Soil texture WRB soil classification systems use 12 textural classes whereas the UK-ADAS system uses 11. These classifications are based on the percentages of sand, silt, and clay in the soil.. In the United States, twelve major soil texture classifications are defined by the USDA. The twelve classifications are sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay. Soil textures are classified by the fractions of each soil separate (sand, silt, and clay) present in a soil. Classifications are typically named for the primary constituent particle size or
Duplex soil is highly variable, with the top-soils ranging from coarse sand to clay loam and the subsoils from light to heavy clay. Some duplex soils are distinguished by the presence of an A2 bleached horizon, a character also used as a diagnostic key for the distinction between these type of soils. The diagnostic properties used by Northcote for the definition of duplex soils consider only the soil texture (texture contrast and type of boundary between horizons A and B) and the colour is used for their differentiation (i.e. brown, red and yellow duplex soils). Under the Australian Soil Classification they can