Lecture 10: All About Soil

Question 1

What is soil?

Answer 1

Unconsolidated cover of the earth, made up of mineral and organic components, water and air, and capable of supporting plant growth

Question 2

What is dirt?

Answer 2

Displaced soil

Question 3

Is soil a renewable resource?

Answer 3

No

Question 4

What are the different profiles of soil?

Answer 4

O Horizon/Layer
A Horizon/Layer
B Horizon/Layer
C Horizon/Layer
R Horizon/Layer

Question 5

What is the O Horizon?

Answer 5

Soil profile that is found in undisturbed fields of forests made of organic matter consisting of plant matter in varying degrees of decomposition

Question 6

What is A horizon?

Answer 6

Topsoil with mineral soil mixed with organic matter.

There are fewer organisms towards the base of the layer

Question 7

What is B Horizon profile?

Answer 7

Subsoil that is usually nutrient rich. It may contain some organic matter.

It has lower concentrations of oxygen and is less penetrable by roots

Question 8

What is C Horizon soil?

Answer 8

Lower subsoil made mostly of mineral rock being broken down.

You will see particles of different sizes

Question 9

What is R Horizon

Answer 9

It is the parent bedrock

Question 10

How are soil horizons developed?

Answer 10

Develop from parent materials

There are variations of parent materials all around the world so soils are not the same everywhere

Question 11

What is weathering?

Answer 11

The break down of rocks into soil

Question 12

What are the different types of physical weathering?

Answer 12

Freezing and thawing
Heating and cooling
Unloading (exfoliation)
Wetting and drying
Grinding or rubbing (Abrasion)
Organism activity

Question 13

What is freezing and thawing weathering?

Answer 13

Water accumulates in an opening of a rock, the water freezes and expands.

Expansive may be big enough to break the rock

Question 14

What is heating and cooling weathering?

Answer 14

Alternating cycles of heating and cooling can cause different minerals in the rock to expand and contract to varying degrees

Question 15

What is unloading weathering?

Answer 15

Release of pressure (erosion) on top of a rock allows the rock to expand and break in sheets along the joints

Question 16

What is wetting and drying weathering?

Answer 16

Different rocks absorb varying amounts of water and the water absorption causes swelling in the rock. Drying in the rock causes contractions.

Question 17

What is the grinding or rubbing weathering?

Answer 17

Movement of rocks between each other, or movement between rocks.

Question 18

What is organism activity weathering?

Answer 18

Caused by living organisms including humans.

Tree roots can grow in and widen cracks in rocks. Animals that tunnel or dig or move on soil can gradually break down rock

Question 19

What does soil consist of? What are the components of soil?

Answer 19

Mineral particles
Organic materials
Living organisms
Air
Water

Question 20

What are the three categories of mineral particles in soil?

Answer 20

Sand, silt, clay

Sand is like a basket ball, silt is like a baseball, clay is like a golf ball

Question 21

What are the characteristics of sandy soils?

Answer 21

Large spaces between particles
Little water holding capacity
Low cohesiveness between particles
Holds fewer plant nutrients
Large capacity for aeration
Warms up and cools down faster than other soils

Question 22

What are the characteristics of silty soil?

Answer 22

Better water holding capacity than sandy soils
Moderate to high nutrient levels, high fertility rating
Low to moderate cohesiveness
Can be easily washed away by rain
Overtilling can cause compaction
Can harden in dry conditions

Question 23

What are the characteristics of clay soils?

Answer 23

High capacity to hold water
High cohesiveness between particles
May be in nutrients, but tight binding to particles may make them unavailable to plants
Take longer to drain and warm up
Become hard when dry

Question 24

What are the characteristics of loam?

Answer 24

Equal proportions of sand and silt, and less of clay
Good drainage, fertility, aeration, water retention
Easy to work with, loose and crumbly texture
Easy for roots to grow in

Question 25

What is soil structure?

Answer 25

Arrangement of sand, silt, and clay particles into clumps, known as aggregates.

Question 26

Why is it important to have good soil structure?

Answer 26

Important for plant growth as it allows water and air to enter the soil and nutrients to be available

Question 27

What are the 7 different categories of soil structure?

Answer 27

Granular Platy Blocky Prismatic Columnar Massive Single grain

Question 28

What is granular soil structure?

Answer 28

Most ideal soil structure It has a good amount of drainage, aeration and biological activity. It's easy to work with and allows for the good development of plant roots. Aggregates are 2 to 5 mm in diameter

Question 29

What is platy soil structure?

Answer 29

Thin horizontal layers of soil often seen in compacted soils. May prevent root growth through the layer

Question 30

What is a blocky soil structure?

Answer 30

Aggregates are irregularly shaped, or cube like. Usually 5 to 50 mm in diameter with sharp or dull edges

Question 31

What is prismatic soil structure?

Answer 31

Aggregates are taller than they are wide with flat tops.

Question 32

What is a columnar soil structure?

Answer 32

Similar to prismatic soil structures but with rounded tops. Often found in salt affected soils

Question 33

What are massive soil structures?

Answer 33

Soil does not have any large pores. It's effectively a massive block.

Question 34

What is single grain soil structure?

Answer 34

No aggregation or definite arrangement of soil particles. Usually found in coarse grained soils like beach sand.

Question 35

What are micropores?

Answer 35

Usually less than 0.08 mm and are usually located within aggregates (inside the aggregate)

Question 36

What is a macropore?

Answer 36

Usually has diameters greater than 0.08 mm and are located inbetween aggregate particles.

Question 37

Sketch a typical soil profile and label the layers.

Answer 37

Draw on paper

Question 38

What is the process of breaking down rocks into soil called?

Answer 38

Weathering

Question 39

What is the proportion of sand, silt, and clay particles in soil called?

Answer 39

Soil texture (not how the soil feels) aka percentage of sand, silt and clay particles

Question 40

What type of soil structure is ideal for plant growth?

Answer 40

Granular soil structure

Question 41

What is a ped?

Answer 41

Groups of aggregates may stick together to form large clumps

Question 42

What is the particle size of sand?

Answer 42

0.05mm to 2mm

Question 43

What is the particle size of silt?

Answer 43

0.002mm to 0.05mm

Question 44

What is the particle size of clay?

Answer 44

Less than 0.002mm

Question 45

What is the ideal soil texture for plants to grow in?

Answer 45

Loamy soil

Question 46

What do soil horizons develop from?

Answer 46

Parent materials