1. Factors And Processes Of Soil Formation
Soils
Factors And Processes Of Soil Formation
Soil Characteristics
Distribution Of Soils

2. What do you know?
The Apple as Planet Earth

3. You have 3 minutes to develop a group consensus definition.
What is soil?
You have 3 minutes to develop a group consensus definition.

4. Definition
Soil is material capable of supporting plant life. Soil forms through a variety of soil formation processes, and includes weathered rock "parent material" combined with dead and living organic matter and air.
Soils are vital to all life on Earth because they support the growth of plants, which supply food and oxygen and absorb carbon dioxide and nitrogen.

5. Soil type Climate Vegetation
What are the three most important factors that determine where populations of people will live?
Soil type
Climate
Vegetation
Regions with poor soils, which cannot be used for growing crops or grazing livestock, have the lowest densities of human population.

6. Urban Sprawls (growing cities)
What event has decreased the area of land available for farmland in the past few decades?
Urban Sprawls (growing cities)
Explain how the event mentioned above has decreased the land available for farmland.
Increased amount of space used for housing, shopping malls, industrial buildings, and highways.

7. Explain the difference between land and soil.
Land: part of the earth not covered by water
Soil: the layer of material that covers the land and supports the growth of plants. The place where seeds germinate and plants anchor their roots in. Contains both eroded rock, decomposed organic matter and living organisms (bacteria, fungi, animals)
Dirt: eroded rocks and decomposed organic matter, but no living organisms

8. What does soil contain?
A: Weathered rock particles, decomposing plant and animal matter, spaces for air and water

10. Weathering and Soils

11. Earth’s Surface Processes
First a definition:
Weathering
– Physical breakdown and chemical alteration of rock at Earth’s surface

12. Source: Tom Bean/DRK Photo

13. Mechanical Weathering
Mechanical weathering breaking of rocks into smaller pieces
Four types of mechanical weathering
1. Frost wedging – freezing and thawing of water in cracks disintegrates rocks w

14. Evidence of Frost Wedging in Wheeler Park, Nevada
Source: Tom Bean/DRK Photo

15. Rockfall caused by frost wedging

16. Mechanical Weathering (continued)
2. Mechanical Exfoliation (AKA Unloading)
- Like peeling layers off an onion
3. Thermal expansion and Contraction– alternate expansion and contraction due to heating and cooling
- important in deserts
4. Biological activity – disintegration resulting from plants and animals
- root wedging, animal burrows

17. Mechanical Exfoliation of a Pluton
AKA “Unloading “

18. Mechanical Exfoliation in Yosemite National Park
Source: Phil Degginger/Earth Scenes

19. Mechanical
Exfoliation
of granite
AKA Unloading

20. Thermal Expansion and Contraction
Source: Tom Bean

21. Tree roots growing in rock fractures, plus animal burrows, expose deep rocks to water
Source: Runk/Schoenberger/Grant Heilman

22. How do pioneer organisms first appear on areas of rock and gravel?
Carried by wind or feet of birds

23. Increase in surface area by mechanical weathering

24. Differential weathering controlled by jointing patterns
Definitions:
Joints and Faults
Deep rock exposed to water

25. Joint-controlled weathering in igneous rocks

26. Joints in sandstone - Canyonlands Natl Park, Utah

27. Breaks down rock and minerals
Chemical Weathering
Breaks down rock and minerals
Important agent in chemical weathering is water
Water dissolves and transports ions and molecules
The dissolved ions later bond & form the cements in sedimentary rocks

28. Source: Ramesh Venkatakrishnan

29. Dissolution Weathered and Unweathered Limestone Boulders
Source: Ramesh Venkatakrishnan

30. Hydrolysis – Feldspar to Clay
Feldspars become
Mechanical fracture due to chemical weathering

31. Angular Boulder Decomposes and Rounds

32. Angular Boulder Decomposes and Rounds
Source: Paul McKelvey/Tony Stone Images

33. Hydrolysis Cleopatra’s Needle, (Egypt)
Granite in a
Dry Climate
Source: New York Public Library, Locan
History and Genealogy Division

34. Hydrolysis Cleopatra’s Needle, (Central Park, NYC)
Granite in a
Wet Climate
Source: Runk/Schoenberger/Grant Heilman

35. Oxidation of Basalt
Rust (Iron Oxide) forms

36. Weathering
Rates of weathering
Mechanical weathering aids chemical weathering by increasing surface area
Others factors affecting weathering
Rock characteristics e.g. minerals
Marble and limestone easily dissolve in weak acidic solutions -Dissolution

37. Soils
Our food grows in soils. Also very important in recognizing past climates

38. Soil by definition
Combination of mineral and organic matter, water, and air able to support the growth of plants

39. Components in soil that support plant growth

40. Soil Formation

41. Factors controlling soil formation
Parent material
parent material is the underlying bedrock - composition affects soil types
Time
Soils get better developed (Thicker, with greater differences between layers)
with more time
Climate
Biggest control on soil formation
Key factors are temperature and precipitation

42. Factors controlling soil formation
Plants and animals
Organisms influence soil properties
Also furnish organic matter to the soil (especially plants)
Slope
Steep slopes have poorly developed soils (due to faster erosion and downslope transport
Flatter terrain accumulates soil faster

43. Describe how lichens help to develop soil on an area of rock.
Lichens establish on bare rock and produce acidic compounds that break the rock down and releases nutrients.
When lichens die, they add more nutrients, which is the start of soil formation.

46. Variations in soil development due to topography
Note location of agriculture

47. Soil Profile
Soil forming processes operate from the surface downward
Vertical differences are called horizons – zones or layers of soil

49. An idealized soil profile with horizons

50. The soil profile High biological activity (animals live here)
O horizon – organic matter
A horizon – organic and mineral matter
High biological activity (animals live here)
Together the O and A horizons make up topsoil
E horizon – little organic matter
Zone of leaching
B horizon – zone of accumulation
C horizon – partly altered parent material
Mnemonic: Only Active Educators Become Champions

51. Remember the different horizons
Organic
Animal Activity
Exited
Back
Crushed Rock O A E B C
Soluble Minerals
Soluble Minerals

52. Describe how the plants and animals in the soil form a biological community.
Decomposers break down material to provide nutrients to the soil. Some bacteria provide nitrogen to the plant. Some organisms use the plants as food.

53. Vegetation and Soil Development
1. Plants use Hydrolysis to get nutrient metals
2. Humic acids and metals returned at death. Acids remove metals from E-layer

54. Animal Activities in “A” horizon
Source: Runk/Schoenberger/Grant Heilman

55. Eluviation & Illuviation

56. Three very generic soil types
The characteristics of each soil type primarily depend on the prevailing climatic conditions
Three very generic soil types
Pedalfer Moist All Year
Best developed under forest landscapes
Pedocal - High Evaporation
Associated with dry grasslands and dry brush vegetation
Laterite e.g. Monsoonal Climate
Alternating Hot dry and Cool Wet tropical climates
Intense chemical weathering
Very thick soils but thin useful topsoil
Trees are Buttressed

57. pedalfer
pedocal
laterite
Evergreen forests
Shortgrass
tropics

58. Pedocal O A E B C
Organic
Activity
Leached
Accumulation
Crushed Rock

59. Soils Around the World

60. Compare and contrast the three A horizons of the soil in grassland, forest and desert soils.
Grassland - A horizon topsoil is deep and supports most root growth,
Forest - A horizon is not as thick as grassland,
Desert – A horizon is very limited due to low precipitation and little decomposing matter

62. What factors affect the ground’s ability to absorb water?
The type of soil
Size of the spaces between eroded rock and decomposing materials
Size of the particles of the soil
Shapes of the particles
Kind of particles that make up the soil
The saturation state of the soil
How much water is already in the soil

63. What factors affect the ground’s ability to absorb water?
Temperature
If the ground is frozen then there is ice filling the available spaces
If the temperature is below freezing, the precipitation will stay on the surface
If the temperature is high, water will evaporate before it has a chance to be absorbed

64. What factors affect the ground’s ability to absorb water?
The nature of water
Water is a “sticky” particle
There is a strong intermolecular force between water particles
This creates surface tension which holds water molecules “together”
This may prevent water from “falling” into the spaces in the soil

65. Describe the overall process of…. primary succession
Lichens grow on bare rock and break it down (soil formation)
Small mosses grow in thin soil. Insects gather and form a community
Decaying material is mixed with broken down rock in cracks. Larger plants grow in these areas
Increased decomposed material increases the soil’s ability to hold water and a larger community develops
One species replaces another (ex: taller plants and trees develop and plants that can’t survive in shade will disappear)

67. Define climax community
A community of organisms that has a maximum level of productivity (maximum amount of biomass being produced)

69. Define secondary succession. Provide an example.
Succession eventually restores a climax community but it is not necessarily starting from bare rock. It builds from remains of previous ecosystem that was damaged. Ex: forest grows back after a forest fire weeds overtake a ploughed field plants grow through the pavement

70. Area affected by agricultural practices
Same pond 10 years after natural succession has taken place

71. Explain the process of remediation to help restore these areas of land to productive ecosystems.
Toxic materials are removed or neutralized (using strong acids)
Soil acidity is restored using calcium carbonate
Fertilizer is added to increase plant growth
Landscaping to provide suitable drainage
Topsoil is added and plants and grass is planted.

72. Soil Erosion Recycling of Earth materials
Natural rates of soil erosion depend on
Soil characteristics
Climate
Slope
Type of vegetation

73. Erosion
Headed for the Sea
Source: Ramesh Venkatakrishnan

74. Soil Erosion
In many regions, the rate of soil erosion is significantly greater than the rate of soil formation
Farmers now:
level fields with lasers to slow loss of topsoil
Terrace the fields
Plant rows of trees to slow wind and soil erosion
Use no- or low-till practices

75. Importance of Soil Organic Farming: Conserving Top Soil
Soil Microbes and Global Warming
Earth Water Filter
Nature's Kidneys
Water Conservation: Israel
Farm Solutions to Water Pollution