& ENV100Y5Y
Environment
Soils Agriculture
Reading: Chapter 7
2010 Pearson Education Inc.
PowerPoint presentation prepared by Barbara Murck
These lectures will help you understand:
The fundamentals of soil
science
The importance of soils to
agriculture
Major historical developments
in agriculture
Causes and consequences of
soil erosion and degradation
Principles of soil conservation
Central Case: Mer Bleue bog
A 35 km2 protected wetland
Peat soils formed over 8000 years; up to 6m thick
Carbon balance in peat:
- Primary production stores carbon
- Decomposition releases carbon
Interdisciplinary research project studying the
influence of climate on carbon balance (and vice
versa)
Soil is a complex material
Soil consists of mineral
matter, organic matter,
water, air, and other gases
- Dead and living
microorganisms and decaying
material
- Bacteria, algae, earthworms,
insects, mammals,
amphibians, reptiles
Can support plant growth
FIGURE 7.1
Soil formation starts with bedrock
Parent material = base geologic material of soil
- Bedrock = the continuous mass of solid rock
comprising the Earths crust
- Regolith (sediment) = broken-up rock
Weathering = processes that break down rocks
- Physical (mechanical) = no chemical changes
in the parent material
- Chemical = substances chemically interact
with parent material
- Biological = organisms break down parent
material
Weathering breaks down rock
FIGURE 7.2
Soil formation is very slow
Factors that affect soil formation:
- Parent material composition (mineral content)
- Climate (temperature, precipitation)
- Topography (steepness of slope)
- Vegetation (root activity; protective cover)
- Biological activity (soil microbes and fauna;
decomposition and accumulation of organic
matter)
It can take 10,000 years or more to form a welldeveloped soil profile.
A soil profile consists of horizons
Soil profile = the cross-section of soil
as a whole
Horizon = each layer of soil
Leaching = dissolved particles move
down through horizons
Topsoil = inorganic and organic
material most nutritive for plants
Humus = dark, spongy, crumbly
organic material formed by partial
decomposition
FIGURE 7.3
Soils are characterized in many ways
Soils are classified into 10 orders based on their
composition, the processes that form them, and
their properties
Properties of soil:
- Colour
- Texture
- Structure
- pH
Soil colour
The colour of a soil is
indicative of its
composition
- Black or dark
brown indicates
organic matter
- Pale gray or white
indicates leaching
FIGURE 7.4
Soil texture
Clay (smallest), silt, sand, gravel (largest)
- Distribution of particle sizes influences how easy it is to
cultivate and let air and water pass through the soil
- Loam = soil with an even mixture of sand-silt-clay
- Silty soils with medium-size pores, or loamy soils with
mixtures of pore sizes are best for plant growth
Soil structure and pH
Structure is a measure of soils clumpiness
- Large clumps can discourage plant roots
- Repeated tilling compacts soil
- Ploughpan = a hard layer resulting from
repeated ploughing; resists water infiltration
and root penetration
Soil pH or acidity influences the soils ability to
support plant growth
- Soils that are too acidic or basic can kill plants
Cation exchange is vital for plant
growth
Cation exchange = process that allows plants to
gain nutrients
- Negatively-charged humus and clay particles
in soil hold positively-charged cations of
calcium, magnesium, and potassium
- Cation exchange capacity is the soils ability to
hold cations, preventing them from leaching,
thereby increasing their availability to plants
- A useful measure of soil fertility
- Greatest in fine soils
Soils support plant growth by
Providing a medium for plant roots
Providing nutrients through cation exchange
Soil is the foundation for feeding a
growing population
Agriculture = production of food (for people),
feed (for animals), fibre (for materials), and fuel
(e.g., corn for ethanol)
- Ager field and cultura to cultivate
- Land devoted to agriculture covers 38%
of Earths land surface
- Cropland = land used to grow plants
- Rangeland = land used for grazing livestock
Canada is an agricultural nation
UN FAO statistics:
- Canada produces 2.5% of the worlds grains
- Canada produces1.7% of the worlds meat
- Canada has 0.5% of the global population
Agriculture and Agri-Foods Canada statistics:
- 7% of Canadas land is arable
- Prairies = 83% of agricultural land
- 8.5% of Canadas GDP
- 3rd largest employer
- # of farms declining, farm size increasing
The prairies are Canadas breadbasket
60% of Canadas cropland
and 80% of rangeland are
in the Prairies
Chernozem soils
The most human-altered ecoregion in Canada.
Farms are managed ecosystems
Agricultural or farming systems:
- Agro-ecosystem
- Domesticated or managed ecosystem
- Other managed ecosystems:
- Aquaculture ponds
- Forest plantation
- Gardens
- Zoos
An agricultural system
MANAGEMENT SYSTEM
HARVEST
PHYSICAL SYSTEM
CROP
LIVESTOCK
EXTERNAL
SYSTEMS
Cities
Streams
Vegetation
Water
P
N
I
T
U
S
Fauna
SOIL
Soils
etc.
Some questions we can ask about
agricultural systems
What are the biotic and abiotic components?
What are the inputs?
How is productivity supported?
What are the outputs?
What are the impacts on external systems?
Before agriculture, people hunted and
gathered their food
Before 10,000 ya
Hunter-gatherers
- Resource extraction
- Nomadic; followed wild herds
- Few or no villages
Agriculture arose 10,000 years ago
FIGURE 7.8
Invented independently by different cultures
Cornerstone human of history and progress, with a legacy of
environmental damage
- The dominant influence on the global landscape outside the
urban centres. UN Food and Agriculture Organization
Agriculture arose 10,000 years ago
Resource production intensification
Emerging technologies:
- Hand-planting, stick for ploughing
- Flint sickle for harvesting
- Stone for grinding
Sedentary lifestyle became possible
- Early major civilizations, e.g., Fertile Crescent
Both plants and animals became
domesticated
Accidental plant hybridization
- Wild wheat + goat grass = emmer
- Emmer + goat grass = bread wheat
- Unable to spread by itself
- Wheat needed humans
- Humans needed wheat
Plant & animal domestication
Reliable food sources increase in carrying
capacity increase in population
New agricultural technologies have
been developed over time
Livestock:
- Selecting/breeding for desired traits
Crops:
- Wooden plough
- Controlled seed dispersal
- Metal tools
- Fertilization
- Irrigation
- Crop rotation
- Mechanization
Many farmers still use traditional agricultural
methods
Traditional agriculture =
biologically-powered,
human and animal muscle
power
- Subsistence agriculture =
families produce only
enough food for
themselves
Industrial agriculture =
large-scale mechanization,
fossil fuels, irrigation, and
fertilizers to boost yields
Traditional vs. industrial agriculture
FIGURE 7.9
The Green Revolution is the hallmark
of modern agriculture
Increase crop yields through:
- New crop species developed by biotechnology
- New and increased amounts of fertilizers
- Improved and expanded irrigation
- New and increased use of pesticides
- Mechanization
What have been the results of the
Green Revolution?
Some questions we will ask (Chapter 8):
- Are the huge increases in yield sustainable in
the long term?
- What are some of the environmental impacts?
- Has the Green Revolution solved the problem
of hunger?
Erosion can degrade ecosystems and
agriculture
Erosion = transport and deposition (someplace
else) of sediment
- occurring faster than new soil is being formed
Wind (aeolian) erosion
Water erosion
FIGURE 7.11
Soil erosion is a global problem
Humans are the primary cause of erosion
19 billion hectares of croplands worldwide suffer
from 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
FIGURE 7.6
Soil degradation has many causes
The nation that destroys its soil destroys itself.
Franklin D. Roosevelt, Former U.S. President
Soil degradation results
from deforestation,
agriculture and
overgrazing
Over the past 50 years,
soil degradation has
reduced global grain
production by 13%
FIGURE 7.7
Desertification reduces productivity of
formerly arable lands
Desertification = loss of more than 10%
productivity of arable land
- Can be natural or anthropogenic (accelerated
desertification)
- A type of land degradation
- From erosion, soil compaction, forest removal,
overgrazing, salinization, climate change,
depletion of water sources
- Most susceptible are arid and semiarid lands
The Dust Bowl
Native prairie grasses originally held erosionprone 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 travelled up to 2000 km
Lung irritation, dust pneumonia, grasshopper
infestations
Soil Conservation Council emerged
from the experience of drought
Prairie Farm Rehabilitation Administration
(PFRA) 1935
Soil Conservation Council of Canada
- National plan
- Better public awareness
- Better communication among stakeholders
- Develop policies and production methods
Soil degradation is a global problem
but there are achievable solutions
Problems
Solutions
- Erosion
- Soil conservation
- Loss of arable soil
- Restoring plant cover
- Desertification
- Better irrigation
practices
- Salinization
- Better fertilization
practices
- Better grazing
practices
Crop rotation
Contour farming
FIGURE 7.14
Crop Rotation = alternating
Contour Farming = plowing
the crops grown field from one
furrows sideways across a
season or year to the next
hillside, perpendicular to its
slope, to prevent rills and gullies
- Cover crops protect soil
Terracing
Intercropping
FIGURE 7.14
Terracing = level
Intercropping = planting
platforms are cut into steep
different types of crops in
hillsides, forming a
alternating bands or other
staircase to contain
mixed arrangements to
water
increase ground cover
Shelterbelts
Reduced tillage
FIGURE 7.14
Shelterbelts and windbreaks = Reduced Tillage = furrows
rows of tall, perennial plants are
are cut in the soil, a seed is
planted along the edges of fields
dropped in and the furrow is
to slow the wind
closed; shallow plough
- Alley cropping = shelterbelts
+ intercropping
Plant cover reduces erosion
Eroding land stabilized
by plants that anchor soil
FIGURE 7.15
China worlds largest
tree-planting program
- Slows erosion
- Agroforestry (mix
crops + trees)
- Plantation forests are
not ecologically
functional
Conclusions
Soil is a complex material with both organic and
inorganic components
Soil is fundamentally important for plant growth
and for agriculture
Farms are domesticated ecosystems
Agriculture is a cornerstone of human civilization
but it has negative environmental impacts
Soil loss and degradation are global problems
Programs in Canada and worldwide have been
successful in reducing topsoil erosion