How can we grow enough food while keeping the soil, water and biodiversity that farming depends on?
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.
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What this topic is asking
The College Board (Topic 5.15) wants you to describe sustainable farming practices that conserve soil and water and maintain long-term productivity, the solutions to the agricultural impacts of Topic 5.4.
The goal
Soil-conserving practices
Wider practices
- Agroforestry: integrating trees with crops or livestock provides shade, windbreaks, and roots that hold soil.
- Rotational grazing: moving livestock between paddocks lets pasture recover, preventing overgrazing.
- Integrated pest management (Topic 5.14) and efficient drip irrigation (Topic 5.5) round out a sustainable system.
Why this matters
Sustainable agriculture is the constructive answer to the unit's agricultural problems. It applies the soil science of Unit 4 (Topics 4.2 and 4.3), conserves the water of the watershed (Topic 4.6), and embodies the sustainability goal of Topic 5.12, growing food at a rate the land can sustain indefinitely.
Try this
Q1. Identify a practice that keeps soil covered between growing seasons. [1 point]
- Cue. Planting a cover crop.
Q2. Explain how crop rotation reduces the need for synthetic fertilizer. [2 points]
- Cue. Rotating in a nitrogen-fixing legume returns nitrogen to the soil naturally, replenishing nutrients that the previous crop removed, so less synthetic nitrogen fertilizer is needed for the next crop.
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 2021 (style)4 marksSection II (FRQ). (a) Describe how crop rotation maintains soil fertility. (b) Explain how contour ploughing reduces soil erosion on a slope. (c) Describe how a cover crop protects soil between growing seasons. (d) Identify one benefit of no-till farming.Show worked answer →
A 4-point FRQ on sustainable agriculture.
(a) Describe (1 point): rotating crops (for example alternating a nitrogen-fixing legume with a grain) replenishes soil nutrients and breaks pest and disease cycles, maintaining fertility without heavy fertilizer.
(b) Explain (1 point): contour ploughing follows the land's contours across the slope rather than up and down, so the ridges slow water flowing downhill and reduce the erosion it causes.
(c) Describe (1 point): a cover crop keeps the soil covered with living roots and foliage between cash crops, holding soil in place, reducing erosion, and adding organic matter.
(d) Identify (1 point): no-till farming leaves residue on the surface and avoids ploughing, reducing erosion, retaining soil moisture and organic matter, and lowering fuel use.
Markers reward nutrient replenishment for rotation, slowing downhill water for contour ploughing, soil cover for cover crops, and a real no-till benefit.
AP 2018 (style)1 marksSection I (multiple choice). Which practice alternates strips of different crops across a slope to reduce erosion and runoff? (A) Monoculture (B) Strip cropping (C) Clearcutting (D) Flood irrigation. Justify your choice.Show worked answer →
A 1-point MCQ on sustainable agriculture. The answer is (B).
Strip cropping alternates strips of different crops (for example a row crop and a cover crop) across a slope; the denser strips slow runoff and trap soil, reducing erosion. Monoculture (A) grows one crop and does not reduce erosion; clearcutting (C) is a logging method; flood irrigation (D) is a water-application method. The trap is confusing strip cropping with monoculture.
Related dot points
- 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.
- Topic 5.14 Integrated Pest Management: describe integrated pest management (IPM) and explain how it combines biological, cultural, mechanical and limited chemical control.
A focused answer to APES Topic 5.14, covering integrated pest management (IPM), its combination of biological, cultural, mechanical and limited chemical controls, monitoring and economic thresholds, and its advantages over relying on pesticides, with a worked threshold example.
- 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 5.12 Introduction to Sustainability: define sustainability and sustainable yield, and explain the indicators used to assess whether resource use is sustainable.
A focused answer to APES Topic 5.12, covering sustainability, sustainable yield, the difference between renewable and non-renewable resources, indicators of sustainability (biodiversity, soil, water, productivity), and the link to natural capital, with a worked sustainable-yield 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)