SOIL EROSION AND DEGRADATIONSOIL EROSION AND DEGRADATION

Soil erosion lowers soil fertility and can Soil erosion lowers soil fertility and can overload nearby bodies of water with eroded overload nearby bodies of water with eroded sediment.sediment. Sheet erosionSheet erosion: surface water or wind peel off : surface water or wind peel off

thin layers of soil.thin layers of soil. Rill erosionRill erosion: fast-flowing little rivulets of surface : fast-flowing little rivulets of surface

water make small channels.water make small channels. Gully erosionGully erosion: fast-flowing water join together to : fast-flowing water join together to

cut wider and deeper ditches or gullies.cut wider and deeper ditches or gullies.

SOIL EROSION AND DEGRADATIONSOIL EROSION AND DEGRADATION

Soil erosion is the Soil erosion is the movement of soil movement of soil components, components, especially surface especially surface litter and topsoil, by litter and topsoil, by wind or water.wind or water.

Soil erosion increases through activities Soil erosion increases through activities such as farming, logging, construction, such as farming, logging, construction, overgrazing, and off-road vehicles.overgrazing, and off-road vehicles.

Figure 13-9Figure 13-9

Global Outlook: Soil ErosionGlobal Outlook: Soil Erosion

Soil is eroding faster than it is forming on more Soil is eroding faster than it is forming on more than one-third of the world’s cropland.than one-third of the world’s cropland.

Figure 13-10Figure 13-10

Fig. 13-10, p. 279

Some concern

Serious concern

Stable or nonvegetative

Case Study: Soil Erosion in the U.S. – Case Study: Soil Erosion in the U.S. – Some Hopeful SignsSome Hopeful Signs

Soil erodes faster than it forms on most U.S. Soil erodes faster than it forms on most U.S. cropland, but since 1985, has been cut by cropland, but since 1985, has been cut by about 40%.about 40%. 1985 Food Security Act (Farm Act): farmers 1985 Food Security Act (Farm Act): farmers

receive a subsidy for taking highly erodible land receive a subsidy for taking highly erodible land out of production and replanting it with soil saving out of production and replanting it with soil saving plants for 10-15 years.plants for 10-15 years.

Fig. 13-11, p. 280

Very severeSevereModerate

Desertification: Degrading DrylandsDesertification: Degrading Drylands

About one-third of the world’s land has lost About one-third of the world’s land has lost some of its productivity because of drought some of its productivity because of drought and human activities that reduce or degrade and human activities that reduce or degrade topsoil.topsoil.

Figure 13-12Figure 13-12

Fig. 13-12, p. 280

Causes Consequences Overgrazing Worsening

droughtDeforestationFamineErosionEconomic losses

SalinizationLower living standardsSoil compaction

Natural climate change

Environmental refugees

Salinization Salinization and and

WaterloggingWaterlogging Repeated Repeated

irrigation can irrigation can reduce crop reduce crop yields by yields by causing salt causing salt buildup in the buildup in the soil and soil and waterlogging of waterlogging of crop plants.crop plants.

Figure 13-13Figure 13-13

Fig. 13-13, p. 281

EvaporationTranspiration

EvaporationEvaporation

Waterlogging

Salinization Waterlogging1. Irrigation water contains small amounts of dissolved salts

2. Evaporation and transpiration leave salts behind.

3. Salt builds up in soil.

1. Precipitation and irrigation water percolate downward.

2. Water table rises.

Less permeable clay layer

Fig. 13-15, p. 281

CleanupPrevention

Soil Salinization

Solutions

Reduce irrigation

Switch to salt-tolerant crops (such as barley, cotton, sugarbeet)

Flush soil (expensive and wastes water)

Stop growing crops for 2–5 years

Install underground drainage systems (expensive)

Salinization and Waterlogging of Salinization and Waterlogging of Soils: A Downside of IrrigationSoils: A Downside of Irrigation

Example of high Example of high evaporation, evaporation, poor drainage, poor drainage, and severe and severe salinization.salinization.

White alkaline White alkaline salts have salts have displaced cops.displaced cops.

Figure 13-14Figure 13-14

SUSTAINABLE AGRICULTURE SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATIONTHROUGH SOIL CONSERVATION

Modern farm machinery can plant crops Modern farm machinery can plant crops without disturbing soil (no-till and minimum without disturbing soil (no-till and minimum tillage.tillage. Conservation-tillage farming:Conservation-tillage farming:

• Increases crop yield.Increases crop yield.• Raises soil carbon content.Raises soil carbon content.• Lowers water use.Lowers water use.• Lowers pesticides.Lowers pesticides.• Uses less tractor fuel.Uses less tractor fuel.

SUSTAINABLE AGRICULTURE SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATIONTHROUGH SOIL CONSERVATION

Terracing, contour Terracing, contour planting, strip planting, strip cropping, alley cropping, alley cropping, and cropping, and windbreaks can windbreaks can reduce soil reduce soil erosion.erosion.

Figure 13-16Figure 13-16

SUSTAINABLE AGRICULTURE SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATIONTHROUGH SOIL CONSERVATION

Fertilizers can help restore soil nutrients, but Fertilizers can help restore soil nutrients, but runoff of inorganic fertilizers can cause water runoff of inorganic fertilizers can cause water pollution.pollution. Organic fertilizersOrganic fertilizers: from plant and animal (fresh, : from plant and animal (fresh,

manure, or compost) materials.manure, or compost) materials. Commercial inorganic fertilizersCommercial inorganic fertilizers: Active : Active

ingredients contain nitrogen, phosphorous, and ingredients contain nitrogen, phosphorous, and potassium and other trace nutrients.potassium and other trace nutrients.

THE GREEN REVOLUTION AND ITS THE GREEN REVOLUTION AND ITS ENVIRONMENTAL IMPACTENVIRONMENTAL IMPACT

Since 1950, high-input agriculture has Since 1950, high-input agriculture has produced more crops per unit of land.produced more crops per unit of land.

In 1967, fast growing dwarf varieties of rice In 1967, fast growing dwarf varieties of rice and wheat were developed for tropics and and wheat were developed for tropics and subtropics.subtropics.

Figure 13-17Figure 13-17

THE GREEN REVOLUTION AND ITS THE GREEN REVOLUTION AND ITS ENVIRONMENTAL IMPACTENVIRONMENTAL IMPACT

Lack of water, high costs for small farmers, Lack of water, high costs for small farmers, and physical limits to increasing crop yields and physical limits to increasing crop yields hinder expansion of the green revolution.hinder expansion of the green revolution.

Since 1978 the amount of irrigated land per Since 1978 the amount of irrigated land per person has declined due to:person has declined due to: Depletion of underground water supplies.Depletion of underground water supplies. Inefficient irrigation methods.Inefficient irrigation methods. Salt build-up.Salt build-up. Cost of irrigating crops.Cost of irrigating crops.

THE GREEN REVOLUTION AND ITS THE GREEN REVOLUTION AND ITS ENVIRONMENTAL IMPACTENVIRONMENTAL IMPACT

Modern agriculture has a greater harmful Modern agriculture has a greater harmful environmental impact than any human environmental impact than any human activity.activity.

Loss of a variety of genetically different crop Loss of a variety of genetically different crop and livestock strains might limit raw material and livestock strains might limit raw material needed for future green and gene needed for future green and gene revolutions.revolutions. In the U.S., 97% of the food plant varieties In the U.S., 97% of the food plant varieties

available in the 1940 no longer exist in large available in the 1940 no longer exist in large quantities.quantities.

Fig. 13-18, p. 285

Biodiversity Loss Soil Water Air Pollution Human Health Loss and degradation of grasslands, forests, and wetlands

Erosion Water waste Greenhouse gas emissions from fossil fuel use

Nitrates in drinking water

Loss of fertility Aquifer depletion

Pesticide residues in drinking water, food, and air

Salinization Increased runoff and flooding from cleared land

Other air pollutants from fossil fuel use

Fish kills from pesticide runoff

Waterlogging

Sediment pollution from erosion Greenhouse gas

emissions of nitrous oxide from use of inorganic fertilizers

Contamination of drinking and swimming water with disease organisms from livestock wastes

Desertification

Killing wild predators to protect livestock

Fish kills from pesticide runoff

Surface and groundwater pollution from pesticides and fertilizers Belching of the

greenhouse gas methane by cattle

Loss of genetic diversity of wild crop strains replaced by monoculture strains

Bacterial contamination of meat

Overfertilization of lakes and rivers from runoff of fertilizers, livestock wastes, and food processing wastes

Pollution from pesticide sprays