GEOG 101: DAYS 7
Finishing Population and Starting Soils
HOUSEKEEPING ITEMS
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
Another Science and Technology Lecture – “An
Overview of Global Fisheries and Aquaculture
Production” – on Wednesday in Building 356, Room 209
(auditorium) from 7 to 8. This is a topic we will look at
later in the semester as well.
Food, Education and Development talks on February 2nd
(Monday) in Building 355, Room 211:
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10:30-11:45: Sara Dent – “The Power of Young Farmers in
the Global Food Movement “
12:00-1:15: Dawn Morrison – “Re-Indigenizing the Global
Food Movement”
1:30-2:45: Brent Mansfield – “The University’s Role in the
Global Food Movement”
3:00-4:15: Felix Martinez – “Temporary Foreign
Agricultural Workers in Canada
5:00-6:15: Vanessa Goodall – “Seed Sovereignty in Canada”
Building 355, Room 211
HOUSEKEEPING ITEMS



Interesting item in the folder about how the death of the
current king of Saudi Arabia may create space for
reforms for women. Already 20% of the seats in the
Saudi parliament are reserved for them. However,
women are still not allowed to drive and are kept mostly
segregated.
Resource that might be useful for your alternative midterm assignment:
http://enviro.nanaimo.ca/index.cfm?tab_ID=2&content_I
D=15 (see whole thing).
I would like to do the small group exercise around
population issues before we move on. Also: we have been
discussing whether population or over-consumption is
the main contributor to environmental decline – keeping
in mind that they are both factors. How would one go
about answering that question?
EXTRA CREDIT (VOLUNTARY) HOMEWORK
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Outlines are due on Thursday.
I have to cancel my office hour on Thursday to attend
convocation, but e-mail me with any issues you have.
There are lots of good films on soil and agriculture – Food
Matters, Food Inc., The World According to Monsanto, The
Future of Food, The Real Dirt on Farmer John, Food Fight,
Fresh, King Corn, Super Size Me, The Garden, and Have You
Got Milk? If you know of others, let me know.
Check out any of them and write a two-page, single-space
handwritten response to it, addressing whatever jumps out at
you – things you didn’t know, particularly vivid images, ideas
for enhancing and conserving soil, or whatever you like, as
long as it’s relevant.
Try to have it in to me by next Tuesday (Feb. 3rd).
UPON SUCCESSFULLY COMPLETING THIS CHAPTER, YOU
WILL BE ABLE TO (WE WILL ONLY HIT HIGHLIGHTS, THEN MOVE
ON AGRICULTURE)
Delineate the fundamentals of soil science,
including soil-forming processes
 Describe some important properties of soil
 Characterize the role of soils in biogeochemical
cycling
 State the importance of soils for agriculture and in
supporting plant growth
 Identify the causes and predict the consequences of
soil erosion and soil degradation
 Outline the history and explain the basic
principles of soil conservation

7-5
SOIL AS A SYSTEM
“The nation that destroys its soil destroys itself.”
– Franklin D. Roosevelt, Former U.S. President
Ganaraska wasteland before World War 2 (northeast of Toronto)
Photo courtesy of John Bacher and Ed Borczon
SOIL AS AN (ECO)SYSTEM
 Soil
consists of mineral
matter, organic matter,
air, and water
 Dead and living
microorganisms, and
decaying material
 Bacteria, algae,
earthworms, insects,
mammals, amphibians,
and reptiles
 It’s like an ecosystem on
to itself
7-7
SOIL IS A COMPLEX, DYNAMIC MIXTURE
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Soil consists of mostly mineral matter with varying
proportions of organic matter, the rest is pore space
taken up by air, water, and other soil gases
Parent material = the base geologic material of soil
 Determines the starting composition of the soil
Organic matter includes living and dead
microorganisms as well as decaying plant and animal
material
Water – is not pure, contains dissolved minerals and
organics and is important for support of plant growth
Air – soil air is not the same as air we breathe
Soil can have an influence on a region’s ecosystem
7-8
SOIL FORMATION IS SLOW AND COMPLEX


Soil formation begins when parent material is
exposed to the effects of the atmosphere,
hydrosphere, and biosphere
 Parent material can be lava, volcanic ash, rock,
dunes or most commonly, bedrock - the
continuous mass of solid rock comprising the
Earth’s crust
Weathering = the physical, chemical, or
biological processes that break down rocks to form
soil
 Physical (mechanical) = wind and rain, no
chemical changes in the parent material
 Chemical = substances chemically interact
with parent material
 Biological = organisms break down parent
material
7-9
SOIL FORMATION IS SLOW AND COMPLEX (CONT’D)
7-10
SOIL FORMATION IS SLOW AND COMPLEX (CONT’D)

Biological activity includes deposition,
decomposition, and accumulation of organic
matter


Humus = a dark, spongy, crumbly mass of material
formed by partial decomposition
Erosion = the dislodging and movement of soil
by wind or water
Occurs when vegetation is absent
 When deposited elsewhere referred to as sediment

7-11
weighing
the issues
EARTH’S SOIL RESOURCES
It can take anywhere from 500 to 100 years to produce 1
cm of natural topsoil, depending on local conditions.
Much of Canada’s land area was scraped free of soil
during the last glaciation by the passage of huge ice
masses, which retreated about 10,000 years ago. Today
much of interior and northern Canada still lacks soil.
Given this very long renewal time, is soil truly a
renewable resource?
How should the very long renewal time influence soil
management?

7-12
A SOIL PROFILE CONSISTS OF LAYERS KNOWN AS
HORIZONS
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Horizon = each layer of soil
Soil profile = the cross-section of
soil as a whole
Topsoil = inorganic and organic
material most nutritive for plants
Leaching = dissolved particles
move down through horizons
Litter = surface deposits of leaves,
branches, mosses, animal waste
7-13
A SOIL PROFILE CONSISTS OF LAYERS KNOWN AS
HORIZONS (CONT’D)

O Horizon – peat deposits

A Horizon – topsoil

B Horizon = subsoil, hardpan
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


C Horizon = broken parent
material
R Horizon = unaltered parent
material
W Horizon = distinct layer of
water in some soils
Permafrost = some arctic soils
contain a perennially frozen layer
7-14
SOILS VARY IN COLOUR, TEXTURE, STRUCTURE,
AND PH
Soils are classified into 10
orders based largely on the
processes thought to form them
 Soils classified into various
categories using properties
such as:
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
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Color
Texture
Structure
pH
Near Nanaimo, the soils tend to be HumoFerric Podzols and Distric Brunisols
7-15
SOILS VARY IN COLOUR, TEXTURE, STRUCTURE, AND PH
(CONT’D)

Soil color = indicates its
composition and fertility
Black or dark brown =
rich in organic matter
 Pale gray or white =
indicates leaching

7-16
SOILS VARY IN COLOUR, TEXTURE, STRUCTURE, AND PH
(CONT’D)
• Soil texture = the size of particles
- Clay (smallest), silt, sand (largest)
• Loam = soil with an even mixture of the three
-
Influences how easy it is to cultivate and let air and
water travel through the soil
• Silty soils with medium-size pores, or loamy soils with
mixtures of pore sizes are best for plant growth and
crop agriculture
7-17
SOILS VARY IN COLOUR, TEXTURE, STRUCTURE, AND PH
(CONT’D)

Soil structure (“tilth”= a measure of soil’s
“clumpiness”
Large clumps can discourage plant roots
 Repeated tilling compacts soil
 Plowpan = a hard layer resulting from repeated plowing
that resists water infiltration and root penetration


Soil pH = influences a soil’s ability to support plant
growth

Soils that are too acidic or basic can kill plants
7-18
BIOGEOCHEMICAL CYCLING IN SOIL
7-19
SOIL IS AN IMPORTANT TERRESTRIAL RESERVOIR
FOR CARBON
Soil plays a crucial role in the global carbon cycle
 Soil represents the largest terrestrial reservoir for
carbon
 Main carbon fluxes in which soil is involved are driven
by photosynthesis and the production of organic matter,
followed by respiration and decay or organic matter
 Decay of soil organic matter produces soil gas that
contains carbon
 Carbon dioxide
 Methane

7-20
One source
I saw said
twice that
of
atmospheric
content
and three
times that
of vegetation! See
http://eusoi
ls.jrc.ec.eu
ropa.eu/pr
ojects/SO
CO/FactSh
eets/ENFa
ctSheet03.pdf
SOIL DEGRADATION: A GLOBAL CONCERN
7-22
SOIL DEGRADATION: A GLOBAL CONCERN
7-23
SOIL DEGRADATION:
A GLOBAL CONCERN
Soil degradation results
from deforestation,
agriculture and
overgrazing
 Over the past 50 years, soil
degradation has reduced
global grain production by
13%

7-24
REGIONAL DIFFERENCES AFFECT SOIL PRODUCTIVITY
Rainforests have high
primary productivity, but
the nutrients are in
plants, not the soil. If the
forests are removed, the
soils dry out and cannot
readily be regenerated.
 Swidden agriculture =
cultivation of a plot for a
few years and then
letting it regrow into
forest

• Temperate grasslands
have lower rainfall and
less nutrient leaching
7-25
EROSION CAN DEGRADE ECOSYSTEMS AND
AGRICULTURE
Deposition = the arrival of eroded material at its new
location
 Flowing water deposits sediment in river valleys and
deltas


Floodplains (e.g. Fraser Delta) are excellent for farming
Erosion occurs faster than new soil is formed
 Erosion increases through: overcultivating fields,
overgrazing rangelands, and clearing forested areas

7-26
SOIL ERODES BY SEVERAL MECHANISMS
Wind (aeolian) erosion
 Water erosion (splash, sheet, rill, gully)


Rill erosion moves the most topsoil, followed by sheet and
splash erosion
Gully erosion
7-27
SOIL EROSION IS WIDESPREAD
Humans are the primary cause of erosion
 19 billion hectares of croplands worldwide suffer from
erosion
 Kazakhstan lost tens of millions of hectares to wind
erosion
 Soil degradation over the next 40 years in Africa could
reduce crop yields by half
 The on-farm cost of agricultural land degradation in
Canada is $670 million per year

7-28
DESERTIFICATION REDUCES PRODUCTIVITY OF
ARID LANDS

Desertification
 A loss of more than 10%
productivity from erosion, soil
compaction, forest removal,
overgrazing, salinization,
climate change, depletion of
water sources
 A type of land degradation
 Affects 1/3 of the planet’s land
area
 Most prone areas are arid and
semiarid lands
 Climate change could result
in displacement of 50 million
people in 10 years
7-29
THE DUST BOWL WAS A MONUMENTAL EVENT IN
NORTH AMERICA (CONT’D)
Native prairie grasses originally held erosion-prone
soils in place
 1879-1929: Widespread cultivation of wheat, and
grazing of many thousands of cattle
 Great Depression brought a cycle of poverty and
overly intensive agricultural practices
 Dust storms (black blizzards) travelled up to 2000
km
 Lung irritation, dust pneumonia, grasshopper
infestations

7-30
THE DUST BOWL WAS A MONUMENTAL EVENT IN
NORTH AMERICA (CONT’D)
7-31
PROTECTING SOILS
7-32
EROSION-CONTROL PRACTICES PROTECT AND RESTORE
PLANT COVER
 Crop
rotation
 Contour farming
 Intercropping and
agroforestry
 Terracing
 Shelterbelts
 Reduced tillage
7-33
CROP ROTATION

Intercropping
Crop Rotation = alternating
• Intercropping = planting
the crops grown field from one
different types of crops in
season or year to the next
alternating bands or other
 Cover crops protect soil
spatially mixed arrangements
to increase ground cover
7-34
Contour Farming
• Contour Farming = plowing
furrows sideways across a
hillside, perpendicular to its
slope, to prevent rills and gullies
Terracing

Terracing = level platforms
are cut into steep hillsides,
forming a “staircase” to
contain water
7-35
SHELTERBELTS

Shelterbelts or Windbreaks =
rows of tall, perennial plants are
planted along the edges of fields
to slow the wind
 Alley cropping =
shelterbelts + intercropping
Reduced tillage
• Reduced Tillage = furrows
are cut in the soil, a seed is
dropped in and the furrow is
closed
7-36
IRRIGATION CAN CAUSE LONG-TERM SOIL
PROBLEMS
 Irrigation
= Artificially providing water to
support agriculture
 Waterlogging = over-irrigated soils which
suffocates roots
 Salinization = the buildup of salts in surface
soil layers
 Salinization inhibits production of 20% of
all irrigated cropland, costing more than
$11 billion/year
7-37
IRRIGATION CAN CAUSE LONG-TERM SOIL PROBLEMS
(CONT’D)

Remedies for correcting salinization once it has
occurred:
 Choose crops appropriate for the area
 Irrigate with low-salt water
 Irrigate efficiently
 Drip irrigation targets water directly to
plants
7-38
OTHER CHEMICALS ALSO CONTRIBUTE TO SOIL
CONTAMINATION
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
Fertilizer = substances that contain essential
nutrients but over-application can damage soils
Inorganic fertilizers = mined or synthetically
manufactured mineral supplements
Organic fertilizers = the remains or wastes of
organisms
 manure, crop residues, fresh vegetation
 Compost = produced when decomposers break
down organic matter
 Not perfect when it gets into the water system,
particularly manure
7-39
OTHER CHEMICALS ALSO CONTRIBUTE TO SOIL
CONTAMINATION (CONT’D)
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Nitrogen and phosphorous runoff from farms and
other sources can lead to algal blooms
Nitrates can leach through soil and contaminate
groundwater
Pesticides are another source of soil contamination
Industrial activity contaminates soil through
inappropriate disposal of wastes and improper
storage
7-40
GRAZING PRACTICES
CAN CONTRIBUTE TO SOIL
DEGRADATION
Overgrazing is largely
responsible for the
permanent drying out of
parts of the Mediterranean –
e.g. Greece and Syria
7-41
CONCLUSION
 The
preservation of arable soil is crucial for
the maintenance of global food security
 Programs in Canada and worldwide have
been successful in reducing topsoil erosion
 However, soil is still being degraded at a
rate that threatens the sustainability of the
resource
 The role of soil as a reservoir in
biogeochemical cycling is also of increasing
interest to scientists
7-42
QUESTION: REVIEW
Physical weathering is characterized by:
a)
b)
c)
d)
The chemical interaction of water with parent material
Organisms breaking down parent material
Wind or rain breaking down parent material
The dislodging or movement of soil by wind
7-43
QUESTION: REVIEW
Which horizon is the most valuable for agriculture?
a)
b)
c)
d)
A horizon
B horizon
C horizon
R horizon
7-44
QUESTION: REVIEW
Erosion increases through all of the following, except:
a)
b)
c)
d)
Excessive tilling
Overgrazing
Clearing forests
All of the above increase erosion
7-45
QUESTION: REVIEW
Which sustainable farming method involves planting rows of
trees along field edges to slow the wind?
a)
b)
c)
d)
Terracing
Crop rotation
Shelterbelts
Contour farming
7-46
QUESTION: WEIGHING THE ISSUES
Should developed nations fund reforestation projects in
developing nations to combat erosion and deforestation?
a)
b)
c)
d)
Absolutely, developing nations are facing a crisis
No, not with money, but developed nations could give advice
No, developed nations had to solve their problems, let the
others solve their own problems
I don’t care, it doesn’t really affect me
7-47
QUESTION: WEIGHING THE ISSUES
Should the Canadian government provide farmers with
financial incentives to use technologies such as no-till
farming and crop rotation?
a)
b)
c)
d)
Absolutely, farmers may be more likely to switch to these
techniques
Yes, but farmers must put any money received into the farm
No, it’s not the government’s job to interfere with farming
practices
I don’t care, it doesn’t really affect me
7-48