Lecture 1b –
Soil as a Resource
• WHAT DOES SOIL DO?
• Soils define culture.
• Throughout history soil has defined
human societies perhaps more
strongly than any other single
environmental variable.
– Soil fertility defines our food, our
population and our economy.
– Soil colors define our art.
– Soil organisms may define our health.
• Yet, the importance of soils in
regulating human society is
frequently overlooked
• Healthy soil gives us clean air and
water, bountiful crops and forests,
productive rangeland, diverse
wildlife, and beautiful landscapes.
• Soil does all this by performing five
essential functions:
Callanish Stones – Isle of Lewis
Scotland UK, age = 4500 years
1) Regulating water.
Spring Snowmelt
• Soil helps control where rain,
snowmelt, and irrigation water goes.
• Water and dissolved solutes flow
over the land or into and through the
soil.
Source: www.naturegrid.org.uk/rivers/watercyclepages/riverbasin-stages.html
Silt from floods in SE Mn
Summer 2007
2) Sustaining plant and animal life.
• The diversity
and
productivity
of living
things
depends on soil.
• Often the more
productive the soil,
the more diversity in
both the plant and
animal community.
3) Filtering potential pollutants.
• The minerals and microbes
in soil are responsible for :
• filtering, buffering,
degrading,immobilizing,and
detoxifying organic and
inorganic materials.
• This includes industrial and
municipal by-products and
atmospheric deposits.
4) Cycling Nutrients.
• Carbon, nitrogen,
phosphorus, and many
other nutrients are
stored, transformed,
and cycled through
soil.
• This is a good thing
for it keeps them out
of our water systems.
• WASHINGTON- “Because fewer farms are raising animals,
the 350 million tons of manure they produce each year is
being spread over smaller tracts of land, causing more of it
to wind up in lakes, streams, and rivers”, according to a new
study by the Agriculture Department.
• The department's Economic Research Service said the
"competition for land for spreading manure could be severe
in regions with high concentrations of animals," making it
more difficult to comply with new environmental regulations
for reducing farm pollution.
• States expected to have the most trouble finding enough
cropland to distribute the manure include North Carolina,
Virginia, Maryland, Delaware, Georgia, Alabama, Arkansas,
and California, the agency said.
When manure can not be land applied it must be
stockpiled in mounds or in tanks or pits.
5) Supporting
Structures
Buildings and roads need stable soil
for support.
The bearing capacity determines
the ease of stable construction.
This road and associated bridge were built
across a mangrove swamp. The bridge,
supported by pylons, has not subsided.
However, the road has slumped because
of the low load-bearing capacity of the
underlying soil material.
This building collapsed when it
underwent liquefaction-induced
bearing capacity failure
Digging for clues of our
past- The Soil holds the
clues till we are ready.
Archeological
treasures associated
with human habitation
are protected in soils.
The kind of the soil
determines the ease
of excavation and
maybe the quality of
the object found.
• Careful
excavations
are used to
uncover
Native
American
remains at
U.S. Army
bases.
Soil needs your respect!
Will everyone, please, at
some time during the next
few days take a handful of
soil and show it some
respect.
Put it in your hand and take
a long, hard look at it.
Marvel at its color, smell, and
feel. Sing in praise of its
chemistry and bless its
bugs. Be amazed at how
it works for you.
Before placing it back from
whence it came say “thank
you” !
Soil is …….
• Detritus from rock
or - sand, silt and
clay particles along
with decomposed
plant remains and
live organisms.
• Or
• The Loose surface
of the earth that
can support plants.
Soil Texture = The 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.
Soil Texture
• Soil texture is
determined by
separating the amount
of sand, silt and clay in a
soil and determining the
% of each.
• Different percentages
of sand, silt and clay
have been given
“Textural Class Names”
• These 12 Names are put
on a Textural Triangle
for the various separate
percentages
Soil Texture of Sandy Loam
& Loamy Sand
• A sandy loam is a loam
with the some
characteristics of
sand,
• while a loamy sand is a
sand with some
characteristics of a
loam. (noun and
adjective)
• ? Discuss two situations
where you were aware of
the soil’s texture.
Soil Structure
• Individual sand silt
and clay particles
will form together
into specified
shapes.
• These shaped
structural peds –
are given names
based on their
appearance.
Peds are formed in the
soil by wetting, drying,
freezing and thawing and
are held by clay and
organic matter
Kinds of Soil Structure
•
•
•
•
•
Granular
Platy
Sub-angular Blocky
Prismatic
Good structure
promotes healthy
soil
(see Unit 3 chap. 1)
Once the virgin land is used for agriculture – the quality of the soil
resource will begin to degrade, the rate of decline will depend on the
skill of the land manager.
U.S. Fish and Wildlife Service
Overgrazing
• According to the
Sierra Club, the
National
Cattlemen's Beef
Association, the
U.S. Forest Service,
and the Bureau of
Land Management:
– Overgrazing is what
happens when there
are too many animals
on the land.
• What grass plants need is
sufficient recovery time
between bites. Therefore,
timing and grazing
management, not numbers,
is the critical factor.
• But this is something that
everybody already
"knows"--that the solution
to overgrazing is to reduce
or eliminate the grazers.
• Increasing the area
available to the animals is
not nearly as effective as
shortening the time period
during which the plant is
exposed to grazing.
•
•
•
•
•
Grazed BLM land on the left
side of the fence, desert
wildflowers on the right.
In 1991, Congress's General
Accounting Office (GAO)
completed a report (RCED-9212) that analyzed the BLM's
permitting of livestock grazing
in the desert. The GAO
concluded that,
"the lands we visited provided
enough evidence of the high
environmental risk and low
economic benefit associated
with livestock grazing in
America's hot deserts for us to
conclude that the program as
currently conducted merits
reconsideration”.
Or some would say that “cows
don’t belong in the desert”
source: www.jdburgessonline.com/
grazing/desert.html .
Deforestation
• The main contributors
to land degradation
are:
– erosion and soil
compaction, as a result
of extensive removal of
vegetation, exposure of
the soils to heavy
rainfall,
– increased evaporation,
– and later wind action.
• The main reasons for
vegetation removal are:
– commercial logging and
tree cutting to provide
domestic fuel,
– clearing of forests for
commercial or subsistence
cultivation.
• Soils in many tropical
areas rapidly decline in
productivity after
logging.
Agriculture
• Agriculture may last
for a few hundred
years or it may last for
thousands of years.
• These terraces have
been in place for
thousands of years in
Bali. (Island in South
Pacific)
• Stone tools and
earthenware vessels,
which were estimated
to be 3000 years old,
were unearthed near
Cekik (west Bali).
•
Source: http://www.promotingbali.com/baliessential/bali-history/
• Agave production on
these fields in Mexico
may last for fewer than
50 years due to soil
erosion which results in
the loss of valuable
topsoil.
• Tequila is an alcoholic
drink made in the arid
highlands of central
Mexico from fermented
and distilled sap of the
agave plant, a succulent.
•
Archeologists say the
agave has been cultivated
for at least 9,000 years
but not on the fields here
http://www.ianchadwick.com/tequila/
Water Erosion
• Water erosion
is the wearing
away of soil
particles.
• Raindrops
detach the soil
particles.
• As infiltration
is reduced,
water moving
down slope
takes the soil
with it.
Wind Erosion
• Wind erosion is
the detachment
of soil particles
by the wind and
moving them to
another
location.
• Snirt = ?
DYAD
•
Where have you seen some kind of soil degradation?
Chemical
Degradation
• Chemical spills can
pollute the soil
beyond which it can
recover naturally.
• Soil remediation
can reclaim the
soil, making it
useful again.
Manure Spill- a chemical degradation
• Manure spills are
chemical spills and they
result in polluting soils,
surface water and
groundwater.
• Problems may occur
during any of the steps
of manure management
including:
– collection, transfer,
storage and
application.
• If a manure spill
reaches a stream it can
create serious problems
for aquatic life as well
as for people and
livestock.
Human Activities Influence Planet Earth
Human activities globally now
move ten times as much earth
and rock as all natural
processes.
• One of the side effects of
this is soil erosion that is
causing the progressive loss of
farmlands at the same time
that the human need for them
is growing.
• Driving this has been our
rapidly increasing human
population.
• Research done by Bruce
Wilkinson of the University of
Michigan has shown that this
human-caused erosion began
to exceed nature's ability to
repair it nearly 1,000 years
ago (Wilkinson Geology 28, 843-846, [2000]).
•
Geologic Erosion
Human Induced Erosion
Human influence on the soil :
Blue = no change,
Red = significant impact on soil
Soil – A Sustainable Natural Resource
•
•
Having a sustainable soil system is everyone's responsibility!
Healthy soil gives us clean air and water, bountiful crops and
forests, productive rangeland, diverse wildlife, beautiful landscapes
and beautiful soils.