Transcript Soil Texture - Ocean County Vocational Technical School

Soils: facts and fiction
Note series for Environmental Science
ENVI 152
Soil Definition (NRCS)

“Soil is a natural body comprised of solids
(minerals and organic matter), liquid, and gases
that occurs on the land surface, occupies space,
and is characterized by one or both of the
following: horizons, or layers, that are
distinguishable from the initial material as a result
of additions, losses, transfers, and transformations
of energy and matter or the ability to support
rooted plants in a natural environment.”
NRCS - Natural Resource Conservation Service
Downer soils (NJ State Soil)
Found in woodland areas with natural
vegetation consisting of mixed oaks, hickory,
and scattered pines.
Occur on over 291,000 acres in NJ (in all
11 counties of southern/central NJ).
Downer was established in the 1960’s in
Gloucester County.
Soil Loss

Through erosion (major problem)
Washes
out potential nutrients that would
be available
Lost
nutrients will negatively impact
plant diversity
Why Soil Loss?
Development (Key factor)
 Clearing of fields for agriculture (LDCs)
 Strip mining (Global)
 Natural weathering (Forming soils)
 Edge effect (Related to Development)
 Sea Level Rise (Loss of Coastal Shoreline)

Soil types
Soils are weathered rocks that create
smaller particles
 Classified as Sand, Silt or Clay
 Depending on the location, there are greater
compositions of soil types (i.e. New Jersey
coastal area has mostly sand, there clay
soils in N. New Jersey
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Soil Contamination

Since soils are in the LITHOSPHERE
(Crust), they will be exposed to more
environmental stresses.
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Acid rain is a problem in that it displaces
cations in the soil and causes changes in soil
chemical compositions and pH
Soil Texture = %Sand, Silt & Clay in a soil.
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Soil texture is the single most important
physical property of the soil. Knowing the
soil texture alone will provide information
about:
1) Infiltration of water
2) Porosity
3) Nutrient holding ability
Textural Triangle
Particle Diameter Size
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Soil particle diameters
range over 6 orders of
magnitude
2
m boulders
 Coarse fragments > 2 mm
 Sand < 2 mm to 0.05 mm
 Silt < 0.05 mm to 0.002 mm
 Clay < 0.002 m
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> 2 mm
Gravels, cobbles,
boulders
Not considered part
of fine earth
fraction
Boulders left in
valley of Big Horn
Mts.(Wy) by a
glacier.
Coarse Fragment
Sand
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< 2 mm to > 0.05 mm
Visible without
microscope
Rounded or angular in
shape
Can contain quartz or
calcium carbonate &
sometimes minerals
Feels Gritty
Sand
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Low specific surface area
Sand has less nutrients for
plants than smaller particles
Voids between sand
particles promote free
drainage and entry of air
Holds little water and prone
to drought
Silt
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< 0.05 mm to > 0.002 mm
Not visible without
microscope
Quartz often dominant
mineral in silt since
other minerals have
weathered away.
Silt
Does not feel gritty
 Floury feel –smooth like
silly putty
 Wet silt does not
exhibit stickiness /
plasticity / malleability
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Silt
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Smaller particles –
retains more water for
plants and have slower
drainage than sand.
Easily washed away by
flowing water – highly
erosive.
Holds more plant
nutrients than sand.
Source of Silt
Clay
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Wet clay is very sticky
and is plastic or it can
be molded readily.
Easily formed into long
ribbons.
Shrink swell – none to
considerable depending
on the kind of clay.
Clay
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Pores spaces are very small
and convoluted
 Movement
very slow
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of water and air
Water holding capacity
 Tremendous
capacity to
adsorb water- not all available
for plants.
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Soil strength- shrink/swell
affects buildings, roads and
walls.
Chemical adsorption is large
Determining Soil Texture - Feel Method
Wet soil in hand
 Make ribbon
 Length of ribbon
indicates clay content
 Grit or lack of grit
indicates sand or silt
 Smoothness indicates
silt
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USDA Textural Classes
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Sandy soils (coarse)
 Fine sand
 Very fine sand
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Loamy soils (medium)
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Clayey soils (fine)
Sandy Soils

Coarse
texture
 Sands
 Loamy
sands
Changes in soil texture
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Over long periods
(1000s yrs)
pedologic processes
alter soil horizon
textures.
As soils get older
sand weathers to
silt and silt
weathers to
clay….therefore old
soils have more
clay.
Naming Soil Horizons
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Soil horizons
(layers in the soil)
are named so
differences
between soils can
be identified.
Naming soil
horizons takes
practice
Organic Horizons
O
- horizon - organic
material (no mineral
materials)
1) forest litter
2) organic soil or peat
soils, or muck
Organic Soil Profile
This trenching
machine is digging
through the Oe
horizon of an
organic soil.
Trenches needed to
remove water so the
peat will dry before
harvest.
Mineral Soil Horizons
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A horizon - surface
horizons that accumulate
B horizon – usually iron
and leached minerals
locally
C horizon – more rock
and “parent material”
A
B
B (t)
B (C)
C