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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 ...
Gradually soil is able to support higher forms of plants and animals, starting with pioneer species and proceeding along ecological succession to more complex plant and animal communities. [6] Topsoils deepen with the accumulation of humus originating from dead remains of higher plants and soil microbes. [7]
Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. [6] Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm 3, though the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm 3. [7]
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. [1]
A further consequence of continued cultivation and traffic is the development of compacted, impermeable layers or 'pans' within the profile. The decline of soil structure under irrigation is usually related to the breakdown of aggregates and dispersion of clay material as a result of rapid wetting.
Field equipment for soil description. Soil morphology is the branch of soil science dedicated to the technical description of soil, [1] particularly physical properties including texture, color, structure, and consistence. Morphological evaluations of soil are typically performed in the field on a soil profile containing multiple horizons. [2]
Soil scientists use the capital letters O, A, B, C, and E to identify the master horizons, and lowercase letters for distinctions of these horizons. Most soils have three major horizons—the surface horizon (A), the subsoil (B), and the substratum (C). Some soils have an organic horizon (O) on the surface, but this horizon can also be buried.