Transcript What is soil?

Chapter 7
Lecture
Outline
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Learning Outcomes
After studying this chapter, you should be able to answer the following
questions:
• How have global food production and population changed?
• How many people are chronically hungry, and why does
hunger persist in a world of surpluses?
• What are some health risks of undernourishment, poor diet,
and overeating?
• What are our primary food crops?
• Describe five components of soil.
• What was the green revolution?
• What are GMOs, and what traits are most commonly
introduced with GMOs?
• Describe some environmental costs of farming, and ways we
can minimize these costs.
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We can’t solve problems by using the same kind of
thinking we used when we created them.
–Albert Einstein
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7.1 Global Trends in Food
and Nutrition
• Food production has been transformed from
small-scale, diversified, family operations to
expansive farms of thousands of hectares,
growing one or two genetically modified
crops, with abundant inputs of fuel and
fertilizer, for a competitive global market.
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Hunger around the world
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Food security is unevenly distributed
• Four decades ago, hunger was one of the world’s
most prominent, persistent problems.
• In 1960, nearly 60 percent of people in
developing countries were chronically
undernourished, and the world’s population was
increasing by more than 2 percent every year.
• Today, some conditions have changed
dramatically; others have changed very little.
• The world’s population has risen from 3 billion to
over 6.5 billion, but food production has
increased even faster.
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Food security is unevenly distributed…
• Food security is the ability to obtain sufficient,
healthy food on a day-to-day basis, is a
combined problem of economic,
environmental, and social conditions.
• In wealthy countries such as the United States,
millions lack a sufficient, healthy diet.
• In the poorest countries, entire national
economies can suffer from a severe drought,
flood, or insect outbreak.
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Famines usually have political and
social roots
• Globally, widespread hunger arises when
political instability, war, and conflict displace
populations, removing villagers from their
farms or making farming too dangerous to
carry on.
• Famines are large-scale food shortages, with
widespread starvation, social disruption, and
economic chaos.
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7.2 Eating Right to Stay Healthy
• A good diet is essential to keep you healthy.
• You need the right nutrients, as well as
enough calories for a productive and
energetic lifestyle.
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A healthy diet includes the right
nutrients
• Malnourishment is a
general term for
nutritional imbalances
caused by a lack of
specific nutrients.
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The Harvard food pyramid
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Overeating is a growing world problem
• Increasing world food supplies and low prices cause
increasing overweight and obese populations.
• In the U.S., and increasingly in Europe, China, and
developing countries, highly processed foods rich in
sugars and fats have become a large part of our diet.
• Some 64 percent of adult Americans are overweight,
up from 40 percent only a decade ago. About one-third
of us are seriously overweight, or obese (generally
considered to mean more than 20 percent over the
ideal weight for a person’s height and sex.
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7.3 The Foods We Eat
• Of the thousands of
edible plants and
animals in the world,
only a few provide
almost all our food.
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A boom in meat production
brings costs and benefits
• Because of dramatic increases in corn and soy
production, meat consumption has grown in
both developed and developing countries.
• Meat is a concentrated, high-value source of
protein, iron, fats, and other nutrients that
give us the energy to lead productive lives.
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Meat is a good indicator of
wealth
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Confined animal feeding operation (CAFO)
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Seafood is both wild and farmed
• Overharvesting and habitat destruction
threaten most of the world’s wild fisheries.
• The problem is too many boats using efficient
but destructive technology to exploit a
dwindling resource base.
• Aquaculture is providing an increasing share
of the world’s seafood.
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Fish pins
• Net pens anchored in nearshore areas allow spread
of diseases, escape of exotic species, and release of
feces, uneaten food, antibiotics, and other
pollutants into surrounding ecosystems.
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Increased production comes
with increased risks
• There are many environmental worries about
this efficient production.
– Land conversion from pasture to soy and corn
fields raises the rate of soil erosion.
– Constant use of antibiotics raises the very real risk
of antibiotic-resistant diseases.
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7.4 Soil Is a Living Resource
• Soil is a marvelous substance, a living resource
of astonishing complexity and frailty.
• It is a complex mixture of:
– mineral grains weathered from rocks,
– partially decomposed organic molecules, and
– a host of living organisms.
• Soil can be considered a living ecosystem by
itself.
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What is soil?
Soil is a complex mixture of six components:
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sand and gravel-mineral particles from bedrock, either in place or
moved from elsewhere, as in wind-blown sand.
silts and clays -extremely small mineral particles; many clays are
sticky and hold water because of their flat surfaces and ionic
charges; others give red color to soil.
dead organic material-decaying plant matter stores nutrients and
gives soils a black or brown color.
soil fauna and flora -living organisms, including soil bacteria, worms,
fungi, roots of plants, and insects, recycle organic compounds and
nutrients.
water -moisture from rainfall or groundwater, essential for soil fauna
and plants.
air -tiny pockets of air help soil bacteria and other organisms survive.
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Soil Horizons
7.5 Ways We Use and Abuse Soil
• Agriculture both causes and suffers from
environmental degradation.
• The causes of this extreme degradation vary:
– In Ethiopia, it is water erosion.
– In Somalia, it is wind; and in Uzbekistan, salt and
toxic chemicals are responsible.
– In Sweden and Finland, fallout from the Chernobyl
nuclear reaction explosion has contaminated large
amounts of grazing land and farmland.
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Causes of Soil Erosion and Degradation
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Farming accelerates erosion
• Erosion is an important natural process,
resulting in the redistribution of the products
of geologic weathering, and it is part of both
soil formation and soil loss.
• Where erosion has worn down mountains and
spread soil over the plains or deposited rich
alluvial silt in river bottoms, we farm it.
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Wind and water move soil
• Sheet erosion: water flowing across a gently sloping,
bare field removing a thin, uniform layer of soil.
• Rill erosion: when little rivulets of running water
gather together and cut small channels in the soil.
• Gully erosion: if rills enlarge to form bigger channels
or ravines that are too large to be removed by
normal tillage operations.
• Desertification: conversion of productive land to
desert.
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Wind and water are the main agents that
move soil around.
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Wind can equal or exceed
water in erosive force
• In extreme conditions, windblown dunes
encroach on useful land and cover roads and
buildings.
• Over the past 30 years, China has lost 93,000
km2 (about the size of Indiana) to
desertification.
• Advancing dunes from the Gobi desert are
now only 160 km (100 mi) from Beijing.
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7.6 Other Agricultural Resources
• Irrigation is necessary for high yields
– Agriculture accounts for the largest single share of global
water use.
– Salinization: mineral salts accumulate in the soil due to
evaporating water from irrigation.
• Fertilizer boosts production
– Much of the doubling in worldwide crop production since
1950 has come from increased inorganic fertilizer use.
• Modern agriculture runs on oil
• Pest control saves crops
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7.7 How We Have Managed to
Feed Billions
• In the developed
countries, 95 percent of
agricultural growth in
the twentieth century
came from improved
crop varieties (the green
revolution) or increased
fertilization, irrigation,
and pesticide use,
rather than from
bringing new land into
production.
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The green revolution has increased yields
• Most of this gain was accomplished by use of
synthetic fertilizers along with conventional plant
breeding: geneticists laboriously hand-pollinating
plants and looking for desired characteristics in the
progeny.
• Starting about 50 years ago, agricultural research
stations began to breed tropical wheat and rice
varieties that would provide food for growing
populations in developing countries.
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Genetic engineering could
have benefits and costs
• Genetic engineering: splicing a gene from
one organism into the chromosome of
another.
• Genetically modified organisms (GMOs):
organisms with entirely new genes, and even
new organisms, often called “transgenic”
organisms.
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Is genetic engineering safe?
• The greatest danger is the ecological effects if these
organisms spread into the native populations.
• There are social and economic implications of GMOs.
Will they help feed the world, or will they lead to a
greater consolidation of corporate power and
economic disparity?
• Are GMO’s required if we hope to reduce
malnutrition and feed eight billion people in 50
years.
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7.8 Alternatives in Food
and Farming
• Soil conservation is essential
– With careful husbandry, soil is a renewable
resource that can be replenished and renewed
indefinitely.
– Water runoff can be reduced by grass strips in
waterways and by contour plowing, plowing
across the hill rather than up and down.
– Terracing is shaping the land to create level
shelves of earth to hold water and soil.
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Soil conservation is essential
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7.9 Consumer Choices
Can Reshape Farming
• You can be a locavore
– Locavore: a person who consumes locally produced food.
• You can eat low on the food chain
– Since there is less energy involved in producing food from
plants, you can reduce your impact by eating more grains,
vegetables, and dairy and a little less meat.
• You can eat organic, low-input foods
– If you buy organic food, you are supporting farmers who
use no pesticides or artificial fertilizers.
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Practice Quiz
1. What is Brazil’s Cerrado, and how is agriculture affecting it?
2. Explain how soybeans grown in Brazil are improving diets in
China.
3. What does it mean to be chronically undernourished? How
many people in the world currently suffer from this condition?
4. Why do nutritionists worry about food security? Who is most
likely to suffer from food insecurity?
5. Describe the conditions that constitute a famine. Why does
Amartya Sen say that famines are caused more by politics and
economics than by natural disasters?
6. Define malnutrition and obesity. How many Americans are
now considered obese?
7. What three crops provide most human caloric intake?
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