The Dust Bowl (1930-1936) • American Midwest; Decades of intense crop farming – plowing up the native grasslands, planting many crops, land not allowed to “rest” and replenish itself, soil left exposed between plantings+ Severe Drought= The “Dust Bowl” • The soil turned to dust and literally blew away (much of it east into the Atlantic Ocean) • 400,000 km2 of farmland became useless
Stock Market Crash (1929) meant several years of poverty….especially those farming in the midwest. President Roosevelt implemented Soil conservation strategies by the late 1930s.
What is soil erosion? • Soil erosion is the process by which soil is moved from one place to another (by wind, water, glacier action) • When soil is eroded, it may become pollution in the water or air. The land where it came from, loses fertility.
The soil (sometimes only 10 or 20 cm thick) may even be completely removed exposing the bedrock beneath it.
Natural or Geologic Erosion: occurs on land not affected by humans. E.g. rounding off of mountains, depositing of sediment in river deltas. • Accelerated Erosion: removes topsoil at an excessive rate due to anthropogenic causes
Factors affecting Erosion • Rainfall intensity and runoff(greatest in spring and during intense storms) • Soil Physical Characteristics---lower permeability = more erosion--- ie. if water takes longer to infiltrate the soil, it has a greater chance to move soil away • Slope(steeper the slope, the greater the erosion) • Root Systems (roots hold soil “in place”) • Vegetation and Residue Cover(protects soil from raindrop splash, slows down movement of water)
Speaking of poor farming practices……. • The Cheltenham “badlands” were formed after heavy overgrazing by cattle in the 1930s removed plants/root systems and the underlying rock was weathered by wind and water
Two Small Scale Solutions A. Silt fences are placed at the bottoms of slopes to hold the soil yet allow the water to flow. This keeps sediment out of streams and lakes and prevents the loss of soil.
B. Planting trees and shrubs in areas where erosion is possible. The roots hold the soil in place The limbs and leaves on the tree slow the impact of rain and fallen leaves cover the ground.
A. Plant on the contour-Planting around slopes rather than up and down them. - helps slow the flow of water- more time to enter the soil rather than run off.
B. Rotate crops-Planting different crops on land from one year to the next- leaves residue on the surface to help hold the soil in place.- different plants leave different nutrients
C. Allowing the land to lie fallow – no crops planted for one year- natural vegetation grows and a root structure holds the soil in place
D. Terraces- ridges or rows of earth mounds placed across a slope. - allows a gradual drop for the flow of water. - also aids in holding soil in place
E. Grassed strips-Small strips covered with grass may be left near plowed areas. - slows the flow of water and helps keeps gullies from forming.
F. Diversion ditches-Small ditches may be built across slopes to slow water movement and divert it in to a safe outlet.
G. Strip cropping is planting alternating strips of crops on sloping land. - slows the flow of water and hold the topsoil in place.
H. Wind breaks - Rows of trees may be planted to slow blowing wind and help prevent wind erosion.
I. Crop Residue – following harvest – leave crop residue on the field (also allows decay and nutrient replenishment)
J. No-till farming – instead of tilling (plowing furrows) and therefore loosening the soil, seeds are simply driven into the ground by a seed driller. Soil remains “clumped” and therefore resists erosion. (Recent studies have also shown that less N2O, a greenhouse gas is released from no-till fields)