Topsoil is the most important aspect of whether an area of land will be able to grow plants. Bad topsoil, or a lack of topsoil altogether, will not provide plants with the nutrients or organic matter they need to survive. Locating quality top soil, according to the Utah State University Cooperative Extension, takes some effort.
Soil is divided in the earth in horizontal layers. Topsoil is located in the uppermost layer, called the "A horizon." Topsoil appears darker than the layers underneath it. Quality topsoil is easy to till, holds water and drains excess water well. Topsoil thickness tends to differ between locations.
One of the measurements of good topsoil is the level of soluble salts in the soil. Too much salt content in the soil prevents plants from absorbing water properly and has toxic effects on landscape plants. Soluble salts may be removed from soil by adding low-salt water to the soil before being placed on a landscape.
High-quality topsoil will break apart easily in the hand and will become slightly spongy when wet. Topsoil that has too much sand in it stays dry and drains water too quickly. Topsoil that has too much clay in it will not absorb water properly and will retain water for too long. The University of Connecticut suggests the best topsoil is a mixture of sandy loam soil and fine sandy loams (the latter for their water retention properties).
Good topsoil should contain at least 2 percent organic matter, but contain no more than 10 percent says the University of Connecticut. Organic matter is material that contains carbon, says the University of Massachusetts, and provides energy to microorganisms that benefit plants. Soil organic matter is made of dead, decaying or living organic matter. This organic matter is broken down as the microorganisms feed on them.
Most topsoil requires soil amendments to reach its top quality. This includes organic matter, fertilizer and the addition of lime. Lime changes the acidity of the soil so that plants will grow properly. Usually, 2 to 3 inches of soil amendment tilled into the top 6 to 8 inches of the topsoil will improve the soil quality. A pH test will determine the topsoil's pH level, and will indicate whether the addition of lime is necessary.