4.3 HUMAN ACTIVITIES AFFECT SOIL

BIG IDEA: Natural forces break rocks apart and form soil, which supports life.

REMEMBER:

· Mechanical and chemical forces break down rocks.

· Weathering and organic processes form soil.

· Human activities affect soil.

SOIL IS A NECESSARY RESOURCE.

- Soil helps sustain all life on Earth by:

• Supporting the growth of plants, which supply food and oxygen for animals.
• Providing crops such as cotton (clothing), medicines, lumber.
• Purifying water as it drains through the ground.
• Breaking sown remains of plants and animals, releasing nutrients that living plants need.
• Providing a home for many organisms.

LAND-USE PRACTICES CAN HARM SOIL.

FARMING

• Humans have been farming for more than 10,000 years.
• Methods have improved, but farming still has some harmful effects and can lead to soil loss.
• Farmers often add fertilizers that may harm microorganisms that produce natural nutrients.
• Fertilizers also add to water pollution when runoff carries excess nutrients to rivers/lakes/oceans.
• Farming may lead to soil loss from clearing of trees and other plants. Wind and water may carry soil away.
• Overgrazing occurs when farm animals eat large amounts of the land cover.
• Overgrazing may lead to desertification- the expansion of desert conditions in areas where the natural plant cover has been destroyed.

CONSTRUCTION AND DEVELOPMENT

• To make roads, houses, malls and office buildings, people need to dig up the soil.
• Removing plant cover loosens the soil and water and wind can carry it to lower lying areas. This causes mud to build up in streams and rivers and flooding results.

MINING

• Strip and open pit mining cause soil loss.
• Exposing rocks and minerals to the air and rainwater accelerate the chemical weathering process.
• Acid drainage from sulfide minerals being exposed can lead to the production of sulfuric acid. This can pollute the soil in surrounding areas.

SOIL CAN BE PROTECTED AND CONSERVED.

• Crop rotation- the practice of planting different crops in the same field over different years or growing seasons. This works because different crops may replace nutrients or bacteria that produce nutrients in the soil.
• Conservation tillage- includes several methods of reducing the number of times fields are tilled, or plowed, in a year. This will reduce soil erosion.
• Terraces- flat, steplike areas built on a hillside to hold rainwater and prevent it from running downhill. Crops are planted on the terraces.
• Contour plowing- the practice of plowing along the curves, or contours, of a slope. This helps to channel rainwater so that it does not run straight downhill and carry away soil. Strip-cropping (where strips of grass or shrubs are planted between crops) is often combined with this.
• Windbreaks- rows of trees planted between fields to reduce the force of winds that carry the soil.