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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):
Highly oxidized red soil in Tirunelveli District, India. Red colors often indicate iron accumulation or oxidation in oxygen-rich, well-aerated soils. [4] Iron concentrations caused by redox reactions because of diffusion of iron in crystalline and metermorphic rock, in periodically saturated soils may also present red colors, particularly along root channels or pores.
About 1,000 soil subgroups are defined in the United States. [6] A soil family category is a group of soils within a subgroup and describes the physical and chemical properties which affect the response of soil to agricultural management and engineering applications. The principal characteristics used to differentiate soil families include ...
In colorimetry, the Munsell color system is a color space that specifies colors based on three properties of color: hue (basic color), value , and chroma (color intensity). It was created by Albert H. Munsell in the first decade of the 20th century and adopted by the United States Department of Agriculture (USDA) as the official color system ...
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.
Soil color is also moisture dependent, specifically the color value. It is important to note the moisture status as "moist" when adding water does not change the soil color, or as "dry" when the soil is air dry. [11] The standard moisture status for describing soil in the field varies regionally; humid areas generally use the moist state while ...
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.
Color analysis can be conducted by-eye, usually matching specimen color with reference charts. This methodology has been used extensively in soil analysis, often using the Munsell color system as the reference. [1] [2] While this is a traditionally used method, it is considerably subjective, relying on the ability of the naked eye to match colors.