Since it is the top layer of soil that is exposed to environmental elements, topsoil is unlike any other layer of soil. It has a distinguishing dark color and texture that make it a choice soil in landscaping and gardening. Understanding what gives topsoil its definition will help you know what to look for when purchasing and using topsoil.
It is the organic matter in topsoil that gives it its dark color, physical structure and water-retaining properties. As the uppermost layer of soil--as the name implies--topsoil develops over time as organic material breaks down and becomes incorporated into the soil.
Topsoil is composed of clay, sand, silt, lime, organic matter, soluble salts and nutrients. As stated by Rich Koenig and Von Isaman of Utah State University Extension, topsoil is high in organic matter and nutrient levels and low in salts.
The key component in topsoil's construction is organic matter. Organic matter develops from the decomposition of plant debris, including leaves, twigs, bark and from animal, insect and worm waste and decay. It is the organic matter in soil that prevents the soil from forming a hard surface layer, since it acts as a sponge that soaks in water and nutrients. Moistened organic matter holds moisture around plant roots, which promotes root health and growth.
Once decaying plant and animal material reaches a state of stability, where its components are no longer rapidly breaking down, this organic matter lightens and aerates the topsoil texture. This is the type of soil that plants thrive very well in.
While topsoil alone is naturally rich in organic matter and nutrients, you may find that your topsoil could use some soil amendments to produce a top-quality product. Since topsoil develops naturally over time, its commercial availability may not be able to keep up with demand. In these cases, topsoil of a lesser grade may be mixed with subsoil and amendments to produce a satisfactory topsoil product.
Peat moss, compost, lime, manure, fertilizer, cover crops and saw dust are a few soil amendments that can greatly increase the quality of your topsoil.
Topsoil is the soil of fertility that mixes minerals, water, air and organic matter into an area's native soil. Through it, many types of vegetation grow and flourish. Topsoil is the foundation of your garden plantings; its condition will greatly impact your garden's yield.