Laboratory Method of Soil textural classes

The mechanical analysis methods have been used by USDA to develop a method for naming the textural class. This is depicted by a triangle shown in Fig. For a given composition of soil, the textural class can be named using this triangle.

The sides of the triangle represent mass percentage of clay, silt and sand. The sum of the percentages of sand, silt and clay at any point in the triangle is 100.  To find the textural class on the basis of the mechanical composition of soil, the percentage of one of the separates (say clay) is first located in the diagram and projected towards the centre  of the triangle running parallel to the adjacent side. Similarly it is done for any of the other two separates, silt or sand. The point at which the two projections cross will identify the class name. Let us take an example to understand this. Suppose a soil has the following composition of the three separates, 35% clay, 25% silt and 40% sand, then we may use any two of the three values and use the above method to arrive at the soil textural class as indicated by pairs of green lines in the figure. This soil is an example of the class, 'clay loam'. You can verify this from Fig.