Explain the causes of erosion and desertification using the Dust Bowl as a case study, and evaluate soil conservation practices.
Erosion -- the removal of topsoil by wind or water -- accelerates dramatically once natural vegetation and its root systems are removed, since roots are what hold soil in place against both forces. The American Dust Bowl of the 1930s is a defining case study: farmers across the Great Plains had plowed under the region's deep-rooted native prairie grasses to plant wheat, leaving bare, shallow-rooted soil exposed; when a multi-year drought hit, there was nothing left to hold the soil down, and the wind carried away enormous volumes of topsoil in massive dust storms. The disaster directly led to the creation of the federal Soil Conservation Service in 1935 (known today as the Natural Resources Conservation Service).
Desertification is a related but distinct problem: the degradation of land in already-dry regions, driven by overgrazing, deforestation, and unsustainable farming, often worsened by drought, until formerly productive land takes on desert-like conditions. Modern conservation practices directly target these problems: contour plowing (plowing along a slope's elevation lines rather than up-and-down it, to slow water runoff), terracing (building stepped, flat areas into a slope), no-till farming (leaving crop residue on the field instead of plowing it under, which protects the surface and retains moisture), cover crops (planting a soil-holding crop between main growing seasons), crop rotation, and shelterbelts (rows of trees planted to block wind).
Mastery looks like: They can match a conservation practice to the specific erosion problem it addresses and explain the Dust Bowl as a combination of a land-use change and a natural trigger.
Common stumbles: Treating the Dust Bowl as caused by drought alone, without the land-use change that made the region vulnerable in the first place; confusing erosion (a physical process) with desertification (a broader land-degradation outcome).