Soil Science & Analysis Flashcards

Which soil horizon designation indicates a layer that has been significantly reduced in clay, iron, and organic matter compared to adjacent horizons?

Answer: E

The E horizon (eluviation horizon) is depleted of clay, iron oxides, and organic matter through leaching and translocation.

A wetland soil has a loamy matrix with 20% distinct, prominent redox concentrations and a chroma of 2. According to the 1987 Corps Manual, this MOST likely satisfies which indicator?

Answer: F3 - Depleted Matrix

Indicator F3 (Depleted Matrix) requires a matrix chroma of ≤2 with ≥2% redox concentrations in loamy or clayey soils.

What does a cation exchange capacity (CEC) greater than 24 cmolc/kg typically indicate about a soil's mineral composition?

Answer: Presence of smectite or vermiculite 2:1 clay minerals

High CEC values (>24 cmolc/kg) in mineral soils are characteristic of 2:1 expanding clay minerals such as smectite (montmorillonite), which have high surface charge.

Which wetland soil phenomenon is described by the term 'plinthite'?

Answer: Iron-rich material that hardens irreversibly on drying

Plinthite is a sesquioxide-rich soil material that irreversibly hardens to ironstone when exposed to repeated wetting and drying cycles.

For wetland delineation purposes, which of the following field observations BEST indicates a seasonal high water table in a soil profile?

Answer: Redox depletions and concentrations within 30 cm of the soil surface

Redoximorphic features within 30 cm of the surface are the primary morphological evidence of seasonal high water table used in hydric soil field identification.

Which soil survey publication provides the primary data source for identifying mapped hydric soils in a project area during a preliminary wetland determination?

Answer: SSURGO database via Web Soil Survey

SSURGO (Soil Survey Geographic Database), accessible through the USDA Web Soil Survey, provides county-level hydric soil map units and component data.

A soil has a bulk density of 0.3 g/cm³. This value MOST likely indicates the soil is composed primarily of:

Answer: Organic material such as peat or muck

Organic soils (peats and mucks) have very low bulk densities, typically 0.1–0.4 g/cm³, due to their high porosity and low mineral content.