Download Chapter 7 Weathering and Soil

Chapter 7
Weathering and Soil
7.2 The nature of soil notes sheet.
Soil
► Soil
is a mixture of weathered rock, decayed
organic material, mineral fragments, water, and
air.
► Soil can take thousands of years to form.
► There are five characteristics that affect soil
formation.
1. Climate
2. Slope of land
3. Types of rock
4. Types of vegetation
5. Amount of time
Soil
► Different
soils can develop in different
climates; tropical soil is different than polar
soil
► Soils that develop on steep slopes are
different than soils that develop on flat land.
Slope will effect soil
Erosion will effect soil…
The composition of soil
► The
rock and mineral fragments found in
soils come from rocks that have been
weathered.
► Organic matter in soil comes from plant
leaves, stems, and roots.
► Decayed organic matter turns to humus, a
source of nutrients for plants.
► Soil has many small spaces between
particles that holds water and air.
Soil Profiles
►
►
►
Different layers of soil are called horizons.
All the horizons of a soil form a soil profile.
There are three main horizons for most soils.
-A horizon: the top layer of soil.
-It is usually covered by litter, made up of leaves,
twigs, and organic matter, which helps prevent erosion and
evaporation of water from the soil.
-Also known as top soil.
-It is dark and fertile.
Soil Profiles
B horizon: the middle layer of soil
-Because there is less organic matter in this
horizon, it is lighter in color than the A
horizon.
► -Contain materials from A horizon that were
moved down by leaching: the removal of
minerals that have been dissolved in water.
Water reacts with humus and carbon
dioxide to form acid. The acid dissolves the
minerals in the A horizon and carries them
to B horizon.
Soil Profiles
►C
horizon: the bottom of the soil profile.
-Consists of partially weathered rock.
-The thickest soil horizon.
-Does not contain much organic matter and
is not affected by leaching.
-The soil layer that is the most like the
parent material.
Soil Profiles
► At
many places of Earth, land is covered by
a thick layer of sediment that is deposited
by glaciers.
-This material is an unsorted mixture of
clay, silt, sand, and boulders that were
left after the glacial ice melted. It is
extremely fertile.
Soil Types
► Many
different types of soil exist, based on
climate and slope.
► Desert soils are dry and have little organic
matter.
► Prairie soils have thick dark A horizons
because of the grasses contributing lots of
organic matter.
Soil Types
► Slope
also affects soils.
-Steep slopes have poor soils because
material moves downhill before it can be
weathered.
-Bottomland soils are thick, dark, and full of
organic matter because sediment and
water are plentiful.
Prairie and Desert Soil
Temperate and Forest Soil
Soil types
► In
terms of soil texture, soil type usually
refers to the different sizes of mineral
particles in a particular sample. Soil is made
up in part of finely ground rock particles,
grouped according to size as sand, silt and
clay. Each size plays a significantly different
role.
Size of particles
► The
size of the three particles that make up
soil are broken down by size
► Sand is the largest of soil particles
► Silt is the middle size of soil particles
► Clay the smallest of the soil particles
Loam
► Loam
is soil composed of sand, silt, and
clay in relatively even concentration (about
40-40-20% concentration respectively),
considered ideal for gardening and
agricultural uses. Loam soils generally
contain more nutrients and humus than
sandy soils, have better infiltration and
drainage than silt soils, and are easier to till
than clay soils.
Sand
► Sand
is a naturally occurring granular
material composed of finely divided rock
and mineral particles
► Sandy soils are ideal for crops such as
watermelons, peaches, and peanuts and
their excellent drainage characteristics make
them suitable for intensive dairy farming.
Silt
► Silt
is soil or rock derived granular material
of a grain size between sand and clay. Silt
may occur as a soil or as suspended
sediment (also known as suspended load) in
a surface water body. It may also exist as
soil deposited at the bottom of a water
body.
► Silt is formed by chemical weathering, ice
wedging, and abrasion.
Clay
► Clay
minerals are typically formed over long
periods of time by the gradual chemical
weathering of rocks
► Clay deposits may be formed in place as
residual deposits in soil, but thick deposits
usually are formed as the result of a secondary
sedimentary deposition process after they have
been eroded and transported from their
original location of formation.
Chapter 7 Sections 3
Soil Erosion Notes Sheet
Soil Erosion
► The
removal and carrying away of sediment
from earth’s surface is called soil erosion
► Soil erosion is harmful because plants do
not grow well where topsoil has been
removed
Causes of Soil Erosion
► Soil
erodes when it is moved from the place
where it was formed
► Water and wind are the 2 main things that
erode soil
► Soil erosion is more severe on steep slopes
then on gentle slopes it is also more severe
in areas with little vegetation
► Humans cause soil to erode faster then new
soil can be formed
Causes of Soil Erosion
► One
way humans do this is by removing
ground cover
► Ground cover is vegetation that covers the
soil and protects it from erosion. When it is
cleared erosion increases
► When farmers clear and till soil for
agricultural cultivation soil erosion
increases. If the topsoil erodes then the
quality of soil becomes reduced, because
topsoil contains many nutrients
Clear Cut Forest
Causes for Soil Erosion
► When
forests are removed soil is exposed
and erosion increases
► When areas are overgrazed by cattle, sheep
and horses erosion increases because there
is very little vegetation left to protect the
soil.
How does this effect soil erosion?
Causes for Soil Erosion
► If
soil erosion is severe excess sediments
can damage the environment. Excess
sediment loads degrade the quality of life by
damaging wildlife habitats and fill in stream
channels
Preventing soil erosion
► Soil
must be managed and protected
► Farmers manage crops to reduce soil
erosion. They plant trees and manage
grazing.
► No till farming- is a process where the seeds
for the next crop are planted in the
vegetation residue from the former crop.
The left over vegetation protects the soil
Preventing soil erosion
► Contour
farming- is used on gentle slopes.
Crops are planted with the natural contours
of the land to slow the flow of water down
the slope
► Terracing is used on steep slopes where
level flat steps are built into the sides of
slopes so that crops can be grown. They
reduce runoff by creating flat areas and
shorter sections of slope
Contour farming
Terracing