3.6 Causes and Impacts of Soil Erosion

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What is Soil Erosion?

Soil erosion is the process by which the top layer of soil — called topsoil — is worn away and carried off by natural forces like wind and water, or by human activities. Topsoil is the most important layer of soil because it contains the nutrients (the "food") that plants need to grow. When it is lost, the land becomes much harder to farm.

Soil erosion is a serious environmental problem that affects millions of people around the world, especially in regions where farming is the main source of food.

1. Removal of Natural Vegetation

Vegetation means plants — trees, grasses, shrubs, and so on. Plant roots act like a natural anchor, holding the soil particles together. The leaves and branches above ground also act like an umbrella, softening the impact of rain and slowing the wind.

When vegetation is removed, the soil is left bare and unprotected. With nothing to hold it in place, the wind and rain can easily wash or blow it away.

Vegetation can be removed in several ways:

a) Over-cultivation

• Over-cultivation means farming the same piece of land too intensively, without giving it time to recover.
• When crops are harvested, the roots are often removed too, leaving bare soil.
• If the same land is ploughed and replanted again and again without rest, the soil structure breaks down — it becomes loose and crumbly.
• Loose soil is very easy for wind and rain to carry away.
• Over time, the soil loses its nutrients and its ability to hold water, making it even more vulnerable to erosion.

b) Overgrazing

• Overgrazing happens when too many animals (cattle, sheep, goats) graze on the same piece of land for too long.
• The animals eat the grass and other plants faster than they can grow back.
• Their heavy hooves also compact (press down and harden) the soil, which damages its structure.
• Without plant cover, the bare soil is exposed to wind and rain and is easily eroded.
• Overgrazing is a major cause of soil erosion in semi-arid (dry but not quite desert) regions of Africa and Asia.