CWD Soil Science & Analysis 2 — Questions and Answers
Question 1: Which soil color matrix notation using the Munsell system indicates the strongest evidence of prolonged saturation?
- 10YR 3/3
- 5Y 4/1 (Correct answer)
- 10YR 5/6
- 7.5YR 4/4
Correct answer: 5Y 4/1
5Y 4/1 has a hue of 5Y and chroma of 1, indicating a gleyed, low-chroma color typical of prolonged anaerobic saturation.
Question 2: In the Corps of Engineers Wetland Delineation Manual, what is the minimum percentage of a soil matrix that must display redoximorphic features to meet the hydric soil criterion under problematic hydric soil indicators?
- 2% (Correct answer)
- 5%
- 10%
- 15%
Correct answer: 2%
Some problematic hydric soil indicators, such as F21 (Red Parent Material), require redox concentrations in at least 2% of the matrix.
Question 3: Which process is primarily responsible for the formation of mottles and redox concentrations in hydric soils?
- Cryoturbation
- Pedoturbation by soil fauna
- Reduction and translocation of iron and manganese (Correct answer)
- Frost heaving of minerals
Correct answer: Reduction and translocation of iron and manganese
Alternating reduction and oxidation cycles mobilize iron and manganese, which precipitate as redox concentrations when re-oxidized.
Question 4: A soil pit reveals a dark gray (N 4/) matrix with no other features in the upper 12 inches. Which hydric soil indicator does this BEST match?
- S5 - Sandy Gleyed Matrix
- A9 - 1 cm Muck
- A4 - Sandy Gleyed Matrix (Correct answer)
- F3 - Depleted Matrix
Correct answer: A4 - Sandy Gleyed Matrix
Indicator A4 (Sandy Gleyed Matrix) applies to sandy soils with a gleyed matrix (N or 10Y/5GY hues) in the upper 15 cm.
Question 5: When measuring soil organic matter content for hydric soil classification, which laboratory method is considered the standard reference?
- Loss on ignition at 360°C
- Walkley-Black wet oxidation (Correct answer)
- Pyrophosphate extraction
- Near-infrared reflectance spectroscopy
Correct answer: Walkley-Black wet oxidation
The Walkley-Black method (wet oxidation with potassium dichromate) is the traditional standard for quantifying soil organic carbon.
Question 6: Which term describes the reddish or yellowish zones of iron and manganese oxide accumulation surrounding macropores in a hydric soil?
- Redox depletions
- Redox concentrations (Correct answer)
- Gleyed matrix
- Sodium adsorption zones
Correct answer: Redox concentrations
Redox concentrations are zones of accumulated iron, manganese, or sulfides, often appearing as pore linings or soft masses in high-chroma colors.
Question 7: A soil classified as a Histosol must have an organic soil horizon of at least how many centimeters when the organic material is saturated for long periods?
- 20 cm
- 30 cm
- 40 cm (Correct answer)
- 60 cm
Correct answer: 40 cm
For saturated organic materials, a Histosol requires an organic layer of 40 cm or more (or 60 cm if the bulk density is less than 0.1 g/cm³).
CWD Soil Science & Analysis 2
Which soil color matrix notation using the Munsell system indicates the strongest evidence of prolonged saturation?