SOIL TEXTURE Science Page

UNITED STATES BOTANIC GARDEN

www.usbg.gov

SOIL PARTICLES
Soil is made up of particles of rock that If a large clay particle
were the size of a pea,
have broken down over time. These particles then a silt particle would
vary in size. They are classified into three be as big as a ping pong
sizes—sand, silt and clay. Soil texture is a ball or bigger, and a
measure of how much sand, silt, and clay grain of sand would be
the size of a basketball
a soil contains. or bigger.
Soil texture is important because it
determines how fast water drains through
a soil. It also determines how much water a
soil can hold, and can be used by plants.

basketball
pea ping pong ball

CLAY SILT
Clay is less than 0.002 mm in Silt is 0.002-0.05 mm in
diameter. Clay particles are diameter. You can see
extremely small, and can be seen silt particles only
only through an electron through a microscope.
microscope.

Silt feels like flour.

It forms into a ball that easily breaks apart. If you squeeze it between
your thumb and fingers, it will not form ribbons.

Clay feels sticky when wet. It easily

forms into a ball and a ribbon at SAND
least 5 cm long. Sand is the largest No matter how much I water,
size rock particle in these plants keep wilting!
Water drains very slowly through soil—0.05-2 mm in
clay soil. Therefore, clay soil diameter. You can see Sandy soils have lots of
remains saturated after a heavy sand particles without air spaces between
rain. When this happens, there is a microscope. particles, so water
little air in the soil, and plant roots drains quickly through
cannot find oxygen. Clay soils can these soils. Because
be difficult for gardeners to plant in. they do not hold water
and nutrients very
This dry clay is as well, you must
This clay soil is hard as concrete! water and fertilize
too wet. It’s as
sandy soils
sticky as gum!
frequently.
Sand feels gritty. You
cannot make wet sand
form a ball that holds
together.

LOAM Composition of different types of loam soils

Loam is a mixture clay loam sandy loam
of sand, silt, and
clay particles. It 33%
75% sand
sand
is ideal for 42%
loam

gardeners. silt
25%
40%
Usually loam is clay
sand
easy to dig, and 18%
clay
is neither too dry 42%
14%
silt
nor too wet during silt 11%
clay
the growing season.
 2. Soil texture by settling
UNITED STATES BOTANIC GARDEN
www.usbg.gov

1. Fill a liter-size jar 2/3 with

PUZZLE water. Add soil until the water
Look at the pie graphs on the front of this page. level is nearly to the top of
They show the composition of different types of the jar.
loam soils. 2. Put the top on the jar and
1. Which soil would form into the longest shake vigorously. Set the jar
ribbon? The shortest ribbon? on a level surface and wait for
the particles to settle. The
2. Which soil would feel the grittiest? smallest particles may take
the stickiest? several days to settle.
3. Water would drain through which soil the 3. Observe the distinct layers of soil that settle
fastest? the slowest? in the jar. Are some layers thicker than
4. Which soil would hold the most water? others? What kinds of particles make up
the least water? these layers?

SPOTLIGHT
TRY THIS! ON RESEARCH
Farmers in different parts of the world use
Here are two simple methods for testing the
soil texture to decide what crops to grow
texture of your soil.
All over the world, farmers have their own
ways of classifying soils. In Burkina Faso, for
1. Soil texture by feel
example, farmers classify soils by texture and
1. Take a small handful of soil, about the size of
by how suitable they are for different crops. A
an egg.
sandy soil called Bflisri is suitable for growing
2. The soil should feel as moist as a wrung out
peanuts. A loamy soil called Bfloogo is suitable
sponge. You should not be able to squeeze
for both red and white sorghum. Soil scientists
any water out of it. Spray with water if it is
recognize that they can learn from local
dry. Add more dry soil if it gets too wet.
farmers about classifying soils.
3. Form the soil into a ball. Squeeze the soil Source: Dialla, B.E. (1992). The adaption of soil conservation
between your thumb and forefinger. Gently practices in Burkina Faso: the role of indigenous knowledge, social
push forward with your thumb to form a structure and institutional support. PhD dissertation. Iowa State
University, Ames.
ribbon. Measure the length of the ribbon in
centimeters. Ha! Ha!

4. Look at the chart on this page. Based on Ha! Ha!

your results, what is the texture of your soil? RIDDLE
What did the clay soil say when the sun came
out?

Soil Texture How It Feels How It Handles

sand gritty; does not stain fingers does not form a ball
loamy sand gritty, stains fingers forms weak ball that breaks easily
sandy loam gritty forms ball that does not break when handled carefully
loam gritty forms ball that does not break when handled carefully; forms
ribbon 0.6-1.2 cm; does not show fingerprint when pressed
silt loam feels like flour when moist forms ball that can be handled without breaking;
and sticky when wet will not ribbon
sandy clay loam gritty forms firm ball; forms ribbon 1.8-2.5 cm long
silty clay loam sticky forms ribbon 2.5-5 cm long; shows fingerprint when
pressed
clay loam sticky forms ribbon 2.5-5 cm long; produces sheen when
rubbed with thumbnail

sandy clay plastic, gritty, and sticky forms firm ball; forms ribbon more than 5 cm long
silty clay plastic, sticky, not gritty forms firm ball; forms ribbon more than 5 cm long
clay sticky and plastic forms strong ball; forms ribbon more than 5 cm
long; very shiny when rubbed with thumbnail