Understanding the texture triangle to analyze the soil profile

The soil texture triangle was developed in the 1930s by researchers at the USDA (United States Department of Agriculture) as part of the formalization of early modern agronomic classifications. Their goal was to provide a simple graphical tool for describing and comparing the physical structure of soils based on their proportions of sand, silt, and clay. By combining these three data points, a point can be located within a specific zone corresponding to a textural class: silty-clay, sandy-silty, clay-sandy, etc. This tool has since become an international standard, used by research institutes, agronomists, and experienced gardeners. This method is used by INRAE ​​(the French National Research Institute for Agriculture, Food and Environment) and the French Soil Geoportal.

This triangle allows us to:

• Knowing the soil texture (fundamental physical property);
• Identify the agronomic strengths and weaknesses of the soil;
• Choose plants that are adapted to the soil texture;
• Adjust water and amendment inputs;
• Anticipate the risks (surface impact, drainage, compaction).

A good understanding of the triangle is therefore essential for any gardening or sustainable agriculture approach.

The triangle is composed of three axes:

• Sand (descending axis from left to right)
• Limon (ascending axis from right to left)
• Clay (downward vertical axis)

To read the triangle:

1. Accurately measure the percentages of sand, silt, and clay in your soil. This is done through particle size analysis , which you can perform yourself with a Pouryère kit or have done by a laboratory.
2. Draw a line parallel to the axis opposite each component:
   • For the percentage of clay, draw a horizontal line from the left vertical axis to the right.
   • For the percentage of silt, draw a diagonal line descending from right to left.
   • For the percentage of sand, draw a diagonal line rising from left to right.
3. The point where the three lines intersect places you in a zone of the triangle. This zone corresponds to a specific textural class (e.g., "silty-sandy", "sandy-clay", "hardy", etc.).
4. Use the triangle legend to read the exact name of this class. The triangle typically contains 12 official classes according to the USDA standard or French variations.

Example: 60% sand, 25% silt, 15% clay → sandy-silty soil.

A simplified version of this tool is integrated into the analysis results of Pouryère to make reading easier for you.

Here is a summary table combining the average proportions, advantages and disadvantages of the main textural classes derived from the texture triangle:

This classification helps you anticipate the specific needs of your soil and adjust your farming practices.

Once the texture is determined, you can adjust your practices:

• Watering : more frequent on sandy soil, less frequent on clay soil.
• Amendments : compost and green manure for all, sand or BRF on clay soil, manure on sandy soil.
• Crop choices : carrots and lavender in sandy soil, potatoes in silt, hostas and willows in clay soil.

Here are some methods to determine the texture of your soil, detailed step by step:

Touch test : a simple and quick method, ideal for a preliminary assessment

1. Take a handful of damp soil.
2. Roll it between your fingers to form a ball.
3. Crush it between your thumb and forefinger.
   • If it is rough and crumbles: sandy soil.
   • If it is soft like talc: loamy soil.
   • If it sticks and smooths easily: clay soil.

Jar test : a visual method of decantation

1. Take a soil sample (without roots or stones).
2. Fill a clear jar halfway with this soil.
3. Add water and a drop of dishwashing liquid.
4. Shake vigorously for 1 to 2 minutes.
5. Let it rest for 24 to 48 hours.
   • The sand settles first (at the bottom).
   • The silt forms the intermediate layer.
   • The clay remains suspended or settles slowly.
6. Measure the height of each layer to calculate the percentages.

Particle size analysis : the most accurate method

1. Take samples from different areas of your plot.
2. Send them to the lab.
3. The results are interpreted using the texture triangle.
4. You will receive a report with cultivation advice tailored to your soil.

At Pouryère, a complete agronomic analysis (organic matter, pH , nutrients) includes characterizing your soil texture. To do this, order our agronomic analysis kit .