Using the Soil Triangle

Soil Texture Soil texture is determined by the relative amounts of three groups of soil particles. The three soil particles are sand, silt, and clay. Texture provides a means to physically describe soil by measuring the percentage of the three soil particles. Soil texture is determined by the relative amounts of three groups of soil particles or soil separates. The three soil separates are sand, silt, and clay. Texture provides a means to physically describe soil by feel or by measuring the proportion (percentage) of the three soil particle size ranges. A coarse soil has a relatively large amount of sand and feels “gritty.” A silt soil has the texture and feel of flour. A clayey soil may feel “slick” or “sticky” depending on its water content. A loam soil has nearly equal amounts of sand, silt, and clay. The relative sizes of the three soil separates are compared in Figure 2.2. Sand particles can be seen by the naked eye. A microscope must be used to see silt particles. An electron microscope is needed to see clay particles.

The Soil Triangle A textural triangle is used to describe soil texture. The three sides of the triangle represent the percentages of sand, silt, or clay. The intersection points of three lines from each side of the triangle determine how the soil texture will be classified.

Soil Triangle

Using the Soil Triangle Example, if a soil has 20 percent clay, 40 percent sand, and 40 percent silt, it is a loam (see the triangle in the area labeled loam).

Practice Determine the soil Classification: Sand = 20% Silt = 50% Clay = 30%

Practice Determine the soil Classification: Sand = 45% Silt = 32% Clay = 23%

Lab Samples Determine the soil classification from your soil sediment lab: