Introduction
Name_______________________________________________
What Soil is:
Soil is a natural body made up of
minerals (rock), organic (living and dead) materials, air, and water. Soil has living and dead parts in it.
There are three main types of soils
called textures. They are: sand, silt,
and clay. Sand has the largest
particles and clay has the smallest.
Soil is the loose material found in
the upper crust of the Earth. It is
both living and non-living.
Soil is naturally found in horizons,
or layers, each with its own unique composition and characteristics.
Soil = Organic Matter + Minerals +
Air + Water
A soils' physical & chemical
properties include:
*bulk
density (strength)
*porosity
(aeration and drainage)
*texture
(type of soil)
*pH
*cation
exchange capacity (CEC)
Physical properties can quickly and
easily be changed both short and long term under certain conditions. The soil can be tilled or amended to
alleviate bulk density and increase porosity and to change the overall texture.
Chemical properties are not as easy
to change. A soils' pH can be modified
by adding lime to make it more alkaline or an acid to make it more acidic, but
in both cases the natural process of weathering and leaching will eventually
restore the original pH status. A
soil's CEC can also be changed by modifying the physical characteristics or by
changing the pH.
1. Soil Texture
This refers to the proportion of
sand, silt, and clay particles that make up a soil. Soil texture determines water and nutrient holding capacity.
Physical and Chemical
Properties of Different Soil Textures
2. Soil Structure
This refers to how the soil
particles are arranged. Various
processes cause the soil to aggregate into clumps creating macropores. These large pores are important for drainage
and aeration of the soil. Compacted
soils have poor structure.
3. Soil pH
A soil's pH determines its nutrient
availability. Some species have very
specific pH requirments. Chlorosis
(leaf yellowing) is a sign that the pH is too high for that species. Urban environments usually have high pH.
4. Soil Drainage (Porosity)
Slowly draining soils limit the
oxygen available to the roots because soil pores are filled with water rather
than air.
*
Gray or blue soils indicate poor drainage.
*
Compacted soils have poor drainage.
Soil ‚ Dirt
It is NOT correct to refer to a
soil-based growing medium as dirt!
Soil as a Resource
A resource is a material that has
been taken from its natural setting and used to satisfy human needs. Examples of resources include animals,
plants, minerals, gases and other natural substances. Resources can be broken down into two types: renewable and non
renewable.
A renewable resource is one that can
eventually be replenished by natural processes without human intervention. A non-renewable resource is one that can not
be replenished because it was "used up" by humans.
In either case, over-usage can
deplete the resource to the point of non-availability. Some renewable resources can take thousands
of years to "renew", thus becoming unavailable in the meantime.
Conservation of Matter dictates that
matter is neither created nor destroyed.
However, it can be irreparably changed as to never resemble the initial
form and function. When a tree is
burned down it is no longer a tree. The
tree is gone!
Soil is classified as a renewable
resource, even though it takes approximately 500 years for nature to make one
inch of it! Is this truly
renewable? Should we be concerned about
depleting it?
Ithaca High School SOIL SCIENCE Unit
Angie Rivenshield
Focus:
To make students aware of (urban)
soil related issues on a local and global scale.
Day One: Introduction
1. Basic Soils Science
2. Definitions and Key terms
3. Visuals and Demos
4. Handouts
a.
soil history and morphology
b.
comparison of urban and natural soils
c.
discussion of local and global issues
Day two:Physical and Chemical
Properties of Soil
1. Texture
2. Structure
3. Porosity
4. Density
a.
sand versus clay
b.
organic versus mineral
c.
porosity and density issues
Day three: Anthropogenic
Manipulation of Soil
1. Compaction
2. Pollution
3. Erosion
4. pH
a.
compacted versus non-compacted
b.
erosion factors (cover, roots, etc.)
c.
acid rain
d.
vegetation and remediation
Day Four: Anthropogenic Manipulation
of Soil (Continuation)
1. Remediation
2. Drainage
3. Cover
4. Economic
Days five (optional): Discussion
1. Slides
2. Samples
3. Opinion versus Fact
4. Debate
POROSITY
Name: ______________________________
Porosity refers to how many pores,
or holes, a soil has. Remember that a
good portion of soil is air and water.
The air and water is in pores that form between individual particles and
between clumps of particles. There are
large pores, called MACROPORES and there are small pores, called
MICROPORES. Keep in mind that most of
the pores found within a soil are microscopic and can not be seen by the naked
eye.
Micropores are those pores most
responsible for holding water.
Macropores are those responsible for holding air. Water drains through the macropores, and
settles into micropores where the water is held very tightly.
1. Run the texture by feel test on
the sand and clay samples. This will
allow you to become comfortable with what these two "pure" types of
soils feel like. Such characteristics
as whether the soil balls and ribbons, and how gritty it feels will become
clear from this exorcise.
Questions to ask yourself:
Which soil will feel grittier? Why?
What determines grittiness of a
soil?
Is this a useful quality? Why or why
not?
Which soil will ribbon best? Why?
A soil that will ribbon is said to
be plastic.
Is being "plastic" a good
quality for a soil to have?
When would this quality be most
useful?
2. Run the texture by feel test on
the unknown soil sample you have been given.
Follow the texture by feel handout.
POROSITY
Name:
_______________________________
Porosity refers to how many pores,
or holes, a soil has. Remember that a
good portion of soil is air and water.
The air and water is in pores that form between individual particles and
between clumps of particles. There are
large pores, called MACROPORES and there are small pores, called
MICROPORES. Keep in mind that most of
the pores found within a soil are microscopic and can not be seen by the naked
eye.
Macropores Hold Air & Micropores
Hold Water
Testing Porosity
Sponges are like soil. The pores within the sponges are just like
the pores within a soil. There are both
large pores and small pores present and they drain just like macropores and
micropores in a soil. There are three
main moisture levels within a soil.
They are:
*Saturation
This happens when all of the pores
are full of water.
*
Field Capacity
This happens when water is removed
by gravity.
The soil is still wet. This is best for most plants.
*Permanent
Wilting Point
This
happens when all water has been removed EXCEPT for the water
held tightly in the smallest pores.
Plants cannot remove water from the
soil at this point.
Testing Porosity Lab
1. Run a porosity test on the sand
and the clay.
Step 1
Fill two prepared cores; one with
sand and one with clay. Do not pack the
soil into the cores, but try to fill the cores keeping the soil loose.
Step 2
Pour 100 ml of water into each
sample at the EXACT same time. Record
that time.
Step 3
Wait for the water to drain, then
record the time for each sample. After
five minutes, measure the amount of water that drained from each sample.
Step 4
Record your results.
2. Run the porosity test on your
unknown.
Soil Type |
Start Time Drainage |
Amount Water Drained |
Sand |
|
|
Clay |
|
|
Unknown |
|
|
Home |
|
|
Urban Soils
Urban soils do not have horizons.
*The
top layer has been removed
*Any
subsequent layers have been mixed together
Urban soils have very little
structure.
*Due
to mixing and moving, the crumbs have been destroyed
*Compaction
due to foot and vehicular traffic squashed the pores
Urban soils are sterile.
*Surface
organic matter is removed
*Soil
macro- and micro-organisms can not live in the destroyed soil
Urban soils have high pH.
*Due
to concrete buildings and sidewalks, lime leaches into the soil
*Most
plants prefer a neutral or slightly acidic pH for nutrient uptake
Focus: Compaction & Remediation
Name:
Soil compaction is one of the
leading causes of tree death in urban areas.
It is usually the result of construction and heavy traffic within the
city. Compaction ruins the soil by
destroying pores (especially macropores) and reducing structure.
Compaction of soil is not always a
bad thing. In the case of construction
sites and building foundations, the soil must be compacted to hold the weight
of the structure without caving in.
Unfortunately, the damage is usually spread beyond the actual site and
becomes a problem for trees and other plants, not to mention animals and plants
that live in the soil.
There are other negative effects of
compacted soils within a city. Runoff
is a huge problem. Water can not
penetrate the soil surface and runs off taking contaminants (usually lawn
pesticides) with it. Soil temperature
is affected by the fact that water can not easily penetrate causing more damage
to an already stressed ecosystem.
There are currently three ways to
fix (REMEDIATE) a destroyed soil:
1. Replace it.
This is expensive and labor
intensive. Most cities refuse to do
this.
2. Cover it up.
This hides the problem but does not
fix it. New problems will arise. Unfortunately, this is what most cities do.
3. Amend it.
By amending the soil you are
actually attempting to bring it back to it's natural state. Amending a soil changes the physical and
chemical properties and , if done properly, will allow the soil to begin to
heal itself. Some cities are starting
to do this.
Compaction Exercise:
1. Compact your samples
a.
Proctor hammer simulates urban construction
b.
Hands simulate pigeon feet
c.
Stick or mallet simulates high heel shoes
2. Test for porosity
a.
At the given time:
*Add 500 ml H2O to sample. Record the time.
*Time how long it takes until the
H2O starts to drain.
*Record how much H2O drained from
each sample.
3. Test for Root Penetration
a.
Use penetrometer
b.
Try to push your finger through
4. Discussion and Results:
What did the compactive effort do to
the soil?
What physical properties have you
changed?
Will this affect the chemical
properties?
What can be done to alleviate the
problem?
Evaluation:
Please answer the following
questions honestly and with some thought.
The answers will help me fine-tune the unit for future students. Thanks!
Ask Yourself....
Did I learn anything NEW about
soils?
Did I learn anything NEW about other
aspects of science?
Will the knowledge I have gained
from this unit benefit me in the "real world"? How?
Did I enjoy the unit?
Would I like to have more units like
this one in the future? If yes, in what
subjects?