Qualitative Properties of Topsoil

Organic Material

• The presence of organic materials in soil is what sets topsoil apart from subsoil and makes it a vital component of productive agriculture. The more organic substances, the better. You can reasonably judge the quality of organic substances in topsoil by observing color and texture. Topsoil with a granular structure and dark color is generally ideal for cultivation. If organic material is inadequate, it can be boosted with the addition of organic amendments like peat moss or compost.

Soil Texture

• Good topsoil has a fine texture, contrasting with the coarser structure found in subsoil layers. You can evaluate topsoil structure by feeling the texture of soil in your hands. Coarse particles indicate the soil is sandy, while smooth particles are signs of clay soil. Crumbly texture is ideal for seed beds and vegetable gardens. Soil texture is a vital component of topsoil quality because it determines the soil's water-holding capacity and the ease of working the soil (tilth). Beware of hard soils, which may have too little organic content or too much clay. Soil amendments available at garden stores are designed to improve soil texture.

Soil Composition

• Usually a combination of sand, clay and silt is the preferred topsoil mixture, as it provides an ideal water-holding capacity for growing plants. Sandy soils have trouble retaining water, and water tends to drain quickly. Clay soils are dense, and their small pores hold water for a long time. High levels of organic matter tend to improve soil tilth, structure, drainage and water-holding capacity. The texture of soil is indicative of its composition.

Color

• The easiest way to determine the quality and depth of topsoil is to dig into the earth until you reach a lighter-colored layer of soil. Good quality topsoil is dark brown or nearly black, while subsoil is of a lighter color. Soils that are light brown usually have a lower organic content. Very light or white soils may have high amounts of salts or lime. Topsoil is composed of lower levels of salts, lime and clay components, which are at higher levels in the subsoil layer.