How do tilling, fertilizing and grazing the land slowly wear it out?
Topic 5.4 The Impact of Agricultural Practices: explain how tillage, fertilizer use, overgrazing and other farming practices degrade soil and water.
A focused answer to APES Topic 5.4, covering how tillage, fertilizer use, overgrazing, and confined animal feeding degrade soil and water through erosion, nutrient runoff, salinisation, desertification and waste, with a worked nutrient-loading calculation.
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What this topic is asking
The College Board (Topic 5.4) wants you to explain how common farming practices, tillage, fertilizer use, overgrazing and intensive animal production, degrade soil and water. This catalogues the costs the Green Revolution introduced.
Tillage and erosion
Fertilizer and eutrophication
Overgrazing and desertification
Irrigation and animal waste
- Irrigation problems (Topic 5.5): poorly drained irrigation causes salinisation (salt build-up that poisons crops) and waterlogging, and over-pumping depletes aquifers.
- Confined animal feeding operations (CAFOs): concentrating many animals produces large volumes of manure that can run off and pollute water with nutrients and pathogens.
Why this matters
These impacts connect agriculture to the soil and water topics of Unit 4 (erosion, watersheds), to the nitrogen and phosphorus cycles (Topics 1.5 and 1.6) through eutrophication, and to the aquatic pollution of Unit 8. They are exactly the problems that sustainable agriculture (Topic 5.15) aims to solve.
Try this
Q1. Identify the process by which salt accumulates in soil under poorly drained irrigation. [1 point]
- Cue. Salinisation.
Q2. Explain how overgrazing can lead to desertification. [2 points]
- Cue. Overgrazing removes the plant cover faster than it regrows, exposing soil to erosion and drying; the degraded, bare, infertile land can turn into desert-like conditions.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2022 (style)4 marksSection II (FRQ). (a) Explain how tilling the soil increases erosion. (b) Describe how excess fertilizer use harms a nearby lake. (c) Explain how overgrazing leads to desertification. (d) Identify one practice that reduces the soil impacts of farming.Show worked answer →
A 4-point FRQ on agricultural impacts.
(a) Explain (1 point): tilling breaks up and loosens the soil and removes protective vegetation, leaving bare soil exposed to wind and water that carry it away.
(b) Describe (1 point): excess fertilizer runs off into the lake, adding nitrogen and phosphorus that cause algal blooms; when the algae die, decomposers use up oxygen (eutrophication), killing fish.
(c) Explain (1 point): overgrazing removes the protective plant cover faster than it can regrow, exposing soil to erosion; the degraded, dry, bare land can become desert-like (desertification).
(d) Identify (1 point): a practice such as no-till farming, cover crops, crop rotation, contour ploughing/terracing, or controlled grazing.
Markers reward loosening and exposing soil for tillage erosion, nutrient runoff and eutrophication for fertilizer, loss of cover for desertification, and a valid soil-conserving practice.
AP 2019 (style)1 marksSection I (multiple choice). The conversion of once-productive land into desert-like conditions, often through overgrazing and poor irrigation, is called: (A) eutrophication (B) salinisation (C) desertification (D) leaching. Justify your choice.Show worked answer →
A 1-point MCQ on agricultural impacts. The answer is (C).
Desertification is the degradation of once-productive land into desert-like conditions, commonly caused by overgrazing, deforestation and poor irrigation. Eutrophication (A) is nutrient over-enrichment of water; salinisation (B) is salt build-up in soil; leaching (D) is the washing of nutrients down through soil. The trap is confusing desertification with salinisation; salinisation is one cause, but desertification is the land turning to desert.
Related dot points
- Topic 5.3 The Green Revolution: describe the methods and benefits of the Green Revolution and explain its environmental costs.
A focused answer to APES Topic 5.3, covering the Green Revolution, high-yield crop varieties, fertilizers, pesticides, irrigation and mechanisation, its benefits for food supply, and its environmental costs, with a worked yield-increase calculation.
- Topic 5.5 Irrigation Methods: compare the main irrigation methods and explain the problems of salinisation, waterlogging and aquifer depletion.
A focused answer to APES Topic 5.5, covering flood (furrow), spray, drip and other irrigation methods, their water efficiency, and the problems of salinisation, waterlogging and aquifer depletion, with a worked irrigation-efficiency calculation.
- Topic 5.7 Meat Production Methods: compare free-range and feedlot (CAFO) meat production and explain the environmental costs of meat, including its high resource use.
A focused answer to APES Topic 5.7, covering free-range and concentrated animal feeding operations (CAFOs), the resource intensity of meat (the 10% rule), water and land use, greenhouse gas and waste impacts, and trade-offs, with a worked feed-efficiency calculation.
- Topic 5.15 Sustainable Agriculture: describe sustainable farming practices that conserve soil and water and maintain long-term productivity.
A focused answer to APES Topic 5.15, covering sustainable agriculture practices (crop rotation, contour ploughing, terracing, no-till, cover crops, strip cropping, agroforestry, rotational grazing) and how each conserves soil and water and maintains productivity, with a worked erosion-reduction calculation.
- Topic 4.2 Soil Formation and Erosion: explain how soil forms from weathered rock and organic matter, describe the soil horizons, and explain the causes and effects of soil erosion.
A focused answer to APES Topic 4.2, covering weathering, the five soil-forming factors, the soil horizons (O, A, B, C, R), the causes and consequences of soil erosion, and conservation, with a worked soil-loss calculation.
Sources & how we know this
- AP Environmental Science Course and Exam Description — College Board (2020)