Soil Texture

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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

Particle Diameter (mm)

 

 

Very coarse sand

2.0-1.0

Coarse sand

1.0-0.5

Medium sand

0.5-0.25

Fine sand

0.25-0.10

Very fine sand

0.10-0.05

Silt

0.05-0.002

Clay

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 xx).

Tools: 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, and 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.

Fill the soil separation tube up to the 10 ml line with soil. Gently tap the tube after each portion is added.

Dilute the sample by adding water up to the 40 ml line.

Add 10 drops of texture dispersing reagent. Hold the bottle vertically when adding the drops.

Cap the tube and shake for 2 minutes.

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.

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.

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.

Now, put the three height readings in the form of percentages. For example;

Height in millimeters after: Corresponds to fraction of: Example - total height in ml: Difference in height, or portion: Portions expressed as percentage:
         
30 seconds sand 9 mL 9 mL 9/16 = 56 %
         
30 minutes silt 13 mL 4 mL 4/16 = 25 %
         
24+ hours clay 16 mL 3 mL 3/16 = 19 %
         
      total = 16 mL  
         

9) Using the soil texture triangle in Figure xx, 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 xx. Soil Texture Triangle.

 

 

Interpretation of Soil Texture: 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 soilís surface and subsurface characteristics, as well as the texture of the soil at various layers.

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I have determined the soil texture on fields in my farm, and consulted the NRCS soil series guide. (blank) (blank) I donít know what my soil texture is, and have never seen the NRCS soil series guide.