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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 ...
A pH of 3.5 has one million times more hydronium ions per litre than a solution with pH of 9.5 (9.5 − 3.5 = 6 or 10 6) and is more acidic. [ 115 ] The effect of pH on a soil is to remove from the soil or to make available certain ions.
The soil production rate due to weathering is approximately 1/10 mm per year. [5] New soils can also deepen from dust deposition. 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]
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]
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 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.
Soil bulk density, when determined at standardized moisture conditions, is an estimate of soil compaction. [3] Soil porosity consists of the void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining.
The process of soil formation is dominated by chemical weathering of silicate minerals, aided by acidic products of pioneering plants and organisms as well as carbonic acid inputs from the atmosphere. Carbonic acid is produced in the atmosphere and soil layers through the carbonation reaction. [4]