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Soil texture

 

 
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Soil texture
 
 
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Soil texture is a soilSoil

Soil is the collection of natural bodies that form in earthy material on the land surface....
 property used to describe the relative proportion of different grain sizes of mineralMineral Summary

Minerals are natural compounds formed through geological processes....
 particles in a soil. Particles are grouped according to their size into what are called soil separates. These separates are typically named clayClay

Clay is a term used to describe a group of hydrous aluminium phyllosilicate minerals , that are typically less than 2 μm...
, siltSilt

Silt is soil or rock derived granular material of a specific grain size....
, and sandSand

Sand is an example of a class of materials called granular matter....
. Soil texture classification is based on the fractions of soil separates present in a soil. The soil texture triangle is a diagram often used to figure out soil textures.

Soil separates



Soil separates are specific ranges of particle sizes. In the United StatesUnited States Summary

The United States of America, also known as the United States, the U.S., the U.S.A., and America, is...
, the smallest particles are clay particles and are classified by the USDA as having diameters of less than 0.002 mm. The next smallest particles are silt particles and have diameters between 0.002 mm and 0.05 mm. The largest particles are sand particles and are larger than 0.05 mm in diameter. Furthermore, large sand particles can be described as coarse, intermediate as medium, and the smaller as fine. Other countries have their own particle size classifications.

Name of soil separate Diameter limits (mm)
Clay less than 0.002
Silt 0.002 - 0.05
Very fine sand 0.05 - 0.10
Fine sand 0.10 - 0.25
Medium sand 0.25 - 0.50
Coarse sand 0.50 - 1.00
Very coarse sand 1.00 - 2.00

Soil texture classification



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 a combination of the most abundant particles sizes, e.g. "sandy clay" or "silty clay." A fourth term, loamLoam

Loam is soil composed of a relatively even mixture of three mineral particle size groups: sand, silt, and clay....
, is used to describe a roughly equal concentration of sand, silt, and clay, and lends to the naming of even more classifications, e.g. "clay loam" or "silt loam."

In the United States, twelve soil texture classifications are defined by the USDA:
  • Clay
  • Silt
  • Sand
  • Loam
  • Silty clay
  • Sandy clay
  • Clay loam
  • Silt loam
  • Sandy Loam
  • Loamy sand
  • Silty clay loam
  • Sandy clay loam


Determining the soil textures is often aided with the use of a soil texture triangle.

History of classification

The first classification, the International system, was first proposed by Atterberg (1905), and was based on his studies in southern Sweden. Atterberg chose 20 µm for the upper limit of silt fraction because particles smaller than that size were not visible to the naked eye, the suspension could be coagulated by salts, capillary riseCapillary action

Capillary action or capillarity is the ability of a substance to draw a liquid upwards against the force of gravity....
 within 24 hours was most rapid in this fraction, and the pores between compacted particles were so small as to prevent the entry of root hairs. Commission One of the International Society of Soil Science (ISSS) recommended its use at the first International Congress of Soil Science in Washington in 1927. Australia adopted this system and according to Marshall (1947) its equal logarithmic intervals are an attractive feature worth maintaining. The USDA adopted its own system in 1938, and the FAOFood and Agriculture Organization

The Food and Agriculture Organization is a specialized agency of the United Nations that works to raise levels of nutrition...
 used the USDAUnited States Department of Agriculture

The United States Department of Agriculture is a United States Federal Executive Department....
 system in the FAO-UNESCO world soil map and recommended its use.