Bell Ringer
1) A rock exposed to high winds, over a long
period of time, loses half of its original size.
This is an example of…
a) Physical weathering
b) Chemical weathering
c) Biological weathering
d) Erosion
e) Decomposition of organic compounds
2) Which of the following answers does NOT
create soil?
a) Biological weathering
b) Deposition of organic matter
c) Erosion
d) Photochemical weathering
e) Decomposition of organic matter
3) By volume, soil is roughly…
a) 50% minerals, 45% organic matter, 5% pore space
b) 50% organic matter, 30% minerals, 20% pore space
c) 50% minerals, 45% pore space, 5% organic matter
d) 50% pore space, 30% minerals, 20% organic matter
e) 50% pore space, 45% minerals, 5% organic matter
AP Practice
4) Leaf litter is known as…
a) A horizon
b) B horizon
c) C horizon
d) E horizon
e) O horizon
Soil Characteristics
pgs. 240-241
Soil Types
• There are 12 major groups of soils found in
the US – scientists classify soils based upon
four characteristics.
1) Color
2) Texture
3) Structure
4) pH
1) Soil Color
• Black or dark brown soils are usually rich in
organic matter, indicating fertility.
• Pale gray and white soils generally indicate
low organic content and a leaching of minerals
into lower soil levels.
2) Soil Texture
• Texture is dependent upon the particles
making up the soil sample.
• Soil is made up of a combination of four
particles: gravel, sand, silt and clay.
2) Soil Texture
• Clay is the smallest particle
(less than 0.002mm in diameter)
• Clay particles adhere to each other, giving clay
a sticky feeling when moist
2) Soil Texture
• Silt is the middle-sized particle
(0.002mm – 0.05mm in diameter)
• Sand is the second largest particle
(0.05mm – 2mm in diameter )
• Gravel is the largest particle
(over 2mm in diameter)
2) Soil Texture
• Soil particles also affect soil porosity – the size
of space between particles.
2) Soil Texture
• Soil particles also affect soil porosity – the size
of space between particles.
• Small particles (like clay) have very little space
between particles, making it harder for water
and air to travel through the soil.
2) Soil Texture
• Soil particles also affect soil porosity – the size
of space between particles.
• Small particles (like clay) have very little space
between particles, making it harder for water
and air to travel through the soil.
• Large particles (like gravel) have larger spaces
between particles, allowing water and air to
pass through too quickly.
2) Soil Texture
• Soil particles also affect soil porosity – the size
of space between particles.
• Small particles (like clay) have very little space
between particles, making it harder for water
and air to travel through the soil.
• Large particles (like gravel) have larger spaces
between particles, allowing water and air to
pass through too quickly.
• The best soils for agriculture are loams –
relatively even mixtures of clay, silt and sand.
3) Soil Structure
• Soil structure is a measure of the “clumpiness”
of soil.
• Greatly compact soils (due to repeated tilling,
etc.) make it harder to soils to absorb water,
causing a decline in soil fertility.
4) Soil pH
• The degree of acidity or alkalinity influences a
soil’s ability to support plant growth.
• A soil that is too acidic or too basic (usually
due to over fertilizing) can cause plant life to
die.
4) Soil pH
• The degree of acidity or alkalinity influences a
soil’s ability to support plant growth.
• A soil that is too acidic or too basic (usually
due to over fertilizing) can cause plant life to
die.
• Most plants prefer
a slightly acidic pH
of 6.5
Bell Ringer
1) Place the following soil particles in order
from smallest to largest:
Silt, Sand, Gravel, Clay
2) Which answer below is NOT a characteristic
used to determine soil type?
a) Texture
b) Color
c) Parent Material
d) pH
e) Structure
3) Starting with the top layer, list the correct
order of soil horizons.
A Horizon, B Horizon, C Horizon, D Horizon
E Horizon, O Horizon
AP Practice
4) Light-colored soils usually indicate…
a) Soil that is low in minerals
b) Soil that is very fertile
c) Soil containing a lot of humus
d) Soil containing a lot of organic material
e) Soil that is good for farming and agriculture
Lab Note
• On the fractionation lab, particles should
settle in this order:
Clay – Top
Silt – Middle
Sand – Bottom