Soil Science & Analysis Flashcards

Which soil morphological feature is described as 'distinct' when the contrast between it and the surrounding matrix requires close examination to see?

Answer: Faint

Faint redoximorphic features are barely visible and require close examination, distinct features are easily seen, and prominent features are obvious.

Which of the following soil properties is MOST directly altered by prolonged anaerobic conditions in wetland soils?

Answer: Soil pH and redox potential (Eh)

Anaerobic conditions drive reduction reactions that lower redox potential (Eh) and often shift soil pH toward neutral (6–7) regardless of initial pH.

In the USDA soil taxonomy, what suffix letter is added to a horizon designation to indicate gleying or strong redoximorphic features?

Answer: 'g' suffix (e.g., Bg or Cg)

The 'g' subscript denotes strong gleying — low-chroma colors due to reduction — and is used in horizon designations like Bg, Cg, or Ag.

What is the primary chemical form of iron that causes the gray to blue-gray colors seen in gleyed wetland soils?

Answer: Ferrous iron (Fe²⁺) in solution or as siderite

Under reducing (anaerobic) conditions, iron is converted to the ferrous (Fe²⁺) state, which is soluble and imparts gray, blue-gray, or greenish colors to the soil matrix.

When using the Field Indicators of Hydric Soils in the United States, Indicator S4 (Sandy Gleyed Matrix) applies to soils in which MLRA-based LRR regions?

Answer: LRR D, F, G, H, P, T and U

Indicator S4 applies specifically to LRRs D, F, G, H, P, T, and U as designated in the current NRCS Field Indicators document.

Which analytical technique directly measures the oxidation-reduction status of a waterlogged soil in the field?

Answer: Platinum electrode redox potential (Eh) measurement

A platinum electrode connected to a reference electrode measures electrical potential (Eh) in millivolts, directly quantifying soil redox status.

A delineator observes a soil with a 10YR 5/1 matrix and 15% distinct, yellowish-brown (10YR 5/6) pore linings in the upper 25 cm. The BEST classification for the pore linings is:

Answer: Redox concentrations (pore linings)

High-chroma (5/6) yellowish-brown coatings on pore surfaces are redox concentrations formed by iron precipitation upon oxidation in macropores.