Unless in a highly managed turfgrass situation, bagging or removing clippings is unnecessary. Below the O horizon is the A horizon or commonly called Topsoil. Healthy topsoil contains further broken-down material called humus, sand particles, gravel pieces, minerals and beneficial organisms. The roots of a plant often thrive here because of the mineral/nutrient material is broken down and material is often less compacted allowing water transport. The A horizon is the most important layer when performing maintenance activities such as fertilizing or aerating.
The E horizon follows and absorbs the finer particles and unused nutrients to form a more rigid and compacted structure layer. Roots continue into this layer and absorb those finer nutrients. In deeper soil environments, a B horizon can be distinguished by a normally darker layer below the E horizon as more nutrients and particles have partially stopped leaching. Most often the E and B horizons can be considered one as they are very similar in composition. Looking back at the vegetation types, if deeper rooted trees and shrubs are desired, a more in-depth horizon sample may be required to determine available nutrients. Nearing the end, you have a C horizon, which is larger cobbles and bedrock material below. Here, the roots and nutrients in the soil along with groundwater are constantly breaking down bedrock material creating that broken cobbly layer.