Definition - What does Topsoil mean?
In the context of viticulture, top soil refers to the top 2 to 8 inches of soil in the vineyard. The depth of topsoil is measured from the ground surface to the first layer of densely packed soil known as the subsoil. Topsoil consists of four elements including organic matter, mineral particles, air and water.
The makeup and quality of topsoil is extremely important to the health of wine grape vines, as the soil distributes nutrients and water to the roots which are supported by the topsoil.
WineFrog explains Topsoil
Top soil quality and make-up is an important consideration in every vineyard. The composition of topsoil influences irrigation and nutrient delivery to the vine. In the vineyard, topsoil should be a thin layer that retains water while allowing for good drainage. If the top soil doesn’t retain water, the vines won't receive enough water, and if the soil doesn’t drain properly, the roots can become over saturated and are at an increased risk for mold and mildew.
Quality topsoil needs to include adequate amounts of calcium, iron, magnesium, potassium and nitrogen, all of which are crucial to the growth and development of the vine and wine grapes. Calcium neutralizes soil PH levels, iron assists in photosynthesis, magnesium is an essential component of chlorophyll, potassium supports the Vines metabolism and health, while nitrogen, in the form of phosphates and nitrates, supports root development. Different types and qualities of soil determine not only the health of the vine but also the characteristics of the varietals. Minerality, for instance is a characteristic found in wines grown in limestone topsoils.