CWD Soil Science & Analysis 3 — Questions and Answers
Question 1: Which redoximorphic feature in a soil profile is considered a depletion rather than a concentration?
- Soft iron-manganese masses
- Pore linings of reddish iron oxides
- Gray zones with low chroma surrounding root channels (Correct answer)
- Nodules of manganese oxide
Correct answer: Gray zones with low chroma surrounding root channels
Redox depletions are zones where iron and manganese have been leached out under reducing conditions, leaving low-chroma gray colors.
Question 2: What is the functional significance of hydrogen sulfide (H₂S) gas detected in a soil pit during a wetland delineation?
- Indicates recent fertilizer application
- Confirms anaerobic conditions and microbial sulfate reduction (Correct answer)
- Signals presence of petroleum contamination
- Indicates high carbonate content
Correct answer: Confirms anaerobic conditions and microbial sulfate reduction
H₂S is produced by sulfate-reducing bacteria under anaerobic conditions and serves as a positive hydric soil indicator (F6 - Sulfidic Odor).
Question 3: Which soil texture class typically has the highest saturated hydraulic conductivity and drains most rapidly following flooding?
- Silty clay loam
- Fine sandy loam
- Coarse sand (Correct answer)
- Silt loam
Correct answer: Coarse sand
Coarse sand has large pores and minimal capillary tension, giving it the highest hydraulic conductivity and fastest drainage rates.
Question 4: For the Histosol order, fibric organic material is defined as having what minimum fiber content after rubbing?
- 10%
- 17% (Correct answer)
- 40%
- 75%
Correct answer: 17%
Fibric material retains ≥40% fibers before rubbing but the post-rubbing threshold defining fibric vs. hemic is 17% fibers by volume.
Question 5: Which soil order is most commonly associated with wetland environments in the southeastern coastal plain of the United States?
- Aridisols
- Ultisols
- Spodosols
- Histosols (Correct answer)
Correct answer: Histosols
Histosols (organic soils) are abundant in southeastern coastal plain wetlands, such as the Everglades and Carolina bays, due to long-term waterlogging.
Question 6: In a typical hydric soil, which horizon is most likely to show the strongest evidence of iron reduction and gleying?
- A horizon (Correct answer)
- B horizon
- E horizon
- C horizon
Correct answer: A horizon
The A horizon is subject to the longest periods of saturation and biotic oxygen demand, making it most prone to gleying and redoximorphic features in hydric soils.
Question 7: The alpha-alpha dipyridyl field test is used to detect which soil condition during wetland delineation?
- Phosphorus saturation
- Ferrous iron indicating active reduction (Correct answer)
- Presence of sulfates
- High sodium adsorption ratio
Correct answer: Ferrous iron indicating active reduction
Alpha-alpha dipyridyl reacts with ferrous iron (Fe²⁺) to produce a bright red color, confirming active reduction conditions in a saturated soil.
CWD Soil Science & Analysis 3
Which redoximorphic feature in a soil profile is considered a depletion rather than a concentration?