Let’s dish some dirt!
 Please
get out
paper for notes.
 Please read the
board.
Dishing the dirt!
Soil Resources
complex mixture of inorganic minerals
(clay, silt, sand), decaying matter, & living
organisms.
• potentially renewable resource;
• typically 200–1000 years to form 2.5
centimeters (1 inch) of topsoil.
© Brooks/Cole Publishing Company / ITP
Soil formation
Physical


Freeze/thaw cycle
Weathering/erosion
Biological


Lichen action
Decomposition
The granite rock cracks and breaks off as it is
heated and cooled each day and season. This
is the first step in the formation of soil.
Physical: Freeze/thaw cycle
Decomposition: adding carbon, N,P,K
during soil formation
Soil Food Webs are complex!
• soil food webs complex;
• figure shows simplified soil food web.
Fig. 13–15
© Brooks/Cole Publishing Company / ITP
Soil Nutrient Cycling
pathways of
nutrients in
soils
Fig. 5–15
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Generalized Soil Profile
• O horizon: leaf litter
• A horizon: topsoil
• B horizon: subsoil
• C horizon: parent material
bedrock
© Brooks/Cole Publishing Company / ITP
Examples of Soil Profiles
Fig. 13–17 a & b
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More Examples of Soil Profiles
Fig. 13–17 c & d
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Ecosystem comparison!
– rich soil (deep, lots of humus,
nutrients)
 Tropical Rainforests – poor soils! Rapid
decomposition increases rate of nutrient
uptake!
 Prairies
Soil types determined by
 Particle
size
 Chemical composition (bedrock material)
 Color
 pH
Soil texture
 Sand
 Silt
 Clay
 Landfills?
 Wetlands?
Soil Texture
determined by particular mix of
clay, silt, & sand
Fig. 13–18
© Brooks/Cole Publishing Company / ITP
Erosion
movement of soil, especially litter & topsoil,
from one place to another
• makes soil less fertile & less able to hold
water;
• topsoil eroding faster than it forms in
about one–third of the world's cropland.
© Brooks/Cole Publishing Company / ITP
Soil Erosion
Fig.13–20
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1930s Dust Bowl
Fig.13–21
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Desertification
causes:
• overgrazing;
• deforestation &
devegetation;
• surface mining;
• poor irrigation;
• salt buildup;
• farming
unsuitable
terrain;
Fig.13–22
• soil
compaction.
© Brooks/Cole Publishing Company / ITP
Problems of Irrigation
• Salinization: salts
build up to levels
that decrease
yields or prevent
cultivation
• Waterlogging
excess irrigation
water raises water
table & lowers crop
productivity
Fig.13–23
© Brooks/Cole Publishing Company / ITP
Soil Conservation
reduces soil erosion & restores fertility
some methods:
• conservation–tillage
• terracing, contour farming, strip cropping,
alley cropping
• organic fertilizers
• crop rotation
© Brooks/Cole Publishing Company / ITP
Conservation-Tillage Farming
• minimizes soil disturbance
• uses special tillers or no–till methods that
inject seeds, fertilizers, & herbicides in
unplowed soil
• poses new problems of heavy herbicide
use
© Brooks/Cole Publishing Company / ITP
Some Means to Prevent Erosion
• terracing protects steep slopes
• contour farming follows natural land
contours
• strip cropping maintains strips of
different vegetation between crops
• alley cropping grows crops between
rows of trees
© Brooks/Cole Publishing Company / ITP
Some Means to Prevent Soil Degradation
• organic fertilizers: manure, "green
manure" = plant matter, & compost
• decreased use of inorganic fertilizers
• crop rotation: alternating between
different crops & fallow times; planting
crops that restore nutrients
© Brooks/Cole Publishing Company / ITP
Pesticides –
“To use or not to use?”
What you already know about
pesticides . . . .

The case FOR
pesticides

The case AGAINST
pesticides
A spectrum of choices
Conventional
Agriculture
Least sustainable
Integrated Pest
management
Organic
farming
Biodynamic
agriculture
most sustainable
Integrated pest management
 Overarching


philosophy:
Eradication of pests is not possible, so the
goal must be pest suppression.
General practice: Monitor pest populations.
When damage of crops will cost more than
the cost of action, IPM managers take steps
to control pests. Pesticides will be used only
as a last resort.
Cultivation/physical
approaches


Crop rotation –
non-legume, legume, fallow field/cover crop
Cultivation/physical approaches
Hedge rows
provide shelter for
beneficial insects, birds
and other pest
predators
Cultivation Approaches

Delayed planting
If the pest can’t find the
crop at the right part
of it’s life cycle, the
pest can’t use the
crop.
Cultivation Approaches

Polyculture,
intercropping
and
agroforestry –
increasing
diversity of
crops!
Biological pest control
Release beneficial
insects (pest
predators),
encourage
insectivorous
birds
Other predators
Biological Pest control

Release of sterile
males: mate with
females, no offspring
produced.
Chemical Pest control

Pheromones: used in
bait traps to lure
insects away from
crops
Chemical control
 Hormone
disruptors prevent molting or
development to next stage.
Chemical control
 As
a last resort, IPM farmers will use
pesticides (herbicides, insecticides,
rodenticides, fungicides)
IPM approaches

Advantages

Disadvantages