Soil Science & Analysis Flashcards

Which soil classification system is used as the international standard and organizes soils into 32 Reference Soil Groups?

Answer: World Reference Base for Soil Resources (WRB)

The World Reference Base for Soil Resources (WRB) is the international standard for soil classification, organizing soils into 32 Reference Soil Groups based on diagnostic horizons and properties.

In vadose zone hydrology, 'preferential flow' refers to:

Answer: Rapid movement of water through macropores, bypassing the soil matrix

Preferential flow occurs when water rapidly moves through macropores (root channels, cracks, worm burrows) while bypassing the bulk soil matrix.

Which soil property most strongly influences the cation exchange capacity (CEC) of a mineral soil?

Answer: Clay content and clay mineralogy

CEC is primarily controlled by clay content and mineralogy, since clay particles carry permanent and pH-dependent negative charges that attract cations.

A soil has a bulk density of 1.5 g/cm³ and a particle density of 2.65 g/cm³. What is the total porosity?

Answer: Approximately 43%

Porosity = 1 – (bulk density / particle density) = 1 – (1.5 / 2.65) ≈ 0.434, or approximately 43%.

The 'T factor' used in the USDA NRCS soil survey context refers to:

Answer: The tolerable soil loss rate (tons/acre/year) that maintains soil productivity

The T factor is the maximum tolerable soil loss (in tons per acre per year) a soil can sustain while maintaining long-term productivity.

Which soil-forming process is primarily responsible for the development of an argillic (Bt) horizon?

Answer: Lessivage (clay translocation)

Lessivage is the mechanical eluviation and illuviation of clay particles from upper horizons downward, forming the clay-enriched argillic (Bt) horizon.

When evaluating a site for a constructed wetland or detention basin, which soil characteristic most directly indicates whether a liner will be needed?

Answer: Saturated hydraulic conductivity (Ksat)

Saturated hydraulic conductivity (Ksat) determines how fast water seeps through the soil; high Ksat soils require liners to retain water in constructed basins.