The last two lessons showed how humans wrest food from the land and the damage that follows. This one is about the counterattack: the practices that let us keep farming without wrecking the soil, water, and ecosystems we depend on. But first we look at two of the most damaging modern practices — industrial meat production in feedlots and overgrazing that turns grassland into desert. Then we flip to solutions: contour plowing, terracing, cover crops, crop rotation, and integrated pest management. If Lesson 15 was the problem, Lesson 16 is the toolkit — and sustainable-agriculture solutions are among the most common FRQ requests on the entire exam.
Producing meat is far more resource-intensive than producing plant food, because of the 10% rule (Lesson 1): feeding grain to animals and then eating the animals loses ~90% of the energy at each trophic step. Eating lower on the food chain (more plants) feeds more people per unit land and water.
Concentrated Animal Feeding Operations (CAFOs / feedlots) raise many animals in confined spaces: - Benefits: efficient, cheap, high output of meat. - Impacts: enormous manure/waste concentrated in one place → water pollution (nutrient runoff, eutrophication, pathogens), air pollution (methane — a greenhouse gas — and ammonia/odor), heavy antibiotic use (breeding antibiotic-resistant bacteria), and high water/grain demand.
Overgrazing occurs when too many livestock graze an area, stripping vegetation faster than it can regrow. Consequences: loss of plant cover → soil erosion, soil compaction, reduced water infiltration, and loss of the roots that hold soil.
Desertification is the degradation of once-productive (often arid/semi-arid) land into desert-like conditions, driven by overgrazing, deforestation, unsustainable farming, and drought/climate change. It reduces agricultural productivity and displaces people. The Sahel region of Africa and the US Dust Bowl are classic examples.
The goal: maintain long-term productivity while minimizing environmental harm. Key techniques:
Soil-conservation / erosion-control methods: - Contour plowing — plowing across (along the contours of) a slope rather than up-and-down, so furrows catch water and slow runoff/erosion. - Terracing — carving flat "steps" into steep slopes to reduce runoff and erosion. - Strip cropping — alternating strips of row crops with cover crops to slow runoff and trap soil. - Windbreaks/shelterbelts — rows of trees that reduce wind erosion. - No-till / conservation tillage — minimal soil disturbance; residue protects soil (Lesson 15).
[DIAGRAM: Hillside showing three techniques. Left: contour plowing (furrows follow the slope's contour lines). Center: terracing (stair-step flat platforms cut into the slope). Right: strip cropping (alternating bands of crops and cover). All reduce downhill water flow and erosion compared with up-and-down plowing.]
Fertility and pest practices: - Crop rotation — alternating crops (e.g., corn then legumes) to restore soil nitrogen (via N-fixing legumes) and disrupt pest/disease cycles. - Cover crops / green manure — planting between seasons to protect and enrich soil, prevent erosion, and take up excess nutrients. - Intercropping / polyculture — growing multiple crops together for diversity and resilience (contrast with monoculture). - Integrated Pest Management (IPM) — combining biological controls (natural predators, e.g., ladybugs for aphids), crop rotation, monitoring, and targeted, minimal pesticide use only when needed. IPM reduces chemical use, slows resistance (breaks the pesticide treadmill), and protects non-target species. - Organic farming — avoiding synthetic fertilizers/pesticides, relying on compost, manure, and biological methods.
Rangeland management to prevent overgrazing: rotational grazing (moving livestock among pastures to allow regrowth) and limiting stocking density.
"Propose sustainable-agriculture solutions" and "how to reduce soil erosion" are among the most frequently asked FRQ prompts. Knowing the specific technique and its mechanism (why contour plowing reduces erosion) is what earns points. CAFO and overgrazing impacts are common MC items and connect to Units 8 (water pollution) and 9 (methane/climate).
A farmer's steep hillside is losing soil to erosion during rains. Name two techniques to reduce it and how each works.
Solution: Terracing — flat steps cut into the slope slow water flow and trap soil. Contour plowing — plowing along the slope's contours creates ridges that catch runoff instead of channeling it downhill. (Also strip cropping.)
Interpretation: On slopes, the goal is to slow downhill water movement.
Explain two environmental impacts of a large cattle feedlot (CAFO).
Solution: (1) Water pollution — concentrated manure runs off or leaches, adding nutrients (eutrophication) and pathogens to waterways. (2) Air/climate impact — cattle emit methane (a potent greenhouse gas), and waste releases ammonia and odor. (Also antibiotic resistance, high water/grain use.)
Interpretation: CAFOs concentrate waste and emissions in one place, overwhelming local capacity to absorb them.
Explain how rotating a cereal crop with a legume crop improves sustainability.
Solution: Legumes host nitrogen-fixing bacteria that add usable nitrogen to the soil (Lesson 2), reducing the need for synthetic fertilizer for the following cereal crop. Rotation also disrupts pest and disease cycles that build up under continuous monoculture, lowering pesticide need.
Interpretation: Rotation restores fertility and breaks pest cycles — two mechanisms, both worth points.
Explain how overgrazing can lead to desertification in a semi-arid region.
Solution: Too many livestock strip vegetation faster than it regrows, exposing and compacting soil. Bare soil loses the roots that hold it, so erosion increases and water infiltration drops. Over time the land loses fertility and vegetation cannot recover, degrading into desert-like conditions (desertification), especially under drought.
Interpretation: Overgrazing → bare, eroded, compacted soil → productivity collapse → desertification.
(B) Moving livestock to allow regrowth.
Any three with mechanism: Contour plowing/terracing — slows downhill runoff to reduce erosion on hills. Crop rotation (with legumes) — restores soil nitrogen and disrupts pest cycles, cutting fertilizer/pesticide need. Integrated Pest Management — biological controls + monitoring + targeted pesticide use slows resistance (breaks the pesticide treadmill). (Also no-till, cover crops, strip cropping, polyculture.)
(a) 12 − 2 = 10 tons/acre/yr reduction (an ~83% reduction). (b) No-till leaves crop residue on the surface and minimizes soil disturbance, so soil stays covered and anchored, resisting wind and water erosion.
FRQ rubric (10 pts): - (a) 1 pt tillage loosens and exposes bare soil; 1 pt on slopes water runs downhill and carries loose soil away (erosion). (2) - (b) 1 pt feedlot concentrates large amounts of manure; 1 pt nutrient/pathogen-laden runoff enters the river (eutrophication/contamination). (2) - (c) Three practices, each 1 pt name + 1 pt mechanism (2 pts each), covering the three problem areas. Erosion: contour plowing/terracing/strip cropping/no-till/cover crops. Fertility/pests: crop rotation/IPM/polyculture/organic amendments. Feedlot: manure lagoons/composting and applying as controlled fertilizer, buffer strips, reducing herd density, methane digesters. (6)
A region of sloped farmland practices intensive tillage and monoculture. It suffers severe soil erosion, declining fertility, nutrient runoff into a nearby river, and a cattle feedlot adds manure pollution.
(a) Explain how intensive tillage on slopes increases erosion. (2 pts) (b) Explain how the feedlot contributes to water pollution. (2 pts) (c) Propose three sustainable practices (at least one for erosion, one for fertility/pests, one for the feedlot) and explain the mechanism of each. (6 pts)
MC: 1. (B) Contour plowing. 2. (B) Concentrated manure/nutrient runoff. 3. (B) Overgrazing and unsustainable land use. 4. (B) Adds nitrogen via nitrogen-fixing bacteria. 5. (B) Reduce pesticide use via biological/cultural controls. 6. (B) ~90% of energy lost per trophic level. 7. (B) Terracing. 8. (B) Protect soil and take up excess nutrients. 9. (B) Greater vulnerability to a single pest/disease. 10. (B) Moving livestock to allow regrowth.
Any three with mechanism: Contour plowing/terracing — slows downhill runoff to reduce erosion on hills. Crop rotation (with legumes) — restores soil nitrogen and disrupts pest cycles, cutting fertilizer/pesticide need. Integrated Pest Management — biological controls + monitoring + targeted pesticide use slows resistance (breaks the pesticide treadmill). (Also no-till, cover crops, strip cropping, polyculture.)
(a) 12 − 2 = 10 tons/acre/yr reduction (an ~83% reduction). (b) No-till leaves crop residue on the surface and minimizes soil disturbance, so soil stays covered and anchored, resisting wind and water erosion.
FRQ rubric (10 pts): - (a) 1 pt tillage loosens and exposes bare soil; 1 pt on slopes water runs downhill and carries loose soil away (erosion). (2) - (b) 1 pt feedlot concentrates large amounts of manure; 1 pt nutrient/pathogen-laden runoff enters the river (eutrophication/contamination). (2) - (c) Three practices, each 1 pt name + 1 pt mechanism (2 pts each), covering the three problem areas. Erosion: contour plowing/terracing/strip cropping/no-till/cover crops. Fertility/pests: crop rotation/IPM/polyculture/organic amendments. Feedlot: manure lagoons/composting and applying as controlled fertilizer, buffer strips, reducing herd density, methane digesters. (6)
⭐ Exam strategy: On "propose sustainable practices" FRQs — one of the most common on the exam — always pair the technique with its MECHANISM (contour plowing → slows runoff → less erosion). Naming alone rarely scores; the "because it does X" clause is where the points live.
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