Understanding Our Environment

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12 Δεκ 2012 (πριν από 4 χρόνια και 6 μήνες)

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Saigo: Environmental Science 7
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Agriculture and Food

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Outline


Nutrition and Food Supplies


Soil


Structure


Erosion


Agricultural Resources


Water


Energy


Genetic Engineering


Sustainable Agriculture

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Subsistence agriculture

Commercial agriculture


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NUTRITION AND FOOD SUPPLIES


World food supplies have more than kept up
with human population growth over the past
two centuries.


1950
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2.5 billion people
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average daily
diet was less than 2,000 calories/person.


2001
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6.0 billion people
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world food supply
can provide more than 2,500
calories/person.

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Nutrition


The most common dietary problem in wealthy
countries is over
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nutrition.


In NA and Europe, average daily caloric
intake is 3,500 calories.


Sub
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Saharan Africa has not kept food
production up to pace of population growth.


Collapse of Soviet Union also led to significant
collapse in food production.


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Chronic Hunger and Food Security


About 1 in 5 people in the developing world
are considered chronically hungry.


200 million children

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Can lead to permanently stunted growth,
mental retardation, and other
developmental disorders.


Poverty

is the greatest threat to food
security (The ability to obtain sufficient
food on a daily basis).

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Chronic Hunger and Food Security

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Essential Nutrients


Malnourishment
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Nutritional imbalance
caused by a lack of specific dietary
components.


In poorer countries, people often cannot
afford to purchase an adequate variety of
foods, including meats and vegetables.



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Risk of Inadequate Nutrition

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Famines


Famines are characterized by large
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scale food
shortages, massive starvation, social
disruption, and economic chaos.


Mass migrations often occur because
productive capacity has been sacrificed.


Environmental conditions are immediate
trigger, but politics and economics are often
underlying problems.

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Arbitrary political boundaries block historic
access to refuge areas.

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Famines


Aid policies of rich countries often serve to
distribute surplus commodities and produce
feeling of generosity.


Food camps have serious drawbacks:

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Stress and crowding

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Lack of sanitation

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Close contact to epidemic diseases

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MAJOR FOOD SOURCES


Three crops deliver majority of world’s
nutrients:


Wheat, Rice and Corn


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Potatoes, barley, oats and rye are
staples in cool, moist climates.

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Cassava, sweet potatoes, and other
roots and tubers are staples in warm wet
climates.


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Meat and Milk


Meat and Milk distribution highly inequitable.


Core makes up 20% of world population,
but consumes 80% of meat and milk.



60% of production occurs in lesser
developed countries.


90% of grain grown in NA is used to feed
livestock.

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Meat


Every 16 kg of grain and soybeans fed to
beef cattle in feedlots produce about 1 kg of
edible beef.


If we ate the grain directly, we would obtain
21x more calories and 8x more protein
than we get from eating the beef.


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Seafood


Seafood is an important protein source.


Since 1989, 13/17 major fisheries have
declined or become commercially inviable.


Between 1970
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1990, number and average
vessel size of world fishing fleet doubled.


Now have twice the capacity needed to
extract total annual sustainable harvest.

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Catching $70 billion cost $124 billion.


1/4 animals considered by
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catch.

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SOIL: A RENEWABLE RESOURCE


Soil

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A complex mixture of weathered
minerals, partially decomposed organic
materials, and a host of living organisms.


At least 20,000 different soil types in the US.

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Vary due to influences of parent material,
time, topography, climate, and organisms.


Can be replenished and renewed.

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Ways we use and abuse soils


Approximately 11% of the earth’s land area
is currently in agricultural production.


Up to four times as much could potentially
be converted to agricultural use.

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Much of this additional land suffers from
constraints.

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Soil Degradation

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Land Resources


In developed countries, 95% of recent
agricultural growth has been from altered
agricultural practices (pesticides
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fertilizer).


Less land cultivated in NA now than 100
years ago.


Many developing countries are reaching limit
of lands that can be exploited for agriculture
without unacceptable social and
environmental costs.

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Land Degradation


Estimated nearly 3 million ha of cropland
ruined annually via erosion, 4 million ha
transformed into deserts, and 8 million ha
converted to non
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agricultural uses.


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Land Degradation


Definitions of degradation are based on both
biological productivity and expectations of
what land should be like.


Generally, land is considered degraded
when soil is impoverished or eroded, run
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off is contaminated, or biodiversity is
diminished.

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Water and wind are the driving forces for
vast majority of soil degradation.


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Land Degradation

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Erosion


Erosion is an important natural process,
resulting in redistribution of the products of
geologic weathering, and is part of both soil
formation and soil loss.


Worldwide, erosion reduces crop
production by equivalent of 1% of world
cropland per year.



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Mechanisms of Erosion


Rill Erosion

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Small rivulets of running water
gather together and cut small channels in the
soil.


Gully Erosion

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Rills enlarge to form bigger
channels too large to be removed by normal
tillage.


Streambank Erosion

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Washing away of soil
from established streambanks.

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Mechanisms of Erosion


Wind can equal or exceed water as an
erosive force, especially in a dry climate and
on flat land.


Intensive farming practices:

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Row crops leave soil exposed

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Weed free
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fields

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Removal of windbreaks

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No crop
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rotation or resting periods

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Continued monocultures

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CHEMICAL

INPUTS


Fertilizers


Pesticides




Fungicides


Herbicides

(weed killers)

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Fertilizer


Lack of nitrogen, potassium, and phosphorus
often limits plant growth.


Adding nutrients via fertilizer usually
stimulates growth and increases crop yields.

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1950
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90 Average of 20 to 91 kg/ha
fertilizer used.


Manure and nitrogen
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fixing bacteria are
alternative methods of replenishing soil
nutrients.

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Pesticide Problems


Non
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Target Species


Up to 90% of pesticides never reach
intended target.


Pesticide Resistance


Resistant members of a population survive
pesticide treatment and produce more
resistant offspring.

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Pest Resurgence

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Pesticide Resistance

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Environmental Persistence and Mobility


Many
persistent organic pollutants

were
banned globally in 2001.


Use was banned or restricted in
developing countries for years, but
between 1994 and 1996, the US shipped
more than 100,000 tons of DDT and POP’s
annually.

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Many returned to US in agricultural
products and migrating wildlife.

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DDT pesticide effect on birds;

U.S. recovery since ban

Still exported


to Periphery

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Human Health Problems


WHO estimates between 3.5 and 5.0 million
people suffer acute pesticide poisoning, and
20,000 die, each year.


At least two
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thirds resulting from
occupational hazards in developing
countries.


Long
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term health effects difficult to
conclusively document.

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PCB’s have been linked to learning
deficiencies in children.


Intake during mother’s pregnancy.

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Alternatives to Pesticide Use



Crop Rotation


Mechanical Cultivation


Flooding Fields


Habitat Diversification


Growing in Pest
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Free Zones


Adjusting Planting Times


Plant Mixed Polycultures

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ENERGY


Farming in industrialized countries is highly
energy
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intensive.


Between 1920
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1980, energy use rose
directly with mechanization of agriculture,
and indirectly with spraying of chemicals.


Altogether, US food system consumes
16% of total energy use.

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Most foods require more energy to
produce, process, and transport than we
yield from them.

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Energy

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NEW CROPS AND GENETIC ENGINEERING


Most of world food comes from 16 widely
grown crops.


At least 3,000 species of plants have been
used for food at some point in time.

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Many new or unconventional varieties
might be valuable food supplies.


Winged
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bean


Triscale

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Green Revolution


Most major improvements in farm production
have come from technological advances and
modification of a few well
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known species.


Corn yields jumped from 25 bushels per
acre to 130 per acre in last century.

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Most of gain accomplished through
conventional plant breeding.


Also seen rise of dwarf varieties.


Green Revolution

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Spread of new varieties
around the world.


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Green Revolution

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“Green Revolution”

benefits



Core exports high
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yield “miracle” seeds



Needed oil
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based fertilizers, pesticides



Asian rice crop up 66% in 1965
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85



Favored areas with good soil, weather

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“Green Revolution”

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“Green Revolution”

drawbacks



Favored farmers who could afford seeds,


inputs, machines, irrigation



Indebted farmers lost land, moved to cities



New “monocrops” lacked resistance to
disease/pests



Environmental contamination, erosion



Oriented to export “cash crops,” not domestic food

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Genetic Engineering


Genetically Modified Organisms (GMO’s)


Contain DNA possessing genes borrowed
from unrelated species.

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Can produce crops with pest
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resistance
and wider tolerance levels.

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Opponents fear traits could spread to
wild varieties, and increased expense
would largely hurt smaller farmers.


70% of all processed foods in NA contain
transgenic products.

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Genetic Engineering

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Genetic Engineering

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Biotechnology:

Using organisms to…


Make or modify products



Improve plants or animals



Develop new microorganisms



Crossing different species


Genetic engineering

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Genetically Modified Organisms (GMO)

Consumer concerns

began in Europe,

now in U.S. too

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Biotechnology

benefits in agriculture


Increase yields



Increase pest resistance



Grow crops in new areas

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Biotechnology

drawbacks in agriculture


High costs (available to few)



Monocrops have less tolerance to disease



Possible health effects, contamination of crops



Corporate patents on life forms



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Bovine Growth

Hormone (BGH)




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Starlink corn




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Monarch butterflies

and corn pollen




Possible

effects of

Bt
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modified

corn pollen

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Cloning




First calf cloned in

Wisconsin, 1997.


Many clones die

of complications.


Ethical and

economic conflicts

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SUSTAINABLE AGRICULTURE


Soil Conservation


Managing Topography

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Contour Plowing

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Plowing across slope
to slow flow of water.

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Strip Farming

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Planting different crops
in alternating strips along land contours.

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Terracing
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Shaping land to create level
shelves of earth to hold water and soil.

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Soil Conservation


Providing Ground Cover


Annual row crops cause highest rates of
erosion because they leave soil bare for
much of the year.

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Leave crop residue after harvest.

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Plant cover crops after harvest.

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Soil Conservation


Reduced Tillage


Minimum Till
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Chisel plow


Conserv
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Till
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Coulter (Disc)


No
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Till

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Drilling



Often farmers using conservation tillage must
depend relatively heavily on pesticides.


Traditional tillage helped control weeds
and pests.

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Summary


Nutrition and Food Supplies


Major Food Sources


Soil


Structure


Erosion


Agricultural Resources


Water


Energy


Genetic Engineering


Sustainable Agriculture

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