Transcript Document

Chapter 14:
Food & Soil Resources
The three systems humans depend on
for their food supply
• Croplands (77%) – land used for planting crops;
vegetables, fruits, and grains
• Rangelands (16%)- Land used for grazing
livestock; meat products
• Ocean fisheries (7%) - shellfish/fish (6% of
protein in human diet)
Human
Food Supply
Croplands
Rangelands
Fisheries
Major increase in food production post-1950
Tractors
Farm Equip.
Irrigation
Fertilizers
Pesticides
i
n
p
u
t
Feedlots
Feed Pens
Growth
Hormones
Careful
Breeding
High-Tech
Gear &
Electronics
Aquaculture
Human Population Growth and Food
Production
• 9 billion humans by 2054
– More food than has been produced in last 10k
yrs
• Is current technology capable?
• Environmental degradation?
– Pollution
– Water supply (irrigation)
– Overgrazing
– Overfishing
– Ecological services (matter; energy)
Lack of Diversity in Food
3 grain crops that
provide “more
than ½ of the
calories people
consume”.
30,000 edible
plant species
But 90% of all food only comes from
15 plants [esp. wheat, rice, corn] and
8 animals- [esp. beef, pork, chicken]
Fish1% energy
6 % protein
Major Types of Agriculture
• Traditional subsistence (20%, 44% pop.)
– Low-input, human labor, "just enough"
– Shifting cultivation; nomadic livestock
• Traditional intensive
– Higher input, "more than enough"
• Plantation
– Monoculture cash crops (bananas, coffee,
sugarcane, etc)
• Industrialized (high-input)
– 25% of all cropland, developed nations
Plantation agriculture
Industrialized agriculture
Nomadic herding
Shifting cultivation
Intensive traditional agriculture
Fig. 12.2, p. 263
No agriculture
The Green Revolution
increased production of food per unit of area of cropland;
planting monocultures, increase use of pesticides, water,
fertilizers, etc.
Since 1950
•
Develop & plant monocultures (ie. corn)
•
Input fertilizer, pesticides, water
•
Multiple cropping on plot of land
Since 1967
•
Fast growing dwarf varieties of rice and wheat
•
More food on less land
•
Increase use of fossil fuels, fertilizers, pesticides, irrigation
Age of Genetic Engineering
•
>2/3 of products on U.S. grocery store shelves contain ingredients from
GE crops!
Green-Revolution- increasing global
food production…
Farm more land =
Increase crop yield / land area
High-yield
monocultures
High Input
High intensity
frequency of
cropping
=
selective breeding
genetic engineering (GMO’s)
=
high energy input (8% world oil)
fertilizers, pesticides, water
=
dwarf varieties- 3-5x yield
multicropping (2-3/year)
Monocultures
• Intensified agriculture meant monocultures, vast
spreads of a single crop.
• This is economically efficient, but increases risk
of catastrophic failure (“all eggs in one basket”).
Wheat monoculture in Washington
Figure 9.4a
Green revolution: Environmental impacts
• Intensification of agriculture causes environmental
harm:
• Pollution from synthetic fertilizers
• Pollution from synthetic pesticides
• Water depleted for irrigation
• Fossil fuels used for heavy equipment
• However, without the green revolution, much more land
would have been converted for agriculture, destroying
forests, wetlands, and other ecosystems.
First green revolution
(developed countries)
Major International agricultural
research centers and seed banks
Second green revolution
(developing countries)
Energy Use in Food Production:
Industrial Agriculture
(United States)
Since1940’s: 2x production on the same amount of land
Agribusiness- big companies and large family farms own 75% of US
food production
- 2% pop.= farmers; 9% pop.= involve in production
- Agriculture provides18% US GNP; 19% jobs (private sect); 0.3% world's
labor
- 17% of world’s grain is produced in the US; ½ the world’s corn & soybean
exports
• Putting food on the table utilizes 17% of US commercial energy,
mostly from oil
• Food production uses 3 units of fossil fuel energy for 1 unit of food
energy obtained. Units of energy take in to account the energy
used to grow, store, process, pack, process, refrigerate, and cook
 Plants involve > energy out than in; Livestock involve > energy in,
than out.
Energy Use in Food Production:
Traditional and Traditional Intensive
• 20% of world food on 75% cultivated land
• Most traditional farmers use INTERPLANTING - growing
several crops on a single plot of land.
Types of interplanting1. Polyvarietals - varieties of 1 crop
2. Intercropping - 2+ different on same plot (legumes/grain)
3. Agroforestry/alley cropping - crops/trees together
4. Polyculture - many plants maturing at different times on same
plot
Advantages include: < energy input, erosion/weather protection,
pest/herbicides not needed
Intercropping
Polyculture
Polyvarietals
Agroforestry
Soil Erosion and Degradation
Causes: water, wind, and people
• Land degradation- when natural or human
induced processes reduce the future ability of
land to support crops, livestock or wild species.
(i.e. soil erosion due to flowing water or wind)
• Erosion of topsoil leads to loss of soil fertility and
increase sediment in nearby surface waters which can
block sunlight, kill fish, and clog irrigation ditches,
channels, etc.
Causes of soil degradation
Most soil degradation
is caused by:
• livestock
overgrazing
• deforestation
• cropland agriculture
Figure 8.2
Types of soil erosion
Splash
erosion
Rill erosion
Gully
erosion
Sheet erosion
Figure 8.11
Desertification
A loss of more than 10% productivity due to:
•
•
•
•
•
•
•
•
Erosion
Soil compaction
Forest removal
Overgrazing
Drought
Salinization
Climate change
Depletion of water resources
When severe,
there is
expansion of
desert areas, or
creation of new
ones, e.g., the
Middle East,
formerly, “Fertile
Crescent”.
The Dust Bowl
• Drought and degraded farmland produced
the 1930s Dust Bowl.
• Storms brought dust from the U.S. Great
Plains all the way to New York and
Washington, and wrecked many lives.
Figure 8.14
Desertification
Causes
Consequences
Overgrazing
Worsening drought
Deforestation
Famine
Erosion
Economic losses
Salinization
Lower living
standards
Soil compaction
Natural climate
change
Environmental
refugees
Preventing soil degradation
Several farming strategies to prevent soil
degradation:
•
•
•
•
•
•
Crop rotation
Contour farming
Intercropping
Terracing
Shelterbelts
Conservation tillage
Soil conservation
As a result of the Dust Bowl, the U.S. Soil
Conservation Act of 1935 and the Soil
Conservation Service (SCS) were created.
• SCS: Local agents in conservation districts
worked with farmers to disseminate scientific
knowledge and help them conserve their soil.
Crop rotation
• Alternating the crop planted (e.g., between
corn and soybeans) can restore nutrients to soil
and fight pests and disease.
Figure 8.16a
Contour farming
• Planting along contour lines of slopes helps
reduce erosion on hillsides.
Figure 8.16b
Intercropping
• Mixing crops such as in strip cropping can provide
nutrients and reduce erosion.
Figure 8.16c
(c) Alley cropping
Terracing
• Cutting stairsteps or terraces is the only way to
farm extremely steep hillsides without causing
massive erosion. It is labor-intensive to create, but
has been a mainstay for centuries in the
Himalayas and the Andes.
Shelterbelts
• Rows of fast-growing trees around crop plantings
provide windbreaks, reducing erosion by wind.
Figure 8.16e
Conservation
tillage
No-till and reduced-tillage
farming leaves old crop residue
on the ground instead of
plowing it into soil. This covers
the soil, keeping it in place.
Conservation tillage is not a solution
for all crops everywhere.
• It often requires more chemical
herbicides (because weeds are not
plowed under).
• It often requires more fertilizer
(because other plants compete
with crops for nutrients).
Here, corn grows up out of a
“cover crop.”
But legume cover crops can keep
weeds at bay while nourishing
soil, and green manures can be
used as organic fertilizers.
Figure 8.16f
Trade-Offs
Conservation Tillage
Advantages
Reduces erosion
Saves fuel
Disadvantages
Can increase
herbicide use for
some crops
Cuts costs
Holds more soil
water
Reduces soil
compaction
Allows several crops
per season
Does not reduce
crop yields
Reduces CO2
release from soil
Leaves stalks that
can harbor crop
pests and fungal
diseases and
increase pesticide
use
Requires
investment
in expensive
equipment
Central Case: No-Till Agriculture in
Brazil
• Southern Brazil’s farmers were suffering falling yields,
erosion, and pollution from agrichemicals.
• They turned to no-till farming, which bypasses plowing.
• Erosion was reduced, soils were enhanced, and yields rose
greatly. No-till methods are spreading worldwide.
Irrigation
• The artificial provision of water to support
agriculture
• 70% of all freshwater used by humans is used for
irrigation.
• Irrigated land globally covers more area than all of
Mexico and Central America combined.
• Irrigation has boosted productivity in many places
… but too much can cause problems.
Waterlogging and salinization
• Overirrigation can raise the water table high enough to
suffocate plant roots with waterlogging.
• Salinization (buildup of salts in surface soil layers) is a more
widespread problem. Salt in soils decreases the osmotic
potential of the soil so that plants can't take up water from it.
The salts can also be directly toxic, but plant troubles usually
result primarily from inability to take up water from salty soils
• Evaporation in arid areas draws water up through the soil,
bringing salts with it. Irrigation causes repeated evaporation,
bringing more salts up.
Solutions
Soil Salinization
Prevention
Reduce irrigation
Cleanup
Flushing soil
(expensive and
wastes water)
Not growing crops
for 2-5 years
Switch to salttolerant crops
(such as barley,
cotton, sugar beet)
Installing underground drainage
systems (expensive)
Global fertilizer usages
• Fertilizer use has risen dramatically in the past
50 years.
Figure 8.19b
Trade-Offs
Inorganic Commercial Fertilizers
Advantages
Disadvantages
Easy to transport
Do not add humus to soil
Easy to store
Reduce organic matter
in soil
Easy to apply
Reduce ability of soil to
hold water
Inexpensive to produce
Lower oxygen content of
soil
Help feed one of every
three people in the
world
Require large amounts of
energy to produce,
transport, and apply
Release the greenhouse
gas nitrous oxide (N2O)
Without commercial
inorganic fertilizers,
world food output could
drop by 40%
Runoff can overfertilize
nearby lakes and kill fish
Overgrazing
• When livestock eat too much plant cover on
rangelands, impeding plant regrowth.
• The contrast between ungrazed and overgrazed land on
either side of a fenceline can be striking.
Figure 8.22
Overgrazing
• Overgrazing can set in motion a series of positive
feedback loops.
Figure 8.21
Global food production
World agricultural production has risen faster
than human population.
Figure 9.1
Global food security
• However, the world still has 800 million hungry
people, largely due to inadequate distribution.
• Considering soil degradation, can we count on
food production continuing to rise?
• Global food security is a goal of scientists and
policymakers worldwide.
Nutrition
• Undernourishment =
too few calories (especially
developing countries)
• Overnutrition =
too many calories (especially
developed world)
• Malnutrition = lack of
nutritional requirements
(causes numerous diseases,
esp. in developing world)
Figure 9.2
Food Production, Nutrition and
Environmental Effects
•
~ 1 in 6 people in developing nations are chronically
undernourished or malnourished
Common nutritional deficiency diseases:
Marasmus and Kwashiorkor
•
•
M = diet low in calories and protein
K = severe protein deficiency
Poverty
Decreased
resistance
to disease
Malnutrition
Decreased
energy
Decreased
ability
to learn
High death
rate for
children
Decreased
ability
to work
Shortened
life
expectancy
Feedback loop
Fig. 12.9, p. 269
Environmental effects of food production
Biodiversity Loss
Loss and degradation of habitat from
clearing grasslands and forests and
draining wetland
Fish kills from pesticide runoff
Killing of wild predators to protect
livestock
Loss of genetic diversity from
replacing thousands of wild crop
strains with a few monoculture strains
Soil
Erosion
Loss of fertility
Salinization
Waterlogging
Desertification
Air Pollution
Greenhouse gas emissions from fossil
Fuel issue
Other air pollutants from fossil fuel use
Pollution from pesticide sprays
Water
Water waste
Aquifer depletion
Surface and groundwater
pollution from pesticides
and fertilizers
Increased runoff and
Overfertilization of lakes
flooding from land cleared and slow-moving rivers
to grow crops
from runoff of nitrates
and phosphates from
Sediment pollution from
fertilizers, livestock
erosion
wastes, and food
processing wastes
Fish kills from pesticide
runoff
Human Health
Nitrates in drinking water
Pesticide residues in drinking water,
food, and air
Contamination of drinking and
swimming water with disease
organisms from livestock wastes
Bacterial contamination of meat
Pesticide use
• Pesticide use is still rising sharply across the world,
although growth has slowed in the U.S.
– 1 billion kg
(2 billion lbs.)
of pesticides are
applied each year in
the U.S.
Figure 9.5
Biological control
• Synthetic chemicals can pollute and be health hazards.
• Biological control (biocontrol) avoids this.
•
Biocontol entails battling pests and weeds with
other organisms that are natural enemies of those
pests and weeds.
•
(“The enemy of my enemy is my friend.”)
Biological control
• Biocontrol has had
success stories.
• Bacillus
thuringiensis (Bt) =
soil bacterium that
kills many insects. In
many cases,
seemingly safe and
effective.
Cactus moth, Cactoblastis
cactorum (above), was used
to wipe out invasive prickly
pear cactus in Australia.
Figure 9.7
But biocontrol is risky
• Most biocontrol agents are introduced from
elsewhere.
• Some may turn invasive and become pests
themselves!
• Cactus moths brought to the Caribbean jumped
to Florida, are eating native cacti, and
spreading.
• Wasps and flies brought to Hawaii to control
crop pests are parasitizing native caterpillars in
wilderness areas.
Integrated pest management (IPM)
• Combines biocontrol, chemical, and other methods
May involve:
•
•
•
•
•
•
•
•
Biocontrol
Pesticides
Close population monitoring
Habitat modification
Crop rotation
Transgenic crops
Alternative tillage
Mechanical pest removal
Genetic modification of food
• Manipulating and engineering genetic
material in the lab may represent the best
hope for increasing agricultural production
further without destroying more natural
lands.
• But many people remain uneasy about
genetically engineering crop plants and other
organisms.
Some GM foods
Golden rice:
Enriched with
vitamin A.
But too much
hype?
Ice-minus strawberries: Frostresistant bacteria sprayed on.
Images alarmed public.
FlavrSavr tomato:
Better taste?
But pulled from market.
Bt crops:
Widely used on
U.S. crops.
But ecological
concerns?
Figure 9.12
Prevalence of GM foods
Figure 9.13
Scientific concerns about GM organisms
• Are there health risks for people?
• Can transgenes escape into wild plants, pollute ecosystems, harm
organisms?
• Can pests evolve resistance to GM crops just as they can to
pesticides?
• Can transgenes jump from crops to weeds and make them into
“superweeds”?
• Can transgenes get into traditional native crop races and ruin their
integrity?
Socioeconomic and political
concerns about GM products
• Should scientists and corporations be “tinkering
with” our food supply?
• Are biotech corporations testing their products
adequately, and is outside oversight adequate?
• Should large multinational corporations exercise
power over global agriculture and small farmers?
Europe vs. America
• Europe: has followed precautionary principle in
approach to GM foods. Governments have listened to
popular opposition among their citizens.
• U.S.: GM foods were introduced and accepted with
relatively little public debate.
• Relations over agricultural trade have been uneasy, and
it remains to be seen whether Europe will accept more
GM foods from the U.S.
Trade-Offs
Genetically Modified Food and Crops
Projected
Advantages
Need less fertilizer
Need less water
More resistant to insects,
plant disease, frost, and
drought
Projected
Disadvantages
Irreversible and
unpredictable genetic
and ecological effects
Harmful toxins in food
From possible plant
cell
Mutations
Faster growth
New allergens in food
Can grow in slightly salty
soils
Less spoilage
Better flavor
Less use of conventional
pesticides
Lower nutrition
Increased evolution of
Pesticide-resistant
Insects and plant
disease
Creation of herbicideResistant weeds
Tolerate higher levels of
pesticide use
Harm beneficial insects
Higher yields
Lower genetic diversity
Preserving crop diversity
• Native cultivars of crops are important to
preserve, in case we need their genes to
overcome future pests or pathogens.
• Diversity of cultivars has been rapidly
disappearing from all crops throughout the
world.
Seed banks preserve seeds, crop
varieties
– Seed banks are living museums
of crop diversity, saving
collections of seeds and growing
them into plants every few years
to renew the collection.
• Careful hand pollination
helps ensure plants of one
type do not interbreed with
plants of another.
Figure 9.14
Animal agriculture: Livestock and poultry
• Consumption of meat has risen faster than
population over the past several decades.
Figure 9.15
Feedlot agriculture
• Increased meat consumption has led to animals
being raised in feedlots (factory farms), huge
pens that deliver energy-rich food to animals
housed at extremely high densities.
Figure 9.16
Feed lots
•
•
•
More production of livestock in smaller, condensed
spaces; Produce more using less space and energy
Increases need for antibiotics due to enclosed
spaces; leads to issues of cruelty to animals
Hormones given to produce larger animals for more
meat= more $!
Feedlot agriculture: Environmental impacts
• Immense amount of waste produced,
polluting air and water nearby
• Intense usage of chemicals (antibiotics,
steroids, hormones), some of which persist in
environment
• However, if all these animals were grazing on
rangeland, how much more natural land
would be converted for agriculture?
Food choices = energy choices
• Energy is lost at each trophic level.
• When we eat meat from a cow fed on grain,
most of the grain’s energy has already been
spent on the cow’s metabolism.
• Eating meat is therefore very energy
inefficient. - Hence, the “Eating Green”
Challenge! Feb. 28- March 7
Grain feed input for animal output
• Some animal
food products
can be produced
with less input of
grain feed than
others.
Figure 9.17
Land and water input for animal output
• Some animal
food products
can be
produced with
less input of
land and water
than others.
Figure 9.18
Aquaculture
• The raising of aquatic organisms for food in
controlled environments
• Provides 1/3 of world’s fish for consumption
• 220 species being farmed
• The fastest growing type of food production
Benefits of aquaculture
• Provides reliable protein source for people,
increases food security
• Can be small-scale, local, and sustainable
• Reduces fishing pressure on wild stocks, and
eliminates bycatch
• Uses fewer fossil fuels than fishing
• Can be very energy efficient
Environmental impacts of aquaculture
• Density of animals leads to disease, antibiotic use, risks to food
security.
• It can generate large amounts of waste.
• Often animals are fed grain, which is not energy efficient.
• Sometimes animals are fed fish meal from wild-caught fish.
• Farmed animals may escape into the wild and interbreed with,
compete with, or spread disease to wild animals.
Catching and Raising More Fish
 Fisheries
 Fishing methods (See Fig. 14-24 p. 299)
 Sustainable yield
 Overfishing- decreased biodiversity; affects aquatic
food chains; bycatch; loss of food
 Commercial extinction
 Aquaculture- collectively involves fish farming and ranching;
salmon and shrimp
Environmental impacts of aquaculture
• Transgenic salmon (top) can compete with or
spread disease to wild salmon (bottom) when they
escape from fish farms.
Figure 9.20
aquaculture
3 methods used to catch fish:
trawl bag
drift net
purse-seine
Trade-Offs
Aquaculture
Advantages
Highly efficient
High yield in small
volume of water
Increased yields
through crossbreeding and genetic
engineering
Can reduce overharvesting of
conventional fisheries
Little use of fuel
Profit not tied to price
of oil
Disadvantages
Large inputs of land, feed,
And water needed
Produces large and
concentrated outputs of
waste
Destroys mangrove forests
Increased grain production
needed to feed some
species
Fish can be killed by
pesticide runoff from
nearby cropland
Dense populations
vulnerable to disease
High profits
Tanks too contaminated to
use after about 5 years
Solutions
More Sustainable Aquaculture
• Reduce use of fishmeal as a feed to reduce depletion of
other fish
• Improve pollution management of aquaculture wastes
• Reduce escape of aquaculture species into the wild
• Restrict location of fish farms to reduce loss of mangrove
forests and other threatened areas
• Farm some aquaculture species (such as salmon and
cobia) in deeply submerged cages to protect them from
wave action and predators and allow dilution of wastes
into the ocean
• Set up a system for certifying sustainable forms of
aquaculture
Sustainable agriculture
• Agriculture that can practiced the same way far into the
future
• Does not deplete soils faster than they form
• Does not reduce healthy soil, clean water, and
genetic diversity essential for long-term crop and
livestock production
• Low-input agriculture = small amounts of pesticides,
fertilizers, water, growth hormones, fossil fuel energy,
etc.
• Organic agriculture = no synthetic chemicals used.
Instead, biocontrol, composting, etc.
Organic farming
• Small percent of market, but is growing fast
– 1% of U.S. market, but growing 20%/yr
– 3–5% of European market, but growing 30%/yr
Organic produce:
• Advantages for consumers: healthier; environmentally
better
• Disadvantages for consumers: less uniform and
appealing-looking; more expensive
Conclusions: Challenges
• Chemical pesticides pollute, and kill pollinators,
and pests evolve resistance.
• GM crops show promise for social and
environmental benefits, but questions linger about
their impacts.
• Much of the world’s crop diversity has vanished.
• Feedlot agriculture and aquaculture pose benefits
and harm for the environment and human health.
Conclusions: Challenges
• Organic farming remains a small portion of agriculture.
• Human population continues to grow, requiring more
food production.
• Soil erosion is a problem worldwide.
• Salinization, waterlogging, and other soil degradation
problems are leading to desertification.
• Grazing and logging, as well as cropland agriculture,
contribute to soil degradation.
Conclusions: Solutions
• Biocontrol and IPM offer alternatives to pesticides.
• Further research and experience with GM crops may
eventually resolve questions about impacts, and allow us
to maximize benefits while minimizing harm.
• More funding for seed banks can rebuild crop diversity.
• Ways are being developed to make feedlot agriculture
and aquaculture safer and cleaner.
Conclusions: Solutions
• Organic farming is popular and growing fast.
• Green revolution advances have kept up with food demand so far.
Improved distribution and slowed population growth would help
further.
• Farming strategies like no-till farming, contour farming, terracing,
etc., help control erosion.
• Government laws, and government extension agents working with
farmers, have helped improve farming practices and control soil
degradation.
• Better grazing and logging practices exist that have far less impact
on soils.
Solutions
Sustainable Agriculture
Increase
Decrease
High-yield polyculture
Soil erosion
Organic fertilizers
Soil salinization
Biological pest control
Aquifer depletion
Integrated pest
management
Overgrazing
Overfishing
Irrigation efficiency
Perennial crops
Loss of
biodiversity
Crop rotation
Loss of prime
cropland
Use of more waterefficient crops
Food waste
Soil conservation
Subsidies for unsustainable
farming and fishing
Subsidies for more
sustainable farming and
fishing
Population growth
Poverty
What Can You Do?
Sustainable Agriculture
•Waste les food
•Reduce or eliminate meat consumption
•Feed pets balanced grain foods instead of meat
•Use organic farming to grow some of your food
•Buy organic food
•Compost your food wastes
REVIEW QUESTIONS!
QUESTION: Review
Integrated pest management may involve all of the
following EXCEPT… ?
a. Close population monitoring
b. Biocontrol
c. Exclusive reliance on pesticides
d. Habitat modification
e. Transgenic crops
QUESTION: Review
What do seed banks do?
a. Lend money to farmers to buy seeds
b. Pay farmers to store seeds
c. Buy seeds from farmers
d. Store seeds to maintain genetic diversity
e. None of the above
QUESTION: Review
Which is NOT a benefit of aquaculture?
a. Provides a reliable protein source
b. Reduces pressure on natural fisheries
c. Produces no waste
d. Uses fewer fossil fuels than commercial fishing
e. All of the above are benefits
QUESTION: Weighing the Issues
Can we call the green revolution a success?
a. A huge success; it has saved millions from
starvation because it increased food production
to keep pace with population growth.
b. Not a success; its environmental impacts have
outweighed its claimed benefits.
c. A success; its environmental impacts are
balanced by the fact that it saved huge areas
from deforestation.
QUESTION: Interpreting Graphs and Data
With 500 kg of water, you could produce … ?
a. 2 kg of protein
from milk
b. Protein from 50
chickens
c. 750 kg of protein
from beef
d. 15 eggs
Figure 9.18b
QUESTION: Viewpoints
Should we encourage the continued development of
GM foods?
a. Yes; they will bring many health, social, and
environmental benefits.
b. No, we should adopt the precautionary
principle, and not introduce novel things until
we know they are safe.
c. Yes, but we should proceed cautiously, and
consider each new crop separately.
QUESTION: Review
Which statement is NOT correct?
a. Soil consists of disintegrated rock, organic
matter, nutrients, and microorganisms.
b. Healthy soil is vital for agriculture.
c. Soil is somewhat renewable.
d. Soil is lifeless dirt.
e. Much of the world’s soil has been degraded.
QUESTION: Review
The A horizon in a soil profile… ?
a. Is often called the “zone of accumulation.”
b. Is often called “topsoil.”
c. Contains mostly organic matter.
d. Is the lowest horizon, deepest underground.
QUESTION: Review
Erosion occurs through… ?
a. Deforestation.
b. Excessive plowing.
c. Overgrazing rangelands.
d. Two of the above.
e. All of the above.
QUESTION: Review
Drip irrigation differs from conventional
irrigation in that … ?
a. It is much less efficient.
b. It can cause salinization.
c. Water is precisely targeted to plants.
d. About 40% is wasted.
QUESTION: Weighing the Issues
You are farming an extremely steep slope that is sunny and
very windy. What strategies would you consider using?
a. Crop rotation
b. Contour farming
c. Intercropping
d. Terracing
e. Shelterbelts
f. No-till farming
QUESTION: Interpreting Graphs and Data
Grain produced per person has… ?
a. Risen steadily
b. Fallen
sharply
c. Increased
since 1983
Figure 8.3
d. Decreased
since 1983