Soil texture classes is a soil classification system that groups soils based on the relative proportions of soil separates (sand, silt and clay) that each soil contains. Apart from having similar relative proportions of soil separates, the soils in each soil texture class also have similar reactions. Rarely does a soil sample consist of only one soil separate; so combinations of at least two separates gives rise to the need to classify soil texture.
Not every soil has the same quantities of sand, silt, and clay and in fact, the values of these separates can vary noticeably in soils that show similar reactions. To accommodate these variations, the soil texture classes are based on percentage ranges rather than specific values. However, before the texture class of a soil can be determined, a soil texture analysis (link to determination of soil texture) has to be conducted after which a soil texture triangle is then used to read the soil texture class. There are twelve (12) soil texture classes and each class is named after the most abundant and/or most influencing soil separate(s). On a general note, a sand soil contains 85% or more sand; a clay soil contains 40% or more clay; a silt soil, 80% or more of silt, while a loam soil contains about 20% clay, 40% clay and 40% silt.
The 12 texture classes are:
Sand: Soils in the sand texture class are made up of 85% or more sand, 10% or less clay and 15% or less silt.
Loamy sand: The soils in this texture class contain 70 – 85% sand, 10 – 15% clay, and 30% or less silt.
Sandy loam: In this soil texture class, the soils contain soil separates within these ranges;
(a) 40% or less silt, 20% or less clay, and 53 – 85% sand.
(b) 50 – 40% silt, Less than 7% clay, and between 43% and 53% sand.
Loam: Soils in this class contain 7 – 27% clay, 28 – 50% silt, and a sand content of 53 – 23%.
Silt Loam: Soils in this texture class have their separates within these ranges;
(a) 50 – 88% silt, 12 to 27% clay and 38% or less sand
(b) 50 – 80% silt, less than 12% clay and 8 – 50% sand.
Silt: This soil texture class is made up of soils that contain 80% or more silt, 20% or less sand, and less than 12% clay.
Sandy clay loam: The soils in this texture class have the following make up: 20 – 35% clay, less than 28% silt and 45 – 80% sand.
Clay loam: The soils that are in this texture class contain 20 – 45% sand, 27 – 40% clay and 60 – 73% silt.
Silty clay loam: In this soil texture class, the soils are made up of 27 – 40% clay, 60 – 73% silt and less than 20% sand.
Sandy clay: The soils in this texture class contain 35 – 55% clay, 20% or less silt and 45 – 65% sand.
Silty clay: This soil texture class is made up of soils that contain 40 – 60% clay, 40 – 60% silt and 20% or less sand.
Clay: The soils in this soil texture class contain 40% or more of clay, 40% or less silt and 20 – 45% sand.
The above outline of the 12 soil texture classes form a graduated sequence from soils that are coarse in texture and easy to handle (sand textures) to the soils that are very fine and difficult to manage (clay textures). The loam textures are in between the two extremes.
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