Principal Surface Soil Classes

  1. Loam--When rubbed between the thumb and fingers, approximately equal influence of sand, silt, and clay is felt. Makes a weak ribbon (less than 2.5 cm long).
  2. Sandy loam - Varies from very fine loam to very coarse. Feels quite sandy or gritty, but contains some silt and a small amount of clay. The amount of silt and clay is sufficient to hold the soil together when moist.Makes a weak ribbon (less than 2.5 cm long).
  3. Silt loam - Silt is the dominant particle in silt loam, which feels quite smooth or floury when rubbed between the thumb and fingers. Makes a weak ribbon (less than 2.5 cm long).
  4. Silty clay loam - Noticeable amounts of both silt and clay are present. Makes a medium ribbon (2.5 to 5 cm long).
  5. Clay loam - Clay dominates a clay loam, which is smooth when dry and slick/sticky when wet. Silt and sand are usually present in noticeable amounts in this texture of soil, but are overshadowed by clay. Makes a medium ribbon (2.5 to 5 cm long).

In general, the finer the texture: the more difficult a soil is to work or till, the greater the water holding capacity, the slower water will enter and move through the soil profile, the more difficult plant root penetration, the more readily surface soil will crust, and the more nutrient rich the soil.

Other textural designations of surface soils are sands, loamy sands, sandy clay loams,silty clay, siltss, and clays. In each textural class there is a range in the amount of sand, silt, or clay that class may contain. These ranges can be expressed as a percentage for each soil texture. The percentages converge on the soil triangle to determine soil textural classes. The composition of each textural class does not allow for overlap from one class to another. (Soil Triangle)

Texture of soil influences many different characteristics. A brief comparison between sandy and clay soils will highlight these points. In general coarse-textured or sandy soils allow water to enter at a faster rate and to move more freely in the soil. In addition, the relatively low water-holding capacity and the large amount of air present in sandy soils allows them to warm up faster than fine-textured soils. However, sandy soils must also be irrigated more often than high clay soils. Sandy soils are also more easily tilled. They are well-suited for the production of vegetables, landscape plants and many types of fruit.


Source: University of Arizona Cooperative Extension. 1998. Arizona Master Gardener Manual: Chapter 2, Soils and Fertilizers. Tucson, AZ. Available at (verified 19 August 2004).