Soil Texture Test
Purpose: Soil texture refers to the relative proportion of mineral particles of various sizes
(soil fractions): sand, slit, and clay expressed as a percentage. The basis of the test is the
particle size and its mass, as related to settling time when dispersed in solution. Size
classes according to their particle diameter are listed in the table below:
Size Class
Very coarse sand
Coarse sand
Medium sand
Fine sand
Very fine sand
Silt
Clay
Particle Diameter (mm)
2.0-1.0
1.0-0.5
0.5-0.25
0.25-0.10
0.10-0.05
0.05-0.002
Less than 0.002
Soil fractions give specific characteristics to the soil. Clay improves the nutrient holding
capacity, increases water retention, soil stability, but is sometimes difficult to till. Soils
high in sand characteristically have good drainage, aeration, and are relatively easy to till.
Soils high in silt will be intermediate. The soil texture classes are determined by plotting
the percentage of sand, silt, and clay on the texture triangle (see Figure 1).
Tools:
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About 10 ml of soil will be required for this test; dried and sieved is best.
For this procedure, a 50 ml plexi-glass vial is used, available from LaMotte (Code
0670 $6.40), with a mark at the 10 ml and 40 ml levels.
LaMotte texture dispersing reagent is also used (Code 5644WTH $5.90 for 60
ml).
A cap for the plexi-glass tube
A measuring ruler marked in mm are also needed
Procedure:
This test is not as precise as the laboratory hydrometer method, but it requires fewer
tools, and is relatively fast. It will help you know if you have an extremely sandy soil,
clayey soil, or something in between.
1. Fill the soil separation tube up to the 10 ml line with soil. Gently tap the tube after
each portion is added.
2. Dilute the sample by adding water up to the 40 ml line.
3. Add 10 drops of texture dispersing reagent. Hold the bottle vertically when
adding the drops.
4. Cap the tube and shake for 2 minutes.
5. Allow the tube to stand for exactly 30 seconds. Measure the height of the soil
particles that have settled at this time. This is the sand portion. Record this value.
6. Allow the tube to stand undisturbed for 30 minutes. Use the ruler to measure the
height of the particles that have settled and record the value. Subtract the first (30
second) reading. This difference is the portion of soil that is silt.
7. Now let the tube of soil stand for at least 24 hours. At the 24-hour point, take
another reading. Subtract the height at the 30 minute reading. This difference is
the clay portion of the soil. If the water is still very cloudy, take another reading
after it has completely cleared. Compare it to the 24-hour reading. If the level has
risen, subtract the 30-minute reading from this value, and use this for the clay
reading. In some cases, we have found that the soil continues to settle, and the
level actually goes down. If this happens, simply use the 24 hour reading, or
assume a zero value for clay.
8. Now, put the three height readings in the form of percentages. For example:
Height in
Corresponds to Total height in ml:
millimeters after:
fraction of:
30 seconds
sand
9 mL
30 minutes
silt
13 mL
24+ hours
clay
16 mL
Difference in Portions expressed
height, or portion: as percentage:
9 mL
9/16 = 56%
4 mL
4/16 = 25%
16 mL
3/16 = 19%
Using the soil texture triangle in Figure 1, find the spot on the diagram that corresponds
to the fractions of sand, silt and clay in your soil test. Write down the name of your soil
texture. In the example, the soil texture as determined by the triangle for a soil with 56%
sand, 25% silt and 19% clay is a sandy clay loam. On the diagram, the asterisk marks this
spot, just below the middle of the word "loam," in the sandy clay loam section. You will
now use this soil texture classification when estimating water, lime, and fertility
requirements of your soil.
Figure 1. Soil Texture Triangle.
Interpretation - The soil texture test is included simply to help provide background
information. It would be a good idea to consult your county NRCS guide to soil series
(soil survey), and learn more about the soil types on your farm. The soils guide will
describe your soil’s surface and subsurface characteristics, as well as the texture of the
soil at various layers.
4
I have determined the
soil texture on fields in
my farm and consulted
the NRCS soil series
guide.
3
I know the soil texture
on my farm through
experience and have
used the "feel method"
and other tests to
validate.
2
I know the soil texture
on my farm through
experience and try to
manage it accordingly.
1
I don’t know what my
soil texture is and have
never seen the NRCS
soil series guide.