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Colorado Master Gardener sm^ Program Colorado Gardener Certificate Training
Colorado State University Extension
GardenNotes
Estimating Soil Texture
Sandy, Loamy or Clayey?
Outline: Sand, silt, and clay, page 1 Soil texture triangle, page 2 Identifying soil texture by measurement, page 3 Identifying soil texture by feel, page 4
Note: For additional information on managing soils refer to CMG GardenNotes #213, Managing Soil Tilth.
Sand, Silt and Clay
Texture refers to the size of the particles that make up the soil. The terms sand , silt , and clay refer to relative sizes of the soil particles. Sand, being the larger size of particles, feels gritty. Silt, being moderate in size, has a smooth or floury texture. Clay, being the smaller size of particles, feels sticky. [Table 1 and Figure 1]
Table 1. The Size of Sand, Silt and Clay
Name particle diameter
Clay below 0.002 millimeters Silt 0.002 to 0.05 millimeters Very fine sand 0.05 to 0.10 millimeters Fine sand 0.10 to 0.25 millimeters Medium sand 0.25 to 0.5 millimeters Coarse sand 0.5 to 1.0 millimeters Very coarse sand 1.0 to 2.0 millimeters Gravel 2.0 to 75.0 millimeters Rock greater than 75.0 millimters (~2โ)
Soil Texture Triangle
The soil texture triangle gives names associated with various combinations of sand, silt and clay. A coarse-textured or sandy soil is one comprised primarily of medium to coarse size sand particles. A fine-textured or clayey soil is one dominated by tiny clay particles. Due to the strong physical properties of clay, a soil with only 20% clay particles behaves as sticky, gummy clayey soil. The term loam refers to a soil with a combination of sand, silt, and clay sized particles. For example, a soil with 30% clay, 50% sand, and 20% silt is called a sandy clay loam. [Figure 2]
Figure 1. Comparative size of sands, silt and clay
Figure 2. Soil Texture Triangle
Identifying Texture by Feel
Feel test โ Rub some moist soil between fingers
- Sand feels gritty.
- Silt feels smooth.
- Clays feel sticky.
Ball squeeze test โ Squeeze a moistened ball of soil in the hand
- Coarse textures (sand or loamy sands) soils break with slight pressure.
- Medium texture (sandy loams and silt loams) stay together but change shape easily.
- Fine textured (clayey or clayey loam) soils resist breaking.
Ribbon test โ Squeeze a moistened ball of soil out between thumb and fingers.
- Ribbons less than 1โ o Feels gritty = coarse texture (sandy) soil o Not gritty feeling = medium texture soil high in silt
- Ribbons 1-2โ o Feels gritty = medium texture soil o Not gritty feeling = fine texture soil
- Ribbons greater than 2โ = fine texture (clayey) soil
Note: A soil with as little as 20% clay will behave as a clayey soil. A soil needs 45% to over 60% medium to coarse sand to behave as a sandy soil. In a soil with 20% clay and 80% sand, the soil will behave as a clayey soil.
Soil Texture by Feel
Yes
Yes
Yes
Forms a ribbon 1-2โ before breaking
CLAY LOAM
Sandy Clay Loam
Clay Loam
Silty Clay Loam
Forms a weak ribbon less than 1โ before breaking
LOAM
Sandy Loam
Loam
Silt Loam
Forms a ribbon 2โ or longer before breaking
CLAY
Sandy Clay
Clay
Silty Clay
Moisten a pinch of soil in palm and rub with forefinger
Does it feel very gritty?
Does it feel equally gritty and smooth?
Does it feel very smooth?
Yes
No
Start: Place soil in palm of hand. Add water drop-wise and knead the soil into a smooth and plastic consistency, like moist putty. Does the soil remain in a ball when squeezed?
Yes
Add more water
Yes
Add dry soil
Is the soil too dry? No Is the soil too wet? No Sand
What kind of ribbon does it form?
No Yes Loamy Sand
Place ball of soil between thumb and forefinger, gently pushing the soil between with the thumb, squeezing it upward into a ribbon. Form a ribbon of uniform thickness and width. Allow ribbon to emerge and extend over the forefinger, breaking from its own weight. Does the soil form a ribbon?
