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This is a somewhat arbitrary definition as mixtures of sand, silt, clay and humus will support biological and agricultural activity before that time. [47] These constituents are moved from one level to another by water and animal activity. As a result, layers (horizons) form in the soil profile.
A soil layer is a zone in the soil, approximately parallel to the soil surface, with properties different from layers above and/or below it. If at least one of these properties is the result of soil-forming processes, the layer is called a soil horizon. In the following, the term layer is used to indicate the possibility that soil-forming ...
Soil structure describes the arrangement of the solid parts of the soil and of the pore spaces located between them (Marshall & Holmes, 1979). [1] Aggregation is the result of the interaction of soil particles through rearrangement, flocculation and cementation.
Soil formation, also known as pedogenesis, is the process of soil genesis as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order within soils.
In soil classification systems, topsoil is known as the O Horizon or A Horizon. [8] [9] Soil horizons are layers parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath.
A soil scientist examining horizons within a soil profile. Soil science is the study of soil as a natural resource on the surface of the Earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils.
Subsoil layer. Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus. The subsoil is labeled the B Horizon in most soil mapping systems.
Since the origin of agriculture, humans have understood that soils contain different properties which affect their ability to grow crops. [4] However, soil science did not become its own scientific discipline until the 19th century, and even then early soil scientists were broadly grouped as either "agro-chemists" or "agro-geologists" due to the enduring strong ties of soil to agriculture.