What Caused the Dust Bowl?

1. Climate and soil factors:
– semiarid climate, sandy soils, high winds
2. Prairie grasses were plowed under, wheat planted
3. Extended drought ‐ 1933 to 1939
4. Severe soil erosion by wind!

In 1935 Congress created what program?

 Congress created the Soil Conservation Service
(now the Natural Resource Conservation Service)

Soils are ______-____________ resources

non-renewable

Erosion destroys which part of soil?

 the most productive part of soil ‐ the topsoil

_____________ is the most widespread contaminant of surface waters. (Hint: Not an element but contains them)

sediment

What type of land erodes the fastest?

Cropland erodes more rapidly than other land uses.

soil erosion occurs __________

Naturally

Why do arid lands erode easier?

Lack of vegetative cover
Intense rainfall events (when it rains)
High winds

Consequences of Erosion "On‐site"?

– Loss of topsoil rich in organic matter, N, P, biological
activity
– Decrease in soil quality

Consequences of erosion "off-site"?

– Windblown dust ‐ health and economic consequences

– Sediment damage to waterways, aquatic life
– Nutrient contamination (N,P) of water

Name 3 Human causes of soil erosion?

Agriculture

Overgrazing

Deforestation

Industry

What is "tolerable soil loss"?

• Tolerable soil loss (T value) is the maximum amount that can be lost without long‐term productivity loss

– 2 to 5 tons/acre/yr (vs average US loss >5 t/a/yr)
~ 1⁄4 to 1⁄2 the thickeness of a dime
– This is based on an assumed rate of soil formation
• At this rate an Ap horizon can be lost in 225 yrs
• T values are lower in shallow, infertile, soils with rocky, impermeable parent materials

Name the 3 erosion processess

What is raindrop splash erosion? How can it be fixed?

 Causes initial detachment. Can be minimized by good
soil cover.

What is surface flow? How can it be fixed?

 Causes transport. 

Can be minimized by good soil cover and anything that reduces slope or slope length.

Can cause rill or gully erosion

What are three major types of soil erosion and describe each one.

Sheet erosion is relatively uniform erosion from the entire soil surface.
 Perched stones and pebbles can protect the soil underneath from sheet erosion.

Rill erosion is initiated when the water concentrates in small channels (rills) as it runs off the soil. Subsequent cultivation may erase rills, but it does not replace the lost soil.

Gully erosion creates deep channels that cannot be erased by cultivation. Although gully erosion looks the most catastrophic of the three, far more total soil is lost by sheet and rill erosion.

 (high erodibility) caused by:

– Soils high in silt and fine sand
– Platy or massive soil structure

Erosion by _________ can be controlled by minimizing detachment and transport

water

How do you Control Water Erosion?

• Control detachment
– protect the soil surface from rain, mechanical disturbance
• keep the soil covered: cover crops, crop residues, no‐ or minimum‐till
– encourage soil aggregation

• Transport is controlled by slowing the velocity of water:
– terraces, contour cultivation or strip cropping

Where do you find wind erosion occurs more frequently?

 Wind erosion is most severe in arid regions and in regions with strong winds.

What type of soil particles are picked up in wind?

(Silt is more easily picked up by the wind but is carried away faster than sand)

Soil structure helps determine erodibility by wind.

 Wind erosion results in soils becoming more coarse in texture.

How do you control detachment?

Detachment is usually best controlled by following practices that result in good soil cover and strong soil structure.

How do you contol transport?

Transport can be controlled by increasing vegetative cover, and reducing field length by planting windbreaks.

What percent of erosion is caused by water?

and wind?

About 60% is from water erosion

and 40% is from wind erosion.