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.
Downer soils are used mostly as woodland. The natural
vegetation consists of mixed oaks, hickory, and scattered
pines.
Downer soils occur on 291,319 acres in New Jersey. These
soils are dominantly in the 11 counties of southern New
Jersey.
Downer soils are on uplands and formed in sandy, Northern
Atlantic Coastal Plain deposits.
The Downer series was established in the 1960’s in Gloucester
County.
Soil Loss
The loss of soils through erosion is a major
problem
 The loss of soil washes out potential
nutrients that would be available
 The loss of soil nutrients will negatively
impact plant diversity
 The loss of soil is becoming a greater
problem today than in the past

Why Soil Loss?
Development
 Clearing of fields for agriculture
 Strip mining
 Natural weathering
 Edge effect
 Sea Level Rise

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

Soil Contamination
Since soils are in the LITHOSPHERE
(Crust), they will be exposed to more
environmental stresses which will
inevitably permeate down the soils possibly
toward groundwater.
 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.

Soil texture is the single most important
physical property of the soil. Knowing the
soil texture alone will provide information
about:

1) water flow potential,

2) water holding capacity,


3) fertility potential,
4) suitability for many urban
uses like bearing capacity
Particle Diameter Size

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




> 2 mm
Gravels, cobbles,
boulders
Not considered part
of fine earth
fraction (soil
texture refers only
to the fine earth
fraction or sand, silt
& clay)
Boulders left in
valley of Big Horn
Mts.(Wy) by a
glacier.
Coarse Fragment





< 2 mm to > 0.05 mm
Visible without
microscope
Rounded or angular in
shape
Sand grains usually
quartz if sand looks
white or many minerals
if sand looks brown,
Some sands in soil will
be brown, yellow, or red
because of Fe and/or Al
oxide coatings.
Sand
Sand
Feels gritty
 Considered noncohesive – does
not stick together
in a mass unless it
is very wet.

Sand




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
< 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

Silt




Smaller size allows rapid
weathering of non quartz
minerals
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
Wet clay is very sticky
and is plastic or it can
be molded readily into a
shape or rod.
 Easily formed into long
ribbons
 Shrink swell – none to
considerable depending
on the kind of clay.

Clay

Pores spaces are very small
and convoluted
 Movement
very slow

of water and air
Water holding capacity
 Tremendous
capacity to
adsorb water- not all available
for plants.


Soil strength- shrink/swell
affects buildings, roads and
walls.
Chemical adsorption is large
USDA Textural Classes

Sandy soils (coarse)


Fine sand
Very fine sand

Loamy soils (medium)

Clayey soils (fine)
Textural Triangle
Sandy Soils

Coarse
texture
 Sands
 Loamy
sands
Changes in soil texture


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.
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

Naming Soil Horizons


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

A horizon - surface
horizons that accumulate
A
B
B (t)
B (C)
C