Download soil intro - Ms Kim`s Biology Class

BELL RINGER 5.11.15
• What makes up soil? (name at least 3)
• Why is soil important to humans? (name
two reasons)
• What is the average thickness of topsoil?
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Introduction to Soils
The most important natural
resource around the earth!
2
What is Soil?
Defined as:
• Mineral & organic material that supports
plant growth on the earth’s surface
• Mixture of particles of rock, organic
materials, living forms, air, water
3
What soil resources help in
supporting life?
• Oxygen: needed for adequate root growth
• Temperature: soil absorbs heat from the
sun – loses heat to atmosphere (plant
growth and seed germination)
• Water: plant growth
• Carbon: organic matter
• Minerals: nutrients and physical makeup
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How is Soil Made?
1. All soil starts as rocks.
2. Powerful forces act on the rocks to break
them into smaller fragments.
3. Water penetrates the cracks in the rock
and when it freezes the water acts as a
wedge to split the rock.
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Soil origin cont.
4. Rivers, glaciers, landslides and
avalanches cause rock particles to grind
against each other wearing them down.
5. Chemicals mix with water to further break
the rocks down.
6. Plants began to grow in the weathered
rocks and as they die, they add organic
matter to the soil which attracts soil
micro-organisms.
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Soil origin cont.
7. When this happens, then the soil is
capable of supporting plant life and can
then truly be called soil.
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What does the Term Weathering
Mean?
• Weathering is the processes that occur to
break down rock into soil.
• This process includes water freezing,
thawing, landslides, wind and chemical
action.
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What is Parent Material?
• Rock material that has undergone some
weathering and change, but not enough to
be called true soil, as it is not capable of
sustaining plant life.
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10
List the 5 factors responsible for
soil development.
1. Parent material
2. Climate
3. Variation in the earth’s surface
(topography)
4. Plant & animal life
5. Time
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Parent Material
• Parent rock from which a soil is formed has a
significant effect on its qualities.
• Parent materials influence the formation of soils by
their rates of weathering, the nutrients that they
supply, and the particle sizes that they contain.
• The less developed a soil is, the more influence
that the parent material has on its characteristics.
12
Climate
• Climate is a dominant factor in the formation of soils.
• The major components of climate that affect soil are
precipitation and temperature.
• With low rainfall an accumulation of lime may occur ,so
these soils are usually alkaline.
• In areas of high rainfall there is intense weathering and
leaching resulting in acid soils.
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Climate continued
• Climate also has an indirect affect on soils by its action
on vegetation.
• Changes in temperature affect the rate of
physical/chemical weathering. Rates of chemical
reactions increase as temperature increases, if sufficient
water is also present.
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Topography
• Topography (the lay of the land) influences drainage and runoff.
• Soil layer on gentle slopes will be generally deeper, sustain more
luxuriant vegetation, and contain more organic matter than soil
profiles on steeper slopes.
• In our hemisphere, mountains often affect the climate and in turn the
soil. The western side of a mountain range often receive more rain
and have more developed soil vs. the drier east side of a mountain.
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Living Organisms
• The activity of living plants and animals (macro and microorganisms)
has major significance on the development of soil.
• Microorganisms help develop soils by decomposing organic matter
and forming weak acids that dissolve minerals faster than would
pure water.
• Fibrous root systems of grasses have a distinctly different effect on
soils than do the coarser roots of trees.
• Lichens, which are a combination of algae and fungi, are often the
first plants that grow on weathering rocks.
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Time
• It requires time, up to about a million years,
to form soils.
• Rocks like granite are extremely hard to
decompose. Softer rocks such as limestone
take less time.
• As soils age they differentiate into defined
profiles consisting of three different layers (A
horizon, B horizon and C horizon).
• Horizons tend to develop faster under
humid, warm, and forested conditions.
• A recognizable soil profile may develop in as
few as 200 years or, under less favorable
conditions, take several thousand years to
develop.
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Soil Development Over Time
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Components of Soil
• Mineral Matter: about 45% of soil (partially
decomposed rock material (sand, silt, clay)
• Organic Matter: about 5% of soil (partially
decomposed plant & animal matter)
• Air: about 25% of soil (constant fluctuation
as soil is dry and wet)
• Water: about 25% of soil
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Plants use soil
A. Anchorage – roots hold plant in
place
B. Water – absorbed through roots
C. Oxygen – all living organisms need
oxygen
-good soil aeration needed for below
ground plant parts to get oxygen
D. Nutrients – roots take in the macro
and micronutrients necessary for
plant growth
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Living Organisms in the soil
• Forms of life:
– Earthworms
– Insects
– Bacteria
– Fungi
– Other organisms
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Bacteria & Fungi Jobs
• Break down organic matter and release
nutrients
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Earthworm & other soil organism
jobs
• Improve soil tilth
– Ease at which soil can be worked
– Create openings in soil as they tunnel
– Enhances drainage and improves air
exchange
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Soil uses in agriculture
•
•
•
•
Cropland
Grazing land
Forest
Water structures (impoundments, retaining
ponds)
• Agriculture depends on soil to grow food,
fiber, and ornamental plants.
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Nonagricultural uses of soil
• Recreation: playgrounds, sports fields,
jogging paths, golf courses, parks,
campgrounds
• Foundations: buildings have to have solid
base
• Waste Disposal
• Building materials
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