Transcript Soils Overview Part 3 - Massachusetts Envirothon

Welcome to the 2004 Massachusetts
Envirothon Workshop
Soils Overview Workshop
Part III
Tom Cochran
USDA-NRCS Franklin Co., MA
Some material courtesy of Jim Turenne
USDA-NRCS, Rhode Island
So what?
Physical differences
The size of sand and clay give a horizon different physical &
chemical properties.
Sand particles are much larger than clay particles and, sand
is blocky shaped while clay is platy.
A collection of sand particles create air spaces that are
larger and more connected than those created by a
collection of clay particles.
Chemical differences
Sand particles have no charge on their surface.
Clay particles have negative charge on their surface and
adsorb elemental nutrients such as Ca, Mg, Fe, NO3, PO4.
Particle surface area
A sand particle that is 1 mm in diameter has a volume of
approximately 0.5 mm3 and a surface area of 6mm2 with no
electrical charge.
A clay particle (0.002mm dia.) has a volume of approximately
4 x 10-9 mm3, so 12.5 million clay particles will fit inside the
1-mm sand particle.
Each clay particle has a surface area of about 0.012 mm2.
Therefore, 12.5 million clay particles will provide 150,000 mm2
of surface area with negative charge sites.
The colloidal surface area of a 15-cm thick slice of a hectare of
clay soil could be 700,000 km2 (270,000 mi2), which is greater
than the area of France (Brady & Weil, 1996).
Soil Structure
Definition: Soil structure is the natural organization of soil
particles into units called peds.
When structure is examined, its type, grade, & size is
determined, and recorded in that order.
Most structure types in New England are granular,
subangular blocky, massive, or single grain because clay
contents are usually less than 40%.
Grades:
Structureless – no discrete unit observable
Weak – units are barely observable
Moderate – unit well-formed & evident
Strong – units are distinct and separate cleanly when
disturbed
Granular
crumb size units; often
associated with A horizons
that contain organic
material
Sub-angular blocky
rounded edges and faces;
often associated with B
horizons
Massive
No structural units;
material is a coherent mass
Single grain
No structural units; loose
sand
Soil structural size
Names for structure size are as follows, and size values
vary by the structural type.
For all structure except platy,
Very fine
Fine
Medium
Coarse
Very coarse
Extremely coarse
For platy structure,
Very thin
Thin
Medium
Thick
Very thick
Extremely coarse
Soil Color
The end product of organic matter decomposition is humus,
which is a black color that stains surfaces. The humus is
responsible for most of the black colors of an A horizon.
Iron oxide coats soil particles and gives them the reddishbrown color of rust.
Sand grains are mostly quartz material, which is naturally a
gray color. Red sand is just quartz coated with iron rust.
Mottling in a well-drained soil is usually due to the mineral
coatings on the particles.
Mottling in wetter soils can be caused by the reduction of the
iron in the coatings.
Major Forms of Iron and Effect on Soil Color
Form
Ferrous oxide
Chemical Formula
FeO
Color
Gray
Ferric oxide
(Hematite)
Fe2O3
Red
Hydrated ferric oxide
(Limonite)
2Fe2O3 3H2O
Yellow
Soil Color Book
The Munsell color book is used
to document color in a standard
notation.
Hue: Dominant spectral color.
Value found in th top right-hand
corner of each page.
Value: The degree of light/dark
of a color in relation to a
neutral gray scale. Values along
the left-hand side of each page.
Chroma: Strength of hue.
Values along the bottom of each
page.
The 10YR page of the
Munsell color book.
Reading Soil Colors
Optimum conditions
Natural light
Clear, sunny day
Midday
Light at right angles
Soil moist
NO sunglasses!
Redoximorphic features
Eating OM
=
e
Free electrons
microbes
In the presence of air, free oxygen molecules (O2) take the
electrons (reduction), but when the soil is saturated there is
no free O2.
Under saturated conditions other oxidized molecules take the
electrons in this order.
NO3
Nitrate
Fe2O3
rust
SO4
sulfate
CO2
carbon dioxide
Scientists use the reduction of rust as an indicator of frequent
saturated conditions because it is the first reduction reaction
that can be seen by the naked eye.
Redoximorphic features continued
Rust is the oxidated state of iron (Fe2O3).
Under saturated conditions, the free electrons produced by
microbial respiration remove the O3 from the iron.
The O3 then forms water with the hydrogen ions that are
plentiful in soil solution.
6e- + 6H+ + Fe2O3 ------ 2Fe2+ + 3H2O
The iron ion (Fe2+) is soluble in the soil solution, and as the
water drains from the soil the iron moves with it.
This causes the iron to be removed from the particle
coatings and be either completely removed from the soil
profile or deposited in another place in the profile.
Scientists interpret the absence of iron and the patterns of
iron concentrations when evaluating the drainage class of a
soil.
Redoximorphic Features
After the matrix color is
determined, record the
color patterns of the
redox features if present.
Can be very complex.
Describe color, abundance,
size, contrast, shape, and
location.
Contrast of Redox
Contrast refers to the degree of
visual distinction between
associated colors
Faint -- evident only on
close examination.
Distinct -- readily seen.
Prominent -- contrasts
strongly.
Abundance and Size of Redox
Abundance
Few -- less than 2%
Common -- 2 to 20%
Many -- more than 20%
Size
Fine -- < 5 mm
Medium -- 5 to 15 mm
Coarse -- > 15 mm
Soil Drainage Classes
Drainage class is determined in the field by observing
landscape position and interpreting redoximorphic features.
The table below is used to interpret the redoximorphic
features.
Drainage class
2 Chroma
depletions
Water Table
Depth
Gray
matrix
Water Table
Depth
Very poorly
0-12” w/umbric
0-1 ft.
0-12”
0-12”
Poorly
0-12” w/ochric
0-1 ft.
6-12”
0-12”
Somewhat poorly
12-18”
1-2 ft.
12-24”
12-24”
Moderately well
18-36”
2-4 ft.
24-48”
24-48”
Well
>36”
>4 ft.
>48”
>48”
Somewhat excessive
>36”
>5 ft.
>48”
>48”
Excessively
>36”
>5 ft.
>48”
>48”
Using a Soil survey
Organization:
Begins with general descriptions of survey area. Information
about the soil forming factors is found here.
Next, are detailed descriptions of each soil map unit.
Typically, information includes
profile depth
drainage class
topographic position
Horizonation
Permeability
Available water capacity
pH range
agricultural suitability
Woodland suitability
urban development suitability
Capability subclass suitability
Organization (continued)
The Use and Management of the Soils section follows the
detailed descriptions.
This section explains the interpretations presented in the
tables that follow, which include
Yields per Acre
Land capability classification
Woodland Management & productivity
Recreational uses
Wildlife habitat
Engineering uses
Building site development
Waste applications
Construction material suitability
Water management
Using the interpretation tables
Let’s practice by using a few of the Tables.
We will use Table 11 (Building Site Development) from the
Worcester Co. South survey to determine the suitability of a
Paxton soil for a dwelling with a basement.
We find the map unit of interest in the left-hand column of
Table 11 and the use of interest in the top row. At the
intersection of this column and row is the interpretation.
Page 61 of the Use and Management of Soils section explains
the meaning of the interpretation listed in the table.
Next, let’s see if we can economically install
an on-site sewage treatment system with our
dwelling.
We will need to use Table 12 (Sanitary Facilities) to see if
there are any limitations to the operation of a septic
absorption field.
Again, page 61 of the Use and Management of Soils section
explains the meaning of the interpretation listed in the table.
Septic tank absorption field ponding on surface.
Farmland Interpretations
Look for thick dark topsoil
layer.
Textures of upper 20 inches
should not be too sandy.
No large stones or boulders.
Not too steep, slope < 8%.
Site may be wooded.