Transcript Chapter 12

Chapter 12
Effects of Agriculture on
the Environment
Botkin and Keller
Environmental Science 5e
Case Study: Clean-Water Farms
• Management practices adopted by a Kansas
farmer reduced erosion and runoff of chemicals by
converting acreage to grassland
• Intensive rotational grazing or managementintensive grazing involves rotating the animals
among paddocks (fenced grazing areas) to
disperse the waste and the allow the forage grass
in idle paddocks to rejuvenate
• Higher quality, lower prices for consumer
Botkin and Keller
Environmental Science 5e
Many environmental problems
result from agriculture:
• Soil erosion
• Sediment transport
and deposition
downstream
• On-site pollution from
fertilizers and
pesticides
• Deforestation
• Desertification
• Degradation of water
aquifers
• Salinization
• Accumulation of toxic
metals and organic
compounds
• Loss of biodiversity
Botkin and Keller
Environmental Science 5e
Reducing Soil Erosion
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Why does the soil erode?
wind-rows to break the wind
contour plowing to reduce erosion by water
no-till agriculture substitutes herbicides as a
means of controlling weeds
– plowing is done in order to remove weeds that would
otherwise compete with the crop.
– soil is especially vulnerable to erosion between plowing
and crop is establishment (WHY?)
Botkin and Keller
Environmental Science 5e
Botkin and Keller
Environmental Science 5e
A Closer Look: Soils
• Be able to describe the horizons (O,B,C, etc.) and how
they differ
• There are many different types of soils. In general,
temperate soils have a larger store of nutrients than tropical
soils. This is due to the speed of decomposition (warm
moist=fast). This influences the kind of agriculture that
can be successfully practiced. In the tropics, most of the
roots are directly on the soil surface where the leaves
decay.
• Soil is composed of organic and mineral parts. The
mineral part includes sand, silt and clay. These names
refer to particle sizes. Sand is the largest, clay the
smallest.
Botkin and Keller
Environmental Science 5e
Where Eroded Soil Goes: Sediments
Also Cause Environmental Problems
Ways to slow erosion:
• Making Soil Sustainable
• Contour Plowing
• No-Till Agriculture
– Combination of farming practices that include
not plowing the land and using herbicides to
keep down weeds.
Botkin and Keller
Environmental Science 5e
Problems with Soil Erosion
• Eroded soil is transported, usually to rivers and lakes. U.S.
rivers carry about 3.6 billion metric tons of sediment per
year, 75% of it from agriculture land
• represents a loss of soil fertility, also has serious negative
impacts on aquatic ecosystems, leading to eutrophication,
killing benthic fauna and flora, and filling reservoirs.
• Soils and agriculture can be sustainable. However, it is
important to make a distinction between sustainable crop
production and a sustainable agricultural ecosystem. The
former may require inputs of chemicals and energy from
elsewhere, whereas the latter does not.
Botkin and Keller
Environmental Science 5e
Botkin and Keller
Environmental Science 5e
Integrated Pest Management
– Pests are any undesirable competitor, parasite or
predator (herbivore)
– Control of agricultural pests using several methods
together, including biological and chemical agents
– Goals:
• To minimize the use of artificial chemicals
• To prevent or slow the buildup of resistance by pests to
chemical pesticides
Botkin and Keller
Environmental Science 5e
History of Pesticides
• The first stage in the technology was one of improvisation involving
the use of fire, herbs, and poisons such as arsenic.
• A second stage starting in the 1930s ushered in the use of petroleumbased chemical sprays that were based on natural plant toxins. For
example, nicotine is an excellent insecticide. These toxic chemicals,
called botanicals, are produced by many plant species as defenses
against herbivores.
• The third stage, the development of synthetic chemical pesticides.
• The fourth stage takes advantage of deep knowledge about the biology
of pests to discover and exploit their weaknesses, such as the use of
biological control agents (fighting fire with fire). The bacterium
Bacillus thuringiensis (known as BT) is a good example of a natural
disease organism that affects insect larvae and that can now be
purchased as spores for use in the garden. There many other biological
controls available and strategies, such as the use of sterile males to end
an invasion by a founder population.
Botkin and Keller
Environmental Science 5e
A Closer Look: DDT
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Insecticide developed in the 1940s.
DDT belongs to a class of insecticides known as the chlorinated hydrocarbons.
It is a broad spectrum insecticide, it has a long half life (a decade or more), and
concentrates in the food chain (biomagnification).
Culminated in near extinction of predatory birds, alarming concentrations of
DDT in human tissue and milk, and a book (Silent Spring, 1962, Rachael
Carson).
In January 1971, EPA issued notices of intent to cancel all Federal registrations
of products containing DDT.
During the 30 years prior to its cancellation, a total of approximately
1,350,000,000 pounds of DDT was used domestically.
DDT concentrates in fat tissue, and by this mechanism it travels up the food
chain becomes more concentrated. BIOMAGNIFICATION
Since its ban, DDT continued to be manufactured in the U.S. for export to
developing countries.
2001, the United States signed the Convention on Persistent Organic Pollutants
(POPs) that commits the signatories to reduce and/or eliminate the production,
use, and/or release of the 12 POPs of greatest concern to the global
community, including DDT.
Botkin and Keller
Environmental Science 5e
Integrated Pest Management
• holistic pest management strategy combines biological
control and crop management with the limited and
judicious use of chemicals.
• 700 million lbs of pesticides are used in the U.S. annually,
about 80% of pesticide use is in developing countries.
• residues of this DDT, and/or its metabolites were found in
approximately 5.6% of all vegetable and fruit samples
tested in 1993 by the EPA
• Pesticides can be transported long distances. Pesticide
residues can be found in Arctic and Antarctic ice.
Herbicides account for about 60% of the pesticides in the
nation’s waters. The effects are not fully understood.
Pesticides that once were considered completely non-toxic
to vertebrate animals (e.g. malathion) are now suspected as
having reproductive side-effects (acting as xenoestrogens).
Botkin and Keller
Environmental Science 5e
Integrated Pest Management
• Biological controls
– No till, low till (predators live in soil)
– Introduce natural predators
• Chemical pesticides
– Limited application (up to 75% less)
• Planting methods
– No monocultures, move away from planting in rows
• Control rather than eliminate.
• Different methods of control for different pests
Botkin and Keller
Environmental Science 5e
Integrated Pest Management
Botkin and Keller
Environmental Science 5e
Genetically Modified Crops
• Faster and more efficient hybrids
– Generally benign (very similar to what is already in existence)
– Worry about super hybrids
• Terminator gene
– Seeds are sterile
– Can’t reproduce at will
– But… Farmers must buy new seeds every year
• Transfer of genetic properties from different types of life.
– Potentially most dangerous.
– BT affects caterpillars and insect larvae, introduced into corn and
potato plants, spread out from pollen and landed on milkweed,
ingested by monarch butterflies
Botkin and Keller
Environmental Science 5e
Problems with GMC
Botkin and Keller
Environmental Science 5e
Grazing on Rangelands
• Overgrazing occurs when the carrying capacity
is exceeded. It can cause severe damage to
lands
• It is important to properly manage livestock,
including using appropriate lands for gazing
and keeping livestock at a sustainable density
• Waste generated by livestock can impact
aquatic ecosystems
Botkin and Keller
Environmental Science 5e
Desertification
• Desertification is the deterioration of land in arid, semi- arid and
dry sub humid areas due to changes in climate and human
activities
• Desertification occurs when grazing or cultivation removes the
native vegetation, leaving the soil vulnerable to wind erosion.
The wind carries the small soil particles away, leaving sand.
Sand is very permeable and holds little water, and this leads to
desert-like conditions.
• Can be caused by
– Poor farming practices
– Conversion of marginal grazing lands to croplands
• About 1/3 of the Earth’s surface should be desert, based on
climate, but 43% is desert, most of it in poor countries
Botkin and Keller
Environmental Science 5e
Does farming change the biosphere?
• Agriculture changes land cover (reflection of light,
evaporation, roughness, chemical exchange rates)
• Increases CO2 (fossil fuel use - CO2 released;
clearing land speeds decomposition)
• Clearing land by fire releases particulates into
atmosphere
• Fertilizer releases nitrogen, changing geochemical
cycles
• Lowers species diversity.
Botkin and Keller
Environmental Science 5e
Should rice be grown in a dry
climate?
• The issue concerns the appropriate use of
water in arid regions, but regional issues
such as the importance of the fields to
migratory birds complicate the issue.
• If human population were to double, what
would be the additional environmental
impacts of agriculture?
Botkin and Keller
Environmental Science 5e