Soil Texture Triangle

A soil texture triangle is a graphical tool used to classify soils based on their proportions of sand, silt, and clay. These three components are the main texture categories in soil science, and their relative amounts determine a soil’s textural class. Here’s a basic breakdown:

1. Sand: Soil particles are larger than 0.05 mm but less than 2 mm in diameter. Sandy soils feel gritty and drain water quickly.

2. Silt: Soil particles are between 0.002 mm and 0.05 mm in diameter. Silty soils are smooth to the touch and retain water better than sandy soils but are prone to erosion.

3. Clay: Soil particles are smaller than 0.002 mm in diameter. Clay soils are sticky when wet and can hold water very well but may have poor drainage and are often hard when dry.

Using the Soil Texture Triangle

1. Determine Percentages: Measure the proportions of sand, silt, and clay in your soil sample.
2. Locating Points: Find the point for each component’s percentage on the respective axis.
   • For sand, the scale runs from 0% at the top of the triangle (against the left axis) to 100% at the bottom right corner.
   • For silt, the scale runs from 0% at the bottom right corner to 100% at the top corner.
   • For clay, the scale runs from 0% at the bottom left corner to 100% at the top left corner.
3. Intersecting Lines: Draw parallel lines from each of these points following the lines that correspond to sand, silt, and clay throughout the triangle. The location where all three lines intersect indicates the soil’s textural class.

Soil Textural Classes

The textural classes are standardized categories like:

• Sandy: >70% sand
• Loamy Sand: Sand with a significant amount of silt and clay
• Sandy Loam: Less than 50% sand, balanced with silt and clay
• Loam: Roughly equal sand, silt, and clay
• Silt Loam: Mostly silt with balanced but lower amounts of sand and clay
• Silty Clay Loam: Mostly clay and silt, less sand
• Clay: >40% clay

Example

If a soil sample contains 30% clay, 20% silt, and 50% sand, you would:

1. Locate 30% on the clay axis.
2. Locate 20% on the silt axis.
3. Locate 50% on the sand axis.
4. Draw lines from these points inward to find their intersection, which would lead you to the textural class on the triangle.

This common tool is essential in fields like agriculture, geology, and environmental science, as it helps in determining soil properties that affect water retention, nutrient availability, and suitability for different plant types.