Soil Erosion: Types, Causes and Agents
The Soil Erosion domain examines how soil is detached and transported, which agent does it, and how erosion loss is predicted. Expect classification questions (splash, sheet, rill, gully; saltation, suspension, creep) and simple USLE arithmetic.
Water erosion sequence
- Raindrop splash detaches particles; sheet erosion removes a thin uniform layer; rills are small channels erased by tillage; gullies are deep channels that cannot be erased by normal tillage.
- Gullies are described by cross-section (V, U, trapezoidal) and by stage of development; a ravine is an advanced network of gullies.
- Stream-bank and channel erosion remove land along water courses.
Wind erosion
- Saltation moves 0.1–0.5 mm particles in bouncing hops (the dominant mode); suspension carries silt and clay high in the air; surface creep rolls coarser sand.
Causes and prediction
- Main causes: deforestation, overgrazing, faulty cultivation on slopes, shifting cultivation, high-intensity rain, low organic matter and bare surfaces.
- USLE: A = R × K × LS × C × P, where R is rainfall erosivity (climate) and K is soil erodibility.
Worked example
R = 300, K = 0.30, LS = 1.5, C = 0.4, P = 0.5. A = 300 × 0.30 × 1.5 × 0.4 × 0.5 = 27 t/ha/year. Reasoning: multiply the factors in order; C and P are fractions below 1 that reduce the base loss.
Traps
Swapping erosivity (climate) with erodibility (soil); calling a rill a gully; attributing saltation to water; treating C (crop cover) and P (support practice) as the same factor.