Soil Erosion Soil Erosion & Degradation& Degradation

Soil erosion: movement of soil components, especially litter & topsoil, from one place to another.

•losing topsoil makes soil less fertile & less able to hold water;•while soil is a potentially renewable resource, it takes long periods of time to form topsoil, typically 200–1000 years to form 2.5 centimeters (1 inch) of topsoil;•topsoil is eroding faster than it forms in about one–third of the world's cropland.

Soil Erosion Soil Erosion & Degradation& Degradation

Major areas of the world are threatened by serious soil erosion.

Soil Erosion Soil Erosion & Degradation& Degradation

• Farming practices such as plowing and tilling can leave soil uncovered and loose.• These practices leaves soil vulnerable to water and wind erosion.

Tilling

Disk Harrow

Soil Erosion Soil Erosion & Degradation:& Degradation: Wind & Water Wind & Water

Soil Erosion & DegradationSoil Erosion & Degradation

Dust BowlDust BowlDuring the 1930s, a combination of drought & poor soil conservation led to severe wind erosion of topsoil in what is known as the Dust Bowl of the Great Plains.

Causes:• overgrazing;• deforestation & devegetation;

• surface mining;• poor irrigation techniques;

• salt buildup;• farming on unsuitable terrain;

• soil compaction by farm machinery.

Desertification of arid & semiarid lands results when land productivity drops markedly.

Dust Storms

Dust

Devil

Dust Storms

Dust Storms

Dust Storms

Asia

Saudi Arabia

Sahara

Problems of Irrigation:

Salinization: salt build-up in irrigated lands to levels that decrease crop yields.

Problems of Irrigation:

Waterlogging results when excess irrigation water raises the water table & lowers crop productivity.

Types of erosion:

• Sheet Erosion: Surface water runs down a slope and erodes layers of topsoil off;

• Rill Erosion: fast-flowing water cuts small rivulets or channels in soil;

• Gully Erosion: rivulets become bigger and join to form gullies

Soil conservation: reducing soil erosion & restoring soil fertility.

• conservation–tillage farming minimizes soil disturbance.

• use of special tillers which loosen subsurface soil without turning over top soil and residues;

• no–till methods that inject seeds, fertilizers, & herbicides in unplowed soil;

By maintaining a layer of crop residue on 30 % or more of the surface, reduces water erosion. Crop residue

Soil ConservationSoil Conservation• terracing protects steep slopes; retains water for crops at each level and reduces erosion by controlling runoff;

• contour farming follows natural land contours; each row of crops acts as a dam to slow water runoff down slopes

Soil ConservationSoil Conservation• strip cropping maintains strips of different

vegetation between crops;

keeps soil covered, slows erosion, and some nitrogen-fixing plants ( such as legumes) can increase fertility.

Soil ConservationSoil Conservation• alley cropping grows crops between rows of trees:

The result is better erosion control, improved crop production, supplemental income, and habitat and travel corridors for wildlife.

Soil ConservationSoil Conservation

• wind breaks uses trees between fields to slow wind erosion

• use of organic fertilizer (manure, "green manure" = plant matter, & compost);

Soil ConservationSoil Conservation crop rotation :

planting crops that restore nutrients; & decrease in use of inorganic fertilizers all help to restore fertility.

Soil ConservationSoil Conservation• Good irrigation techniques can help slow wind and water erosion without waterlogging, causing excess runoff, or depleting water supplies

• Grass in waterway slows water erosion.

Soil Erosion Soil Erosion & Degradation& Degradation