 Farm subsidies in many countries are protected by
powerful political and economic interests.
 Agricultural subsidies encourage surpluses and
allow American farmers to sell products overseas
at prices below production costs.
 Most aid goes to just a few crops such as corn,
wheat, soybeans, rice and cotton.
 Aid encourages intensive farming of land which
encourages erosion.
 Arable Land – Land that is fertile and can be used to grow
crops.
 Soil - A complex mixture of minerals, decomposing organic
materials, and living organisms. A renewable resource.
 Soil is generated from rock by two processes:
 Physical weathering – Rock is broken down by wind and
water
 Chemical weathering – Rock reacts with substances such as
acid or water.
 15,000 different types in the US alone.
 The best soils for farming have deep topsoil layers.
 Grasslands, deciduous forests.
2
 Particle size affects soil characteristics.
 Spaces between sand particles give sandy soil good
drainage and allow aeration.
 Can easily dry out
 Tight packing of small particles in clay soils makes
them less permeable to air and water.
 Sandy loam is best for farming.
 Humus - residue of decomposed plant and animal
material. Gives soil the spongy texture that holds
water and nutrients.
 Activity of organisms living in soil helps create
structure, fertility, and cultivation suitability (tilth).
 Micorrhizal symbiosis - an association between roots
of plants and certain fungi. Plant feeds the fungus
and the fungus provides water and inorganic
nutrients to the plant to enable it to grow better.
5
 Soils are stratified into horizontal layers called soil
horizons.
 Horizons taken together make up soil profile.
 O Horizon (Organic layer)
 Leaf litter, partially decomposed organisms
 A Horizon (Topsoil)
 Mineral particles mixed with organic material
 E Horizon (Leached)
 Depleted of soluble nutrients
 B Horizon (Subsoil)
 Often dense texture from accumulating
nutrients
 C Horizon or regolith (Parent Material)
 Weathered rock fragments with little organic
material
 North America and Europe are particularly well
suited to growing while some other parts of the
world lack suitable soil, topography and water.
 Available cropland is shrinking.
 Exceptions are South America and Oceania, where
forests are being converted to farms
 Gains in agricultural production have come from
increased fertilization, pesticides and irrigation
rather than more land.
 Much of the arable land on Earth has been lost.
 Estimates:
 3 million hectares of cropland ruined annually via erosion,
 4 million transformed into deserts
 8 million paved or built upon.
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 Desertification – Dry areas become more desert-like due
to human activities.
 Overgrazing
 Global climate change
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 Erosion is any natural process that redistributes soil and
minerals across the earth.
 Erosion becomes a problem when it occurs too quickly.
 Two biggest causes of erosion:
 Wind
 Water
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 Sheet Erosion - Thin, uniform layer of soil removed by
high winds.
 Rill Erosion - Small rivulets of running water gather and
cut small channels in the soil.
 Gully Erosion - Rills enlarge to form channels too large to
be removed by normal tillage.
 Streambank Erosion - Washing away of soil from
established streambanks.
13
14
15
 Wind can be a strong force of erosion, especially in a dry
climate and on flat land.
 Wind erosion is worsened by intensive farming practices:
 Planting crops in rows, leaving the soil in between exposed.
 Having fields completely free of weeds
 Removal of windbreaks such as trees
 No crop-rotation or resting periods
 Continued monocultures
 Growing the same crop every year
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 Agriculture accounts for largest single share of global
water use.
 Most irrigation systems are inefficient.
 Only about 20% of water withdrawn for irrigation reaches
the plant roots.
 Where does the rest go?
 Two main types of irrigation systems:
 Overhead sprinkler systems
 Underground drip systems
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20
21
 Lack of three nutrients can slow plant growth: nitrogen,
phosphorous, and potassium.
 Adding these nutrients via fertilizer usually stimulates growth
and increases crop yields.
 1950 - Average of 7kg/acre used
 2000 - Average of 25kg/acre used
 Adding fertilizer and manure is replenishes soil nutrients
depleted from previous years.
 Problems with fertilizer?
 Can runoff into water sources and cause aquatic plants
(algae) populations to expand rapidly
 Manure can cause bacterial contamination
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 Industrialized farming is energy-intensive.
 Energy use in agriculture has risen for two reasons:
 Increase in use of machines
 Spraying of chemical pesticide and fertilizers
 In the U.S., the food system consumes 16% of total energy
use.
 Most foods require more energy to produce, process, and
transport than we yield from them.
23
 Total food production has increased steadily in the last
50 years, in spite of a decrease in the actual number of
farms.
24
 The green revolution marked three major changes in farming
and food production:
1. Usage of monocultures of highly-bred or genetically
modified species.
2. Increased input of irrigation, fertilizer, herbicides, and
pesticides.
3. Produce more than one type of crop each year on a plot of
land.
 The net effect of the Green revolution and the industrial food
system has been to keep food prices artificially low.
 Americans only spend 10% of their household income on food.
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 Genetically Modified Organisms (GMO’s)
 Contain DNA possessing genes borrowed from unrelated
species.
 Can produce crops with new traits only found in other species.
 Can produce crops with pest-resistance and wider
tolerance levels to frost, drought, low nutrient soils,
salty soils, etc.
 Can improve protein or vitamin content of crop
 Can incorporate oral vaccines into foods such as
bananas for use in developing nations
 Animals can be modified to grow faster or produce
pharmaceuticals in their milk.
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Opponents fear GMOs are untested and may cause health
effects when eaten, such as allergies
 60% of all processed foods in North America contain
transgenic products.
 Most common in corn and soy. Examples:
 A gene from the bacterium Bacillus thuringiensis (Bt)
makes toxins that are lethal to butterflies and beetles.
These genes have been transferred into corn, potatoes
and cotton. Reduces pesticide use and increases yield.
 Roundup Ready and Liberty Link are two most popular.
Crops can grow in the presence of the pesticides (called
Roundup and Liberty) while weeds within the field are
killed.
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Food
Properties
Percent Modified in US
Soybeans
Resistant to certain
herbicides
89%
Corn
Cotton (cottonseed oil)
Hawaiian papaya
Resistant to certain
herbicides
Insect resistance - using Bt
proteins from a bacterium
Vitamin-enriched corn,
with 169x increase in
Vitamin A,
6x the vitamin C and 2x
folate.
Pest-resistant cotton
Variety is resistant to the
papaya ringspot virus.
60%
83%
50%
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Food
Tomatoes
Potatoes
Canola
Sugar cane
Sugar beet
Sweet corn
Rice
Properties
Percent Modified in US
Ripening enzyme is
Taken off the market due to
suppressed, lengthening shelfcommercial failure.
life.
Industrial production
Produces amylopectin instead of amylopectin for glossy
of starch.
paper coatings and
adhesive cement.
Resistance to herbicides,
Resistance to certain
pesticides, high sucrose
content.
Resistance to herbicides
Produces its own bioinsecticide
(Bt toxin)
Genetically modified to contain
high amounts of Vitamin A
75%
?
?
?
?
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 Sustainable agriculture attempts to produce food and fiber on
a sustainable basis and repair the damage caused by
destructive practices.
 Managing Topography
 Contour Plowing - Plowing across slope to slow flow of water.
 Strip Farming - Planting different crops in alternating strips
along land contours.
 Terracing - Shaping land to create level shelves of earth to hold
water and soil.
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Fig. 10-19, p. 229
32
Fig. 10-19, p. 229
Fig. 10-19, p. 229
Fig. 10-19, p. 229
 Providing Ground Cover
 The most erosion occurs in fields that are bare – do not
have any cover.
 Ways to avoid bare ground:
 Leave crop residue after harvest.
 Plant different crops each season.
 Lay down mulch.
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