Topsoil

topsoil [′täp‚sȯil]

(geology)

Soil presumed to be fertile and used to cover areas of special planting.

Surface soil, usually corresponding with the A horizon, as distinguished from subsoil.

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topsoil

1. The surface of upper layer of soil, as distinct from the subsoil; usually contains organic matter.

2.See loam.

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Topsoil 

the surface layer of soil that is regularly worked by tillage equipment. Topsoil 20–22 cm deep is considered normal. If it is less than 20 cm deep, it is considered shallow; if it is 22–35 cm or greater in depth it is considered deep. Between 80 and 90 percent of the roots of cultivated plants is concentrated in the topsoil. Therefore, the soil must be fertile, containing adequate amounts of the nutrients, moisture, and oxygen needed for both the roots and the soil microorganisms that break down organic remains into compounds assimilable by the plants. Organic and inorganic fertilizers are applied to the topsoil to enrich it with nutrients. The soil is loosened to increase its absorption of precipitation and its oxygen content.