soil erosion and degradation

1. Soil Erosion andSoil Erosion and
DegradationDegradation

2. Nature Is Speaking –
Edward Norton is The Soil

3. SOIL: A RENEWABLE RESOURCESOIL: A RENEWABLE RESOURCE
TopsoilTopsoil – fertile top few inches that supports– fertile top few inches that supports
agriculture – slowly renewableagriculture – slowly renewable

4. LoamLoam – texture best suited for plant growth– texture best suited for plant growth
SOIL: A RENEWABLE RESOURCESOIL: A RENEWABLE RESOURCE

5. SOIL EROSION AND DEGRADATIONSOIL EROSION AND DEGRADATION
 Soil erosionSoil erosion – movement of soil components– movement of soil components
– especially surface litter and topsoil – from– especially surface litter and topsoil – from
one place to another by wind or waterone place to another by wind or water

Lowers soil fertilityLowers soil fertility

Can overload nearby waterbodies with sedimentCan overload nearby waterbodies with sediment

6. SOIL EROSION AND DEGRADATIONSOIL EROSION AND DEGRADATION
 Plant roots anchor soilsPlant roots anchor soils
 Destroyed through:Destroyed through:

FarmingFarming

LoggingLogging

ConstructionConstruction

OvergrazingOvergrazing

Off road vehiclesOff road vehicles

7. SOIL EROSION AND DEGRADATIONSOIL EROSION AND DEGRADATION
 Sheet erosionSheet erosion – surface water or wind peel off– surface water or wind peel off
thin layers of soil – not always noticeablethin layers of soil – not always noticeable
 Rill erosionRill erosion – fast-flowing little rivulets of– fast-flowing little rivulets of
surface water make small channelssurface water make small channels
 Gully erosionGully erosion – fast-flowing water join together– fast-flowing water join together
to cut wider and deeper ditches or gulliesto cut wider and deeper ditches or gullies

8. Global Outlook: Soil ErosionGlobal Outlook: Soil Erosion
 Soil is eroding faster than it is forming on moreSoil is eroding faster than it is forming on more
than one-third of the world’s croplandthan one-third of the world’s cropland

9. Case Study: Soil Erosion in the U.S. –Case Study: Soil Erosion in the U.S. –
Some Hopeful SignsSome Hopeful Signs
 Soil erosion > formation on most U.S. croplandSoil erosion > formation on most U.S. cropland

Since 1985 – cut by 40%Since 1985 – cut by 40%

1985 Food Security Act (Farm Act) – farmers1985 Food Security Act (Farm Act) – farmers
receive a subsidy for taking highly erodible landreceive a subsidy for taking highly erodible land
out of production and replanting it with soil savingout of production and replanting it with soil saving
plants for 10-15 yearsplants for 10-15 years

10. Desertification: Degrading DrylandsDesertification: Degrading Drylands
 DesertificationDesertification - process by which fertile- process by which fertile
land becomes desert, typically as a result ofland becomes desert, typically as a result of
drought, deforestation or inappropriate ag.drought, deforestation or inappropriate ag.
 1/3 of world’s land has lost some productivity1/3 of world’s land has lost some productivity
because of drought and human activities thatbecause of drought and human activities that
reduce or degrade topsoilreduce or degrade topsoil
Figure 13-12Figure 13-12

11. Fig. 13-11, p. 280
Very severeSevereModerate
Desertification around the world

12. Case Study: The Dust BowlCase Study: The Dust Bowl
 U.S. Plains – 1930s – most topsoil lost –U.S. Plains – 1930s – most topsoil lost –
poor soil practices and drought (1926 -1937)poor soil practices and drought (1926 -1937)

Plowing, left bare, overgrazingPlowing, left bare, overgrazing

Dust stormsDust storms

Farmers migrated – no jobs – Great DepressionFarmers migrated – no jobs – Great Depression

13. Case Study: The Dust BowlCase Study: The Dust Bowl
 1935 –1935 – Soil Erosion ActSoil Erosion Act – established– established SoilSoil
Conservation ServiceConservation Service (part of USDA- now(part of USDA- now
Natural Resources Conservation ServiceNatural Resources Conservation Service))

Local soil conservation districts set upLocal soil conservation districts set up
 1985 –1985 – Conservation Reserve ProgramConservation Reserve Program ––
part ofpart of Farm ActFarm Act – paid farmers to cover– paid farmers to cover
highly erodible landhighly erodible land

14. Salinization &Salinization &
WaterloggingWaterlogging
 RepeatedRepeated
irrigation canirrigation can
reduce cropreduce crop
yields byyields by
causingcausing
salinizationsalinization
(salt buildup) in(salt buildup) in
the soil andthe soil and
waterloggingwaterlogging
of crop plantsof crop plants
Figure 13-13Figure 13-13

15. 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)

16. Salinization and Waterlogging ofSalinization and Waterlogging of
Soils: A Downside of IrrigationSoils: A Downside of Irrigation
 Example of highExample of high
evaporation,evaporation,
poor drainage,poor drainage,
and severeand severe
salinizationsalinization
 White alkalineWhite alkaline
salts havesalts have
displaced cropsdisplaced crops

17. Desertification