1. Soil Erosion Explain why soil is important.
Evaluate ways that human activity has affected Earth’s soil.
Describe ways to reduce soil erosion.

2. Soil Erosion
Causes of soil erosion:
Water flow
Wind

3. Soil Erosion
Normally soil erodes at the same rate that it is produced.
Humans, however, sometimes cause erosion to occur faster than new soil can form.
Example when people remove ground cover.

4. Soil Erosion Agricultural Cultivation:
If topsoil is eroded, the quality of the soil is reduced.
Plants need nutrients to grow. Each year, nutrients are both added to the soil and removed from the soil.

5. Soil Erosion
Question: If nutrients are reduced from the soil what does the farmer do to compensate?
Might have to add more fertilizer.
Remaining soil might not have the same open structure and water holding ability.
Soil Erosion

6. Soil Erosion
Forest Harvesting: When forests are removed, soil is exposed and erosion increases.

7. Soil Erosion
Soil in tropical rain forests appear rich in nutrients but are almost infertile below a few centimeters.
If a rain forest are cleared for farming the land is only good for a few years before the topsoil is gone.

8. Soil Erosion Overgrazing: Overgrazing can increase soil erosion.
When vegetation is removed in areas with little rain, plants are slow to grow back. Without protection, soil is carried away by the wind.

9. Soil Erosion
Excess Sediment: Eroded soil can foul streams.

10. Preventing Soil Erosion
No Till Farming: Farmers leave plant stalks in the field over winter. A narrow slot is plowed in the soil and seeds are planted in this slot.

11. Preventing Soil Erosion
Contour Farming: Planting along the natural contours of the land. Slows the flow of water down the slope.

12. Preventing Soil Erosion
Terracing: Level topped areas are built into the sides of steep hills and mountains so that crops can be grown.