Soil texture is determined in the field, simply by making paste and testing it for stickiness (presence of clay), grittiness (presence of sand), and being or not soapy (presence of a certain amount of silt). See the pictures below.

Figure 5.1: Determining Soil Texture

The soil texture is clay if the prepared paste (from the soil sample) is sticky, and easily forming long ribbon (Figure 5.1). Ribbon is formed by rubbing on the paste between fore-finger and thumb. It is recommended to use your left hand, in order to keep your right hand clean for writing, using Munsell Color Charts, or Soil Classification book, etc.

See Figure 5.2: In an indoor exercise, students are trained to feel how different texture classes can be determined in field.

Ribbons are also formed if the sample is clay loam, which is different in Figure 5.3. In Figure 5.3, the ribbon is bending down around fore fingers. In addition, the soil is not so sticky as in the case of clay.

With loam one cannot form a good ribbon. A striking characteristic of loam is that the soil paste feels very soft and smooth. Any of these textures (clay, clay loam and loam) can have more than a given amount of sand (see the USDA Textural Triangle) in which case the adjective “sandy” will be added to the name, that is, sandy clay, sandy clay loam, and sandy loam, respectively. If there is too much sand in “loam” so far that no ball can be formed, then we would have “loamy sand”. If one hesitates between the two (sandy loam and loamy sand) make then a ball from the paste and throw it up for about 50cm and catch it back in the hand palm. If soil sample stays as a ball it is sandy loam but if it collapses it is “loamy sand”.

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Determining Soil Properties in Practice

The texture classes loam, clay loam, and clay may be silty, that is, when silt percentage is more than a certain amount (see the USDA Textural Triangle). Then we will have silt loam, silty clay loam, and silty clay, respectively. In field, a few drops of water is added to the soil sample and gently rubbed with the thumb in order to check whether the soil feels soapy or not. If soapy, it is then silty.

The tests mentioned above include some general hints which help determining texture, but it is very important to check these feelings with the laboratory, and/or with a senior soil surveyor. This is specially important when you go to a new study area. Obviously, one cannot expect that young soils, old soils, volcanic soils, soils with kaolinite clay type will react similarly.