Download SOIL PROFILE DESCRIPTION LAB

SOIL PROFILE DESCRIPTION LAB
Terminology:
soil profile
soil horizons
parent material
soil color
hue
value
chroma
texture
structure
In this lab, you will learn how to describe a soil profile. A profile is a vertical slice of soil
from a site. A profile description uses a precise vocabulary to describe the soil horizons,
from the top to the unaltered parent material. In a horizon profile description, you
identify and describe each distinct layer. A new layer is identified when there is a
noticeable change in soil color, texture or structure. In this lab, you will describe each
horizon in terms of the following characteristics: color, horizon, texture, structure,
boundary, effervescence, mottles, and depth.
Make a table like the following in your lab book.
Horizon
Depth
Color
Texture
Dry Moist
Structure
Boundary
HCl
Mottles Notes
Horizon: For this lab, it is necessary to identify major horizons only (O,A,B,E,C,R).
Depth: Record the depth of each horizon in centimeters (e.g., 0-12 cm., 47-89 cm.)
Color: Use the Munsell Soil Color Chart
(photo MUNSELL here)
to identify soil colors. Find the color chip that EXACTLY matches the soil’s color.The
pages represent hues, the rows designate value, and the columns represent chroma.
Munsell colors are always designated in the order of hue, value, and then chroma. For
example, a 7.5YR 3/2 soil has a hue of 7.5, a value of 3 and a chroma of 2. In addition to
giving the Munsell number, also give the verbal description of the color, which can be
found on the facing page in the Munsell book. For example a 7.5 YR 3/2 soil is “dark
brown”. You will notice that soils have different colors when wet and dry. That is why it
is necessary to indicate whether you are giving the dry or moist color in your
descriptions.
Texture: Soil texture is the relative amount of sand, silt and clay sized particles in a soil.
In addition to soil particle sizes, you should also describe inclusions that are larger than
soil size, for example, gravel, cobbles, and stones. The following table gives the diameter
classifications for these inclusions:
fine
2 – 5 mm.
Gravel
medium
5 – 20 mm.
coarse
20 – 76 mm.
Cobbles
Stones
Boulders
76 – 250 mm.
250 – 600 mm.
>600 mm.
The soil itself is made up of particles smaller than 2 mm. in diameter, which is too small
to measure with a ruler. Sand particles are .05 – 2 mm.; silt are .002 - .05 mm. , and clay
are < .002 mm. in diameter. To determine the relative amounts of sand, silt and clay in
the soil, the following field method is used.
Place 25-50 g soil in palm. Add
water slowly and knead soil to wet
all aggregates. Soil is at the proper
consistency when plastic and
moldable, like moist putty.
Add more dry soil.
YES
YES
NO
Does soil remain in a ball
when squeezed?
NO
Is soil too
dry?
Is soil too
wet?
NO
SAND
YES
Place ball of soil between thumb and forefinger gently pushing the soil with the thumb, squeezing it upward
into a ribbon. Form a ribbon of uniform thickness and width. Allow the ribbon to emerge and extend over
forefinger, breaking from its own weight.
NO
Does the soil form a ribbon?
LOAMY
SAND
YES
Does soil make a
ribbon 2.5 cm or less
before breaking?
NO
Does soil make a
ribbon 2.5 – 5 cm
before breaking?
YES
NO
Does soil make a ribbon
5 cm or longer before
breaking?
YES
YES
Excessively wet a small pinch of soil in palm and rub with forefinger.
SANDY
LOAM
Does gritty
feeling
predominate?
SANDY
CLAY
LOAM
Does smooth
feeling
predominate?
SILTY
CLAY
LOAM
YES
Does gritty
feeling
predominate?
SANDY
CLAY
YES
YES
SILT
LOAM
YES
Does smooth
feeling
predominate?
YES
NO
SILT
LOAM
NO
CLAY
LOAM
SANDY
CLAY
YES
Does gritty
feeling
predominate?
Does smooth
feeling
predominate?
NO
CLAY