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Impact of Modern Agriculture on Environment and Human Health

FAB-465 (Lecture 5)

Outline

• Impact of Agriculture on the Environmental resources

– Land and soil

– Water

– Use of pesticides and fertilizers

– Advantages and disadvantages of modern fertilizers and pesticides

• Issues related to human health

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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.

• Much of this additional land suffers from constraints.

Soil Degradation

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Land Resources

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

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

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-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-off is contaminated, or biodiversity is diminished.

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

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.

Loss of Topsoil

• 15–20 cm of topsoil prevents mass starvation

• Centuries to replenish 2.5 cm of topsoil

• Soil erosion – Erosion faster than formation – soil a nonrenewable

resource – Soil fertility declines – Water pollution occurs – Natural and due to human activity

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Mechanisms of Erosion

• Rill Erosion - Small rivulets of running water gather together and cut small channels in the soil.

• Gully Erosion - Rills enlarge to form bigger channels too large to be removed by normal tillage.

• Streambank Erosion - Washing away of soil from established streambanks.

Streambank Erosion

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Severe Gully Erosion in Bolivia

Rill erosion

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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:

• Row crops leave soil exposed

• Weed free-fields

• Removal of windbreaks

• No crop-rotation or resting periods

• Continued monocultures

Global Soil Erosion

Fig. 10-6, p. 205

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Approaches to Reducing Soil Erosion

• Planting crops without disturbing soil

• Soil conservation programs

• Subsidies for taking erodible land out of production

Effects of Irrigation

• Leaves behind salts in topsoil

• Salinization

• Remedies expensive and complex

• Waterlogging – Attempts to leach salts deeper but raises water table – Growing worse

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Waterlogging

Salinization and Waterlogging

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Severe Salinization

Fig. 10-10, p. 207

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

CHEMICAL

INPUTS

Fertilizers

Pesticides

Fungicides

Herbicides

(weed killers)

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Fertilizers

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

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

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

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

Pesticide Problems

• Non-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.

• Pest Resurgence

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Pesticide Resistance

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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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-thirds resulting from occupational

hazards in developing countries.

– Long-term health effects difficult to conclusively document. • PCB’s (Polychlorinated Biphenyls) have been linked to

learning deficiencies in children. – Intake during mother’s pregnancy.

Alternatives to Pesticide Use

– Crop Rotation

– Flooding Fields

– Habitat Diversification

– Growing in Pest-Free Zones

– Adjusting Planting Times

– Plant Mixed Polycultures

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Advantages of Modern Pesticides

• Save human lives

• Increase food supplies

• Increase profits for farmers

• Work fast

• Low health risks when used properly

• Newer pesticides safer and more effective

Disadvantages of Modern Pesticides • Pests become genetically resistant

• Put farmers on a financial treadmill

• Some insecticides kill natural enemies

• May pollute environment

• Harmful to wildlife

• Threaten human health

• Use has not reduced U.S. crop losses

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Alternatives to Pesticides

• Provide homes for pest enemies

• Implant genetic resistance

• Pheromones to trap pests or attract predators

• Hormones to disrupt life cycle

• Integrated pest management – combination of approaches

• Natural enemies

Nature’s Pest Control

• Polycultures – pests controlled by natural enemies

• Monocultures and land clearing

– Loss of natural enemies

– Require pesticides

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Spiders: Natural Enemy of Pests