Search results
Results From The WOW.Com Content Network
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.
For example, GW-GM corresponds to "well-graded gravel with silt." If the soil has more than 15% by weight retained on a #4 sieve (R #4 > 15%), there is a significant amount of gravel, and the suffix "with gravel" may be added to the group name, but the group symbol does not change.
Field characteristics (described according to Annex 1 of the WRB Manual): A soil developed from loess shows a marked clay increase in around 60 cm depth and clay coatings in the clay-richer horizon. According to the landscape setting, we presume that high-activity clays dominate. In the field, a pH of 6 is measured in the subsoil.
USDA soil taxonomy (ST) developed by the United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters (most commonly their properties) and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series.
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 AASHTO Soil Classification System was developed by the American Association of State Highway and Transportation Officials, and is used as a guide for the classification of soils and soil-aggregate mixtures for highway construction purposes.
Iron oxides and clay minerals accumulate as a result of weathering. In soil, where substances move down from the topsoil, this is the layer where they accumulate. The process of accumulation of clay minerals, iron, aluminum, and organic compounds, is referred to as illuviation. The B horizon has generally a soil structure.
Vertisols have a high content of expansive clay minerals, many of them belonging to the montmorillonites that form deep cracks in drier seasons or years. In a phenomenon known as argillipedoturbation, alternate shrinking and swelling causes self-ploughing, where the soil material consistently mixes itself, causing some vertisols to have an extremely deep A horizon and no B horizon.