Download Introduction to Soils - Ms Kim`s Biology Class

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• What makes up soil?
• What is topsoil (take a guess!)?
• What is the average amount of topsoil (in
• What is soil used for? (name two different
Introduction to Soil
The most important natural
resource around the earth!
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, gas (air), water
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
Briefly explain the process of soil
• All soil originated as rocks.
• Soils are formed by weathering of rocks.
– Powerful forces act on the rocks to break
them down into smaller fragments.
– Water penetrates the cracks in the rock and
when it freezes the water acts as a wedge to
split the rock.
Soil origin cont.
• Rivers, glaciers, landslides and
avalanches cause rock particles to grind
against each other wearing them down.
• Chemicals mix with water to further break
the rocks down.
• Plants began to grow in the weathered
rocks and as they die, they add organic
matter to the soil which attracts soil microorganisms.
Soil origin cont.
• When this happens, the soil is capable of
supporting plant life and can then truly be
called soil.
What does the term weathering
• Weathering is the processes that occur to
break down rock into soil.
• This process includes water freezing,
thawing, landslides, wind and chemical
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.
List the 5 factors responsible for
soil development.
1. Parent material
2. Climate
3. Variation in the earth’s surface
4. Plant & animal life
5. Time
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.
• Mineral particle size has a great effect on the properties
of soil in the field.
• 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.
Climate continued
• Erosion of sloping lands removes developing layers of soil and
deposits them down slope.
• Erosion, leaching and weathering are more intense and take place
over a longer period each year in warm and humid areas.
• Climate also has an indirect affect on soils by its action on
• Changes in temperature affect the rate of physical/chemical
weathering. Rates of chemical reactions increase as temperature
increases, if sufficient water is also present.
• Topography (the lay of the land) influences drainage and runoff.
• The profile 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.
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.
• 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
• A recognizable soil profile may develop in as few as 200 years or,
under less favorable conditions, take several thousand years to
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
Water in the soil
• Infiltration: process of water soaking into
the soil (surface downward)
• Percolation: water movement downward
through soil and rock (below the surface)
• Permeable: quality of soil that allows for
both infiltration and percolation – then it is
said to be permeable
Living Organisms in the soil
• Forms of life:
– Earthworms
– Insects
– Bacteria
– Fungi
– Other organisms
Bacteria & Fungi Jobs
• Break down organic matter and release
Earthworm & other soil organism
• Improve soil tilth
– Ease at which soil can be worked
– Create openings in soil as they tunnel
– Enhances drainage and improves air
Plants use soil
A. Anchorage – roots
B. Water – absorbed through roots
C. Oxygen – all living organisms need
-plants release oxygen during photosynthesis
and consume oxygen during respiration
-good soil aeration needed for below ground
plant parts to get oxygen
Plants use soil cont.
D. Nutrients – of the 16 essential nutrients
for plant growth – 13 are obtained from the
-root hairs absorb the nutrients dissolved in soil
What is Topsoil?
• Topsoil is the upper, outermost layer of soil,
usually the top 2 inches (5.1 cm) to 8 inches
(20 cm). It has the highest concentration of
organic matter and microorganisms and is
where most of the Earth’s biological soil
activity occurs.
Importance? Commercial
• Importance: Plants generally concentrate
their roots in and obtain most of their nutrients from
this layer.
• Commercial application: A variety of soil mixtures
are sold commercially as topsoil, usually for use in
improving gardens and lawns.
• Erosion: A major environmental concern known as
topsoil erosion occurs when the topsoil layer is
blown or washed away. Without topsoil, little plant
life is possible.
• When starting a gardening project, it is
very crucial to check whether or not the
soil is satisfactory. Following are the
desired levels of Topsoil nutrients:
Desired Results
pH Level
5.8 to 6.2
Phosphorus (P)
Index of 50
Potassium (K)
Index of 50
Calcium (Ca%)
40-60 %
Magnesium (Mg%)
Base saturation (BS%)
Soil uses in agriculture
Grazing land
Water structures
• Agriculture depends on soil to grow food,
fiber, and ornamental plants.
Nonagricultural uses of soil
• Recreation: playgrounds, sports fields,
jogging paths, golf courses, parks,
• Foundations: buildings have to have solid
• Waste Disposal
• Building materials
Exit Slip
1. List 3 factors that are responsible for soil
2. What are the four components of soil?
3. How does water move in the soil?
4. What living organisms are found in the
5. How do plants use soil?