Weathering and Soil
Formation
Soil Composition:
 Soil is a mixture of four materials:
 Weathered rock particles
(Main ingredient)
 Organic matter (5 Percent)
 Water (20 to 30 percent of soil)
 Air (20 to 30 percent of soil)
Weathering and Organic
Processes from soil
 Water and air make
up about 20-30% of a
soils volume.
 5% comes from
organic matter which
is remains and
wastes of plants,
animals, and other
living organisms.
Organic Matter
 The word Organic means, “coming from
living organisms.”
 It comes from the remains and waste
products of plants, animals, and other
living organisms.
 (example: leaves fall to the forest floor, decay, and
become part of the soil.)
 This decayed organic matter is called Humus.
Different Soils:
 Different soils are made of different ingredients
and different amounts.
 (Black soil- which is much darker tends to have
more humus, or decayed organic matter.)
 Black soil- also contains more water.
 The combination of these two things make
darker soil much better for growing things.
Weathering and Organic
Processes from soil





There are four world soil types
1. Tropical Soils
2. Desert Soils
3. Temperate Soils
4. Arctic Soils
Weathering and Organic
Processes from soil
 Tropical soils from in
warm, rainy regions.
Heavy rains wash
away minerals,
leaving only a thin
surface layer of
Humus. Tropical soils
are not suitable for
growing most crops.
Weathering and Organic
Processes from soil
 Climate will control
what types of soil you
find in that area.
 The shape of the land
also affects soil.
Mountainous regions
can be very different
from soils found in
valleys. Why?
Weathering and Organic
Processes from soil
 Desert Soils form in
dry regions. These
soils are shallow and
contain little organic
matter. With the low
rainfall, chemical
weathering and soil
formation occur very
slowly.
Weathering and Organic
Processes from soil
 Temperate soils from
in regions with
moderate rainfall and
temperatures. Some
temperate soils are
dark colored, rich in
organic matter and
minerals and good for
growing crops.
Weathering and Organic
Processes from soil
 Arctic soils form in
cold, dry regions
where chemical
weathering is slow.
They usually don’t
have well developed
horizons.
Kind of soil depends on
many factors






The kind of rock in the area
The area’s climate or weather pattern
The landforms in the area
The plant cover in the area
The animals and other organisms.
Time (how long it has to form.)
Layers Upon Layers
 Soil Horizon: is a layer of soil with
properties that are different from those of
the layer above.
 Soil Profile: in any location there can be
different horizons that make up a profile.
Basic Soil Profile
Old
Al
Eats
Beans
Corn and
Rhubarb
O Horizon - The top, organic
layer of soil, made up mostly of
leaf litter and humus
A Horizon - The layer called
topsoil; is made up of humus
mixed with mineral particles.
E Horizon - This layer is light in
color; It is made up mostly of sand
and silt, having lost most of its
minerals and clay as water drips
through the soil
B Horizon - Also called the
subsoil - It contains clay and
mineral deposits (like iron,
aluminum oxides, and calcium
carbonate).
C Horizon - slightly broken-up
bedrock
R Horizon - The unweathered
rock (bedrock) layer that is
beneath all the other layers.
Soil Horizons
 O Horizon - The top, organic layer of soil, made up mostly of
leaf litter and humus
 A Horizon - The layer called topsoil; is made up of humus
mixed with mineral particles. (black soil)
 E Horizon - This layer is light in color; It is made up mostly of
sand and silt, having lost most of its minerals and clay as water
drips through the soil
 B Horizon - Also called the subsoil - It contains clay and
mineral deposits (like iron, aluminum oxides, and calcium
carbonate).
 C Horizon - slightly broken-up bedrock
 R Horizon - The unweathered rock (bedrock) layer that is
beneath all the other layers.
Properties of Soil
 Texture:
 Color:
 Pore Space:
 Chemistry:
Soil Texture
 A soil’s texture Is determined by the size
of weathered rock particles.
 The particles are classified as either
 Sand- the largest particle, gritty feeling,
doesn’t hold water well.
 Silt – smaller, is smooth and silky when wet,
it holds water better than sand.
 Clay- The smallest, sticky when wet,
absorbs the most water. (dries very hard.)




 Dirt Knowledge
Not all dirt is the same. Based on it's
components the suitability for planting can be
very different.
Things like a very high clay content may mean
it holds water very well or if there is too much
clay then it could actually create a real problem
and not allow any water to pass creating
ponding.
Too high a sand content can cause the
opposite effect It will not hold enough water to
support the plant in hot weather or high wind.
Silt is an in-between situation in that it's particle
size is smaller than sand, it is less plastic than
clay and often has a higher organic content
associated with it.
Weathering and Organic
Processes from soil
 What are the differences between the
two soils, think about how soil is made.
Soil Color
 The color of the soil is a clue to it’s other
properties.
 Black or brown soils usually contain a lot of
humus.
 Reddish soil usually contains more Iron.
Pore Space
 Pore space
 is the space between soil particles.
 has two things, Air and Water
 Plants will grow the best when the
pore space has 50% air and 50%
water.
Soil Chemistry
 The water in soil has a specific PH level.
 This term PH is a measurement of
acidity.
 When water reaches a certain PH
level, it is best to help plants grow.
 By knowing this about soil, farmers
can make soil more acidic or less
acidic to help plants grow.
PH scale and
Nutrient availability
Test the two soil’s PH
 Follow the instructions carefully.




In the clear tube, pour 3 ml of the pH indicator solution.
Put only a small pinch (1 ml) of soil into the tube.
Put the cap on the tube and shake for 30 seconds.
Allow the soil to settle and the solution should change
colors.
 Compare the color of the solution to the Ph color chart.
 How would being about to do this be useful?
(summary)
The End