Transcript Science Tuesday, November 16th (week 3)

Soils
The dirty truth!
What is soil and how is it made?
• http://www.brainpop.com/science/earthsyste
m/soil/
• Check out the FYI
We can’t live without it
• All land life depends on it
• There isn’t very much good soil available on
Earth (apple demonstration)
• Required to grow plants
• All animal life on land depends on plants
What is Soil?
• Air—about 25%
• Water—about 25%
• Minerals—about 45%
• Decayed organic material--varies
Most soils have all of
the "ingredients" shown
but some soils are
missing some
"ingredients"
Missing water=dry soil
Missing organics or
minerals=poor soil
Missing air= compacted
soil
Soil is a mixture of what four materials?
A.
B.
C.
D.
Granite, limestone, nitrogen, and air
Rock particles, humus, air, and water
Rock particles, plant roots, humus, and nitrogen
Plant roots, iron oxides, water, and air
Where does soil come from?
• All soil starts from rock. Rock that has never
been worn down is called bedrock.
• Rock must weather (break down) into smaller
and smaller pieces
• Rock can break down in two ways.
– Chemical weathering
– Physical weathering
Chemical and Mechanical Weathering
• http://www.brainpop.com/science/weather/
weathering/
Weathered Rock
• Weathered rock doesn’t stay put, but is
usually moved by erosion
• Erosion can happen from
wind
water
ice
Erosion
• http://www.brainpop.com/science/earthsyste
m/erosion/
Soil Horizons
• Soil has layers
• First the C layer
forms
• Next the A layer
• Last the B layer
Soil formation from Bedrock
• The topsoil (A horizon) has the most humus.
• The weathered rock layer (C horizon) has the
least humus.
• Active Art on soil formation
Characteristics of Soil
(how we can describe soils)
•
•
•
•
Color
Particle Size
Texture
Consistency
• pH
• Moisture
• Temperature
Soil Color
Two sources of color in soils
• Minerals in the soil: for example. red clay soils
have a lot of iron; brown/black soils have
manganese….different minerals have different
colors
• Mica is dark
Quartz is light
Hematite is red
Soil Color, continued
• The more organic material, the darker the soil.
Organic material comes from dead plants and
animals. Organic material in soil is called
humus.
• Humus is THE most important factor in soil
color. The more humus, the darker the soil.
Soil color can tell a lot about the contents of soil.
According to the graph of soil profiles, what
inference, or guess, could you make about soil
sample “C”?
Where do you think soil sample “B” came from?
A.The top layer of soil
B. The middle layer of soil
C. The deepest layer of soil
D.Depth of soil does not affect its color
Soil Particle Sizes
• Sand—smaller than gravel, you can still see it, feels
grainy, water flows through easily
• Silt—smaller than sand, can’t see individual particles,
feels smooth like powder, water has a harder time
flowing through
• Clay—smaller than silt, feels sticky, water usually
doesn’t flow through
Sedimentation Tube
• See Demonstration
Clay pot soil Activity
• Soil texture means how much of each size
particle is in soil
• Are you sand, silt or clay?
• Sand lets water flow quickly through, while
clay holds water and won’t let it flow
Which soil sample will hold the most water?
A.
B.
C.
D.
Soil sample A will hold the most water
Soil sample B will hold the most water
They will both hold the same amount of water
Only silt can hold water
Consistency
• Soil consistency means how the soil likes to
stick together. It depends on the kinds of
minerals in the soil and how much water is in
the soil
• Does it stick together when you squeeze a
handful of it? Does it crumble apart? Is it
sticky?
Soil pH
• pH is the way we measure how acid or basic
something is
• It usually ranges from 0 to 14. 1 is very acidic while
14 is very basic, 7 is neutral like pure water
• Acids: lemon juice, orange juice, sodas
• Bases: Clorox, ammonia, baking soda
Some Plants like acid soils
Other plants like basic soils
• But if soil is too acid or basic, no plants can
grow
What does the pH level do?
• pH of the soil affects how minerals dissolve.
The best pH for soils and plants is between 67, slightly acidic.
• At this pH, the nutrients from minerals
become available to plants. The water in the
soil will dissolve the nutrients from the
minerals in the soil! Happy plants!
Nutrients
• Nutrients are the
chemicals that an
organism needs to
grow or maintain
its life.
The pH of soil helps to
A. Hold water for plants
B. Produce minerals
C. Increase pore space
D. Dissolve nutrients for plants
Soil moisture
• Plants need moisture. If soil is too dry, plants
won’t grow. If soil is too wet, plants won’t
grow. Moisture must fall in a range for plants
to grow.
too wet
too dry
• When soil becomes too dry, it can more easily
erode in the wind.
• An important example of this is the Dust Bowl
from the 1930s. A drought in the plains
states, along with poor farming practices,
caused heavy erosion of topsoil.
Dust Bowl, cont.
• Dust bowl lasted 10 years!
• It took place in the southern Plains States
United Streaming
Dust Bowl Video
http://player.discoveryeducation.com/index.cfm
?guidAssetId=92FA06A9-396A-4919-B9CC4FEE5627158B&blnFromSearch=1&productco
de=US
Soil temperature
• If soil temperatures are too high or low,
plants can’t grow
Review of Good Soil
• Dark in color means high nutrients, both
organic (humus) and inorganic (mineral)
• Not too dry or wet
• Slightly acidic pH
• Not too much sand or clay
• Deep layer of topsoil
Soil is so valuable….
How do we protect it?
• Good farming practices
• Contour plowing-when plowing around
a hill, make rows around the hill, not up
and down!
Conservation plowing
• Don’t plow unless you need to. When soil
isn’t plowed up, it doesn’t wash or blow away
as easily
• Plowing creates loose soil. Not plowing keeps plants
in the ground and roots lock soil into the ground
Crop Rotation
• If you plant the same crops in the soil year
after year, the soil loses nutrients.
• Plants won’t grow as well in that soil after
years of this kind of farming
• To avoid it, you should plant different plants in
an area every
few years. This is
called crop rotation
Aaron noticed that when the fields were plowed, a lot
of soil was blowing away in the air. If the amount
of plowing DECREASED, which statement would
probably be true?
A.
B.
C.
D.
The amount of soil lost each year will not change
The amount of soil lost each year will decrease
The amount of soil lost each year will increase
New soil will grow to replace lost soil
Bob’s farm is on a hillside. How can contour plowing
(plowing along the curves of the hill) help
conserve the soil on the hillside?
A. Contour plowing allows rainwater to run straight
downhill which helps shift the soil sideways.
B. Contour plowing block rainwater from running
along the curve which helps soil to flow downhill
C. Contour plowing allows rainwater to run along the
curves which helps to keep soil in place
D. Contour plowing blocks rainwater from reaching
the plants which helps conserve soil nutrients.
Without Protection, Soil….
• can wash away in a mudflow following heavy
rains
• can erode and deposit in a new place
• can create landslides
• and can slump
• Active art on soil movement
Summary of Soil Conservation
• Don’t leave soil bare, keep plants in the soil
• Use conservation and contour plowing
techniques
• Rotate crops that are planted so nutrients stay
in the soil
Which of the following could help prevent soil
erosion?
A.
B.
C.
D.
Planting tree between fields
Strip mining and open pit mining
Building highways and shopping malls
Cutting down all of the trees