What Is a Soil Texture Pyramid?

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What Is a Soil Texture Pyramid?
The soil texture pyramid uses particle sizes to determine overall soil texture. (Photos.com/Photos.com/Getty Images)

Soil scientists use a soil texture pyramid, or soil texture triangle, to determine the exact type of soil present at a given location. Scientists use the percentage of clay, silt and sand in a sample to determine the name for the soil texture. The soil texture pyramid allows you to use individual measurements of soil particle sizes to determine an overall texture profile.

Soil Texture

Soil textures consist of sands, silts, clays and loams. Twelve separate soil texture designations within the texture pyramid consist of single particle sizes and mixtures. The percentage of particle sizes within the soil sample dictates which of the 12 textures the soil possesses. The single particle size textures are sand, silt and clay. Loam is a mixture of all three particle sizes. Other designations, such as sandy clay and silty loam, are mixtures with one dominant particle size.

Reading the Soil Texture Pyramid

The soil texture pyramid is a triangle where the left side is clay, the right side is silt and the bottom is sand. Each side lists the percentages from zero through 100 in increments of 10s along the side. Each point in the triangle represents zero per cent of one particle size and 100 per cent of another size. The interior of the pyramid contains lines to mark the percentages at intervals of 10.

Plotting the Soil Data

The key to determining the soil texture is to plot the analytical data properly. You can begin with any of the particle sizes. Rotate the triangle so you are looking at one side of the triangle. Using a ruler, draw a line along the corresponding percentage for that particle type. For example, if your soil sample has 55-percent sand, draw a line halfway between the 50-percent and 60-percent marks on the sand side of the triangle. Plot each of the particle sizes in this manner.

Determining the Texture Name

After you plot each of the particle sizes onto the soil texture triangle, you can determine the name of the overall texture of the soil. The three lines of the plotted data for sand, silt and clay will intersect at a point. The point will plot into a specific section of the triangle with a texture name such as clay loam or sandy clay. Each soil texture has a small range of particle size percentages; however, the overall texture is the same.

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