Environmental Management (0680) | Impact of agriculture

IGCSE Environmental Management (0680) Study Notes: Impact of Agriculture

Hello future environmental expert! This chapter is all about understanding how the way we grow food impacts our planet. Since agriculture is essential for feeding the world, it's crucial to understand both its benefits and its negative consequences. Don't worry if some concepts seem heavy—we'll break them down using simple language and everyday examples!

1. The Environmental Impacts of Intensive Agricultural Practices (Syllabus 3.5)

Modern farming often uses intense methods (like lots of machinery and chemicals) to produce maximum yields. While this helps feed a large population, it can severely damage the environment and people.

Impact 1: Chemical Overuse (Pesticides and Fertilisers)

Farmers use chemicals to help plants grow faster and to protect them from pests and weeds. But these chemicals don't stay in the field.

A. Overuse of Insecticides and Herbicides (Pesticides):

• Problem: Pesticides (chemicals that kill pests) can accumulate in food chains, a process called bioaccumulation.
• How it works: Small amounts of the pesticide are consumed by tiny organisms. When a larger animal eats many of these small organisms, the concentration of the pesticide builds up significantly in the predator.
• Example: If fish eat contaminated insects, and then birds eat many contaminated fish, the birds receive a highly concentrated dose, which can lead to illness or death (or, famously, weak eggshells).

B. Overuse of Fertilisers:

• Purpose: Fertilisers provide essential mineral ions like nitrates (\(\text{NO}_3^-\)) and phosphates (\(\text{PO}_4^{3-}\)) to boost crop growth.
• Problem: Excess fertiliser is often washed into rivers and lakes, causing eutrophication.
• Step-by-step Eutrophication:
  1. Nutrient Enrichment: Fertiliser runoff enters the water body.
  2. Algal Bloom: These excess nutrients cause rapid growth of algae (an algal bloom).
  3. Oxygen Depletion: When the algae die, decomposers (bacteria) break them down. This decomposition uses up vast amounts of oxygen in the water.
  4. Death: Fish and other aquatic life die due to lack of oxygen.

Impact 2: Mismanagement of Irrigation

Irrigation (artificially supplying water to crops) is essential in dry areas. If done poorly, it can ruin the soil structure.

• Waterlogging: This happens when fields are flooded with too much water, filling all the air spaces in the soil. Plant roots need air to respire, so they effectively "drown" and the crop dies.
• Salinisation: This is the build-up of salts in the top layer of the soil.
  • When irrigation water evaporates from the surface, the salts it contained are left behind.
  • Over time, the concentration of salt becomes so high that most crops cannot grow, turning fertile land barren. (Think of a white, crusty layer forming on the soil surface.)

Did you know? Salinisation has destroyed large areas of farmland throughout history, including ancient Mesopotamia, due to unsustainable irrigation practices.

Impact 3: Social and Economic Issues

• Overproduction and Waste: Highly efficient commercial farming can lead to a surplus of food that cannot be sold or stored, leading to massive waste.
• Exhaustion of Mineral Ion Content: Continuous cropping without proper rotation or rest removes vital minerals from the soil. If only chemical fertilisers are used, the soil structure and organic content suffer, making it less fertile long-term.
• Cash Crops Replacing Food Crops: Farmers often switch from growing local food (like beans or vegetables) to growing cash crops (like cotton, tobacco, or bio-fuel crops) because they are more profitable for export. This can lead to food insecurity for the local population who relied on that land for survival.

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Quick Key Takeaway (Section 1): Modern farming uses chemicals and intensive water use, leading to pollution (eutrophication, bioaccumulation) and soil destruction (salinisation, waterlogging).

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2. Soil Erosion: Causes, Impacts, and Management (Syllabus 3.6 & 3.7)

Soil erosion is the removal of the top, most fertile layer of soil, usually by wind or water. The topsoil is vital because it contains the nutrients needed for plant growth.

2.1 Causes of Soil Erosion (3.6)

The main causes relate to removing the natural protection the land once had:

• Removal of Natural Vegetation: When forests are cut down or grasslands are plowed, the roots that previously held the soil together are gone.
• Over Cultivation: Plowing land too frequently, or planting the same crop year after year, breaks up the soil structure, making it fine and easily blown or washed away.
• Overgrazing: Too many livestock (like cattle or sheep) eating too much vegetation in one area destroys the grass cover and compacts the soil with their hooves. This leaves the soil bare and exposed.
• Water Erosion: Heavy rainfall creates sheet erosion (uniform removal) or gully erosion (deep channels).
• Wind Erosion: In dry, exposed areas, wind picks up and carries away fine, dry soil particles.

2.2 Impacts of Soil Erosion (3.6)

The consequences of losing topsoil are severe and affect both the environment and people:

• Loss of Habitats: Eroding farmland means the disappearance of ecosystems, leading to a loss of biodiversity.
• Desertification: This is the process where fertile land is turned into unproductive desert-like land due (mostly) to human activities like overgrazing and deforestation, often worsened by drought.
• Silting of Rivers: Soil washed into rivers settles on the bottom, making the river shallower. This increases the risk of flooding and can kill aquatic life.
• Displacement of People: When farmland becomes unusable (due to desertification or severe erosion), people must leave their homes to find new places to live and farm.
• Malnutrition and Famine: Reduced crop yields on degraded land lead directly to food shortages.

2.3 Strategies to Reduce Soil Erosion (3.7)

The goal of these strategies is to keep the soil in place and protect it from wind and water.

A. Changing the Landscape:

• Terracing: Building step-like platforms on steep slopes. (Imagine a giant staircase.) This slows down water runoff, allowing it to soak into the soil instead of washing it away.
• Contour Ploughing: Ploughing or planting across the slope, following the natural curves (contours) of the land, instead of up and down. Each ridge acts as a small dam to catch water.
• Bunds: Small banks or mounds of earth built along the contours to trap rainwater and prevent soil from flowing downhill.

B. Using Plants and Organic Matter:

• Wind Breaks / Shelter Belts: Planting rows of trees or hedges along the edges of fields to reduce wind speed, preventing wind erosion.
• Maintaining Vegetation Cover (Cover Crops): Planting crops or leaving residue (stems and leaves) on the soil outside the growing season so the soil is never bare.
• Addition of Organic Matter: Adding manure or compost improves the soil structure (making it stickier and less easily eroded) and allows more water infiltration.

C. Changing Cropping Methods:

• Crop Rotation: Changing the type of crop grown in a specific field each season to avoid exhausting the mineral content and to maintain soil structure.
• Mixed Cropping / Intercropping: Growing two or more types of crops together in the same field. This provides more ground cover and uses water/nutrients more efficiently.
• Planting Trees: Trees stabilize the land, especially along riverbanks or steep slopes, reducing erosion.

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Quick Review (Soil Erosion): Erosion is the loss of topsoil, mainly caused by stripping the land bare (overgrazing, over cultivation). We fight it by building barriers (terracing, bunds) and using plants to cover and hold the soil (wind breaks, cover crops).

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3. Strategies for Sustainable Agriculture (Syllabus 3.8)

Sustainable agriculture means farming methods that meet the needs of the present population without damaging the environment or compromising the ability of future generations to meet their own needs.

These strategies often overlap with soil erosion management and aim to reduce reliance on intensive, high-impact techniques.

A. Soil Health and Nutrient Management

• Organic Fertiliser: Using natural materials like manure (animal waste) or crop residue (leftover plant parts) instead of chemical fertilisers. This improves soil structure and reduces the risk of eutrophication.
• Crop Rotation: This is a key sustainable practice. It helps maintain fertility (e.g., planting nitrogen-fixing legumes) and also helps break pest and disease cycles.

B. Water Efficiency

• Trickle Drip Irrigation: Delivering water directly to the base of the plant through thin pipes. This is far more efficient than flood irrigation because it minimises water loss through evaporation and reduces the risk of waterlogging and salinisation.
• Rainwater Harvesting: Collecting and storing rainfall (in ponds, tanks, or underground) for use during dry periods.
• Use of Drought Resistant Varieties of Crops: Choosing or developing crops (through selective breeding or GMOs) that can survive and thrive in dry conditions, requiring less irrigation.

C. Livestock and Pest Management

• Managed Grazing (Livestock Rotation): Moving livestock regularly between different fenced pastures. This prevents overgrazing in one area, allowing the pasture time to recover and regrow grass cover.
• Use of Pest Resistant Varieties of Crops: Similar to drought resistance, selecting plants that are naturally less attractive or vulnerable to common pests, thereby reducing the need for insecticides.

Encouragement: Understanding the impact of agriculture is about balance. We need food, but we must protect our resources. Learning these sustainable methods shows how clever management can achieve both goals!