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Soil texture classification

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Soil texture represents the relative composition of sand, silt and clay in soil.
Soil texture assessment is usually carried out by manual working of a soil sample. The results allow the classification of the soil into texture groups e.g. sands, sandy loams, loams, clay loams, light clays and medium-heavy clays.


Overview

The first classification, the International system, was first proposed by Atterberg (1905), and was based on his studies in southern Sweden. Atterberg chose 20 m 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 rise within 24 h 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 FAO used the USDA system in the FAO-UNESCO world soil map and recommended its use.


Particle-size classification

Each country has its own classification.


Texture diagram

The particle-size distribution is usually represented in a texture diagram, relating the percentages of sand, silt and clay to a texture class.
The first texture diagram relating the particle-size distribution to textural classes was drawn in 1911 by Whitney (1911) where the clay and silt percentages were represented on a right-angled triangle. Davis and Bennett (1927) replaced it by a more difficult to read ternary diagram which shows percentages of clay, silt, and sand. In 1945, the USDA revised its texture triangle to accommodate changes in analytical procedure and particle-size limits.

Prescott et al. (1934) devised a texture diagram for the International system based on mechanical analysis and field descriptions made by the CSIR (Council for Scientific and Industrial Research) Division of Soils at that time. This was later revised by Marshall (1947) and has been used in Australia until the present.

Toogood (1958) presented a ’simplified’ Canadian texture diagram (which is similar to the USDA) in which percentages of sand and clay are plotted on a right triangle.

Different countries have their own texture diagram.


References

  • Atterberg A (1905) Die rationalle Klassifikation der Sande und Kiese. Chemiker Zeitung 29, 195-198.
  • Davis ROE, Bennett HH (1927) Grouping of soils on the basis of mechanical analysis. United States Department of Agriculture Departmental Circulation No. 419.
  • Marshall TJ (1947) Mechanical composition of soil in relation to field descriptions of texture. Council for Scientific and Industrial Research, Bulletin No. 224, Melbourne.
  • Prescott JA, Taylor JK, Marshall TJ (1934) The relationship between the mechanical composition of the soil and the estimate of texture in the field. Transactions of the First Commission of the International Society of Soil Science 1, 143-153.
  • Toogood JA (1958) A simplified textural classification diagram. Canadian Journal of Soil Science 38, 54-55.
  • Whitney M (1911) The use of soils east of the Great Plains region. United States Department of Agriculture Bureau of Soils Bulletin No. 78.

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