Environmental Impacts of Agricultural Practices (College Board AP® Environmental Science) : Study Guide

Environmental damage caused by agricultural practices

• Agricultural activities provide food and raw materials but often have negative environmental consequences

• Key farming techniques such as tilling, slash-and-burn farming, and fertilizer use contribute to soil degradation, pollution, and biodiversity loss

Tilling

• Tilling is the practice of mechanically turning over soil to prepare for planting

• Environmental impacts:

  • Soil erosion: Loosens soil, making it more prone to being washed away by rain or blown away by wind

  • Loss of soil fertility: Disrupts soil structure and depletes nutrients

  • Carbon release: Disturbs stored carbon in soil, contributing to greenhouse gas emissions

    • When soil is tilled, carbon stored in organic matter is exposed to oxygen

    • This accelerates microbial decomposition and releases carbon dioxide (CO₂) into the atmosphere

    • Healthy, undisturbed soil acts as a carbon sink, storing carbon for long periods—frequent tilling reduces this capacity, increasing net carbon emissions

    • In some cases, tilling can disturb anaerobic (oxygen-lacking) environments, leading to the release of methane (CH₄), a potent greenhouse gas

• Example: Intensive tilling in the U.S. Midwest has led to widespread topsoil erosion and declining soil fertility

Awaiting image: Effects of tilling on soil
Image caption: Tilling can damage soil ecosystems and has other environmental impacts

Slash-and-burn farming

• Slash-and-burn is a method where forests or grasslands are cleared by cutting and burning the vegetation to prepare land for agriculture

• Environmental impacts:

  • Deforestation: Large areas of forests are lost, reducing carbon storage

  • Air pollution: Burning releases CO₂ and other pollutants into the atmosphere

  • Soil degradation: Burning depletes nutrients, making land less productive over time

• Example: Slash-and-burn practices in the Amazon Rainforest contribute to deforestation and biodiversity loss

Fertilizer use

• Chemical fertilizers provide essential nutrients to crops but can harm the environment when overused

• Environmental impacts:

  • Water pollution: Excess nutrients run off into rivers and lakes, causing eutrophication and harmful algal blooms

  • Soil acidification: Continuous use of fertilizers can alter soil pH, reducing its productivity

  • Greenhouse gas emissions: Fertilizers release nitrous oxide (N₂O), a potent greenhouse gas

• Example: Excess fertilizer runoff from farms in the Mississippi River Basin contributes to the Gulf of Mexico dead zone, where low oxygen levels kill marine life