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The soil moisture regime, often reflective of climatic factors, is a major determinant of the productivity of terrestrial ecosystems, including agricultural systems. The soil moisture regimes are defined based on the levels of the groundwater table and the amounts of soil water available to plants during a given year in a particular region.
Examples are the World Reference Base for Soil Resources [4] (WRB) and the USDA soil taxonomy. [5] Other systems do not ask whether the properties are the result of soil formation or not. An example is the Australian Soil Classification. [6] A convenient way to define a soil type is referring to soil horizons. However, this is not always ...
Soil texture triangle showing the USDA classification system based on grain size Map of global soil regions from the USDA. For soil resources, experience has shown that a natural system approach to classification, i.e. grouping soils by their intrinsic property (soil morphology), behaviour, or genesis, results in classes that can be interpreted for many diverse uses.
The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials, and is represented by a two-letter symbol. Each letter is described below (with the exception of Pt):
The concept that sediments in shallow water environments undergo soil-forming processes, are capable of supporting rooted plants (such as Eelgrass), and meet the definition of soil according to criteria in Soil Taxonomy has been moving soil scientists into a new frontier of soil survey – mapping subaqueous soils.
A fourth term, loam, is used to describe equal properties of sand, silt, and clay in a soil sample, and lends to the naming of even more classifications, e.g. "clay loam" or "silt loam". Determining soil texture is often aided with the use of a soil texture triangle plot. [5] An example of a soil triangle is found on the right side of the page.
Organic soil material has an organic carbon content (by weight) of 12 percent or more (Soil Taxonomy) or 20 percent or more (WRB). These materials include muck (sapric soil material), mucky peat (hemic soil material), or peat (fibric soil material). Many Histosols show aquic conditions or artificial drainage, [3] some (Folists in Soil Taxonomy ...
The 106 Soil Units form 26 Soil Groups. The FAO soil map was a very simple classification system with units very broad, but was the first truly international system, and most soils could be accommodated on the basis of their field descriptions. The FAO soil map was intended for mapping soils at a continental scale but not at local scale.