CEP Soil Science & Analysis 2 — Questions and Answers
Question 1: Which soil horizon is typically characterized by the accumulation of illuviated clays, iron, and aluminum oxides?
- O horizon
- A horizon
- B horizon (Correct answer)
- C horizon
Correct answer: B horizon
The B horizon (subsoil) is the zone of illuviation where materials leached from upper horizons accumulate, including clays, iron, and aluminum oxides.
Question 2: A soil with a cation exchange capacity (CEC) of 40 meq/100g is most likely dominated by which clay mineral?
- Kaolinite
- Smectite (montmorillonite) (Correct answer)
- Illite
- Chlorite
Correct answer: Smectite (montmorillonite)
Smectite (montmorillonite) has a very high CEC of 80–150 meq/100g due to its expanding lattice and large surface area, making it the likely dominant clay at 40 meq/100g.
Question 3: In the USDA soil texture triangle, which textural class contains approximately 40% sand, 40% silt, and 20% clay?
- Sandy loam
- Loam (Correct answer)
- Silt loam
- Clay loam
Correct answer: Loam
Loam is defined as approximately 25–50% sand, 25–50% silt, and 10–25% clay, making the 40/40/20 composition a classic loam.
Question 4: Which process describes the downward movement of dissolved or suspended material through the soil profile?
- Eluviation (Correct answer)
- Illuviation
- Gleization
- Ferralization
Correct answer: Eluviation
Eluviation is the process by which water moving through the soil carries dissolved or suspended materials downward out of a horizon.
Question 5: Soil pH of 4.5 would most likely be found in which of the following environmental settings in the United States?
- Arid desert soils of the Southwest
- Mollisols of the Great Plains
- Spodosols under coniferous forest in the Northeast (Correct answer)
- Vertisols of the Texas Blackland Prairie
Correct answer: Spodosols under coniferous forest in the Northeast
Spodosols found under coniferous forests in humid northeastern regions are strongly acidic due to organic acid inputs from needle litter and high leaching.
Question 6: Which of the following best describes the concept of 'soil structure' in environmental planning contexts?
- The mineral composition of the soil parent material
- The arrangement of soil particles into aggregates or peds (Correct answer)
- The ratio of sand to silt to clay by mass
- The depth to the seasonal high water table
Correct answer: The arrangement of soil particles into aggregates or peds
Soil structure refers to the way individual soil particles are arranged and bound together into aggregates (peds), which affects porosity, drainage, and root penetration.
Question 7: When evaluating a site for a septic system, which soil characteristic is the MOST critical limiting factor?
- Soil color in the A horizon
- Hydraulic conductivity and seasonal high water table depth (Correct answer)
- Percentage of organic matter
- Soil pH and buffer capacity
Correct answer: Hydraulic conductivity and seasonal high water table depth
Hydraulic conductivity determines how well the soil can absorb effluent, and the seasonal high water table depth determines the minimum safe separation distance to prevent contamination.
CEP Soil Science & Analysis 2
Which soil horizon is typically characterized by the accumulation of illuviated clays, iron, and aluminum oxides?