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Investigating Soil
Purpose: To investigate the property of texture in soils.
Question: How can we classify different soils?
Background Information: Soil is made of three particle sizes – sand, silt, and clay. Sand is the largest particle;
these particles are 0.05-2 mm in diameter. Silt is the particle in the middle; the diameter of these particles is
0.05 – 0.002 mm. Clay is the smallest of the soil particles. The diameter of clay particles is less than 0.002
mm. Soil textures depend on the amount of sand, silt, and clay in the soil. Loam is composed of a mixture of
sand, clay, silt, and organic matter.
Soil texture is classified in 14 different ways.
The United States Department of Agriculture
Soil texture classes are sand, loamy sands, sandy
loams, loam, silt loam, silt, sandy clay loam, clay
loam, silty clay loam, sandy clay, silty clay, and
clay.
A soil texture triangle is used to classify the
texture class of a soil. The sides of the soil
texture triangle are scaled for the percentages
of sand, silt, and clay. Clay percentages are read
from left to right across the triangle (dashed
lines). Silt is read from the upper right to lower
left (light, dotted lines). Sand from lower right
towards the upper left portion of the triangle
(bold, solid lines). The boundaries of the soil texture classes are highlighted in blue. The intersection of the
three sizes on the triangle give the texture class.
Soils are put into texture classes by the way they feel and respond to handling. Sand feels gritty and the grains
do not stick together when squeezed. Silt feels velvety or like flour when dry and forms a “ribbon” when wet.
Dry clay feels smooth, clods are very hard and difficult to crush by hand. Wet clay feels sticky or smooth.
Think about what you just read.
What is the m idea in the background information?
M. Poarch 2013
science-class.net
Permission granted to copy for non-profit, educational use only.
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Materials: Soil samples, water, eye dropper
Procedure:
1. Use the chart below to classify each soil sample.
http://soils.usda.gov
M. Poarch 2013
science-class.net
Permission granted to copy for non-profit, educational use only.
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Data:
Sample #
Soil Sample Classification
Classification
1
2
3
4
5
6
Questions and Conclusions: Use the Soil Texture Triangle to answer the following questions.
1. If you have a soil that was composed of 35% clay, 55% silt, and 10% sand, how would you classify that
soil? _______________________________________________________________________________
2. What is the maximum percentage of silt found in Sandy Clay?
__________________________________________________________________________________
3. Why is knowing the texture of a soil important?
Think about
it!
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M. Poarch 2013
science-class.net
Permission granted to copy for non-profit, educational use only.