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This topic covers how humans use land for food production, the impacts of modern farming techniques, and sustainable alternatives. The Green Revolution (1950s–1960s) dramatically increased crop yields using high-yield varieties, synthetic fertilizers, and irrigation—but at environmental costs like soil degradation and water pollution. Monocropping (growing a single crop repeatedly) boosts efficiency but reduces biodiversity and increases pest outbreaks. Integrated Pest Management (IPM) offers a middle ground, using ecological strategies to control pests without over-relying on chemicals. These concepts appear frequently on the AP exam, often in FRQs about agricultural trade-offs, sustainability, or human impacts on ecosystems.
Real-world example: The Irish Potato Famine (1845–1852) was worsened by monocropping—farmers grew only one potato variety, so when a fungus (Phytophthora infestans) spread, the entire crop failed, leading to mass starvation. This disaster highlights the risks of genetic uniformity in agriculture.
Key components: HYVs, mechanization, chemical inputs, irrigation expansion.
Monocropping: Growing the same crop on the same land year after year (e.g., corn in the U.S. Midwest, soybeans in Brazil). Increases efficiency but depletes soil nutrients, reduces biodiversity, and makes crops vulnerable to pests/diseases.
Example: Iowa’s cornfields—over 90% of Iowa’s farmland is planted with just two crops (corn and soybeans).
Pesticide Treadmill: A cycle where pests develop resistance to pesticides, forcing farmers to use stronger/more chemicals, which kills beneficial species (e.g., pollinators) and harms human health.
Example: DDT (a now-banned insecticide) led to resistant mosquitoes, requiring even more toxic alternatives.
Integrated Pest Management (IPM): A sustainable pest-control strategy that combines biological, cultural, mechanical, and chemical methods to minimize environmental harm.
Key steps:
Soil Degradation: Loss of soil quality due to erosion, nutrient depletion, salinization, or compaction. Caused by overgrazing, deforestation, and poor farming practices.
Example: The Dust Bowl (1930s)—overplowing grasslands in the Great Plains led to massive soil erosion during drought, creating "black blizzards."
Salinization: Buildup of salts in soil due to over-irrigation (water evaporates, leaving salts behind). Reduces crop yields and can make land unusable.
Example: Colorado River Basin—heavy irrigation has caused salinization in California’s Imperial Valley, reducing farm productivity.
Agroforestry: Integrating trees and shrubs into crop/livestock systems to improve biodiversity, soil health, and carbon sequestration.
Example: Shade-grown coffee—coffee plants grown under trees support bird habitats and reduce the need for fertilizers.
Crop Rotation: Planting different crops in the same field across seasons to replenish soil nutrients and reduce pest/disease buildup.
Example: Corn-Soybeans-Alfalfa (corn depletes nitrogen; soybeans fix nitrogen; alfalfa adds organic matter).
Contour Plowing: Plowing along the curves of a slope (not up/down) to reduce soil erosion from water runoff.
Example: Used in hilly regions like the Palouse (Washington state) to prevent topsoil loss.
No-Till Agriculture: Planting crops without plowing, leaving crop residue to protect soil from erosion and retain moisture.
Benefits: Reduces CO? emissions (less fuel used), improves soil structure, and increases water retention.
Food Security: When all people have reliable access to sufficient, safe, and nutritious food. Threatened by climate change, population growth, and unsustainable farming.
Example FRQ Application: "Explain how the Green Revolution increased food production and describe two environmental consequences of its methods." - Step 1: Define the Green Revolution (HYVs, fertilizers, irrigation). - Step 2: Explain how these methods boosted yields (e.g., "HYVs produce more grain per plant"). - Step 3: List consequences (e.g., "Synthetic fertilizers cause algal blooms; irrigation depletes aquifers").
Human impacts of the Green Revolution (e.g., "How did the Green Revolution affect water use in India?").
Multiple-Choice Traps:
"Crop rotation is only for pest control"-It also replenishes soil nutrients (e.g., legumes fix nitrogen).
Tricky Distinctions:
Synthetic vs. Organic Fertilizers:
Data Interpretation:
Which of the following is a direct environmental consequence of the Green Revolution’s reliance on synthetic fertilizers? (A) Increased soil salinization (B) Higher rates of eutrophication in nearby water bodies (C) Greater biodiversity in agricultural fields (D) Reduced need for irrigation
Answer: (B) Higher rates of eutrophication in nearby water bodies. Explanation: Synthetic fertilizers (e.g., nitrogen, phosphorus) run off into waterways, causing algal blooms and dead zones.
"Farmers in a region have been using monocropping for decades. Describe two environmental problems associated with this practice and one sustainable alternative that could address these issues."
Sample Answer:1. Environmental Problem 1: Soil nutrient depletion—growing the same crop repeatedly removes specific nutrients (e.g., corn depletes nitrogen), requiring more fertilizers.2. Environmental Problem 2: Increased pest outbreaks—monocultures lack biodiversity, making it easier for pests to spread (e.g., corn borers in Iowa).3. Sustainable Alternative: Crop rotation—planting legumes (e.g., soybeans) after corn replenishes nitrogen naturally and disrupts pest life cycles.
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