Soil classification

Soil classification is a dynamic subject, from the structure of the system, to the definitions of classes, to the application in the field.

[1] Ancient Greek scholars produced a number of classification based on several different qualities of the soil.

It distinguishes sands from gravels by grain size, classifying some as "well-graded" and the rest as "poorly-graded".

Despite these differences, in a well-constructed system, classification criteria group similar concepts so that interpretations do not vary widely.

Another approach is numerical classification, also called ordination, where soil individuals are grouped by multivariate statistical methods such as cluster analysis.

The USDA classification was originally developed by Guy Donald Smith, director of the U.S. Department of Agriculture's soil survey investigations.

The European Union uses the World Reference Base for Soil Resources (WRB), currently the fourth edition is valid.

[12] The U.S. Occupational Safety and Health Administration (OSHA) requires the classification of soils to protect workers from injury when working in excavations and trenches.

Such technical classifications are developed with specific applications in mind, such as soil-water relationships, land quality assessment or geotechnical engineering.